6560-50-P

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 58

 [EPA-HQ-OAR-2006-0922; FRL-]

Primary National Ambient Air Quality Standard for Nitrogen Dioxide

AGENCY:  Environmental Protection Agency (EPA).

ACTION:  Final Rule 

SUMMARY:  Based on its review of the air quality criteria for oxides of
nitrogen and the primary national ambient air quality standard (NAAQS)
for oxides of nitrogen as measured by nitrogen dioxide (NO2), EPA is
making revisions to the primary NO2 NAAQS in order to provide requisite
protection of public health.  Specifically, EPA is establishing a new
1-hour standard at a level of 100 ppb, based on the 3-year average of
the 98th percentile of the yearly distribution of 1-hour daily maximum
concentrations, to supplement the existing annual standard.  EPA is also
establishing requirements for an NO2 monitoring network that will
include monitors at locations where maximum NO2 concentrations are
expected to occur, including within 50 meters of major roadways, as well
as monitors sited to measure the area-wide NO2 concentrations that occur
more broadly across communities.  

DATES: This final rule is effective on [insert date 60 days after date
of publication in the Federal Register].  

ADDRESSES EPA has established a docket for this action under Docket ID
No. EPA-HQ-OAR-2006-0922.  All documents in the docket are listed on the
  HYPERLINK "http://www.regulations.gov"  www.regulations.gov  website. 
Although listed in the index, some information is not publicly
available, e.g., confidential business information or other information
whose disclosure is restricted by statute.  Certain other material, such
as copyrighted material, will be publicly available only in hard copy
form.  Publicly available docket materials are available either
electronically through   HYPERLINK "http://www.regulations.gov" 
www.regulations.gov  or in hard copy at the Air and Radiation Docket and
Information Center, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave.,
NW, Washington, DC.  The Public Reading Room is open from 8:30 a.m. to
4:30 p.m., Monday through Friday, excluding legal holidays.  The
telephone number for the Public Reading Room is (202) 566-1744 and the
telephone number for the Air and Radiation Docket and Information Center
is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT:  Dr. Scott Jenkins,  Health and
Environmental Impacts Division, Office of Air Quality Planning and
Standards, U.S. Environmental Protection Agency, Mail code C504-06, 
Research Triangle Park, NC 27711; telephone: 919-541-1167; fax:
919-541-0237; email:   HYPERLINK "mailto:jenkins.scott@epa.gov" 
jenkins.scott@epa.gov .

SUPPLEMENTARY INFORMATION:   

Table of Contents 

The following topics are discussed in this preamble:

I.	Background

A.	Summary of revisions to the NO2 primary NAAQS 

B.	Legislative requirements

C.	Related NO2 control programs

D.	Review of the Air Quality Criteria and Standards for Oxides of
Nitrogen 

E.	Summary of proposed revisions to the NO2 primary NAAQS

F.	Organization and approach to final NO2 primary NAAQS decisions

II.	Rationale for Final Decisions on the NO2 Primary Standard 

A.	Characterization of NO2 air quality  

	1.	Current patterns of NO2 air quality 

	2.	NO2 air quality and gradients around roadways 

B.	Health effects information

1.	Adverse respiratory effects and short-term exposure to NO2

2.	Other effects with short-term exposure to NO2 

	a.	Mortality

	b.	Cardiovascular effects 

		3.	Health effects with long-term exposure to NO2 

		a.	Respiratory morbidity

		b.	Mortality

c.	Carcinogenic, cardiovascular, and reproductive/developmental effects

4.	NO2-related impacts on public health  

C.	Human exposure and health risk characterization 

D.	Approach for reviewing the need to retain or revise the current
standard

E.	Adequacy of the current standard

1.	Rationale for proposed decision 

2.	Comments on the adequacy of the current standard 

a.	Comments on EPA’s interpretation of the epidemiologic evidence 

b.	Comments on EPA’s interpretation of the controlled human exposure
evidence 

c.	Comments on EPA’s characterization of NO2-associated exposures and
health risks 

3.	Conclusions on the adequacy of the current standard

F.	Elements of a new short-term standard 

1.	Indicator

	a.	Rationale for proposed decision

	b.	Comments on indicator

	c.	Conclusions regarding indicator

2.	Averaging time 

	a.	Rationale for proposed decision

b.	Comments on averaging time

	c.	Conclusions on averaging time  

3.	Form	

a.	Rationale for proposed decision

	b.	CASAC and public comments on form

	c.	Conclusions on form

4.	Level

			a.	Rationale for proposed decisions on approach and level 

b.	Rationale for alternative decisions on approach and level 

c.	Comments on approach and level 

	i.	CASAC comments on the approach to setting the standard 

	ii.	Public comments on the approach to setting the standard

iii.	CASAC comments on standard level

iv.	Public comments on standard level 

	d.	Conclusions on approach and standard level  

G.	Annual standard 

H.	Summary of final decisions on the primary NO2 standard 

III.	Ambient Monitoring and Reporting Requirements 

A.	Monitoring Methods

1.	Chemiluminescence FRM and Alternative Methods

2.	Allowable FRM and FEMs for comparison to the NAAQS

a.	Proposed changes to FRM and FEMs that may be compared to the NAAQS

b.	Comments

c.	Decisions on allowable FRM and FEMs for comparison to the NAAQS

B.	Network Design

1.	Two-tiered Network Design

a.	Proposed Two-tier Network Design

b.	Comments

c.	Conclusions Regarding the Two-tier Network Design

2.	First Tier (Near-road Monitoring Component) of the NO2 Network Design

a.	Proposed First Tier (Near-road Monitoring Component) of the Network
Design

b.	Comments

c.	Conclusions Regarding the First Tier (Near-road Monitoring Component)
of the Network Design

3.	Second Tier (Area-wide Monitoring Component) of the Network Design

a.	Proposed Second Tier (Area-wide Monitoring Component) of the Network
Design 

b.	Comments

c.	Conclusions on the Second Tier (Area-wide Monitoring Component) of
the Network Design

4.	Regional Administrator Authority

a.	Proposed Regional Administrator Authority

b.	Comments

c.	Conclusions on Regional Administrator Authority

5.	Monitoring Network Implementation

a.	Proposed Monitoring Network Implementation Approach

b.	Comments

c.	Conclusions on Monitoring Network Implementation

6.	Near-road Site Selection 

a.	Proposed Near-road Site Selection Criterion	

b.	Comments

c.	Conclusions on Near-road Site Selection

7.	Near-road Siting Criteria

a.	Proposed Near-road Siting Criteria

b.	Comments

c.	Conclusions on Near-road Siting Criteria

8.	Area-wide Monitor Site Selection and Siting Criteria

a.	Proposed Area-wide Monitor Site Selection and Siting Criteria

b.	Comments

c.	Conclusions on Area-wide Monitor Site Selection and Siting Criteria

9.	Meteorological Measurements

a.	Proposed Meteorological Measurements

b.	Comments

c.	Conclusions on Meteorological Measurements

C.	Data Reporting

1.	Proposed Data Quality Objectives and Measurement Uncertainty 

2.	Comments

3.	Conclusions on Data Quality Objectives and Measurement Uncertainty

IV. 	Appendix S--Interpretation of the Primary NAAQS for Oxides of
Nitrogen and Revisions to the Exceptional Events Rule

A.	Interpretation of the primary NAAQS for oxides of nitrogen for the
annual primary standard

1.	Proposed interpretation of the annual standard

2.	Comments on interpretation of the annual standard

	3.	Conclusions on interpretation of the annual standard

B.	Interpretation of the primary NAAQS for oxides of nitrogen 1-hour
primary standard		

1.	Proposed interpretation of the 1-hour standard

2.	Comments on interpretation of the 1-hour standard

		         3.         Conclusions on interpretation of the 1-hour
standard

	C.        Exceptional Events Information Submission Schedule

V.	Designation of Areas 

A.  	Proposed process

B.	Public comments 

C.  	Final designations process

VI.	Clean Air Act Implementation Requirements 

A.	Classifications

1.	Proposal

2.	Public comments

3.	Final

B. 	Attainment Dates

1.	Attaining the NAAQS  

			a.	Proposal

b.	Final

2.	Consequences of Failing to Attain by the Statutory Attainment Date

a.	Proposal

b.	Final

C.	Section 110(a)(2) NAAQS Infrastructure Requirements 

1.	Proposal

2.	Final

D.  	Attainment Planning Requirements 

1.	Nonattainment Area SIPs

a.	Proposal

b.	Public comments

c.	Final

2.	New Source Review and Prevention of Significant Deterioration 
Requirements 

a.	Proposal

b.	Public comments 

c.	Final

3.	General Conformity

a.	Proposal

4.	Transportation Conformity

a.	Proposal

b.	Public comments 

c.	Final 

VII.	Communication of Public Health Information

VIII.	Statutory and Executive Order Reviews  

References  

I.	Background 

A.	Summary of revisions to the NO2 primary NAAQS

Based on its review of the air quality criteria for oxides of nitrogen
and the primary national ambient air quality standard (NAAQS) for oxides
of nitrogen as measured by nitrogen dioxide (NO2), EPA is making
revisions to the primary NO2 NAAQS in order to provide requisite
protection of public health as appropriate under section 109 of the
Clean Air Act (Act or CAA).  Specifically, EPA is supplementing the
existing annual standard for NO2 of 53 parts per billion (ppb) by
establishing a new short-term standard based on the 3-year average of
the 98th percentile of the yearly distribution of 1-hour daily maximum
concentrations.  EPA is setting the level of this new standard at 100
ppb.  EPA is making changes in data handling conventions for NO2 by
adding provisions for this new 1-hour primary standard.  EPA is also
establishing requirements for an NO2 monitoring network.  These new
provisions require monitors at locations where maximum NO2
concentrations are expected to occur, including within 50 meters of
major roadways, as well as monitors sited to measure the area-wide NO2
concentrations that occur more broadly across communities.  EPA is
making conforming changes to the air quality index (AQI).  

B.	Legislative Requirements

Two sections of the CAA govern the establishment and revision of the
NAAQS.  Section 108 of the Act directs the Administrator to identify and
list air pollutants that meet certain criteria, including that the air
pollutant “in [her] judgment, cause[s] or contribute[s] to air
pollution which may reasonably be anticipated to endanger public health
and welfare” and “the presence of which in the ambient air results
from numerous or diverse mobile or stationary sources.”  42 U.S.C. 21
7408(a)(1)(A) & (B).  For those air pollutants listed, section 108
requires the Administrator to issue air quality criteria  that
“accurately reflect the latest scientific knowledge useful in
indicating the kind and extent of all identifiable effects on public
health or welfare which may be expected from the presence of [a]
pollutant in ambient air . . .”  42 U.S.C. 7408(2).  

Section 109(a) of the Act directs the Administrator to promulgate
“primary” and “secondary” NAAQS for pollutants for which air
quality criteria have been issued.  42 U.S.C. 7409(1).  Section
109(b)(1) defines a primary standard as one “the attainment and
maintenance of which in the judgment of the Administrator, based on [the
air quality] criteria and allowing an adequate margin of safety, are
requisite to protect the public health.”  42 U.S.C. 7409(b)(1).  A
secondary standard, in turn,  must “specify a level of air quality the
attainment and maintenance of which, in the judgment of the
Administrator, based on [the air quality] criteria, is requisite to
protect the public welfare from any known or anticipated adverse effects
associated with the presence of such pollutant in the ambient air.” 
42 U.S.C. 7409(b)(2).  

The requirement that primary standards include an adequate margin of
safety is intended to address uncertainties associated with inconclusive
scientific and technical information available at the time of standard
setting.  It is also intended to provide a reasonable degree of
protection against hazards that research has not yet identified. Lead
Industries Association v. EPA, 647 F.2d 1130, 1154 (D.C. Cir 1980),
cert. denied, 449 U.S. 1042 (1980); American Petroleum Institute v.
Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert. denied, 455 U.S.
1034 (1982).  Both kinds of uncertainties are components of the risk
associated with pollution at levels below those at which human health
effects can be said to occur with reasonable scientific certainty. 
Thus, in selecting primary standards that include an adequate margin of
safety, the Administrator is seeking not only to prevent pollution
levels that have been demonstrated to be harmful but also to prevent
lower pollutant levels that may pose an unacceptable risk of harm, even
if the risk is not precisely identified as to nature or degree.

In addressing the requirement for a margin of safety, EPA considers such
factors as the nature and severity of the health effects involved, the
size of the at-risk population(s), and the kind and degree of the
uncertainties that must be addressed.  The selection of any particular
approach to providing an adequate margin of safety is a policy choice
left specifically to the Administrator’s judgment. Lead Industries
Association v. EPA, supra, 647 F.2d at 1161-62.

In setting standards that are “requisite” to protect public health
and welfare, as provided in section 109(b), EPA’s task is to establish
standards that are neither more nor less stringent than necessary for
these purposes.  In so doing, EPA may not consider the costs of
implementing the standards.  Whitman v. American Trucking Associations,
531 U.S. 457, 471, 475-76 (2001).

Section 109(d)(1) of the Act requires the Administrator to periodically
undertake a thorough review of the air quality criteria published under
section 108 and the NAAQS and to  revise the criteria and standards as
may be appropriate.   42 U.S.C. 7409(d)(1).  The Act also requires the
Administrator to appoint an independent scientific review committee
composed of seven members, including at least one member of the National
Academy of Sciences, one physician, and one person representing State
air pollution control agencies, to review the air quality criteria and
NAAQS and to “recommend to the Administrator any new … standards and
revisions of existing criteria and standards as may be appropriate under
section 108 and subsection (b) of this section."  42 U.S.C. 7409(d)(2). 
This independent review function is performed by the Clean Air
Scientific Advisory Committee (CASAC) of EPA’s Science Advisory Board.
 

C.	Related NO2 Control Programs

States are primarily responsible for ensuring attainment and maintenance
of ambient air quality standards once EPA has established them.  Under
section 110 of the Act, 42 U.S.C. 7410, and related provisions, States
are to submit, for EPA approval, State implementation plans (SIPs) that
provide for the attainment and maintenance of such standards through
control programs directed to sources of the pollutants involved.  The
States, in conjunction with EPA, also administer the prevention of
significant deterioration program that covers these pollutants.  See 42
U.S.C. 7470-7479.   In addition, Federal programs provide for nationwide
reductions in emissions of these and other air pollutants under Title II
of the Act, 42 U.S.C. 7521–7574, which involves controls for
automobile, truck, bus, motorcycle, nonroad engine and equipment, and
aircraft emissions; the new source performance standards under section
111 of the Act, 42 U.S.C. 7411; and the national emission standards for
hazardous air pollutants under section 112 of the Act, 42 U.S.C. 7412.  

Currently there are no areas in the United States that are designated as
nonattainment of the NO2 NAAQS.  With the revisions to the NO2 NAAQS
that result from this review, however, some areas could be classified as
non-attainment.  Certain States will be required to develop SIPs that
identify and implement specific air pollution control measures to reduce
ambient NO2 concentrations to attain and maintain the revised NO2 NAAQS,
most likely by requiring air pollution controls on sources that emit
oxides of nitrogen (NOX).  

While NOX is emitted from a wide variety of source types, the top three
categories of sources of NOX emissions are on-road mobile sources,
electricity generating units, and non-road mobile sources.  EPA
anticipates that NOX emissions will decrease substantially over the next
20 years as a result of the ongoing implementation of mobile source
emissions standards.  In particular, Tier 2 NOX emission standards for
light-duty vehicle emissions began phasing into the fleet beginning with
model year 2004, in combination with low-sulfur gasoline fuel standards.
 For heavy-duty engines, new NOX standards are phasing in between the
2007 and 2010 model years, following the introduction of ultra-low
sulfur diesel fuel.  Lower NOX standards for nonroad diesel engines,
locomotives, and certain marine engines are becoming effective
throughout the next decade.  In future decades, these lower- NOX
vehicles and engines will become an increasingly large fraction of
in-use mobile sources, effecting large NOX emission reductions.

D.	Review of the Air Quality Criteria and Standards for Oxides of
Nitrogen 

On April 30, 1971, EPA promulgated identical primary and secondary NAAQS
for NO2 under section 109 of the Act.  The standards were set at 0.053
parts per million (ppm) (53 ppb), annual average (36 FR 8186).  EPA
completed reviews of the air quality criteria and NO2 standards in 1985
and 1996 with decisions to retain the standard (50 FR 25532, June 19,
1985; 61 FR 52852, October 8, 1996).  

 EPA initiated the current review of the air quality criteria for oxides
of nitrogen and the NO2 primary NAAQS on December 9, 2005 (70 FR 73236)
with a general call for information.  EPA’s draft Integrated Review
Plan for the Primary National Ambient Air Quality Standard for Nitrogen
Dioxide (EPA, 2007a) was made available in February, 2007 for public
comment and was discussed by the CASAC via a publicly accessible
teleconference on May 11, 2007.  As noted in that plan, NOX includes
multiple gaseous (e.g., NO2, NO) and particulate (e.g., nitrate)
species.  Because the health effects associated with particulate species
of NOX have been considered within the context of the health effects of
ambient particles in the Agency’s review of the NAAQS for particulate
matter (PM), the current review of the primary NO2 NAAQS is focused on
the gaseous species of NOX and is not intended to address health effects
directly associated with particulate species.  

The first draft of the Integrated Science Assessment for Oxides of
Nitrogen-Health Criteria (ISA) and the Nitrogen Dioxide Health
Assessment Plan: Scope and Methods for Exposure and Risk Assessment
(EPA, 2007b) were reviewed by CASAC at a public meeting held on October
24-25, 2007.  Based on comments received from CASAC and the public, EPA
developed the second draft of the ISA and the first draft of the Risk
and Exposure Assessment to Support the Review of the NO2 Primary
National Ambient Air Quality Standard (Risk and Exposure Assessment
(REA)).  These documents were reviewed by CASAC at a public meeting held
on May 1-2, 2008.  Based on comments received from CASAC and the public
at this meeting, EPA released the final ISA in July of 2008 (EPA,
2008a).  In addition, comments received were considered in developing
the second draft of the REA, which was released for public review and
comment in two parts.  The first part of this document, containing
chapters 1-7, 9 and appendices A and C as well as part of appendix B,
was released in August 2008.  The second part of this document,
containing chapter 8 (describing the Atlanta exposure assessment) and a
completed appendix B, was released in October of 2008.  This document
was the subject of CASAC reviews at public meetings on September 9 and
10, 2008 (for the first part) and on October 22, 2008 (for the second
part).  In preparing the final REA (EPA, 2008b), EPA considered comments
received from the CASAC and the public at those meetings.

In the course of reviewing the second draft REA, CASAC expressed the
view that the document would be incomplete without the addition of a
policy assessment chapter presenting an integration of evidence-based
considerations and risk and exposure assessment results.  CASAC stated
that such a chapter would be “critical for considering options for the
NAAQS for NO2” (Samet, 2008a).  In addition, within the period of
CASAC’s review of the second draft REA, EPA’s Deputy Administrator
indicated in a letter to the chair of CASAC, addressing earlier CASAC
comments on the NAAQS review process (Henderson, 2008), that the risk
and exposure assessment will include “a broader discussion of the
science and how uncertainties may effect decisions on the standard”
and “all analyses and approaches for considering the level of the
standard under review, including risk assessment and weight of evidence
methodologies” (Peacock, 2008, p.3; September 8, 2008).  

Accordingly, the final REA included a new policy assessment chapter. 
This policy assessment chapter considered the scientific evidence in the
ISA and the exposure and risk characterization results presented in
other chapters of the REA as they relate to the adequacy of the current
NO2 primary NAAQS and potential alternative primary NO2 standards.  In
considering the current and potential alternative standards, the policy
assessment chapter of the final REA focused on the information that is
most pertinent to evaluating the basic elements of national ambient air
quality standards:  indicator, averaging time, form, and level.  These
elements, which together serve to define each standard, must be
considered collectively in evaluating the health protection afforded. 
CASAC discussed the final version of the REA, with an emphasis on the
policy assessment chapter, during a public teleconference held on
December 5, 2008.  Following that teleconference, CASAC offered comments
and advice on the NO2 primary NAAQS in a letter to the Administrator
(Samet, 2008b).  

The schedule for completion of this review is governed by a judicial
order resolving a lawsuit filed in September 2005, concerning the timing
of the current review.  The order that now governs this review, entered
by the court in August 2007 and amended in December 2008, provides that
the Administrator will sign, for publication, notices of proposed and
final rulemaking concerning the review of the primary NO2 NAAQS no later
than June 26, 2009 and January 22, 2010, respectively.  In accordance
with this schedule, the Administrator signed a notice of proposed
rulemaking on June 26, 2009 (FR 74 34404).  This action presents the
Administrator’s final decisions on the primary NO2 standard.  

E.	Summary of proposed revisions to the NO2 primary NAAQS 

For the reasons discussed in the preamble of the proposal for the NO2
primary NAAQS (74 FR 34404), EPA proposed to make revisions to the
primary NO2 NAAQS and to make related revisions for NO2 data handling
conventions in order to provide requisite protection of public health. 
EPA also proposed to make corresponding changes to the AQI for NO2. 
Specifically, EPA proposed to supplement the current annual standard by
establishing a new short-term NO2 standard that would reflect the
maximum allowable NO2 concentration anywhere in an area.  EPA proposed
that this new short-term standard would be based on the 3-year average
of the 99th percentile (or 4th highest) of the yearly distribution of
1-hour daily maximum NO2 concentrations and solicited comment on using
the 3-year average of the 98th percentile (or 7th or 8th highest) of the
yearly distribution of 1-hour daily maximum NO2 concentrations.  EPA
proposed to set the level of this new 1-hour standard within the range
of 80 to 100 ppb and solicited comment on standard levels as low as 65
ppb and as high as 150 ppb.  EPA proposed to specify the level of the
standard to the nearest ppb.  EPA also proposed to establish
requirements for an NO2 monitoring network at locations where maximum
NO2 concentrations are expected to occur, including monitors within 50
meters of major roadways, as well as area-wide monitors sited to measure
the NO2 concentrations that can occur more broadly across communities. 
EPA also solicited comment on the alternative approach of setting a
1-hour standard that would reflect the allowable area-wide NO2
concentration.          

F.	Organization and approach to final NO2 primary NAAQS decisions

This action presents the Administrator’s final decisions regarding the
need to revise the current NO2 primary NAAQS.  Revisions to the primary
NAAQS for NO2, and the rationale supporting those revisions, are
described below in section II.  Requirements for the NO2 ambient
monitoring network are described in section III.  Related requirements
for data completeness, data handling, data reporting, rounding
conventions, and exceptional events are described in section IV. 
Implementation of the revised NO2 primary NAAQS is discussed in sections
V and VI.  Communication of public health information through the AQI is
discussed in section VII and a discussion of statutory and executive
order reviews is provided in section VIII.  

	Today's final decisions are based on a thorough review in the ISA of
scientific information on known and potential human health effects
associated with exposure to NO2 in the air.  These final decisions also
take into account:  (1) assessments in the REA of the most
policy-relevant information in the ISA as well as quantitative exposure
and risk analyses based on that information; (2) CASAC Panel advice and
recommendations, as reflected in its letters to the Administrator and
its public discussions of the ISA, the REA, and the notice of proposed
rulemaking; (3) public comments received during the development of ISA
and REA;  and (4) public comments received on the proposed rulemaking. 

Some commenters have referred to and discussed individual scientific
analyses on the health effects of NO2 that were not included in the ISA
(EPA, 2008a) (“new studies”).  In considering and responding to
comments for which such “new studies” were cited in support, EPA has
provisionally considered the cited studies in the context of the
findings of the ISA.  

As in prior NAAQS reviews, EPA is basing its decision in this review on
studies and related information included in the ISA and staff’s policy
assessment, which have undergone CASAC and public review.  In this NO2
NAAQS review, staff’s policy assessment was presented in the form of a
policy assessment chapter of the REA (EPA, 2008b).  The studies assessed
in the ISA and REA, and the integration of the scientific evidence
presented in them, have undergone extensive critical review by EPA,
CASAC, and the public.  The rigor of that review makes these studies,
and their integrative assessment, the most reliable source of scientific
information on which to base decisions on the NAAQS, decisions that all
parties recognize as of great import.  NAAQS decisions can have profound
impacts on public health and welfare, and NAAQS decisions should be
based on studies that have been rigorously assessed in an integrative
manner not only by EPA but also by the statutorily mandated independent
advisory committee, as well as the public review that accompanies this
process.  EPA’s provisional consideration of “new studies” did not
and could not provide that kind of in-depth critical review. 

This decision is consistent with EPA’s practice in prior NAAQS reviews
and its interpretation of the requirements of the CAA.  Since the 1970
amendments, the EPA has taken the view that NAAQS decisions are to be
based on scientific studies and related information that have been
assessed as a part of the pertinent air quality criteria, and has
consistently followed this approach.  This longstanding interpretation
was strengthened by new legislative requirements enacted in 1977, which
added section 109(d)(2) of the Act concerning CASAC review of air
quality criteria.  See 71 FR 61144, 61148 (October 17, 2006) (final
decision on review of PM NAAQS) for a detailed discussion of this issue
and EPA’s past practice.  

As discussed in EPA’s 1993 decision not to revise the NAAQS for ozone
(O3), ‘‘new studies” may sometimes be of such significance that it
is appropriate to delay a decision on revision of a NAAQS and to
supplement the pertinent air quality criteria so the studies can be
taken into account (58 FR at 13013–13014, March 9, 1993).  In the
present case, EPA’s provisional consideration of ‘‘new studies”
concludes that, taken in context, the ‘‘new’’ information and
findings do not materially change any of the broad scientific
conclusions regarding the health effects of NO2 made in the air quality
criteria.  For this reason, reopening the air quality criteria review
would not be warranted even if there were time to do so under the court
order governing the schedule for this rulemaking. 

Accordingly, EPA is basing the final decisions in this review on the
studies and related information included in the NO2 air quality criteria
that have undergone CASAC and public review.  EPA will consider the
“new studies” for purposes of decision-making in the next periodic
review of the NO2 NAAQS, which will provide the opportunity to fully
assess these studies through a more rigorous review process involving
EPA, CASAC, and the public.  Further discussion of these ‘‘new
studies” can be found below, in section II.E, and in the Response to
Comments document.  

II.	Rationale for Final Decisions on the NO2 Primary Standard

This section presents the rationale for the Administrator’s decision
to revise the existing NO2 primary standard by supplementing the current
annual standard with a new 1-hour standard.  In developing this
rationale, EPA has drawn upon an integrative synthesis of the entire
body of evidence on human health effects associated with the presence of
NO2 in the air.  As summarized below in section II.B, this body of
evidence addresses a broad range of health endpoints associated with
exposure to NO2.  In considering this entire body of evidence, EPA
focuses in particular on those health endpoints for which the ISA finds
associations with NO2 to be causal or likely causal.  This rationale
also draws upon the results of quantitative exposure and risk
assessments, summarized below in section II.C.    

As discussed below, a substantial amount of new research has been
conducted since the last review of the NO2 NAAQS, with important new
information coming from epidemiologic studies in particular.  The newly
available research studies evaluated in the ISA have undergone intensive
scrutiny through multiple layers of peer review and opportunities for
public review and comment.  While important uncertainties remain in the
qualitative and quantitative characterizations of health effects
attributable to exposure to ambient NO2, the review of this information
has been extensive and deliberate.    

The remainder of this section provides background information that
informed the Administrator’s decisions on the primary standard and
discusses the rationale for those decisions.  Section II.A presents a
discussion of NO2 air quality.  Section II.B includes an overview of the
scientific evidence related to health effects associated with NO2
exposure.  This overview includes discussion of the health endpoints and
at-risk populations considered in the ISA.  Section II.C discusses the
approaches taken by EPA to assess exposures and health risks associated
with NO2, including a discussion of key results.  Section II.D
summarizes the approach that was used in the current review of the NO2
NAAQS with regard to consideration of the scientific evidence and
exposure-/risk-based results related to the adequacy of the current
standard and potential alternative standards.  Sections II.E-II.G
discuss the Administrator’s decisions regarding the adequacy of the
current standard, elements of a new 1-hour standard, and retention of
the current annual standard, respectively, taking into consideration
public comments on the proposed decisions.  Section II.H summarizes the
Administrator’s decisions with regard to the NO2 primary NAAQS.  

A.	Characterization of NO2 air quality

1.	Current patterns of NO2 air quality

The size of the State and local NO2 monitoring network has remained
relatively stable since the early 1980s, and currently has approximately
400 monitors reporting data to EPA’s Air Quality System (AQS)
database. At present, there are no minimum monitoring requirements for
NO2 in 40 CFR part 58 Appendix D, other than a requirement for EPA
Regional Administrator approval before removing any existing monitors,
and that any ongoing NO2 monitoring must have at least one monitor sited
to measure the maximum concentration of NO2 in that area (though, as
discussed below monitors in the current network do not measure peak
concentrations associated with on-road mobile sources that can occur
near major roadways because the network was not designed for this
purpose).  EPA removed the specific minimum monitoring requirements for
NO2 of two monitoring sites per area with a population of 1,000,000 or
more in the 2006 monitoring rule revisions (71 FR 61236), based on the
fact that there were no NO2 nonattainment areas at that time, coupled
with trends evidence showing an increasing gap between national average
NO2 concentrations and the current annual standard.  Additionally, the
minimum requirements were removed to provide State, local, and tribal
air monitoring agencies flexibility in meeting higher priority
monitoring needs for pollutants such as O3 and PM2.5, or implementing
the new multi-pollutant sites (NCore network) required by the 2006 rule
revisions, by allowing them to discontinue lower priority monitoring. 
There are requirements in 40 CFR part 58 Appendix D for NO2 monitoring
as part of the Photochemical Assessment Monitoring Stations (PAMS)
network.  However, of the approximately 400 NO2 monitors currently in
operation, only about 10 percent may be due to the PAMS requirements. 

An analysis of the approximately 400 monitors comprising the current NO2
monitoring network (Watkins and Thompson, 2008) indicates that the
current NO2 network has largely remained unchanged in terms of size and
target monitor objective categories since it was introduced in the May
10, 1979 monitoring rule (44 FR 27571).  The review of the current
network found that the assessment of concentrations for general
population exposure and maximum concentrations at neighborhood and
larger scales were the top objectives.  A review of the distribution of
listed spatial scales of representation shows that only approximately 3
monitors are described as microscale, representing an area on the order
of several meters to 100 meters, and approximately 23 monitors are
described as middle scale, which represents an area on the order of 100
to 500 meters. This low percentage of smaller spatially representative
scale sites within the network of approximately 400 monitoring sites
indicates that the majority of monitors have, in fact, been sited to
assess area-wide exposures on the neighborhood, urban, and regional
scales, as would be expected for a network sited to support the current
annual NO2 standard and PAMS objectives.  The current network does not
include monitors placed near major roadways and, therefore, monitors in
the current network do not necessarily measure the maximum
concentrations that can occur on a localized scale near these roadways
(as discussed in the next section).  It should be noted that the network
not only accommodates NAAQS related monitoring but also serves other
monitoring objectives, such as support for photochemistry analysis, O3
modeling and forecasting, and particulate matter precursor tracking.

2.	NO2 air quality and gradients around roadways 

	On-road and non-road mobile sources account for approximately 60% of
NOX emissions (ISA, table 2.2-1) and traffic-related exposures can
dominate personal exposures to NO2 (ISA section 2.5.4).  While driving,
personal exposure concentrations in the cabin of a vehicle could be
substantially higher than ambient concentrations measured nearby (ISA,
section 2.5.4).  For example, estimates presented in the REA suggest
that on/near roadway NO2 concentrations could be approximately 80% (REA,
section 7.3.2) higher on average across locations than concentrations
away from roadways and that roadway-associated environments could be
responsible for the majority of 1-hour peak NO2 exposures (REA, Figures
8-17 and 8-18).  Because monitors in the current network are not sited
to measure peak roadway-associated NO2 concentrations, individuals who
spend time on and/or near major roadways could experience NO2
concentrations that are considerably higher than indicated by monitors
in the current area-wide NO2 monitoring network.  

Research suggests that the concentrations of on-road mobile source
pollutants such as NOX, carbon monoxide (CO), directly emitted air
toxics, and certain size distributions of particulate matter (PM), such
as ultrafine PM, typically display peak concentrations on or immediately
adjacent to roads (ISA, section 2.5).  This situation typically produces
a gradient in pollutant concentrations, with concentrations decreasing
with increasing distance from the road, and concentrations generally
decreasing to near area-wide ambient levels, or typical upwind urban
background levels, within a few hundred meters downwind. While such a
concentration gradient is present on almost all roads, the
characteristics of the gradient, including the distance from the road
that a mobile source pollutant signature can be differentiated from
background concentrations, are heavily dependent on factors such as
traffic volumes, local topography, roadside features, meteorology, and
photochemical reactivity conditions (Baldauf, et al., 2009; Beckerman et
al., 2008; Clements et al., 2008; Hagler et al., 2009; Janssen et al.,
2001; Rodes and Holland, 1981; Roorda-Knape et al., 1998; Singer et al.,
2004; Zhou and Levy, 2007).  

Because NO2 in the ambient air is due largely to the atmospheric
oxidation of NO emitted from combustion sources (ISA, section 2.2.1),
elevated NO2 concentrations can extend farther away from roadways than
the primary pollutants also emitted by on-road mobile sources.  More
specifically, review of the technical literature suggests that NO2
concentrations may return to area-wide or typical urban background
concentrations within distances up to 500 meters of roads, though the
actual distance will vary with topography, roadside features,
meteorology, and photochemical reactivity conditions (Baldauf et al.,
2009; Beckerman et al., 2008; Clements et al., 2008; Gilbert et al.
2003; Rodes and Holland, 1981; Singer et al., 2004; Zhou and Levy,
2007).  Efforts to quantify the extent and slope of the concentration
gradient that may exist from peak near-road concentrations to the
typical urban background concentrations must consider the variability
that exists across locations and for a given location over time.  As a
result, we have identified a range of concentration gradients in the
technical literature which indicate that, on average, peak NO2
concentrations on or immediately adjacent to roads may typically be
between 30 and 100 percent greater than concentrations monitored in the
same area but farther away from the road (ISA, Section 2.5.4; Beckerman
et al., 2008; Gilbert et al., 2003; Rodes and Holland, 1981;
Roorda-Knape et al., 1998; Singer et al., 2004).  This range of
concentration gradients has implications for revising the NO2 primary
standard and for the NO2 monitoring network (discussed in sections
II.F.4 and III).  

B.	Health effects information   

In the last review of the NO2 NAAQS, the 1993 NOX Air Quality Criteria
Document (1993 AQCD) (EPA, 1993) concluded that there were two key
health effects of greatest concern at ambient or near-ambient
concentrations of NO2 (ISA, section 5.3.1).  The first was increased
airway responsiveness in asthmatic individuals after short-term
exposures.  The second was increased respiratory illness among children
associated with longer-term exposures to NO2.  Evidence also was found
for increased risk of emphysema, but this appeared to be of major
concern only with exposures to NO2 at levels much higher than then
current ambient levels (ISA, section 5.3.1).  Controlled human exposure
and animal toxicological studies provided qualitative evidence for
airway hyperresponsiveness and lung function changes while epidemiologic
studies provided evidence for increased respiratory symptoms with
increased indoor NO2 exposures.  Animal toxicological findings of lung
host defense system changes with NO2 exposure provided a
biologically-plausible basis for the epidemiologic results. 
Subpopulations considered potentially more susceptible to the effects of
NO2 exposure included persons with preexisting respiratory disease,
children, and the elderly.  The epidemiologic evidence for respiratory
health effects was limited, and no studies had considered endpoints such
as hospital admissions, emergency department visits, or mortality (ISA,
section 5.3.1).

As summarized below and discussed more fully in section II.B of the
proposal notice, evidence published since the last review generally has
confirmed and extended the conclusions articulated in the 1993 AQCD
(ISA, section 5.3.2).  The epidemiologic evidence has grown
substantially with the addition of field and panel studies, intervention
studies, time-series studies of endpoints such as hospital admissions,
and a substantial number of studies evaluating mortality risk associated
with short-term NO2 exposures.  While not as marked as the growth in the
epidemiologic literature, a number of recent toxicological and
controlled human exposure studies also provide insights into
relationships between NO2 exposure and health effects.  This body of
evidence focuses the current review on NO2-related respiratory effects
at lower ambient and exposure concentrations than considered in the
previous review.   

1.	Adverse respiratory effects and short-term exposure to NO2 

The ISA concluded that the findings of epidemiologic, controlled human
exposure, and animal toxicological studies provide evidence that is
sufficient to infer a likely causal relationship for respiratory effects
following short-term NO2 exposure (ISA, sections 3.1.7 and 5.3.2.1). 
The ISA (section 5.4) concluded that the strongest evidence for an
association between NO2 exposure and adverse human health effects comes
from epidemiologic studies of respiratory symptoms, emergency department
visits, and hospital admissions.  These studies include panel and field
studies, studies that control for the effects of co-occurring
pollutants, and studies conducted in areas where the whole distribution
of ambient 24-hour average NO2 concentrations was below the current
NAAQS level of 53 ppb (annual average).  With regard to this evidence,
the ISA concluded that NO2 epidemiologic studies provide “little
evidence of any effect threshold” (ISA, section 5.3.2.9, p. 5-15).  In
studies that have evaluated concentration-response relationships, they
appear linear within the observed range of data (ISA, section 5.3.2.9). 
  

Overall, the epidemiologic evidence for respiratory effects has been
characterized in the ISA as consistent, in that associations are
reported in studies conducted in numerous locations with a variety of
methodological approaches, and coherent, in that the studies report
associations with respiratory health outcomes that are logically linked
together.  In addition, a number of these associations are statistically
significant, particularly the more precise effect estimates (ISA,
section 5.3.2.1).  These epidemiologic studies are supported by evidence
from toxicological and controlled human exposure studies, particularly
those that evaluated airway hyperresponsiveness in asthmatic individuals
(ISA, section 5.4).  The ISA concluded that together, the epidemiologic
and experimental data sets form a plausible, consistent, and coherent
description of a relationship between NO2 exposures and an array of
adverse respiratory health effects that range from the onset of
respiratory symptoms to hospital admissions.    

In considering the uncertainties associated with the epidemiologic
evidence, the ISA (section 5.4) noted that it is difficult to determine
“the extent to which NO2 is independently associated with respiratory
effects or if NO2 is a marker for the effects of another traffic-related
pollutant or mix of pollutants.”  On-road vehicle exhaust emissions
are a widespread source of combustion pollutant mixtures that include
NOX and are an important contributor to NO2 levels in near-road
locations.  Although the presence of other pollutants from vehicle
exhaust emissions complicates efforts to quantify specific NO2-related
health effects, a number of epidemiologic studies have evaluated
associations with NO2 in models that also include co-occurring
pollutants such as PM, O3, CO, and/or SO2.  The evidence summarized in
the ISA indicates that NO2 associations generally remain robust in these
multi-pollutant models and supports a direct effect of short-term NO2
exposure on respiratory morbidity (see ISA Figures 3.1-7, 3.1-10,
3.1-11).  The plausibility and coherence of these effects are also
supported by epidemiologic studies of indoor NO2 as well as experimental
(i.e., toxicological and controlled human exposure) studies that have
evaluated host defense and immune system changes, airway inflammation,
and airway responsiveness (see subsequent sections of this proposal and
the ISA, section 5.3.2.1).  The ISA (section 5.4) concluded that the
robustness of epidemiologic findings to adjustment for co-pollutants,
coupled with data from animal and human experimental studies, support a
determination that the relationship between NO2 and respiratory
morbidity is likely causal, while still recognizing the relationship
between NO2 and other traffic related pollutants.  

The epidemiologic and experimental studies encompass a number of
respiratory-related health endpoints, including emergency department
visits and hospitalizations, respiratory symptoms, airway
hyperresponsiveness, airway inflammation, and lung function.  The
findings relevant to these endpoints, which provide the rationale to
support the judgment of a likely causal relationship, are described in
more detail in section II.B.1 of the proposal.  

2.	Other effects with short-term exposure to NO2      

a.	Mortality 

The ISA concluded that the epidemiologic evidence is suggestive, but not
sufficient, to infer a causal relationship between short-term exposure
to NO2 and all-cause and cardiopulmonary-related mortality (ISA, section
5.3.2.3).  Results from several large United States and European
multicity studies and a meta-analysis study indicate positive
associations between ambient NO2 concentrations and the risk of
all-cause (nonaccidental) mortality, with effect estimates ranging from
0.5 to 3.6% excess risk in mortality per standardized increment (20 ppb
for 24-hour averaging time, 30 ppb for 1-hour averaging time) (ISA,
section 3.3.1, Figure 3.3-2, section 5.3.2.3).  In general, the ISA
concluded that NO2 effect estimates were robust to adjustment for
co-pollutants.  Both cardiovascular and respiratory mortality have been
associated with increased NO2 concentrations in epidemiologic studies
(ISA, Figure 3.3-3); however, similar associations were observed for
other pollutants, including PM and SO2.  The range of risk estimates for
excess mortality is generally smaller than that for other pollutants
such as PM.  In addition, while NO2 exposure, alone or in conjunction
with other pollutants, may contribute to increased mortality, evaluation
of the specificity of this effect is difficult.  Clinical studies
showing hematologic effects and animal toxicological studies showing
biochemical, lung host defense, permeability, and inflammation changes
with short-term exposures to NO2 provide limited evidence of plausible
pathways by which risks of mortality may be increased, but no coherent
picture is evident at this time (ISA, section 5.3.2.3).  

b.	Cardiovascular effects 

The ISA concluded that the available evidence on cardiovascular health
effects following short-term exposure to NO2 is inadequate to infer the
presence or absence of a causal relationship at this time (ISA, section
5.3.2.2).  Evidence from epidemiologic studies of heart rate
variability, repolarization changes, and cardiac rhythm disorders among
heart patients with ischemic cardiac disease are inconsistent (ISA,
section 5.3.2.2).  In most studies, associations with PM were found to
be similar or stronger than associations with NO2.  Generally positive
associations between ambient NO2 concentrations and hospital admissions
or emergency department visits for cardiovascular disease have been
reported in single-pollutant models (ISA, section 5.3.2.2); however,
most of these effect estimate values were diminished in multi-pollutant
models that also contained CO and PM indices (ISA, section 5.3.2.2). 
Mechanistic evidence of a role for NO2 in the development of
cardiovascular diseases from studies of biomarkers of inflammation, cell
adhesion, coagulation, and thrombosis is lacking (ISA, section 5.3.2.2).
 Furthermore, the effects of NO2 on various hematological parameters in
animals are inconsistent and, thus, provide little biological
plausibility for effects of NO2 on the cardiovascular system (ISA,
section 5.3.2.2).  

3.	Health effects with long-term exposure to NO2 

a.	Respiratory morbidity 

The ISA concluded that overall, the epidemiologic and experimental
evidence is suggestive, but not sufficient, to infer a causal
relationship between long-term NO2 exposure and respiratory morbidity
(ISA, section 5.3.2.4).  The available database evaluating the
relationship between respiratory illness in children and long-term
exposures to NO2 has increased since the 1996 review of the NO2 NAAQS
(see section II.B.3 of the proposal for a more detailed discussion).  A
number of epidemiologic studies have examined the effects of long-term
exposure to NO2 and reported positive associations with decrements in
lung function and partially irreversible decrements in lung function
growth (ISA, section 3.4.1, Figures 3.4-1 and 3.4-2).  While animal
toxicological studies may provide biological plausibility for the
chronic effects of NO2 that have been observed in epidemiologic studies
(ISA, sections 3.4.5 and 5.3.2.4), the high correlation among
traffic-related pollutants in epidemiologic studies makes it difficult
to accurately estimate independent effects (ISA, section 5.3.2.4).    

b.	Mortality 

The ISA concluded that the epidemiologic evidence is inadequate to infer
the presence or absence of a causal relationship between long-term
exposure to NO2 and mortality (ISA, section 5.3.2.6).  In the United
States and European cohort studies examining the relationship between
long-term exposure to NO2 and mortality, results have been inconsistent
(ISA, section 5.3.2.6).  Further, when associations were suggested, they
were not specific to NO2 but also implicated PM and other traffic
indicators.  The relatively high correlations reported between NO2 and
PM indices make it difficult to interpret these observed associations at
this time (ISA, section 5.3.2.6). 

c.	Carcinogenic, cardiovascular, and reproductive/developmental effects

The ISA concluded that the available epidemiologic and toxicological
evidence is inadequate to infer the presence or absence of a causal
relationship for carcinogenic, cardiovascular, and reproductive and
developmental effects related to long-term NO2 exposure (ISA, section
5.3.2.5).  Epidemiologic studies conducted in Europe have shown an
association between long-term NO2 exposure and increased incidence of
cancer (ISA, section 5.3.2.5). However, the animal toxicological studies
have provided no clear evidence that NO2 acts as a carcinogen (ISA,
section 5.3.2.5).  The very limited epidemiologic and toxicological
evidence do not suggest that long-term exposure to NO2 has
cardiovascular effects (ISA, section 5.3.2.5).  The epidemiologic
evidence is not consistent for associations between NO2 exposure and
fetal growth retardation; however, some evidence is accumulating for
effects on preterm delivery (ISA, section 5.3.2.5).  Scant animal
evidence supports a weak association between NO2 exposure and adverse
birth outcomes and provides little mechanistic information or biological
plausibility for the epidemiologic findings. 

4.	NO2-related impacts on public health 

Specific groups within the general population are likely at increased
risk for suffering adverse effects from NO2 exposure.  This could occur
because they are affected by lower levels of NO2 than the general
population or because they experience a larger health impact than the
general population to a given level of exposure (susceptibility) and/or
because they are exposed to higher levels of NO2 than the general
population (vulnerability).  The term susceptibility generally
encompasses innate (e.g., genetic or developmental) and/or acquired
(e.g., age or disease) factors that make individuals more likely to
experience effects with exposure to pollutants.  The severity of health
effects experienced by a susceptible subgroup may be much greater than
that experienced by the population at large.  Factors that may influence
susceptibility to the effects of air pollution include age (e.g.,
infants, children, elderly); gender; race/ethnicity; genetic factors;
and pre-existing disease/condition (e.g., obesity, diabetes, respiratory
disease, asthma, chronic obstructive pulmonary disease (COPD),
cardiovascular disease, airway hyperresponsiveness, respiratory
infection, adverse birth outcome) (ISA, sections 4.3.1, 4.3.5, and
5.3.2.8).  In addition, certain groups may experience relatively high
exposure to NO2, thus forming a potentially vulnerable population (ISA,
section 4.3.6).  Factors that may influence susceptibility and
vulnerability to air pollution include socioeconomic status (SES),
education level, air conditioning use, proximity to roadways, geographic
location, level of physical activity, and work environment (e.g., indoor
versus outdoor) (ISA, section 4.3.5).  The ISA discussed factors that
can confer susceptibility and/or vulnerability to air pollution with
most of the discussion devoted to factors for which NO2-specific
evidence exists (ISA, section 4.3).  These factors include pre-existing
disease (e.g., asthma), age (i.e., infants, children, older adults),
genetic factors, gender, socioeconomic status, and proximity to roadways
(see section II.B.4 in proposal for more detailed discussion of these
factors).  

As discussed in more detail in the proposal (section II.B.4), the
population potentially affected by NO2 is large.  A considerable
fraction of the population resides, works, or attends school near major
roadways, and these individuals are likely to have increased exposure to
NO2 (ISA, section 4.4).  Based on data from the 2003 American Housing
Survey, approximately 36 million individuals live within 300 feet (~90
meters) of a four-lane highway, railroad, or airport (ISA, section 4.4).
 Furthermore, in California, 2.3% of schools, with a total enrollment of
more than 150,000 students were located within approximately 500 feet of
high-traffic roads, with a higher proportion of non-white and
economically disadvantaged students attending those schools (ISA,
section 4.4).  Of this population, asthmatics and members of other
susceptible groups discussed above will have even greater risks of
experiencing health effects related to NO2 exposure.  In the United
States, approximately 10% of adults and 13% of children (approximately
22.2 million people in 2005) have been diagnosed with asthma, and 6% of
adults have been diagnosed with COPD (ISA, section 4.4).  The prevalence
and severity of asthma is higher among certain ethnic or racial groups
such as Puerto Ricans, American Indians, Alaskan Natives, and African
Americans (ISA, section 4.4).  A higher prevalence of asthma among
persons of lower SES and an excess burden of asthma hospitalizations and
mortality in minority and inner-city communities have been observed
(ISA, section 4.4).  In addition, based on United States census data
from 2000, about 72.3 million (26%) of the United States population are
under 18 years of age, 18.3 million (7.4%) are under 5 years of age, and
35 million (12%) are 65 years of age or older.  Therefore, large
portions of the United States population are in age groups that are
likely at-risk for health effects associated with exposure to ambient
NO2.  The size of the potentially at-risk population suggests that
exposure to ambient NO2 could have a significant impact on public health
in the United States.  

C.	Human exposure and health risk characterization

To put judgments about NO2-associated health effects into a broader
public health context, EPA has drawn upon the results of the
quantitative exposure and risk assessments.  Judgments reflecting the
nature of the evidence and the overall weight of the evidence are taken
into consideration in these quantitative exposure and risk assessments,
discussed below.  These assessments provide estimates of the likelihood
that asthmatic individuals would experience exposures of potential
concern and estimates of the incidence of NO2-associated respiratory
emergency department visits under varying air quality scenarios (e.g.,
just meeting the current or alternative standards), as well as
characterizations of the kind and degree of uncertainties inherent in
such estimates.  As discussed more fully in section II.C of the
proposal, this section summarizes the approach taken in the REA to
characterize NO2-related exposures and health risks.  Goals of the REA
included estimating short-term exposures and potential human health
risks associated with (1) recent levels of ambient NO2; 2) NO2 levels
adjusted to simulate just meeting the current standard; and 3) NO2
levels adjusted to simulate just meeting potential alternative
standards.  

For purposes of the quantitative characterization of NO2 health risks,
the REA determined that it was appropriate to focus on endpoints for
which the ISA concluded that the available evidence is sufficient to
infer either a causal or a likely causal relationship.  This was
generally consistent with judgments made in other recent NAAQS reviews
(e.g., see EPA, 2005).  As noted above in section II.A, the only health
effect category for which the evidence was judged in the ISA to be
sufficient to infer either a causal or a likely causal relationship is
respiratory morbidity following short-term NO2 exposure.  Therefore, for
purposes of characterizing health risks associated with NO2, the REA
focused on respiratory morbidity endpoints that have been associated
with short-term NO2 exposures.    

In evaluating the appropriateness of specific endpoints for use in the
NO2 risk characterization, the REA considered both epidemiologic and
controlled human exposure studies.  As described in more detail in the
proposal (section II.C.1), the characterization of NO2-associated health
risks was based on an epidemiology study conducted in Atlanta, Georgia
by Tolbert et al. (2007) and a meta-analysis of controlled human
exposure studies of NO2 and airway responsiveness in asthmatics (ISA,
Table 3.1-3).  

As noted above, the purpose of the assessments described in the REA was
to characterize air quality, exposures, and health risks associated with
recent ambient levels of NO2, with NO2 levels that could be associated
with just meeting the current NO2 NAAQS, and with NO2 levels that could
be associated with just meeting potential alternative standards.  To
characterize health risks, the REA employed three approaches.  In the
first approach, for each air quality scenario, NO2 concentrations at
fixed-site monitors and simulated concentrations on/near roadways were
compared to potential health effect benchmark values derived from the
controlled human exposure literature.  In the second approach, modeled
estimates of exposures in asthmatics were compared to potential health
effect benchmarks.  In the third approach, concentration-response
relationships from an epidemiologic study were used in conjunction with
baseline incidence data and recent or simulated ambient concentrations
to estimate health impacts.  An overview of the approaches to
characterizing health risks is provided in the proposal (section II.C.2)
and each approach, along with its limitations and uncertainties (see
proposal, section II.C.3) has been described in more detail in the REA
(chapters 6 through 9).     

Chapters 7-9 of the REA estimated exposures and health risks associated
with recent air quality and with air quality, as measured at monitors in
the current area-wide network, which had been adjusted to simulate just
meeting the current and potential alternative standards.  The specific
standard levels evaluated, for an area-wide standard based on the 3-year
average of the 98th and 99th percentile 1-hour daily maximum NO2
concentrations, were 50, 100, 150, and 200 ppb.  In interpreting these
results within the context of the current revisions to the NO2 primary
NAAQS (see below), we note that simulation of different standard levels
was based on adjusting NO2 concentrations at available area-wide
monitors.  Therefore, the standard levels referred to above reflect the
allowable area-wide NO2 concentrations, not the maximum allowable
concentrations.  As a consequence, the maximum concentrations in an area
that just meets one of these standard levels would be expected to be
higher than the standard level.  For example, given that near-road NO2
concentrations can be 30% to 100% higher than area-wide concentrations
(see section II.E.2), an area-wide concentration of 50 ppb could
correspond to near-road concentrations from 65 to 100 ppb.  

Key results of the air quality, exposure, and risk analyses were
presented in the policy assessment chapter of the REA and summarized in
the proposal (Table 1 in proposal).  In considering these results, the
policy assessment chapter of the REA concluded that the risks estimated
to be associated with just meeting the current annual standard can be
judged important from a public health perspective.  The results for
specific 1-hour standard levels estimate that limiting the 98th/99th
percentile of the distribution of 1-hour daily maximum NO2
concentrations measured at area-wide monitors to 50 or 100 ppb could
substantially reduce exposures to ambient NO2 and associated health
risks (compared to just meeting the current standard).  In contrast,
limiting these area-wide NO2 concentrations to 150 or 200 ppb is
estimated to result in similar, or in some cases higher, NO2-associated
exposures and health risks than just meeting the current standard.  The
pattern of results was similar for standards just meeting either the
98th or the 99th percentile 1-hour daily maximum area-wide standards
(REA, Chapters 7, 8, and 9). 

D.	Approach for reviewing the need to retain or revise the current
standard

EPA notes that the final decision on retaining or revising the current
primary NO2 standard is a public health policy judgment to be made by
the Administrator.  This judgment has been informed by a recognition
that the available health effects evidence reflects a continuum
consisting of ambient levels of NO2 at which scientists generally agree
that health effects are likely to occur, through lower levels at which
the likelihood and magnitude of the response become increasingly
uncertain.  The Administrator’s final decisions draw upon scientific
information and analyses related to health effects, population
exposures, and risks; judgments about the appropriate response to the
range of uncertainties that are inherent in the scientific evidence and
analyses; and comments received from CASAC and the public.  

To evaluate whether the current primary NO2 standard is requisite or
whether consideration of revisions is appropriate, EPA has used an
approach in this review that was described in the policy assessment
chapter of the REA.  This approach builds upon those used in reviews of
other criteria pollutants, including the most recent reviews of the Pb,
O3, and PM NAAQS (EPA, 2007d; EPA, 2007e; EPA, 2005), and reflects the
body of evidence and information that is currently available.  As in
other recent reviews, EPA's considerations included the implications of
placing more or less weight or emphasis on different aspects of the
scientific evidence and the exposure/risk-based information, recognizing
that the weight to be given to various elements of the evidence and
exposure/risk information is part of the public health policy judgments
that the Administrator will make in reaching decisions on the standard. 


A series of general questions framed this approach to considering the
scientific evidence and exposure-/risk-based information.  First,
EPA’s consideration of the scientific evidence and exposure/risk
information with regard to the adequacy of the current standard has been
framed by the following questions: 

To what extent does evidence that has become available since the last
review reinforce or call into question evidence for NO2-associated
effects that were identified in the last review?

To what extent has evidence for different health effects and/or
sensitive populations become available since the last review?

To what extent have uncertainties identified in the last review been
reduced and/or have new uncertainties emerged?

To what extent does evidence and exposure-/risk-based information that
has become available since the last review reinforce or call into
question any of the basic elements of the current standard?

To the extent that the available evidence and exposure-/risk-based
information suggests it may be appropriate to consider revision of the
current standard, EPA considers that evidence and information with
regard to its support for consideration of a standard that is either
more or less protective than the current standard.  This evaluation has
been framed by the following questions: 

Is there evidence that associations, especially causal or likely causal
associations, extend to ambient NO2 concentrations as low as, or lower
than, the concentrations that have previously been associated with
health effects?  If so, what are the important uncertainties associated
with that evidence?

Are exposures above benchmark levels and/or health risks estimated to
occur in areas that meet the current standard?  If so, are the estimated
exposures and health risks important from a public health perspective? 
What are the important uncertainties associated with the estimated
risks?

To the extent that there is support for consideration of a revised
standard, EPA then considers the specific elements of the standard
(indicator, averaging time, form, and level) within the context of the
currently available information.  In so doing, the Agency has addressed
the following questions: 

Does the evidence provide support for considering a different indicator
for gaseous NOX?

Does the evidence provide support for considering different averaging
times?

What ranges of levels and forms of alternative standards are supported
by the evidence, and what are the associated uncertainties and
limitations?

To what extent do specific averaging times, levels, and forms of
alternative standards reduce the estimated exposures above benchmark
levels and risks attributable to NO2, and what are the uncertainties
associated with the estimated exposure and risk reductions?

The questions outlined above have been addressed in the REA, the
proposal, and in this final rulemaking.  The following sections present
the rationale for proposed decisions, discussion of public comments, and
the Administrator’s conclusions on the adequacy of the current
standard and potential alternative standards in terms of indicator,
averaging time, form, and level.   

E.	Adequacy of the current standard 

	This section discusses considerations related to the decision as to
whether the current NO2 primary NAAQS is requisite to protect public
health with an adequate margin of safety.  Specifically, section II.E.1
provides an overview of the rationale supporting the Administrator’s
conclusion in the proposal that the current standard alone does not
provide adequate public health protection; section II.E.2 discusses
comments received on the adequacy of the current standard; and section
II.E.3 discusses the Administrator’s final decision on whether the
current NO2 primary NAAQS is requisite to protect public health with an
adequate margin of safety.  

1.	Rationale for proposed decision

In reaching a conclusion regarding the adequacy of the current NO2 NAAQS
in the proposal (section II.E.5), the Administrator considered the
scientific evidence assessed in the ISA and the conclusions of the ISA,
the exposure and risk information presented in the REA and the
conclusions of the policy assessment chapter of the REA, and the views
expressed by CASAC.  These considerations are discussed in detail in the
proposal (II.E.) and are summarized in this section.  In the proposal,
the Administrator noted the following in considering the adequacy of the
current standard:

The ISA concluded that the results of epidemiologic and experimental
studies form a plausible and coherent data set that supports a
relationship between NO2 exposures and respiratory endpoints, including
respiratory symptoms and respiratory-related hospital admissions and
emergency department visits, at ambient concentrations that are present
in areas that meet the current NO2 NAAQS (ISA, section 5.4).  

The policy assessment chapter of the REA concluded that risks estimated
to be associated with air quality adjusted upward to simulate just
meeting the current standard can reasonably be judged important from a
public health perspective (REA, section 10.3.3). 

The policy assessment chapter of the REA concluded that exposure- and
risk-based results reinforce the scientific evidence in supporting the
conclusion that consideration should be given to revising the current
NO2 NAAQS so as to provide increased public health protection,
especially for at-risk groups, from NO2-related adverse health effects
associated with short-term, and potential long-term, exposures (REA,
section 10.3.3).  

CASAC agreed that the current annual standard alone is not sufficient to
protect public health against the types of exposures that could lead to
these health effects.  Specifically, in their letter to the
Administrator on the final REA, they stated that “CASAC concurs with
EPA’s judgment that the current NAAQS does not protect the public’s
health and that it should be revised” (Samet, 2008b).  

Based on these considerations (discussed in more detail in the proposal,
section II.E), the Administrator concluded in the proposal that the
current NO2 primary NAAQS is not requisite to protect public health with
an adequate margin of safety against adverse respiratory effects
associated with short-term exposures.  In considering approaches to
revising the current standard, the Administrator concluded that it is
appropriate to consider setting a new short-term standard in addition to
retaining the current annual standard.  The Administrator noted that
such a short-term standard could provide increased public health
protection, especially for members of at-risk groups, from effects
described in both epidemiologic and controlled human exposure studies to
be associated with short-term exposures to NO2.  

2.	Comments on the adequacy of the current standard 

This section discusses comments received from CASAC and public
commenters on the proposal that either supported or opposed the
Administrator’s proposed decision to revise the current NO2 primary
NAAQS.  Comments on the adequacy of the current standard that focused on
the scientific and/or the exposure/risk basis for the Administrator’s
proposed conclusions are discussed in sections II.E.2.a-II.E.2.c. 
Comments on the epidemiologic evidence are considered in section
II.E.2.a.  Comments on the controlled human exposure evidence are
considered in section II.E.2.b.  Comments on human exposure and health
risk assessments are considered in section II.E.2.c.  To the extent
these comments on the evidence and information are also used to justify
commenters’ conclusions on decisions related to indicator, averaging
time, level, or form, they are noted in the appropriate sections below
(II.F.1-II.F.4).  

In their comments on the proposal (Samet, 2009), CASAC reiterated their
support for the need to revise the current annual NO2 NAAQS in order to
increase public health protection.  As noted above, in its letter to the
Administrator on the final REA (Samet, 2008b) CASAC stated that it
“concurs with EPA’s judgment that the current NAAQS does not protect
the public’s health and that it should be revised.”  In supporting
adoption of a more stringent NAAQS for NO2, CASAC considered the
assessment of the scientific evidence presented in the ISA, the results
of assessments presented in the REA, and the conclusions of the policy
assessment chapter of the REA.  As such, CASAC’s rationale for
revising the current standard was consistent with the Administrator’s
rationale as discussed in the proposal.  

Many public commenters agreed with CASAC that, based on the available
information, the current NO2 standard is not requisite to protect public
health with an adequate margin of safety and that revisions to the
standard are appropriate.  Among those calling for revisions to the
standard were environmental groups (e.g., Clean Air Council (CAC), Earth
Justice (EJ), Environmental Defense Fund (EDF), Natural Resources
Defense Council (NRDC), Group Against Smog and Pollution (GASP));
medical/public health organizations (e.g., American Lung Association
(ALA), American Medical Association (AMA), American Thoracic Society
(ATS), National Association for the Medical Direction of Respiratory
Care (NAMDRC), National Association of Cardiovascular and Pulmonary
Rehabilitation (NACPR), American College of Chest Physicians (ACCP)); a
large number of State agencies and organizations (e.g., National
Association of Clean Air Agencies (NACAA), Northeast States for
Coordinated Air Use Management (NESCAUM), and state or local agencies in
CA, IA, IL, MI, MO, NC, NM, NY, TX, VA, WI); Tribes (e.g., National
Tribal Air Association (NTAA), Fond du Lac Band of Lake Superior
Chippewa (Fond du Lac)), and a number of individual commenters.  These
commenters concluded that the current NO2 standard needs to be revised
and that a more stringent standard is needed to protect the health of
sensitive population groups.  In supporting the need to adopt a more
stringent NAAQS for NO2, these commenters often referenced the
conclusions of CASAC and relied on the evidence and information
presented in the proposal.  As such, similar to CASAC, the rationale
offered by these commenters was consistent with that presented in the
proposal to support the Administrator’s proposed decision to revise
the current NO2 NAAQS.  

Some industry commenters (e.g., Alliance of Automobile Manufacturers
(AAM), American Petroleum Institute (API), Interstate Natural Gas
Association of America (INGAA), Utility Air Regulatory Group (UARG)) and
one State commenter (IN Department of Environmental Management)
expressed support for retaining the current annual standard alone.  In
supporting this view, these commenters generally concluded that the
current standard is requisite to protect public health with an adequate
margin of safety and that the available evidence is not sufficient to
support revision of the standard.  For example, UARG stated that “EPA
has failed to demonstrate that the present NO2 NAAQS is no longer at the
level requisite to protect public health with an adequate margin of
safety.”  In addition, INGAA stated that

“…EPA should be compelled to retain the current standard and defer a
decision on a new short-term standard until the science is more clearly
defined.”    

	In support of their views, these commenters provided specific comments
on the epidemiologic and controlled human exposure evidence as discussed
below.  In responding to these specific comments, we note that the
Administrator relied in the proposal on the evidence, information and
judgments contained in the ISA and the REA (including the policy
assessment chapter) as well as on the advice of CASAC.  In considering
the evidence, information, and judgments of the ISA and the REA, the
Agency notes that these documents have been reviewed extensively by
CASAC and have been discussed by CASAC at multiple public meetings (see
section I.D).  In their letter to the Administrator regarding the second
draft ISA (Henderson, 2008b), CASAC noted the following:

Panel members concur with the primary conclusions reached in the ISA
with regard to health risks that are associated with NO2 exposure. In
particular, the Panel agrees with the conclusion that the current
scientific evidence is “sufficient to infer a likely causal
relationship between short term NO2 exposure and adverse effects on the
respiratory system.” The strongest evidence in support of this
conclusion comes from epidemiology studies that show generally positive
associations between NO2 and respiratory symptoms, hospitalizations or
emergency department visits, as summarized in Figure 5.3.1.” 

Similarly, in their letter to the Administrator on the final REA (Samet,
2008b), CASAC noted the following:

Overall, CASAC found this version of the REA satisfactory in its
approach to moving from the scientific foundation developed in the
Integrated Science Assessment (ISA) to setting out evidence-based
options for the NAAQS. The REA provides the needed bridge from the
evidence presented in the ISA to a characterization of the exposures and
the associated risks with different profiles of exposure. It draws on
toxicological and epidemiological evidence and addresses risk to an
identified susceptible population, people with asthmatic conditions. EPA
has also systematically described uncertainties associated with the risk
assessments. We commend EPA for developing a succinct and thoughtfully
developed synthesis in Chapter 10. This summary chapter represents a
long-needed and transparent model for linking a substantial body of
scientific evidence to the four elements of the NAAQS. 

Therefore, in discussing comments on the interpretation of the
scientific evidence and exposure/risk information, we note that CASAC
has endorsed the approaches and conclusions of the ISA and the REA. 
These approaches and conclusions are discussed below in more detail,
within the context of specific public comments.  

a.	Comments on EPA’s interpretation of the epidemiologic evidence 

	Several industry groups (e.g., API, National Mining Association (NMA),
American Chemistry Council (ACC), AAM, Annapolis Center for
Science-Based Public Policy (ACSBPP), Engine Manufacturers Association
(EMA), ExxonMobil (Exxon), National Association of Manufacturers (NAM))
commented that, given the presence of numerous co-pollutants in the air,
epidemiologic studies do not support the contention that NO2 itself is
causing health effects.  

While EPA has recognized that multiple factors can contribute to the
etiology of respiratory disease and that more than one air pollutant
could independently impact respiratory health, we continue to judge, as
discussed in the ISA, that the available evidence supports the
conclusion that there is an independent effect of NO2 on respiratory
morbidity.  In reaching this judgment, we recognize that a major
methodological issue affecting NO2 epidemiologic studies concerns the
evaluation of the extent to which other air pollutants may confound or
modify NO2-related effect estimates.  The use of multipollutant
regression models is the most common approach for controlling potential
confounding by copollutants in epidemiologic studies.  The issues
related to confounding and the evidence of potential confounding by
copollutants has been thoroughly reviewed in the ISA (see Figures 3.1-10
and 3.1-11) and in previous assessments (e.g., EPA, 2004).  NO2 risk
estimates for respiratory morbidity endpoints, in general, were not
sensitive to the inclusion of copollutants, including particulate and
gaseous pollutants.  As observed in Figures 3.1-10 and 3.1-11 in the
ISA, relative risks for hospital admissions or emergency department
visits are generally unchanged, nor is their interpretation modified,
upon inclusion of PM or gaseous co-pollutants in the models.  Similarly,
associations between short-term NO2 exposure and asthma symptoms are
generally robust to adjustment for copollutants in multipollutant
models, as shown in Figures 3.1-5 and 3.1-7 of the ISA.  These results,
in conjunction with the results of a randomized intervention study
evaluating respiratory effects of indoor exposure to NO2 (ISA, section
3.1.4.1), led to the conclusion that the effect of NO2 on respiratory
health outcomes is robust and independent of the effects of other
ambient copollutants.  

In addition, experimental studies conducted in animals and humans
provide support for the plausibility of the associations reported in
epidemiologic studies.  These controlled human exposure and animal
toxicological studies have reported effects of NO2 on immune system
function, lung host defense, airway inflammation, and airway
responsiveness (ISA, section 5.4).  These experimental study results
support an independent contribution of NO2 to the respiratory health
effects reported in epidemiologic studies (ISA Section 5.4).    

In considering the entire body of evidence, including epidemiologic and
experimental studies, the ISA (section 5.4, p. 5-16) concluded the
following: 

Although this [presence of co-pollutants] complicates the efforts to
disentangle specific NO2-related health effects, the evidence summarized
in this assessment indicates that NO2 associations generally remain
robust in multi-pollutant models and supports a direct effect of
short-term NO2 exposure on respiratory morbidity at ambient
concentrations below the current NAAQS. The robustness of epidemiologic
findings to adjustment for co-pollutants, coupled with data from animal
and human experimental studies, support a determination that the
relationship between NO2 and respiratory morbidity is likely causal,
while still recognizing the relationship between NO2 and other
traffic-related pollutants.

Comments on specific epidemiologic studies are discussed below.    

The National Association of Manufacturers (NAM) commented that the final
REA relied on an epidemiologic study (Delfino et al. 2002) not
critically reviewed in the final ISA.  Contrary to NAM’s contention,
the study by Delfino et al. (2002) was critically reviewed by EPA staff
and pertinent information was extracted from the study.  The respiratory
health effects of NO2 on asthma reported in this study are included in
Figure 5.3-1, Table 5.4-1, and Annex Table AX6.3-2 of the ISA.  While
NAM comments on the narrative discussion of this study in the final ISA,
their contention that EPA scientists did not critically analyze the
study while preparing the final ISA is incorrect.  The inclusion of the
study in the figures and tables in this ISA, as well as inclusion in the
2004 PM AQCD, indicate critical analysis of the study that was
implemented throughout the review process.  The narrative discussion in
the ISA focused on multicity studies (specifically those by Schwartz et
al. 1994, Mortimer et al. 2002 and Schildcrout et al. 2006), which
provide substantial epidemiologic evidence for the respiratory health
effects of NO2 on asthma among children.  

Additional comments from NAM contend that EPA’s interpretation of
three individual epidemiologic studies (e.g. Krewski et al. 2000;
Schildcrout et al. 2006; Mortimer et al. 2002) is inconsistent across
different NAAQS reviews.  The NAM comments on all three studies are
discussed below.  

NAM stated the following regarding the study by Krewski et al:

In the Final ISA, EPA cites the Krewski, et al. (2000) study as evidence
of a significant association between NO2 exposure and mortality.
Although EPA acknowledges that exposure to NO2 was “highly
correlated” with other pollutants, including PM2.5 and SO2, EPA does
not consider the analysis of the respective contributions of single
pollutants in the same study that EPA included in its prior Staff Paper
for Particulate Matter. In that document, EPA stated: “In
single-pollutant models, none of the gaseous co-pollutants was
significantly associated with mortality except SO2.” If EPA has not
altered its scientific views concerning this study as expressed in the
PM Staff Paper, it is entirely inappropriate for EPA to suggest that the
Krewski, et al. (2000) study provides any evidence of an association
between NO2 exposure and mortality. 

In these comments, NAM fails to recognize that the Krewski et al. (2000)
report contains a reanalysis of two cohort studies, the Harvard Six
Cities and the American Cancer Society (ACS) studies.  NAM correctly
quotes from the PM Staff Paper (2005) regarding the results of single
pollutant models on associations with mortality.  However, this
statement in the PM Staff Paper is referring to the results of the ACS
Study.  In contrast, the characterization in the NOX ISA of the study by
Krewski et al. (2000), referenced by NAM in their comments, refers to
the reanalysis of the Harvard Six Cities Study.  As stated in the NOX
ISA (p. 3-74): 

Krewski et al. (2000) conducted a sensitivity analysis of the Harvard
Six Cities study and examined associations between gaseous pollutants
(i.e., O3, NO2, SO2, CO) and mortality. NO2 showed risk estimates
similar to those for PM2.5 per “low to high” range increment with
total (1.15 [95% CI: 1.04, 1.27] per 10-ppb increase), cardiopulmonary
(1.17 [95% CI: 1.02, 1.34]), and lung cancer (1.09 [95% CI: 0.76, 1.57])
deaths; however, in this dataset NO2 was highly correlated with PM2.5
(r=0.78), SO4 2– (r=0.78), and SO2 (r=0.84).

In the subsequent paragraph, the NOX ISA presents results from the
Krewski et al. (2000) reanalysis of the ACS study, observing that “NO2
showed no associations with mortality outcomes” (ISA, p.3-74).  This
is consistent with the quote drawn from the PM Staff Paper.  Thus, there
is no inconsistency in the interpretation of the results of the study by
Krewski et al. (2000) in the PM Staff Paper (2005) and the NOX ISA
(2008).  NAM is confusing the conclusions on the results of the
reanalysis of the Harvard Six Cities Study in the NOX ISA with
conclusions regarding the reanalysis of the ACS study in the PM Staff
Paper.  

NAM also commented that EPA has relied on a study by Schildcrout et al.
(2006) in the NOX ISA but declined to rely on the same study for the
previous review of the O3 NAAQS.  NAM made the following comment
regarding the study by Schildcrout et al:

Another example of how EPA has reached different scientific conclusions
in the Final ISA than in prior NAAQS documents is provided by the
Schildcrout, et al. (2006) study. In the Final ISA, EPA includes an
extensive discussion of this study of asthmatic children and the
relationship purportedly found in this study between NO2 and various
respiratory symptoms. In contrast, as part of the NAAQS review for
ozone, EPA expressly declined to rely on this same study because of
specific limitations in the study design. Among the limitations EPA
cites were the fact that the Schildcrout, et al. (2006) study included
“children in which the severity of their asthma was not clearly
identified,” and the use of a study population that was “not
comparable to other large multi-city studies.” EPA must explain why it
chose to discount the value of the Schildcrout, et al. (2006) study when
evaluating the effects of ozone, but has relied on it extensively in the
Final ISA for NO2. 

The study by Schildcrout et al. (2006) appeared in the peer-review
literature too late to be considered in the 2006 O3 AQCD; however, this
study was included in the O3 Provisional Assessment.  The purpose of the
Provisional Assessment was to determine if new literature materially
changed any of the broad scientific conclusions regarding the health
effects of O3 exposure as stated in the 2006 O3 AQCD.  EPA concluded
that, taken in context, the “new” information and findings did not
materially change any of the broad scientific conclusions regarding the
health effects of O3 exposure made in the O3 AQCD.  Therefore, NAM’s
contention that EPA “declined” to rely on the Schildcrout study for
the O3 review because of limitations in study design is not correct.  

The observations NAM draws from the O3 Provisional Assessment regarding
severity of asthma and the study population do not indicate limitations
that resulted in EPA “discounting” the study results.  Rather, these
observations were intended to put the study in perspective for purposes
of interpreting the results within the context of the larger body of O3
health effects evidence.  These observations were drawn from comments
submitted by Dr. Schildcrout regarding the interpretation of the results
of his study in the decision to revise the ozone standards (see docket
ID EPA-HQ-OAR-2005-0172-6991).  The results of this study will be fully
considered in the upcoming review of the ozone NAAQS. 

Finally, NAM contends that EPA reached differing scientific conclusions
on the use of self-reported peak expiratory flow (PEF) depending on
regulatory context, particularly in the large multi-city trial by
Mortimer et al.   ADDIN
LC_ITEM<references><reference><heroid>30281</heroid><citation>Mortimer
KM; Neas LM; Dockery DW; Redline S; Tager IB. (2002). The effect of air
pollution on inner-city children with asthma. Eur Respir J, 19:
699-705.</citation><shortcitation>Mortimer et
al.</shortcitation><year>2002</year><link>http://cfpub.epa.gov/ncea/hero
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(2002) .  EPA consistently examines clinical measurements of lung
function, which include PEF, forced expiratory flow in 1 second (FEV1),
forced vital capacity (FVC), maximal midexpiratory flow (MMEF), maximal
expiratory flow at 50% (MEF50), maximal expiratory flow at 25% (MEF25),
and forced expiratory flow at 25 to 75% of FVC (FEF25-75).  Evidence for
all of these clinical measurements is considered before drawing a
conclusion related to the association of lung function with a criteria
pollutant.  In different reviews, there may be more evidence from one of
these clinical measurements than another.  In the previous NAAQS review
of ozone, EPA identified statistically significant associations between
increased ozone levels and morning PEF, which remained significant even
when concentrations exceeding 0.08 ppm were excluded from the analysis
(Mortimer et al. 2002).  EPA used this as evidence, along with evidence
of other clinical measurements of lung function, in drawing conclusions
on the relationship between ozone and lung function.  Similarly, in the
final NOX ISA, EPA weighed the all of the evidence pertinent to lung
function, including studies that produced no statistically significant
results for PEF, and the summary section (3.1.5.3) of the NO2 ISA
states:

In summary, epidemiologic studies using data from supervised lung
function measurements (spirometry or peak flow meters) report small
decrements in lung function   ADDIN
LC_ITEM<references><reference><heroid>46184</heroid><citation>Hoek G;
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id>90771</heroid><citation>Moshammer H; Hutter H-P; Hauck H; Neuberger
M. (2006). Low levels of air pollution induce changes of lung function
in a panel of schoolchildren. Eur Respir J, 27:
1138-1143.</citation><shortcitation>Moshammer et
al.</shortcitation><year>2006</year><link>http://cfpub.epa.gov/ncea/hero
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Scarlett JF; Strachan DP; Anderson HR. (2003). Acute effects of winter
air pollution on respiratory function in schoolchildren in southern
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id>14576</heroid><citation>Schindler C; Kunzli N; Bongard J-P;
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(2001). Short-term variation in air pollution and in average lung
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(Hoek and Brunekreef, 1995; Linn et al., 1996; Moshammer et al., 2006;
Peacock et al., 2003; Schindler et al., 2001) .  No significant
associations were reported in any studies using unsupervised,
self-administered peak flow [PEF] measurements with portable devices.

This evaluation of the evidence is consistent with the way that the
evidence from multiple clinical measures of lung function was used in
making similar statements during the NAAQS review for ozone.   

b.	Comments on EPA’s interpretation of the controlled human exposure
evidence 

A number of industry groups (e.g., AAM, ACC, API, Dow Chemical Company
(Dow), EMA, NAM, UARG) disagreed with EPA’s reliance on a
meta-analysis of controlled human exposure studies of airway
responsiveness in asthmatics.  Based on this meta-analysis (ISA, Table
3.1-3 for results), the ISA concluded that “small but significant
increases in nonspecific airway hyperresponsiveness were observed…at
0.1 ppm NO2 for 60-min exposures in asthmatics” (ISA, p. 5-11). 
Industry groups raised a number of objections to this analysis and the
way in which it has been used in the current review.  

Several of these industry groups concluded that, in relying on this
analysis, EPA has inappropriately relied on a new unpublished
meta-analysis that has not been peer-reviewed, was not reviewed by
CASAC, and was not conducted in a transparent manner.  For example, as
part of a Request for Correction submitted under EPA’s Information
Quality Guidelines, NAM stated that “EPA’s substantial reliance on
an unpublished assessment described as a “meta-analysis” of the
relation between NO2 exposure and changes in airway responsiveness
violates EPA Guidelines requiring “transparency about data and
methods.”  

EPA disagrees with this characterization of the updated meta-analysis
included in the final ISA.  As described in the ISA (p. 3-16), this
meta-analysis is based on an earlier analysis by Folinsbee (1992) that
has been subject to peer-review, that was published in a scientific
journal (Toxicol Ind Health. 8:1-11, 1992), and that was reviewed by
CASAC as part of the previous review of the NO2 NAAQS (EPA, 1993, Table
15-10).  The updates to this earlier analysis did not include
substantive changes to the approach.  As discussed in the final ISA (p.
3-16), the changes made to the analysis were to remove the results of
one allergen study and add results from a non-specific responsiveness
study, which focused the meta-analysis on non-specific airway
responsiveness, and to discuss results for an additional exposure
concentration (i.e., 100 ppb).  The information needed to reproduce this
meta-analysis is provided in the ISA (Tables 3.1-2 and 3.1-3, including
footnotes).  

While the ISA meta-analysis reports findings on airway responsiveness in
asthmatics following exposure to 100 ppb NO2, a concentration not
specifically discussed in the findings of the original report by
Folinsbee (1992), this does not constitute a substantive change to that
original analysis.  For exposures at rest, four of the studies included
in the analysis by Folinsbee evaluated the effects of exposure to 100
ppb NO2.  In that original meta-analysis, these studies were grouped
with another study that evaluated exposures to 140 ppb NO2.  When
analyzed together, exposures to NO2 concentrations of 100 ppb and 140
ppb (grouped together in the manuscript and described as less than 0.2
ppm) increased airway responsiveness in 65% of resting asthmatics (p <
0.01).  Therefore, reporting results at 100 ppb NO2 in the ISA
meta-analysis reflects a change in the way the data are presented and
does not reflect a substantive change to the study.  This change in
presentation allows specific consideration of the potential for
exposures to 100 ppb NO2 to increase airway responsiveness, rather than
grouping results at 100 ppb with results at other exposure
concentrations.  

In addition, the updated meta-analysis was considered by CASAC during
their review of the REA (REA, Table 4-5 reports the results of the
updated meta-analysis), which based part of the assessment of
NO2-associated health risks on the results of the meta-analysis.  In
their letter to the Administrator on the final REA (Samet, 2008b), CASAC
stated that “[t]he evidence reviewed in the REA indicates that adverse
health effects have been documented in clinical studies of persons with
asthma at 100 ppb” and that “CASAC firmly recommends that the upper
end of the range [of standard levels] not exceed 100 ppb, given the
findings of the REA.”  In addition, in their comments on the proposal,
CASAC reiterated this advice in their statement that “the level of the
one-hour NO2 standard should be within the range of 80-100 ppb and not
above 100 ppb.”  These statements indicate that CASAC did specifically
consider the results of the updated meta-analysis and that they used
those results to inform their recommendations on the range of standard
levels supported by the scientific evidence.  

In summary, we note the following:

The original meta-analysis was published in a peer-reviewed journal and
was reviewed by CASAC in the previous review of the NO2 NAAQS

The updated meta-analysis does not include substantive changes to the
methodology of this original analysis 

The changes that were made are clearly described in the ISA 

CASAC specifically reviewed and considered the ISA meta-analysis in
making recommendations regarding the range of standard levels supported
by the science

  

Many of these same industry groups also referred in their comments to a
recent meta-analysis of controlled human exposure studies evaluating the
airway response in asthmatics following NO2 exposure (Goodman et al.,
2009).  These groups generally recommended that EPA rely on this
meta-analysis and on the authors’ conclusions with regard to NO2 and
airway responsiveness.  Specific comments based on the manuscript by
Goodman et al., as well as EPA’s responses, are discussed below in
more detail.  

Industry commenters generally claimed that the meta-analysis by Goodman
et al. supports the conclusion that no adverse effects occur following
exposures up to 600 ppb NO2.  However, Table 4 of the Goodman study
reports that 64% (95% Confidence Interval: 58%, 71%) of resting
asthmatics exposed to NO2 experienced an increase in airway
responsiveness.  Furthermore, Figure 2a of this manuscript reports that
for exposures <0.2 ppm, the fraction affected is 0.61 (95% CI: 0.52,
0.70) while for exposures of 0.2 ppm to <0.3 ppm, the fraction affected
is 0.66 (95% CI: 0.59, 0.74).  These findings are consistent with those
reported in the meta-analysis by Folinsbee and in the updated
meta-analysis that was included in the final ISA.    

Also based on the meta-analysis by Goodman et al. (2009), several
industry commenters concluded that NO2-induced airway
hyperresponsiveness is not adverse and, therefore, should not be
considered in setting standards.  The basis for this comment appears to
be the conclusions reached by Goodman et al. that there is no
dose-response relationship for NO2 and that the magnitude of any NO2
effect on airway responsiveness is too small to be considered adverse.  

Due to differences in study protocols in the NO2-airway response
literature (ISA, section 3.1.3), EPA disagrees with the approach taken
in the Goodman study to use existing data to attempt to evaluate the
presence of a dose-response relationship and to determine the magnitude
of the NO2 response.  Examples of differences in the study protocols
include the NO2 exposure method (i.e., mouthpiece versus chamber),
subject activity level (i.e., rest versus exercise) during NO2 exposure,
choice of airway challenge agent, and physiological endpoint used to
quantify airway responses.  Goodman et al. (2009) also recognized
heterogeneity among studies as a limitation in their analyses.  

As a result of these differences, EPA judged it appropriate in the ISA
meta-analysis to assess only the fraction of asthmatics experiencing
increased or decreased airway responsiveness following NO2 exposure.  We
have acknowledged in the REA, the proposal, and in this final rulemaking
that there is uncertainty with regard to the magnitude and the
clinical-significance of NO2-induced increases in airway responsiveness
(see sections II.C.3 and II.F.4.a in the proposed rulemaking as well as
II.F.3 in this final rulemaking).  The REA stated the following (p.
302): 

[O]ne of the important uncertainties associated with these [NO2-induced
airway hyperresponsiveness] results is that, because the meta-analysis
evaluated only the direction of the change in airway responsiveness, it
is not possible to discern the magnitude of the change from these data. 
This limitation makes it particularly difficult to quantify the public
health implications of these results. 

While we acknowledge this uncertainty, EPA disagrees with the conclusion
that the NO2-induced increase in airway responsiveness in asthmatics
exposed to NO2 concentrations up to 600 ppb is not adverse and should
not be considered in setting standards.  Specifically, we note that the
ISA concluded that “[t]ransient increases in airway responsiveness
following NO2 exposure have the potential to increase symptoms and
worsen asthma control” (ISA, section 5.4).  The uncertainty over the
adversity of the response reported in controlled human exposure studies
does not mean that the NO2-induced increase in airway responsiveness is
not adverse.  Rather, it means that there is a risk of adversity,
especially for asthmatics with more than mild asthma, but that this risk
cannot be fully characterized based on existing studies.  The studies of
NO2 and airway responsiveness included in the meta-analysis have
generally evaluated mild asthmatics, rather than more severely affected
asthmatics who could be more susceptible to the NO2-induced increase in
airway responsiveness (ISA, section 3.1.3.2).  Given that this is the
case, and given the large percentage of asthmatics that experienced an
NO2-induced increase in airway responsiveness in the studies and the
large size of the asthmatic population in the United States, the REA
concluded that it is appropriate to consider NO2-induced airway
hyperresponsiveness in characterizing NO2-associated health risks (REA,
section 10.3.2).  As noted above, CASAC endorsed this conclusion in
their letters to the Administrator on the final REA and on the proposal
(Samet, 2008b; Samet, 2009).    

c.	Comments on EPA’s characterization of NO2-associated exposures and
health risks 

Several commenters discussed the analyses of NO2-associated exposures
and health risks presented in the REA.  As in past reviews (EPA 2005,
2007d, 2007e), EPA has estimated allowable risks associated with the
current standard and potential alternative standards to inform judgments
on the public health risks that could exist under different standard
options.  Some industry commenters (e.g., API, NMA) concluded that the
Administrator should consider modeled exposures and risks associated
with actual NO2 air quality rather than with NO2 concentrations adjusted
to simulate just meeting the current annual standard or potential
alternative 1-hour standards.  These commenters pointed out that such
simulations require large adjustments to air quality and are highly
uncertain and that NAAQS are intended to address actual, rather than
highly improbable, risks to health.    

We disagree with these commenters that exposure- and risk-related
considerations in the NAAQS review should rely only on unadjusted air
quality.  In considering whether the current standard is requisite to
protect public health with an adequate margin of safety, air quality
adjustments allow estimates of NO2-related exposures and health risks
that could exist in areas that just meet that standard.  That is, these
adjustments allow consideration of exposures and risks that would be
permissible under the current standard.  Therefore, such adjustments are
clearly useful to inform a decision on the issue before EPA (i.e., the
adequacy of the level of public health protection associated with
allowable NO2 air quality under the standard).  Similarly, air quality
adjustments to simulate different potential alternative standards
provide information on exposures and risks that would be permissible
under these alternatives.   As noted above, in their letter to the
Administrator on the final REA (Samet, 2008b), CASAC concluded that
“The REA provides the needed bridge from the evidence presented in the
ISA to a characterization of the exposures and the associated risks with
different profiles of exposure.”  

We agree that there are uncertainties inherent in air quality
adjustments.  These uncertainties are discussed thoroughly in the REA
(sections 7.4, 8.12, 9.6, and 10.3.2.1) and in the proposed rule
(section II.C.3).  For example, the policy assessment chapter of the REA
(section 10.3.2.1) noted the following regarding adjustment of NO2
concentrations: 

In order to simulate just meeting the current annual standard and many
of the alternative 1-h standards analyzed, an upward adjustment of
recent ambient NO2 concentrations was required.  We note that this
adjustment does not reflect a judgment that levels of NO2 are likely to
increase under the current standard or any of the potential alternative
standards under consideration.  Rather, these adjustments reflect the
fact that the current standard, as well as some of the alternatives
under consideration, could allow for such increases in ambient NO2
concentrations.  In adjusting air quality to simulate just meeting these
standards, we have assumed that the overall shape of the distribution of
NO2 concentrations would not change.  While we believe this is a
reasonable assumption in the absence of evidence supporting a different
distribution and we note that available analyses support this approach
(Rizzo, 2008), we recognize this as an important uncertainty.  It may be
an especially important uncertainty for those scenarios where
considerable upward adjustment is required to simulate just meeting one
or more of the standards.

These air quality adjustments are not meant to imply an expectation that
NO2 concentrations will increase broadly across the United States or in
any given area (REA, section 10.3.2.1).  Rather, as noted above, they
are meant to estimate NO2-related exposures and health risks that would
be permitted under the current and potential alternative standards. 
Such estimates can inform decisions on whether the current standard, or
particular potential alternative standards, provide the requisite
protection of public health. 

3.	Conclusions regarding the adequacy of the current standard 

In considering the adequacy of the current standard, the Administrator
has considered the scientific evidence assessed in the ISA, the exposure
and risk results presented in the REA, the conclusions of the policy
assessment chapter of the REA, and comments from CASAC and the public. 
These considerations are described below.    

In considering the scientific evidence as it relates to the adequacy of
the current standard, the Administrator notes that the epidemiologic
evidence has grown substantially since the last review with the addition
of field and panel studies, intervention studies, and time-series
studies of effects such as emergency department visits and hospital
admissions associated with short-term NO2 exposures.  No epidemiologic
studies were available in 1993 assessing relationships between NO2 and
outcomes such as hospital admissions or emergency department visits.  In
contrast, dozens of epidemiologic studies on such outcomes, conducted at
recent and current ambient NO2 concentrations, are now included in this
evaluation (ISA, chapter 3).      

As an initial consideration with regard to the adequacy of the current
standard, the Administrator notes that the evidence relating long-term
(weeks to years) NO2 exposures at current ambient concentrations to
adverse health effects was judged in the ISA to be either “suggestive
but not sufficient to infer a causal relationship” (respiratory
morbidity) or “inadequate to infer the presence or absence of a causal
relationship” (mortality, cancer, cardiovascular effects,
reproductive/developmental effects) (ISA, sections 5.3.2.4-5.3.2.6).  In
contrast, the evidence relating short-term (minutes to hours) NO2
exposures to respiratory morbidity was judged to be “sufficient to
infer a likely causal relationship” (ISA, section 5.3.2.1).  This
conclusion was supported primarily by a large body of recent
epidemiologic studies that evaluated associations of short-term NO2
concentrations with respiratory symptoms, emergency department visits,
and hospital admissions.  Given these conclusions from the ISA, the
Administrator judges that, at a minimum, consideration of the adequacy
of the current annual standard should take into account the extent to
which that standard provides protection against respiratory effects
associated with short-term NO2 exposures.  

In considering the NO2 epidemiologic studies as they relate to the
adequacy of the current standard, the Administrator notes that annual
average NO2 concentrations were below the level of the current annual
NO2 NAAQS in many of the locations where positive, and often
statistically significant, associations with respiratory morbidity
endpoints have been reported (ISA, section 5.4).  As discussed
previously, the ISA characterized that evidence for respiratory effects
as consistent and coherent.  The evidence is consistent in that
associations are reported in studies conducted in numerous locations and
with a variety of methodological approaches (ISA, section 5.3.2.1).  It
is coherent in the sense that the studies report associations with
respiratory health outcomes that are logically linked together (ISA,
section 5.3.2.1).  The ISA noted that when the epidemiologic literature
is considered as a whole, there are generally positive associations
between NO2 and respiratory symptoms, hospital admissions, and emergency
department visits.  A number of these associations are statistically
significant, particularly the more precise effect estimates (ISA,
section 5.3.2.1).  

As discussed in the proposal (II.E.1) and above, the Administrator
acknowledges that the interpretation of these NO2 epidemiologic studies
is complicated by the fact that on-road vehicle exhaust emissions are a
nearly ubiquitous source of combustion pollutant mixtures that include
NO2.  She notes that, in order to provide some perspective on the
uncertainty related to the presence of co-pollutants the ISA evaluated
epidemiologic studies that employed multi-pollutant models,
epidemiologic studies of indoor NO2 exposure, and experimental studies. 
Specifically, the ISA noted that a number of NO2 epidemiologic studies
have attempted to disentangle the effects of NO2 from those of
co-occurring pollutants by employing multi-pollutant models.  When
evaluated as a whole, NO2 effect estimates in these models generally
remained robust when co-pollutants were included.  Therefore, despite
uncertainties associated with separating the effects of NO2 from those
of co-occurring pollutants, the ISA (section 5.4, p. 5-16) concluded
that “the evidence summarized in this assessment indicates that NO2
associations generally remain robust in multi-pollutant models and
supports a direct effect of short-term NO2 exposure on respiratory
morbidity at ambient concentrations below the current NAAQS.”  With
regard to indoor studies, the ISA noted that these studies can test
hypotheses related to NO2 specifically (ISA, section 3.1.4.1).  Although
confounding by indoor combustion sources is a concern, indoor studies
are not confounded by the same mix of co-pollutants present in the
ambient air or by the contribution of NO2 to the formation of secondary
particles or O3 (ISA, section 3.1.4.1).  The ISA noted that the findings
of indoor NO2 studies are consistent with those of studies using ambient
concentrations from central site monitors and concluded that indoor
studies provide evidence of coherence for respiratory effects (ISA,
section 3.1.4.1).  With regard to experimental studies, the REA noted
that they have the advantage of providing information on health effects
that are specifically associated with exposure to NO2 in the absence of
co-pollutants.  The ISA concluded that the NO2 epidemiologic literature
is supported by 1) evidence from controlled human exposure studies of
airway hyperresponsiveness in asthmatics, 2) controlled human exposure
and animal toxicological studies of impaired host-defense systems and
increased risk of susceptibility to viral and bacterial infection, and
3) controlled human exposure and animal toxicological studies of airway
inflammation (ISA, section 5.3.2.1 and 5.4).  Given the above
consideration of the evidence, particularly the epidemiologic studies
reporting NO2-associated health effects in locations that meet the
current standard, the Administrator agrees with the conclusion in the
policy assessment chapter of the REA that the scientific evidence calls
into question the adequacy of the current standard to protect public
health. 

In addition to the evidence-based considerations described above, the
Administrator has considered the extent to which exposure- and
risk-based information can inform decisions regarding the adequacy of
the current annual NO2 standard.  While she acknowledges the
uncertainties associated with adjusting air quality in these analyses,
she judges that such analyses are appropriate for consideration in this
review of the NO2 primary NAAQS.  In reaching this conclusion she notes
the considerations discussed above, particularly the endorsement by
CASAC of the REA and its characterization of NO2-associated exposures
and health risks.  

In considering the exposure- and risk-based information with regard to
the adequacy of the current annual NO2 standard to protect the public
health, the Administrator notes the conclusion in the policy assessment
chapter of the REA that risks estimated to be associated with air
quality adjusted upward to simulate just meeting the current standard
can reasonably be concluded to be important from a public health
perspective.  In particular, a large percentage (8-9%) of
respiratory-related ED visits in Atlanta could be associated with
short-term NO2 exposures, most asthmatics in Atlanta could be exposed on
multiple days per year to NO2 concentrations at or above 300 ppb, and
most locations evaluated could experience on-/near-road NO2
concentrations above 100 ppb on more than half of the days in a given
year.  Therefore, after considering the results of the exposure and risk
analyses presented in the REA the Administrator agrees with the
conclusion of the policy assessment chapter of the REA that exposure-
and risk-based results reinforce the scientific evidence in supporting
the conclusion that consideration should be given to revising the
current standard so as to provide increased public health protection,
especially for at-risk groups, from NO2-related adverse health effects
associated with short-term, and potential long-term, exposures.  

In reaching a conclusion on the adequacy of the current standard, the
Administrator has also considered advice received from CASAC.  In their
comments on the final REA, CASAC agreed that the primary concern in this
review is to protect against health effects that have been associated
with short-term NO2 exposures.  CASAC also agreed that the current
annual standard is not sufficient to protect public health against the
types of exposures that could lead to these health effects.  As noted in
their letter to the EPA Administrator, “CASAC concurs with EPA’s
judgment that the current NAAQS does not protect the public’s health
and that it should be revised” (Samet, 2008b).  

Based on the considerations discussed above, the Administrator concludes
that the current NO2 primary NAAQS alone is not requisite to protect
public health with an adequate margin of safety.  Accordingly, she
concludes that the NO2 primary standard should be revised in order to
provide increased public health protection against respiratory effects
associated with short-term exposures, particularly for susceptible
populations such as asthmatics, children, and older adults.  In
considering approaches to revising the current standard, the
Administrator concludes that it is appropriate to consider setting a new
short-term standard (see below).  The Administrator notes that such a
short-term standard could provide increased public health protection,
especially for members of at-risk groups, from effects described in both
epidemiologic and controlled human exposure studies to be associated
with short-term exposures to NO2.  

F.	Elements of a new short-term standard 

In considering a revised NO2 primary NAAQS, the Administrator notes the
need to protect at-risk individuals from short-term exposures to NO2 air
quality that could cause the types of respiratory morbidity effects
reported in epidemiologic studies and the need to protect at-risk
individuals from short-term exposure to NO2 concentrations reported in
controlled human exposure studies to increase airway responsiveness in
asthmatics.  The Administrator’s considerations with regard to her
decisions are discussed in the following sections in terms of indicator
(II.F.1), averaging time (II.F.2), level (II.F.3), and form (II.F.4). 

1.	Indicator

a.	Rationale for proposed decision 

In past reviews, EPA has focused on NO2 as the most appropriate
indicator for ambient NOX.  In making a decision in the current review
on the most appropriate indicator, the Administrator considered the
conclusions of the ISA and the policy assessment chapter of the REA as
well as the view expressed by CASAC.  The policy assessment chapter of
the REA noted that, while the presence of NOX species other than NO2 has
been recognized, no alternative to NO2 has been advanced as being a more
appropriate surrogate.  Controlled human exposure studies and animal
toxicology studies assessed in the ISA provide specific evidence for
health effects following exposure to NO2.  Epidemiologic studies also
typically report levels of NO2 though the degree to which monitored NO2
reflects actual NO2 levels, as opposed to NO2 plus other gaseous NOX,
can vary (REA, section 2.2.3).   In addition, because emissions that
lead to the formation of NO2 generally also lead to the formation of
other NOX oxidation products, measures leading to reductions in
population exposures to NO2 can generally be expected to lead to
reductions in population exposures to other gaseous NOX.  Therefore, an
NO2 standard can also be expected to provide some degree of protection
against potential health effects that may be independently associated
with other gaseous NOX even though such effects are not discernable from
currently available studies indexed by NO2 alone.  Given these key
points, the policy assessment chapter of the REA concluded that the
evidence supports retaining NO2 as the indicator.  Consistent with this
conclusion, the CASAC Panel stated in its letter to the EPA
Administrator that it “concurs with retention of NO2 as the
indicator” (Samet, 2008b).  In light of the above considerations, the
Administrator proposed to retain NO2 as the indicator in the current
review. 

b.	Comments on indicator 

A relatively small number of comments directly addressed the issue of
the indicator for the standard (CASAC, Dow, API, AAM, and the Missouri
Department of Natural Resources Air Pollution Control Program (MODNR)). 
All of these commenters endorsed the proposal to continue to use NO2 as
the indicator for ambient NOX.  

 c.	Conclusions on indicator 

	Based on the available information discussed above, and consistent with
the views of CASAC and other commenters, the Administrator concludes
that it is appropriate to continue to use NO2 as the indicator for a
standard that is intended to address effects associated with exposure to
NO2, alone or in combination with other gaseous NOX.  In so doing, the
Administrator recognizes that measures leading to reductions in
population exposures to NO2 will also reduce exposures to other nitrogen
oxides. 

2.	Averaging time 

	This section discusses considerations related to the averaging time of
the NO2 primary NAAQS.  Specifically, this section summarizes the
rationale for the Administrator’s proposed decision regarding
averaging time (II.F.2.a; see section II.F.2 of the proposal for more
detail), discusses comments related to averaging time (II.F.2.b), and
presents the Administrator’s final conclusions regarding averaging
time (II.F.2.c).   

a.	Rationale for proposed decision

In considering the most appropriate averaging time for the NO2 primary
NAAQS, the Administrator noted in the proposal the conclusions and
judgments made in the ISA about available scientific evidence, air
quality correlations discussed in the REA, conclusions of the policy
assessment chapter of the REA, and CASAC recommendations (section II.F.2
in the proposal).  Specifically, she noted the following: 

Experimental studies in humans and animals have reported respiratory
effects following NO2 exposures lasting from less than 1-hour up to
several hours.  Epidemiologic studies have reported associations between
respiratory effects and both 1-hour and 24-hour NO2 concentrations. 
Therefore, the experimental evidence provides support for an averaging
time of shorter duration than 24 hours (e.g., 1-hour) while the
epidemiologic evidence provides support for both 1-hour and 24-hour
averaging times.  At a minimum, this suggests that a primary concern
with regard to averaging time is the level of protection provided
against 1-hour NO2 concentrations.  

Air quality correlations presented in the policy assessment chapter of
the REA illustrated the relatively high degree of variability in the
ratios of annual average to short-term NO2 concentrations (REA, Table
10-2).  This variability suggests that a standard based on annual
average NO2 concentrations would not likely be an effective or efficient
approach to focus protection on short-term exposures.  

These air quality correlations (REA, Table 10-1) suggested that a
standard based on 1-hour daily maximum NO2 concentrations could also be
effective at protecting against 24-hour NO2 concentrations.  

The policy assessment chapter of the REA concluded that the scientific
evidence, combined with the air quality correlations, support the
appropriateness of a standard based on 1-hour daily maximum NO2
concentrations to protect against health effects associated with
short-term exposures.  

CASAC concurred “with having a short-term NAAQS primary standard for
oxides of nitrogen and using the one-hour maximum NO2 value” (Samet,
2008b).  

Based on these considerations, the Administrator proposed to set a new
standard based on 1-hour daily maximum NO2 concentrations.  

b.	Comments on averaging time

As discussed above, CASAC endorsed the establishment of a new standard
with a 1-hour averaging time.  CASAC stated the following in their
comments on the proposal (Samet, 2009): 

In reviewing the REA, CASAC supported a short-term standard for NO2 and
in reviewing the proposal, CASAC supports the proposed one-hour
averaging time in EPA's proposed rule.  

The supporting rationale offered by CASAC in support of a new 1-hour
standard was generally the same as that put forward in the final REA and
the proposal.  Specifically, that rationale considered the available
scientific evidence, which supports a link between 1-hour NO2
concentrations and adverse respiratory effects, and air quality
information presented in the REA, which suggests that a 1-hour standard
can protect against effects linked to short-term NO2 exposures while an
annual standard would not be an effective or efficient approach to
protecting against these effects.  

A large number of public commenters also endorsed the establishment of a
new standard with a 1-hour averaging time.  These included a number of
State agencies and organizations (e.g., NACAA, NESCAUM and agencies in
CA, IL, NM, TX, VA); environmental, medical, and public health
organizations (e.g., ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP, NACPR,
NAMDRC, NRDC); and most individual commenters.  The supporting
rationales offered by these commenters often acknowledged the
recommendations of CASAC and the Administrator’s rationale as
discussed in the proposal.     

Though many industry commenters recommended not revising the current
annual standard (as discussed above in section II.E.2), several of these
groups did conclude that if a short-term standard were to be set, a
1-hour averaging time would be appropriate (e.g., Colorado Petroleum
Association (CPA), Dow, NAM, Petroleum Association of Wyoming (PAW),
Utah Petroleum Association (UPA)).  As discussed above, industry
commenters who disagreed with setting a new 1-hour standard generally
based this conclusion on their interpretation of the scientific evidence
and their conclusion that this evidence does not support the need to
revise the current annual standard.  These comments, and EPA’s
responses, are discussed in more detail above (section II.E) and in the
Response to Comments document.  

c.	Conclusions on averaging time

In considering the most appropriate averaging time for the NO2 primary
NAAQS, the Administrator notes the available scientific evidence as
assessed in the ISA, the air quality analyses presented in the REA, the
conclusions of the policy assessment chapter of the REA, CASAC
recommendations, and public comments received.  These considerations are
described below.  

When considering averaging time, the Administrator notes that the
evidence relating short-term (minutes to hours) NO2 exposures to
respiratory morbidity was judged in the ISA to be “sufficient to infer
a likely causal relationship” (ISA, section 5.3.2.1) while the
evidence relating long-term (weeks to years) NO2 exposures to adverse
health effects was judged to be either “suggestive but not sufficient
to infer a causal relationship” (respiratory morbidity) or
“inadequate to infer the presence or absence of a causal
relationship” (mortality, cancer, cardiovascular effects,
reproductive/developmental effects) (ISA, sections 5.3.2.4-5.3.2.6). 
Thus, the Administrator concludes that these judgments most directly
support an averaging time that focuses protection on short-term
exposures to NO2.    

As in past reviews of the NO2 NAAQS, the Administrator notes that it is
instructive to evaluate the potential for a standard based on annual
average NO2 concentrations, as is the current standard, to provide
protection against short-term NO2 exposures.  To this end, the
Administrator notes that Table 10-1 in the REA reported the ratios of
short-term to annual average NO2 concentrations.  Ratios of 1-hour daily
maximum concentrations (98th and 99th percentile) to annual average
concentrations across 14 locations ranged from 2.5 to 8.7 while ratios
of 24-hour average concentrations to annual average concentrations
ranged from 1.6 to 3.8 (see Thompson, 2008 for more details).  The
policy assessment chapter of the REA concluded that the variability in
these ratios across locations, particularly those for 1-hour
concentrations, suggested that a standard based on annual average NO2
concentrations would not likely be an effective or efficient approach to
focus protection on short-term NO2 exposures.  For example, in an area
with a relatively high ratio (e.g., 8), the current annual standard (53
ppb) would be expected to allow 1-hour daily maximum NO2 concentrations
of about 400 ppb.  In contrast, in an area with a relatively low ratio
(e.g., 3), the current standard would be expected to allow 1-hour daily
maximum NO2 concentrations of about 150 ppb.  Thus, for purposes of
protecting against the range of 1-hour NO2 exposures, the REA noted that
a standard based on annual average concentrations would likely require
more control than necessary in some areas and less control than
necessary in others, depending on the standard level selected. 

In considering the level of support available for specific short-term
averaging times, the Administrator notes that the policy assessment
chapter of the REA considered evidence from both experimental and
epidemiologic studies.  Controlled human exposure studies and animal
toxicological studies provide evidence that NO2 exposures from less than
1-hour up to 3-hours can result in respiratory effects such as increased
airway responsiveness and inflammation (ISA, section 5.3.2.7). 
Specifically, the ISA concluded that NO2 exposures of 100 ppb for 1-hour
(or 200 ppb to 300 ppb for 30-min) can result in small but significant
increases in nonspecific airway responsiveness (ISA, section 5.3.2.1). 
In contrast, the epidemiologic literature provides support for
short-term averaging times ranging from approximately 1-hour up to
24-hours (ISA, section 5.3.2.7).  A number of epidemiologic studies have
detected positive associations between respiratory morbidity and 1-hour
(daily maximum) and/or 24-hour NO2 concentrations.  A few epidemiologic
studies have considered both 1-hour and 24-hour averaging times,
allowing comparisons to be made.  The ISA reported that such comparisons
in studies that evaluate asthma emergency department visits failed to
reveal differences between effect estimates based on a 1-hour averaging
time and those based on a 24-hour averaging time (ISA, section 5.3.2.7).
 Therefore, the ISA concluded that it is not possible, from the
available epidemiologic evidence, to discern whether effects observed
are attributable to average daily (or multi-day) concentrations (24-hour
average) or high, peak exposures (1-hour maximum) (ISA, section
5.3.2.7).    

As noted in the policy assessment chapter of the REA, given the above
conclusions, the experimental evidence provides support for an averaging
time of shorter duration than 24 hours (e.g., 1-h) while the
epidemiologic evidence provides support for both 1-hour and 24-hour
averaging times.  The Administrator concludes that, at a minimum, this
suggests that a primary concern with regard to averaging time is the
level of protection provided against 1-hour NO2 concentrations. 
However, she also notes that it is important to consider the ability of
a 1-hour averaging time to protect against 24-hour average NO2
concentrations.  To this end, the Administrator notes that Table 10-2 in
the REA presented correlations between 1-hour daily maximum NO2
concentrations and 24-hour average NO2 concentrations (98th and 99th
percentile) across 14 locations (see Thompson, 2008 for more detail). 
Typical ratios ranged from 1.5 to 2.0, though one ratio (Las Vegas) was
3.1.  These ratios were far less variable than those discussed above for
annual average concentrations, suggesting that a standard based on
1-hour daily maximum NO2 concentrations could also be effective at
protecting against 24-hour NO2 concentrations.  The REA concluded that
the scientific evidence, combined with the air quality correlations
described above, support the appropriateness of a standard based on
1-hour daily maximum NO2 concentrations to protect against health
effects associated with short-term exposures.

Based on these considerations, the Administrator concludes that a
standard with a 1-hour averaging time can effectively limit short-term
(i.e., 1- to 24-hours) exposures that have been linked to adverse
respiratory effects.  This conclusion is based on the observations
summarized above and in more detail in the proposal, particularly that:
1) the 1-hour averaging time has been directly associated with
respiratory effects in both epidemiologic and experimental studies and
that 2) results from air quality analyses suggest that a 1-hour standard
could also effectively control 24-hour NO2 concentrations.  In addition,
the Administrator notes the support provided for a 1-hour averaging time
in comments from CASAC, States, environmental groups, and medical/public
health groups.  The Administrator notes that arguments offered by some
industry groups against setting a 1-hour NO2 standard generally focus on
commenters’ conclusions regarding uncertainties in the scientific
evidence.  As discussed in more detail above (section II.E.2), the
Administrator disagrees with the conclusions of these commenters
regarding the appropriate interpretation of the scientific evidence and
associated uncertainties.  Given these considerations, the Administrator
judges that it is appropriate to set a new NO2 standard with a 1-hour
averaging time.  

3.	Form 

This section discusses considerations related to the form of the 1-hour
NO2 primary NAAQS.  Specifically, this section summarizes the rationale
for the Administrator’s proposed decision regarding form (II.F.4.a;
see section II.F.3 of the proposal for more detail), discusses comments
related to form (II.F.4.b), and presents the Administrator’s final
conclusions regarding form (II.F.4.c).   

a.	Rationale for proposed decision

When considering alternative forms in the proposal, the Administrator
noted the conclusions in the policy assessment chapter of the REA. 
Specifically, she noted the conclusion that the adequacy of the public
health protection provided by the combination of standard level and form
should be the foremost consideration.  With regard to this, she noted
that concentration-based forms can better reflect pollutant-associated
health risks than forms based on expected exceedances.  This is the case
because concentration-based forms give proportionally greater weight to
years when pollutant concentrations are well above the level of the
standard than to years when the concentrations are just above the
standard, while an expected exceedance form would give the same weight
to years with concentrations that just exceed the standard as to years
when concentrations greatly exceed the standard.  The Administrator also
recognized the conclusion in the policy assessment chapter of the REA
that it is desirable from a public health perspective to have a form
that is reasonably stable and insulated from the impacts of extreme
meteorological events.  With regard to this, she noted that a form that
calls for averaging concentrations over three years would provide
greater regulatory stability than a form based on a single year of
concentrations.  Therefore, consistent with recent reviews of the O3 and
PM NAAQS, the proposal focused on concentration-based forms averaged
over 3 years, as evaluated in the REA.

In considering specific concentration-based forms, the REA focused on
98th and 99th percentile concentrations averaged over 3 years.  This
focus on the upper percentiles of the distribution is appropriate given
the reliance, in part, on NO2 health evidence from experimental studies,
which provide information on specific exposure concentrations that are
linked to specific health effects.  The REA noted that a 99th percentile
form for a 1-hour daily maximum standard would correspond approximately
to the 4th highest daily maximum concentration in a year (which is the
form of the current O3 NAAQS) while a 98th percentile form (which is the
form of the current short-term PM2.5 NAAQS) would correspond
approximately to the 7th or 8th highest daily maximum concentration in a
year (REA, Table 10-4; see Thompson, 2008 for methods).  

Consideration in the REA of an appropriate form for a 1-hour standard
was based on analyses of standard levels that reflected the allowable
area-wide NO2 concentration, not the maximum allowable concentration. 
Therefore, in their review of the final REA, CASAC did not have the
opportunity to comment on the appropriateness of specific forms in
conjunction with a standard level that reflects the maximum allowable
NO2 concentration anywhere in an area.  Given this, when considering
alternative forms for the 1-hour standard in the proposal, the
Administrator judged that it was appropriate to consider both forms
evaluated in the REA (i.e., 98th and 99th percentiles).  Therefore, she
proposed to adopt either a 99th percentile or a 4th highest form,
averaged over 3 years, and she solicited comment on both 98th percentile
and 7th or 8th highest forms.  

b.	CASAC and public comments on form

In their letter to the Administrator, CASAC discussed the issue of form
within the context of the proposed approach of setting a 1-hour standard
level that reflects the maximum allowable NO2 concentration anywhere in
an area.  CASAC recommended that, for such a standard, EPA adopt a form
based on the 3-year average of the 98th percentile of the distribution
of 1-hour daily maximum NO2 concentrations.  Specifically, they stated
the following in their comments on the proposal (Samet, 2009): 

The 98th percentile is preferred by CASAC for the form, given the likely
instability of measurements at the upper range and the absence of data
from the proposed two-tier approach.

As indicated in their letter, CASAC concluded that the potential
instability in higher percentile NO2 concentrations near major roads
argues for a 98th, rather than a 99th, percentile form.  Several State
organizations and agencies (e.g., NESCAUM and agencies in IN, NC, SD,
VA) and industry groups (e.g., AAM, ACC, API, AirQuality Research and
Logistics (AQRL), CPA, Dow, ExxonMobil, IPAMS, PAW, UPA) also
recommended a 98th percentile form in order to provide regulatory
stability.  In contrast, a small number of State and local agencies
(e.g., in MO and TX), several environmental organizations (e.g., EDF,
EJ, GASP, NRDC), and medical/public health organizations (e.g., ALA,
ATS) recommended either a 99th percentile form or a more stringent form
(e.g., no exceedance) to further limit the occurrence of NO2
concentrations that exceed the standard level in locations that attain
the standard.    

c.	Conclusions on form 

The Administrator recognizes that there is not a clear health basis for
selecting one specific form over another.  She also recognizes that the
analyses of different forms in the REA are most directly relevant to a
standard that reflects NO2 concentrations permitted to occur broadly
across a community, rather than the maximum concentration that can occur
anywhere in the area.  In contrast, as discussed below (section
II.F.4.c), the Administrator has judged it appropriate to set a new
1-hour standard that reflects the maximum allowable NO2 concentration
anywhere in an area.  In light of this, the Administrator places
particular emphasis on the comments received on form from CASAC relating
to a 1-hour standard level that reflects the maximum allowable NO2
concentration anywhere in an area.  In particular, the Administrator
notes that CASAC recommended a 98th percentile form averaged over 3
years for such a standard, given the potential for instability in the
higher percentile concentrations around major roadways.  

In considering this recommendation, the Administrator recognizes that
the public health protection provided by the 1-hour NO2 standard is
based on the approach used to set the standard and the level of the
standard (see below), in conjunction with the form of the standard. 
Given that the Administrator is setting a standard that reflects the
maximum allowable NO2 concentration anywhere in an area, rather than a
standard that reflects the allowable area-wide NO2 concentration, she
agrees with CASAC that an appropriate consideration with regard to form
is the extent to which specific statistics could be unstable at
locations where maximum NO2 concentrations are expected, such as near
major roads.  When considering alternative forms for the standard, the
Administrator notes that an unstable form could result in areas shifting
in and out of attainment, potentially disrupting ongoing air quality
planning without achieving public health goals.  Given the limited
available information on the variability in peak NO2 concentrations near
important sources of NO2 such as major roadways, and given the
recommendation from CASAC that the potential for instability in the 99th
percentile concentration is cause for supporting a 98th percentile form,
the Administrator judges it appropriate to set the form based on the
3-year average of the 98th percentile of the annual distribution of
1-hour daily maximum NO2 concentrations.  

4.	Level 

As discussed below and in more detail in the proposal (section II.F.4),
the Administrator has considered two different approaches to setting the
1-hour NO2 primary NAAQS.  In the proposal, each of these approaches was
linked with a different range of standard levels.  Specifically, the
Administrator proposed to set a 1-hour standard reflecting the maximum
allowable NO2 concentration anywhere in an area and to set the level of
such a standard from 80 to 100 ppb.  The Administrator also solicited
comment on the alternative approach of setting a standard that reflects
the allowable area-wide NO2 concentration and setting the standard level
from 50 to 75 ppb.  This section summarizes the rationale for the
Administrator’s proposed approach and range of standard levels
(II.F.3.a), describes the alternative approach and range of standard
levels (II.F.3.b), discusses comments related to each approach and range
of standard levels (II.F.3.c), and presents the Administrator’s final
conclusions regarding the approach and level (II.F.3.d).   

a.	Rationale for proposed decisions on approach and level 

In assessing the most appropriate approach to setting the 1-hour
standard and the most appropriate range of standard levels to propose,
the Administrator considered the broad body of scientific evidence
assessed in the ISA, including epidemiologic and controlled human
exposure studies, as well as the results of exposure/risk analyses
presented in the REA.  In light of the body of available evidence and
analyses, as described above, the Administrator concluded in the
proposal that it is necessary to provide increased public health
protection for at-risk individuals against an array of adverse
respiratory health effects linked with short-term (i.e., 30 minutes to
24 hours) exposures to NO2.  Such health effects have been associated
with exposure to the distribution of short-term ambient NO2
concentrations across an area, including higher short-term (i.e., peak)
exposure concentrations, such as those that can occur on or near major
roadways and near other sources of NO2, as well as the lower short-term
exposure concentrations that can occur in areas not near major roadways
or other sources of NO2.  The Administrator’s proposed decisions on
approach and level, as discussed in detail in the proposal (section
II.F.4), are outlined below.

In considering a standard-setting approach, the Administrator was
mindful in the proposal that the available evidence and analyses from
the ISA and REA support the public health importance of
roadway-associated NO2 exposures.  The exposure assessment described in
the REA estimated that roadway-associated exposures account for the
majority of exposures to peak NO2 concentrations (REA, Figures 8-17,
8-18).  The ISA concluded (section 4.3.6) that NO2 concentrations in
heavy traffic or on freeways “can be twice the residential outdoor or
residential/arterial road level.”  In considering the potential
variability in the NO2 concentration gradient, the proposal noted that
available monitoring studies suggest that NO2 concentrations could be 30
to 100% higher than those in the same area but away from the road.    

The Administrator also considered that millions of people in the United
States live, work, and/or attend school near important sources of NO2
such as major roadways (ISA, section 4.4), and that ambient NO2
concentrations in these locations vary depending on the distance from
major roads (i.e., the closer to a major road, the higher the NO2
concentration) (ISA, section 2.5.4).  Therefore, these populations,
which likely include a disproportionate number of individuals in groups
with higher prevalence of asthma and higher hospitalization rates for
asthma (e.g. ethnic or racial minorities and individuals of low
socioeconomic status ) (ISA, section 4.4), are likely exposed to NO2
concentrations that are higher than those occurring away from major
roadways.  

Given the above considerations, the Administrator proposed an approach
to setting the 1-hour NO2 primary NAAQS whereby the standard would
reflect the maximum allowable NO2 concentration anywhere in an area.  In
many locations, this concentration is likely to occur on or near a major
roadway.  EPA proposed to set the level of the standard such that, when
available information regarding the concentration gradient around roads
is considered, appropriate public health protection would be provided by
limiting the higher short-term peak exposure concentrations expected to
occur on and near major roadways, as well as the lower short-term
exposure concentrations expected to occur away from those roadways.  The
Administrator concluded that this approach to setting the 1-hour NO2
NAAQS would be expected to protect public health against exposure to the
distribution of short-term NO2 concentrations across an area and would
provide a relatively high degree of confidence regarding the protection
provided against peak exposures to higher NO2 concentrations, such as
those that can occur around major roadways.  The remainder of this
section discusses the proposed range of standard levels.    

In considering the appropriate range of levels to propose for a standard
that reflects the maximum allowable NO2 concentration anywhere in an
area, the Administrator considered the broad body of scientific evidence
and exposure/risk information as well as available information on the
relationship between NO2 concentrations near roads and those away from
roads.  Specifically, she considered the extent to which a variety of
levels would be expected to protect at-risk individuals against
increased airway responsiveness, respiratory symptoms, and
respiratory-related emergency department visits and hospital admissions.
 

After considering the scientific evidence and the exposure/risk
information (see sections II.B, II.C, and II.F.4.a.1 through II.F.4.a.3
in the proposal), as well as the available information on the NO2
concentration gradient around roadways (section II.A.2 above and in the
proposal), the Administrator concluded that the strongest support is for
a standard level at or somewhat below 100 ppb.  The Administrator’s
rationale in reaching this proposed conclusion is provided below.    

The Administrator noted that a standard level at or somewhat below 100
ppb in conjunction with the proposed approach would be expected to limit
short-term NO2 exposures to concentrations that have been reported to
increase airway responsiveness in asthmatics (i.e., at or above 100
ppb).  While she acknowledged that exposure to NO2 concentrations below
100 ppb could potentially increase airway responsiveness in some
asthmatics, the Administrator also noted uncertainties regarding the
magnitude and the clinical significance of the NO2-induced increase in
airway responsiveness, as discussed in the policy assessment chapter of
the REA (section 10.3.2.1, discussed in section II.F.4.e in the
proposal).  Given these uncertainties, the Administrator concluded in
the proposal that controlled human exposure studies provide support for
limiting exposures at or somewhat below 100 ppb NO2.    

The Administrator also noted that a standard level at or somewhat below
100 ppb in conjunction with the proposed approach would be expected to
maintain peak area-wide NO2 concentrations considerably below those
measured in locations where key U.S. epidemiologic studies have reported
associations with more serious respiratory effects, as indicated by
increased emergency department visits and hospital admissions. 
Specifically, the Administrator noted that 5 key U.S. studies provide
evidence for such associations in locations where the 99th percentile of
the distribution of 1-hour daily maximum NO2 concentrations measured at
area-wide monitors ranged from 93 to 112 ppb (Ito et al., 2007; Jaffe et
al., 2003; Peel et al., 2005; Tolbert et al., 2007; and a study by the
New York State Department of Health, 2006).  The Administrator concluded
that these studies provide support for a 1-hour standard that limits the
99th percentile of the distribution of 1-hour daily maximum area-wide
NO2 concentrations to below 90 ppb (corresponds to a 98th percentile
concentration of 85 ppb), and that limiting area-wide concentrations to
considerably below 90 ppb would be appropriate in order to provide an
adequate margin of safety.  The Administrator noted that, based on
available information about the NO2 concentration gradient around roads,
a standard level at or somewhat below 100 ppb set in conjunction with
the proposed approach would be expected to accomplish this. 
Specifically, she noted that given available information regarding NO2
concentration gradients around roads (see section II.A.2), a standard
level at or below 100 ppb (with either a 99th or 98th percentile form)
would be expected to limit peak area-wide NO2 concentrations to
approximately 75 ppb or below.  Therefore, the Administrator concluded
that a standard level at or somewhat below 100 ppb under the proposed
approach would be expected to maintain peak area-wide NO2 concentrations
well below 90 ppb across locations despite the expected variation in the
NO2 concentration gradient that can exist around roadways in different
locations and over time.  

The Administrator also noted that a study by Delfino provides mixed
evidence for effects in a location with area-wide 98th and 99th
percentile 1-hour daily maximum NO2 concentrations of 50 and 53 ppb,
respectively.  In that study, NO2 effect estimates were positive, but
some reported 95% confidence limits for the odds ratio (OR) that
included values less than 1.00.  Given the mixed results of the Delfino
study, the Administrator concluded that it may not be necessary to
maintain area-wide NO2 concentrations at or below 50 ppb to provide
protection against the effects reported in epidemiologic studies.  

In addition to these evidence-based considerations, the Administrator
noted that a standard level at or somewhat below 100 ppb under the
proposed approach would be consistent with the results of the exposure
and risk analyses presented in the REA.  As discussed in section II.C of
the proposal, the results of these analyses provide support for setting
a standard that limits 1-hour area-wide NO2 concentrations to between 50
and 100 ppb.  As described above, a standard level of 100 ppb that
reflects the maximum allowable NO2 concentration would be expected to
maintain area-wide NO2 concentrations at or below approximately 75 ppb. 
Given all of these considerations, the Administrator concluded in the
proposal that a standard level at or somewhat below 100 ppb (with a 99th
percentile form), in conjunction with the proposed approach, would be
requisite to protect public health with an adequate margin of safety
against the array of NO2-associated health effects.  

In addition to the considerations discussed above, which support setting
a standard level at or somewhat below 100 ppb, the Administrator also
considered the extent to which available evidence could support standard
levels below 100 ppb.  The Administrator concluded that the evidence
could support setting the standard level below 100 ppb to the extent the
following were emphasized:

The possibility that an NO2-induced increase in airway responsiveness
could occur in asthmatics following exposures to concentrations below
100 ppb and/or the possibility that such an increase could be clinically
significant 

The mixed results reported in the study by Delfino et al. (2002) of an
association between respiratory symptoms and the relatively low ambient
NO2 concentrations measured in the study area 

Specifically, she noted that a standard level of 80 ppb (99th percentile
form), in conjunction with the proposed approach, could limit area-wide
NO2 concentrations to 50 ppb and would be expected to limit exposure
concentrations to below those that have been reported to increase airway
responsiveness in asthmatics.  For the reasons stated above, the
Administrator proposed to set the level of a new 1-hour standard between
80 ppb and 100 ppb.  

b.	Rationale for the alternative approach and range of levels 

As described above, the Administrator proposed to set a 1-hour NO2 NAAQS
reflecting the maximum allowable NO2 concentration anywhere in an area
and to set the level of such a standard from 80 to 100 ppb.  However,
prior to the proposal, the approach of setting a 1-hour NO2 NAAQS that
reflects the maximum allowable NO2 concentration anywhere in an area had
not been discussed by EPA in the REA or considered by CASAC.  Rather,
the potential alternative standards discussed in the REA, and reviewed
by CASAC, reflected allowable area-wide NO2 concentrations (i.e.,
concentrations that occur broadly across communities).     

Given this, the Administrator noted in the proposal that comments
received on the approach to setting the 1-hour standard (i.e., from
CASAC and from members of the public) could provide important new
information for consideration.  Therefore, the Administrator also
solicited comment on the alternative approach of setting a 1-hour NO2
primary NAAQS that would reflect the allowable area-wide NO2
concentration, analogous to the standards evaluated in the REA, and with
a level set within the range of 50 to 75 ppb.  In discussing this
alternative approach with a standard level from 50 to 75 ppb, the
Administrator noted the following in the proposal: 

Such a standard would be expected to maintain area-wide NO2
concentrations below peak 1-hour area-wide concentrations measured in
locations where key U.S. epidemiologic studies have reported
associations with respiratory-related emergency department visits and
hospital admissions.  

Standard levels from the lower end of the range would be expected to
limit roadway-associated exposures to NO2 concentrations that have been
reported in controlled human exposure studies to increase airway
responsiveness in asthmatics.  Specifically, a standard level of 50 ppb
under this approach could limit near-road concentrations to between
approximately 65 and 100 ppb, depending on the relationship between
near-road NO2 concentrations and area-wide concentrations.  

This alternative approach would provide relatively more confidence
regarding the degree to which a specific standard level would limit
area-wide NO2 concentrations and less confidence regarding the degree to
which a specific standard level would limit the peak NO2 concentrations
likely to occur near major roadways. 

c.	Comments on approach and level

 In the proposal, each approach to setting the 1-hour standard, and each
range of standard levels, was linked to different requirements for the
design of the NO2 monitoring network.  Specifically, in conjunction with
the proposed approach (i.e., standard reflects the maximum allowable NO2
concentration anywhere in an area and the level is set within the range
of 80 to 100 ppb), the Administrator proposed to establish a 2-tiered
monitoring network that would include monitors sited to measure the
maximum NO2 concentrations anywhere in an area, including near major
roadways, and monitors sited to measure maximum area-wide NO2
concentrations.  In conjunction with the alternative approach (i.e.,
standard reflects the allowable area-wide NO2 concentration and the
level is set within the range of 50 to 75 ppb), the Administrator
solicited comment on a monitoring network that would only include
area-wide NO2 monitors.  Because of these linkages in the proposal, most
commenters combined their comments on the approach to setting a 1-hour
standard and on the standard level with their comments on the monitoring
requirements.  In this section, we discuss comments from CASAC and
public commenters on the approach to setting a 1-hour standard and on
the standard level.  Comments on the monitoring network are also
discussed in this section to the extent they indicate a preference for
either the proposed or alternative approach to setting the 1-hour
standard.  More specific comments on monitor placement and network
design are discussed below in section III.B.2 and in the Response to
Comments document.  EPA responses to technical comments on the
scientific evidence and the exposure/response information are discussed
above in section II.E.2 and in the Response to Comments document.  The
Administrator’s response to commenters’ views on the approach to
setting the 1-hour standard and on the standard level is embodied in the
discussed in section II.F.4.d. 

i.	CASAC comments on the approach to setting the standard 

A majority of CASAC and CASAC Panel members favored the proposed
approach of setting a 1-hour standard that reflects the maximum
allowable NO2 concentration anywhere in an area and linking such a
standard with a 2-tiered monitoring network that would include both
near-road and area-wide monitors, though CASAC did not reach consensus
on this approach.  Specifically, in their letter to the Administrator
(Samet, 2009), CASAC stated the following: 

There was a split view on the two approaches among both CASAC and CASAC
panel members with a majority of each favoring the Agency's proposed
two-tiered monitoring network because they thought this approach would
be more effective in limiting near-roadway exposures that may reach
levels in the range at which some individuals with asthma may be
adversely affected. Other members acknowledged the need for research and
development of near-road monitoring data for criteria pollutants in
general but favored retention of EPA's current area-wide monitoring for
NO2 regulatory purposes, due to the lack of epidemiological data based
on near-roadway exposure measurements and issues related to implementing
a near-road monitoring system for NO2. 

Thus, the recommendation of the majority of CASAC Panel members was
based on their conclusion that the proposed approach would be more
effective than the alternative at limiting near-roadway exposures to NO2
concentrations that could adversely affect asthmatics.  In addition,
these CASAC Panel members noted important uncertainties with the
alternative approach.  Specifically, they stated the following (Samet,
2009): 

Panel members also supported the proposed two-tiered approach because
basing regulations on area-wide monitoring alone was problematic. Such
an approach would require EPA to embed uncertainties and assumptions
about the relationship between area-wide and road-side monitoring into
the area-wide standard.

 

A minority of CASAC Panel members expressed support for the alternative
approach of setting a 1-hour standard that reflects the allowable
area-wide NO2 concentration.  These CASAC Panel members concluded that
there would be important uncertainties associated with the proposed
approach.  Specifically, they noted that the key U.S. NO2 epidemiologic
studies relied upon area-wide NO2 concentrations.  In their view, the
use of area-wide concentrations in these studies introduces uncertainty
into the selection of a standard level for a standard that reflects the
maximum allowable NO2 concentration anywhere in an area and that is
linked with a requirement to place monitors near major roads.  As a
result of this uncertainty, CASAC Panel members who favored the
alternative approach noted that “it would be better to set the
standard on the same area-wide monitoring basis as employed in the
epidemiologic studies upon which it [the standard] now relies” (Samet,
2009).  These CASAC Panel members also strongly supported obtaining
monitoring data near major roads, while recognizing uncertainties
associated with identifying appropriate monitoring sites near roads (see
section III.B.2 and the Response to Comments document for more
discussion of CASAC’s monitoring comments).  

ii.	Public comments on the approach to setting the standard 

Consistent with the views expressed by the majority of CASAC members, a
number of commenters concluded that the most appropriate approach would
be to set a 1-hour standard that reflects the maximum allowable NO2
concentration anywhere in an area and to couple that standard with a
requirement that monitors be placed in locations where maximum
concentrations are expected, including near major roads.  This view was
expressed by some State and local agencies (e.g., in CA, IA, NY, TX, WA,
WI), by a number of environmental organizations (e.g., CAC, EDF, EJ,
GASP, NRDC), by the ALA, and individual commenters.  Several additional
medical and public health organizations (ACCP, AMA, ATS, NADRC, NACPR)
did not explicitly express a recommendation regarding the approach
though these organizations did recommend that, in setting a 1-hour
standard, particular attention should be paid to NOX concentrations
around major roadways.  In support of their recommendation to adopt the
proposed approach and to focus monitoring around major roads, these
commenters generally concluded that a primary consideration should be
the extent to which the NO2 NAAQS protects at-risk populations that live
and/or attend school near important sources of NO2 such as major roads. 
As such, these comments supported the rationale in the proposal for
setting a 1-hour standard that reflects the maximum allowable NO2
concentration anywhere in an area.  

	A number of State commenters expressed the view that area-wide monitors
should be used for attainment/non-attainment determinations (e.g.,
NACAA, NESCAUM and agencies in IL, IN, MI, MS, NC, NM, SC).  One State
commenter (NESCAUM) agreed with EPA concerns about near-road exposures
but concluded that it is premature to establish a large near-road
monitoring network at this time due to uncertainty regarding the
relationship between near-road and area-wide NO2 concentrations and the
variability in that relationship.  NESCAUM recommended that EPA work
with States to establish a targeted monitoring program in select urban
areas to gather data that would inform future modifications to the
monitoring network, but that “The existing area-wide monitoring
network should be used to identify initial nonattainment areas.” 
Other State commenters also concluded that the most appropriate approach
would be to base non-attainment determinations only on area-wide
monitors.  Based on their monitoring comments, many of these commenters
appeared to support setting a 1-hour standard that reflects the
allowable area-wide NO2 concentration.  State concerns with the proposed
approach often included uncertainties associated with identifying and
accessing appropriate monitor sites near major roads, as well as
concerns related to implementation and cost to States (as discussed
further in the Response to Comments document, the Administrator may not
consider cost of implementation in decisions on a NAAQS).  

One commenter (AAM) concluded that the focus of the proposed approach on
NO2 concentrations around major roadways is not justified because the
REA and the proposal overstate the extent to which NO2 concentrations
near roads are higher than NO2 concentrations farther away from the
road.  This conclusion is based on an analysis of 42 existing NO2
monitors in 6 locations.  Comparing NO2 concentrations measured by these
monitors, some of which are close to roads and other of which are
farther from roads, led AAM to conclude that “roadside monitors are
not measuring high NO2 concentrations.”  

We agree that there is uncertainty associated with estimates of
roadway-associated NO2 concentrations (see REA, sections 7.4.6 and
8.4.8.3 for detailed discussion of these uncertainties) and in
identifying locations where maximum concentrations are expected to
occur.  However, we note that the Administrator’s conclusions
regarding the relationship between NO2 concentrations near roads and
those away from roads rely on multiple lines of scientific evidence and
information.  Specifically, the administrator relied in the proposal on
the following in drawing conclusions regarding the distribution of NO2
concentrations across areas:

Monitoring studies discussed in the ISA and REA that were designed to
characterize the NO2 concentration gradient around roads, which
indicated that NO2 concentrations near roads can be approximately 30 to
100% higher than concentrations in the same area but away from the road 

Air quality and exposure analyses presented in the REA which estimate
that NO2 concentrations on roads could be 80% higher than away from the
road, on average across locations, and that roadway-associated exposures
account for the majority of exposures to NO2 concentrations at or above
100 ppb

In contrast, while the analysis submitted by AAM does provide
information on NO2 concentrations at different distances from roads, the
existing NO2 monitoring network was not designed to characterize the
spatial gradients in NO2 concentrations surrounding roadways.  Rather,
concentrations of NO2 measured by existing monitors are likely to
reflect contributions from a combination of mobile and stationary
sources, with one or the other dominating depending on the proximity of
these sources to the monitors.  Therefore, we conclude that the analysis
submitted by AAM, which does not consider other relevant lines of
evidence and information, does not appropriately characterize the
relationship between NO2 concentrations near roads and those away from
roads. (See the Response to Comments document for a more detailed
discussion of AAM comments).  

In addition, we note that, although the Administrator concluded in the
proposal that maximum NO2 concentrations in many areas are likely to
occur around major roads, she also allowed for situations where this is
not the case.  Specifically, she proposed to set a 1-hour NO2 standard
that reflects the maximum allowable NO2 concentration anywhere in an
area, regardless of where that maximum concentration occurs.  
Therefore, the proposed approach to setting the standard would be
expected to limit the maximum NO2 concentrations anywhere in an area
even if in some areas, as is contended by AAM, those maximum NO2
concentrations do not occur near roads.  

iii.	CASAC comments on standard level 

In commenting on the proposal, CASAC discussed both the proposed range
of standard levels (i.e., 80-100 ppb) and the alternative range of
standard levels (i.e., 50-75 ppb).  CASAC did express the consensus
conclusion that if the Agency finalizes a 1-hour standard in accordance
with the proposed approach (i.e., standard level reflects the maximum
allowable NO2 concentration anywhere in an area), then it is appropriate
to consider the proposed range of standard levels from 80 to 100 ppb. 
Specifically, the CASAC letter to the Administrator on the proposal
(Samet, 2009) stated the following with regard to the proposed approach:
 

[T]he level of the one-hour NO2 standard should be within the range of
80-100 ppb and not above 100 ppb. In its letter of December 2, 2008,
CASAC strongly voiced a consensus view that the upper end of the range
should not exceed 100 ppb, based on evidence of risk at that
concentration. The lower limit of 80 ppb was viewed as reasonable by
CASAC; selection of a value lower than 80ppb would represent a policy
judgment based on uncertainty and the degree of public health protection
sought, given the limited health-based evidence at concentrations below
100 ppb.

CASAC also recommended that this level be employed with a 98th
percentile form, in order to promote the stability of the standard (see
above for discussion of form). 

iv.	Public comments on standard level 

A number of State and local agencies and organizations expressed support
for setting the level of the 1-hour NO2 standard within the proposed
range of 80 to 100 ppb.  While some State and local agencies (e.g., in
CA, IA, MI, NY, TX) made this recommendation in conjunction with a
recommendation to focus monitoring near major roads and other important
sources of NO2, a number of State commenters (e.g., NACAA, NESCAUM and
agencies in IL, NC, NM, TX, VA) recommended a standard level from 80 to
100 ppb in conjunction with a recommendation that only area-wide
monitors be deployed for purposes of determining attainment with the
standard.  Based on these monitoring comments, these State commenters
appear to favor an approach where a standard level from 80 to 100 ppb
would reflect the allowable area-wide NO2 concentration.  As discussed
above (and in more detail in section III.B.2 and the Response to
Comments document), State commenters often based these recommendations
on uncertainties in designing an appropriate national near-road
monitoring network.  

A number of environmental organizations (e.g., CAC, EDF, EJ, GASP, NRDC)
and medical/public health organizations (e.g., ACCP, ALA, AMA, ATS,
NACPR, NAMDRC) supported setting a standard level below 80 ppb for a
standard that reflects the maximum allowable NO2 concentration anywhere
in an area.  Several of these groups recommended a standard level of 50
ppb.  This recommendation was typically based on the commenters’
interpretation of the epidemiologic and controlled human exposure
evidence, as described below.  

Some of these commenters noted that the 98th percentile area-wide NO2
concentration was below 80 ppb in the location of a single key U.S.
epidemiologic study (i.e., 50 ppb in study by Delfino).  Given this,
commenters concluded that the standard level should be set at 50 ppb. 
Their comments on the monitoring network generally favored a requirement
to place monitors near major roads and, therefore, these commenters
appeared to favor a standard level as low as 50 ppb and to recommend
that such a standard level reflect the maximum allowable NO2
concentration anywhere in an area.  In their comments, the ALA, EDF, EJ,
and NRDC stated the following: 

Considering the Delfino study alone on EPA’s terms, that is, focusing
on the 98th percentile of the 1-hour daily maximum concentrations, EPA
reports a concentration of 50 ppb where asthma symptoms were observed.
Based primarily on this study, EPA concluded in the REA that it was
appropriate to set the lower end of the range at 50 ppb, which
corresponded to the lowest-observed effects level of airway
hyperresponsiveness in asthmatics. To provide the strongest public
health protection, we therefore urge the level of the standard be set at
50 ppb. 

In some cases, the same commenters also appeared to recommend setting a
standard level below 50 ppb because mean area-wide NO2 concentrations
reported in locations of key U.S. epidemiologic studies are below this
concentration.  Specifically, with regard to the key U.S. epidemiologic
studies, these commenters (e.g., ALA, EDF, EJ, NRDC) stated the
following: 

These studies clearly identify adverse health effects such as emergency
room visits and hospital admissions for respiratory causes at
concentrations currently occurring in the United States. Mean
concentrations for all but two of these studies are about or below 50
ppb, suggesting that the standard must be set below this level to allow
for a margin of safety.

The Administrator’s consideration of the Delfino study as it relates
to a decision on standard level is discussed below (section II.F.4.d). 
Regarding the recommendation to set the level below 50 ppb based on mean
area-wide NO2 concentrations in epidemiologic study locations, we note
that the Administrator proposed to set a standard that reflects the
maximum allowable NO2 concentration anywhere in an area and to set the
form of that standard at the upper end of the distribution of 1-hour
daily maximum NO2 concentrations.  As described in the proposal, such a
standard, with a level from the proposed range of 80 to 100 ppb, would
be expected to maintain peak area-wide NO2 concentrations below the peak
area-wide concentrations measured in locations where key U.S.
epidemiologic studies have reported associations with
respiratory-related emergency department visits and hospital admissions.
 Because reducing NOX emissions to meet a 98th percentile NO2 standard
should lower the distribution of NO2 concentrations, including the mean,
a standard that limits the 98th percentile of the distribution of 1-hour
daily maximum concentrations would also be expected to limit mean
concentrations.  Therefore, although we acknowledge that the
relationship between peak and mean NO2 concentrations will likely vary
across locations and over time, if peak area-wide NO2 concentrations are
maintained below those in key epidemiologic study locations, mean
area-wide NO2 concentrations would also be expected to be maintained
below the mean area-wide concentrations in those locations (see ISA,
figure 2.4-13 for information on the relationship between peak and mean
NO2 concentrations).  

As discussed above (section, II.E.2), a number of industry groups did
not support setting a new 1-hour NO2 standard.  However, several of
these groups (e.g., AAM, Dow, NAM, NPRA) also concluded that, if EPA
does choose to set a new 1-hour standard, the level of that standard
should be above 100 ppb.  As a basis for this recommendation, these
groups emphasized uncertainties in the scientific evidence. 
Specifically, as discussed in more detail above (section II.E.2), these
commenters typically concluded that available epidemiologic studies do
not support the conclusion that NO2 causes reported health effects. 
This was based on their assertion that the presence of co-pollutants in
the ambient air precludes the identification of a specific NO2
contribution to reported effects.  As a result, these commenters
recommended that a 1-hour standard should be based on the controlled
human exposure evidence and that, in considering that evidence, EPA
should rely on the meta-analysis of NO2 airway responsiveness studies
conducted by Goodman et al., (2009) rather than the meta-analysis
included in the final ISA.  As described above, they concluded that in
relying on the ISA meta-analysis, EPA has inappropriately relied on a
new unpublished meta-analysis that has not been peer-reviewed, was not
reviewed by CASAC, and was not conducted in a transparent manner.  EPA
recognizes the uncertainties in the scientific evidence that are
discussed by these industry commenters; however, we strongly disagree
with their conclusions regarding the implications of these uncertainties
for decisions on the NO2 NAAQS.  These comments, and EPA’s responses,
are discussed in detail above (section II.E.2) and in the Response to
Comments document and are summarized briefly below.  

As noted in section II.E.2, we agree that the presence of co-pollutants
in the ambient air complicates the interpretation of epidemiologic
studies; however, our conclusions regarding causality are based on
consideration of the broad body of epidemiologic studies (including
those employing multi-pollutant models) as well as animal toxicological
and controlled human exposure studies.  The ISA concluded that this body
of evidence “supports a direct effect of short-term NO2 exposure on
respiratory morbidity at ambient concentrations below the current NAAQS
level” (ISA, p. 5-16).  In addition, the ISA (p. 5-15) concluded the
following:

[T]he strongest evidence for an association between NO2 exposure and
adverse human health effects comes from epidemiologic studies of
respiratory symptoms and ED visits and hospital admissions. These new
findings were based on numerous studies, including panel and field
studies, multipollutant studies that control for the effects of other
pollutants, and studies conducted in areas where the whole distribution
of ambient 24-h avg NO2 concentrations was below the current NAAQS level
of 0.053 ppm (53 ppb) (annual average). 

Given that epidemiologic studies provide the strongest support for an
association between NO2 and respiratory morbidity, and that a number of
these studies controlled for the presence of other pollutants with
multi-pollutant models (in which NO2 effect estimates remained robust),
we disagree that NO2 epidemiologic studies should not be used to inform
a decision on the level of the 1-hour NO2 standard.  

In addition, we agree that uncertainty exists regarding the extent to
which the NO2-induced increase in airway responsiveness is adverse (REA,
section 10.3.2.1); however, as discussed in detail above (section
II.E.2), we disagree with the conclusion by many industry commenters
that this effect is not adverse in asthmatics following exposures from
100 to 600 ppb NO2.  Specifically, we do not agree that the approach
taken in the study by Goodman et al. (2009), which was used by many
industry commenters to support their conclusions, was appropriate.  The
authors of the Goodman study used data from existing NO2 studies to
characterize the dose-response relationship of NO2 and airway
responsiveness and to calculate the magnitude of the NO2 effect.  Given
the protocol differences in existing studies of NO2 and airway
responsiveness, we do not agree that it is appropriate to base such an
analysis on these studies.  

The Administrator’s consideration of these uncertainties, within the
context of setting a standard level, is discussed in the next section.  

d.	Conclusions on approach and standard level

Having carefully considered the public comments on the appropriate
approach and level for a 1-hour NO2 standard, as discussed above, the
Administrator believes the fundamental conclusions reached in the ISA
and REA remain valid.  In considering the approach, the Administrator
continues to place primary emphasis on the conclusions of the ISA and
the analyses of the REA, both of which focus attention on the importance
of roadways in contributing to peak NO2 exposures, given that
roadway-associated exposures can dominate personal exposures to NO2.  In
considering the level at which the 1-hour primary NO2 standard should be
set, the Administrator continues to place primary emphasis on the body
of scientific evidence assessed in the ISA, as summarized above in
section II.B, while viewing the results of exposure and risk analyses,
discussed above in section II.C, as providing information in support of
her decision.    

With regard to her decision on the approach to setting the 1-hour
standard, the Administrator continues to judge it appropriate to provide
increased public health protection for at-risk individuals against an
array of adverse respiratory health effects linked with short-term
exposures to NO2, where such health effects have been associated with
exposure to the distribution of short-term ambient NO2 concentrations
across an area.  In protecting public health against exposure to the
distribution of short-term NO2 concentrations across an area, the
Administrator is placing emphasis on providing a relatively high degree
of confidence regarding the protection provided against exposures to
peak concentrations of NO2, such as those that can occur around major
roadways.  Available evidence and information suggest that roadways
account for the majority of exposures to peak NO2 concentrations and,
therefore, are important contributors to NO2-associated public health
risks.  In reaching this conclusion, the Administrator notes the
following: 

Mobile sources account for the majority of NOX emissions (ISA, Table
2.2-1). 

The ISA stated that NO2 concentrations in heavy traffic or on freeways
“can be twice the residential outdoor or residential/arterial road
level,” that “exposure in traffic can dominate personal exposure to
NO2,” and that “NO2 levels are strongly associated with distance
from major roads (i.e., the closer to a major road, the higher the NO2
concentration)” (ISA, sections 2.5.4, 4.3.6).  

The exposure assessment presented in the REA estimated that
roadway-associated exposures account for the majority of exposures to
peak NO2 concentrations (REA, Figures 8-17, 8-18). 

Monitoring studies suggest that NO2 concentrations near roads can be
considerably higher than those in the same area but away from the road
(e.g., by 30-100%, see section II.A.2).  

In their comments on the approach to setting the 1-hour NO2 standard,
the majority of CASAC Panel members emphasized the importance of setting
a standard that limits roadway-associated exposures to NO2
concentrations that could adversely affect asthmatics.  These CASAC
Panel members favored the proposed approach, including its focus on
roads.  

In addition, the Administrator notes that a considerable fraction of the
population resides, works, or attends school near major roadways and
that these populations are likely to have increased exposure to NO2
(ISA, section 4.4).  Based on data from the 2003 American Housing
Survey, approximately 36 million individuals live within 300 feet (~90
meters) of a four-lane highway, railroad, or airport (ISA, section 4.4).
 Furthermore, in California, 2.3% of schools with a total enrollment of
more than 150,000 students were located within approximately 500 feet of
high-traffic roads (ISA, section 4.4).  Of this population, which likely
includes a disproportionate number of individuals in groups with higher
prevalence of asthma and higher hospitalization rates for asthma (e.g.
ethnic or racial minorities and individuals of low socioeconomic status)
(ISA, section 4.4), asthmatics and members of other susceptible groups
(e.g., children, elderly) will have the greatest risks of experiencing
health effects related to NO2 exposure.  In the United States,
approximately 10% of adults and 13% of children have been diagnosed with
asthma, and 6% of adults have been diagnosed with COPD (ISA, section
4.4).    

In considering the approach to setting the 1-hour standard, the
Administrator also notes that concerns with the proposed approach
expressed by the minority of CASAC Panel members included concern with
the uncertainty in the relationship between near-road and area-wide NO2
concentrations, given that U.S. epidemiologic studies have been based on
concentrations measured at area-wide monitors.  However, as discussed by
the majority of CASAC Panel members, a similar uncertainty would be
involved in setting a standard with the alternative approach (Samet,
2009).  The Administrator agrees with the majority of CASAC members and
concludes that uncertainty in the relationship between near-road and
area-wide NO2 concentrations should be considered regardless of the
approach selected to set the standard.  She recognizes that this
uncertainty can and should be taken into consideration when considering
the level of the standard.  

In drawing conclusions on the approach, the Administrator has considered
the extent to which each approach, in conjunction with the ranges of
standard levels discussed in the proposal, would be expected to limit
the distribution of NO2 concentrations across an area and, therefore,
would be expected to protect against risks associated with NO2
exposures.  Specifically, she has considered the extent to which a
standard set with each approach would be expected to limit maximum NO2
concentrations and area-wide NO2 concentrations.  

With regard to expected maximum concentrations, the Administrator notes
the following: 

A standard reflecting the maximum allowable NO2 concentration anywhere
in an area would provide a relatively high degree of confidence
regarding the level of protection provided against peak exposures, such
as those that can occur on or near major roadways.  A standard level
from anywhere within the proposed range (i.e., 80 to 100 ppb) would be
expected to limit exposures to NO2 concentrations reported to increase
airway responsiveness in asthmatics.  

A standard reflecting the allowable area-wide NO2 concentration would
not provide a high degree of confidence regarding the extent to which
maximum NO2 concentrations would be limited.  Maximum NO2 concentrations
would be expected to be controlled to varying degrees across locations
depending on the NO2 concentration gradient around roads.  Most standard
levels within the range considered in the proposal with this option
(i.e., 50 to 75 ppb) would not be expected to limit the occurrence,
across locations, of NO2 concentrations that have been reported to
increase airway responsiveness in asthmatics.   

With regard to expected area-wide concentrations, the Administrator
notes the following:

The extent to which a standard reflecting the maximum allowable NO2
concentration anywhere in an area would be expected to limit area-wide
NO2 concentrations would vary across locations, e.g., depending on the
NO2 concentration gradient around roads.  However, in conjunction with a
standard level from anywhere within the proposed range (i.e., 80-100
ppb), such an approach would be expected to maintain area-wide NO2
concentrations below those measured in locations where key U.S.
epidemiologic studies have reported associations between ambient NO2 and
respiratory-related hospital admissions and emergency department visits
(based on available information regarding the NO2 concentration gradient
around roads as discussed below).  

A standard reflecting the maximum allowable area-wide NO2 concentration
would provide a relatively high degree of certainty regarding the extent
to which area-wide NO2 concentrations are limited.  In conjunction with
a standard level from anywhere within the range of levels discussed in
the proposal (i.e., 50-75 ppb) with this alternative approach, such a
standard would be expected to maintain area-wide NO2 concentrations
below those measured in locations where key U.S. epidemiologic studies
have reported associations between ambient NO2 and respiratory-related
hospital admissions and emergency department visits. 

Given the above considerations, the Administrator notes that both
approaches, in conjunction with appropriate standard levels, would be
expected to maintain area-wide NO2 concentrations below those measured
in locations where key U.S. epidemiologic studies have reported
associations between ambient NO2 and respiratory-related hospital
admissions and emergency department visits.  In contrast, only a
standard reflecting the maximum allowable NO2 concentration anywhere in
an area would be expected to effectively and efficiently (i.e., the
standard would be neither more nor less stringent than necessary) limit
peak exposures to NO2 at concentrations that have been reported to
increase airway responsiveness in asthmatics.  Only the very lowest part
of the range considered for the area-wide approach would be expected to
effectively limit such peak exposures.  After considering the evidence
and uncertainties, and the advice of the CASAC Panel, the Administrator
judges that the most appropriate approach to setting a 1-hour standard
to protect against the distribution of short-term NO2 concentrations
across an area, including the higher concentrations that can occur
around roads and result in elevated exposure concentrations, is to set a
standard that reflects the maximum allowable NO2 concentration anywhere
in an area.  

In considering the level of a 1-hour NO2 standard that reflects the
maximum allowable NO2 concentration anywhere in an area, the
Administrator notes that there is no bright line clearly directing the
choice of level.  Rather, the choice of what is appropriate is a public
health policy judgment entrusted to the Administrator.  This judgment
must include consideration of the strengths and limitations of the
evidence and the appropriate inferences to be drawn from the evidence
and the exposure and risk assessments.  Specifically, the Administrator
notes the following: 

Controlled human exposure studies have reported that various NO2
exposure concentrations increased airway responsiveness in mostly mild
asthmatics (section II above and II.B.1.d in proposal).  These studies
can inform an evaluation of the risks associated with exposure to
specific NO2 concentrations, regardless of where those exposures occur
in an area.  Because concentrations evaluated in controlled human
exposure studies are at the high end of the distribution of ambient NO2
concentrations (ISA, section 5.3.2.1), these studies most directly
inform consideration of the risks associated with exposure to peak
short-term NO2 concentrations.  

Epidemiologic studies (section II.B.1.a and b) conducted in the United
States have reported associations between ambient NO2 concentrations
measured at area-wide monitors in the current network and increased
respiratory symptoms, emergency department visits, and hospital
admissions.  Area-wide monitors in the urban areas in which these
epidemiologic studies were conducted are not sited in locations where
localized peak concentrations are likely to occur.  Thus, they do not
measure the full range of ambient NO2 concentrations across the area. 
Rather, the area-wide NO2 concentrations measured by these monitors are
used as surrogates for the distribution of ambient NO2 concentrations
across the area, a distribution that includes NO2 concentrations both
higher than (e.g., around major roadways) and lower than the area-wide
concentrations measured in study locations.  Epidemiologic studies then
evaluate whether area-wide NO2 concentrations are associated with the
risk of respiratory morbidity.  Therefore, in considering these
epidemiologic studies within the context of the level of a standard that
reflects the maximum allowable NO2 concentration anywhere in an area,
available information on the distribution of NO2 concentrations across
areas (e.g., concentration gradients around roads) should be considered.
 Considering available information on the relationship between maximum
and area-wide NO2 concentrations allows consideration of the extent to
which a particular standard level would be expected to protect the
public health against risks associated with the distribution of NO2
concentrations across an area, as indicated by area-wide concentrations
measured in epidemiologic study locations. 

The risk and exposure analyses presented in the REA provide information
on the potential public health implications of setting standards that
limit area-wide NO2 concentrations to specific levels.  While the
Administrator acknowledges the uncertainties associated with these
analyses which, as discussed in the REA, could result in either over- or
underestimates of NO2-associated health risks, she judges that these
analyses are informative for considering the relative levels of public
health protection that could be provided by different standards.  

The Administrator’s consideration of the controlled human exposure
evidence, epidemiologic evidence, and exposure/risk information are
discussed below specifically with regard to a decision on the level of a
standard that reflects the maximum allowable NO2 concentration anywhere
in an area.  

In considering the potential for controlled human exposure studies of
NO2 and airway responsiveness to inform a decision on standard level,
the Administrator notes the following: 

NO2-induced increases in airway responsiveness, as reported in
controlled human exposure studies, are logically linked to the adverse
respiratory effects that have been reported in NO2 epidemiologic
studies.  

The meta-analysis of controlled human exposure data in the ISA reported
increased airway responsiveness in a large percentage of asthmatics at
rest following exposures at and above 100 ppb NO2, the lowest NO2
concentration for which airway responsiveness data are available in
humans.  

This meta-analysis does not provide any evidence of a threshold below
which effects do not occur.  The studies included in the meta-analysis
evaluated primarily mild asthmatics while more severely affected
individuals could respond to lower concentrations.  Therefore, it is
possible that exposure to NO2 concentrations below 100 ppb could
increase airway responsiveness in some asthmatics. 

In considering the evidence, the Administrator recognizes that the
NO2-induced increases in airway responsiveness reported for exposures to
NO2 concentrations at or above 100 ppb could be adverse for some
asthmatics.  However, she also notes that important uncertainties exist
with regard to the extent to which NO2-induced increases in airway
responsiveness are adverse.  Specifically, she notes the following with
regard to these uncertainties:

The magnitude of the NO2-induced increase in airway responsiveness, and
the extent to which it is adverse, cannot be quantified from the ISA
meta-analysis (REA, section 10.3.2.1).   

The NO2-induced increase in airway responsiveness in resting asthmatics
was typically not accompanied by increased respiratory symptoms, even
following exposures to NO2 concentrations well above 100 ppb (ISA,
section 3.1.3.3).  

The increase in airway responsiveness that was reported for resting
asthmatics was not present in exercising asthmatics (ISA, Table 3.1-3). 

Taking into consideration all of the above, the Administrator concludes
that existing evidence supports the conclusion that the NO2-induced
increase in airway responsiveness at or above 100 ppb presents a risk of
adverse effects for some asthmatics, especially those with more serious
(i.e., more than mild) asthma.  The Administrator notes that the risks
associated with increased airway responsiveness cannot be fully
characterized by these studies, and thus she is not able to determine
whether the increased airway responsiveness experienced by asthmatics in
these studies is an adverse health effect.  However, based on these
studies, the Administrator is concluding that asthmatics, particularly
those suffering from more severe asthma, warrant protection from the
risk of adverse effects associated with the NO2-induced increase in
airway responsiveness.  Therefore, the Administrator concludes that the
controlled human exposure evidence supports setting a standard level no
higher than 100 ppb to reflect a cautious approach to the uncertainty
regarding the adversity of the effect.  However, those uncertainties
lead her to also conclude that this evidence does not support setting a
standard level lower than 100 ppb.  

In considering the more serious health effects reported in NO2
epidemiologic studies, as they relate to the level of a standard that
reflects the maximum allowable NO2 concentration anywhere in an area,
the Administrator notes the following: 

A cluster of 5 key U.S. epidemiologic studies (Ito et al., 2007; Jaffe
et al., 2003; Peel et al., 2005; Tolbert et al., 2007; and a study by
the New York State Department of Health, 2006) provide evidence for
associations between NO2 and respiratory-related emergency department
visits and hospital admissions in locations where 98th percentile 1-hour
daily maximum NO2 concentrations measured at area-wide monitors ranged
from 85 to 94 ppb.  The Administrator judges it appropriate to place
substantial weight on this cluster of key U.S. epidemiologic studies in
selecting a standard level, as they are a group of studies that reported
positive, and often statistically significant, associations between NO2
and respiratory morbidity in multiple cities across the United States.  

A single study (Delfino et al., 2002) provides mixed evidence for NO2
effects (i.e., respiratory symptoms) in a location with a 98th
percentile 1-hour daily maximum NO2 concentration, as measured by an
area-wide monitor, of 50 ppb.  In that study, most of the reported NO2
effect estimates were positive, but not statistically significant. 
Given the variability in the NO2 effect estimates in this study, as well
as the lack of studies in other locations with similarly low NO2
concentrations, the Administrator judges it appropriate to place limited
weight on this study, compared to the cluster of 5 studies as noted
above.  

Given these considerations, the Administrator concludes that the
epidemiologic evidence provides strong support for setting a standard
that limits the 98th percentile of the distribution of 1-hour daily
maximum area-wide NO2 concentrations to below 85 ppb.  This judgment
takes into account the determinations in the ISA, based on a much
broader body of evidence, that there is a likely causal association
between exposure to NO2 and the types of respiratory morbidity effects
reported in these studies.  Given the considerations discussed above,
the Administrator judges that it is not necessary, based on existing
evidence, to set a standard that maintains peak area-wide NO2
concentrations to below 50 ppb.  

In considering specific standard levels supported by the epidemiologic
evidence, the Administrator notes that a level of 100 ppb, for a
standard reflecting the maximum allowable NO2 concentration anywhere in
the area, would be expected to maintain area-wide NO2 concentrations
well below 85 ppb, which is the lowest 98th percentile concentration in
the cluster of 5 studies.  With regard to this, she specifically notes
the following: 

If NO2 concentrations near roads are 100% higher than concentrations
away from roads, a standard level of 100 ppb would limit area-wide
concentrations to approximately 50 ppb.  

If NO2 concentrations near roads are 30% higher than concentrations away
from roads, a standard level of 100 ppb would limit area-wide
concentrations to approximately 75 ppb. 

The Administrator has also considered the NO2 exposure and risk
information within the context of the above conclusions on standard
level.  Specifically, she notes that the results of exposure and risk
analyses were interpreted as providing support for limiting area-wide
NO2 concentrations to no higher than 100 ppb.  Specifically, these
analyses estimated that a standard that limits area-wide NO2
concentrations to approximately 100 ppb or below would be expected to
result in important reductions in respiratory risks, relative to the
level of risk permitted by the current annual standard alone.  As
discussed above, a standard level of 100 ppb, for a standard that
reflects the maximum allowable NO2 concentration, would be expected to
maintain area-wide NO2 concentrations to within a range of approximately
50 to 75 ppb.  Given this, the Administrator concludes that a standard
level of 100 ppb, for a standard that reflects the maximum allowable NO2
concentration anywhere in an area, is consistent with conclusions based
on the NO2 exposure and risk information.  

Finally, the Administrator notes that a standard level of 100 ppb for a
standard that reflects the maximum allowable NO2 concentration anywhere
in an area is consistent with the consensus recommendation of CASAC.  

Given the above considerations and the comments received on the
proposal, the Administrator determines that the appropriate judgment,
based on the entire body of evidence and information available in this
review, is a standard that reflects the maximum allowable NO2
concentration anywhere in an area and with a level of 100 ppb. 
Specifically, she concludes that such a standard, with the averaging
time and form discussed above, will provide a significant increase in
public health protection compared to that provided by the current annual
standard alone and would be expected to protect against the respiratory
effects that have been linked with NO2 exposures in both controlled
human exposure and epidemiologic studies.  This includes focusing on and
limiting exposures at and above 100 ppb for the vast majority of people,
including those in at-risk groups, and maintaining area-wide NO2
concentrations well below those in locations where key U.S.
epidemiologic studies have reported that ambient NO2 is associated with
clearly adverse respiratory health effects, as indicated by increased
hospital admissions and emergency department visits. 

In setting the standard level at 100 ppb rather than a lower level, the
Administrator also acknowledges the uncertainties associated with the
scientific evidence.  She notes that a 1-hour standard with a level
lower than 100 ppb would only result in significant further public
health protection if, in fact, there is a continuum of serious, adverse
health risks caused by exposure to NO2 concentrations below 100 ppb
and/or associated with area-wide NO2 concentrations well-below those in
locations where key U.S. epidemiologic studies have reported
associations with respiratory-related emergency department visits and
hospital admissions.  Based on the available evidence, the Administrator
does not believe that such assumptions are warranted.  Taking into
account the uncertainties that remain in interpreting the evidence from
available controlled human exposure and epidemiologic studies, the
Administrator notes that the likelihood of obtaining benefits to public
health with a standard set below 100 ppb decreases, while the likelihood
of requiring reductions in ambient concentrations that go beyond those
that are needed to protect public health increases. 

Therefore, the Administrator judges that a standard reflecting the
maximum allowable NO2 concentration anywhere in an area set at 100 ppb
would be sufficient to protect public health with an adequate margin of
safety, including the health of at-risk populations, from adverse
respiratory effects that have been linked with short-term exposures to
NO2 and for which the evidence has been judged sufficient to support a
likely causal relationship with NO2 exposures.  The Administrator does
not believe that a lower standard level is needed to provide this degree
of protection.  These conclusions by the Administrator appropriately
consider the requirement for a standard that is neither more nor less
stringent than necessary for this purpose and recognizes that the CAA
does not require that primary standards be set at a zero-risk level or
to protect the most sensitive individual, but rather at a level that
reduces risk sufficiently so as to protect the public health with an
adequate margin of safety.        

G.	Annual Standard

In the proposal, the Administrator noted that some evidence supports a
link between long-term exposures to NO2 and adverse respiratory effects
and that CASAC recommended in their comments prior to the proposal that,
in addition to setting a new 1-hour standard to increase public health
protection, the current annual standard be retained.  CASAC’s
recommendation was based on the scientific evidence and on their
conclusion that a 1-hour standard might not provide adequate protection
against exposure to long-term NO2 concentrations (Samet, 2008b).  

With regard to an annual standard, CASAC and a large number of public
commenters (e.g., NACAA, NESCAUM; agencies from States including CA, IN,
MO, NC, NY, SC, TX, VA; tribal organizations including Fon du Lac and
the National Tribal Air Organization; environmental/medical/public
health groups including ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP, NACPR,
NAMDRC, NRDC) agreed with the proposed decision to maintain an annual
standard, though their recommendations with regard to the level of that
annual standard differed (see below).    

As noted above, CASAC recommended “retaining the current standard
based on the annual average” based on the “limited evidence related
to potential long-term effects of NO2 exposure and the lack of strong
evidence of no effect” and that “the findings of the REA do not
provide assurance that a short-term standard based on the one-hour
maximum will necessarily protect the population from long-term exposures
at levels potentially leading to adverse health effects” (Samet,
2008b).  A number of State agencies and organizations also recommended
maintaining the current level of the annual standard (i.e., 53 ppb). 
This recommendation was based on the conclusion that, while some
evidence supports a link between long-term NO2 exposures and adverse
respiratory effects, that evidence is not sufficient to support a
standard level either higher or lower than the current level.  In
addition, a number of industry groups (e.g., AAM, API, Dow, INGAA, UARG)
recommended retaining the level of the current annual standard but, as
described above, did so within the context of a recommendation that EPA
should not set a new 1-hour standard. 

In contrast, some environmental organizations and medical/public health
organizations as well as a small number of States (e.g., ALA, EDF, EJ,
NRDC, and organizations in CA) recommended setting a lower level for the
annual standard.  These commenters generally supported their
recommendation by pointing to the State of California’s annual
standard of 30 ppb and to studies where long-term ambient NO2
concentrations have been associated with adverse respiratory effects
such as impairments in lung function growth.  

As discussed above (II.B.3), the evidence relating long-term NO2
exposures to adverse health effects was judged in the ISA to be either
“suggestive but not sufficient to infer a causal relationship”
(respiratory morbidity) or “inadequate to infer the presence or
absence of a causal relationship” (mortality, cancer, cardiovascular
effects, reproductive/developmental effects) (ISA, sections
5.3.2.4-5.3.2.6).  In the case of respiratory morbidity, the ISA
(section 5.3.2.4) concluded that “The high correlation among
traffic-related pollutants made it difficult to accurately estimate the
independent effects in these long-term exposure studies.”  Given these
uncertainties associated with the role of long-term NO2 exposures in
causing the reported effects, the Administrator concluded in the
proposal that, consistent with the CASAC recommendation, existing
evidence is not sufficient to justify setting an annual standard with
either a higher or lower level than the current standard.  Commenters
have not submitted any new analyses or information that would change
this conclusion.  Therefore, the Administrator does not agree with the
commenters who recommended a lower level for the annual standard. 

The Administrator judges that her conclusions in the proposal regarding
the annual standard remain appropriate.  Specifically, she continues to
agree with the conclusion that, though some evidence does support the
need to limit long-term exposures to NO2, the existing evidence for
adverse health effects following long-term NO2 exposures does not
support either increasing or decreasing the level of the annual
standard.  In light of this and considering the recommendation from
CASAC to retain the current level of the annual standard, the
Administrator judges it appropriate to maintain the level of the annual
standard at 53 ppb.  

H.	Summary of final decisions on the primary NO2 standard 

For the reasons discussed above, and taking into account information and
assessments presented in the ISA and REA, the advice and recommendations
of the CASAC, and public comments, the Administrator has decided to
revise the existing primary NO2 standard.  Specifically, the
Administrator has determined that the current annual standard by itself
is not requisite to protect public health with an adequate margin of
safety.   In order to provide protection for asthmatics and other
at-risk populations against an array of adverse respiratory health
effects related to short-term NO2 exposure, the Administrator is
establishing a short-term NO2 standard defined by the 3-year average of
the 98th percentile of the yearly distribution of 1-hour daily maximum
NO2 concentrations.  She is setting the level of this standard at 100
ppb, which is to reflect the maximum allowable NO2 concentration
anywhere in an area.  In addition to setting a new 1-hour standard, the
Administrator retains the current annual standard with a level of 53
ppb.  The new 1-hour standard, in combination with the annual standard,
will provide protection for susceptible groups against adverse
respiratory health effects associated with short-term exposures to NO2
and effects potentially associated with long-term exposures to NO2.  

III.	Ambient Monitoring and Reporting Requirements

The EPA is finalizing several changes to the ambient air monitoring,
reporting, and network design requirements for the NO2 NAAQS. This
section discusses the changes we are finalizing which are intended to
support the proposed 1-hour NAAQS and retention of the current annual
NAAQS as discussed in Section II. Ambient NO2 monitoring data are used
to determine whether an area is in violation of the NO2 NAAQS. Ambient
NO2 monitoring data are collected by state, local, and Tribal monitoring
agencies (“monitoring agencies”) in accordance with the monitoring
requirements contained in 40 CFR parts 50, 53, and 58 

A.	Monitoring Methods

We are finalizing the proposed changes regarding the NO2 Federal
Reference Method (FRM) or Federal Equivalent Method (FEM) analyzers. 
Specifically, we are continuing to use the NO2 chemiluminescence FRM and
are finalizing the requirement that any NO2 FRM or FEM used for making
primary NAAQS decisions must be capable of providing hourly averaged
concentration data.  The following paragraphs provide background and
rationale for the continued use of the chemiluminescence FRM and the
decision to finalize the proposed changes.

1.	Chemiluminescence FRM and Alternative Methods

The current monitoring method in use by most State and local monitoring
agencies is the gas-phase chemiluminescence FRM (40 CFR Part 50,
Appendix F), which was implemented into the NO2 monitoring network in
the early 1980s.  EPA did not propose to discontinue using the
chemiluminescence FRM, although we received comment raising concerns
about using a method that is subject to known interferences from certain
species of oxides of nitrogen known as NOZ.  Important components of
ambient NOZ include nitrous acid (HNO2), nitric acid (HNO3), and the
peroxyacetyl nitrates (PANs).  

The issue of concern in public comments is that the reduction of NO2 to
NO on the MoOX converter substrate used in chemiluminescent FRMs is not
specific to NO2; hence, chemiluminescence method analyzers are subject
to varying interferences produced by the presence in the air sample of
the NOZ species listed above and others occurring in trace amounts in
ambient air.  This interference is often termed a “positive
artifact” in the reported NO2 concentration since the presence of NOZ
results in an over-estimate in the reported measurement of the actual
ambient NO2 concentration.  This interference by NOZ compounds has long
been known and evaluated (Fehsenfeld et al., 1987; Nunnermacker et al.,
1998; Parrish and Fehsenfeld, 2000; McClenny et al., 2002; U.S.
Environmental Protection Agency, 1993, 2006a).  Further, as noted in the
ISA, it appears that interference by NOZ on chemiluminescence FRMs is
not more than 10 percent of the reported NO2 concentration during most
or all of the day during winter (cold temperatures), but larger
interference ranging up to 70 percent can be found during summer (warm
temperatures) in the afternoon at sites away and downwind from strong
emission sources. 

The EPA acknowledges that the NOZ interference in the reported NO2
concentrations collected downwind of NOX source areas and in relatively
remote areas away from concentrated point, area, or mobile sources is
significantly larger than the NOZ interference in NO2 measurements taken
in urban cores or other areas with fresh NOX emissions.  To meet the
primary objective of monitoring maximum NO2 concentrations in an area
the EPA is requiring NO2 monitors to be placed in locations of the
expected highest concentrations, which will generally place monitors
near fresh NOX sources or in areas of dense NOX emissions.  Therefore,
EPA believes that the positive artifact issue, although present, is
small, relative to the actual NO2 being measured..  As a result EPA
believes the chemiluminescence FRM is suitable for continued use in the
ambient NO2 monitoring network, as the potential positive bias from NOZ
species is not significant enough to discontinue using the
chemiluminescence FRM.  

EPA also received support through public comments in furthering the
development of alternative methods in determining NO2 concentrations. 
Such alternative methods suggested included the
photolytic-chemiluminescent method and cavity ring-down spectroscopy. 
As a result, EPA, both the Office of Research and Development and the
Office of Air, will further efforts, working with commercial and
industrial vendors, to identify and evaluate such new technologies. 
These efforts may include potentially field testing instruments and
possibly characterizing methods in a laboratory setting of potential
future reference and equivalent methods that may more accurately and/or
directly measure NO2 . 

2.	Allowable FRM and FEMs for comparison to the NAAQS

The current CFR language does not prohibit the use of any particular FRM
or FEM to be used in comparison to the standard.  There are designated
wet chemical methods that are only able to report ambient concentration
values averaged across multiple hours.  With the establishment of a
1-hour NAAQS, any FRM or FEM which is a wet chemical based method would
not be appropriate for use in determining compliance of the 1-hour
NAAQS.  EPA addressed this issue by proposing that only those methods
capable of providing 1-hour measurements be comparable to the NAAQS. 

a.	Proposed changes to FRM and FEMs that may be compared to the NAAQS

EPA proposed that only those FRMs or FEMs that are capable of providing
hourly averaged concentration data may be used for comparison to the
NAAQS.

b.	Comments

EPA did not receive any substantive public comments that objected to
only allowing those FRMs or FEMs that are capable of providing hourly
averaged concentration data may be used for comparison to the NAAQS, and
received some comments that supported this concept. 

c.	Decisions on allowable FRM and FEMs for comparison to the NAAQS

As a result of the supporting public comments, and a lack of public
objections, EPA is finalizing the proposed changes to 40 CFR Part 58
Appendix C to only allow data from FRM or FEMs that are capable of
providing hourly data to be used for comparison to the NAAQS.

B.	Network Design

With the establishment of a 1-hour NO2 NAAQS intended to limit exposure
to maximum concentrations that may occur anywhere in an area, EPA
recognizes that the current NO2 network is inadequate to assess
compliance with the revised NAAQS.  As a result, EPA is promulgating new
NO2 network design requirements.  The following sections provide
background, rationale, and details for the final changes to the NO2
network design requirements.

1.	Two-tiered Network Design

The ISA and REA indicate that one of the largest factors affecting
ambient exposures to NO2 above health benchmarks concentrations are
mobile source emissions, particularly at locations near major roads. 
Information in the ISA and the REA shows that concentrations of mobile
source pollutants, including NO2, typically display peak concentrations
on or immediately adjacent to roads, producing a gradient in pollutant
concentrations where concentrations decrease with increasing distance
from roads (ISA sections 2.5.4 and 4.3.6 and table 2.2-1; REA section
7.3.2 and Figures 8-17 and 8-18).  Since the intent of the revised NAAQS
is to limit exposure to NO2 concentrations that occur anywhere in an
area, monitors intended to measure the maximum allowable NO2
concentration in an area should include measurements of the peak
concentrations that occur on and near roads due to on-road mobile
sources.  This need to measure maximum concentrations is the basis for
the first tier of the proposed network design, which focuses monitoring
near highly trafficked roads in urban areas where peak NO2
concentrations are expected to occur. The basis for the second tier of
the network design is to utilize monitors sited to measure area-wide
concentrations to characterize the wider area impact of NO2 sources on
urban populations.  Area-wide monitoring of NO2 also serves to maintain
continuity in collecting data to inform long-term pollutant
concentration trends analysis and health and scientific research.

This section discusses the two-tier network design approach versus the
alternative network design which was also presented for comment in
conjunction with a solicitation for comment on an alternative NAAQS. The
details of the two-tier network design, including how many monitors are
required, where they are to be located, and the related siting criteria
are discussed in subsequent sections.

a.	Proposed Two-tier Network Design

EPA proposed a two-tier network design composed of (1) near-road
monitors which would be placed in locations of expected maximum 1-hour
NO2 concentrations near heavily trafficked roads in urban areas and (2)
monitors located to characterize areas with the highest expected NO2
concentrations at the neighborhood and larger spatial scales (also
referred to as “area-wide” monitors).  As an alternative, and in
conjunction with a solicitation for comment on an alternative NAAQS, EPA
solicited comment on a network comprised of only area-wide monitors.

b.	Comments

EPA received many comments on the overall two-tier network design, with
commenters who made statements with a relatively clear position on the
issue generally falling into four categories: (1) those who support the
adoption of the proposed two-tier design approach, (2) ) those who
support the adoption of the two-tier concept, but with modifications,
(3) those who only supported the adoption of the alternative network
design, and (4) those who encourage EPA to commit to further research
the near-road environment by monitoring near-roads, but not to use
near-road data for regulatory purposes, and therefore supported the
alternative network design. 

Those commenters who generally support the proposed two-tier network as
proposed, which requires monitoring near-roads and area-wide monitoring,
included the Clean Air Scientific Advisory Committee (although there was
not a consensus, there was a majority in support of the proposed network
design), health groups (e.g. American Thoracic Society, American Medical
Association, and the National Association for the Medical Direction of
Respiratory Care, the American Association of Cardiovascular and
Pulmonary Rehabilitation, and the American College of Chest Physicians),
several state groups (e.g. the Central Pennsylvania Clean Air Board ,
the New York City Law Department and the Metropolitan Washington Air
Quality Committee), and some industry commenters (e.g. American
Chemistry Council, The Clean Energy Group, and Dow Chemical). 

Those commenters who support the adoption of the two-tier network design
concept, but suggest modifications to the actual design include some
health and environmental groups (e.g. the American Lung Association,
Earthjustice, the Environmental Defense Fund, and the National Resource
Defense Council), some states (e.g. California, the Central Pennsylvania
Clean Air Board, Harris County (Texas), Iowa, New York, San Joaquin Air
Pollution Control District, Spokane Regional Clean Air Agency, the Texas
Commission on Environmental Quality, and Wisconsin), and some industry
commenters, including the American Petroleum Institute and the Utility
Air Regulatory Group, who are cited by other industry commenters, which
make statements in context that indicate the two-tier network is an
acceptable approach..  The comments and suggestions made by this group
of commenters are discussed in greater detail in the following sections.

Those commenters who only supported the adoption of the alternative
network design included state and industry groups (e.g. the state of
Indiana, the New York Department of Transportation, Alliance of
Automobile Manufacturers, and the Engine Manufacturers Association). 
These commenters typically made comments on the two-tier network design,
but did not do so in a context that clearly supported near-road
research.  

EPA received comments from some states or state groups (e.g. National
Association of Clean Air Agencies (NACAA), the Northeast States for
Coordinated Air Use Management (NESCAUM), and 10 other individual states
or state groups) and industry commenters (e.g. American Association of
State Highway Transportation Officials, Edison Electric, and the
National Association of Manufacturers) that encouraged EPA to further
research the near-road environment, but not to require near-road monitor
produced data for regulatory purposes, and therefore supported the
adoption of the alternative network design for regulatory purposes.  For
example, with regard to implementing the two-tier network design that
includes near-road regulatory monitoring, the National Association of
Clean Air Agencies (NACAA) stated that “…a major new network –
particularly one that is inherently complicated and untried – should
not be rolled out without the benefit of an effective near-road
monitoring research program that can address many of the relevant data
questions, and inform the specific siting requirements of the rule.” 
The National Association of Manufacturers stated that “Conducting such
a near road [research] monitoring program would allow EPA to collect
necessary data that can be used to better understand the health impacts
associated with short term NO2 exposures.”  EPA notes that the
existing scientific research referenced in the proposal document and
this document show that there are on- and near-road peaks of NO2
concentrations, relative to upwind or background levels, which exist due
to on-road mobile source emissions.  This research, as a body of
evidence, also identifies the multiple local factors that affect how,
where, and when peak NO2 concentrations occur on or near a particular
road segment.  These factors include traffic volume, fleet mix, roadway
design, congestion patterns, terrain, and meteorology.  Although the
near-road environment may be complex with regard to mobile source
pollutant behavior, there is sufficient information from existing
research on what factors to consider when identifying locations of
expected maximum concentrations due to on-road mobile sources, and EPA
and states have access to these data.  Further, EPA notes that near-road
monitoring is not a new concept for the ambient air monitoring community
as near-road carbon monoxide monitoring has been a part of routine
networks for nearly three decades and therefore there is some experience
within the whole of EPA and state and local agencies on conducting
ambient monitoring near-roads.  EPA believes that the existing research
provides sufficient information with which we may require a near-road
monitoring network and the collective experience that exists in the
ambient monitoring community will allow for successful implementation of
that network.  EPA also believes that the two-tier network design will
provide a network that has a reasonable degree of similarity across the
country where the required near-road monitors are targeting the maximum
NO2 concentrations in an area particularly attributable to on-road
mobile sources.  The process using the factors noted above in the
selection of a near-road monitoring site and the associated monitor
siting criteria are explained in subsequent sections. 

Some industry commenters (e.g. Engine Manufacturers Association, S.C.
Chamber of Commerce, S.C. Manufacturers Alliance) who supported the
adoption of the alternative network design suggested that monitoring in
the near-road environment would not be indicative of exposure for
general populations, and that EPA should not focus on the near-road
micro-environment when requiring monitoring.  For example, the South
Carolina Chamber of Commerce and the South Carolina Manufacturers
Alliance both state that “It appears the proposed monitoring network
will result in a collection of microscale data, which is not at all
representative of air quality relevant to population exposure.”  EPA
notes that the intent of near-road monitoring is to support the NAAQS in
preventing exposure to NO2 concentrations that may occur anywhere in an
area.  EPA recognizes that there is variability in the properties (such
as traffic counts, fleet mix, and localized features) among the road
segments that may exist in an area, but on the whole, roads are
ubiquitous, particularly in urban environments, thus much of the public
may be exposed to near-road environments.  The US Department of
Transportation (US DOT) Federal Highway Administration (FHWA) “Status
of the Nation’s Highways, Bridges, and Transit: 2006 Conditions and
Performance” document (  HYPERLINK
"http://www.fhwa.dot.gov/policy/2006cpr/es02h.htm" 
http://www.fhwa.dot.gov/policy/2006cpr/es02h.htm ) states that “while
urban mileage constitutes only 24.9 percent of total (US) mileage, these
roads carried 64.1 percent of the 3 trillion vehicles miles (VMT)
travelled in the United States in 2004.”  The document also states
that “urban interstate highways made up only 0.4 percent of total (US)
mileage but carried 15.5 percent of total VMT.”  These statements
indicate how much more traffic volume exists on roads in urban areas
versus the more rural areas that have significant amounts mileage of the
total public road inventory.  The 2007 American Housing Survey ( 
HYPERLINK "http://www.census.gov/hhes/www/housing/ahs/ahs07/ahs07.html" 
http://www.census.gov/hhes/www/housing/ahs/ahs07/ahs07.html ) estimates
that over 20 million housing units are within 300 feet (~91 meters) of a
4-lane highway, airport, or railroad.  Although that survey includes
airports and railroads, roads are the most pervasive of the three,
indicating that a significant number of the general population live near
roads.  Resultantly, EPA believes that near-road monitors are indicative
of exposure for a significant component of the general population.  

EPA received many comments from states and industry on the two-tier
network design specifically concerning the funding to implement and
operate the monitoring network.  These comments on funding permeated
almost all of the comments form state and local monitoring agencies,
regardless of their position on the network design.  EPA notes that it
has historically funded part of the cost of the installation and
operation of monitors used to satisfy Federal monitoring requirements. 
EPA understands these concerns although the CAA requirements from which
this final rule derives (Secion 103 (c)(2) of the CAA) are note
contingent on EPA providing funding to states to assist in meeting
monitoring requirements.  However, EPA plans to work with state and
local air agencies in identifying available State and Tribal Air Grant
(STAG) funds and planning for increasing resource needs in future
budgets to better accommodate the implementation costs that new minimum
monitoring requirements such as those in this rule incur.

c.	Conclusions Regarding the Two-tier Network Design

As noted in Section II.F.3 above, the Administrator is setting a new
1-hour NO2 standard that reflects the maximum allowable NO2
concentration anywhere in an area.  After considering NO2 monitoring
studies assessed in the ISA and discussed in the REA, as well as
modeling simulations presented in the REA, the Administrator concluded
that maximum NO2 concentrations are expected to occur around major roads
in many areas (see section II.F.3 for more detail).  Because of this,
and because a considerable fraction of the population lives, works, or
attends school near major roadways, the Administrator concludes that it
is appropriate to require NO2 monitors near major roads in urban areas. 
Monitoring NO2 concentrations by major roadways will provide additional
protection for asthmatics and members of other susceptible groups that
may experience greater risks of health effects related to NO2 exposure. 
The Administrator notes that this decision makes progress in identifying
and addressing the health burdens faced by communities
disproportionately impacted by pollution from major roadways. 

Although near-road monitoring is a new approach for NO2, it is a form of
source-oriented monitoring, which is not a new concept with regard to
monitoring to characterize stationary source impacts.  The novel aspect
of this NO2 network design is that the near-road monitoring component is
targeting mobile sources instead of stationary sources. The required
near-road NO2 monitors are to be located in locations of expected
maximum 1-hour concentrations (discussed in a subsequent section) and
will likely represent the highest NO2 concentrations in an area directly
attributable to mobile sources or a group of sources that includes
mobile sources.  Unlike a network with monitors focused primarily on
stationary sources, if a near-road monitor shows data for a given area
indicating concentrations below the NAAQS, it is likely that all
near-road concentrations throughout the area are likely below the NAAQS.
 In addition, if a near-road monitor shows data that are above the
NAAQS, it is probable that measures that may be taken to bring
concentrations back down below the NAAQS will likely affect some or all
of the mobile sources in the area, reducing mobile source emissions
across an area.  

EPA also recognizes the need to have monitors away from roads that
represent area-wide concentrations that serve multiple monitoring
objectives including comparison to the NAAQS, photochemical pollutant
assessment, aiding in ozone forecasting, and characterization of point
and area source impacts.  

After considering the scientific data and the public comments regarding
the proposed network design, EPA is selecting to implement the two-tier
network design composed of (1) near-road monitors which would be placed
in locations of expected maximum 1-hour NO2 concentrations near heavily
trafficked roads in urban areas and (2) monitors located to characterize
areas with the highest expected NO2 concentrations at the neighborhood
and larger spatial scales (also referred to as “area-wide”
monitors).  

2.	First Tier (Near-road Monitoring Component) of the NO2 Network Design

The following paragraphs provide background, rationale, and details for
the final changes to the first tier of the two-tier NO2 network design.
In particular, this section will focus on the thresholds that trigger
monitoring requirements.  Near-road site selection and siting criteria
details will be discussed in subsequent sections. 

a.	Proposed First Tier (Near-road Monitoring Component) of the Network
Design

	EPA proposed that the first tier of the two-tier NO2 monitoring network
design focus monitors in locations of expected maximum 1-hour
concentrations near major roads in urban areas.  As noted in previous
section, the ISA and REA indicate that one of the largest factors
affecting ambient exposures to NO2 above health benchmarks
concentrations are mobile source emissions, particularly at locations
near major roads.  Since the combination of increased mobile source
emissions and increased urban population densities can lead to increased
exposures and associated risks, urban areas are the appropriate areas to
concentrate required near-road monitoring efforts. Therefore, we
proposed that one near-road NO2 monitor be required in CBSAs with a
population greater than or equal to 350,000 persons.  Based on 2008
Census Bureau statistics, this will result in approximately 143 sites in
as many CBSAs.

We also proposed that a second near-road monitor be required in CBSAs
with a population greater than or equal to 2,500,000 persons, or in any
CBSAs with one or more road segments with an Annual Average Daily
Traffic (AADT) count greater than or equal to 250,000.  Based on 2008
Census Bureau statistics and data from the 2007 Highway Performance
Monitoring System (HPMS) maintained by the US Department of
Transportation (DOT) Federal Highway Administration (FHWA), this
particular element of the minimum monitoring requirements will add
approximately 24 sites to the approximate 143 near-road sites in CBSAs
that already will have one near-road monitor required due to the 350,000
population threshold. Of the 24 additional sites, two sites are
triggered due to the 250,000 AADT threshold and are attributed to the
Las Vegas, Nevada and Sacramento, California CBSAs. Overall, this first
tier of the proposed network design is estimated to require 167
near-road sites in 143 CBSAs.

b.	Comments

EPA received comments from some industry and public health groups
supporting our proposed population thresholds which trigger minimum
near-road monitoring requirements.  For example, Dow Chemical Company
stated that “Dow comments that the proposed population thresholds are
reasonable for implementation of the new network design and that we
don't see a need to establish a threshold lower than 350,000 people for
the lower bound.”  

EPA also received comments from some states and state groups suggesting
that a combination of population and AADT counts or just AADT should be
used to trigger minimum near-road monitoring requirements.  For example,
the San Joaquin Air Pollution Control District in California suggested
that we modify minimum monitoring requirements so that one near-road NO2
monitor be required for any CBSA with a population of 350,000 people and
that had one or more road segments that had AADT counts of 125,000 or
more.  In another example, Harris County Public Health and Environmental
Services suggested that “…rather than specifying population limits
for the monitoring, HCPHES supports a metric like the Annual Average
Daily Traffic (AADT) as a threshold for requiring a near-road monitor.
An initial focus on an AADT in excess of 250,000 is acceptable as a
starting point but EPA should revisit that level and consider lowering
it to 100,000 in five years.”  EPA notes that, in general, roads with
higher AADT counts have relatively higher amounts of mobile source
emissions, which provide an increased potential to lead to relatively
higher on-road and roadside NO2 concentrations.  This concept is
supported, for example, by Gilbert et al. 2007, who state that the NO2
concentrations analyzed in their study are significantly associated with
distance from the nearest highway and the traffic count on the nearest
highway.  EPA believes that part of the intent of suggestions to include
AADT as part of, or distinctly as the requirement threshold is to
further increase the focus of the near-road network to locations where
NO2 concentrations are expected to be highest.  However, EPA chose the
population threshold approach to trigger near-road monitoring in lieu of
a population-AADT count combination or a distinct AADT count threshold
because of the uncertainty in defining which AADT counts would be
appropriate to use in such an approach.  The depth of knowledge and
certainty in the understanding of what particular AADT count might be
expected to contribute to some specific NO2 concentration is not
sufficient to translate into a specific, nationally applicable AADT
count threshold that could be used as part of a population-AADT
threshold approach to require near-road monitors.  Therefore, EPA chose
not to utilize a population-AADT or an AADT-only threshold to trigger
near-road monitoring because of the lack of a quantitative, nationally
applicable relationship between a certain AADT and an expected NO2
concentration.

A few commenters suggested focusing more near-road monitors only in the
larger CBSAs.  For example, the New York Department of Environmental
Conservation (NY DEC) suggested to require, at minimum, two near-road
monitors in any CBSA of 2,500,000 people or more, but none in CBSAs
below that population threshold.  In their comments they point out the
variety of near-road environments that exist in the larger CBSAs such as
New York City.  EPA concurs with NY DEC, and notes that the larger
CBSAs, such as those with a population of 2,500,000 or more persons, are
more likely to have a greater number of major roads across a potentially
larger geographic area, and a corresponding increase in potential for
exposure in different settings.  This is the reasoning behind the
requirement for two monitors in CBSAs with more than 2,500,000 people. 
EPA also believes that having multiple monitors in the largest CBSAs
will also allow better understanding of the differences that may exist
between different roads in the same CBSAs due to fleet mix, congestion
patterns, terrain, or geographic locations within those individual
CBSAs. However, EPA believes that a network with less overall monitors
in a fewer number of CBSAs than that which was proposed would lead to an
insufficiently sized network and would be an unbalanced approach for a
regulatory network intended to support the revised NAAQS.  Considering
the potential variability that may exist from one CBSA to the next with
regard to the number of roads, the populations that live near roads, the
fleet mix, the terrain, and the local meteorology, EPA believes a
network that has more monitors in a greater number of CBSAs is more
appropriate to fulfill the intent of the revised NAAQS, where the public
are to be protected from NO2 concentrations exceeding the NAAQS anywhere
in an area. 

EPA proposed to require a second monitor in CBSAs with a population
greater than or equal to 2,500,000 persons, to allow for further
characterization of larger urban areas that are more likely to have a
greater number of major roads across a potentially larger geographic
area, and a corresponding increase in potential for exposure.  The
additional provision for any CBSAs with one or more road segments with
an Annual Average Daily Traffic (AADT) count greater than or equal to
250,000 to have a second monitor if they do not already have two
near-road monitors required due their population is to cover situations
where a relatively less populated area has a very highly trafficked
road.  In this case, EPA believes that because those road segments with
250,000 AADT have been identified by US DOT FHWA (  HYPERLINK
"http://www.fhwa.dot.gov/policyinformation/tables/02.cfm" 
http://www.fhwa.dot.gov/policyinformation/tables/02.cfm ) as being the
top 0.03 percent of the most traveled public road segments, that they
are the most heavily trafficked roads in the country.  These roads
segments may correspond to the greatest potential for high exposures
directly connected to motor vehicle emissions in the entire country. 
Typically, these very highly trafficked roads are in the largest
populated CBSAs, such as those with 2,500,000 people or more, and are
somewhat atypical for CBSAs with less than 2,500,000 people.  As a
result, EPA believes it is appropriate to require a second monitor in a
CBSA that has one or more road segments with 250,000 AADT counts or more
if they do not already have two near-road monitors required due their
population.  

 EPA received a few comments requesting explanation of the reasoning
behind the selection of the population thresholds that trigger minimum
monitoring requirements.  For example, the New York Department of
Transportation suggested that this final rule explain the basis for the
350,000 and 2,500,000 population thresholds that will establish
near-road monitors.  In using the population threshold approach to
trigger monitoring requirements, EPA proposed that those CBSAs with
populations equal to or greater than 350,000 and 2,500,000 shall have
one or two required near-road monitors, respectively.  The selection of
the CBSA population level of 350,000 to trigger the requirement of one
near-road monitor was chosen to require monitoring in CBSAs that will
provide near-road monitoring data with a more diverse array of CBSAs in
terms of population, potential fleet mixes, geographic extent, and
geographic setting, from across the country relative to a network
triggered by a higher population threshold.  EPA reviewed the spatial
extent and the population included in CBSAs of certain sizes when making
selecting the population thresholds.  There are 143 CBSAs with 350,000
people across the country (including territories) which contain
approximately 72% of the total population according to 2008 U.S. Census
Bureau estimates (www.census.gov).  This collection of CBSAs
collectively represents territory in 44 states, the District of
Columbia, and Puerto Rico. For comparison, there are 52 CBSAs with
1,000,000 or more people, which contain approximately 55% of the total
population.  This particular collection of CBSAs collectively represents
territory in only [SPACE RESERVED FOR DATA – NEED TO VERIFY IN
ArcGIS].  EPA believes that selecting 350,000 as a threshold to
minimally require one near-road monitor provides a sufficiently sized
network with good spatial representation across the country in a diverse
set of CBSAs that represent a significant portion of the population. 
The selection of the 2,500,000 population threshold to trigger a second
near-road monitor, as noted earlier in this section, is based on the
fact that the larger urban areas in the country are more likely to have
a greater number of major roads across a potentially larger geographic
area, and have a corresponding increase in potential for exposure in
different settings. 

EPA received many state comments suggesting adjustments to the overall
near-road network components’ size, without giving distinct
suggestions on how to do so.  For example, the Regional Air Pollution
Control Agency, who represents a portion of Ohio, stated “Given the
fairly standard fleet of vehicles on the nation's major highways, we
urge EPA to consider the need for 142 near-roadway monitors. Perhaps a
limited number of monitors across the country would suffice to
sufficiently characterize near-roadway NO2 levels.”  This group of
commenters had various reasons for why they suggested the network be
reduced, including funding concerns (discussed above), safety issues
(discussed below), the perceived need to do additional research
monitoring (discussed above), problems with state implementation plans
(discussed in ??), and designation issues (discussed in ??).  EPA
understands the issues and concerns presented, and believe that many of
these issues are addressed throughout this document.  However, in regard
to reducing the size of the first tier of the network design, EPA
believes that a significantly smaller network than what was proposed
would be insufficient in supporting the revised NAAQS by assuring that a
significant amount of populations across the country are informed and
ultimately protected by having near-road NO2 data that can be compared
to the NAAQS.  The intent of the first tier of the network design is to
require near-road monitoring in CBSAs that will provide near-road
monitoring data with a more diverse array of CBSAs in terms of
population, potential fleet mixes, geographic extent, and geographic
setting, from across the country.

c.	Conclusions Regarding the First Tier (Near-road Monitoring Component)
of the Network Design

	EPA notes that there is a significant lack of routine near-road NO2
monitoring data from different locations around the country.  If the
proposed monitoring network is to support the intent of the revised
NAAQS, preventing exposures to NO2 concentrations above the NAAQS
anywhere in an area, and recognizing that mobile sources have been
identified as a major contributor to exposure risks, a sufficiently
sized network including near-road monitors, such as that proposed, is
appropriate.. The number and distribution of the monitors in the
proposed network will allow states and EPA to gather data for comparison
to the NAAQS and ultimately inform the public on what NO2 concentrations
populations in a diverse array of urban areas, that contain over 72% of
the total U.S. population (based on 2008 U.S. Census Bureau estimates),
may routinely be exposed to on and near roads.  Therefore, we are
finalizing the thresholds that will trigger minimally required near-road
NO2 monitors as they were proposed, where one near-road NO2 monitor is
required in CBSAs with a population greater than or equal to 350,000
persons and a second near-road monitor is required in CBSAs with a
population greater than or equal to 2,500,000 persons, or in any CBSAs
with one or more road segments with an Annual Average Daily Traffic
(AADT) count greater than or equal to 250,000.

3.	Second Tier (Area-wide Monitoring Component) of the Network Design

The following paragraphs provide background, rationale, and details for
the final changes to the second tier of the two-tier NO2 network design.
In particular, this section will focus on the threshold that triggers
monitoring requirements.  Area-wide site selection and siting criteria
details will be discussed in a subsequent section.

a.	Proposed Second Tier (Area-wide Monitoring Component) of the Network
Design 

	As the second tier of the proposed two-tier network design, EPA
proposed to require monitors to characterize the highest expected NO2
concentrations at the neighborhood and larger (area-wide) spatial scales
in a area.  This component of the two-tier network design provides
information on area-wide type exposures that may occur in an area due to
an individual or a group of point, area, on-road, and/or non-road
sources.  Further, area-wide sites serve multiple monitoring objectives
aside from NAAQS comparison including photochemical pollutant
assessment, aiding in ozone forecasting, aiding in particulate matter
precursor analysis and particulate matter forecasting.  We proposed to
require one area-wide monitoring site in each CBSA with a population
greater than or equal to 1,000,000. These area-wide sites are proposed
to be sited to represent an area of highest concentration at the
neighborhood or larger spatial scales. Based on 2008 Census Bureau
statistics, this minimum monitoring requirement is expected to trigger
52 area-wide monitors in as many CBSAs.  EPA also proposed to allow any
current photochemical assessment monitoring station (PAMS) sites that
are situated to address the highest NO2 concentrations in an urban area
and sited at neighborhood or urban scales to satisfy this proposed
area-wide monitoring requirement.

b.	Comments

	Most commenters who made comments on area-wide monitoring did so in
regard to their support of the adoption of the alternative area-wide
network design and not specifically about the area-wide monitoring
component of the proposed two-tier network design.  However, EPA did
receive comments from health groups on area-wide monitoring in context
of the proposed network design.  The health group commenters, including
the American Lung Association, Earthjustice, the Environmental Defense
Fund, and the National Resource Defense Council, stated they “oppose
the proposed requirement to retain only 52 air monitors to measure
area-wide concentrations of NO2.”  EPA understands the perceived
concern to be that we are actively reducing the number of required
area-wide monitors.  

Prior to this rulemaking, the 2006 monitoring rule (REFERENCE) removed
minimum monitoring requirements for NO2, however the rule has had a
limited impact to date, evidenced by the fact that the size of the NO2
network has remained relatively steady, with around 400 monitors, a
majority of which are area-wide monitors, were operating in 2008
(Watkins and Thompson, 2008).  This is due to multiple reasons, but in
large part due to the fact that area-wide monitors serve multiple
monitoring objectives, as noted earlier, which includes photochemical
pollutant assessment, aiding in pollutant forecasting, and in some cases
in support to ongoing health research.  Noting that states always have
the right to conduct monitoring above the minimum Federal requirements,
and recognizing the objectives of programs such as the Photochemical
Assessment Monitoring Stations (PAMS), EPA believes that the actual
number of area-wide monitors that will operate in the NO2 network will
be greater than the minimally required 52 sites.   As a result, EPA does
not believe that a modification to the two-tier network design that
increases the number of required area-wide NO2 sites as was proposed is
necessary. 

c.	Conclusions on the Second Tier (Area-wide Monitoring Component) of
the Network Design

	EPA recognizes that significant portion of the existing NO2 monitoring
network can be characterized as area-wide monitors and that these
monitoring sites serve multiple monitoring objectives, as noted above,
even thought they were not previously required to operate.  In order to
ensure that a minimum number of area-wide monitors continue operating
into the future, we are finalizing the proposed minimum monitoring
requirements for area-wide monitors, where one area-wide monitor is
required in any CBSA with 1,000,000 people or more.  Since there were no
objections to allowing PAMS stations that meet siting criteria
(discussed in a subsequent section) to satisfy minimum monitoring
requirements for area-wide monitors, we are finalizing that allowance as
proposed.  In addition, EPA encourages states to use the network
assessment process to review existing area-wide NO2 sites to help
determine what monitors might meet minimum monitoring requirements and
whether or not other existing monitors warrant continued operation.  EPA
would expect that this process would occur gradually over several years,
but would greatly assist in streamlining the NO2 network, as states move
to meet new minimum monitoring requirements and modify the network to
reflect the intent of the revised NAAQS and the needs of other ongoing
monitoring objectives. 

4.	Regional Administrator Authority

The following paragraphs provide background, rationale, and details for
the final changes to Regional Administrator’s authority to use their
discretion in requiring additional NO2 monitors in addition to those
required in the minimum monitoring requirements of the two-tier network
design.

a.	Proposed Regional Administrator Authority

	EPA proposed that the Regional Administrator will have discretion to
require monitoring above the minimum requirements as necessary to
address situations where the required near-road monitors do not
represent a location or locations where the expected maximum hourly NO2
concentrations exist in a CBSA.  We also proposed to allow Regional
Administrators the discretion to require additional near-road monitoring
sites to address situations where minimum monitoring requirements are
not sufficient to meet monitoring objectives, such as a situation where
there is a variety of exposure potential in an area due to variety in
the amount or types of fleet mix, congestion patterns, terrain, or
geographic areas within a CBSA. Finally, we proposed that EPA Regional
Administrators have the discretion to require additional area-wide NO2
monitoring sites above the minimum monitoring requirements where the
minimum monitoring requirements for area-wide monitors are not
sufficient to meet monitoring objectives.

b.	Comments

	EPA received comments from some state groups (e.g. the New York
Department of Environmental Conservation, New York Department of
Transportation, and the New York City Law Department) and an industry
group (the Council of Industrial Boiler Operators) who requested greater
clarification on how Regional Administrators may use their authority to
require additional monitors above the minimum requirements.  For
example, the Council of Industrial Boiler Operators stated that “This
[Regional Administrator Authority] unreasonably vests an unbounded
amount of discretion in EPA to determine when "minimum monitoring
requirements are not sufficient" and which neighborhoods are "uniquely
affected," and impose additional monitoring requirements where all
applicable monitoring requirements are already met by the State and
local agency.” 

 	EPA believes that although minimum monitoring requirement do provide a
sufficiently sized and targeted monitoring network, a nationally
applicable network design can not always be guaranteed to account for
all the potential pollution exposure situations that can exist in every
area of the country.  This is the basis for allowing Regional
Administrators the authority to use their discretion to require
additional monitors.  The process by which an Regional Administrator
would use this authority usually is part of a collaborative process with
state agencies.  Typically, Regional Administrators will work with state
and local agencies to design and/or maintain the most appropriate NO2
network to service the needs for a given area.  For all the situations
proposed where a Regional Administrator may require additional
monitoring, EPA expects that Regional Administrators would work on a
case-by-case basis in requiring any additional monitors.  One example
might be a location impacted by a stationary source where the required
near-road NO2 monitor site is not the location of maximum hourly
concentration in a CBSA. As a result, that location could be the
location of expected maximum concentration in the area.  This situation
could arise due to impacts from one of or a combination of multiple
sources that could include point, area, and non-road source emissions in
addition to on-road mobile source emissions. Alternatively, in this
example, if the sources responsible for this situation are producing
more widespread impacts on a community or area, the Regional
Administrator may require an area-wide monitor to assess population
exposures, or support other monitor objectives served by area-wide
monitors such as photochemical pollutant assessment or pollutant
forecasting.  Another example might be in a CBSA where a state or local
agency is fulfilling its minimum monitoring requirements near-road
monitors, but an additional location is identified where near-road
population exposure exists, at concentrations near or above the NAAQS,
that is unique, relative to the minimally required near-road monitor
locations.  For this example, the unique situation might be due to the
particular population or community that is affected, or the differences
in fleet mix, congestion patterns, terrain, or geographic area, relative
to any minimally required monitoring site(s) in that area. 

EPA recognizes that a variety of exposures scenarios can occur in an
area, and we believe that Regional Administrators should have the
discretion to require additional monitoring if such a unique situation
is recognized in an area.  In such situations, the actual locations
where additional monitoring could be required would likely have already
been identified by state or EPA Regional staff through data analysis,
such as the evaluation of existing ambient data and/or emissions data,
or through air quality modeling. Such information may indicate that an
area might have ground-level NO2 concentrations that may exceed the
NAAQS, and that a there is potential for population exposure to those
concentrations.  

c.	Conclusions on Regional Administrator Authority

Due to the fact that EPA recognizes that a nationally applied monitoring
network may not always provide the intended monitoring coverage due to
case-by-case type situations, we are finalizing, as proposed, that (1)
Regional Administrators shall have the discretion to require monitoring
above the minimum requirements as necessary to address situations where
the required near-road monitors do not represent a location or locations
where the expected maximum hourly NO2 concentrations exist in a CBSA. 
(2) Regional Administrators shall have the discretion to require
additional near-road monitoring sites to address situations where
minimum monitoring requirements are not sufficient to meet monitoring
objectives, such as a situation where there is a variety of exposure
potential in an area due to variety in the amount or types of fleet mix,
congestion patterns, terrain, or geographic areas within a CBSA.  (3)
Regional Administrators shall have the discretion to require additional
area-wide NO2 monitoring sites above the minimum monitoring requirements
where the minimum monitoring requirements for area-wide monitors are not
sufficient to meet monitoring objectives.  In any case where a Regional
Administrator might be in a position to use their authority to require
additional monitoring, EPA expects that the state and the Regional
Administrator would work together to evaluate evidence that suggests an
area may warrant additional monitoring.  EPA also notes that if
additional monitoring should be required, the state would present
information on any potential new sites through its Annual Monitoring
Network Plan, as required by 40 CFR §58.10, which includes a
requirement for public inspection or comment, and approval by the EPA
Regional Administrator.  

5.	Monitoring Network Implementation

The following paragraphs provide background, rationale, and details for
the final changes to the approach for the monitoring network
implementation.

a.	Proposed Monitoring Network Implementation Approach

	EPA proposed that state and, when appropriate, local air monitoring
agencies provide a plan for deploying monitors in accordance with the
proposed network design by July 1, 2011.  EPA also proposed that the
proposed NO2 network be physically established no later than January 1,
2013

b.	Comments

	Most environmental and public health group commenters made comments
that suggested EPA change the implementation date from the proposed
January 1, 2013 to a date that would require the minimally required NO2
network deployed sooner than proposed.  Most states and state group
commenters, along with industry group commenters, recommended that EPA
keep the network implementation date as January 1, 2013, or move it
later than proposed.  Some of the commenters who suggested moving it
later noted that issues with monitoring site identification, site
development, and overall lack of experience working in the near-road
environment would make implementation difficult under the proposed
implementation deadline.  

EPA recognizes that a lot of work must occur to deploy the two-tier
network design by the January 1, 2013 date.  We recognize the need for
guidance and  plan to aid state agencies in the network implementation
process, particularly through guidance documentation that will be
developed.  EPA agrees with the suggestion by NACAA that the CASAC
Ambient Air Monitoring Methods subcommittee should be consulted as part
of any guidance development for near-road monitoring.  Further, EPA
believes that collaboration with the states and state groups in
developing guidance will be highly beneficial to the implementation
process.  This would allow for those states that do have increased
experience in near-road monitoring to lend to guidance development and
provide a conduit for sharing experiences amongst all stakeholders.  

In perspective, EPA believes that the approximate 2 years and 11 months
between promulgation of this rulemaking and the mandated January 1, 2013
network implementation date include extra time relative to what was
traditionally allowed for network implementation following rulemakings
such as this.  Additionally, we note that are being cognizant of the
time needed to collect complete data that would allow data from the
two-tier network to be considered in the next NO2 NAAQS review.  EPA
would need to have data from 2013, 2014, and 2015 to have a chance to
include data in the next NAAQS review since it is intended to be
performed on a 5-year cycle.  Finally, delaying the installation of the
minimally required monitors, particularly the near-road NO2 sites, will
also delay the acquisition of the three years of data that are needed to
use in determining attainment, which, as noted in XX of this document,
would not occur until 2017, at the earliest.  

c.	Conclusions on Monitoring Network Implementation

	We are finalizing the date by which state and, when appropriate, local
air monitoring agencies shall establish the required NO2 monitoring
network as January 1, 2013, as was proposed.  We believe that the
allotted time for implementation will allow for the development of
guidance documentation, particularly allowing for interactions with
CASAC and NACAA, and for the processes that will be involved in
deploying this network, including the assessment of road segments in
CBSAs, identifying and working with local transportation officials as
needed on issues regarding access and safety, and the exchange of
information and feedback on potential sites with EPA, prior to any
commitment to any sites in an annual monitoring plan. However, based on
feedback received through public comments, and to allow for more time to
process guidance information, to carry out the previously mentioned
deployment processes, and to allow for information exchanges to occur,
we are changing the date by which state and, when appropriate, local air
monitoring agencies shall provide a plan for deploying monitors in
accordance with required network design from July 1, 2011 to July 1,
2012. However, EPA encourages states and local air agencies to supply as
much information as possible on the NO2 sites they may be considering,
or have possibly selected, to satisfy the minimum NO2 network monitoring
requirements in their Annual Monitoring Network Plan submitted July 1,
2011. 

6.	Near-road Site Selection 

The following paragraphs provide background, rationale, and details for
the final changes to the approach and criteria by which required
near-road sites shall be selected. 

a.	Proposed Near-road Site Selection Criterion	

EPA proposed that minimally required near-road NO2 monitoring stations
shall be selected by ranking all road segments within a CBSA by AADT and
then identifying a location or locations adjacent to those highest
ranked road segments where maximum hourly NO2 concentrations are
expected to be highest and siting criteria (discussed below) can be met
in accordance with that proposed for 40 CFR Part 58 Appendix E. Where a
state or local air monitoring agency identifies multiple acceptable
candidate sites where maximum hourly NO2 concentrations are expected to
occur, the monitoring agency should consider taking into account the
potential for population exposure in the criteria utilized to select the
final site location. Where one CBSA is required to have two near-road
NO2 monitoring stations, we proposed that the sites shall be
differentiated from each other by one or more of the following factors:
fleet mix; congestion patterns; terrain; geographic area within the
CBSA; or different route, interstate, or freeway designation.

b.	Comments

	EPA received many comments from CASAC, public health groups, states and
state groups, and industry groups on the proposed procedure by which
states will select near-road sites.  CASAC, along with some health group
and state commenters noted that interpreted proposed language to intend
that states should select a site near the road with the highest ranked
AADT possible, without considering other factors.  For example, one
CASAC panel member noted that siting monitors based on traffic counts
alone might miss locations where maximum NO2 concentrations would occur.
They proceeded to recommend the use of modeling to assist in the site
selection process.  In another example, the ALA, EDJ, EJ, and NRDC,
stated that “Near-road monitor placement should be determined not only
by the highest AADT volumes in a given CBSA, but also by the highest
heavy-duty truck volumes.”  In one more example, in NACAA statements
they make a comment about “…basing monitor locations on the annual
average daily traffic (AADT) without regard to vehicle mix or dispersion
characteristics…”.  

EPA does not intend for AADT counts to be the sole reason a near-road
site is selected.  As noted earlier in paragraph 2(b) of this section,
there is a general relationship between AADT and mobile source
pollution, where higher traffic counts correspond to higher mobile
source emissions.  The use of AADT counts is intended to be a mechanism
by which the locations of expected maximum NO2 concentrations due to
mobile sources are identified.  EPA notes that there other factors that
can influence which road segment in a CBSA may be the actual location
where the maximum NO2 concentrations might occur.  These factors include
vehicle fleet mix, roadway design, congestion patterns, terrain, and
meteorology.  When states identify their top-ranked road segments by
AADT, EPA intends for states to evaluate all of the factors listed above
that influence where the location of expected maximum NO2 concentration
may occur from the pool of candidate target road segments and monitoring
sties. As a result of the comments on this interpretation of the
proposal, EPA will specifically list the factors that will be used
considered by states in their site selection process once a state has
identified the most heavily trafficked roads in a CBSA via AADT counts.
In addition, these same factors were proposed to be considered by states
who are required to place two near-road monitors in one CBSA.  EPA
maintains that these factors will be key to differentiate the two
monitoring sites from each other, providing further characterization of
near-road environments in larger urban areas that are more likely to
have a greater number of major roads across a potentially larger
geographic area, and a corresponding increase in potential for exposure
in different settings.

	EPA received comments from some state and industry commenters (e.g.
Iowa, NY DEC, Edison Electric, and Savannah River Nuclear Solutions) who
suggested that population exposure should be a first-level consideration
in the near-road monitoring site selection, instead of a second-level
consideration which EPA proposed it to be.

EPA notes that the intent of the revised primary NO2 NAAQS is to protect
against the maximum allowable NO2 concentration anywhere in an area,
which includes ambient air on and around roads, which would limit
exposures to peak NO2 concentrations, across locations and over time,
with a relatively high degree of confidence.  We also note the
agency’s historical practice of locating monitors in locations of
maximum concentration, at the appropriate spatial scale, so long as the
monitor is characterizing ambient air.  If EPA were to allow population,
population density, or another population weighted metric to influence
where near-road monitors are located, it is possible that the required
near-road monitors in a CBSA would not be where the location of expected
maximum NO2 concentration, due to mobile sources, would occur.  By
monitoring in the location of expected maximum 1-hour concentrations,
near-road monitoring sites will likely represent the highest NO2
concentrations in an area directly attributable to mobile sources or a
group of sources that includes mobile sources.  EPA agrees that
population should not be ignored, however, which is reflected in the
rule language as it was proposed that says that if a states  identifies
multiple acceptable candidate sites where maximum hourly NO2
concentrations are expected to occur, the monitoring agency should
consider taking into account the potential for population exposure in
the criteria utilized to select the final site location.  

	EPA received commenters from [NEED PUBLIC COMMENTER ID] who suggested
that near-road monitoring site selection should take into consideration
the location of other major mobile and point sources for NO2 emissions,
such as airports, seaports, and power plants.  Further, some of these
commenters also suggested that state and local agencies have increased
flexibility in determining the appropriate balance between locating
near-road monitors along the busiest roadways, areas most likely to have
the highest NO2 concentrations, and diverse types of roadways.  

EPA agrees that other major NO2 sources that have the potential to
violate the NAAQS should be monitored.  The issue is whether such
monitoring should be handled through a more inclusive set of minimum
requirements or whether case-by-case treatment is appropriate.  EPA
believes that any of these mobile sources and any stationary source that
may be causing ground-level NO2 concentrations that are near or above
the NAAQS are able to be monitored through a requirement by the Regional
Administrator (discussed above) or possibly through state and local
initiative.  The reason that Regional Administrators have discretion to
require additional monitors is to provide the ability to deal with
situations where other locations in an area might warrant monitoring,
which EPA believes was the root of the respondent’s comment.

	One state commenter, the Wisconsin Department of Natural Resources,
requested that the term “major road” be defined and also requested
clarification on what “top-ranked” means with regard to AADT counts
on road segments.  The term “major road” is widely used in
literature and can be found to be defined differently from one
scientific study to another.  In this document and the proposal, EPA
simply means for “major road” to be synonymous with a road that is
relatively heavily trafficked.  EPA also does not believe it is
appropriate to define whether “top-ranked” means, for example, 5%,
10%, or 15%, of all road segments, as this would be arbitrary.  Each
CBSA will have a different distribution of total road segments and
corresponding AADT counts on those segments.  The intent of the
requirement to rank all road segments by AADT counts and select a site,
considering the other local factors noted above, near a “top-ranked”
road segment is to focus attention on the most heavily trafficked roads,
around which there is higher potential for maximum NO2 concentrations to
occur.  

c.	Conclusions on Near-road Site Selection

	We are finalizing the near-road site selection criteria as proposed,
and are clarifying the original intent that the selection criteria
include the consideration of localized factors. As a result, minimally
required near-road NO2 monitoring stations shall be selected by ranking
all road segments within a CBSA by AADT and then identifying a location
or locations adjacent to those highest ranked road segments, considering
fleet mix, roadway design, congestion patterns, terrain, and
meteorology, where maximum hourly NO2 concentrations are expected to be
highest and siting criteria can be met in accordance with 40 CFR Part 58
Appendix E.  As was noted in the network implementation section above,
EPA will work with states to assist with the near-road site selection
process through the development of guidance material and through
information exchanges amongst the air monitoring community.

	We are also finalizing the requirement, as proposed, that when one CBSA
is required to have two near-road NO2 monitoring stations, the sites
shall be differentiated from each other by one or more of the following
factors: fleet mix; congestion patterns; terrain; geographic area within
the CBSA; or different route, interstate, or freeway designation, as was
proposed.

7.	Near-road Siting Criteria

The following paragraphs provide background, rationale, and details for
the final changes to the siting criteria for required near-road
monitoring sites. 

a.	Proposed Near-road Siting Criteria

We proposed that near-road NO2 monitoring stations must be sited so that
the NO2 monitor probe is no greater than 50 meters away, horizontally,
from the outside nearest edge of the traffic lanes of the target road
segment, and shall have no obstructions in the fetch between the monitor
probe and roadway traffic such as noise barriers or vegetation higher
than the monitor probe height. We solicited comment on whether the
near-road sites should be located on the predominantly downwind side of
the target roadways.

We proposed that the monitor probe be located within 2 to 7 meters above
the ground, as is required for microscale PM2.5 sites.  We also proposed
that monitor probe placement on noise barriers or buildings, where the
inlet probe height is no less than 2 meters and no more than 7 meters
above the target road, will be acceptable, so long as the inlet probe is
at least 1 meter vertically or horizontally away (in the direction of
the target road) from any supporting wall or structure, and the
subsequent residence time of the pollutant in the sample line between
the inlet probe and the analyzer does not exceed 20 seconds. 

b.	Comments

	EPA received many comments state (e.g. LIST) and industry groups (e.g.
LIST) indicating that the near-road network poses significant safety
issues and a related need for increased logistical flexibility for
installing a monitoring site. [INSERT QUOTE HERE].

EPA notes that in all instances of field work, safety is a top priority.
 EPA believes that there are various ways to install near-road sites
while ensuring worker and traffic safety, and that safety is an
important part of the logistical considerations that states should
account for when selecting and installing near-road sites.  An example
of a step that could be taken to alleviate safety concerns might be
purposefully placing a monitoring site behind existing barriers like
guardrails and fencing, or possibly by installing a short distance of
such barriers to protect the site workers, site infrastructure, and
nearby traffic.  In addition to intentional measures that can be taken
to enhance safety, EPA notes that the 50m distance proposed is wide
enough to accommodate a sites that would satisfy many setback provisions
that exist for private or commercial building permits near roads, and
may be viewed as a confirmation that our proposed siting criteria are
safely attainable.

	Many commenters suggested that the allowable maximum distance a
near-road monitoring probe can be from the target road be increased from
50 meters to something wider, such as 200 meters.  Conversely, there
were some commenters who suggested that EPA reduce the allowable
distance to as close as 30 meters to the target road.  EPA believes that
increasing the allowable distance above 50 meters would compromise the
intent of near-road monitoring.  As was noted in the proposal language,
scientific literature indicates that on-road, mobile source derived NO2
exhibits a peak concentration on or very near the source road, and those
concentrations decay over a variable but relatively short distance back
to near area-wide or background (upwind of the target road)
concentrations.  Literature values indicate that the distance required
for NO2 concentrations to return to near area-wide or background
concentrations away from major roadways can range up to 500 meters. The
actual distance is variable, and highly dependent on topography,
roadside features, meteorology, and the related photochemical reactivity
conditions (Baldauf et al., 2008; Beckerman et al., 2007; Clements et
al., 2008; Gilbert et al. 2003; Hagler et al., 2009; Rodes and Holland,
1980; Singer et al., 2003; Zhou and Levy, 2007).  Therefore, monitor
probe placement at increasing distances from a road, such as 200 meters,
will correspondingly decrease the potential for sampling maximum
concentrations of NO2 due to the traffic on the target road.  Baldauf et
al. (2009) indicate that monitoring probes would ideally be situated
between 10 and 20 meters from the nearest traffic lane for near-road
pollutant monitoring. 

Having received comments suggesting widening and shortening the
allowable distance that an NO2 monitor probe may be from the target
road, EPA believes the proposed allowable distance a near-road NO2 probe
can be from the target road of 50 meters provides enough flexibility for
site placement while not sacrificing the potential to actually monitor
the peak NO2 concentrations.  However, in light of the information
provided here on how NO2 peak concentrations can decay over relatively
short distances, EPA encourages states to place near-road sites as close
as safely possible to target roads to increase the probability of
measuring the peak NO2 concentrations that occur in the near-road
environment, again noting that Baldauf et al. (2009) indicate that
monitor probes would ideally be situated between 10 and 20 meters from
the nearest traffic lane for near-road pollutant monitoring.

EPA received several comments on the solicitation for comment on
requiring near-road monitoring sites to be placed on the downwind side
of the target road where the commenters encouraged such a requirement. 
Conversely, other commenters suggested that such a requirement is
unnecessary, with one commenting that siting monitors in downwind
locations would not be feasible for all locations and that EPA should
allow upwind monitoring so long as upwind monitors are used in
conjunction with air dispersion modeling.  EPA noted in its proposal
that research literature indicates that in certain cases, mobile source
derived pollutant concentrations, including NO2, can be detected upwind
of roads, above background levels, due to a phenomenon called upwind
meandering.  Kalthoff et al. (2007) indicates that mobile source derived
pollutants can meander upwind on the order of tens of meters, mainly due
to vehicle induced turbulence, while Beckerman et al. (2008) note that
near-road pollutant concentrations on the predominantly upwind side of
their study sites dropped off to near background levels within the first
50 meters, but were above background in this short and variable upwind
range, which could be due, at least in part, to vehicle induced
turbulence.  This upwind meandering characteristic of pollutants in the
near-road environment provides an additional basis for locating
near-road sites within 50 meters of target road segments, but also
reduces the absolute need to be downwind of the road.  EPA believes that
very few, if any, near-road sites would be able to be situated in a
location that was always downwind.  For example, a hypothetical site may
have winds routinely out of several different cardinal directions
throughout the year, without one being a dominant direction. As a
result, for some period of a year, and given the variability
meteorology, some period of a day, or even an hour, the near-road site
may not be downwind of the target road, no matter which side of the road
its on.  EPA is not going to finalize a requirement that near-road sites
must be climatologically downwind of the target road segment because of
the additional limitations this introduces to finding potential site
candidates in exchange for what may be a small increase in the
opportunity to monitor peak NO2 concentrations.  However, EPA encourages
states to place monitors in the climatologically downwind direction
whenever possible, in an attempt to measure the peak NO2 concentrations
more often than not. 

EPA proposed that required near-road NO2 monitor probes be located
within 2 to 7 meters above the ground, as is required for microscale
PM2.5 sites.  Two commenters commented that monitor probes distributed
across the range of 2 to 7 meters may generate variability in
concentrations from site to site.  One of those two went further to
suggest that the allowable height range be reduced to 2.5 to 3.5 meters
above the ground.  Another group of commenters commented that the 2 to 7
meter range may not be practical for many sites and suggested guidelines
for alternate siting requirements. Finally, another group of commenters
commented that “the lower end of the proposed height of 2 to 7 meters
appears to capture the highest NO2 concentrations, and more accurately
represents human exposure at the breathing zone.”  In the proposal,
EPA noted that near-road monitoring sites will be adjacent to a variety
of road types, where some target roads will be on an even plane with the
monitoring station, while others may be cut roads (i.e., below the plane
of the monitoring station) or fill and open elevated roads (i.e., where
the road plane is above the monitoring station). EPA noted in the
proposal that it is appropriate to place the NO2 monitor probe as close
to the plane of the target road segment as possible, while staying
between 2 to 7 meters above the ground.  An allowable range between 2
and 7 meters provides more flexibility in site installation, which EPA
considers important because of the variety of siting situations each
state may have to deal with for each individual site.  While EPA agrees
that tighter allowable range such as 2.5 to 3.5 meters would reduce site
to site variability and keep probes nearer the “breathing zone” as
it was commented, the wider range of 2 to 7 meters is still appropriate.
EPA encourages states, where possible, to have monitor probes closer to
the suggested heights of 2.5 to 3.5 meters, while also attempting to
keep monitor probes as close to the plane of the target road as
possible.

In the proposal, EPA proposed in the siting criteria language that the
subsequent residence time of the pollutant in the sample line between
the inlet probe and the analyzer can not exceed 20 seconds.  EPA
received two comments regarding guidelines for maximum allowable inlet
length and sample residence time.  EPA notes that in 40 CFR Part 58
Appendix E, paragraph (9)(c), it is written that sample probes for
reactive gas analyzers at NCore monitoring sites must have a sample
residence time less than 20 seconds.  EPA believes this rule is also
appropriate for NO2 monitors, particularly if a monitor inlet manifold
is extended away from the main monitoring shelter. EPA also notes that
this concept was proposed in the proposal preamble language, but was
omitted from the proposed regulation text.  The final version of the
regulation text will have the revised language for this requirement in
40 CFR Part 58 Appendix E, paragraph (9)(c).

c.	Conclusions on Near-road Siting Criteria

We are finalizing the near-road NO2 monitor siting criteria, as
proposed, where (1) required near-road NO2 monitor probes shall be as
near as practicable to the outside nearest edge of the traffic lanes of
the target road segment; but shall not be located at a distance greater
than 50 meters, in the horizontal, from the outside nearest edge of the
traffic lanes of the target road segment, (2) required near-road NO2
monitor probes shall have an unobstructed air flow, where no obstacles
exist at or above the height of the monitor probe, between the monitor
probe and the outside nearest edge of the traffic lanes of the target
road segment, (3) required near-road NO2 monitors are required to have
sampler inlets between 2 and 7 meters above ground level, and (4)
residence time of NO2 in the sample line between the inlet probe and the
analyzer does not exceed 20 seconds.

8.	Area-wide Monitor Site Selection and Siting Criteria

The following paragraphs provide background, rationale, and details for
the final changes to the site selection and monitor siting criteria for
required area-wide monitoring sites. 

a.	Proposed Area-wide Monitor Site Selection and Siting Criteria

	EPA proposed that sites required as part of the second tier of the NO2
monitoring network design, known as the area-wide monitoring component,
be sited to characterize the highest expected NO2 concentrations at the
neighborhood and larger (area-wide) spatial scales in a CBSA.

b.	Comments

	While many commenters made comment supporting area-wide monitoring in
regard to the adoption of the alternative area-wide network design in
lieu of the proposed approach, only a relative few made comments that
related to the actual sites and siting criteria.  Of those comments
related to the siting of area-wide monitors, one respondent noted that
they should be located at least 1,000 meters away from any major roads
or intersections to ensure that the concentration of NO2 measured is
representative of an area-wide concentration instead of peak near-road
concentrations.  EPA notes that in order for an NO2 monitoring site to
be classified as a neighborhood (or larger) spatial scale site, it must
meet the roadway set-back requirements in Table E-1 of 40 CFR Part 58
Appendix E.  EPA believes that this existing set-back table is
appropriate to use to ensure that any NO2 site that may be intended to
be an area-wide site will be sufficiently distanced from any major road.
 

c.	Conclusions on Area-wide Monitor Site Selection and Siting Criteria

	We are finalizing the requirement that any sites required as part of
the second tier of the NO2 monitoring network design, known as the
area-wide monitoring component, be sited to characterize the highest
expected NO2 concentrations at the neighborhood and larger (area-wide)
spatial scales in a CBSA.

9.	Meteorological Measurements

The following paragraphs provide background, rationale, and details for
the final changes to the requirement of meteorological monitoring at
near-road monitoring sites. 

a.	Proposed Meteorological Measurements

	In further support of characterizing the peak NO2 concentrations
occurring in the near-road environment, EPA proposed to require
three-dimensional anemometry, providing wind vector data in the
horizontal and vertical planes, along with temperature and relative
humidity measurements, at all required near-road monitoring sites.

b.	Comments

	EPA received comments from several states (e.g. LIST) that did not
support the proposed meteorological measurement requirements.  They
noted issues with siting the probe nearer to structures and to the
ground than is typically done and averaging periods were called into
question.  One respondent commented that the recording of air turbulence
data at near-road monitoring stations ought to be encouraged but not
required.  As a result, EPA will not require meteorological monitoring
at near-road NO2 monitoring stations, but encourages states to do some
form of meteorological monitoring to better inform the conditions in
which they are acquiring NO2 data.  At a minimum, basic anemometry data
would be useful in identifying whether the site is upwind, downwind, or
otherwise oriented, relative to the target road.

c.	Conclusions on Meteorological Measurements

	We are not finalizing the proposal to require three-dimensional
anemometry, providing wind vector data in the horizontal and vertical
planes, along with temperature and relative humidity measurements, at
all required near-road monitoring sites.

C.	Data Reporting

The following paragraphs provide background, rationale, and details for
the final changes to the data reporting requirements, data quality
objectives, and measurement uncertainty. 

1.	Proposed Data Quality Objectives and Measurement Uncertainty 

In the proposal, EPA noted that state and local monitoring agencies are
required to report hourly NO, NO2, and NOx data to AQS within 90 days of
the end of each calendar quarter. We also noted that many agencies also
voluntarily report their pre-validated data on an hourly basis to
EPA’s real time AIRNow data system, where the data may be used by air
quality forecasters to assist in ozone forecasting. We believe these
data reporting procedures are appropriate to support the revised primary
NO2 NAAQS.  

EPA proposed to develop data quality objectives (DQOs) for the proposed
NO2 network.  We proposed a goal for acceptable measurement uncertainty
for NO2 methods to be defined for precision as an upper 90 percent
confidence limit for the coefficient of variation (CV) of 15 percent and
for bias as an upper 95 percent confidence limit for the absolute bias
of 15 percent.

2.	Comments

	EPA received no substantive comments that disagreed with the proposed
language on data reporting, the data quality objectives, or goals for
measurement uncertainty.

3.	Conclusions on Data Quality Objectives and Measurement Uncertainty

	We are finalizing the approach to develop data quality objectives, and
the proposed goal for measurement uncertainty, as proposed. 

IV. 	Appendix S--Interpretation of the Primary NAAQS for Oxides of
Nitrogen and Revisions to the Exceptional Events Rule

	The EPA proposed to add Appendix S, Interpretation of the Primary
National Ambient Air Quality Standards for Oxides of Nitrogen, to 40 CFR
part 50 in order to provide data handling procedures for the proposed
NO2 1-hour primary standard and for the existing NO2 annual primary
standard.  The proposed Appendix S detailed the computations necessary
for determining when the proposed 1-hour and existing annual primary NO2
NAAQS are met. The proposed Appendix S also addressed data reporting,
data completeness considerations, and rounding conventions.

	Two versions of Appendix S were proposed. The first applied to a 1-hour
primary standard based on the annual 4th high value form, while the
second applied to a 1-hour primary standard based on the 99th percentile
daily value form.  

	The final version of Appendix S is printed at the end of this notice
and applies to an annual primary standard and a 1-hour primary standard
based on the 98th percentile daily value form.  Appendix S is based on
the near-roadway approach to the setting the level of the 1-hour
standard and to siting monitors.  As such, these versions place no
geographical restrictions on which monitoring sites’ concentration
data can and will be compared to the 1-hour standard when making
nonattainment determinations and other findings related to attainment or
violation of the standard.  

	The EPA is amending and moving the provisions of 40 CFR 50.11 related
to data completeness for the existing annual primary standard to the new
Appendix S, and adding provisions for the proposed 1-hour primary
standard.  Substantively, the data handling procedures for the annual
primary standard in Appendix S are the same as the existing provisions
in 40 CFR 50.11 for that standard, except for an addition of a
cross-reference to the Exceptional Events Rule, the addition of
Administrator discretion to consider otherwise incomplete data complete,
and the addition of a provision addressing the possibility of there
being multiple NO2 monitors at one site.  The procedures for the 1-hour
primary standard are entirely new.

	The EPA is also making NO2-specific changes to the deadlines, in 40 CFR
50.14, by which States must flag ambient air data that they believe have
been affected by exceptional events and submit initial descriptions of
those events, and the deadlines by which States must submit detailed
justifications to support the exclusion of that data from EPA
determinations of attainment or nonattainment with the NAAQS. The
deadlines now contained in 40 CFR 50.14 are generic, and are not always
appropriate for NO2 given the anticipated schedule for the designations
of areas under the final NO2 NAAQS.

	The purpose of a data interpretation appendix in general is to provide
the practical details on how to make a comparison between multi-day and
possibly multi-monitor ambient air concentration data and the level of
the NAAQS, so that determinations of compliance and violation are as
objective as possible. Data interpretation guidelines also provide
criteria for determining whether there are sufficient data to make a
NAAQS level comparison at all.  The regulatory language for the
pre-existing annual NO2 NAAQS, originally adopted in 1977, contained
data interpretation instructions only for the issue of data
completeness. This situation contrasts with the situations for ozone,
PM2.5, PM10, and most recently Pb for which there are detailed data
interpretation appendices in 40 CFR part 50 addressing more issues that
can arise in comparing monitoring data to the NAAQS. 

A.	Interpretation of the primary NAAQS for oxides of nitrogen for the
annual primary standard

	The purpose of a data interpretation rule for the NO2  NAAQS is to give
effect to the form, level, averaging time, and indicator specified in
the regulatory text at 40 CFR 50.11, anticipating and resolving in
advance various future situations that could occur. Appendix S provides
common definitions and requirements that apply to both the annual and
the 1-hour primary standards for NO2. The common requirements concern
how ambient data are to be reported, what ambient data are to be
considered (including the issue of which of multiple monitors’ data
sets will be used when more than one monitor has operated at a site),
and the applicability of the Exceptional Events Rule to the primary NO2 
NAAQS. 

	The proposed Appendix S also addressed several issues in ways which are
specific to the individual primary NO2 standards, as described below.

1.	Proposed interpretation of the annual standard

	The proposed data interpretation provisions for the annual standard are
consistent with the pre-existing instructions included along with the
statement of the level and form of the standard in 40 CFR 50.11.  These
are the following:  (1) At least 75% of the hours in the year must have
reported concentration data. (2) The available hourly data are
arithmetically averaged, and then rounded (not truncated) to whole parts
per billion. (3) The design value is this rounded annual average
concentration.  (4) The design value is compared with the level of the
annual primary standard (expressed in parts per billion).  

	In the proposal, EPA noted that it would be possible to introduce
additional steps for the annual primary standard which in principle
could make the design value a more reliable indicator of actual annual
average concentration in cases where some monitoring data have been
lost.  For example, averaging within a calendar quarter first and then
averaging across quarters could help compensate for uneven data capture
across the year. For some aspects of the data interpretation procedures
for some other pollutants, the current data interpretation appendices do
contain such additional steps. The proposed provisions for the proposed
1-hour NO2 standard also incorporated some such features.  

2.	Comments on interpretation of the annual standard

	We received four comments, all from state agencies, on data
interpretation for the annual NO2 standard.  Of the four commenters, two
recommended the use of a weighted annual mean to appropriately implement
the annual primary standard.  Two other commenters asserted that there
is no strong seasonality in NO2 concentrations, and that therefore there
is no need to use a weighted annual mean or to require data completeness
quarter-by-quarter.

3.	Conclusions on interpretation of the annual standard

Upon investigating the issue of NO2 seasonality using data from AQS as
part of considering the comments, we have found that there are notable
variations in quarterly mean NO2 concentrations.  It is therefore quite
possible that an unweighted annual mean calculated without a
quarter-by-quarter data completeness requirement might not represent the
true annual mean as well as a weighted annual mean calculated with a
quarter-by-quarter completeness requirement. However, the current
practice of requiring 75% completeness of all of the hours in the year
and calculating the annual mean without weighting has been retained in
the final rule, because of its simplicity and because we believe it will
not interfere with effective implementation of the annual NAAQS.  No
area presently is nonattainment for or comes close to violating the
annual standard.  Therefore, the choice between the two approaches can
only have a practical effect, if any, on whether at some time in the
future an area is determined to be newly violating the annual standard. 
 If a monitor has a complete and valid design value below the standard
using the unweighted mean approach (with only an annual data
completeness requirement) but the design value would be considered 
incomplete and invalid under a hypothetical weighted mean approach (with
a quarterly completeness requirement), the monitor would in either case
be considered not to be violating and its data would not be the basis
for a nonattainment designation.  If a monitor has a design value above
the standard using the unweighted annual mean approach but is incomplete
with respect to a hypothetical quarterly completeness requirement, then
the two approaches would have different implications for the
determination of a violation.  A quarterly completeness requirement
would make a finding of violation impossible, unless the Administrator
chose to treat the data as if complete under another provision of the
final rule. The unweighted annual mean approach would allow but not
force a finding of violation, because the Administrator will have
discretion to make any such findings because there will be no mandatory
round of designations for the annual standard given that the annual
standard has not been revised in this review.  The Administrator will be
able to consider the representativeness of the unweighted annual mean
when deciding whether to make a discretionary nonattainment
redesignation.  Given that the annual standard requires only one year of
monitoring data for the calculation of a design value, little time will
be lost if the Administrator chooses to work with a state to obtain a
new design value based on more complete and/or seasonally balanced
monitoring data.   

B.	Interpretation of the primary NAAQS for oxides of nitrogen 1-hour
primary standard	

1.	Proposed interpretation of the 1-hour standard

	With regard to data completeness for the 1-hour primary standard with a
4th highest daily value form, the proposed Appendix followed past EPA
practice for other NAAQS pollutants by requiring that in general at
least 75% of the monitoring data that should have resulted from
following the planned monitoring schedule in a period must be available
for the key air quality statistic from that period to be considered
valid. For the 1-hour primary NO2 NAAQS, the key air quality statistics
are the daily maximum 1-hour concentrations in three successive years.
It is important that sampling within a day encompass the period when
concentrations are likely to be highest and that all seasons of the year
are well represented.  Hence, the 75% requirement was proposed to be
applied at the daily and quarterly levels. 

	Recognizing that there may be years with incomplete data, the proposed
text provided that a design value derived from incomplete data would
nevertheless be considered valid in either of two situations.  

	First, if the design value calculated from at least four days of
monitoring observations in each of these years exceeds the level of the
1-hour primary standard, it would be valid.  This situation could arise
if monitoring was intermittent but high NO2 levels were measured on
enough hours and days for the mean of the three annual 4th high values
to exceed the standard.  In this situation, more complete monitoring
could not possibly have indicated that the standard was actually met.  

	Second, we proposed a diagnostic data substitution test which was
intended to identify those cases with incomplete data in which it
nevertheless is very likely, if not virtually certain, that the daily
1-hour design value would have been observed to be below the level of
the NAAQS if monitoring data had been minimally complete. 

	It should be noted that one possible outcome of applying the proposed
substitution test is that a year with incomplete data may nevertheless
be determined to not have a valid design value and thus to be unusable
in making 1-hour primary NAAQS compliance determinations for that 3-year
period.

	Also, we proposed that the Administrator have general discretion to use
incomplete data based on case-specific factors, either at the request of
a state or at her own initiative.  Similar provisions exist already for
some other NAAQS.

	The second version of the proposed Appendix S contained proposed
interpretation procedures for a 1-hour primary standard based on the
99th percentile daily value form.  The 4th high daily value form and the
99th percentile daily value form would yield the same design value in a
situation in which every hour and day of the year has reported
monitoring data, since the 99th percentile of 365 daily values is the
4th highest value.  However, the two forms diverge if data completeness
is 82% or less, because in that case the 99th percentile value is the
3rd highest (or higher) value, to compensate for the lack of monitoring
data on days when concentrations could also have been high.

	Logically, provisions to address possible data incompleteness under the
99th percentile daily value form should be somewhat different from those
for the 4th highest form.  With a 4th highest form, incompleteness
should not invalidate a design value that exceeds the standard, for
reasons explained above. With the 99th percentile form, however, a
design value exceeding the standard stemming from incomplete data should
not automatically be considered valid, because concentrations on the
unmonitored days could have been relatively low, such that the actual
99th percentile value for the year could have been lower, and the design
value could have been below the standard.  The second proposed version
of Appendix S accordingly had somewhat different provisions for dealing
with data incompleteness.  One difference was the addition of another
diagnostic test based on data substitution, which in some cases can
validate a design value based on incomplete data that exceeds the
standard.

	The second version of the proposed Appendix S provided a table for
determining which day’s maximum 1-hour concentration will be used as
the 99th percentile concentration for the year.  The proposed table is
similar to one used now for the 24-hour PM2.5 NAAQS, which is based on a
 98th percentile form, but adjusted to reflect a 99th percentile form
for the 1-hour primary NO2 standard.  The proposed Appendix S also
provided instructions for rounding (not truncating) the average of three
annual 99th percentile hourly concentrations before comparison to the
level of the primary NAAQS.

2.	Comments on interpretation of the 1-hour standard 

	Three commenters expressed the view that the 75% completion per quarter
requirement should apply with respect to the 1-hour standard.  A fourth
commenter recommended that the requirement be increased to 82%.  Another
person commented that the requirement of 75% of the hours in a day is
too stringent.  The commenter noted that it would be inappropriate not
to count the day if the maximum concentration observed in the hours
measured is sufficiently high to make a difference with regard to
compliance with the NAAQS.  A comment was received that the substitution
test should not be included, on the grounds that nonattainment should
not be declared without irrefutable proof. This commenters also said
that the same completeness requirement as used for nonattainment should
be used for attainment.  We received one comment that the computation of
design values where multiple monitors are present at a site should be
averaged and not taken from a designated primary monitor. 

3.	Conclusions on interpretation of the 1-hour standard 

	Consistent with the Administrator’s decision to adopt a 98th
percentile form for the 1-hour NAAQS, the final version of Appendix S is
based on that form. Table 1 has been revised from the version that was
proposed, so that it results in the selection of the 98th percentile
value rather than the 99th percentile value.

	We agree with the three comments expressing the view that the
requirement for 75% data completeness per quarter should apply with
respect to the 1-hour standard.  A fourth comment recommended that the
requirement be increased to 82%.  We believe 82% is too stringent
because of the number of monitors that would not achieve such a
requirement and we believe that 75% captures the season.  We agree that
an incomplete day should be counted if  the maximum concentration
observed in the hours measured is sufficiently high to make a difference
with regard to compliance with the NAAQS, and we have accounted for that
in section 3.2.c.i by validating the design value if it is above the
level of the primary 1-hour standard when at least 75 percent of the
days in each quarter have at least one reported hourly value.  We agree
that substitution should not be used for the establishment of
attainment/nonattainment.  The commenter who remarked on this issue
appears not to have understood that the specific proposed substitution
tests have essentially zero probability of making a clean area fail the
NAAQS, or vice versa, because the substituted values are chosen to be
conservative against such an outcome. As noted in section 3.2(c)(i),
when substitution is used, the 3-year design value based on the data
actually reported, not the ‘‘test design value’’, shall be used
as the valid design value.

	In the course of considering the above comment regarding data
substitution tests to be used in cases of data incompleteness, EPA has
realized that there could be some cases of data incompleteness in which
the proposed procedure for calculating the 1-hour design value might
result in an in appropriately low design value.  As proposed, only days
with measurements for at least 75% of the hours in the day would be
considered in any way when identifying the 99th percentile value (99th
for purposes of the adopted NAAQS).  However, there could be individual
hours in other, incompletely monitored days that had measured
concentrations higher than the identified 98th percentile value from the
complete days. It would be inappropriate not to consider those hours and
days in some way. However, if all days with at least one hourly
concentration were used to identify the 99th percentile value without
any regard to their incompleteness, this could also result in a design
value that is biased low because the extra days could increase the
number of “annual number of days with valid data” enough to affect
which row of Table 1 of Appendix S is used.  It could, for example,
result in the 8th highest ranked daily maximum concentration being
identified as the 98th percentile value (based on Table 1 of Appendix S)
rather than a higher ranked concentration; this would also be
inappropriate because days which were not monitored intensively enough
to give a reasonable likelihood of catching the maximum hourly
concentration would in effect be treated as if they had such a
likelihood.  For example, 50 days with only one hourly measurement
during a time of day with lower concentrations would “earn” the
state the right to drop one notch lower in the ranking of days when
identifying the 98th percentile day, inappropriately.  The final version
of Appendix S solves this problem by providing that two procedures be
used to identifying the 98th percentile value, the first based only on
days with 75% data completeness and the second based on all days with at
least one hourly measurement.  The final design value is the higher of
the two values that result from these two procedures. 

	Lastly, with regard to situations with multiple monitors operating at
one site, we think that designation of a primary monitor is preferable
to averaging the data from multiple monitors based on administrative
simplicity and transparency for the public, and is unbiased with respect
to compliance outcome provided the state is able to make the designation
only before any data has been collected.  

C.	Exceptional Events Information Submission Schedule

	The Exceptional Events Rule at 40 CFR 50.14 contains generic deadlines
for a state to submit to EPA specified information about exceptional
events and associated air pollutant concentration data.  A state must
initially notify EPA that data has been affected by an event by July 1
of the year after the data are collected; this is done by flagging the
data in AQS and providing an initial event description.  The state must
also, after notice and opportunity for public comment, submit a
demonstration to justify any claim within 3 years after the quarter in
which the data were collected.  However, if a regulatory decision based
on the data (for example, a designation action) is anticipated, the
schedule to flag data in AQS and submit complete documentation to EPA
for review is foreshortened, and all information must be submitted to
EPA no later than one year before the decision is to be made.  

	These generic deadlines are suitable for the period after initial
designations have been made under a NAAQS, when the decision that may
depend on data exclusion is a redesignation from attainment to
nonattainment or from nonattainment to attainment.  However, these
deadlines present problems with respect to initial designations under a
newly revised NAAQS.  One problem is that some of the deadlines,
especially the deadlines for flagging some relevant data, may have
already passed by the time the revised NAAQS is promulgated.  Until the
level and form of the NAAQS have been promulgated a state does not know
whether the criteria for excluding data (which are tied to the level and
form of the NAAQS) were met on a given day.  The only way a state could
guard against this possibility is to flag all data that could possibly
be eligible for exclusion under a future NAAQS.  This could result in
flagging far more data than will eventually be eligible for exclusion. 
EPA believes this is an inefficient use of state and EPA resources, and
is potentially confusing and misleading to the public and regulated
entities.  Another problem is that it may not be feasible for
information on some exceptional events that may affect final
designations to be collected and submitted to EPA at least one year in
advance of the final designation decision.  This could have the
unintended consequence of EPA designating an area nonattainment as a
result of uncontrollable natural or other qualified exceptional events. 


	When Section 50.14 was revised in March 2007, EPA was mindful that
designations were needed under the recently revised PM2.5 NAAQS, so
exceptions to the generic deadline were included for PM2.5.  The EPA was
also mindful that similar issues would arise for subsequent new or
revised NAAQS.  The Exceptional Events Rule at section 50.14(c)(2)(v)
indicates “when EPA sets a NAAQS for a new pollutant, or revises the
NAAQS for an existing pollutant, it may revise or set a new schedule for
flagging data for initial designation of areas for those NAAQS.”

	EPA proposed revised exceptional event data flagging and documentation
deadlines in FR 34404 [Federal Register / Vol. 74, No. 134 / Wednesday,
July 15, 2009 / Proposed Rules] and invited comments from the public. 
The Agency received no comments related to the revised proposed schedule
for NO2 exceptional event data flagging and documentation deadlines.

	For the specific case of NO2, EPA anticipates that initial designations
under the revised NAAQS may be made by January 22, 2012 based on air
quality data from the years 2008-2010. (See Section VI below for more
detailed discussion of the designation schedule and what data EPA
intends to use.)    If final designations are made by January 22, 2012,
all events to be considered during the designations process must be
flagged and fully documented by states one year prior to designations,
by January 22, 2011.  This date also coincides with the Clean Air Act
deadline for Governors to submit to EPA their recommendations for
designating all areas of their states.

	The final rule text at the end of this notice shows the changes that
will apply if a revised NO2 NAAQS is promulgated by January 22, 2010,
and designations are made two years after promulgation of a NO2 NAAQS
revision.    

	Table 1 below summarizes the data flagging and documentation deadlines
corresponding to the two year designation schedule discussed in this
section.  If the promulgation date for a revised NO2 NAAQS occurs on a
different date than January 22, 2010, EPA will revise the final NO2
exceptional event flagging and documentation submission deadlines
accordingly to provide states with reasonably adequate opportunity to
review, identify, and document exceptional events that may affect an
area designation under a revised NAAQS.  



Table 1.  Schedule for Exceptional Event Flagging and Documentation
Submission for Data to be Used in Designations Decisions for New or
Revised NAAQS

NAAQS Pollutant/

Standard/(Level)/

Promulgation Date	Air Quality Data Collected for Calendar Year	Event
Flagging & Initial Description Deadline	Detailed Documentation
Submission Deadline

NO2/1-Hour Standard(100 PPB)	2008	July 1, 2010a	January 22, 2011

	2009	July 1, 2010 	January 22, 2011

	2010	 April 1, 2011a	July 1, 2011a



aIndicates change from general schedule in 40 CFR 50.14.

Note:  EPA notes that the table of revised deadlines only applies to
data EPA will use to establish the final initial designations for new or
revised NAAQS.  The general schedule applies for all other purposes,
most notably, for data used by EPA for redesignations to attainment.





V.	Designation of Areas

A.  	Proposed process 			

	The CAA requires EPA and the states to take steps to ensure that the
new or revised NAAQS are met following promulgation.  The first step is
to identify areas of the country that do not meet the new or revised
NAAQS.  Section 107(d)(1) provides that, “By such date as the
Administrator may reasonably require, but not later than 1 year after
promulgation of a new or revised NAAQS for any pollutant under section
109, the Governor of each state shall * * * submit to the Administrator
a list of all areas (or portions thereof) in the state” that should be
designated as nonattainment, attainment, or unclassifiable for the new
NAAQS.  Section 107(d)(1)(B)(i) further provides,  “Upon promulgation
or revision of a NAAQS, the Administrator shall promulgate the
designations of all areas (or portions thereof) * * * as expeditiously
as practicable, but in no case later than 2 years from the date of
promulgation.” 

No later than 120 days prior to promulgating designations, EPA is
required to notify states of any intended modifications to their
designations as EPA may deem necessary.  States then have an opportunity
to comment on EPA's tentative decision. Whether or not a state provides
a recommendation, the EPA must promulgate the designation that it deems
appropriate.

Accordingly, Governors must submit their initial NO2 designation
recommendations to EPA no later than January 2011.  If the Administrator
intends to modify any state’s recommendation, the EPA will notify the
Governor no later than 120 days prior to designations in January 2012. 
States that believe the Administrator’s modification is inappropriate
will have an opportunity to demonstrate why they believe their
recommendation is more appropriate before designations are finalized.  

B.	Public comments 

	Several industry commenters requested that EPA slow the timeline for
implementing a near-roadway monitoring network and designating roadway
areas because they believe EPA lacks significant information about the
implementation and performance of a national, near-roadway monitoring
network.  Two commenters also requested that if a near-roadway
monitoring network is deployed, that 1-hour NO2 standards be made more
lenient until the next review period so that more information will be
available about near-roadway NO2 concentrations before a stringent
standard is selected.

	A response to commenters’ requests that EPA slow the monitoring
implementation schedule and the request that EPA make the 1-hour NO2
standard more lenient until the next review period are addressed in
sections III.B.5 and II.F.4.D, respectively.   

	Section 110(d)(1)(B) requires the EPA to designate areas no later than
2 years following promulgation of a new or revised NAAQS (i.e., by
January 2012).  While the CAA provides the Agency an additional third
year from promulgation of a NAAQS to complete designations in the event
that there is insufficient information to make NAAQS compliance
determinations, we anticipate that delaying designations for an
additional year would not result in significant new data to inform the
initial designations.  A near-roadway monitoring network is not expected
to be fully deployed until January 2013 therefore, EPA must proceed with
initial designations using air quality data from the existing NO2
monitoring network.  Because none of the current NO2 monitors are sited
to measure near-roadway ambient air, we expect that most areas in the
country with current NO2 monitors will not violate the new NO2 NAAQS. 
In the event that a current NO2 monitor indicates a violation of the
revised standards, EPA intends to designate such areas
“nonattainment” no later than 2 years following promulgation of the
revised standards.  We intend to designate the rest of the country as
“unclassifiable” for the revised NO2 NAAQS until sufficient air
quality data is collected from a near-roadway monitoring network.  Once
the near-roadway network is fully deployed and 3 years of air quality
data are available, the EPA has authority under the CAA to redesignate
areas as appropriate from “unclassifiable” to “attainment” or
“nonattainment.”  We anticipate that sufficient data to conduct
designations would be available after 2015.    

	A number of commenters, largely from industry groups, focused on the
concern that a near-roadway monitoring network would lead to regional
nonattainment on the basis of high NO2 concentrations found near
roadways.  These commenters requested that any future nonattainment
areas be limited to the area directly surrounding roadways found to have
above-standard NO2 concentrations.

The CAA requires that any area that does not meet a NAAQS or that
contributes to a violation in a nearby area that does not meet the NAAQS
be designated “nonattainment.”  States and EPA will need to
determine which sources and activities contribute to a NAAQS violation
in each area.  Depending on the circumstances in each area this may
include sources and activities in areas beyond the area directly
surrounding a major roadway.  EPA intends to issue nonattainment area
boundary guidance after additional information is gathered on the
probable contributors to violating near-roadway NO2 monitors. 

C.  	Final designations process 	

	The EPA intends to promulgate initial NO2 designations by January 2012
(2 years after promulgation of the revised NAAQS).  Along with today’s
action EPA is also promulgating new monitoring rules that focus on
roadways.  As noted in section III, states must site required NO2
near-roadway monitors and have them operational by January 1, 2013. 
States will need an additional 3 years thereafter to collect air quality
data in order to determine compliance with the revised NAAQS.  This
means that a full set of air quality data from the new network will not
be available until after 2015.  Since we anticipate that data from the
new network will not be available prior to the CAA designation deadlines
discussed above, the EPA intends to complete initial NO2 designations by
January 2012 using the 3 most recent years of quality-assured air
quality data from the current monitoring network, which would be for the
years 2008-2010.  The EPA will designate as “nonattainment” any
areas with NO2 monitors recording violations of the revised NO2 NAAQS. 
We intend to designate all other areas of the country as
“unclassifiable” to indicate that there is insufficient data to
determine whether or not they are attaining the revised NO2 NAAQS. 

	Once the NO2 monitors are positioned in locations meeting the
near-roadway siting requirements and monitoring data become available,
the Agency has authority under section 107(d)(3) of the CAA to
redesignate areas as appropriate from “unclassifiable” to
“attainment” or “nonattainment.”  The EPA intends to issue
guidance on the factors that states should consider when determining
nonattainment boundaries after additional information is gathered on the
probable contributors to violating near-roadway NO2 monitors.    

VI.	Clean Air Act Implementation Requirements 

This section of the preamble discusses the Clean Air Act (CAA)
requirements that states and emissions sources must address when
implementing new or revised NO2 NAAQS based on the structure outlined in
the CAA and existing rules.   EPA may provide additional guidance in the
future, as necessary, to assist states and emissions sources to comply
with the CAA requirements for implementing new or revised NO2 NAAQS. 

The CAA assigns important roles to EPA, states, and, in specified
circumstances, Tribal governments to achieve the NAAQS.  States have the
primary responsibility for developing and implementing State
Implementation Plans (SIPs) that contain state measures necessary to
achieve the air quality standards in each area.  EPA provides assistance
to states by providing technical tools, assistance, and guidance,
including information on the potential control measures that may help
areas meet the standards. 

States are primarily responsible for ensuring attainment and maintenance
of ambient air quality standards once they have been established by EPA.
 Under section 110 of the CAA, 42 U.S.C. § 7410, and related
provisions, states are required to submit, for EPA approval, SIPs that
provide for the attainment and maintenance of such standards through
control programs directed at sources of NO2 emissions.  If a state fails
to adopt and implement the required SIPs by the time periods provided in
the CAA, the EPA has responsibility under the CAA to adopt a Federal
Implementation Plan (FIP) to assure that areas attain the NAAQS in an
expeditious manner.  

The states, in conjunction with EPA, also administer the prevention of
significant deterioration (PSD) program for NO2 and nonattainment new
source review (NSR).  See sections 160-169 of the CAA.   In addition,
Federal programs provide for nationwide reductions in emissions of NO2
and other air pollutants under Title II of the Act, 42 U.S.C.
§§7521–7574, which involves controls for automobiles, trucks, buses,
motorcycles, nonroad engines, and aircraft emissions; the new source
performance standards (NSPS) for stationary sources under section 111 of
the CAA, 42 § U.S.C. 7411.

	CAA Section 301(d) authorizes EPA to treat eligible Indian tribes in
the same manner as states (TAS) under the CAA and requires EPA to
promulgate regulations specifying the provisions of the statute for
which such treatment is appropriate.  EPA has promulgated these
regulations – known as the Tribal Authority Rule or TAR – at 40
C.F.R. Part 49.  See 63 Fed. Reg. 7254 (February 12, 1998).  The TAR
establishes the process for Indian tribes to seek TAS eligibility and
sets forth the CAA functions for which TAS will be available.  Under the
TAR, eligible tribes may seek approval for all CAA and regulatory
purposes other than a small number of functions enumerated at section
49.4.  Implementation plans under section 110 are included within the
scope of CAA functions for which eligible tribes may obtain approval. 
Section 110(o) also specifically describes tribal roles in submitting
implementation plans.  Eligible Indian tribes may thus submit
implementation plans covering their reservations and other areas under
their jurisdiction.

	Under the CAA and TAR, tribes are not, however, required to apply for
TAS or implement any CAA program.  In promulgating the TAR EPA
explicitly determined that it was not appropriate to treat tribes
similarly to states for purposes of, among other things, specific plan
submittal and implementation deadlines for NAAQS-related requirements. 
40 C.F.R. § 49.4(a).  In addition, where tribes do seek approval of CAA
programs, including section 110 implementation plans, the TAR provides
flexibility and allows them to submit partial program elements, so long
as such elements are reasonably severable – i.e., “not integrally
related to program elements that are not included in the plan submittal,
and are consistent with applicable statutory and regulatory
requirements.”  40 C.F.R. §49.7.

	To date, very few tribes have sought TAS for purposes of section 110
implementation plans.  However, some tribes may be interested in
pursuing such plans to implement today’s proposed standard.  As noted
above, such tribes may seek approval of partial, reasonably severable
plan elements, or they may seek to implement all relevant components of
an air quality program for purposes of meeting the requirements of the
Act.  In several sections of this preamble, EPA describes the various
roles and requirements states will address in implementing today’s
proposed standard.  Such references to states are generally intended to
include eligible Indian tribes to the extent consistent with the
flexibility provided to tribes under the TAR.  Where tribes do not seek
TAS for section 110 implementation plans, EPA will promulgate Federal
implementation plans as “necessary or appropriate to protect air
quality.”  40 C. F. R. §49.11(a).  EPA also notes that some tribes
operate air quality monitoring networks in their areas.  For such
monitors to be used to measure attainment with this primary NAAQS for
NO2, the criteria and procedures identified in this rule would apply. 

A.	Classifications

1.	Proposal

Section 172(a)(1)(A) of the CAA authorizes EPA to classify areas
designated as nonattainment for the purpose of applying an attainment
date pursuant to section 172(a)(2), or for other reasons.  In
determining the appropriate classification, EPA may consider such
factors as the severity of the nonattainment problem and the
availability and feasibility of pollution control measures (see section
172(a)(1)(A) of the CAA).  The EPA may classify NO2 nonattainment areas,
but is not required to do so.  The primary reason to establish
classifications is to set different deadlines for each class of
nonattainment area to complete the planning process and to provide for
different attainment dates based upon the severity of the nonattainment
problem for the affected area. However, the CAA separately establishes
specific planning and attainment deadlines for certain pollutants
including NO2 in sections 191 and 192: 18 months from nonattainment
designation for the submittal of an attainment plan, and as
expeditiously as possible, but no later than 5 years from nonattainment
designation for areas to attain the standard.  In the proposal, EPA
stated its belief that classifications are unnecessary in light of these
relatively short deadlines.

2.	Public comments

One commenter stated that they disagree with EPA’s decision not to
impose non-attainment classifications on areas with measured near-road
NO2 concentrations in excess of the new NO2 standard, and urged EPA to
provide a graduated non-attainment classification system for the new
standard.  According to the commenter, “a classification system
defining higher levels of non-attainment with increasingly stringent
requirements at those levels is one that allows for finer calibration of
air quality regulatory response defined at the federal level.”  

As stated in the proposed rule, Section 192(a), of part D, of the CAA
specifically provides an attainment date for areas designated as
nonattainment for the NO2 NAAQS.  Therefore, EPA has legal authority to
classify NO2 nonattainment areas, but the 5-year attainment date
addressed under section 192(a) cannot be extended pursuant to section
172(a)(2)(D).  Based on this limitation, EPA proposed not to establish
classifications within the 5- year interval for attaining any new or
revised NO2 NAAQS.  It is also EPA’s belief that given the short
deadlines that States have to develop and submit SIP’s and for areas
to achieve emissions reductions in order to attain the standard within
the 5 year attainment period, a graduated classifications system would
not be appropriate.  Therefore, EPA is using it’s discretion under the
CAA not to establish classifications. 

3.	Final

	EPA is not making any changes to the discussion on classifications in
the proposed rule. Therefore, there will be no classifications for the
revised NO2 NAAQS. 

B. 	Attainment Dates

	The maximum deadline by which an area is required to attain the NO2
NAAQS is determined from the effective date of the nonattainment
designation for the affected area.  For areas designated nonattainment
for the revised NO2 NAAQS, SIPs must provide for attainment of the NAAQS
as expeditiously as practicable, but no later than 5 years from the date
of the nonattainment designation for the area (see section 192(a) of the
CAA).  The EPA will determine whether an area has demonstrated
attainment of the NO2 NAAQS by evaluating air quality monitoring data
consistent with the form of the NAAQS for NO2 if revised, which will be
codified at 40 CFR part 50, Appendix F. 

1.	Attaining the NAAQS  

a.	Proposal

In order for an area to be redesignated as attainment, the state must
comply with the five requirements as provided under section 107(d)(3)(E)
of the CAA.  This section requires that:

- 	EPA must have determined that the area has met the NO2 NAAQS; 

- 	EPA has fully approved the state’s implementation plan; 

- 	the improvement in air quality in the affected area is due to
permanent and enforceable reductions in emissions;

- 	EPA has fully approved a maintenance plan for the area; and

- 	the state(s) containing the area have met all applicable requirements
under section 110 and part D. 

b.	Final

	EPA did not receive any comments on this aspect of the proposed rule
and is not making any changes to the discussion on attaining the NAAQS
in the proposed rule.	

2.	Consequences of Failing to Attain by the Statutory Attainment Date

a.	Proposal 

	Any NO2 nonattainment area that fails to attain by its statutory
attainment date would be subject to the requirements of sections 179(c)
and (d) of the CAA.  EPA is required to make a finding of failure to
attain no later than 6 months after the specified attainment date and
publish a notice in the Federal Register.  The state would be required
to submit an implementation plan revision, no later than one year
following the effective date of the Federal Register notice making the
determination of the area’s failure to attain, which demonstrates that
the standard will be attained as expeditiously as practicable, but no
later than 5 years from the effective date of EPA’s finding that the
area failed to attain.  In addition, section 179(d)(2) provides that the
SIP revision must include any specific additional measures as may be
reasonably prescribed by EPA, including “all measures that can be
feasibly implemented in the area in light of technological
achievability, costs, and any nonair quality and other air
quality-related health and environmental impacts.”  

b.	Final

	EPA did not receive any comments on this aspect of the proposed rule
and is not making any changes to the discussion on consequences of
failing to attain by the statutory attainment date in the proposed rule.


C.	Section 110(a)(2) NAAQS Infrastructure Requirements 

1.	Proposal

	Section 110(a)(2) of the CAA requires all states to develop and
maintain a solid air quality management infrastructure, including
enforceable emission limitations, an ambient monitoring program, an
enforcement program, air quality modeling, and adequate personnel,
resources, and legal authority.  Section 110(a)(2)(D) also requires
state plans to prohibit emissions from within the state which contribute
significantly to nonattainment or maintenance areas in any other state,
or which interfere with programs under part C to prevent significant
deterioration of air quality or to achieve reasonable progress toward
the national visibility goal for Federal class I areas (national parks
and wilderness areas).	 

	Under section 110(a)(1) and (2) of the CAA, all states are required to
submit SIPs to EPA which demonstrate that basic program elements have
been addressed within 3 years of the promulgation of any new or revised
NAAQS.  Subsections (A) through (M) of section 110(a)(2) listed below,
set forth the elements that a state’s program must contain in the SIP.
 The list of section 110(a)(2) NAAQS implementation requirements are the
following: 

Ambient air quality monitoring/data system:  Section 110(a)(2)(B)
requires SIPs to provide for setting up and operating ambient air
quality monitors, collecting and analyzing data and making these data
available to EPA upon request.

Program for enforcement of control measures:  Section 110(a)(2)(C)
requires SIPs to include a program providing for enforcement of measures
and regulation and permitting of new/modified sources.

Interstate transport:  Section 110(a)(2)(D) requires SIPs to include
provisions prohibiting any source or other type of emissions activity in
the state from contributing significantly to nonattainment in another
state or from interfering with measures required to prevent significant
deterioration of air quality or to protect visibility. 

Adequate resources:  Section 110(a)(2)(E) requires states to provide
assurances of adequate funding, personnel and legal authority for
implementation of their SIPs.

Stationary source monitoring system:  Section 110(a)(2)(F) requires
states to establish a system to monitor emissions from stationary
sources and to submit periodic emissions reports to EPA.

Emergency power:  Section 110(a)(2)(G) requires states to include
contingency plans, and adequate authority to implement them, for
emergency episodes in their SIPs.  

Provisions for SIP revision due to NAAQS changes or findings of
inadequacies:  Section 110(a)(2)(H) requires states to provide for
revisions of their SIPs in response to changes in the NAAQS,
availability of improved methods for attaining the NAAQS, or in response
to an EPA finding that the SIP is inadequate.

Consultation with local and Federal government officials:  Section
110(a)(2)(J) requires states to meet applicable local and Federal
government consultation requirements when developing SIP and reviewing
preconstruction permits.

Public notification of NAAQS exceedances:  Section 110(a)(2)(J) requires
states to adopt measures to notify the public of instances or areas in
which a NAAQS is exceeded.

PSD and visibility protection:  Section 110(a)(2)(J) also requires
states to adopt emissions limitations, and such other measures, as may
be necessary to prevent significant deterioration of air quality in
attainment areas and protect visibility in Federal Class I areas in
accordance with the requirements of CAA Title I, part C. 

Air quality modeling/data:  Section 110(a)(2)(K) requires that SIPs
provide for performing air quality modeling for predicting effects on
air quality of emissions of any NAAQS pollutant and submission of data
to EPA upon request.

Permitting fees:  Section 110(a)(2)(L) requires the SIP to include
requirements for each major stationary source to pay permitting fees to
cover the cost of reviewing, approving, implementing and enforcing a
permit.

Consultation and participation by affected local government:  Section
110(a)(2)(M) requires states to provide for consultation and
participation by local political subdivisions affected by the SIP.

2.	Final

	EPA did not receive any comments on this aspect of the proposed rule
and is not making any changes to the discussion on section 110(a)(2)
NAAQS infrastructure requirements in the proposed rule.	

D.  	Attainment Planning Requirements 

1.	Nonattainment Area SIPs

a.	Proposal

Any state containing an area designated as nonattainment with respect to
the NO2 NAAQS must develop for submission a SIP meeting the requirements
of part D, Title I, of the CAA, providing for attainment by the
applicable statutory attainment date (see sections 191(a) and 192(a) of
the CAA).  As indicated in section 191(a) all components of the NO2 part
D SIP must be submitted within 18 months of the effective date of an
area’s designation as nonattainment.  

Section 172 of the CAA includes general requirements for all designated
nonattainment areas.  Section 172(c)(1) requires that each nonattainment
area plan “provide for the implementation of all reasonably available
control measures (RACM) as expeditiously as practicable (including such
reductions in emissions from existing sources in the area as may be
obtained through the adoption, at a minimum, of  Reasonably Available
Control Technology (RACT)), and shall provide for attainment of the
national primary ambient air quality standards.”  States are required
to implement RACM and RACT in order to attain “as expeditiously as
practicable”.  

  tc " " 	Section 172(c) requires states with nonattainment areas to
submit a SIP for these areas which contains an attainment demonstration
that shows that the affected area will attain the standard by the
applicable statutory attainment date.  The state must also show that the
area will attain the standards as expeditiously as practicable, and it
must include an analysis of whether implementation of reasonably
available measures will advance the attainment date for the area. 

	Part D SIPs must also provide for reasonable further progress (RFP)
(see section 172(c)(2) of the CAA).  The CAA defines RFP as “such
annual incremental reductions in emissions of the relevant air pollution
as are required by part D, or may reasonably be required by the
Administrator for the purpose of ensuring attainment of the applicable
NAAQS by the applicable attainment date.” (See section 171 of the CAA)
Historically, for some pollutants, RFP has been met by showing annual
incremental emission reductions sufficient to maintain generally linear
progress toward attainment by the applicable attainment date.  

All NO2 nonattainment area SIPs must include contingency measures which
must be implemented in the event that an area fails to meet RFP or fails
to attain the standards by its attainment date. (See section 172(c)(9))
These contingency measures must be fully adopted rules or control
measures that take effect without further action by the state or the
Administrator. The EPA interprets this requirement to mean that the
contingency measures must be implemented with only minimal further
action by the state or the affected sources with no additional
rulemaking actions such as public hearings or legislative review.  

	Emission inventories are also critical for the efforts of state, local,
and Federal agencies to attain and maintain the NAAQS that EPA has
established for criteria pollutants including NO2.  Section 191(a) in
conjunction with section 172(c) requires that areas designated as
nonattainment for NO2 submit an emission inventory to EPA no later than
18 months after designation as nonattainment.  In the case of NO2,
sections 191(a) and 172(c) also require that states submit periodic
emission inventories for nonattainment areas.  The periodic inventory
must include emissions of NO2 for point, nonpoint, mobile (on-road and
non-road), and area sources. 

b.	Public comments

Several commenters indicated that EPA should take steps to ensure that
states actually require mobile source emissions reductions in order to
attain the NO2 NAAQS as opposed to controlling point sources.  Another
commenter went further and stated that states be required to control
on-road emissions as opposed to emissions from stationary sources and in
particular EGUs.  This commenter also indicated that EPA should delay
nonattainment designations until states had a cost effective means of
reducing on-road emissions of NO2.

EPA cannot require states to develop a SIP that only addresses one type
of source, in this case on-road mobile sources.  States may select
appropriate control measures to attain the NAAQS and EPA must approve
them if they otherwise meet all applicable requirements of the Act.  See
CAA § 116.  EPA expects that states will evaluate a range of control
measures that will reduce NO2 emissions within the time allowed to
attain the standard.  This would include the emissions reductions
attributable to Federal controls on on-road and non-road mobile sources,
and controls that they have put in place to reduce NOX emissions in
order to attain the 8-hour ozone NAAQS and/or the PM2.5 NAAQS.  If these
existing controls are not sufficient for an area to reach attainment
with the NO2 NAAQS, EPA would expect the state to implement additional
control measures that would bring the area into attainment by the
deadline.  For a designation based on data from a near roadway monitor
EPA would expect the states to give primary consideration to controlling
emissions from on-road sources; however, it is likely that other types
of sources contribute to the concentrations that are measured at a near
roadway monitor and a state may decide to implement controls on these
other contributing sources. 

The Clean Air Act requires that EPA finalize designations within two
years after a NAAQS is revised unless the available air quality data is
insufficient to make designations by that time.  In that case, EPA must
finalize designations within three years after the NAAQS is revised.  As
discussed elsewhere in today’s final rule, EPA believes that it has
sufficient data to make designations within two years and that most
areas will be designated as unclassifiable at that time.  Taking the
additional year provided by the CAA would not allow additional data from
the new near roadway monitors to be factored into the designations
process in any event.  Therefore, it is EPA’s intention to designate
areas within two years as required by the Act.  EPA intends to
redesignate areas once it has sufficient data from the new monitoring
network to designate areas as clearly attaining or not attaining the
standard.

c.	Final

	The EPA is not making any changes to the discussion on nonattainment
area SIPs in the proposed rule.

2.	New Source Review and Prevention of Significant Deterioration
Requirements 

a.	Proposal

The Prevention of Significant Deterioration (PSD) and nonattainment New
Source Review (NSR) programs contained in parts C and D of Title I of
the CAA govern preconstruction review of any new or modified major
stationary sources of air pollutants regulated under the CAA as well as
any precursors to the formation of that pollutant when identified for
regulation by the Administrator.  The EPA rules addressing these
programs can be found at 40 CFR 51.165, 51.166, 52.21, 52.24, and part
51, appendix S.  States which have areas designated as nonattainment for
the NO2 NAAQS must submit, as a part of the SIP due 18 months after an
area is designated as nonattainment, provisions requiring permits for
the construction and operation of new or modified stationary sources
anywhere in the nonattainment area. SIPs that address the PSD
requirements related to attainment areas are due no later than 3 years
after the promulgation of a revised NAAQS for NO2. 

The NSR program is composed of three different permit programs:

Prevention of Significant Deterioration (PSD)

Nonattainment NSR (NA NSR)

Minor NSR.

The PSD program applies when a major source, that is located in an area
that is designated as attainment or unclassifiable for any criteria
pollutant, is constructed, or undergoes a major modification.  The
nonattainment NSR program applies on a pollutant-specific basis when a
major source constructs or modifies in an area that is designated as
nonattainment for that pollutant.  The minor source NSR program
addresses both major and minor sources which undergo construction or
modification activities that do not qualify as major, and it applies, as
necessary to assure attainment, regardless of the designation of the
area in which a source is located.  

	The PSD requirements include but are not limited to the following:

installation of Best Available Control Technology (BACT);

air quality monitoring and modeling analyses to ensure that a
project’s emissions will not cause or contribute to a violation of any
NAAQS or maximum allowable pollutant increase (PSD increment);

notification of Federal Land Manager of nearby Class I areas; and

public comment on permit.

Nonattainment NSR requirements include but are not limited to:

installation of Lowest Achievable Emissions Rate (LAER) control
technology;

offsetting new emissions with creditable emissions reductions;

a certification that all major sources owned and operated in the state
by the same owner are in compliance with all applicable requirements
under the CAA;

an alternative siting analysis demonstrating that the benefits of a
proposed source significantly outweigh the environmental and social
costs imposed as a result of its location, construction, or
modification; and

public comment on the permit.

Minor NSR programs must meet the statutory requirements in section
110(a)(2)(C) of the CAA which requires “…regulation of the
modification and construction of any stationary source …as necessary
to assure that the [NAAQS] are achieved.” Areas which are newly
designated as nonattainment for the NO2 NAAQS as a result of any changes
made to the NAAQS will be required to adopt a nonattainment NSR program
to address major sources of NO2 where the program does not currently
exist for the NO2 NAAQS and may need to amend their minor source program
as well.  Prior to adoption of the SIP revision addressing major source
nonattainment NSR for NO2 nonattainment areas, the requirements of 40
CFR part 51, appendix S may apply.

b.	Public comments 

One commenter claimed that EPA’s setting of a more stringent standard,
i.e., short-term NO2 NAAQS, could have important implications for NSR
and PSD and title V permits. 

Another commenter indicated that the promulgation of a new 1-hr NO2
short-term standard could create the need for a short-term PSD
increment.  Another commenter stated that a 1-hr NO2 Significant Impact
Level (SIL) should be developed.

The EPA acknowledges that a decision to promulgate a new short-term NO2
NAAQS will clearly have implications for the air permitting process. 
The full extent of how a new short-term NO2 NAAAQS will affect the NSR
process will need to be carefully evaluated.  First, major new and
modified sources applying for NSR/PSD permits will initially be required
to demonstrate that their proposed emissions increases of NOX will not
cause or contribute to a violation of either the annual or 1-hour NO2
NAAQS and the annual PSD increment.  In addition, we believe that
section 166 of the CAA authorizes us to consider the need to promulgate
a new 1-hour increment.  Historically, EPA has developed increments for
each applicable averaging period for which a NAAQS has been promulgated.
 However, increments for a particular pollutant do not necessarily need
to match the averaging periods that have been established for NAAQS for
the same pollutant.  Environmental Defense Fund, Inc. v. EPA, 898 F.2d
183, 189-190 (D.C. Cir. 1990)(“… the ‘goals and purposes’ of the
PSD program, set forth in § 160, are not identical to the criteria on
which the ambient standards are based.”)  Thus, we would need to
evaluate the need for a new 1-hour NO2 increment in association with the
goals and purposes of the statutory PSD program requirements.

We also believe that there may be a need to revise the screening tools
currently used under the NSR/PSD program for completing NO2 analyses. 
These screening tools include the significant impact levels (SILs), as
mentioned by one commenter, but also include the significant emissions
rate for emissions of NOX and the significant monitoring concentration
(SMC) for NO2.  EPA intends to evaluate the need for possible changes or
additions to each of these important screening tools for NOX/NO2 due to
the addition of a 1-hour NO2 NAAQS.  If changes or additions are deemed
necessary, EPA will propose any such changes for public notice and
comment in a separate action. 

c.	Final

	The EPA is not making any changes to the discussion concerning the
requirements for NSR and PSD as stated in the proposed rule.

3.	General Conformity

a.	Proposal

Section 176(c) of the CAA, as amended (42 U.S.C. 7401 et seq.), requires
that all Federal actions conform to an applicable implementation plan
developed pursuant to section 110 and part D of the CAA.  The EPA rules,
developed under the authority of section 176(c) of the CAA, prescribe
the criteria and procedures for demonstrating and assuring conformity of
Federal actions to a SIP.  Each Federal agency must determine that any
actions covered by the general conformity rule conform to the applicable
SIP before the action is taken.  The criteria and procedures for
conformity apply only in nonattainment areas and those areas
redesignated attainment since 1990 (“maintenance areas”) with
respect to the criteria pollutants under the CAA:  carbon monoxide (CO),
lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM2.5
and PM10), and sulfur dioxide (SO2).  The general conformity rules apply
one year following the effective date of designations for any new or
revised NAAQS.

	The general conformity determination examines the impacts of direct and
indirect emissions related to Federal actions.  The general conformity
rule provides several options to satisfy air quality criteria, such as
modeling or offsets, and requires the Federal action to also meet any
applicable SIP requirements and emissions milestones. The general
conformity rule also requires that notices of draft and final general
conformity determinations be provided directly to air quality regulatory
agencies and to the public by publication in a local newspaper.

b.	Final

	EPA did not receive any comments on this aspect of the proposed rule
and is not making any changes to the discussion concerning general
conformity stated in the proposed rule. 

4.	Transportation Conformity

a.	Proposal

Transportation conformity is required under CAA section 176(c) (42
U.S.C. 7506(c)) to ensure that transportation plans, transportation
improvement programs (TIPs) and federally supported highway and transit
projects will not cause new air quality violations, worsen existing
violations, or delay timely attainment of the relevant NAAQS or interim
reductions and milestones.  Transportation conformity applies to areas
that are designated nonattainment and maintenance for
transportation-related criteria pollutants:  carbon monoxide (CO), ozone
(O3), nitrogen dioxide (NO2), and particulate matter (PM2.5 and PM10). 
Transportation conformity for a revised NO2 NAAQS does not apply until
one year after the effective date of a nonattainment designation. (See
CAA section 176(c)(6) and 40 CFR 93.102(d)).  

EPA’s Transportation Conformity Rule (40 CFR 51.390, and Part 93, 

Subpart A establishes the criteria and procedures for determining
whether transportation activities conform to the SIP.  The EPA is not
making changes to the Transportation Conformity rule in this rulemaking.
 However, in the future, EPA will review the need to conduct a
rulemaking to establish any new or revised transportation conformity
tests that would apply under a revision to the NO2 NAAQS for
transportation plans, TIPs, and applicable highway and transit projects.

b.	Public comments 

Several commenters stated that transportation conformity could stop the
funding of highway and transit projects in NO2 nonattainment areas. 
These commenters stated that if an area fails to demonstrate conformity
it enters a conformity lapse and only certain types of projects can be
funded during a lapse.  The commenters further stated that the NO2 NAAQS
will require more areas to determine conformity for the first time.  The
commenters also expressed concern that the NO2 NAAQS proposal did not
contain sufficient information to understand to what extent revisions to
the NAAQS, and the NO2 monitoring requirements, will result in
transportation conformity requirements for individual transportation
projects such as the need for a hot-spot analysis.  The commenters
further stated that hot-spot analyses could result in needless delays
for transportation improvement projects.

With regard to the comment that more areas will have to demonstrate
conformity for the first time due to the revisions to the NO2 NAAQS,
given that today’s final rule is requiring that near roadway
monitoring be carried out in urban areas with populations greater than
350K, EPA believes that most areas with such populations that would be
designated nonattainment for NO2 are already designated nonattainment or
maintenance for one or more of the other transportation-related criteria
pollutants (ozone, PM2.5, PM10 and carbon monoxide).  As such, these
areas would have experience in making transportation conformity
determinations.  If areas with no conformity experience are designated
nonattainment for the NO2 NAAQS, EPA and US DOT would be available to
assist areas in implementing the transportation conformity requirements.
 

The commenter expressed concern that transportation conformity could
stop highway and transit funding because areas could experience a
conformity lapse and in such cases only certain types of projects could
be funded.  A conformity lapse occurs when an area misses a deadline for
a required conformity determination.  A new nonattainment area must
demonstrate conformity within one year after the effective date of its
designation.  For any areas designated nonattainment for the revised NO2
NAAQS in early-2012, they would have to determine conformity within one
year of the effective date of that designation which would be in
early-2013.  If that date was missed, a lapse would occur and only
projects exempt from conformity such as safety projects, transportation
control measures in an approved SIP for the area and projects or project
phases that were approved by US DOT before the lapse began can proceed
during the lapse.  EPA’s experience in implementing the 1997 ozone and
PM2.5 NAAQS shows that nearly all areas make their initial conformity
determinations within the one-year grace period.  Areas can also lapse
if they fail to determine conformity by an applicable deadline such as
determining conformity within two years after motor vehicle emissions
budgets are found adequate.  However, areas that miss one of these
conformity deadlines have a one-year grace period before the lapse goes
into effect.  During the grace period, the area can continue to advance
projects from the transportation plan and transportation improvement
program.  EPA’s experience is that areas generally are able to make a
conformity determination before the end of the grace period.

The commenter expressed concern that the NO2 NAAQS proposal did not
contain sufficient detail concerning possible project-level requirements
for transportation projects and that any requirements for hot-spot
analyses could needlessly delay transportation projects.  As EPA
indicated in the NPRM, EPA is considering whether to revise the
transportation conformity rule to establish requirements that would
apply to transportation plans, transportation improvement programs
and/or transportation projects in NO2 nonattainment and maintenance
areas.  If EPA concludes that the conformity rule must be revised in
light of the final NO2 NAAQS, we will conduct notice and comment
rulemaking to accomplish the revisions.  At that time interested parties
will have the opportunity to comment on any transportation conformity
NPRM.  This is the same course of action that EPA has taken with respect
to revising the transportation conformity rule for the ozone and PM2.5
NAAQS.  

With regard to the commenter’s assertion that a requirement for
hot-spot analyses for individual projects would needlessly delay
transportation projects, EPA disagrees.  First, CAA section 176(c)(1)(B)
requires that transportation projects not cause new violations or make
existing violations worse, or delay timely attainment or cause an
interim milestone to be missed.  EPA would only impose a hot-spot
requirement for projects in NO2 nonattainment and maintenance areas if
they are necessary to comply with CAA conformity requirements and
therefore are needed to protect public health by reducing exposures to
unhealthy levels of NO2 that could be created by the implementation of a
proposed highway or transit project. The public would be exposed to
unhealthy levels of NO2 if a highway or transit project caused a new
violation of the NO2 NAAQS, made an existing violation worse, or delayed
timely attainment or delayed achieving an interim emissions milestone. 
If any delay in the project did occur, it would not be viewed as
needless as it occurred for the important purpose of protecting the
exposed public’s health. Second, EPA does not agree that requiring a
hot-spot analysis would needlessly delay projects in NO2 nonattainment
areas.  Such hot-spot analyses, if they are eventually required,
generally would be done as part of the NEPA process, which these
projects are already subject to; therefore, conducting an NO2 hot-spot
analysis would not be introducing a new step to a project’s approval
process, but rather would add one additional analysis which must be
completed as part of an existing project approval process.

c.	Final 

EPA is not making any changes to the discussion concerning
transportation conformity as stated in the proposed rule.  

VII.	Communication of Public Health Information

Information on the public health implications of ambient concentrations
of criteria pollutants is currently made available primarily through
EPA’s Air Quality Index (AQI) program.  This section describes the
conforming changes that were proposed, major comments received on these
changes, EPA’s responses to these comments and final decisions on the
AQI breakpoints.  Recognizing the importance of revising the AQI in a
timely manner to be consistent with any revisions to the NAAQS, EPA
proposed conforming changes to the AQI in connection with the final
decision on the NO2 NAAQS if revisions to the primary standard were
promulgated.  Conforming changes would include setting the 100 level of
the AQI at the same level as the revised primary NO2 NAAQS and also
setting the other AQI breakpoints at the lower end of the AQI scale
(i.e., AQI values of 50 and 150).  EPA did not propose to change
breakpoints at the higher end of the AQI scale (from 200 to 500), which
would apply to state contingency plans or the Significant Harm Level (40
CFR 51.16), because the information from this review does not inform
decisions about breakpoints at those higher levels. 

With regard to an AQI value of 50, the breakpoint between the good and
moderate categories, EPA proposed to set this value to be between 0.040
and 0.053 ppm NO2, 1-hour average.  EPA proposed that the figure towards
the lower end of this range would be appropriate if the standard is set
towards the lower end of the proposed range for the standard (e.g. 80
ppb), while figures towards the higher end of the range would be more
appropriate for standards set at the higher end of the range for the
standard (e.g., 100 ppb).  EPA noted that historically this value is set
at the level of the annual NAAQS, if there is one, or one-half the level
of the short-term NAAQS in the absence of an annual NAAQS, and solicited
comments on this range for an AQI of 50 and the appropriate basis for
selecting an AQI of 50 within this range. 

With regard to an AQI value of 150, the breakpoint between the unhealthy
for sensitive groups and unhealthy categories, the range of 0.360 to
0.370 ppm NO2, 1-hour average, represents the midpoint between the
proposed range for the short-term standard and the level of an AQI value
of 200 (0.64 ppm NO2, 1-hour average). Therefore, EPA proposed to set
the AQI value of 150 to be between 0.360 and 0.370 ppm NO2, 1-hour
average.  

EPA received comments from several state environmental agencies and
organizations of state and local agencies that generally expressed the
view that the AQI was designed to provide the public with information
about regional air quality and therefore it should be based on
community-wide monitors.  These commenters went on to state that using
near-road NO2 monitors for the AQI would present problems because they
would not represent regional NO2 concentrations and it would be
difficult to communicate this type of information to the public using
the AQI.  Some expressed concern that NO2 measured at near-roadway
monitors could be the critical pollutant and could drive the AQI even
though it may not represent air quality across the area.  Other agencies
expressed concern that there is currently no way to forecast ambient NO2
levels near roadways.  One state agency commented that the AQI is
intended to represent air quality where people live work and play.

EPA agrees with commenters that the AQI should represent regional air
quality, and that measurements that apply to a limited area should not
be used to characterize air quality across the region.  Community-wide
NO2 monitors should be used to characterize air quality across the
region.  However, the AQI reporting requirements encourage, but do not
require, the reporting of index values of sub-areas of an MSA.  We agree
with the commenter that stated the view that the AQI is intended to
represent air quality where people live work and play.  To the extent
that near-roadway monitoring occurs in areas where people live, work or
play, EPA encourages reporting of the AQI for that specific sub-area of
the MSA (64 FR 42548, August 4, 1999).  We also agree that it may be
difficult to communicate this type of information and we plan to work
with state and local air agencies to figure out the best way to present
this information to the public using the AQI.  Air quality forecasting
is recommended but not required (64 FR 42548, August 4, 1999).  EPA will
work with state agencies that want to develop a forecasting program.  

With regard to the proposed breakpoints, EPA received few comments.  The
National Association of Clean Air Agencies commented that it would be
confusing to the public to have an AQI value of 50 set below the level
of the annual NO2 standard.  No other comments were received on the
basis for setting this value.  We agree with this comment, and therefore
have decided that it is appropriate to leave the AQI value of 50, the
breakpoint between the good and moderate ranges, set at the numerical
level of the annual standard, 53 ppb NO2, 1-hour average.  The AQI value
of 100, the breakpoint between the moderate and unhealthy for sensitive
groups category, is set at 100 ppb, 1-hour average, the level of the
primary NO2 NAAQS.  EPA is setting an AQI value of 150, the breakpoint
between the unhealthy for sensitive groups and unhealthy categories, at
0.360 ppm NO2, 1-hour average.  

VIII.	Statutory and Executive Order Reviews  

A.	Executive Order 12866: Regulatory Planning and Review

Under section 3(f)(1) of Executive Order 12866 (58 FR 51735, October 4,
1993), this action is an “economically significant regulatory
action” because it is likely to have an annual effect on the economy
of $100 million or more.  Accordingly, EPA submitted this action to the
Office of Management and Budget (OMB) for review under EO 12866 and any
changes made in response to OMB recommendations have been documented in
the docket for this action.  In addition, EPA prepared a Regulatory
Impact Analysis (RIA) of the potential costs and benefits associated
with this action. However, the CAA and judicial decisions make clear
that the economic and technical feasibility of attaining ambient
standards are not to be considered in setting or revising NAAQS,
although such factors may be considered in the development of State
plans to implement the standards.  Accordingly, although an RIA has been
prepared, the results of the RIA have not been considered in developing
this final rule.

B.	Paperwork Reduction Act

The information collection requirements in this final rule have been
submitted for approval to the Office of Management and Budget (OMB)
under the Paperwork Reduction Act, 44 U.S.C. 3501 et seq.  The
Information Collection Request (ICR) document prepared by EPA for these
revisions to part 58 has been assigned EPA ICR number 2358.02.

The information collected under 40 CFR part 53 (e.g., test results,
monitoring records, instruction manual, and other associated
information) is needed to determine whether a candidate method intended
for use in determining attainment of the National Ambient Air Quality
Standards (NAAQS) in 40 CFR part 50 will meet the design, performance,
and/or comparability requirements for designation as a Federal reference
method (FRM) or Federal equivalent method (FEM).  We do not expect the
number of FRM or FEM determinations to increase over the number that is
currently used to estimate burden associated with NO2 FRM/FEM
determinations provided in the current ICR for 40 CFR part 53 (EPA ICR
numbers  2358.01).  As such, no change in the burden estimate for 40 CFR
part 53 has been made as part of this rulemaking. 

The information collected and reported under 40 CFR part 58 is needed to
determine compliance with the NAAQS, to characterize air quality and
associated health impacts, to develop emissions control strategies, and
to measure progress for the air pollution program.  The amendments would
revise the technical requirements for NO2 monitoring sites, require the
siting and operation of additional NO2 ambient air monitors, and the
reporting of the collected ambient NO2 monitoring data to EPA’s Air
Quality System (AQS).  The annual average reporting burden for the
collection under 40 CFR part 58 (averaged over the first 3 years of this
ICR) is $3,616,487.  Burden is defined at 5 CFR 1320.3(b).  State,
local, and tribal entities are eligible for State assistance grants
provided by the Federal government under the CAA which can be used for
monitors and related activities.

An agency may not conduct or sponsor, and a person is not required to
respond to, a collection of information unless it displays a currently
valid OMB control number.  The OMB control numbers for EPA's regulations
in 40 CFR are listed in 40 CFR part 9.  

C.	Regulatory Flexibility Act

The Regulatory Flexibility Act (RFA) generally requires an agency to
prepare a regulatory flexibility analysis of any rule subject to notice
and comment rulemaking requirements under the Administrative Procedure
Act or any other statute unless the agency certifies that the rule will
not have a significant economic impact on a substantial number of small
entities.  Small entities include small businesses, small organizations,
and small governmental jurisdictions.

For purposes of assessing the impacts of this rule on small entities,
small entity is defined as:  (1) a small business that is a small
industrial entity as defined by the Small Business Administration’s
(SBA) regulations at 13 CFR 121.201;  (2) a small governmental
jurisdiction that is a government of a city, county, town, school
district or special district with a population of less than 50,000; and
(3) a small organization that is any not-for-profit enterprise which is
independently owned and operated and is not dominant in its field.

After considering the economic impacts of this final rule on small
entities, I certify that this action will not have a significant
economic impact on a substantial number of small entities.  This final
rule will not impose any requirements on small entities.  Rather, this
rule establishes national standards for allowable concentrations of NO2
in ambient air as required by section 109 of the CAA.  American Trucking
Ass’ns v. EPA, 175 F. 3d 1027, 1044-45 (D.C. cir. 1999) (NAAQS do not
have significant impacts upon small entities because NAAQS themselves
impose no regulations upon small entities). Similarly, the amendments to
40 CFR part 58 address the requirements for States to collect
information and report compliance with the NAAQS and will not impose any
requirements on small entities.  

D.	Unfunded Mandates Reform Act

Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public Law
104-4, establishes requirements for Federal agencies to assess the
effects of their regulatory actions on State, local, and tribal
governments and the private sector.  Unless otherwise prohibited by law,
under section 202 of the UMRA, EPA generally must prepare a written
statement, including a cost-benefit analysis, for proposed and final
rules with “Federal mandates” that may result in expenditures to
State, local, and tribal governments, in the aggregate, or to the
private sector, of $100 million or more in any one year.  Before
promulgating an EPA rule for which a written statement is required under
section 202, section 205 of the UMRA generally requires EPA to identify
and consider a reasonable number of regulatory alternatives and to adopt
the least costly, most cost-effective or least burdensome alternative
that achieves the objectives of the rule.  The provisions of section 205
do not apply when they are inconsistent with applicable law.  Moreover,
section 205 allows EPA to adopt an alternative other than the least
costly, most cost-effective or least burdensome alternative if the
Administrator publishes with the final rule an explanation why that
alternative was not adopted.  Before EPA establishes any regulatory
requirements that may significantly or uniquely affect small
governments, including tribal governments, it must have developed under
section 203 of the UMRA a small government agency plan.  The plan must
provide for notifying potentially affected small governments, enabling
officials of affected small governments to have meaningful and timely
input in the development of EPA regulatory proposals with significant
Federal intergovernmental mandates, and informing, educating, and
advising small governments on compliance with the regulatory
requirements. 

This action is not subject to the requirements of sections 202 and 205
of the UMRA.  EPA has determined that this final rule does not contain a
Federal mandate that may result in expenditures of $100 million or more
for State, local, and tribal governments, in the aggregate, or the
private sector in any one year.  The revisions to the NO2 NAAQS impose
no enforceable duty on any State, local or Tribal governments or the
private sector.  The expected costs associated with the monitoring
requirements are described in EPA’s ICR document, but those costs are
not expected to exceed $100 million in the aggregate for any year. 
Furthermore, as indicated previously, in setting a NAAQS EPA cannot
consider the economic or technological feasibility of attaining ambient
air quality standards.  Because the Clean Air Act prohibits EPA from
considering the types of estimates and assessments described in section
202 when setting the NAAQS, the UMRA does not require EPA to prepare a
written statement under section 202 for the revisions to the NO2 NAAQS. 

With regard to implementation guidance, the CAA imposes the obligation
for States to submit SIPs to implement the NO2 NAAQS. In this final
rule, EPA is merely providing an interpretation of those requirements.
However, even if this rule did establish an independent obligation for
States to submit SIPs, it is questionable whether an obligation to
submit a SIP revision would constitute a Federal mandate in any case.
The obligation for a State to submit a SIP that arises out of section
110 and section 191 of the CAA is not legally enforceable by a court of
law, and at most is a condition for continued receipt of highway funds.
Therefore, it is possible to view an action requiring such a submittal
as not creating any enforceable duty within the meaning of 2 U.S.C. 658
for purposes of the UMRA. Even if it did, the duty could be viewed as
falling within the exception for a condition of Federal assistance under
2 U.S.C. 658.

EPA has determined that this final rule contains no regulatory
requirements that might significantly or uniquely affect small
governments because it imposes no enforceable duty on any small
governments.  Therefore, this rule is not subject to the requirements of
section 203 of the UMRA.

E.	Executive Order 13132: Federalism

Executive Order 13132, entitled “Federalism” (64 FR 43255, August
10, 1999), requires EPA to develop an accountable process to ensure
“meaningful and timely input by State and local officials in the
development of regulatory policies that have federalism implications.”
 “Policies that have federalism implications” is defined in the
Executive Order to include regulations that have “substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government.”  

This final rule does not have federalism implications.  It will not have
substantial direct effects on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government, as
specified in Executive Order 13132.  The rule does not alter the
relationship between the Federal government and the States regarding the
establishment and implementation of air quality improvement programs as
codified in the CAA.  Under section 109 of the CAA, EPA is mandated to
establish NAAQS; however, CAA section 116 preserves the rights of States
to establish more stringent requirements if deemed necessary by a State.
 Furthermore, this rule does not impact CAA section 107 which
establishes that the States have primary responsibility for
implementation of the NAAQS.  Finally, as noted in section E (above) on
UMRA, this rule does not impose significant costs on State, local, or
tribal governments or the private sector.  Thus, Executive Order 13132
does not apply to this rule.

F.	Executive Order 13175: Consultation and Coordination with Indian
Tribal Governments

Executive Order 13175, entitled “Consultation and Coordination with
Indian Tribal Governments” (65 FR 67249, November 9, 2000), requires
EPA to develop an accountable process to ensure “meaningful and timely
input by tribal officials in the development of regulatory policies that
have tribal implications.”  This final rule does not have tribal
implications, as specified in Executive Order 13175.  It does not have a
substantial direct effect on one or more Indian tribes, on the
relationship between the Federal government and Indian tribes, or on the
distribution of power and responsibilities between the Federal
government and tribes.  The rule does not alter the relationship between
the Federal government and tribes as established in the CAA and the TAR.
 Under section 109 of the CAA, EPA is mandated to establish NAAQS;
however, this rule does not infringe existing tribal authorities to
regulate air quality under their own programs or under programs
submitted to EPA for approval.  Furthermore, this rule does not affect
the flexibility afforded to tribes in seeking to implement CAA programs
consistent with the TAR, nor does it impose any new obligation on tribes
to adopt or implement any NAAQS.  Finally, as noted in section E (above)
on UMRA, this rule does not impose significant costs on tribal
governments.  Thus, Executive Order 13175 does not apply to this rule.  

G.	Executive Order 13045: Protection of Children from Environmental
Health & Safety Risks

This action is subject to Executive Order (62 FR 19885, April 23, 1997)
because it is an economically significant regulatory action as defined
by Executive Order 12866, and we believe that the environmental health
risk addressed by this action has a disproportionate effect on children.
 The final rule will establish uniform national ambient air quality
standards for NO2; these standards are designed to protect public health
with an adequate margin of safety, as required by CAA section 109.  The
protection offered by these standards may be especially important for
asthmatics, including asthmatic children, because respiratory effects in
asthmatics are among the most sensitive health endpoints for NO2
exposure.  Because asthmatic children are considered a sensitive
population, we have evaluated the potential health effects of exposure
to NO2 pollution among asthmatic children.  These effects and the size
of the population affected are discussed in chapters 3 and 4 of the ISA;
chapters 3, 4, and 8 of the REA, and sections II.A through II.E of this
preamble.

H.	Executive Order 13211: Actions that Significantly Affect Energy
Supply, Distribution or Use

This rule is not a “significant energy action” as defined in
Executive Order 13211, “Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution, or Use” (66 FR 28355
(May 22, 2001)) because it is not likely to have a significant adverse
effect on the supply, distribution, or use of energy.  The purpose of
this rule is to establish revised NAAQS for NO2.  The rule does not
prescribe specific control strategies by which these ambient standards
will be met.  Such strategies will be developed by States on a
case-by-case basis, and EPA cannot predict whether the control options
selected by States will include regulations on energy suppliers,
distributors, or users.  Thus, EPA concludes that this rule is not
likely to have any adverse energy effects.

 I.	National Technology Transfer and Advancement Act

Section 12(d) of the National Technology Transfer and Advancement Act of
1995 (NTTAA), Public Law 104-113, section 12(d) (15 U.S.C. 272 note)
directs EPA to use voluntary consensus standards in its regulatory
activities unless to do so would be inconsistent with applicable law or
otherwise impractical.  Voluntary consensus standards are technical
standards (e.g., materials specifications, test methods, sampling
procedures, and business practices) that are developed or adopted by
voluntary consensus standards bodies.  The NTTAA directs EPA to provide
Congress, through OMB, explanations when the Agency decides not to use
available and applicable voluntary consensus standards.

This final rulemaking involves technical standards with regard to
ambient monitoring of NO2.  The use of this voluntary consensus standard
would be impractical because the analysis method does not provide for
the method detection limits necessary to adequately characterize ambient
NO2 concentrations for the purpose of determining compliance with the
revisions to the NO2 NAAQS.  

J.	Executive Order 12898: Federal Actions to Address Environmental
Justice in Minority Populations and Low-Income Populations

Executive Order 12898 (59 FR 7629; Feb. 16, 1994) establishes Federal
executive policy on environmental justice.  Its main provision directs
Federal agencies, to the greatest extent practicable and permitted by
law, to make environmental justice part of their mission by identifying
and addressing, as appropriate, disproportionately high and adverse
human health or environmental effects of their programs, policies, and
activities on minority populations and low-income populations in the
United States.  

EPA has determined that this final rule will not have disproportionately
high and adverse human health or environmental effects on minority or
low-income populations because it increases the level of environmental
protection for all affected populations without having any
disproportionately high and adverse human health effects on any
population, including any minority or low-income population.  The final
rule will establish uniform national standards for NO2 in ambient air.  

K.	Congressional Review Act 

The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the
Small Business Regulatory Enforcement Fairness Act of 1996, generally
provides that before a rule may take effect, the agency promulgating the
rule must submit a rule report, which includes a copy of the rule, to
each House of the Congress and to the Comptroller General of the United
States. EPA will submit a report containing this rule and other required
information to the U.S. Senate, the U.S. House of Representatives, and
the Comptroller General of the United States prior to publication of the
rule in the Federal Register. A Major rule cannot take effect until 60
days after it is published in the Federal Register. This action is a
“major rule” as defined by 5 U.S.C. 804(2). This rule will be
effective on [insert date 60 days after date of publication in the
Federal Register].

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List of Subjects 

40 CFR Part 50

	Environmental protection, Air pollution control, Carbon monoxide, Lead,
Nitrogen dioxide, Ozone, Particulate matter, Sulfur oxides.

40 CFR Part 58

	Environmental protection, Administrative practice and procedure, Air
pollution control, Intergovernmental relations, Reporting and
recordkeeping requirements 

Dated: January 22, 2010.

Lisa P. Jackson,

Administrator.

For the reasons stated in the preamble, title 40, chapter I of the Code
of Federal Regulations is amended as follows: 

PART 50-NATIONAL PRIMARY AMBIENT AIR QUALITY STANDARDS 

1.  The authority citation for part 50 continues to read as follows:

Authority: 42 U.S.C. 7401, et seq.

Subpart A—General Provisions

2.  Section 50.11 is amended by redesignating paragraphs (b) and (c) as
paragraphs (c) and (d), respectively, and amending the other provisions
as follows--

§ 50.11   National primary and secondary ambient air quality
standards for oxides of nitrogen (nitrogen dioxide) 

(a) The level of the national primary annual ambient air quality
standard for oxides of nitrogen is 53 parts per billion (ppb, which is 1
part in 1,000,000,000), annual average concentration, measured in the
ambient air as nitrogen dioxide.

(b) The level of the national primary 1-hour ambient air quality
standard for oxides of nitrogen is 100 ppb, 1-hour average
concentration, measured in the ambient air as nitrogen dioxide. 

(c) The level of the national secondary ambient air quality standard for
nitrogen dioxide is 0.053 parts per million (100 micrograms per cubic
meter), annual arithmetic mean concentration.

(d) The levels of the standards shall be measured by:

(1) a reference method based on appendix F to this part, or 

(2) by a Federal equivalent method (FEM) designated in accordance with
part 53 of this chapter.

(e) The annual primary standard is met when the annual average
concentration in a calendar year is less than or equal to 53 ppb, as
determined in accordance with Appendix S for the annual standard.

(f) The 1-hour primary standard is met when the three-year average of
the annual 98th percentile of the daily maximum 1-hour average
concentration is less than or equal to 100 ppb, as determined in
accordance with Appendix S for the 1-hour standard.

 (g) The secondary standard is attained when the annual arithmetic mean
concentration in a calendar year is less than or equal to 0.053 ppm,
rounded to three decimal places (fractional parts equal to or greater
than 0.0005 ppm must be rounded up). To demonstrate attainment, an
annual mean must be based upon hourly data that are at least 75 percent
complete or upon data derived from manual methods that are at least 75
percent complete for the scheduled sampling days in each calendar
quarter.  

3.  Section 50.14 is amended by adding an entry to the end of table of 
paragraph (c)(2)(vi) to read as follows:

§50.14 Treatment of air quality monitoring data influenced by
exceptional events.

* * * * *

(c) ***

(2) ***

(vi) *** 

Table 1.  Schedule for Exceptional Event Flagging and Documentation
Submission for Data to be Used in Designations Decisions for New or
Revised NAAQS

NAAQS Pollutant/

Standard/(Level)/

Promulgation Date	Air Quality Data Collected for Calendar Year	Event
Flagging & Initial Description Deadline	Detailed Documentation
Submission Deadline



*******

NO2/1-Hour Standard(100 PPB)	2008	July 1, 2010a	January 22, 2011

	2009	July 1, 2010 	January 22, 2011

	2010	 April 1, 2011a	July 1, 2011a



aIndicates change from general schedule in 40 CFR 50.14.

Note:  EPA notes that the table of revised deadlines only applies to
data EPA will use to establish the final initial designations for new or
revised NAAQS.  The general schedule applies for all other purposes,
most notably, for data used by EPA for redesignations to attainment.



 *****

4. Appendix S is added to read as follows: 

Appendix S to Part 50—Interpretation of the Primary National Ambient
Air Quality Standards for Oxides of Nitrogen (Nitrogen Dioxide) 

 1. General.

(a) This appendix explains the data handling conventions and
computations necessary for determining when the primary national ambient
air quality standards for oxides of nitrogen as measured by nitrogen
dioxide (“NO2 NAAQS”) specified in § 50.11 are met.  Nitrogen
dioxide (NO2) is measured in the ambient air by a Federal reference
method (FRM) based on appendix F to this part or by a Federal equivalent
method (FEM) designated in accordance with part 53 of this chapter. Data
handling and computation procedures to be used in making comparisons
between reported NO2 concentrations and the levels of the NO2 NAAQS are
specified in the following sections.

(b) Whether to exclude, retain, or make adjustments to the data affected
by exceptional events, including natural events, is determined by the
requirements and process deadlines specified in §§ 50.1, 50.14 and
51.930 of this chapter.

(c) The terms used in this appendix are defined as follows: 

Annual mean refers to the annual average of all of the 1-hour
concentration values as defined in section 5.1 of this appendix.

Daily maximum 1-hour values for NO2 refers to the maximum 1-hour NO2
concentration values measured from midnight to midnight (local standard
time) that are used in NAAQS computations.

Design values are the metrics (i.e., statistics) that are compared to
the NAAQS levels to determine compliance, calculated as specified in
section 5 of this appendix.  The design values for the primary NAAQS
are:

 (1) The annual mean value for a monitoring site for one year (referred
to as the “annual primary standard design value”). 

(2) The 3-year average of annual 98th percentile daily maximum 1-hour
values for a monitoring site (referred to as the “1-hour primary
standard design value”).

98th percentile daily maximum 1-hour value  is the value below which
nominally 98 percent of all daily maximum 1-hour concentration values
fall, using the ranking and selection method specified in section 5.2 of
this appendix.

Quarter refers to a calendar quarter.

Year refers to a calendar year.

2. Requirements for Data Used for Comparisons with the NO2 NAAQS and
Data

Reporting Considerations.

(a) All valid FRM/FEM NO2 hourly data required to be submitted to
EPA’s Air Quality System (AQS), or otherwise available to EPA, meeting
the requirements of part 58 of this chapter including appendices A, C,
and E shall be used in design value calculations.  Multi-hour average
concentration values collected by wet chemistry methods shall not be
used.

(b) When two or more NO2 monitors are operated at a site, the state may
in advance designate one of them as the primary monitor.  If the state
has not made this designation, the Administrator will make the
designation, either in advance or retrospectively.  Design values will
be developed using only the data from the primary monitor, if this
results in a valid design value.  If data from the primary monitor do
not allow the development of a valid design value, data solely from the
other monitor(s) will be used in turn to develop a valid design value,
if this results in a valid design value.  If there are three or more
monitors, the order for such comparison of the other monitors will be
determined by the Administrator.  The Administrator may combine data
from different monitors in different years for the purpose of developing
a valid 1-hour primary standard design value, if a valid design value
cannot be developed solely with the data from a single monitor. 
However, data from two or more monitors in the same year at the same
site will not be combined in an attempt to meet data completeness
requirements, except if one monitor has physically replaced another
instrument permanently, in which case the two instruments will be
considered to be the same monitor, or if the state has switched the
designation of the primary monitor from one instrument to another during
the year.

(c) Hourly NO2 measurement data shall be reported to AQS in units of
parts per billion (ppb), to at most one place after the decimal, with
additional digits to the right being truncated with no further rounding.

3. Comparisons with the NO2 NAAQS.

3.1 The Annual Primary NO2 NAAQS.

(a) The annual primary NO2 NAAQS is met at a site when the valid annual
primary standard design value is less than or equal to 53 parts per
billion (ppb).

(b) An annual primary standard design value is valid when at least 75
percent of the hours in the year are reported. 

(c) An annual primary standard design value based on data that do not
meet the completeness criteria stated in section 3.1(b) may also be
considered valid with the approval of, or at the initiative of, the
Administrator, who may consider factors such as monitoring site
closures/moves, monitoring diligence, the consistency and levels of the
valid concentration measurements that are available, and nearby
concentrations in determining whether to use such data. 

(d) The procedures for calculating the annual primary standard design
values are given in section 5.1 of this appendix.

3.2 The 1-hour Primary NO2 NAAQS.

(a) The 1-hour primary NO2 NAAQS is met at a site when the valid 1-hour
primary standard design value is less than or equal to 100 parts per
billion (ppb).

(b) An NO2 1-hour primary standard design value is valid if it
encompasses three consecutive calendar years of complete data.  A year
meets data completeness requirements when all 4 quarters are complete. 
A quarter is complete when at least 75 percent of the sampling days for
each quarter have complete data. A sampling day has complete data if 75
percent of the hourly concentration values are reported.

 (c) In the case of one, two, or three years that do not meet the
completeness requirements of section 3.2(b) of this appendix and thus
would normally not be useable for the calculation of a valid 3-year
1-hour primary standard design value, the 3-year 1-hour primary standard
design value shall nevertheless be considered valid if one of the
following conditions is true.  

(i) At least 75 percent of the days in each quarter of each of three
consecutive years have at least one reported hourly value, and the
design value calculated according to the procedures specified in section
5.2 is above the level of the primary 1-hour standard.

(ii) (A) A 1-hour primary standard design value that is below the level
of the NAAQS can be validated if the substitution test in section
3.2(c)(ii)(B) results in a “test design value” that is below the
level of the NAAQS.  The test substitutes actual ‘‘high’’
reported daily maximum 1-hour values from the same site at about the
same time of the year (specifically, in the same calendar quarter) for
unknown values that were not successfully measured.  Note that the test
is merely diagnostic in nature, intended to confirm that there is a very
high likelihood that the original design value (the one with less than
75 percent data capture of hours by day and of days by quarter) reflects
the true under-NAAQS-level status for that 3-year period; the result of
this data substitution test (the ‘‘test design value”, as defined
in section 3.2(c)(ii)(B)) is not considered the actual design value. For
this test, substitution is permitted only if there are at least 200 days
across the three matching quarters of the three years under
consideration (which is about 75 percent of all possible daily values in
those three quarters) for which 75 percent of the hours in the day have
reported concentrations. However, maximum 1-hour values from days with
less than 75 percent of the hours reported shall also be considered in
identifying the high value to be used for substitution.

(B) The substitution test is as follows: Data substitution will be
performed in all quarter periods that have less than 75 percent data
capture but at least 50 percent data capture; if any quarter has less
than 50 percent data capture then this substitution test cannot be used.
 Identify for each quarter (e.g., January-March) the highest reported
daily maximum 1-hour value for that quarter, looking across those three
months of all three years under consideration.  All daily maximum 1-hour
values from all days in the quarter period shall be considered when
identifying this highest value, including days with less than 75 percent
data capture. If after substituting the highest reported daily maximum
1-hour value for a quarter for as much of the missing daily data in the
matching deficient quarter(s) as is needed to make them 100 percent
complete, the procedure in section 5.2 yields a recalculated 3-year
1-hour standard “test design value” below the level of the standard,
then the 1-hour primary standard design value is deemed to have passed
the diagnostic test and is valid, and the level of the standard is
deemed to have been met in that 3-year period. As noted in section
3.2(c)(i), in such a case, the 3-year design value based on the data
actually reported, not the ‘‘test design value’’, shall be used
as the valid design value.

(iii) (A) A 1-hour primary standard design value that is above the level
of the NAAQS can be validated if the substitution test in section
3.2(c)(iii)(B) results in a “test design value” that is above the
level of the NAAQS.  The test substitutes actual ‘‘low” reported
daily maximum 1-hour values from the same site at about the same time of
the year (specifically, in the same three months of the calendar) for
unknown values that were not successfully measured.  Note that the test
is merely diagnostic in nature, intended to confirm that there is a very
high likelihood that the original design value (the one with less than
75 percent data capture of hours by day and of days by quarter) reflects
the true above-NAAQS-level status for that 3-year period; the result of
this data substitution test (the ‘‘test design value”, as defined
in section 3.2(c)(iii)(B)) is not considered the actual design value.
For this test, substitution is permitted only if there are a minimum
number of available daily data points from which to identify the low
quarter-specific daily maximum 1-hour values, specifically if there are
at least 200 days across the three matching quarters of the three years
under consideration (which is about 75 percent of all possible daily
values in those three quarters) for which 75 percent of the hours in the
day have reported concentrations. Only days with at least 75 percent of
the hours reported shall be considered in identifying the low value to
be used for substitution.

(B) The substitution test is as follows: Data substitution will be
performed in all quarter periods that have less than 75 percent data
capture.  Identify for each quarter (e.g., January-March) the lowest
reported daily maximum 1-hour value for that quarter, looking across
those three months of all three years under consideration.  All daily
maximum 1-hour values from all days with at least 75 percent capture in
the quarter period shall be considered when identifying this lowest
value. If after substituting the lowest reported daily maximum 1-hour
value for a quarter for as much of the missing daily data in the
matching deficient quarter(s) as is needed to make them 75 percent
complete, the procedure in section 5.2 yields a recalculated 3-year
1-hour standard “test design value” above the level of the standard,
then the 1-hour primary standard design value is deemed to have passed
the diagnostic test and is valid, and the level of the standard is
deemed to have been exceeded in that 3-year period. As noted in section
3.2(c)(i), in such a case, the 3-year design value based on the data
actually reported, not the ‘‘test design value’’, shall be used
as the valid design value.

 (d) A 1-hour primary standard design value based on data that do not
meet the completeness criteria stated in 3.2(b) and also do not satisfy
section 3.2(c), may also be considered valid with the approval of, or at
the initiative of, the Administrator, who may consider factors such as
monitoring site closures/moves, monitoring diligence, the consistency
and levels of the valid concentration measurements that are available,
and nearby concentrations in determining whether to use such data.

(e) The procedures for calculating the 1-hour primary standard design
values are given in section 5.2 of this appendix.

4. Rounding Conventions. 

4.1 Rounding Conventions for the Annual Primary NO2 NAAQS.

(a) Hourly NO2 measurement data shall be reported to AQS in units of
parts per billion (ppb), to at most one place after the decimal, with
additional digits to the right being truncated with no further rounding.

(b) The annual primary standard design value is calculated pursuant to
section 5.1 and then rounded to the nearest whole number or 1 ppb
(decimals 0.5 and greater are rounded up to the nearest whole number,
and any decimal lower than 0.5 is rounded down to the nearest whole
number).

4.2 Rounding Conventions for the 1-hour Primary NO2 NAAQS.

(a) Hourly NO2 measurement data shall be reported to AQS in units of
parts per billion (ppb), to at most one place after the decimal, with
additional digits to the right being truncated with no further rounding.

(b) Daily maximum 1-hour values are not rounded.

 (c) The 1-hour primary standard design value is calculated pursuant to
section 5.2 and then  rounded to the nearest whole number or 1 ppb
(decimals 0.5 and greater are rounded up to the nearest whole number,
and any decimal lower than 0.5 is rounded down to the nearest whole
number).

5. Calculation Procedures for the Primary NO2 NAAQS.

5.1 Procedures for the Annual Primary NO2 NAAQS.

(a) When the data for a site and year meet the data completeness
requirements in section 3.1(b) of this appendix, or if the Administrator
exercises the discretionary authority in section 3.1(c), the annual mean
is simply the arithmetic average of all of the reported 1-hour values.

(b) The annual primary standard design value for a site is the valid
annual mean rounded according to the conventions in section 4.1.

5.2 Calculation Procedures for the 1-hour Primary NO2 NAAQS.

(a) Procedure for identifying annual 98th percentile values. When the
data for a particular site and year meet the data completeness
requirements in section 3.2(b), or if one of the conditions of section
3.2(c) is met, or if the Administrator exercises the discretionary
authority in section 3.2(d), identification of annual 98th percentile
value is accomplished as follows.

(i) The annual 98th percentile value for a year is the higher of the two
values resulting from the following two procedures.

(1) Procedure 1.  For the year, determine the number of days with at
least 75 percent of the hourly values reported.

(A) For the year, from only the days with at least 75 percent of the
hourly values reported, select from each day the maximum hourly value. 

(B) Sort all these daily maximum hourly values from a particular site
and year by descending value. (For example: (x[1], x[2], x[3],
 *  *  *, x[n]). In this case, x[1] is the largest number and x[n]
is the smallest value.) The 98th percentile is determined from this
sorted series of daily values which is ordered from the highest to the
lowest number. Using the left column of Table 1, determine the
appropriate range (i.e., row) for the annual number of days with valid
data for year y (cny). The corresponding “n” value in the right
column identifies the rank of the annual 98th percentile value in the
descending sorted list of daily site values for year y. Thus, P0.98, y=
the nth largest value. 

(2) Procedure 2.  For the year, determine the number of days with at
least one hourly value reported. 

(A) For the year, from all the days with at least one hourly value
reported, select from each day the maximum hourly value. 

(B) Sort all these daily maximum values from a particular site and year
by descending value. (For example: (x[1], x[2], x[3],  *  *  *,
x[n]). In this case, x[1] is the largest number and x[n] is the smallest
value.) The 98th percentile is determined from this sorted series of
daily values which is ordered from the highest to the lowest number.
Using the left column of Table 1, determine the appropriate range (i.e.,
row) for the annual number of days with valid data for year y (cny). The
corresponding “n” value in the right column identifies the rank of
the annual 98th percentile value in the descending sorted list of daily
site values for year y. Thus, P0.98, y= the nth largest value.

(b) The 1-hour primary standard design value for a site is mean of the
three annual 98th percentile values, rounded according to the
conventions in section 4.

Table 1

Annual number of days with valid data for year “y” (cny)	P0.98, y is
the nth maximum value of the year, where n is the listed number

1–50	1

51-100	2

101-150	3

151-200	4

201-250.	5

251-300	6

301-350	7

351-366	8



PART 58--AMBIENT AIR QUALITY SURVEILLANCE

The authority citation for part 58 continues to read as follows:

Authority:   42 U.S.C. 7403, 7410, 7601(a), 7611, and 7619.

Subpart A [AMENDED]

Section 58.1, is amended by adding the following definitions in
alphabetical order to read as follows:

AADT means the annual average daily traffic.

***

Near-road NO2 Monitor means any NO2 monitor meeting the specifications
in 4.3.2 of Appendix D and paragraphs 2, 4(b), 6.1, and 6.4 of Appendix
E of this part.

* * * * *

Subpart B [AMENDED]

Section 58.10, is amended by adding paragraph (a)(5) and adding
paragraph (b)(12) to read as follows:

§ 58.10   Annual monitoring network plan and periodic network
assessment.

* * * * *

	(a) * * * 

(5)  A plan for establishing NO2 monitoring sites in accordance with the
requirements of appendix D to this part shall be submitted to the
Administrator by July 1, 2012.  The plan shall provide for all required
stations to be operational by January 1, 2013.

* * * * *

(b) * * *

(12)  The identification of required NO2 monitors as either near-road or
area-wide sites in accordance with Appendix D, Section 4.3 of this part.


* * * * *

Section 58.13 is amended by adding paragraph (c) to read as follows:

§ 58.13 Monitoring network completion.

* * * * *

(c) The network of NO2 monitors must be physically established no later
than January 1, 2013, and at that time, must be operating under all of
the requirements of this part, including the requirements of appendices
A, C, D, and E to this part. 

* * * * *

Section 58.16 is amended by revising paragraph (a) to read as follows:

§ 58.16   Data submittal and archiving requirements.

* * * * *

(a) The State, or where appropriate, local agency, shall report to the
Administrator, via AQS all ambient air quality data and associated
quality assurance data for SO2; CO; O3; NO2; NO; NOY; NOX; Pb-TSP mass
concentration; Pb-PM10 mass concentration; PM10 mass concentration;
PM2.5mass concentration; for filter-based PM2.5FRM/FEM the field blank
mass, sampler-generated average daily temperature, and sampler-generated
average daily pressure; chemically speciated PM2.5 mass concentration
data; PM10–2.5 mass concentration; chemically speciated PM10–2.5
mass concentration data; meteorological data from NCore and PAMS sites;
average daily temperature and average daily pressure for Pb sites if not
already reported from sampler generated records; and metadata records
and information specified by the AQS Data Coding Manual
(http://www.epa.gov/ttn/airs/airsaqs/manuals/manuals.htm ). The State,
or where appropriate, local agency, may report site specific
meteorological measurements generated by onsite equipment
(meteorological instruments, or sampler generated) or measurements from
the nearest airport reporting ambient pressure and temperature.  Such
air quality data and information must be submitted directly to the AQS
via electronic transmission on the specified quarterly schedule
described in paragraph (b) of this section.

* * * * *

Appendix A to Part 58 is amended as by adding paragraph 2.3.1.5 to read
as follows:

Appendix A to Part 58—Quality Assurance Requirements for SLAMS, SPMs
and PSD Air Monitoring

	2.3.1.5 Measurement Uncertainty for NO2. The goal for acceptable
measurement uncertainty is defined for precision as an upper 90 percent
confidence limit for the coefficient of variation (CV) of 15 percent and
for bias as an upper 95 percent confidence limit for the absolute bias
of 15 percent.

* * * * *

Appendix C to Part 58 is amended as by adding paragraph 2.1.1 to read as
follows:

Appendix C to Part 58—Ambient Air Quality Monitoring Methodology

* * * * *

2.1.1 Any NO2 FRM or FEM used for making primary NAAQS decisions must be
capable of providing hourly averaged concentration data.

* * * * *

Appendix D to Part 58 is amended as by replacing paragraph 4.3 to read
as follows:

Appendix D to Part 58—Network Design Criteria for Ambient Air Quality
Monitoring

* * * * *

4.3 Nitrogen Dioxide (NO2) Design Criteria. 

4.3.1 General Requirement s. (a) State and, where appropriate, local
agencies must operate a minimum number of required NO2 monitoring sites
as described below. 

4.3.2 Requirement for Near-road NO2 Monitors. (a)  Within the NO2
network, there must be one microscale near-road NO2 monitoring station
in each CBSA with a population of 350,000 or more persons to monitor a
location of expected maximum hourly concentrations sited near a major
road with high AADT counts as specified in paragraph 4.3.2(a)(1) of this
appendix. An additional near-road NO2 monitoring station is required for
any CBSA with a population of 2,500,000 persons or more, or in any CBSA
with a population of 350,000 or more persons that has one or more
roadway segments with 250,000 or greater AADT counts to monitor a second
location of expected maximum hourly concentrations.  CBSA populations
shall be based on the latest available census figures.

(1) The near-road NO2 monitoring stations shall be selected by ranking
all road segments within a CBSA by AADT and then identifying a location
or locations adjacent to those highest ranked road segments, considering
fleet mix, roadway design, congestion patterns, terrain, and
meteorology, where maximum hourly NO2 concentrations are expected to be
highest and siting criteria can be met in accordance with appendix E of
this part. Where a state or local air monitoring agency identifies
multiple acceptable candidate sites where maximum hourly NO2
concentrations are expected to occur, the monitoring agency shall
consider the potential for population exposure in the criteria utilized
to select the final site location. Where one CBSA is required to have
two near-road NO2 monitoring stations, the sites shall be differentiated
from each other by one or more of the following factors: fleet mix;
congestion patterns; terrain; geographic area within the CBSA; or
different route, interstate, or freeway designation. 

 (b) Measurements at required near-road NO2 monitor sites utilizing
chemiluminescent FRMs must include at a minimum: NO, NO2, and NOX.. 

4.3.3 Requirement for Area-wide NO2 Monitoring. (a) Within the NO2
network, there must be one monitoring station in each CBSA with a
population of 1,000,000 or more persons to monitor a location of
expected highest NO2 concentrations representing the neighborhood or
larger spatial scales. PAMS sites collecting NO2 data that are situated
in an area of expected high NO2 concentrations at the neighborhood or
larger spatial scale may be used to satisfy this minimum monitoring
requirement when the NO2 monitor is operated year round.  Emission
inventories and meteorological analysis should be used to identify the
appropriate locations within a CBSA for locating required area-wide NO2
monitoring stations. CBSA populations shall be based on the latest
available census figures.

  4.3.4 Regional Administrator Required Monitoring. (a) The Regional
Administrator may require additional NO2 monitoring stations above the
minimum requirements to monitor in locations away from roads, or sites
that do not meet near-road NO2 monitor siting criteria noted in appendix
E of this part, where required near-road monitors do not represent a
location or locations where the expected maximum hourly NO2
concentrations exist in a CBSA.  The Regional Administrator may also
require additional near-road NO2 monitoring stations above the minimum
required in situations where the minimum monitoring requirements are not
sufficient to meet monitoring objectives, and may consider additional
locations of expected high NO2 concentrations and the variety of
exposure potential due to increased variety in amount or types of fleet
mix, congestion patterns, terrain, or geographic areas within a CBSA. 
The Regional Administrator and the responsible State or local air
monitoring agency should work together to design and/or maintain the
most appropriate NO2 network to service the variety of data needs for an
area.

(b) The Regional Administrator may require additional NO2 monitoring
stations for area-wide NO2 monitors at the neighborhood and larger
spatial scales above the minimum monitoring requirements where the
minimum monitoring requirements are not sufficient to meet monitoring
objectives for an area, such as supporting photochemical pollutant
assessment, air quality forecasting, PM precursor analysis, and
characterizing impacts of NO2 sources on certain communities. The
Regional Administrator and the responsible State or local air monitoring
agency should work together to design and/or maintain the most
appropriate NO2 network to service the variety of data needs for an
area.  

4.3.5 NO2 Monitoring Spatial Scales. (a) The most important spatial
scale for near-road NO2 monitoring stations to effectively characterize
the maximum expected hourly NO2 concentration due to mobile source
emissions on major roadways is the microscale. The most important
spatial scales for other monitoring stations characterizing maximum
expected hourly NO2 concentrations are the microscale and middle scale. 
The most important spatial scale for area-wide monitoring of high NO2
concentrations is the neighborhood scale. 

(1) Microscale —This scale would typify areas in close proximity to
major roadways or point and area sources. Emissions from roadways result
in high ground level NO2 concentrations at the microscale, where
concentration gradients generally exhibit a marked decrease with
increasing downwind distance from major roads.  As noted in appendix E
of this part, near-road NO2 monitoring stations are required to be
within 50 meters of target road segments in order to measure expected
peak concentrations.  Emissions from stationary point and area sources,
and non-road sources may, under certain plume conditions, result in high
ground level concentrations at the microscale. The microscale typically
represents an area impacted by the plume with dimensions extending up to
approximately 100 meters. 

(2) Middle scale —This scale generally represents air quality levels
in areas up to several city blocks in size with dimensions on the order
of approximately 100 meters to 500 meters. The middle scale may include
locations of expected maximum hourly concentrations due to proximity to
major NO2 point, area, and/or non-road sources. 

 (3) Neighborhood scale —The neighborhood scale would characterize air
quality conditions throughout some relatively uniform land use areas
with dimensions in the 0.5 to 4.0 kilometer range. Emissions from
stationary point and area sources may, under certain plume conditions,
result in high NO2 concentrations at the neighborhood scale. Where a
neighborhood site is located away from immediate NO2 sources, the site
may be useful in representing typical air quality values for a larger
residential area, and therefore suitable for population exposure and
trends analyses.

(4) Urban scale – Measurements in this scale would be used to estimate
concentrations over large portions of an urban area with dimensions from
4 to 50 kilometers. Such measurements would be useful for assessing
trends in area-wide air quality, and hence, the effectiveness of large
scale air pollution control strategies.  Urban scale sites may also
support other monitoring objectives of the NO2 monitoring network
identified in paragraph 4.3.4 above.

4.3.6 NOy Monitoring. (a) NO/ NOy measurements are included within the
NCore multipollutant site requirements and the PAMS program.  These NO/
NOy measurements will produce conservative estimates for NO2 that can be
used to ensure tracking continued compliance with the NO2 NAAQS.  NO/
NOy monitors are used at these sites because it is important to collect
data on total reactive nitrogen species for understanding O3
photochemistry.

* * * * *

Appendix E to Part 58 is amended by revising paragraph 2, 4(b), 6.1,
adding paragraph 6.4 and revising paragraph 9(c) and Table E-4 to read
as follows:

Appendix E to Part 58—Probe and Monitoring Path Siting Criteria for
Ambient Air Quality Monitoring

* * * * *

2. Horizontal and Vertical Placement

The probe or at least 80 percent of the monitoring path must be located
between 2 and 15 meters above ground level for all ozone and sulfur
dioxide monitoring sites, and for neighborhood or larger spatial scale
Pb, PM10, PM10-2.5, PM2.5, NO2 and carbon monoxide sites. Middle scale
PM10-2.5 sites are required to have sampler inlets between 2 and 7
meters above ground level. Microscale Pb, PM10, PM10-2.5 and PM2.5 sites
are required to have sampler inlets between 2 and 7 meters above ground
level. Microscale near-road NO2 monitoring sites are required to have
sampler inlets between 2 and 7 meters above ground level. The inlet
probes for microscale carbon monoxide monitors that are being used to
measure concentrations near roadways must be 3+ ½ meters above ground
level. The probe or at least 90 percent of the monitoring path must be
at least 1 meter vertically or horizontally away from any supporting
structure, walls, parapets, penthouses, etc., and away from dusty or
dirty areas. If the probe or a significant portion of the monitoring
path is located near the side of a building or wall, then it should be
located on the windward side of the building relative to the prevailing
wind direction during the season of highest concentration potential for
the pollutant being measured. 

* * * * *

4. Spacing from Obstructions

(a) * * *

(b) * * *

(c) * * *

(d) For near-road NO2 monitoring stations, the monitor probe shall have
an unobstructed air flow, where no obstacles exist at or above the
height of the monitor probe, between the monitor probe and the outside
nearest edge of the traffic lanes of the target road segment.

* * * * *

6. Spacing from Roadways

6.1 Spacing for Ozone Probes and Monitoring Paths. In siting an O3
analyzer, it is important to minimize destructive interferences form
sources of NO, since NO readily reacts with O3. Table E-1 of this
appendix provides the required minimum separation distances between a
roadway and a probe or, where applicable, at least 90 percent of a
monitoring path for various ranges of daily roadway traffic. A sampling
site having a point analyzer probe located closer to a roadway than
allowed by the Table E-1 requirements should be classified as microscale
or middle scale, rather than neighborhood or urban scale, since the
measurements from such a site would more closely represent the middle
scale. If an open path analyzer is used at a site, the monitoring
path(s) must not cross over a roadway with an average daily traffic
count of 10,000 vehicles per day or more. For those situations where a
monitoring path crosses a roadway with fewer than 10,000 vehicles per
day, monitoring agencies must consider the entire segment of the
monitoring path in the area of potential atmospheric interference from
automobile emissions. Therefore, this calculation must include the
length of the monitoring path over the roadway plus any segments of the
monitoring path that lie in the area between the roadway and minimum
separation distance, as determined from the Table E-1 of this appendix.
The sum of these distances must not be greater than 10 percent of the
total monitoring path length.

* * * * *	

	6.4 Spacing for Nitrogen Dioxide (NO2) Probes and Monitoring Paths (a)
In siting near-road NO2 monitors as required in paragraph 4.3.2 of
appendix D of this part, the monitor probe shall be as near as
practicable to the outside nearest edge of the traffic lanes of the
target road segment; but shall not be located at a distance greater than
50 meters, in the horizontal, from the outside nearest edge of the
traffic lanes of the target road segment.

(b) In siting NO2 monitors for neighborhood and larger scale monitoring,
it is important to minimize near-road influences. Table E-1 of this
appendix provides the required minimum separation distances between a
roadway and a probe or, where applicable, at least 90 percent of a
monitoring path for various ranges of daily roadway traffic. A sampling
site having a point analyzer probe located closer to a roadway than
allowed by the Table E-1 requirements should be classified as microscale
or middle scale rather than neighborhood or urban scale.  If an open
path analyzer is used at a site, the monitoring path(s) must not cross
over a roadway with an average daily traffic count of 10,000 vehicles
per day or more. For those situations where a monitoring path crosses a
roadway with fewer than 10,000 vehicles per day, monitoring agencies
must consider the entire segment of the monitoring path in the area of
potential atmospheric interference form automobile emissions. Therefore,
this calculation must include the length of the monitoring path over the
roadway plus any segments of the monitoring path that lie in the area
between the roadway and minimum separation distance, as determined form
the Table E-1 of this appendix. The sum of these distances must not be
greater than 10 percent of the total monitoring path length.

* * * * *

	9. Probe Material and Pollutant Sample Residence Time

(a) * * *

(b) * * *

(c) No matter how nonreactive the sampling probe material is initially,
after a period of use reactive particulate matter is deposited on the
probe walls.  Therefore, the time it takes the gas to transfer from the
probe inlet to the sampling device is also critical.  Ozone in the
presence of nitrogen oxide (NO) will show significant losses even in the
most inert probe material when the residence time exceeds 20 seconds.26 
Other studies 27-28 indicate that a 10 second or less residence time is
easily achievable.  Therefore, sampling probes for reactive gas monitors
at NCore and at NO2 sites must have a sample residence time less than 20
seconds.

* * * * *

	11. Summary 

Table E-4 of this appendix presents a summary of the general
requirements for probe and monitoring path siting criteria with respect
to distances and heights. It is apparent from Table E-4 that different
elevation distances above the ground are shown for the various
pollutants. The discussion in this appendix for each of the pollutants
describes reasons for elevating the monitor, probe, or monitoring path.
The differences in the specified range of heights are based on the
vertical concentration gradients. For CO and near-road NO2 monitors, the
gradients in the vertical direction are very large for the microscale,
so a small range of heights are used. The upper limit of 15 meters is
specified for the consistency between pollutants and to allow the use of
a single manifold or monitoring path for monitoring more than one
pollutant.

Table E-4 of Appendix E to Part 58.  Summary of Probe and Monitoring
Path Siting Criteria

Pollutant

	Scale (maximum monitoring path length, meters)	Height from ground to
probe, inlet or 80% of monitoring path1	Horizontal and vertical distance
from supporting structures2 to probe, inlet or 90% of monitoring path1
(meters)	Distance from trees to probe, inlet or 90% of monitoring path1
(meters)	Distance from roadways to probe, inlet or monitoring path1
(meters)

SO2 3,4,5,6

	Middle

(300 m)

Neighborhood

Urban, and 

Regional

(1 km)	2-15 	> 1 	> 10 	N/A

CO 4,5,7

	Micro, middle

3½: 2-15 	> 1 	> 10 	2-10; see Table E-2 of this appendix for middle
and neighborhood scales.

O3 3,4,5

		Middle (300 m)

Neighborhood,  Urban, and Regional (1 km) 	2-15	> 1 	> 10 	See Table E-1
of this appendix for all scales.

NO2 3,4,5 	Micro (Near-road [50-300]) 

Middle(300m)

Neighborhood, Urban, and Regional (1 km)	2-7 (micro);

2-15(all other scales)

	> 1	> 10	< 50 meters for near-road microscale;

See Table E-1 of this appendix for all other scales

Ozone precursors (for PAMS)3,4,5	Neighborhood and Urban (1 km)	2-15

	> 1 	> 10 	See Table E-4 of this appendix for all scales.

PM,Pb 3,4,5,6,8	Micro: Middle,

Neighborhood,

Urban and

Regional	2-7 (micro);

2-7 (middle PM10-2.5);

2-15 (all other scales)	> 2 (all scales, horizontal distance only)

	> 10 (all scales)	2-10 (micro); see Figure E-1 of this appendix for all
other scales.

N/A--Not applicable.

1 Monitoring path for open path analyzers is applicable only to middle
or neighborhood scale CO monitoring, middle, neighborhood, urban, and
regional scale NO2 monitoring, and all applicable scales for monitoring
SO2,O3, and O3 precursors.

2 When probe is located on a rooftop, this separation distance is in
reference to walls, parapets, or penthouses located on roof.

3 Should be >20 meters from the dripline of tree(s) and must be 10
meters from the dripline when the tree(s) act as an obstruction.

4 Distance from sampler, probe, or 90% of monitoring path to obstacle,
such as a building, must be at least twice the height the obstacle
protrudes above the sampler, probe, or monitoring path.  Sites not
meeting this criterion may be classified as middle scale (see text).

5 Must have unrestricted airflow 270 degrees around the probe or
sampler; 180 degrees if the probe is on the side of a building or a
wall.

6 The probe, sampler, or monitoring path should be away from minor
sources, such as furnace or incineration flues.  The separation distance
is dependent on the height of the minor source's emission point (such as
a flue), the type of fuel or waste burned, and the quality of the fuel
(sulfur, ash, or lead content).  This criterion is designed to avoid
undue influences from minor sources.

7 For microscale CO monitoring sites, the probe must be >10 meters from
a street intersection and preferably at a midblock location.

8 Collocated monitors must be within 4 meters of each other and at least
2 meters apart for flow rates greater than 200 liters/min or at least 1
meter apart for samplers having flow rates less than 200 liters/min to
preclude airflow interference.

* * * * *

Appendix G to Part 58 is amended as by revising paragraph 9 and Table 2
to read as follows:

Appendix G to Part 58 - Uniform Air Quality Index (AQI) and Daily
Reporting

* * * * * 

9. How Does the AQI Relate to Air Pollution Levels?

For each pollutant, the AQI transforms ambient concentrations to a scale
from 0 to 500. The AQI is keyed as appropriate to the national ambient
air quality standards (NAAQS) for each pollutant. In most cases, the
index value of 100 is associated with the numerical level of the
short-term (i.e., averaging time of 24-hours or less) standard for each
pollutant. The index value of 50 is associated with one of the
following: the numerical level of the annual standard for a pollutant,
if there is one; one-half the level of the short-term standard for the
pollutant; or the level at which it is appropriate to begin to provide
guidance on cautionary language. Higher categories of the index are
based on increasingly serious health effects that affect increasing
proportions of the population. An index value is calculated each day for
each pollutant (as described in section 12 of this appendix), unless
that pollutant is specifically excluded (see section 8 of this
appendix). The pollutant with the highest index value for the day is the
“critical” pollutant, and must be included in the daily AQI report. 
As a result, the AQI for any given day is equal to the index value of
the critical pollutant for that day. For the purposes of reporting the
AQI, the indexes for PM10 and PM2.5 are to be considered separately.

* * * * *



TABLE 2.—BREAKPOINTS FOR THE AQI

These breakpoints	Equal these AQI’s

O3 (ppm)

8-hour	O3 (ppm)

1-hour1	PM2.5

(µg/m3)	PM10

(µg/m3)	CO (ppm)	SO2 (ppm)	NO2 (ppm)

1-hour	AQI	Category

0.000-0.059	..................	0.0-15.4	0-54	0.0-4.4	0.000-0.034	0 –
(0.040 – 0.053)	0-50	Good.

0.060-0.075	..................	15.5-40.4	55-154	4.5-9.4	0.035-0.144
(0.041 – 0.054) – (0.080 – 0.100)	51-100	Moderate.

0.076-0.095	0.125-0.164	40.5-65.4	155-254	9.5-12.4	0.145-0.224	(0.081
– 0.101) – (0.360 –  0.370)	101-150	Unhealthy for Sensitive
Groups.

0.096-0.115	0.165-0.204	365.5-150.4	255-354	12.5-15.4	0.225-0.304	(0.361
– 0.371) – 0.64	151-200	Unhealthy.

0.116-0.374	0.205-0.404	3150.5-250.4	355-424	15.5-30.4	0.305-0.604	0.65
– 1.24	201-300	Very Unhealthy.

(2)...............	0.405-0.504	3250.5-350.4	425-504	30.5-40.4
0.605-0.804	1.25 – 1.64	301-400	Hazardous.

(2)...............	0.505-0.604	3350.5-500.4	505-604	40.5-50.4
0.805-1.004	1.65 – 2.04	401-500	Hazardous.

1 Areas are generally required to report the AQI based on 8-hour ozone
values.  However, there are a small number of areas where an AQI based
on 1-hour ozone values would be more precautionary.  In these cases, in
addition to calculating the 8-hour ozone index value, the 1-hour ozone
index value may be calculated, and the maximum of the two values
reported.

2 8-hour O3 values do not define higher AQI values (( 301).  AQI values
of 301 or greater are calculated with 1-hour O3 concentrations.

3 If a different SHL for PM2.5 is promulgated, these numbers will change
accordingly.

 The legislative history of section 109 indicates that a primary
standard is to be set at “the maximum permissible ambient air level .
. . which will protect the health of any [sensitive] group of the
population,” and that for this purpose “reference should be made to
a representative sample of persons comprising the sensitive group rather
than to a single person in such a group.” S. Rep. No. 91-1196, 91st
Cong., 2d Sess. 10 (1970)

 EPA is currently conducting a separate review of the secondary NO2
NAAQS jointly with a review of the secondary SO2 NAAQS.

 In this document, the terms “oxides of nitrogen” and “nitrogen
oxides” (NOX) refer to all forms of oxidized nitrogen (N) compounds,
including NO, NO2, and all other oxidized N-containing compounds formed
from NO and NO2.  This follows usage in the Clean Air Act Section
108(c): “Such criteria [for oxides of nitrogen] shall include a
discussion of nitric and nitrous acids, nitrites, nitrates,
nitrosamines, and other carcinogenic and potentially carcinogenic
derivatives of oxides of nitrogen.”  By contrast, within the air
pollution research and control communities, the terms “oxides of
nitrogen” and “nitrogen oxides” are restricted to refer only to
the sum of NO and NO2, and this sum is commonly abbreviated as NOX. The
category label used by this community for the sum of all forms of
oxidized nitrogen compounds including those listed in Section 108(c) is
NOY.  

 The “form” of a standard defines the air quality statistic that is
to be compared to the level of the standard in determining whether an
area attains the standard.  

 It should be noted that the ISA (section 2.4.1) references a different
number of active monitors in the NO2 network. The discrepancy between
the ISA numbers and the number presented here is due to differing
metrics used in pulling data from AQS. The ISA only references SLAMS,
NAMS, and PAMS sites with defined monitoring objectives, while Watkins
and Thompson (2008) considered all NO2 sites reporting data at any point
during the year. Based on this approach, Watkins and Thompson (2008)
also noted that the size of the NO2 monitoring network has remained
relatively stable since the early 1980s.

 The most current American Housing Survey (  HYPERLINK
"http://www.census.gov/hhes/www/housing/ahs/ahs.html" 
http://www.census.gov/hhes/www/housing/ahs/ahs.html ) is from 2007 and
lists a higher fraction of housing units within the 300 foot boundary
than do prior surveys.  According to Table 1A-6 from that report
(http://www.census.gov/hhes/www/housing/ahs/ahs07/tab1a-6.pdf), out of
128,203,000 total housing units in the United States, 20,016,000 were
reported by the surveyed occupant or landlord as being within 300 feet
of a 4-or-more lane highway, railroad, or airport.  That constitutes
15.613% of the total housing units in the U.S.  Assuming equal
distributions, with a current population of 306,330,199, that means that
there would be 47.8 million people meeting the 300 foot criteria.

 The study by Tolbert et al. (2007) reported positive associations
between 1-hour ambient NO2 concentrations and respiratory-related
emergency department visits.  The meta-analysis was included in the ISA
and reported that short-term exposures to NO2 concentrations at or above
100 ppb increased airway responsiveness in most asthmatics.  

  EPA considers the Goodman study to be a “new study” on which, as
discussed above in section 1.B, it would not be appropriate to base a
standard in the absence of thorough CASAC and public review of the study
and its methodology.  However, as discussed below, EPA has considered
the study in the context of responding to public comments on the
proposal and has concluded it does not provide a basis to materially
change any of the broad scientific conclusions regarding the health
effects of NO2 made in the air quality criteria. 

 Once EPA determines whether to retain or revise the current standard,
the actual air quality levels in various areas of the country are
clearly relevant under the NAAQS implementation provisions for the Act,
such as the provision for designation of areas based on whether or not
they attain the required NAAQS.  

 As discussed below, 98th and 99th percentile forms were evaluated in
the REA.  A 99th percentile form corresponds approximately to the 4th
highest 1-hour concentration in a year while a 98th percentile form
corresponds approximately to the 7th or 8th highest 1-hour concentration
in a year.  A 4th highest concentration form has been used previously in
the O3 NAAQS while a 98th percentile form has been used previously in
the PM2.5 NAAQS.  

 In addition, the air quality analyses presented in the REA estimated
that on-road NO2 concentrations are about 80% higher on average than
concentrations away from the road (REA, section 7.3.2) and that NO2
monitors within 20 m of roads measure NO2 concentrations that are, on
average across locations, 40% higher than concentrations measured by
monitors at least 100 m from the road (REA, compare Tables 7-11 and
7-13).  

 The 98th percentile concentrations in these study locations ranged from
85 to 94 ppb.  

 For a standard of 100 ppb, area-wide concentrations would be expected
to range from approximately 50 ppb (assuming near-road concentrations
are 100% higher than area-wide concentrations) to 75 ppb (assuming
near-road concentrations are 30% higher than area-wide concentrations). 

 This conclusion assumes that near-road NO2 concentrations are 65%
higher than area-wide concentrations, reflecting the mid-point in the
range of 30 to 100%.  Based on available information suggesting that
near-road concentrations can be 30 to 100% higher than area-wide
concentrations, a standard level of 80 ppb could limit area-wide
concentrations to between 40 and 60 ppb.  

 CASAC members were also part of the CASAC Panel for the NO2 NAAQS
review (i.e., the Oxides of Nitrogen Primary National Ambient Air
Quality Standards Panel).  Therefore, references to the CASAC Panel
include both CASAC members and Panel members. 

 To measure maximum concentrations, the Administrator proposed
monitoring provisions that would require monitors within 50 meters of
major roads and to allow the Regional Administrator to require
additional monitors in situations where maximum concentrations would be
expected to occur in locations other than near major roads (e.g., due to
the influence of multiple smaller roads and/or stationary sources). 

 As discussed above, the Administrator has selected the 98th percentile
as the form for the new 1-hour NO2 standard. 

 The most current American Housing Survey (  HYPERLINK
"http://www.census.gov/hhes/www/housing/ahs/ahs.html" 
http://www.census.gov/hhes/www/housing/ahs/ahs.html ) is from 2007 and
lists a higher fraction of housing units within the 300 foot boundary. 
According to Table 1A-6 from that report
(http://www.census.gov/hhes/www/housing/ahs/ahs07/tab1a-6.pdf), out of
128.2 million total housing units in the United States, about 20 million
were reported by the surveyed occupant or landlord as being within 300
feet of a 4-or-more lane highway, railroad, or airport.  That
constitutes 15.6% of the total housing units in the U.S.  Assuming equal
distributions, with a current population of 306.3 million, that means
that there would be 47.8 million people meeting the 300 foot criteria.

 Some of these studies also included susceptible and vulnerable
populations (e.g., children in Peel et al. (2005); poor and minority
populations in Ito et al., 2007).  

  Since EPA is retaining the annual standard without revision, the
discussion in this section relates to implementation of the proposed
1-hour standard, rather than the annual standard.  

  Two elements identified in section 110(a)(2) are not listed below
because, as EPA interprets the CAA, SIPs incorporating any necessary
local nonattainment area controls would not be due within 3 years, but
rather are due at the time the nonattainment area planning requirements
are due.  These elements are: (1) Emission limits and other control
measures, section 110(a)(2)(A), and (2) Provisions for meeting part D,
section 110(a)(2)(I), which requires areas designated as nonattainment
to meet the applicable nonattainment planning requirements of part D,
title I of the CAA.  

 The terms “major” and “minor” define the size of a stationary
source, for applicability purposes, in terms of an annual emissions rate
(tons per year, tpy) for a pollutant.  Generally, a minor source is any
source that is not “major.”  “Major” is defined by the
applicable regulations—PSD or nonattainment NSR.

 In addition, the PSD program applies to non-criteria pollutants subject
to regulation under the Act, except those pollutants regulated under
section 112 and pollutants subject to regulation only under section
211(o).

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Criteria pollutants are those pollutants for which EPA has established a
NAAQS under section 109 of the CAA.

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