										6560-50-P  

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 51 and 52

[EPA-HQ-OAR-2006-0605; FRL-XXXX-X]

Prevention of Significant Deterioration (PSD) for Particulate Matter
Less Than 2.5 Micrometers (PM2.5) – Increments, Significant Impact
Levels (SILs) and Significant Monitoring Concentration (SMC)

AGENCY:  Environmental Protection Agency (EPA).

ACTION:  Proposed rule.

SUMMARY: 	The Clean Air Act (Act) authorizes EPA to establish
regulations to prevent significant deterioration of air quality due to
emissions of any pollutant for which a national ambient air quality
standard (NAAQS) has been promulgated.  The NAAQS for particulate matter
using the PM2.5 indicator were promulgated in 1997.  The EPA is
proposing to facilitate implementation of a PM2.5 Prevention of
Significant Deterioration (PSD) program in areas attaining the
particulate matter less than 2.5 micrometers (PM2.5) NAAQS by developing
PM2.5 increments, Significant Impact Levels (SILs), and a Significant
Monitoring Concentration (SMC).  In addition, EPA is proposing to revoke
the annual PM10 increments.

	“Increments” are maximum increases in ambient PM2.5 concentrations
(PM2.5 increments) allowed in an area above the baseline concentration. 
The SILs and SMCs are numerical values that represent thresholds of
insignificant, i.e., de minimis, modeled source impacts or monitored
(ambient) concentrations, respectively.  The EPA is proposing such
values for PM2.5 that will be used as screening tools by a major source
subject to PSD to determine the subsequent level of analysis and data
gathering required for a PSD permit application for emissions of PM2.5. 

DATES:  Comments must be received on or before [INSERT DATE 60 DAYS
AFTER PUBLICATION IN THE FEDERAL REGISTER].  Under the Paperwork
Reduction Act, comments on the information collection provisions must be
received by the Office of Management and Budget (OMB) on or before
[INSERT DATE 30 DAYS AFTER PUBLICATION IN THE FEDERAL REGISTER.]

Public Hearing.    SEQ CHAPTER \h \r 1 If anyone contacts us requesting
to speak at a public hearing by [INSERT DATE 20 DAYS AFTER PUBLICATION
IN THE FEDERAL REGISTER], we will hold a public hearing.  Additional
information about the hearing would be published in a subsequent Federal
Register notice.

ADDRESSES:  Submit your comments, identified by Docket ID No.
EPA-HQ-OAR-2006-0605, by one of the following methods:

  HYPERLINK "http://www.regulations.gov"  www.regulations.gov .  Follow
the on-line instructions for submitting comments.

E-mail:    HYPERLINK "mailto:a-and-r-docket@.epa.gov" 
a-and-r-docket@.epa.gov . 

Mail:  Air and Radiation Docket and Information Center, Environmental
Protection Agency, Mailcode: 2822T, 1200 Pennsylvania Avenue, NW,
Washington, DC 20460.  Please include a total of two copies.  In
addition, please mail a copy of your comments on the information
collection provisions to the Office of Information and Regulatory
Affairs, Office of Management and Budget 

(OMB), Attn: Desk Officer for EPA, 725 17th Street, Northwest,,
Washington, DC 20503.

Hand Delivery:  Air and Radiation Docket and Information Center, EPA/DC,
EPA West, Room 3334, 1301 Constitution Avenue, NW, Washington, DC 20004.
 Such deliveries are only accepted during the Docket(s normal hours of
operation, and special arrangements should be made for deliveries of
boxed information.

Instructions:  Direct your comments to Docket ID No.
EPA-HQ-OAR-2006-0605.  The EPA’s policy is that all comments received
will be included in the public docket without change and may be made
available online at   HYPERLINK "http://www.regulations.gov" 
www.regulations.gov , including any personal information provided,
unless the comment includes information claimed to be Confidential
Business Information (CBI) or other information whose disclosure is
restricted by statute.  Do not submit information that you consider to
be CBI or otherwise protected through   HYPERLINK
"http://www.regulations.gov"  www.regulations.gov   or e-mail.  The  
HYPERLINK "http://www.regulations.gov"  www.regulations.gov  website is
an “anonymous access” system, which means EPA will not know your
identity or contact information unless you provide it in the body of
your comment.  If you send an e-mail comment directly to EPA without
going through   HYPERLINK "www.regulations.gov%20"  www.regulations.gov 
your e-mail address will be automatically captured and included as part
of the comment that is placed in the public docket and made available on
the Internet.  If you submit an electronic comment, EPA recommends that
you include your name and other contact information in the body of your
comment and with any disk or CD-ROM you submit.  If EPA cannot read your
comment due to technical difficulties and cannot contact you for
clarification, EPA may not be able to consider your comment.  Electronic
files should avoid the use of special characters, any form of
encryption, and be free of any defects or viruses.  For additional
instructions on submitting comments, go to section I.B of the
SUPPLEMENTARY INFORMATION section of this document.

Docket:  All documents in the docket are listed in the   HYPERLINK
"http://www.regulations.gov"  www.regulations.gov  index.  Although
listed in the index, some information is not publicly available, e.g.,
CBI or other information whose disclosure is restricted by statute. 
Certain other material, such as copyrighted material, will be publicly
available only in hard copy.  Publicly available docket materials are
available either electronically in   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 Avenue, Northwest, 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:  Raj Rao, Air Quality Policy Division,
Office of Air Quality Planning and Standards (C504-03), Environmental
Protection Agency, Research Triangle Park, North Carolina 27711;
telephone number (919) 541-5344; fax number (919) 541-5509; email
address:   HYPERLINK "mailto:rao.raj@epa.gov"  rao.raj@epa.gov  or Dan
deRoeck, Air Quality Policy Division, Office of Air Quality Planning and
Standards (C504-03), Environmental Protection Agency, Research Triangle
Park, North Carolina 27711; telephone number (919) 541-5593; fax number
(919) 541-5509; email address:   HYPERLINK "mailto:deroeck.dan@epa.gov" 
deroeck.dan@epa.gov .  To request a public hearing or information
pertaining to a public hearing on this document, contact Ms. Pamela S.
Long, Air Quality Policy Division, Office of Air Quality Planning and
Standards (C504-03), Environmental Protection Agency, Research Triangle
Park, North Carolina 27711; telephone number (919) 541-0641; fax number
(919) 541-5509; email address:   HYPERLINK "mailto:long.pam@epa.gov" 
long.pam@epa.gov .

SUPPLEMENTARY INFORMATION:

General Information

Does this action apply to me?

Entities potentially affected by this proposed action include owners and
operators of emission sources in all industry groups, as well as the EPA
and State, local, and tribal governments that are delegated authority to
implement these regulations.  The majority of sources potentially
affected are expected to be in the following groups:

Category	

	NAICSa	

Industry group



Industry		

221111, 221112, 221113, 221119, 221121, 221122	

Electric services



	

32411	

Petroleum refining



	

325181, 32512, 325131, 325182, 211112, 325998, 331311, 325188	

Industrial inorganic chemicals

	

32511, 325132, 325192, 325188, 325193, 32512, 325199	

Industrial organic chemicals

	

32552, 32592, 32591, 325182, 32551	

Miscellaneous chemical products

	

211112	

Natural gas liquids



	

48621, 22121	

Natural gas transport



	

32211, 322121, 322122, 32213	

Pulp and paper mills

	

322121, 322122	

Paper mills



	

336111, 336112, 336712, 336211, 336992, 336322, 336312, 33633, 33634,
33635, 336399, 336212, 336213	

Automobile manufacturing



	

325411, 325412, 325413, 325414	

Pharmaceuticals



Federal government		

924110	

Administration of Air and Water Resources and Solid Waste Management
Programs



State/local/tribal

Government		

924110

	

Administration of Air and Water Resources and Solid Waste Management
Programs

a North American Industry Classification System.

This table is not intended to be exhaustive, but rather provides a guide
for readers regarding entities likely to be regulated by this action. 
To determine whether your facility is regulated by this action, you
should examine the applicability criteria in the PSD rules for
attainment areas (40 CFR 52.21).  If you have any questions regarding
the 

applicability of this action to a particular entity, contact the person
listed in the preceding FOR FURTHER INFORMATION CONTACT section.

What should I consider as I prepare my comments for EPA?

1.  Submitting CBI.   tc \l2 "C.	How should I submit Confidential
Business Information (CBI) to the Agency? Do not submit this information
to EPA through   HYPERLINK "http://www.regulations.gov" 
www.regulations.gov  or e-mail.  Clearly mark the part or all of the
information that you claim to be CBI.  For CBI information in a disk or
CD ROM that you mail to EPA, mark the outside of the disk or CD ROM as
CBI and then identify electronically within the disk or CD ROM the
specific information that is claimed as CBI.  In addition to one
complete version of the comment that includes information claimed as
CBI, a copy of the comment that does not contain the information claimed
as CBI must be submitted for inclusion in the public docket. 
Information so marked will not be disclosed except in accordance with
procedures set forth in 40 CFR part 2.  Send or deliver information
identified as CBI only to the following address: Roberto Morales, OAQPS
Document Control Officer (C404-02), Environmental Protection Agency,
Research Triangle Park, NC 27711, Attention Docket ID No.
EPA-HQ-OAR-2006-0605.

2.  Tips for Preparing Your Comments.  When submitting comments,
remember to: tc \l2 "D.	What should I consider as I prepare my comments
for the EPA? 

Identify the rulemaking by docket number and other identifying
information (subject heading, Federal Register date and page number).

Follow directions - The agency may ask you to respond to specific
questions or organize comments by referencing a Code of Federal
Regulations (CFR) part or section number.

Explain why you agree or disagree, suggest alternatives, and substitute
language for your requested changes.

Describe any assumptions and provide any technical information and/or
data that you used.

If you estimate potential costs or burdens, explain how you arrived at
your estimate in sufficient detail to allow for it to be reproduced.

Provide specific examples to illustrate your concerns, and suggest
alternatives.

Explain your views as clearly as possible, avoiding the use of profanity
or personal threats.

Make sure to submit your comments by the comment period deadline
identified.

Where can I get a copy of this document and other related information?

In addition to being available in the docket, an electronic copy of this
proposal will also be available on the World Wide Web.  Following
signature by the EPA Administrator, a copy of this notice will be posted
in the regulations and standards section of our NSR home page located at
http://www.epa.gov/nsr.

How can I find information about a possible Public Hearing?

Persons interested in presenting oral testimony should contact Ms.
Pamela Long, New Source Review Group, Air Quality Policy Division
(C504-03), Environmental Protection Agency, Research Triangle Park, NC
27711; telephone number (919) 541-0641 or e-mail   HYPERLINK
"mailto:long.pam@epa.gov"  long.pam@epa.gov  at least 2 days in advance
of the public hearing.  Persons interested in attending the public
hearing should also contact Ms. Long to verify the time, date, and
location of the hearing.  The public hearing will provide interested
parties the opportunity to present data, views, or arguments concerning
these proposed rules.

The information presented in this preamble is organized as follows:

  TOC \o "1-4" \n \h \z \u    HYPERLINK \l "_Toc158574655"  I.	General
Information 

  HYPERLINK \l "_Toc158574656"  A.	Does this action apply to me? 

  HYPERLINK \l "_Toc158574657"  B.	What should I consider as I prepare
my comments for EPA? 

  HYPERLINK \l "_Toc158574658"  C.	Where can I get a copy of this
document and other related information? 

  HYPERLINK \l "_Toc158574659"  D.	How can I find information about a
possible Public Hearing? 

  HYPERLINK \l "_Toc158574660"  II.	Overview of Proposed Regulations 

  HYPERLINK \l "_Toc158574661"  A.	Summary of Proposed Options for
Increments 

  HYPERLINK \l "_Toc158574662"  B.	Summary of Proposed Options for SILs 

  HYPERLINK \l "_Toc158574663"  C.	Summary of Proposed Options for the
PM2.5 SMC 

  HYPERLINK \l "_Toc158574664"  III.	Background 

  HYPERLINK \l "_Toc158574665"  A.	PSD Program 

  HYPERLINK \l "_Toc158574666"  B.	History of PM NAAQS 

  HYPERLINK \l "_Toc158574667"  1.	TSP and PM10 NAAQS 

  HYPERLINK \l "_Toc158574668"  2.	PM2.5 NAAQS 

  HYPERLINK \l "_Toc158574669"  3.	Revised PM2.5 and PM10 NAAQS 

  HYPERLINK \l "_Toc158574670"  C.	Implementation of NSR for PM2.5 

  HYPERLINK \l "_Toc158574671"  D.	Background on Implementation of PSD
Increments 

  HYPERLINK \l "_Toc158574672"  E.	Historical Approaches for Developing
Increments 

  HYPERLINK \l "_Toc158574673"  1.	Congressional enactment of increments
for PM and SO2. 

  HYPERLINK \l "_Toc158574674"  2.	EPA’s promulgation of increments
for NO2 and PM10 

  HYPERLINK \l "_Toc158574675"  a.	Increments for NOx using the
“contingent safe harbor” approach under section 166(a) of the Act. 

  HYPERLINK \l "_Toc158574676"  b.	Increments for PM10 using
“equivalent substitution” approach under section 166(f). 

  HYPERLINK \l "_Toc158574677"  IV.	EPA’s Interpretation of Section
166 of the Clean Air Act 

  HYPERLINK \l "_Toc158574678"  A.	Which Criteria In Section 166 Should
EPA Use to Develop Increments for PM2.5? 

  HYPERLINK \l "_Toc158574679"  1.	Support for “contingent safe
harbor” approach for PM2.5 under section 166(a) 

  HYPERLINK \l "_Toc158574680"  2.	Support of “equivalent
substitution” approach for PM2.5 under section 166(f) 

  HYPERLINK \l "_Toc158574681"  B.	Requirements of Sections 166(a)-(d)
of the Clean Air Act 

  HYPERLINK \l "_Toc158574682"  1.	Regulations as a whole should fulfill
statutory requirements 

  HYPERLINK \l "_Toc158574683"  2.	Contingent safe harbor approach 

  HYPERLINK \l "_Toc158574684"  3.	The statutory factors applicable
under section 166(c) 

  HYPERLINK \l "_Toc158574685"  4.	Balancing the factors applicable
under section 166(c) 

  HYPERLINK \l "_Toc158574686"  C.	Requirements of Section 166(f) of the
Clean Air Act 

  HYPERLINK \l "_Toc158574687"  V.	Increments and other measures to
prevent significant deterioration 

  HYPERLINK \l "_Toc158574688"  A.	Option 1 – Contingent Safe Harbor
Approach for Annual and Short-Term Increments – Section 166(a) 

  HYPERLINK \l "_Toc158574689"  1.	Proposed framework for pollutant
specific PSD regulations for PM2.5 

  HYPERLINK \l "_Toc158574690"  a.	Increment system 

  HYPERLINK \l "_Toc158574691"  b.	Area classifications 

  HYPERLINK \l "_Toc158574692"  c.	Permitting procedures 

  HYPERLINK \l "_Toc158574693"  d.	Air Quality Related Values review by
Federal Land Manager and permitting authority. 

  HYPERLINK \l "_Toc158574694"  e.	Additional impacts analysis. 

  HYPERLINK \l "_Toc158574695"  f.	Installation of Best Available
Control Technology. 

  HYPERLINK \l "_Toc158574696"  2.	Proposed increments 

  HYPERLINK \l "_Toc158574697"  a.	Identification of safe harbor
increments 

  HYPERLINK \l "_Toc158574698"  b.	Data utilized by EPA for the
evaluation of the safe harbor increments for PM2.5. 

  HYPERLINK \l "_Toc158574699"  c.	Scope of effects considered 

  HYPERLINK \l "_Toc158574700"  d.	Evaluation of the health and welfare
effects of PM2.5 

  HYPERLINK \l "_Toc158574701"  e.	Fundamental elements of increments 

  HYPERLINK \l "_Toc158574702"  f.	Evaluation of the safe harbor
increments. 

  HYPERLINK \l "_Toc158574703"  3.	Proposed baseline dates for PM2.5
increments under option 1. 

  HYPERLINK \l "_Toc158574704"  4.	Revocation of PM10 annual increments 

  HYPERLINK \l "_Toc158574705"  B.	Option 2 – Equivalent Substitution
Approach For Annual Increments – Section 166(f) 

  HYPERLINK \l "_Toc158574706"  1.	Development of equivalent increments 

  HYPERLINK \l "_Toc158574707"  2.	Proposed annual increments for PM2.5 

  HYPERLINK \l "_Toc158574708"  a.	Option 2A 

  HYPERLINK \l "_Toc158574709"  b.	Option 2B 

  HYPERLINK \l "_Toc158574710"  3.	Baseline dates 

  HYPERLINK \l "_Toc158574711"  VI.	Significant Impact Levels (SILS) 

  HYPERLINK \l "_Toc158574712"  A.	Background on SILs 

  HYPERLINK \l "_Toc158574713"  1.	EPA’s guidance on SILs in the PSD
program 

  HYPERLINK \l "_Toc158574714"  B.	Legal Basis for SILs 

  HYPERLINK \l "_Toc158574715"  C.	Relationship of SILs to AQRVs 

  HYPERLINK \l "_Toc158574716"  D.	Proposed Options for PM2.5 SILs (for
PSD and NA-NSR) 

  HYPERLINK \l "_Toc158574717"  1.	Option 1 - Propose SILs using the
approach we proposed for PM10 in 1996 

  HYPERLINK \l "_Toc158574718"  2.	Option 2.  PM2.5 to PM10 emissions
ratio 

  HYPERLINK \l "_Toc158574719"  3.	Option 3.  PM2.5 to PM10 NAAQS ratio 

  HYPERLINK \l "_Toc158574720"  VII.	Significant Monitoring
Concentrations (SMCs) 

  HYPERLINK \l "_Toc158574721"  A.	Background on SMCs 

  HYPERLINK \l "_Toc158574722"  1.	Preconstruction monitoring and
itsit’s role in NSR program 

  HYPERLINK \l "_Toc158574723"  2.	History of SMC rules adopted by EPA 

  HYPERLINK \l "_Toc158574724"  B.	Legal Basis for SMCs 

  HYPERLINK \l "_Toc158574725"  C.	Proposed Options for PM2.5 SMC 

  HYPERLINK \l "_Toc158574726"  1.	Option 1.  Lowest detectable
concentration 

  HYPERLINK \l "_Toc158574727"  2.	Option 2.  PM2.5 to PM10 emissions
ratio 

  HYPERLINK \l "_Toc158574728"  3.	Option 3.  PM2.5 to PM10 NAAQS ratio 

  HYPERLINK \l "_Toc158574729"  D.	Correction of Cross References 

  HYPERLINK \l "_Toc158574730"  VIII.	Effective Date of the Final Rule,
SIP Submittal/Approval Deadlines and PM10 Revocation Deadline. 

  HYPERLINK \l "_Toc158574731"  A.	Option 1:  Increments promulgated
pursuant to section 166(a) of the Act. 

  HYPERLINK \l "_Toc158574732"  1.	Effective date of Final Rule 

  HYPERLINK \l "_Toc158574733"  2.	State Program 

  HYPERLINK \l "_Toc158574734"  B.	Option 2:  Increments promulgated
pursuant to section 166(f) of the Act. 

  HYPERLINK \l "_Toc158574735"  1.	Effective date of Final Rule 

  HYPERLINK \l "_Toc158574736"  2.	State Program 

  HYPERLINK \l "_Toc158574737"  3.	Federal Program 

  HYPERLINK \l "_Toc158574738"  C.	Revocation of the  PM10Increment 

  HYPERLINK \l "_Toc158574739"  D.	Transition Period 

  HYPERLINK \l "_Toc158574740"  E.	Effective Date for SILs and SMCs 

  HYPERLINK \l "_Toc158574741"  IX.	Statutory and Executive Order
Reviews 

  HYPERLINK \l "_Toc158574742"  A.	Executive Order 12866:  Regulatory
Planning and Review 

  HYPERLINK \l "_Toc158574743"  B.	Paperwork Reduction Act 

  HYPERLINK \l "_Toc158574744"  C.	Regulatory Flexibility Act 

  HYPERLINK \l "_Toc158574745"  D.	Unfunded Mandates Reform Act 

  HYPERLINK \l "_Toc158574746"  E.	Executive Order 13132:  Federalism 

  HYPERLINK \l "_Toc158574747"  F.	Executive Order 13175:  Consultation
and Coordination with Indian Tribal Governments 

  HYPERLINK \l "_Toc158574748"  G.	Executive Order 13045:  Protection of
Children from Environmental Health & Safety Risks 

  HYPERLINK \l "_Toc158574749"  H.	Executive Order 13211:  Actions that
Significantly Affect Energy Supply, Distribution, or Use 

  HYPERLINK \l "_Toc158574750"  I.	National Technology Transfer and
Advancement Act 

  HYPERLINK \l "_Toc158574751"  J.	Executive Order 12898: Federal
Actions to Address Environmental Justice in Minority Populations and
Low-Income Populations 

  HYPERLINK \l "_Toc158574752"  X.	Statutory Authority 

 

Overview of Proposed Regulations  

This proposal is the first step in the rulemaking process for
promulgating PM2.5 increments, SILs, and a SMC.  The purpose of this
proposed rulemaking is to develop the final elements that will aid
implementation of the PSD requirements program  for PM2.5.  When final,
these requirements elements proposed will supplement the upcoming final
NSR implementation rule for PM2.5.  Following final action on this
proposal and the PM2.5 implementation rule for NSR, the Federal PM2.5
NSR programs will no longer have to rely on the PM10 program as a
surrogate, as has been the practice under our existing guidance.  A
State implementing a NSR program in an EPA approved State Implementation
Plan (SIP) may continue to rely on the interim surrogate policy until we
approve a revised SIP addressing these requirements.

In this rulemaking, we1 are proposing several options for increments,
SILs and the SMC, respectively.

Summary of Proposed Options for Increments 

For the first option, we are proposing an identical approach to the
section 166 (a) through (d) approach that we established in the October
2005 NOx increment regulations.  The other two options (options 2A and
2B) are variations of the section 166(f) “Equivalent Increment”
approach, which we used to develop PM10 increments (substituting TSP
increments) in 1993.  The increment values resulting from these options
are We are proposing three sets of PM2.5 increments, based on several
approaches that are described in greater detail later in this preamble. 
For the first set (option 1), we are relying on an approach that treats
PM2.5 as a new pollutant.  This option follows our statutory authority
section 166(a) of the Act to develop increments for “pollutants for
which national ambient air quality standards are promulgated after the
date of enactment of this part….”  This is the same approach that we
used to establish NOx increment regulations on October 12, 2005 (70 FR
at 59586).  The second and third options (options 2A and 2B) rely on an
approach that we used in 1993 to promulgate PM10 increments in lieu of
the statutory increments for particulate matter following our
replacement of the then existing indicator for the PM NAAQS based on
total suspended particulate with a new indicator based on PM10.  (58 FR
31622, June 3, 1993.)  These two options represent variations of the
approach used under the authority of section 166(f) of the Act to
“substitute” PM10 increments for TSP increments.  The increment
values resulting from each of these three options are:

Option	Proposed Increments ((g/m3)	NAAQS ((g/m3)

	Class I	Class II	Class III



Annual	24-hr	Annual	24-hr	Annual	24-hr	Annual	24-hr

1	1	2	4	9	8	18	15	35

2A	1	2	4	9	8	18



2B	1	2	5	9	10	18





Summary of Proposed Options for SILs 

We are also proposing three options for SILs.  The first option utilizes
the same approach we proposed for PM10 in the 1996 NSR Reform proposal. 
For option 2, we are proposing to scale the PM10 SIL values by the ratio
of direct PM2.5 to direct PM10 emissions.  The PM2.5/PM10 emissions
ratio is the national average derived from the 2001 extrapolation of the
1999 National Emissions Inventory. For option 3, we are proposing to
scale the PM10 SIL values by the ratio of the PM2.5 NAAQS to the PM10
NAAQS. The SIL values resulting from each of these options are:

Option	Proposed SILs ((g/m3)

	Class I	Class II	Class III

	Annual	24-hr	Annual	24-hr	Annual	24-hr

1	0.04	0.08	1.0	5.0	1.0	5.0

2	0.16	0.24	0.8	4.0	0.8	4.0

3	0.06	0.07	0.3	1.2	0.3	1.2



Summary of Proposed Options for the PM2.5 SMC 

The first option we are proposing for the SMC is the “Lowest Detection
Concentration” or LDC approach that we used for establishing the SMC
for TSP and PM10.  For option 2, we are proposing to scale the PM10 SMC
value by the ratio of direct PM2.5 to direct PM10 emissions.  The
PM2.5/PM10 emissions ratio is the national average derived from the 2001
extrapolation of the 1999 National Emissions Inventory. For option 3, we
are proposing to scale the PM10 SMC value by the ratio of the PM2.5
NAAQS to the PM10 NAAQS. The proposed SMC values for each of these
options for the 24-hr averaging period are:

Option 1 – 10 µg/m3

Option 2 – 7.9 µg/m3

Option 3 – 2.3 µg/m3	

Background 

PSD Program

The NSR provisions of the Act are a combination of air quality planning
and air pollution control technology program requirements for new and
modified stationary sources of air pollution.  In brief, section 109 of
the Act requires us to promulgate primary NAAQS to protect public health
and secondary NAAQS to protect public welfare.  Once we have set these
standards, States must develop, adopt, and submit to us for approval
SIPs that contain emission limitations and other control measures to
attain and maintain the NAAQS and to meet the other requirements of
section 110(a) of the Act.    SEQ CHAPTER \h \r 1 Part C of title I of
the Act contains the requirements for a component of the major new
source review (NSR) program known as the PSD program.  This program sets
forth procedures for the preconstruction review and permitting of new
and modified major 

stationary sources of air pollution locating in areas meeting the NAAQS
(“attainment” areas) and areas for which there is insufficient
information to classify an area as either attainment or nonattainment
(“unclassifiable” areas).  Most states have SIP-approved
preconstruction permit (major NSR) programs.  The Federal PSD program at
40 CFR 52.21 applies in some States that lack a SIP-approved permit
program, and in Indian Country.2   The applicability of the PSD program
to a major stationary source must be determined in advance of
construction and is a pollutant specific determination.  Once a major
source is determined to be subject to the PSD program (PSD source),
among other requirements, it must undertake a series of analyses to
demonstrate that it will use the best available control technology
(BACT) and will not cause or contribute to a violation of any NAAQS or
incremental ambient pollutant concentration increase (increment).  In
cases where the source’s emissions may adversely affect an area
classified as a Class I area, additional review is conducted to protect
the increments and special attributes of such an area defined as “air
quality related values.”

As part of the analysis of air quality impacts to determine compliance
with the NAAQS and increment, the permit applicant and reviewing
authority may compare the source’s impacts for a pollutant with the
corresponding SIL for that pollutant to show that a cumulative air
quality impacts analysis is not necessary.  Similarly, the permit
applicant and reviewing authority may use the corresponding SMC for that
pollutant to determine if pre-application site-specific ambient
monitoring data is needed to conduct the air quality analysis.

  SEQ CHAPTER \h \r 1 When the permitting authority reaches a
preliminary decision to authorize construction of each proposed major
new source or major modification, it must provide notice of the
preliminary decision and an opportunity for comment by the general
public, industry, and other persons that may be affected by the
emissions of the major source or major modification.  After considering
these comments, the permitting authority may issue a final determination
on the construction permit in accordance with the PSD regulations.  

History of PM NAAQS 

TSP and PM10 NAAQS

The EPA initially established NAAQS for particulate matter in 1971,
measured by the TSP indicator.  Based on the size of the particles
collected by the “high-volume sampler,” which was the reference
method for determining ambient concentrations, TSP included all PM up to
a nominal size of 25 to 45 micrometers.  We established both annual and
24-hour NAAQS for TSP.

On July 1, 1987, we promulgated new NAAQS for particulate matter in
which we changed the indicator from TSP to PM10, the latter including
particles with a mean aerodynamic diameter less than or equal to 10
micrometers.  These smaller particles are the subset of inhalable
particles small enough to penetrate to the thoracic region (including
the tracheobronchial and alveolar regions) of the respiratory tract
(referred to as thoracic particles).  We established annual and 24-hour
NAAQS for PM10, and revoked the NAAQS for TSP.  (52 FR 24634). 

PM2.5 NAAQS

On July 18, 1997, we again revised the NAAQS for particulate matter in
several respects.  While we determined that the NAAQS should continue to
focus on particles less than or equal to 10 micrometers in diameter, we
also determined that the fine and coarse fractions of PM10 should be
considered separately.  We established new annual and 24-hour NAAQS for
PM2.5 (referring to particles with a nominal mean aerodynamic diameter
less than or equal to 2.5 micrometers) as the indicator for fine
particles.  Our 1997 rules also modified the PM10 NAAQS for the purpose
of regulating the coarse fraction of PM10 (referred to as thoracic
coarse particles or coarse-fraction particles; generally including
particles with a nominal mean aerodynamic diameter greater than   2.5
micrometers and less than or equal to 10 micrometers, or PM10-2.5),
however this part 

of the action was vacated during subsequent litigation, leaving the
pre-existing 1987 PM10 NAAQS in place (62 FR 38652).  

Revised PM2.5 and PM10 NAAQS  

On October 17, 2006, we promulgated revisions to the NAAQS for PM2.5 and
PM10 with an effective date of December 18, 2006 (71 FR 61144).  We
lowered the 24-hour NAAQS for PM2.5 from 65 micrograms per cubic meter
((g/m3) to 35 (g/m3, and retained the existing annual PM2.5 NAAQS of 15
(g/m3.  In addition, we retained the existing PM10 24-hour NAAQS of 150
(g/m3, and revoked the annual PM10 NAAQS (previously set at 50 (g/m3). 

Implementation of NSR for PM2.5

	

After we established new annual and 24-hour NAAQS for PM2.5 (referring
to particles with a nominal mean aerodynamic diameter less than or equal
to                      2.5 micrometers) as the indicator for fine
particles in July 1997, we issued a guidance document “Interim
Implementation for the New Source Review Requirements for PM2.5,” John
S. Seitz, Director, Office of Air Quality Planning and Standards, EPA,
October 23, 1997.  As noted in that guidance, section 165 of the Act
implies that PSD requirements become effective for a new NAAQS upon the
effective date of the NAAQS.           Section 165(a)(1) of the Act
provides that no new or modified major source may be constructed without
a PSD permit that meets all of the section 165(a) requirements with
respect to the regulated pollutant.  Moreover, section 165(a)(3)
provides that the emissions from any such source may not cause or
contribute to a violation of any increment or NAAQS.  Also, section
165(a)(4) requires BACT for each pollutant subject to PSD regulation. 
The 1997 guidance stated that sources would be allowed to use
implementation of a PM10 program as a surrogate for meeting PM2.5 NSR
requirements until certain difficulties were resolved.  These
difficulties included the lack of necessary tools to calculate the
emissions of PM2.5 and related precursors, the lack of adequate modeling
techniques to project ambient impacts, and the lack of PM2.5 monitoring
sites.  

On April 5, 2005, we issued a guidance document entitled
“Implementation of New Source Review Requirements in PM-2.5
Nonattainment Areas,” Stephen D. Page, Director, Office of Air Quality
Planning and Standards, EPA. This memorandum provides guidance on the
implementation of the nonattainment major NSR provisions in PM2.5
nonattainment areas in the interim period between the effective date of
the PM2.5 NAAQS designations (April 5, 2005) and when we promulgate
regulations to implement nonattainment major NSR for the PM2.5  NAAQS. 
In addition to affirming the continued use of the John S. Seitz guidance
memo in PM2.5 attainment areas, this memo recommends that until we
promulgate the PM2.5 major NSR regulations, States should use a PM10 
nonattainment major NSR program as a surrogate to address the
requirements of nonattainment major NSR for the PM2.5 NAAQS.

On November 1, 2005, we proposed a rule to implement the PM2.5 NAAQS,
including proposed revisions to the NSR program.  Upon finalization of
that rule, States that accept delegation of the Federal PSD program in
40 CFR 52.21 would implement the final rule beginning on its effective
date.  For those States with EPA-approved PSD programs, we proposed to
continue the 1997 NSR guidance to use PM10 as a surrogate for PM2.5, but
only during the SIP development period.  We also indicate in that
proposal that we will develop increments, SILs, and SMC in a separate
rulemaking – i.e. this proposed rulemaking.  In several comments on
the proposed PM2.5 implementation rule, State and local reviewing
authorities urged EPA to expedite promulgation of PM2.5 increments,
SILs, and SMC to enable them to implement an independent PM2.5 PSD
program. Since there was an interim surrogate NSR program in place, EPA
decided to first promulgate the non-NSR part of the implementation rule
(including attainment demonstrations, designations, control measures
etc.) – which was promulgated on April 25, 2007.  The NSR part of the
implementation rule is anticipated to be promulgated in September 2007. 
Additionally, once this proposed rulemaking is finalized, States will be
able to fully implement a PM2.5 NSR program.

Background on Implementation of PSD Increments

Under section 165(a)(3) of the Act, a PSD permit applicant must
demonstrate that emissions from the proposed construction and operation
of a facility ‘‘will not cause, or contribute to, air pollution in
excess of any (A) maximum allowable increase or maximum allowable
concentration for any pollutant….’’ 42 U.S.C. 7475(a)(3).  The
“maximum allowable increase” of an air pollutant that is allowed to
occur above the applicable baseline concentration for that pollutant is
known as the PSD increment.  By establishing the maximum allowable level
of ambient pollutant concentration increase in a particular area, an
increment defines ‘‘significant deterioration.’’

For PSD baseline purposes, a baseline area for a particular pollutant
emitted from a source includes the attainment or unclassifiable area in
which the source is located as well as any other attainment or
unclassifiable area in which the source’s emissions of that pollutant
are projected (by air quality modeling) to result in an ambient
pollutant increase of at least 1 μg/m3 (annual average).  See, e.g., 40
CFR 52.21(b)(15)(i).  Once the baseline area is established, subsequent
PSD sources locating in that area need to consider that a portion of the
available increment may have already been consumed by previous emissions
increases. 

Three dates related to the PSD baseline concept are important in
calculating the amount of increment consumed by pollutant emissions from
the major source undergoing PSD review and other applicable emissions
increases and decreases in a particular baseline area.  In general, the
submittal date of the first complete PSD permit application in a
particular area is the operative “baseline date.”3  On or before the
date of the first complete PSD application, emissions generally are
considered to be part of the baseline concentration, except for certain
emissions from major stationary sources, as explained in the following
discussion of baseline dates.  Most emissions increases that occur after
the baseline date will be counted toward the amount of increment
consumed.  Similarly, emissions decreases after the baseline date
restore or expand the amount of increment that is available.  

In practice, three dates related to the PSD baseline concept are
important in understanding how to calculate the amount of increment
consumed—(1) trigger date; (2) minor source baseline date; and (3)
major source baseline date.  Chronologically, the first relevant date is
the trigger date.  The trigger date, as the name implies, triggers the
overall increment consumption process nationwide.  Specifically, this is
a fixed date which must occur before the minor source baseline date can
be established for the pollutant-specific increment in a particular
attainment area.  See, e.g., 40 CFR 52.21(b)(14)(ii).  For PM and SO2,
Congress defined the applicable trigger date as August 7, 1977 – the
date of the 1977 amendments to the Act when the original statutory
increments were established by Congress.  For NO2, we selected the
trigger date as February 8, 1988 – the date on which we proposed
increments for NO2.  See 53 FR 40656, 40658; October 17, 1988.  In this
action, as described later, we are proposing to add a new trigger date
for purposes of calculating the new PM2.5 increments.

In actuality, there are two baseline dates that are related to the
determination of how much increment is being consumed in a particular
baseline area.  These two remaining dates—“minor source baseline
date” and “major source baseline date”, as described later, are
necessary to properly account for the emissions that are to be counted
toward increment consumed following the national trigger date, in
accordance with the statutory definition of “baseline concentration”
in section 169(4) of the Act.  The statutory definition provides that
the baseline concentration of a pollutant for a particular baseline area
is generally the air quality at the time of the first application for a
PSD permit in the area.  Consequently, any increases in actual emissions
occurring after that date (with some possible exceptions that we will
discuss later) would be considered to consume the applicable PSD
increment.  However, the statutory definition in section 169(4) also
provides that “[E]missions of sulfur oxides and particulate matter
from any major emitting facility on which construction commenced after
January 6, 1975 shall not be included in the baseline and shall be
counted in pollutant concentrations established under this part.”  

To make this distinction between the date when emissions changes in
general (i.e., from both major and minor sources) affect the increment
and the date when emissions resulting from the construction at a major
stationary source consume the increment, we established the terms
“minor source baseline date” and “major source baseline date,”
respectively.  See 40 CFR 51.166(b)(14) and 52.21(b)(14).  Accordingly,
the “minor source baseline date” is the date on which the first
complete application for a PSD permit is filed in a particular area. 
Any change in actual emissions after that date affects the PSD increment
for that area.  

The “major source baseline date” is the date after which actual
emissions increases associated with construction at any major stationary
source affect the PSD increment.  In accordance with the statutory
definition of “baseline concentration,” the PSD regulations define a
fixed date to represent the major source baseline date for each
pollutant for which an increment exists.  Congress defined the major
source baseline date for the statutory increments for PM and SO2 as
January 6, 1975.  For the NO2 increments, which we promulgated in 1988
under our authority to establish an increment system under section
166(a) of the Act, the major source baseline date we selected is
February 8, 1988 – the date on which we proposed increments for NO2. 
53 FR 40656.  In this action, as described later, we are proposing to
add a new major source baseline date for PM2.5.

The PSD regulations set out the third date that is relevant to the PSD
baseline concept.  These regulations provide that the earliest date on
which the minor source baseline date can be established is the date
immediately following the “trigger date” for the pollutant-specific
increment.  See, e.g., 40 CFR 52.21(b)(14)(ii).  For PM and SO2,
Congress defined the applicable trigger date as August 7, 1977 – the
date of the 1977 amendments to the Act when the original statutory
increments were established by Congress.  For NO2, we selected the
trigger date as February 8, 1988 – the date on which we proposed
increments for NO2.  See 53 FR 40656, 40658; October 17, 1988.

Once the minor source baseline date associated with the first PSD permit
application for a proposed new major stationary source or major
modification in an area is established, the new emissions from that
source consume a portion of the increment in that area, as do any
subsequent actual emissions increases that occur from any new or
existing source in the area.  When the maximum pollutant concentration
increase defined by the increment has been reached, additional PSD
permits cannot be issued until sufficient amounts of the increment are
“freed up” via emissions reductions that may occur voluntarily,
e.g., via source shutdowns, or via control requirements imposed by the
reviewing authority.  Moreover, the air quality in a region cannot
deteriorate to a level in excess of the applicable NAAQS, even if all
the increment has not been consumed.  Therefore, new or modified sources
located in areas where the air pollutant concentration is near the level
allowed by the NAAQS may not have full use of the amount of pollutant
concentration increase allowed by the increment.	

Under EPA guidance, the actual increment analysis that a proposed new or
modified source undergoing PSD review must complete depends on the area
impacted by the source’s new emissions.  We have also provided
approved air quality models and guidelines for sources to use to project
the air quality impact of each pollutant (over each averaging period)
for which an increment analysis must be done.  In addition, we
established significant impact levels for each pollutant under the
nonattainment major NSR program that have also been used under the PSD
program to identify levels below which the source’s modeled impact is
regarded as de minimis.  See 40 CFR 51.165(b) and part 51, appendix S,
section III.A.  In the event that a source’s modeled impacts of a
particular pollutant are below the applicable significant impact level
at all ambient air locations modeled, i.e., de minimis everywhere, EPA
policy provides that no further modeling analysis is required for that
pollutant.  Our policy is that when a preliminary screening analysis
based on the significant impact level is sufficient to demonstrate that
the source’s emissions will not cause or contribute to a violation of
the increment, there is no need for a full impacts analysis involving a
cumulative evaluation of the emissions from the proposed source and
other sources affecting the area. 

Within the impact area of a source that does have a significant impact,
increment consumption is calculated using the source’s proposed
emissions increase, along with other emissions increases or decreases of
the particular pollutant from sources in the area which have occurred
since the minor source baseline date established for that area.  (For
major sources, emissions increases or decreases that have occurred since
the major source baseline date consume or expand increment.)  Thus, an
emissions inventory of sources whose emissions consume or expand the
available increment in the area must be compiled.  The inventory
includes not only sources located directly in the impact area, but
sources outside the impact area that affect the air quality within the
impact area.  

	The inventory of emissions includes emissions from increment-affecting
sources at two separate time periods – the baseline date and the
current period of time.  For each source that was in existence on the
relevant baseline date (major source or minor source), the inventory
includes the source’s actual emissions on the baseline date and
itsit’s current actual emissions.  The change in emissions over these
time periods represents the emissions that consume increment (or, if
emissions have gone down, expand the available increment).  For sources
constructed since the relevant baseline date, all their current actual
emissions consume increment and are included in the inventory.  

When the inventory of emissions has been compiled, computer modeling is
used to determine the change in ambient concentration that will result
from these emissions when combined with the proposed emissions increase
from the new major source or major modification that is undergoing PSD
review.  The modeling has generally been guided by the “Guideline on
Air Quality Models” (40 CFR part 51, appendix W), which  includes
provisions on air quality models and the meteorological data input into
these models.  The model output (expressed as a change in concentration)
for each relevant averaging period is then compared to the corresponding
allowable PSD increment.  

Historical Approaches for Developing Increments 

Congressional enactment of increments for PM and SO2.

Congress established the first increments defining significant
deterioration of air quality in the 1977 Amendments to the Act.  These
amendments to the Act, among other things, added subpart C to title I,
setting out the requirements for PSD.  In section 163, Congress included
numerical increments for particulate matter and sulfur dioxide (SO2) for
Class I, II, and III areas. 

The three area classificationses are part of the increment system
originally established by Congress.  Congress designated Class I areas
(including certain national parks and wilderness areas) as areas of
special national concern, where the need to prevent deterioration of air
quality is the greatest.  Consequently, the allowable level of
incremental change is the smallest relative to the other area classes,
i.e., most stringent, in Class I areas.  The increments of Class II
areas are larger than those of Class I areas and allow for a moderate
degree of emissions growth.  For future redesignation purposes, Congress
defined as Class III any existing Class II area for which a State may
desire to promote a higher level of industrial development (and
emissions growth).  Thus, Class III areas are allowed to have the
greatest amount of pollutant increase of the three area classes while
still achieving the NAAQS.  There have been no Class III redesignations
to date.

In establishing these PSD increments, Congress used the then-existing
NAAQS for those pollutants as the benchmark for determining what
constitutes “significant deterioration.”  Congress established the
increments for particulate matter as a percentage of the then-existing
particulate matter NAAQS.  At the time the Act was amended in 1977, the
NAAQS for particulate matter were expressed in terms of ambient
concentrations of total suspended particulate (TSP).  Thus, EPA
interpreted the statutory increments for particulate matter using the
same ambient “indicator.”   

EPA’s promulgation of increments for NO2 and PM10

Congress also provided authority for EPA to promulgate additional
increments and to update the original particulate matter increments
created by statute.  EPA has promulgated two regulations pursuant to
this authority. 

Increments for NOx using the “contingent safe harbor” approach under
section 166(a) of the Act.

As enacted in 1977, subpart C of the Act also included sections 166(a)
through 166(e), which set out requirements related to increments for
other pollutants.          Section 166(a) requires EPA to develop
regulations to prevent the significant deterioration of air quality due
to emissions of certain named pollutants, and to develop such
regulations for any pollutants for which NAAQS are subsequently
promulgated.  Section 166(b) prescribes timelines for the effective date
of such regulations, and for corresponding SIP submittals and EPA
approvals.  Specifically, regulations, including increments, developed
pursuant to section 166(a) become effective one year after the date of
promulgation, and State plan revisions containing the new regulations
are to be submitted to EPA for review within 21 months of promulgation. 
The same provision then calls for EPA’s approval or disapproval of the
revised plan within 25 months of promulgation.  The lLegislative
Hhistory indicates that this one-year delay before the new PSD
requirements, including the new increments, become effective is to allow
Congress an opportunity to review them before States are required to
implement them.  (cite)  Section 166(c) and (d) set forth criteria and
goals that such regulations must meet.  

Based on section 166 of the Act, on October 17, 1988, EPA promulgated
increments for nitrogen dioxide (NO2) to prevent significant
deterioration of air quality due to emissions of  NOx (53 FR 40656). 
The EPA based these increments on percentages of the NAAQS in the same
way that Congress derived the statutory increments for PM and SO2. 
Those NO2 increments were challenged in 1988 by the Environmental
Defense Fund (now Environmental Defense, or “ED”) when ED filed suit
in the U.S. Court of Appeals for the District of Columbia Circuit
against the Administrator (Environmental Defense Fund, Inc. v. Reilly,
No. 88–1882).  Environmental Defense successfully argued that we
failed to sufficiently consider certain provisions in section 166 of the
Act.  The court remanded the case to EPA “to develop an interpretation
of section 166 that considers both subsections (c) and (d), and if
necessary to take new evidence and modify the regulations.”  See
Environmental Defense Fund v. EPA, 898 F.2d 183, 190 (D.C. Cir. 1990). 
Section 166(c) of the Act requires the PSD regulations to, among other
things, meet the goals and purposes set forth in sections 101 and 160 of
the Act.  Section 166(d) requires these regulations be at least as
effective as the increments established for particulate matter (in the
form of TSP) and SO2 in    section 163 of the Act. The court considered
the NO2 increment values determined using the percentage-of-NAAQS
approach as “safe harbor” increments which met the requirements of
section 166(d) of the Act.  However, the court also determined that
EPA’s reliance on such increment levels was contingent upon our
completing the analyses required under section 166(c), which provided
that the final increment values must address the goals of sections 101
and 160 of the Act to protect public health and welfare, parks, and air
quality related values (AQRVs) and to ensure economic growth.

In response to the court’s decision, we proposed rulemaking on
increments for NOx on February 23, 2005 (70 FR 8880) and finalized the
rules on October 12, 2005    (70 FR 59582).  In the final rule, we
established our policy on how to interpret and apply the requirements of
sections 166(c) and (d) of the Act.  In accordance with the court
ruling, we conducted further analyses (considering the health and
welfare effects of NOx) and concluded that the existing NO2 increments
were adequate to fulfill the requirements of section 166(c).  See 70 FR
59586 for our detailed analysis of how pollutant regulations satisfy the
requirements of section 166 of the Act.  Hence, we retained the existing
NO2 increments along with other parts of the existing framework of
pollutant-specific PSD regulations for NOx.  We also amended the
requirements of 40 CFR 51.166 to make it clear that States may seek EPA
approval of SIPs that utilize a different approach than EPA used to
establish these NO2 increments.  To receive our approval of an
alternative program, a State must demonstrate that itsit’s program
satisfies the requirements of    sections 166(c) and 166(d) of the Act
and prevents significant deterioration of air quality from emissions of
NOx.4  

Increments for PM10 using “equivalent substitution” approach under
section 166(f).

On October 5, 1989, we proposed new PM10 increments.  See 54 FR 41218. 
Although section 163 did not expressly define the existing statutory
increments for PM in terms of a specific indicator, EPA reasoned that
Congress’ knowledge that TSP was the indicator for the PM NAAQS, and
that the TSP standards were the starting point for the increments levels
when the increments were established in 1977, meant that TSP was also
the appropriate measure for the PM increments in section 163.  As a
consequence, EPA believed that the statutory PM increments could not
simply be administratively redefined as PM10 increments, retaining the
same numerical values, following the revision of the PM NAAQS.  Rather,
we stated our belief that with the promulgation of the PM10 NAAQS, EPA
had both the responsibility and the authority under sections 166 and 301
of the Act to promulgate new increments for particulate matter to be
measured in terms of PM10.  We further concluded that promulgating PM10
increments to replace, rather than supplement, the statutory TSP
increments under section 163 represented the most sensible approach for
preventing significant deterioration with respect to particulate matter.
 See 54 FR 41220-41221.

We promulgated PM10 increments to replace the existing TSP increments on
  June 3, 1993 (58 FR 31622).  In the interim between proposal and
promulgation, Congress enacted the 1990 Act Amendments.  As part of
these Act Amendments, Congress amended section 166 to add a new section
166(f).  This section specifically authorized EPA to substitute PM10
increments for the existing section 163 particulate 

matter increments based on TSP, provided that the substituted increments
are “of equal stringency in effect” as the section 163 increments.

  Thus, we were able to replace the TSP increments under section 163 of
the Act using PM10 increments based directly on the newly enacted
authority under section 166(f) of the Act.  In the PM10 rule, we
maintained the existing baseline dates and baseline areas for
particulate matter that had been previously established using the TSP
indicator.  Also as proposed, we promulgated PM10 increments developed
based on an approach we called the “equivalent to statutory
increments” approach.  Under this approach, we used the original TSP
increments as a benchmark for calculating the PM10 increments, thereby
retaining roughly the same limitations on future deterioration of air
quality as was allowed under the TSP increments.  In using this
approach, we considered the historical consumption of TSP increment by a
sample population of permitted PSD sources, and then determined the PM10
increments for each area classification and averaging time that would
provide approximately the same percentage of PM10 increment consumption,
on average, by the same population of sources.  Then, all future
calculations of increment consumption after the PM10 implementation date
would be based on PM10 emissions.  See 58 FR 31622 and 31625.

EPA’s Interpretation of Section 166 of the Clean Air Act 

Which Criteria In Section 166 Should EPA Use to Develop Increments for
PM2.5?

The EPA interprets section 166 of the Act to give the Administrator the
discretion to use either the “contingent safe harbor” approach or
the “equivalent substitution” approach to establish increments for
PM2.5.  Since sections 166(a) and section 166(f) contain or incorporate
different criteria for establishing PSD regulations containing
increments or other measures, the interpretation that EPA chooses to
follow could have an impact on the increments or other measures that EPA
adopts.  Regulations promulgated under section 166(a) must be based on
the criteria in section 166(c) and 166(d).  42 U.S.C. 7476(c)-(d). 
Regulations promulgated under section 166(f) must “be of equal
stringency in effect as those specific in the provisions for which they
are substituted.”  42 U.S.C. 7476(f).  Furthermore, section 166(a)
calls broadly for regulations, which may include increments, whereas
section 166(f) addresses only increments. 

Section 166(a) provides authority for EPA to promulgate additional
pollutant-specific PSD regulations, which may include increments, for
the pollutants specifically identified in that provision plus additional
pollutants for which EPA may promulgate a 

NAAQS after a specific date.  42 U.S.C. 7476(a).  The last sentence of
section 166(a) provides the following:  

In the case of pollutants for which national ambient air quality
standards are promulgated after August 7, 1977, [the Administrator]
shall promulgate such regulations not more than 2 years after the date
of promulgation of such standards.

Since EPA promulgated an additional NAAQS for PM, based on the PM2.5
indicator, in 1997, one potential approach for developing increments for
PM2.5 is for EPA to promulgate these increments under the authority of
section 166(a).  Under this approach, EPA would promulgate increments or
other measures for PM2.5 that satisfy the standards set forth in
subsections (c) and (d) of section 166, as interpreted by EPA in itsour
recent rulemaking for nitrogen oxides.  

However, in light of the provisions in section 163 and 166(f) of the Act
that address increments for TSP and PM10, respectively, there is some
ambiguity on the question of the legal authority EPA should rely upon to
establish increments for PM2.5.   In 1993, EPA construed section 166(f)
to establish the sole criteria for promulgation of a new particulate
matter increment and thus did not base itsour final  PM10 increment on
section 166(a) of the Act.  Considering sections 163, 166(a), and 166(f)
together, an alternative interpretation of these provisions might be
that Congress intended that section 163 and 166(f) alone cover
particulate matter.    Under this reading, EPA would promulgate
additional increments for particular matter based on the section 163
increments and 166(f) of the Act, which are the only provisions that
specifically mention particulate matter and PSD increments.  However, as
discussed later, it may also be possible to read sections 166(a) and
166(f) in harmony. Thus, we propose to adopt one of   the following
legal theories to support promulgation of increments for PM2.5 using
either of the two methods that EPA used in prior rules to develop PSD
increments. 

Support for “contingent safe harbor” approach for PM2.5 under
section 166(a)

The EPA believes it is permissible to interpret section 166(a) to apply
to PM2.5.  Although EPA has generally characterized the NAAQS for PM2.5
as a NAAQS for a new indicator of particulate matter, EPA did not
replace the PM10 NAAQS with the NAAQS for PM2.5 in 1997.  Rather, EPA
established an additional NAAQS for PM2.5 as if it were a new pollutant,
even though EPA had already developed air quality criteria for
particulate matter generally.  Thus, for purposes of section 166(a), the
addition of a 

NAAQS for PM2.5 is functionally the same as establishing a NAAQS for an
additional pollutant after 1977.  

We read section 166(a) to authorize EPA to promulgate pollutant-specific
PSD regulations meeting the requirements of sections 166(c) and 166(d)
for any pollutant for which EPA promulgates a NAAQS after 1977. Most of
the pollutants identified in section 166(a) (nitrogen oxides,
photochemical oxidants, carbon monoxide) are pollutants for which EPA
had established NAAQS in 1977 when Congress adopted section 166 of the
Act.  There was no need for Congress to list other criteria pollutants,
sulfur dioxide and particular matter, in section 166(a) because Congress
had already established increments for these pollutants in section 163
of the Act.  In addition to requiring regulations for the enumerated
pollutants, Congress clearly intended to authorize EPA to establish
additional pollutant-specific PSD regulations, potentially containing
increments, for any additional pollutants for which EPA promulgated a
NAAQS under section 109 of the Act.  Furthermore, because the Act refers
to pollutants for which EPA promulgates NAAQS after 1977, and does not
use the phrase “additional pollutants” we believe that Section
166(a) provides authority for EPA to promulgate new increments after
revising an existing NAAQS (including one first promulgated before
1977), when we find that such action is appropriate.

In our 1989 proposal on the PM10 increments, EPA construed section
166(a) to apply to PM10, even though EPA regarded PM10 to be a new
indicator for particulate matter.  58 FR 31623-24.  Thus, before the
adoption of section 166(f), EPA read the language of section 166(a) to
apply to the promulgation of increments using a new indicator for
particulate matter and did not limit the application of section 166(a)
to wholly new criteria pollutants.  Similarly, in the current proposal,
EPA believes it can continue to interpret section 166(a) to apply to the
promulgation of an additional increment for a new indicator of an
existing criteria pollutant since EPA promulgated a NAAQS for a new
indicator of that pollutant after 1977.  

Although EPA ultimately applied the standard in section 166(f) as the
sole basis for itsour PM10 increments in 1993, that provision does not
necessarily govern the situation EPA currently faces with PM2.5.  One
could read section 166(f) to address only EPA’s authority to
substitute new particulate matter increments for the
congressionally-established increments for TSP rather than the distinct
issue now faced by EPA concerning the promulgation of additional
particulate matter increments for PM2.5 without necessarily revoking
existing increments.  Furthermore, the language in section 166(f) could
be read to limit the scope of this provision to only increments using
the PM10 indicator.   Thus, section 166(f) may not necessarily be
applicable to the substitution of PM10 increments with PM2.5 increments.
 

The EPA believes that section 166(a) could apply to the adoption of new
increments, without the revocation of existing increments.  As reflected
in the 2005 increments rule for  NOx and the court decision in EDF v.
EPA, when sections 166(a)-(d) apply, EPA is obligated to evaluate which
indicator or form should be used in our pollutant-specific PSD
regulations to meet these requirements in the Act.  Based on this
interpretation, we are proposing to use a contingent safe harbor
approach (option 1) that involves first deriving increment values based
on percentage of the NAAQS and then evaluating whether alternative
increments or additional measures are necessary to meet the criteria in
section 166(c).  

Support of “equivalent substitution” approach for PM2.5 under
section 166(f)

 The EPA believes it is also permissible for the Agency to construe
section 166(f) as a continuing grant of authority for the Administrator
to update the increments for particular matter whenever the
Administrator decides to adopt a new form of particular matter as the
indicator for the NAAQS.  Although the terms of section 166(f) of the
Act appear to address PM10 alone, the overall intent of this provision
was to clarify that EPA had the authority to update the original TSP
increments to reflect changes in the NAAQS indicator.   Language
describing the PM10 indicator was used in the Act because this was the
indicator for particulate matter that EPA was seeking to incorporate
into the PSD program at the time of the 1990 Amendments when section
166(f) was adopted.  However, we believe it is reasonable to conclude
that Congress intended to authorize 

EPA to continue updating the particular matter increments contained in
section 163 if EPA promulgated a NAAQS for another appropriate indicator
for particular matter.  

We believe EPA is  authorized to promulgate increments for PM2.5 as a
substitute for the PM10 increments, as well as the original TSP
increments, so long as the new increments for PM2.5 are of “equal
stringency in effect as those specified in the provisions for which they
are substituted.”  42 U.S.C. 7476(f).  Based on this interpretation,
we propose two approaches (options 2A and 2B discussed later) for
developing PM2.5 increments that would meet the “equal stringency in
effect” standard contained in section 166(f). 

While we believe section 166(f) may be construed to provide continuing
authority to “update” the increments for particulate matter to
conform to the NAAQS, section 166(f) describes a process in which EPA
would “substitute” one particulate matter increment for another. 
The language in section 166(f) does not address whether EPA may adopt
additional increments for other particulate matter indicators while
retaining the existing particulate matter increments.  In contrast,
section 166(a) does contain language addressing the promulgation of PSD
regulations when EPA adds to itsthe suite of NAAQS.  Thus, we construe
section 166(a) to have the closest connection to the task of adding,
rather than the substituting or replacing, PSD increments for
particulate matter.  As a result, for purposes of establishing the
proposed 24-hr PM2.5 increments, we propose only one option – using
the contingent safe harbor approach described in option 1 -- because we
are not proposing to replace the existing 24-hour PM10 increment with a
new 24-hour PM2.5 increment, since we have retained the 24-hr PM10
NAAQS. However, we also seek comment on whether we could rely on section
166(f) to promulgate the 24-hr PM2.5 increments using the same
methodology as for the annual PM2.5 increments described later, even
though the 24-hr PM10 NAAQS is not being revoked.

Requirements of Sections 166(a)-(d) of the Clean Air Act

If we determine that section 166(a) applies to PM2.5, we propose to
follow the interpretation of sections 166(a)-(d) that we adopted in our
most recent increments rule 

for NOx,.  This interpretation was upheld in a recent court decision
E.D. v. EPA, No. 05-1446 (June 19, 2007 DC Cir.).  We summarize the key
elements of this interpretation later, but a more detailed discussion
can be found in our October 2005 final rule for NOx.  70 FR 59582.  

In   SEQ CHAPTER \h \r 1 section 166(a) of the Act, Congress directed
EPA to develop pollutant-specific regulations to prevent significant
deterioration of air quality.  Congress further specified 

that such regulations meet the following requirements set forth in
sections 166(c) and 166(d):

	(c)  Such regulations shall provide specific numerical measures against
which permit applications may be evaluated, a framework for stimulating
improved control technology, protection of air quality values, and
fulfill the goals and purposes set forth in section 101 and section 160.

	(d)  The regulations * * * shall provide specific measures at least as
effective as the increments established in section 163 [for SO2 and PM]
to fulfill such goals and purposes, and may contain air quality
increments, emission density requirements, or other measures.

The goals and purposes of the PSD program set forth in section 160 are
as follows:

	(1)  to protect public health and welfare from any actual or potential
adverse effect which in the Administrator’s judgment may reasonably be
anticipate[d] to occur from air pollution or from exposures to
pollutants in other media, which pollutants originate as emissions to
the ambient air, notwithstanding attainment and maintenance of all
national ambient air quality standards;

	(2)  to preserve, protect, and enhance the air quality in national
parks, national wilderness areas, national monuments, national
seashores, and other areas of special national or regional natural,
recreational, scenic, or historic value;

	(3) to insure that economic growth will occur in a manner consistent
with the preservation of existing clean air resources;

	(4)  to assure that emissions from any source in any State will not
interfere with any portion of the applicable implementation plan to
prevent significant deterioration of air quality for any other State;
and

	(5)  to assure that any decision to permit increased air pollution in
any area to which this section applies is made only after careful
evaluation of all the consequences of such a decision and after adequate
procedural 

opportunities for informed public participation in the decisionmaking 
process.

  SEQ CHAPTER \h \r 1  As described in our 2005 rule for NOx, EPA’s
interpretation of these provisions is grounded on five central elements.
 First, we read section 166 of the Act to direct EPA to conduct a
holistic analysis that considers how a complete system of regulations
will collectively satisfy the applicable criteria, rather than
evaluating one individual part of a regulatory scheme in isolation. 
Second, we use a “contingent safe harbor” approach which calls for
EPA to first establish the minimum level of effectiveness necessary to
satisfy section 166(d) and then to conduct further analysis to determine
if additional measures are necessary to fulfill the requirements of
section 166(c).  Third, we interpreted section 166(c) of the Act to
identify eight statutory factors that EPA must apply when promulgating
pollutant-specific regulations to prevent significant deterioration of
air quality.  Fourth, we interpreted the requirements to simultaneously
satisfy each of these factors to establish a balancing test in cases
where certain objectives may be at odds with each other.  Fifth, we
recognized that the requirements of section 166 may be satisfied by
adopting other measures besides an increment and that EPA may 

allow States to demonstrate that alternatives to increment contained in
a SIP meet the requirements of sections 166(c) and 166(d).  

  SEQ CHAPTER \h \r 1 Regulations as a whole should fulfill statutory
requirements

Section 166(a) directs EPA to develop pollutant-specific regulations to
prevent the significant deterioration of air quality.  Sections 166(c)
and 166(d) provide detail on the contents of those regulations, but do
not necessarily require the same type of increment system Congress
created in section 163 of the Act.  Thus, in order to develop
pollutant-specific regulations under subsection (a), EPA must establish
both the overall regulatory framework for those regulations (such as
system of increments) and fill details around that framework (such as
the level of the increments).  Thus, EPA interprets section 166 to
require that the entire system of PSD regulations (the framework and
details) for a particular pollutant must, as a whole, satisfy the
criteria in sections 166(c) and 166(d).  We propose to use the same
approach to establish pollutant-specific regulations for PM2.5 under
option 1 of this proposal.

When we propose a framework involving numerical increments under section
166(a) of the Act, we do not look at increments in isolation, but we
also consider how these increments work in conjunction with other
measures to satisfy the statutory criteria.  The other measures that EPA
may consider include new measures proposed by EPA for that pollutant or
measures applicable to other pollutants that EPA proposes to apply to
additional pollutants.  Examples of other measures are an area
classification system, AQRV review in Class I areas, additional impacts
analysis, and control technology 

requirements.  This approach is consistent with section 166(d), which
says that pollutant-specific PSD regulations “may contain”
increments or “other measures.”  

Contingent safe harbor approach

The EPA continues to view the “contingent safe harbor” approach to
be an appropriate methodology for ensuring that itsour
pollutant-specific PSD regulations meet the requirements of sections
166(c) and 166(d).  Subsection (c) of section 166 describes the kinds of
measures to be contained in the regulations to prevent significant
deterioration of air quality called for in section 166(a) and specifies
that these regulations are to “fulfill the goals and purposes” set
forth in sections 160 and 101 of the Act.  Then, under subsection (d),
to “fulfill such goals and purposes,” EPA must promulgate
“specific measures at least as effective as the increments established
in section 7473 of this title [section 163 of the Act].”  42 U.S.C.
7476.  Thus, subsection (d) can be construed to require that EPA
identify a minimum level of effectiveness, or safe harbor, for the body
of pollutant-specific PSD regulations adopted under section 166. 
Subsection (c) may then be read to require that EPA conduct further
review to determine whether, based on the criteria in subsection (c),
EPA’s pollutant-specific PSD regulations under section 166 should
contain measures that deviate from the minimum “safe harbor”
identified under subsection (d).  EPA construes subsection (d) to
require that the measures be “at least as stringent” as the
statutory increments set forth in section 163.

  SEQ CHAPTER \h \r 1 When EPA employs an increment and area
classification system in regulations promulgated under section 166 of
the Act, we interpret the Act to require that EPA, at minimum, establish
increments that are consistent with the statutory increments established
by Congress in section 163 of the Act.  Thus, we start by identifying
“safe harbor” increments for each area classification (Class I, II,
or III) that are established (1) using an equivalent percentage of the
NAAQS as the statutory increments; (2) for the same pollutants as the
NAAQS; and (3) for the same time period as the NAAQS.  We then conduct
further review to determine whether these “safe harbor” increments,
in conjunction with existing elements of the PSD program or additional
measures proposed under section 166 to augment the increments,
sufficiently fulfill the criteria in subsection (c) of section 166.  In
this review, we weigh and balance the criteria set forth in subsection
(c) (and the incorporated goals and purposes of the Act in section 101
and the PSD program in section 160) to determine whether additional
measures are needed to satisfy the criteria in subsection (c).

  The statutory factors applicable under section 166(c) tc "3.  The
Statutory Factors Applicable Under Section 166(c) " \l 3 

The EPA interprets section 166(c) of the Act to establish eight factors
to be considered in the development of PSD regulations for the
pollutants covered by this provision.  These factors are three of the
four criteria listed in section 166(c) and the five goals and purposes
identified in section 160 of the Act.  The three stand-alone criteria in
section 166(c) indicate that PSD regulations for specific pollutants
should provide (1) specific numerical measures for evaluating permit
applications; (2) a framework for stimulating improved control
technology; and (3) protection of air quality values.          42 U.S.C.
7476(c).  The five goals and purposes in section 160 are incorporated
into the analysis by virtue of the fourth criterion in section 166(c),
which directs that EPA’s pollutant-specific PSD regulations “fulfill
the goals and purposes” set forth in sections 160 and 101 of the Act. 
We construe the term “fulfill the goals and purposes,” as used in
section 166(c), to mean that EPA should apply the goals and purposes
listed in section 160 as factors applicable to pollutant-specific PSD
regulations established under section 166.  The Agency’s view is that
PSD measures that satisfy the specific goals and 

purposes of section 160 also satisfy the more general purposes and goals
identified in section 101 of the Act.

Balancing the factors applicable under section 166(c) tc "4.  Balancing
the Factors Applicable Under Section 166(c) " \l 3 

	The EPA interprets the Act to establish a balancing test among the
eight factors.  Since, as discussed further later, many of the factors
can be satisfied by using an increment framework, when determining the
characteristics of numerical increments themselves within that
framework, EPA focuses on balancing the goal to promote economic growth
with the factors that direct us to protect: (1) AQRVs; (2) the public
health and welfare from reasonably anticipated foreseeable adverse
effects, and (3) the air quality in parks and special areas.  Section
166 of the Act authorizes EPA to promulgate pollutant-specific PSD
regulations that satisfy each of the eight factors.  While these
objectives are generally complementary, there are circumstances where
some of the objectives may be in conflict.  In these situations, some
degree of balance or accommodation is inherent in the requirement to
establish regulations that satisfy all of these factors.  

	As discussed in our PSD regulations for NOx, we believe this balancing
test derives primarily from the third goal and purpose set forth in
section 160.  Section 160(3) directs us to “insure that economic
growth will occur in a manner consistent with the preservation of
existing clean air resources.”  To some extent, this goal of the PSD
program in section 160(3) more specifically articulates the broader
purpose of the Act, described in section 101(b)(1) of the Act, to
“protect and enhance the quality of the Nation’s air resources so as
to promote the public health and welfare and the productive capacity of
itsit’s population.”  42 U.S.C. 7401(b)(1).  Sections 160(3) and
101(b)(1) are similar in that both sections reflect the goal to protect
air quality and maximize opportunities for economic growth.  Thus, in
interpreting the meaning of section 160(3) when used as a factor
applicable under section 166(c), we also consider the broader purpose of
the Act set forth in section 101(b)(1).	

	The need to balance the applicable factors to achieve these objectives
is also supported by our interpretation of the second goal in section
160(2) of the Act to “protect public health and welfare.”  The
precise meaning of this goal in the context of the PSD program is
somewhat ambiguous because it appears to mirror the legal standards
applicable to the promulgation of the primary and secondary NAAQS. 
Under section 109(b) of the Act, the primary NAAQS must “protect the
public health” with an adequate margin of safety (section 109(b)(1))
and the secondary NAAQS must “protect the public welfare from any
known or anticipated adverse effects” associated with ambient
concentrations of the pollutant (section 109(b)(2)).  The term
“welfare” is defined in the Act to include “effects on soils,
water, crops, vegetation, man-made materials, animals, wildlife,
weather, visibility, and climate.”  Section 302(h) of the Act.

	When applied as one of the factors applicable to pollutant-specific PSD
regulations under section 166(c) of the Act, we construe the goal in
section 160(3) of the to “protect public health and welfare” to mean
EPA should evaluate whether reasonably anticipated adverse effects may
occur as a result of increases in ambient pollutant concentrations to
levels below the NAAQS.  If such effects may occur in some areas of the
country, then EPA would establish PSD regulations that protect public
health and welfare against those effects where they may occur.  However,
we do not interpret the 

PSD program to require regulations that eliminate all negative effects
that may result from increases in pollution in attainment areas. 

	The PSD program is, as itsit’s title indicates, designed to prevent
“significant deterioration” from a baseline concentration.  See S.
Rep. 95-127 at 11 (3 LH at 1385) (“This legislation defines
‘significant deterioration’ in all clean air areas as a specified
amount of additional pollution....  This definition is intended to
prevent any major decline in air quality currently existing in clean air
areas.” (emphasis added)).  Thus, some decline in air quality
(relative to the baseline air quality concentration) is permissible for
any particular area of the country that is currently achieving the
NAAQS, as long as it is not “significant.”

	When EPA employs an area classification system in itsit’s section 166
regulations, we generally weigh these factors in each type of area
(Class I, Class II, and Class III).  However, the weight given to each
factor may be more or less, depending on the area involved and the
amount of deterioration deemed “significant” for that type of area. 
For example, economic growth may be the most important factor in a Class
III area, but our PSD regulations for such areas should offer some level
of protection for existing clean air resources.  In a Class I area, our
PSD regulations should allow some level of economic growth, even though
preservation of existing clean air resources may be the dominant factor
for these areas.

Authority for States to Adopt Alternatives to Increments

While section 166 of the Act authorizes EPA to promulgate increments for
pollutants listed under section 166(a), we also interpret the section to
authorize States to employ approaches other than increments to prevent
significant deterioration of air quality, so long as such an approach
otherwise meets the requirements of sections 166(c) and 166(d).  As
described earlier, we explained this interpretation in the 2005 NOx
increment rulemaking whereupon we amended we amended the PSD regulations
at 40 CFR 51.166 by adding new paragraph (c)(2) to codify this statutory
authority.  However, in establishing the new provision, the language at
(c)(2) reflected the authority for States to adopt alternative measures
only with respect to increments for NOx.  In order to clarify our
interpretation that the authority to adopt alternative measures covers
any pollutant listed in section 166(a), we are proposing in this action
to revise existing §51.166(c)(2)  to make it inclusive to applicable
pollutants rather than just NOx.

Requirements of Section 166(f) of the Clean Air Act

If we decide to use the equivalent substitution options in this proposal
for PM2.5, EPA proposes to interpret section 166(f) of the Act in the
same manner that the Agency interpreted that provision in itsour 1993
rule for PM10.  In 1993, EPA construed section 166(f) as authorizing EPA
to follow the path that EPA laid out in itsour 1989 proposal for
developing equivalent increments for particulate matter measured as
PM10.  58 FR 31626.  Thus, in itsour 1993 rulemaking, EPA developed
itsour PM10 increments using the “equivalent to statutory
increments” option that EPA described in itsour notice of proposed
rulemaking.  The EPA did not interpret the “equivalent stringency in
effect” standard in section 166(f) to require EPA to use the second
approach from the proposal, the “percentage of NAAQS” approach that
Congress had originally used to establish TSP increments.  The Agency
observed that if Congress intended to require EPA to update the TSP
increments using a straight percentage, Congress could have easily
revised the increments in section 163 instead of providing EPA
discretion to establish increments following the standard provided in
section 166(f).  58 FR 31626.  The EPA thus construed section 166(f) as
providing EPA discretion to  determine appropriate equivalent levels of
PM10.  Id.  The EPA identified equivalent levels by developing a ratio
based on a comparison of the TSP and PM10 impacts of stationary sources.
 58 FR 31627.  

In this rulemaking, EPA proposes to apply the same type of ratio
approach to establish equivalent increments for PM10 under section
166(f) of the Act.  Since this ratio approach was the foundation of
EPA’s equivalency method in the 1989 proposal, we believe it is
permissible, as we did in 1993, to construe section 166(f) as
authorizing EPA to continue utilizing this approach to establish
equivalent increments for particulate matter. 

In 1993, EPA disagreed with commenters who recommended that EPA consider
welfare effects and visibility impairments when establishing PM10
increments under section 166(f) for class I areas.  EPA observed that
there was no evidence that Congress itself adopted increments that would
ensure specific levels of welfare and visibility protection at each
Class I area throughout the nation.  The increments established by
Congress did not establish an absolute ceiling on air quality, but
rather limited the marginal amount of deterioration in air quality above
a baseline concentration that varies for each area, and thus permitted
each area with the same classification to deteriorate in the same amount
without regard to its particular sensitivities as compared to other
areas with the same classification.  58 FR 31625.  The EPA concluded
that the PM10 increments should be designed to protect each area from
large adverse changes in air quality while the air quality related
values analysis was the main tool for protecting specific
ecologically-based attributes in particular class I areas.  Id. 

In this rulemaking for PM2.5, we maintain the view that the “equal
stringency in effect” language in section 166(f) does not require EPA
to consider welfare effects and visibility when promulgating replacement
increments under that provision.  However, as reflected in our recent
increments rule for NOx, when promulgating PSD increments under section
166(a), welfare effects and visibility impacts are factors in the
contingent safe harbor analysis under the criteria in sections 166(c)
and 160 of the Act.  Consistent with our recent PSD regulations for NOx,
we continue to believe that increments (whether promulgated under
section 166(a) or166(f)) should be designed to provide each area with a
basic level of protection from large adverse changes in air quality
without necessarily reflecting the unique air pollution sensitivities in
each class I area.  The EPA considers welfare and visibility impacts
across the nation when establishing increments under section 166(a), but
we continue to believe that the Air Quality Related Values (AQRV) review
is the preferred tool for identification and protection of specific
ecologically-based attributes within particular class I areas.  See 58
FR 31625. 

Increments and other measures to prevent significant deterioration

In this action, EPA is proposing three options for establishing
increments for PM2.5.  The first option described uses the “contingent
safe harbor” approach (using percentages of the NAAQS as our initial
basis) following section 166(a) of the Act.  The other two options are
variations of the section 166(f) “Equivalent Increment” approach. 
EPA is proposing option 1 as our preferred option and seeking comments
on the other two options. 

Option 1 – Contingent Safe Harbor Approach for Annual and Short-Term
Increments – Section 166(a)

Under the first option, we would consider PM2.5 to be a new pollutant5
for which a NAAQS was promulgated after the date of enactment of subpart
C, and we would use the authority of section 166(a) of the Act to
develop new increments for PM2.5.  Using this option, we are proposing
to establish a system of increments at the safe harbor level in
conjunction with the other measures described as follows:  

Proposed framework for pollutant specific PSD regulations for PM2.5

Under this option, EPA proposes to apply the same basic framework
reflected in our regulation for NOx in pollutant-specific PSD
regulations for PM2.5.  Thus, we propose to adopt an increment and area
classification system for PM2.5 and to apply an AQRV review process to
PM2.5 as well.  As discussed further later, EPA believes that many of
the factors applicable under section 166(c) are fulfilled by using this
type of framework for pollutant-specific PSD regulations under section
166(a) of the Act.  For other factors, this framework of regulations
partially contributes to the fulfillment of an applicable factor but may
not fully satisfy that factor.  In these instances, the details of our
regulations (such as the characteristics of the increments themselves)
are also important and we evaluate the effectiveness of the framework in
conjunction with more detailed elements of our regulations.  The EPA
believes itsour obligations under section 166(c) of the Act are
satisfied when the PSD regulations collectively satisfy the factors
applicable under 166(c) of the Act.

Increment system

An increment is the maximum allowable level of ambient pollutant
concentration increase that is allowed to occur above the applicable
baseline concentration in a particular area.  As such, an increment
defines “significant deterioration.”  Establishing an increment
system for PM2.5 will fulfill two of the factors applicable under
section 166(c).  

An increment-based program satisfies the requirements under 166(c) to
provide “specific numerical measures against which permit applications
may be evaluated.”  Under section 165(a)(3) of the Act, a permit
applicant must demonstrate that emissions from the proposed construction
and operation of a facility “will not cause, or contribute to, air
pollution in excess of any (A) maximum allowable increase or maximum
allowable concentration for any pollutant.”  42 U.S.C. 7475(a)(3). 
Once the baseline date associated with the first proposed new major
stationary source or major modification in an area is established, the
new emissions from that source consume a portion of the increment in
that area, as do any subsequent emissions increases that occur from any
source in the area.  When the maximum pollutant concentration increase
defined by the increment has been reached, additional PSD permits cannot
be issued until sufficient amounts of the increment are “freed up”
via emissions reductions that may be required by the permitting
authority.  Thus, an increment is a quantitative value that establishes
a “maximum allowable increase” for a particular pollutant.  It
functions, therefore, as a specific numerical measure that can be used
to evaluate whether an applicant’s proposed project will cause or
contribute to air pollution in excess of allowable levels.

Increments also satisfy the second factor in section 166(c) by providing
“a framework for stimulating improved control technology.” 
Increments establish an incentive to apply improved control technologies
in order to avoid violating the increment and to “free-up” available
increment to promote continued economic growth.    These control
technologies may become the basis of BACT determinations elsewhere, as
the technologies become more commonplace and the costs tend to decline. 
See also S. Rep. 95-127 at 18, 30 (3 LH at 1392, 1404) (“the
incremental ceiling should serve as an incentive to technology, as a
potential source may wish to push the frontiers of technology in a
particular case to obtain greater productive capacity within the limits
of the increments”).  

However, we recognize that an increment system is not the only way to
fulfill the requirements of section 166 of the Act.  Congress did not
require EPA to utilize increments in itsour PSD regulations for NOx but
gave EPA the discretion to employ increments if appropriate to meet the
criteria and goals and purposes set forth in    sections 166 and 160 of
the Act.  42 U.S.C. 7474(d); EDF v. EPA, 898 F.2d at 185 (“Congress
contemplated that EPA might use increments”).  Thus, in this action,
we are also proposing to allow States to develop alternatives to an
increment system at their discretion, and to submit any such alternative
program to EPA so that we can determine whether it satisfies the
requirements of section 166.  

Area classifications

The EPA proposes to establish the same three-tiered area classification
system for PM2.5 that is applicable to NOx and other pollutants under
the PSD program and the Clean Air Act.  Accordingly, areas that are
currently Class I for other pollutants would also be Class I for PM2.5
and all other areas would be Class II for PM2.5 unless we redesignated
the area based on a request by a state or tribe pursuant to the process
in section 164 of the Act and EPA’s regulations at 40 CFR 51.166(g)
and 52.21(g).  

As explained earlier, in section III.E.1, Class I areas are areas where
especially clean air is most desirable.  In contrast, Class III areas,
which are those areas in which a State wishes to permit the highest
relative level of industrial development, have the largest increment
level.  Areas that are not especially sensitive or that do not wish to
allow for a higher level of industrial growth are classified as Class
II.  When Congress established this three-tiered scheme for SO2 and PM,
it intended that Class II areas be subject to an increment that allows
“moderately large increases over existing pollution.”  H.R. Rep.
95-294, 4 LH at 2609.  

Establishing increments at different levels for each of the three area
classifications helps to fulfill two of the factors applicable under
section 166(c) of the Act.  Establishing the smallest increments in
Class I areas helps fulfill EPA’s obligation to establish regulations
that “preserve, protect, and enhance the air quality” in parks and
special areas.  Class I areas are primarily the kinds of parks and
special areas covered by section 160(2) of the Act.  With the air
quality in Class I areas subject to the greatest protection, this scheme
then provides two additional area classifications with higher increment
levels to help satisfy the goal in section 160(3) of the Act that EPA
“insure that economic growth will occur in a manner consistent with
preservation of clean air resources.”  In those areas where clean air
resources may not require as much protection, more growth is allowed. 
By employing an intermediate level (Class II areas) and higher level
(Class III areas), this classification scheme helps ensure that growth
can occur where it is needed (Class III areas) without putting as much
pressure on existing clean air resources in other areas where some
growth is still desired (Class II areas).

By requesting that EPA redesignate an existing Class II area to Class
III, States may accommodate economic growth and air quality in areas
where the Class II increment is too small to allow the siting of new or
modified sources.  The procedures specified by the Act for such a
redesignation require a commitment by the State government to create
such an area, extensive public review, local government participation in
the SIP area redesignation process, and a finding that the redesignation
will not result in the applicable increment being exceeded in a nearby
Class I or Class II area.  See 42 U.S.C. 7474(a)-(b) (Section
164(a)-(b)).  The EPA believes that the three-tiered classification
system has allowed for economic growth, consistent with the preservation
of clean air resources.

However, an area classification system alone may not completely satisfy
the factors applicable under section 166(c) of the Act.  The increment
that is employed for each class of area is also relevant to an
evaluation of whether the area classification scheme achieves the goals
of the PSD program.  We discuss the characteristics of increments later.

Permitting procedures

Two of the factors applicable under section 166(c) are fulfilled by the
case-by-case permit review procedures that are built into our existing
regulations.  The framework of our existing PSD regulations employs the
preconstruction permitting system and procedures required under section
165 of the Act.  42 U.S.C. 7475.  These requirements are generally
reflected in 40 CFR 51.166 and 52.21 of EPA’s PSD regulations in Title
40 of the Code of Federal Regulations.  These permitting and review
procedures, which we interpret to apply to construction of new major
sources and to major modifications at existing sources, fulfill the
goals set forth in sections 160(4) and 160(5) of the Act.  These goals
require that PSD programs in one State not interfere with the PSD
programs in other States and that PSD programs assure that any decision
to permit increased air pollution is made after careful evaluation and
public participation in the decisionmaking process.  For the same
reasons discussed in our proposal for the pollutant-specific PSD
regulations for NOx regulations, 70 FR 8896, we believe these factors
are also fulfilled for PM2.5 by employing the permit review procedures.

Air Quality Related Values review by Federal Land Manager and permitting
authority.

The EPA also proposes to apply the requirement to evaluate impacts on
AQRVs in Class I areas to PM2.5.  The AQRV review provides the Federal
Land Managers (FLM) the opportunity to review source impacts on
site-specific AQRVs in Class I areas and to bring any adverse impacts to
the attention of the permitting authority..  Under an increment
approach, we consider this review to be an additional measure that helps
to satisfy the factors in sections 166(c) and 160(2) which require that
EPA’s pollutant-specific PSD regulations protect air quality values,
and parks and other special areas, respectively.  

In our rulemakings addressing PSD for NOx, EPA extended the AQRV review
procedures set forth in 40 CFR 51.166(p) and 52.21(p) to cover NO2. 
These AQRV review procedures were established based on section 165(d) of
the Act, and they were originally applied only in the context of the
statutory increments for PM and SO2.  However, because they also address
many of the factors applicable under section 166(c) of the Act, EPA also
applied them to NOx through regulation.  We propose the same approach
for PM2.5 in this rulemaking.  

Section 165(d) creates a scheme in which the FLM and permitting
authority must review the impacts of a proposed new or modified
source’s emissions on AQRVs.  The Act assigns to the FLM an
“affirmative responsibility” to protect the AQRVs in Class I areas. 
The FLM may object to or concur in the issuance of a PSD permit based on
the impact, or lack thereof, that new emissions may have on any affected
AQRV that the FLM has identified and for which information is available
to the general public.  If the proposed source’s emissions do not
cause or contribute to a violation of a Class I increment, the FLM may
still prevent issuance of the permit by demonstrating to the
satisfaction of the permitting authority that the source or modification
will have an adverse impact on AQRVs.  Section 165(d)(2)(C).  On the
other hand, if the proposed source will cause or contribute to a
violation of a Class I increment, the permitting authority (State or
EPA) shall not issue the permit unless the owner or operator
demonstrates to the satisfaction of the FLM that there will be no
adverse impact on AQRVs.6  Thus, the compliance with the increment
determines whether the FLM or the permit applicant has the burden of
satisfactorily demonstrating whether or not the proposed source’s
emissions would have an adverse impact on AQRVs.7  Although the FLM has
the burden of proof when the increment is protected, In any event, the
FLM plays an important and material role by raising these issues for
consideration by the permitting authority, which in the majority of
cases will be the State.

Incorporating these AQRV review procedures into the PSD regulations for
PM2.5 helps to provide protection for parks and special areas (which are
generally the Class I areas subject to this review) and air quality
values (which are factors considered in the review).  As discussed
later, we believe the factors applicable under section 166(c) of the Act
can be fulfilled when the review of AQRVs is applied in conjunction with
increments and other aspects of our PSD regulations.  In those cases
where the increment is not violated and the permitting authority agrees
that a proposed project will adversely affect AQRVs, the parks and other
special areas will be protected by denying issuance of the permit or by
requiring the applicant to modify the project to alleviate the adverse
impact.  Legislative history suggests that the AQRV review provisions of
section 165(d) were intended to provide another layer of protection,
beyond that provided by increments.  The Senate committee report stated
the following:  “A second test of protection is provided in specified
Federal land areas (Class I areas), such as national parks and
wilderness areas; these areas are also subjected to a review process
based on the effect of pollution on the area's air quality related
values.”  S. Rep. 95-127, at 17, 4 LH at 1401.

As we stated in the NOx rule, we believe the term “air quality
values” should be given the same meaning as “air quality related
values.” 

Legislative history indicates that the term “air quality value” was
used interchangeably with the term “air quality related value”
(AQRV) regarding Class I lands.8

Additional impacts analysis.

	The additional impacts analysis set forth in our regulations also helps
fulfill the criteria and goals and purposes in sections 166(c) and 160. 
The additional impacts 

analysis involves a case-by-case review of potential harm to visibility,
soils, and vegetation that could occur from the construction or
modification of a source.

	40 CFR 51.166(o)(1) and 52.21(o)(1) of the PSD regulations require that
a permit provide the following analysis:

an analysis of the impairment to visibility, soils and vegetation that
would occur as a result of the source or modification, and general
commercial, residential, industrial and other growth associated with the
source or modification.  The owner or operator need not provide an
analysis of the impact on vegetation having no significant commercial or
recreational value.

This requirement was based on section 165(e)(3)(B) of the Act, which
provides that EPA establish regulations that require “an analysis of
the ambient air quality, climate and meteorology, terrain, soils and
vegetation, and visibility at the site of the proposed major emitting
facility and in the area potentially affected by emissions from such
facility ....”  42 U.S.C. 7475(e)(3)(B).

	This portion of the additional impacts analysis is especially helpful
for satisfying the requirements of section 166(c) in Class II and Class
III areas.  These areas are not subject to the additional AQRV review
that applies only in Class I areas.  While not as intensive a review as
AQRV analysis required in Class I areas, considering impairments to
visibility, soils, and vegetation through the additional impacts
analysis contributes to satisfying the factors applicable under section
166(c) of the Act in all areas, including Class II and Class III areas.

Installation of Best Available Control Technology.

The requirement that new sources and modified sources subject to PSD
apply BACT is an additional measure that helps to satisfy the factors in
sections 166(c), 160(1), and 160(2) of the Act.  This requirement, based
on section 165(a)(4) of the Act, is already included in EPA’s PSD
regulations and thus we consider it to be a part of the regulatory
framework for the Agency’s pollutant-specific regulations for PM2.5. 
40 CFR 52.21(j); 40 CFR 51.166(j).  Our existing regulations define
“best available control technology” as “an emission limitation ...
based on the maximum degree of reduction for each pollutant subject to
regulation under the Act ... which the Administrator, on a case-by-case
basis, taking into account energy, environmental, and economic impacts
and other costs, determines is achievable for such source through
application of production processes or available methods, systems, and
techniques ....”  40 CFR 52.21(b)(12); 40 CFR 52.166(b)(12).  This
pollutant control technology requirement in practice has required
significant reductions in the pollutant emissions increases from new and
modified sources while also stimulating the on-going improvement of
control technology.  The control of PM2.5 emissions through the
application of BACT helps to protect air quality values, public health
and welfare, and parks and other special areas.

Proposed increments

Based on our evaluation of the effects of PM2.5 and a balancing of the
criteria in section 166(c) of the Act (and the incorporated goals and
purposes of the Act in section 101 and the PSD program in section 160),
EPA proposes to find that the “safe harbor” increments for PM2.5
(which meet the minimum requirements in section 166(d) of the Act) are
sufficient to fulfill the criteria in section 166(c) when combined with
the other measures described earlier that we propose to apply to PM2.5. 
Since several of the eight factors applicable under section 166(c) are
satisfied by adopting the framework and other measures described
earlier, our development of the proposed increments for PM2.5 was guided
by the four remaining factors that may not be fully satisfied by the
framework and other measures: (1) protecting AQRVs; (2) protecting the
public health and welfare from reasonably-anticipated adverse effects;
(3) protecting the air quality in parks and special areas; and (4)
ensuring economic growth.9  In accordance with the contingent safe
harbor approach, to determine the specific characteristics of the
proposed increments, we first established the minimum level of
effectiveness necessary to satisfy section 166(d) and then conducted
further analysis to determine if additional measures are necessary to
fulfill the requirements of section 166(c).  

Identification of safe harbor increments 

Using the percentage-of-NAAQS approach, we derived the following safe
harbor increments for PM2.5:

Averaging Period	NAAQS

((g/m3)	Increments ((g/m3)



Class I	Class II	Class III

Annual	       15	1	4	8

24-hour	       35	2	9	18



The PM2.5 levels of both the primary and secondary NAAQS are 15
micrograms per cubic meter ((g/m3) for the annual averaging time and 35
(g/m3 for the 24-hour averaging time.  See 40 CFR 50.7.  We calculated
the safe harbor increments based on the same percentages that were used
by Congress to establish the original PM increments (measured as TSP) in
section 163 of the Act i.e. 6.6% of the NAAQS for Class I areas; 25 % of
the NAAQS for Class II areas and 50 % of the NAAQS for Class III areas .
 Increments with these characteristics are sufficient to satisfy the
requirement in section 166(d) requirement that we adopt increments (or
other PSD regulations) that are “at least as effective as” the
increments established in section 163 of the Act.  42 U.S.C. 7476(d);
See EDF v. EPA, 898 F.2d at 188, 190. 

Data utilized by EPA for the evaluation of the safe harbor increments
for PM2.5. 

We evaluated whether measures other than the safe harbor increments are
necessary by analyzing primarily the scientific and technical
information on the health 

and welfare effects of PM2.5 contained in the June 2005 OAQPS Staff
Paper (SP) used for the periodic review of the 2004 PM air quality
Criteria Document. (CD).10 

Section 166 provides that EPA is to establish pollutant-specific PSD
regulations, including increments, after the establishment of a NAAQS
for the applicable pollutants.  42 U.S.C. 7476(a).  Under normal
circumstances, the Act provides that EPA promulgate new PSD regulations
under section 166, including new increments if appropriate, within 2
years from the promulgation of any NAAQS after 1977.  42 U.S.C. 7476(a).
 In such instances, the health and welfare information used for the
setting of the NAAQS would also be (current( for purposes of
establishing pollutant-specific PSD regulations.  We believe this timing
reflects Congressional intent that EPA consider  the same body of
information concerning a pollutant(s health and welfare effects when it
promulgates the NAAQS and subsequent PSD increments (or other measures)
defining significant air quality deterioration for the same pollutant. 
However, when we use that same information as the basis for our
pollutant-specific PSD regulations, we must evaluate that information
under the legal criteria in section 166 of the Act rather than the
criteria in section 109 applicable to the promulgation of NAAQS.  See,
EDF v. EPA, 898 F.2d at 190. 

Since we just completed a review of the PM2.5 NAAQS, the information
used in that review is current and timely for purposes of this proposal
to establish pollutant-specific PSD regulations for PM2.5.  As discussed
earlier, on October 17, 2006, based primarily on considerable new data
on the air quality and human health effects for PM2.5 directly, EPA
revised the primary and secondary NAAQS to provide increased protection
of public health and welfare by retaining the level of the annual
standard and tightening the level of the 24-hour standard from 65 to 35
μg/m3 while retaining the 24-hour PM10 NAAQS and revoking the annual
PM10 NAAQS.  The information contained in the 2004 CD and 2005 SP that
we also consider for purposes of this proposed rule was used for this
latest review of the PM NAAQS.  

The 2004 CD and 2005 SP are the products of a rigorous process that is
followed to validate and interpret the available scientific and
technical information, and provided the basis for recommending the PM2.5
NAAQS. In accordance with the Act, the NAAQS process begins with the
development of (air quality criteria( under section 108 for air
pollutants that (may reasonably be anticipated to endanger public health
or welfare( and that come from (numerous or diverse( sources.  Section
108(a)(1).  For each NAAQS review, the Administrator must appoint (an
independent scientific review committee composed of seven members of the
National Academy of Sciences, one physician, and one person representing
State air pollution control agencies,( known as the Clean Air Scientific
Advisory Committee (CASAC).  Section 109(d)(2)(A).  The CASAC is charged
with recommending revisions to the criteria document and NAAQS, and
advising the Administrator on several issues, including areas in which
additional knowledge is required to appraise the adequacy and basis of
existing, new or revised NAAQS.  Section 109(d)(2)(B),(C). 

(Air quality criteria( must reflect the latest scientific knowledge on
(all identifiable effects on public health or welfare( that may result
from a pollutant(s presence in the ambient air.  42 U.S.C. 7408(a)(2). 
The scientific assessments constituting air quality criteria generally
take the form of a (criteria document,( a rigorous review of all
pertinent scientific studies and related information.  The EPA also
develops a (staff paper( to (bridge the gap( between the scientific
review and the judgments the Administrator must make to set standards. 
See Natural Resources Defense Council v. EPA ((NRDC(), 902 F.2d 962, 967
(D.C. Cir. 1990).  Both documents undergo extensive scientific
peer-review as well as public notice and comment.  See e.g., 62 FR
38654/1-2. 

Scope of effects considered 

The effects of ambient PM2.5 concentrations may include
secondarily-formed PM2.5.  Hence, in this analysis we have evaluated the
health and welfare effects of both direct PM2.5 and secondarily-formed
PM2.5 that may result from the transformation of other pollutants such
as SO2 and NOx.  This is consistent with the approach we described 

for addressing these effects in the recently completed review of our
pollutant-specific PSD regulations for NOx.  70 FR 59590. 

Evaluation of the health and welfare effects of PM2.5 

Airborne PM is not a specific chemical entity, but rather is a mixture
of liquid and solid particles from different sources and of different
sizes, compositions and properties. Particle size distributions show
that atmospheric particles exist in two classes: fine particles and
coarse particles. PM2.5 is an indicator for fine particles and
represents particles that are mostly less than 2.5 micrometers in size. 
PM10-2.5   is an indicator for thoracic coarse particles and represents
particles sized between 2.5 and 10 micrometers.  In the last two reviews
of the PM NAAQS, EPA concluded that these two indicators, because of
their different sources, composition and formation processes should be
treated as separate subclasses of particulate matter pollution for
purposes of setting ambient air quality standards.

Coarse particles are generally primary particles, emitted directly from
their source as particles.  These particles result from mechanical
disruption of large particles by crushing or grinding, from evaporation
of sprays, or from dust resuspension.  In addition, some
combustion-generated particles may be found as coarse particles.  By
comparison, fine PM is derived directly from combustion material that
has volatilized and then condensed to form primary PM or from precursor
gases, such as SO2 and NOx, reacting in the atmosphere to form secondary
PM. Because of the complexity of the composition of ambient PM2.5 and
PM10-2.5, sources are best discussed in terms of individual constituents
of both primary and secondary PM2.5 and PM10-2.5.  Each of these
constituents can have anthropogenic and natural sources. Major
components of fine particles are sulfates, strong acid, ammonium
nitrate, organic compounds, trace elements (including metals), elemental
carbon, and water.  Primary and secondary fine particles have long
lifetimes in the atmosphere (days to weeks) and travel long distances
(hundreds to thousands of kilometers). They tend to be uniformly
distributed over urban areas and larger regions, especially in the
eastern United States. As a result, they are not easily traced back to
their individual sources.  By contrast, coarse particles are not readily
transported across urban or broader areas.  These particles can settle
rapidly from the atmosphere with lifetimes ranging from minutes to days
depending on their specific size, atmospheric conditions, and altitude. 

Health Effects.  

The EPA reported important progress since the last PM NAAQS review in
advancing our understanding of potential mechanisms by which ambient
PM2.5, alone and in combination with other pollutants, is causally
linked to a number of key health effects.  The more extensive and
stronger body of evidence used by EPA to study the health effects of
PM2.5 in itsour latest review identified a broader range of effects than
those previously documented, involving premature mortality and indices
of morbidity (including respiratory hospital admissions and emergency
room visits, school absences, work loss days, restricted activity days,
effects on lung function and symptoms, morphological changes, and
altered host defense mechanisms)  associated with both long- and
short-term exposure to PM2.5.  

An overview of the scientific and technical evidence considered in the
2004 CD and 2005 SP can be found in our proposed rule for revising the
NAAQS for PM published at 70 FR 2619, January 17, 2006, beginning at
page 2626.  The discussion which follows is only a brief summary of
those effects, with an explanation of the range of PM2.5 concentrations
that we examined in considering revisions to the primary PM2.5 NAAQS.

	While most epidemiological studies continue to be indexed by PM2.5,
some studies also implicate various components within the mix of fine
particles that have been more commonly studied (e.g., sulfates,
nitrates, carbon, organic compounds, and metals) as being associated
with adverse effects.  Furthermore, the available information suggests
that many different chemical components of fine particles and a variety
of different types of source categories are all associated with, and
probably contribute to effects associated with PM2.5.  While there
remains uncertainty about the role and relative toxicity of various
components of fine PM, the current evidence continues to support the
view that fine particles should be addressed as a group for purposes of
public health protection.

Short-term exposure (from less than one day up to several days) to PM2.5
is likely causally associated with mortality from cardiopulmonary
diseases, increased hospitalization and emergency department visits for
cardiopulmonary diseases, increased respiratory symptoms, decreased lung
function, and changes in physiological indicators for cardiovascular
health.  Effects associated with short-term exposure identified since
the last NAAQS review include increased non-hospital medical visits
(physician visits) and aggravation of asthma associated with short-term
exposure to PM2.5.  Although a growing body of studies provided evidence
of effects associated with exposure periods shorter than 24-hours (e.g.,
one to several hours), EPA concluded in itsour 2004 SP that this
information was too limited to serve as a basis for establishing a
primary fine particle standard with less than a 24-hour averaging time. 
However, it was concluded that this information added weight to the
importance of a 24-hour standard   In addition, some studies suggested
consideration of a multiple-day averaging time, but EPA concluded that a
multiple-day averaging time would add complexity without providing more
effective protection than a 24-hour averaging time. 

μg/m3,  the Administrator concluded that a standard set at a higher
level would not likely result in improvement in air quality in areas
across the country in which short-term exposure to PM2.5 can reasonably
be expected to be associated with serious health effects.  Similarly, a
standard set at a lower level was rejected because of uncertainties in
interpreting the available epidemiologic studies that could causally
relate the reported associations of health risks to PM2.5 at those lower
levels.

 concentration was 18 μg/m3, within an overall range of 11 to 30
μg/m3.  In the extended ACS study, the mean for the more recent time
period used in the analysis was 14 μg/m3, while the confidence
intervals around the relative risk functions start to become appreciably
wider (more uncertain) below approximately 12 to 13 μg/m3.  Based on
this and other sets of evidence, EPA decided to consider, for setting
the level of the annual PM2.5 standard, a range of annual PM2.5
concentrations beginning somewhat below 15 μg/m3 (the then-existing
primary annual PM2.5 NAAQS) down to about 12 μg/m3.   However, after
carefully considering public comments and relevant studies, including
the uncertainties in interpreting the available long-term exposure
epidemiologic studies, the Administrator decided to retain the level of
the primary annual PM2.5 standard at 15 μg/m3 to protect public health
with an adequate margin of safety from serious health effects.  See 71
FR at 61177.

	Despite the advances in knowledge about the effects of PM2.5 on human
health, the 2005 SP noted the continued difficulty of being able to
establish a dose-response relationship between PM2.5 concentrations and
specific health-related effects.  “The available toxicologic studies
have generally not been designed to quantify dose-response
relationships…. Among the studies reviewed [in the 2004 CD] are some
that report no evidence of a dose-response relationship gradient, (CD,
p. 7-152), while some do (CD, p. 7-155), and the CD draws no overall
conclusions regarding dose-response relationships from toxicologic
studies.  Therefore, while epidemiologic studies provide clear
indication of increasing response with increasing concentration, no
conclusions can be drawn from toxicologic evidence.”  2005 SP at 3-30.

Welfare Effects

	Ambient particulate matter alone, and in combination with other
pollutants, can have a variety of effects on public welfare.  While
visibility impairment is the most noticeable effect of fine particles
present in the atmosphere, both fine and coarse particles can have other
significant welfare-related effects, including effects on vegetation and
ecosystems, materials (e.g., soiling and corrosion), and climate change
processes.  In 1997, EPA established a suite of secondary PM standards,
including annual and 24-hour PM2.5 standards and annual and 24-hour PM10
standards, to address visibility impairment associated with fine
particles, and materials damage and soiling related to both fine and
coarse particles.  See 62 FR 38683.  In 2006, EPA considered the
then-currently available evidence and decided to revise the current
suite of PM2.5 secondary standards by making them identical in all
respects to the revised suite of primary PM2.5 standards, retain the
current 24-hour PM10 secondary standard and revoke the current annual
PM10 secondary standard.

	In reaching itsour decision in 2006 to revise the suite of PM secondary
standards, EPA factored in several key conclusions from the scientific
and technical information contained in the 2004 CD and 2005 SP.  These
conclusions included the following: (1) PM-related visibility impairment
is principally related to fine particle levels, and most directly
related to instantaneous levels of visual air quality associated with
short-term averaging periods; (2) PM2.5 concentrations can be used as a
general surrogate for visibility impairment in urban areas; (3) any
secondary NAAQS for visibility protection should be considered in
conjunction with the regional haze program as a means of achieving
appropriate levels of protection against PM-related visibility
impairment in urban, non-urban, and Class I areas nationwide; (4) the
available evidence is not sufficient to support distinct secondary
standards for fine or coarse particles for any non-visibility related
welfare effects; and (5) the secondary standards should be considered in
conjunction with protection afforded by other programs intended to
address various aspects of air pollution effects on ecosystems and
vegetation, such as the acid deposition program and other regional
approaches to reducing pollutants linked to nitrate or acidic
deposition.  

	Notwithstanding the conclusions reached in setting the NAAQS for PM,
EPA has reviewed the scientific and technical information concerning
welfare related effects considered in the 2004 CD and 2005 SP to
determine whether there is any basis for modifying the safe harbor
increments developed for PM2.5 to satisfy the criteria under sections
166(c) and 160 of the Act.  The EPA’s review began with visibility
impairment, 

followed by effects on vegetation and other ecosystem components,
materials and soiling, and climate changes.

Visibility impairment.

  

The EPA has long recognized that impairment of visibility is an
important effect of PM on public welfare.  Visibility can be defined as
the degree to which the atmosphere is transparent to visible light. 
Visibility conditions are determined by the scattering and absorption of
light by particles and gases from both natural and anthropogenic
sources.  The classes of fine particles principally responsible for
visibility impairment are sulfates, nitrates, organic matter, elemental
carbon, and soil dust.  

	Visibility impairment can occur in two principal ways: as local
visibility impairment (e.g., localized plumes) and as regional haze. 
Local-scale impairment is generally the result of the plume from a
single source or small group of local sources, rather than from
long-range transport from more distant sources.  With this type of
impairment, a band or layer of discoloration can be observed well above
the terrain, obscuring the sky or horizon relatively near the source, or
sources, which cause it.  Such visibility problems in urban areas are
often dominated by local sources, which may include stationary, mobile
and area sources.  Visibility impairment from the combined effects of
urban sources have been studied in several major cities because of
concerns about fine particles and their significant impacts on residents
of large metropolitan areas.  

The second type of impairment, regional haze, generally results from
pollutant emissions from a multitude of sources located across a broad
geographic region. Regional haze can impair visibility in every
direction over a relatively large area, in some cases over multi-state
regions.  Regional haze is principally responsible for impairment in
national parks and wilderness areas (Class I areas) across the country
where scenic views are considered an important attribute.  Fine
particles transported from urban and industrialized areas may, in some
cases, be significant contributors to regional-scale impairment in Class
I and other rural areas.

Annual average visibility conditions vary regionally across the U.S. 
Higher visibility impairment tends to occur more in the East, and is due
to generally higher concentrations of anthropogenic fine particles and
higher relative humidity conditions.  In addition, the rural East
generally has higher levels of impairment than remote sites in the West.
 For Class I areas, visibility levels on the 20% haziest days in the
West are about equal to levels on the 20% best days in the East.  For
urban areas, however, East/West 

visibility differences from fine particles are substantially smaller
than they are in rural areas.

	The EPA’s latest PM NAAQS review focused on visibility impairment
primarily in urban areas for the following reasons: (1) the efforts now
underway to address all human-caused visibility impairment in Class I
areas through regional strategies under the regional haze program (65 FR
35713, July 1, 1999), and (2) new information from visibility and fine
particle monitoring networks since the last PM NAAQS review that has
allowed for updated characterizations of visibility trends and current
levels in urban areas.  Given the strong link between visibility
impairment and short-term PM2.5 concentrations, EPA gave significant
consideration to the question of whether 

visibility impairment in urban areas allowed by the original 24-hour
secondary NAAQS for PM2.5 could be considered adverse to public welfare.
 

	New data available on PM2.5, primarily in urban areas, enabled EPA to
better characterize urban visibility than was previously possible.  Such
data includes Federal Reference Method (FRM) measurements of PM2.5 mass,
continuous measurements of hourly PM2.5mass, and PM2.5chemical
speciation measurements.  Using the new data EPA sought to explore the
factors that historically complicated efforts to address visibility
impairment nationally, including regional differences related to levels
of primarily fine particles and relative humidity.  Using the most
recent monitoring information and analyses, as well as photographic
representations of visibility impairment in several urban areas to help
inform judgments about the acceptability of varying levels of visual air
quality in urban areas, EPA observed that: 

 μg/m3), which equates to visual ranges roughly around 10 kilometers (6
miles), scenic views around and within the urban areas, are
significantly obscured from view.

	(2)  Appreciable improvement in the visual clarity of the scenic views
occurs at PM2.5 concentrations below 35 to 40 μg/m3, which equates to
visual ranges generally above 20 kilometers for the urban areas
considered.

	(3)  Visual air quality appears to be good at PM2.5 concentrations
generally below 20 μg/m3, corresponding to visual ranges of
approximately 25 to 35 kilometers.

	While being mindful of the limitations in using visual representations
from a small number of areas as a basis for considering national
visibility-based secondary standards, EPA concluded that the
observations noted earlier supported consideration of revising the then
current PM2.5 secondary standards to enhance visual air quality,
particularly with a focus on urban areas.  This lead to the evaluation
of information related to indicator, averaging time, level and form to
identify a range of alternative PM standards that would protect visual
air quality, primarily in urban areas.  Notwithstanding the selection
process used in selecting the primary and secondary NAAQS for PM, for
this PM increment proposal we are examining the same information to
determine whether it might justify modifying the safe harbor increments
for PM2.5, which follow the indicator, averaging times and form of the
NAAQS for PM2.5, as described earlier as option 1.

PM indicator.  While both fine and coarse particles to contribute to
visibility impairment; visibility impairment is the most noticeable
effect of fine particles present in the atmosphere.  Analyses of hourly
PM2.5 measurements and other information demonstrate that fine particles
contribute to visibility impairment directly in proportion to their
concentration in the ambient air.  Moreover, hygroscopic components of
fine particles, in particular sulfates and nitrates, contribute
disproportionately to visibility impairment under high humidity
conditions, when such components reach particle diameters up to and even
above 2.5 μm.  EPA’s analyses of how well PM2.5 concentrations
correlated with visibility in urban locations across the U.S. lead to
the conclusion that the observed correlations were strong enough to
support the use of PM2.5 as the indicator for standards to address
visibility impairment in urban areas, especially when the indicator is
defined for a relatively short period of daylight hours.

Averaging time.  While EPA selected the 24-hour averaging time for the
PM2.5 secondary standard to address visibility impairment primarily in
urban areas, a range of shorter term (sub-daily) daylight averaging
times were also considered.  Strong correlations between visibility and
PM2.5 concentrations were found to occur at the 24-hour averaging time,
but the strongest correlations were found to occur at the sub-daily
daylight averaging times, e.g., 4- to 8-hour daylight averaging times. 
In fact, the correlation was greatest in the 4-hour time period between
12:00 and 4:00 pm.  At the 

sub-daily daylight averaging times correlations between PM2.5
concentrations and light extinction were less influenced by relative
humidity and more consistent across regions.

	A number of different daylight time periods was selected to compare
correlations between visibility and hourly PM2.5 concentrations in urban
areas across the U.S. and in eastern and western regions.  Ultimately,
EPA staff recommended consideration of a short-term averaging time,
within the range of 4 to 8 hours, within a daylight time period between
approximately 10:00 am to 6:00 pm, to target the driest part of the day.
 Most CASAC Panel members supported the Staff Paper recommendation of a
sub-daily averaging time.

	Following careful consideration of the various sets of data and
evidence concerning visibility impairment, the Administrator proposed to
revise the secondary 24-hour standard for PM2.5 to make it identical to
the proposed revised primary PM2.5 standard (based on a 24-hour
averaging time for the short-term standard).  Consistent with
recommendations to consider a sub-daily averaging time, the
Administrator also solicited comment on 4- to 8-hour averaging time for
the secondary PM2.5 standard.  In reaching his final decision to rely on
the 24-hour averaging period to set the secondary standard for PM2.5,
the Administrator concluded that the relative protection against adverse
effects on public welfare provided by the proposed primary standards was
equivalent or more protective than several of the 4-hour secondary
standard alternatives in the range recommended by CASAC and the Staff
Paper.  He also believed that caution was warranted in establishing a
distinct secondary standard for visibility impairment 

primarily in urban areas, given the limitations in the underlying
studies and the subjective nature of the judgment required. 

Level of increment.  In evaluating the adequacy of the levels of the
contingent safe harbor increments for PM2.5, we examined the range of
PM2.5 concentrations considered in setting a national visibility
standard primarily for urban areas.  We had established that range of
concentrations by using the results of public perception and attitude
surveys conducted in the U.S. and Canada, State and local visibility
standards within the U.S., and visual inspection of photographic
representations of several urban areas across the U.S.  These approaches
are detailed in the 2005 SP (pp. 6-18 to 6-23.)  

The public perception and attitude studies were used to gain an
understanding of what the public regarded as an acceptable visible
range.  In some urban areas, poor visibility has led to more localized
efforts to better characterize, as well as improve, urban visibility
conditions.  Public perception surveys used in Denver, Phoenix, and
British Columbia studies yielded reasonably consistent results, with
each study indicating that a majority of citizens find value in
protecting local visibility to with a visual range of about 40 to 60 km.
 Visibility standards for the Lake Tahoe area in California and for
areas within the State of Vermont are both targeted at a visual range of
about 50 km.  In contrast, California’s longstanding general
state-wide visibility standard is a visual range of approximately 16 km.

	Aided by photographic representations of varying levels of visual air
quality developed for several cities across the U.S., EPA staff reached
the conclusion that a national visibility standard in the PM2.5
concentration range of 30 to 20 μg/m3 should be considered.  Further
analyses to characterize the distributions of PM2.5 concentrations,
4-hour averages in the 12:00 to 4:00 pm time frame, by region, that
correspond to various visual range target levels, resulted in a finding
that concentrations of 30, 25, and 20 μg/m3 correspond to the target
visual ranges of approximately 25, 30 and 35 km, respectively.  Thus, it
was determined that a standard set within the range of 30 to 20 μg/m3
could be expected to correspond generally to media visual range levels
of approximately 25 to 35 km in urban areas across the U.S.  This range
was generally consistent with a national target visual range below 40
km, the level suggested by the public perception surveys and the local
visibility standards and goals.  Nevertheless, EPA staff noted that a
standard set at any specific PM2.5 concentration will necessarily result
in visual ranges that vary somewhat in urban areas across the country,
reflecting in part the less-than-perfect correlation between PM2.5
concentrations and reconstructed light extinction.  2005 SP at page 7-8.
 

Form of increment.  In considering a reasonable range of forms for a
PM2.5 standard within the range of PM2.5 concentration levels being
considered, EPA staff took into account the same general factors that
were taken into account in considering an appropriate form for the
primary PM2.5 standard.  In that case, EPA staff concluded that a
concentration-based form should be considered because of itsit’s
advantages over the previously used expected-exceedance form.11  For
visibility, the advantages are that the concentration-based form (1)
would give proportionally greater weight to days when the PM-related
visibility impairment is substantially higher than to days just above
the standard, and (2) has greater stability.  2005 SP at 7-11.  To
identify a range of concentration percentiles that would be appropriate
for consideration, it was concluded that the upper end of the range of
consideration should be the 98th to 99th percentile, consistent with the
forms being considered for the 24-hour primary PM2.5 standard.  For the
lower end of the range, EPA staff used the 92nd percentile because it
represented the mean of the distribution of the 20% worst days,
consistent with the fact that the regional haze program targets the 20%
most impaired days for improvements in visual air quality in Class I
areas.  2005 SP at 7-12.

	While EPA staff regarded PM2.5 as the best indicator for addressing
visibility impairment in urban areas, they considered a range of
averaging times, levels, and forms for setting a PM secondary standard. 
In summary, EPA staff recommended that consideration be given to a
short-term averaging time for a PM2.5 standard, within the range of 4 to
8 hours, within a daylight time period between approximately 10:00 a.m.
to 6:00 p.m.  In addition, they recommended that consideration should be
given to the adoption of federal equivalent methods for appropriate
continuous methods for measurement of short-term average PM2.5
concentrations to facilitate implementation of the standard.  Within the
recommended 4- to 8-hour averaging time, the EPA staff recommended
consideration of a standard level within the range of 30 to 20 ug/m3,
depending in part on the form of the standard selected.  Finally, staff
recommended consideration of a percentile-based form, focusing on a
range from the 92nd percentile up to the 98th percentile of the annual
distribution of daily short-term PM2.5 concentrations averaged over 3
years.  2005 SP at 7-13.

Vegetation and other ecosystem components.

  

The 2004 CD found that then-current PM levels in the U.S. “[had] the
potential to alter ecosystem structure and function in ways that may
reduce their ability to meet societal needs” (CD, p. 4-153).  However,
studies show that vegetation and other ecosystem components result
predominantly from exposure to excess amounts of specific chemical
species than from particle source, predominant form (particle, gas or
liquid) or size fraction.  The 2004 CD discussed the effects of a number
of different chemical species, including dust, trace metals, and
organics, found within ambient PM, but ultimately focused on particulate
nitrates and sulfates based on the conclusion that these latter
constituents of PM were “of greatest and most widespread environmental
significance.”  Thus, the 2005 SP focused on the welfare effects of
particulate nitrates and sulfates, either individually, in combination,
and/or as contributors to total reactive nitrogen deposition and total
deposition of acidifying compounds on sensitive ecosystem components and
essential ecological attributes.

	Nitrogen and sulfur in varying amounts are necessary and beneficial
nutrients for most organisms that make up ecosystems.  It is when
unintentional additions of atmospherically derived nutrient and
acidifying compounds containing nitrogen and sulfur force unintended
change on ecosystems, resulting in adverse impacts on essential
ecological attributes, that deposited particulate nitrate and sulfate
are termed ecosystem “stressors.”  In order for any specific
chemical stressor present in ambient PM to impact ecosystems, it must
first be removed from the atmosphere through any of three different
types of deposition: wet (rain/frozen precipitation), dry, or occult
(fog, mist or cloud).  At the national scale, all types of deposition
must be considered in determining potential impacts to vegetation and
ecosystems because each type may dominate over specific intervals of
time or space.

	The most significant PM-related ecosystem-level effects result from
long-term cumulative deposition of a given chemical species (e.g.,
nitrate) or mix (e.g., acidic or acidifying deposition) that exceeds the
natural buffering or storage capacity of the ecosystem and/or affects
the nutrient status of the ecosystem.  The 2005 SP examined the
environmental effects of both reactive nitrogen (of concern is the
reactive nitrogen resulting from the conversion of both atmospheric N2
and fossil nitrogen during the combustion of fossil fuels) and
PM-related acidic and acidifying deposition on various ecosystems,
including vegetation, terrestrial ecosystems, threatened and endangered
species, and aquatic habitat.

Vegetation.  Various studies indicate that at current ambient levels,
risks to vegetation from short-term exposures to dry deposited
particulate nitrate or sulfate are low; however, when found in
acidifying deposition, such particles do have the potential to cause
direct foliar injury.  The 2005 SP concluded on the basis of available
information that the risk of injury occurring from acid precipitation in
the eastern U.S. is high, noting that acid precipitation with levels of
acidity associated with adverse foliar effects exist in some locations
of the U.S.  Such adverse effects may include damage to leaf surface
structure; increased permeability of leaf surface to toxic material,
water, and disease agents; increased leaching of nutrients from foliage;
altered reproductive processes; and overall weakening of trees making
them more susceptible to other stressors.  Having said all this, the
2005 SP also found that the contribution of particulate sulfates and
nitrates to the total acidity found in the acid precipitation impacting
eastern vegetation is not clear. 

Terrestrial ecosystems.  The 2005 SP concluded that excess nitrogen
deposition is having a “profound and adverse impact on the essential
ecological attributes associated with terrestrial ecosystems.”
Terrestrial ecosystems may be adversely impacted by (1) increased
nitrogen associated with atmospheric deposition, surface runoff, or
leaching from nitrogen saturated soils into ground or surface waters;
and (2) acidic and acidifying deposition.  

	Long-term, chronic additions of reactive nitrogen (including nitrate
deposition and ammonium from ambient PM) can cause the nitrogen input to
plants to exceed the natural capacity of plants and soil microorganisms
to utilize and retain the nitrogen needed for normal growth.  As this
excess occurs over time, a detrimental ecological condition known as
‘nitrogen saturation’ is said to exist.

	Nitrogen saturation does not occur at a specific point in time, but
reflects a set of gradually developing critical changes in the ecosystem
process.  In addition, not all vegetation, organisms, or ecosystems
react in the same manner to increased nitrogen availability from
nitrogen deposition.  Those plants that are predisposed to capitalize on
any increases in nitrogen availability gain an advantage over those that
are not as responsive to added nitrogen.  Over time, this shift in the
competitive advantage may lead to shifts in overall plant community
composition.  Whether this shift is considered adverse would depend on
the management context within which that ecosystem falls and the ripple
effects of this shift on other ecosystem components, essential ecosystem
 attributes, and ecosystems.  

	The addition of nitrogen on plant community succession patterns and
biodiversity has been studied in several long-term nitrogen
fertilization studies in both the U.S. and Europe.  These studies
suggest that some forests receiving chronic inputs of nitrogen may
decline in productivity and experience greater mortality.  Some of the
U.S. forests that are showing severe symptoms of nitrogen saturation
are: the northern hardwoods and mixed conifer forests in the Adirondack
and Catskill Mountains of New York; the red spruce forests at Whitetop
Mountain, Virginia, and Great Smoky Mountains National Park, North
Carolina; mixed hardwood watersheds at Fernow Experimental Forest in
West Virginia; American beech forests in Great Smoky Mountains National
Park, Tennessee; and mixed conifer forests and chaparral watersheds in
southern California and the southwestern Sierra Nevada in Central
California.  (2005 SP at 6-31.)

	Studies have shown that acid deposition has changed the chemical
composition of soils by depleting the content of available plant
nutrient cations (e.g., Ca2+, Mg2+, and K+) by increasing the mobility
of aluminum, and by increasing the sulfur and nitrogen content.  Effects
of acidic deposition have been extensively documented, as discussed in
the 2004 CD and reports referenced therein.  For example, effects on
some species of forest trees linked to acidic deposition include
increased permeability of leaf surfaces to toxic materials, water, and
disease agents; increased leaching of nutrients from foliage; and
altered reproductive processes; all of which serve to weaken trees so
that they are more susceptible to other stresses (e.g., extreme weather,
pests, and pathogens).  In particular, acidic deposition has been
implicated as a causal factor in the northeastern high-elevation decline
of red spruce. Although U.S. forest ecosystems other than the
high-elevation spruce-fir forests are not currently manifesting symptoms
of injury directly attributable to acid deposition, less sensitive
forests throughout the U.S. are experiencing gradual losses of base
cation nutrients, which in many cases will reduce the quality of forest
nutrition over the long term. 

Threatened and endangered species.  The adverse ecological effects of PM
include those effects on rare and unique ecosystems, including both
plant and wildlife species.  Nitrogen deposition, including particulate
nitrate, may have a direct adverse affect on some plant species, while
for others the harm results when added nitrogen serves as a nutrient for
some invasive species that eventually replace the more sensitive, rare
species.  

	In some instances, as sensitive vegetation is harmed or lost, wildlife
species that depend on these plants are also adversely affected. 
Several threatened or endangered species listed by the U.S. Fish and
Wildlife Service, such as the desert tortoise and checkerspot butterfly
have declined as a result of native food supplies being replaced by
invasive plant species whose productivity is enhanced in part by
nitrogen deposition.  

Aquatic habitat. Adverse effects of particulate matter on aquatic
systems (streams, rivers, lakes, estuaries, and oceans) can be the
result of either elevated levels of reactive nitrogen input or
acidification.  In either case, the nitrogen input contribution from
particulate matter may be the result of atmospheric deposition directly
into the water body or on terrestrial ecosystems, reaching the water
body via surface runoff or leaching from nitrogen saturated soils into
ground or surface waters.  However, it is not clear how much of the
total nitrogen input to aquatic systems results from atmospheric
deposition rather than from other nitrogen sources.

	Estuaries receive far greater nutrient inputs than other systems. 
Excess nitrogen in estuaries results in eutrophic conditions whereupon
dissolved oxygen is significantly reduced; yielding an environment that
favors plant life over animal life.  The 2005 SP describes research
being done in the Pamlico Sound in North Carolina, which is a key
fisheries nursery in the southeastern U.S.  Studies have shown that
direct nitrogen deposition onto waterways feeding into the Pamlico Sound
or onto the Sound itself and indirect nitrogen inputs via runoff from
the upstream watersheds contribute to conditions of severe water oxygen
depletion; formation of algae blooms in portions of the Pamlico Sound
estuarine complex; altered fish distributions, catches and physiological
states; and increases in the incidence of disease. (2005 SP at p. 6-35.)

Other studies have shown that under extreme rainfall events, massive
influxes of reactive nitrogen (in combination with excess loadings of
metals or other nutrients) into watersheds and sounds can lead to
dramatic decreases of oxygen in water and the creation of widespread
“dead zones” and/or increases of algae blooms that can cause
extensive fish kills and damage to commercial fish and sea food
harvesting.  (2005 SP at p. 6-35.)	

	The 2005 SP indicates that there is a clear link between acidic water,
which results from atmospheric deposition of strong acids, and fish
mortality.  Studies have shown that inputs of acid deposition to regions
with base-poor soils have resulted in the acidification of soil waters,
shallow ground waters, streams, and lakes in a number of locations with
the U.S.  This can result in lower pH and higher concentrations of
inorganic monomeric aluminum, which causes changes in chemical
conditions that are toxic to fish and other aquatic animals.  

Materials damage and soiling.  

As part of the review for setting secondary standards for PM, the 2004
CD and 2005 SP considered the adverse effects that the deposition of
ambient PM can have on materials such as metals, paint finishes, and
building stone and concrete.  Substantial evidence exists to show that
ambient PM plays a role in both physical damage and impaired aesthetic
qualities of materials.  Physical damage to materials, including
corrosion, degradation, and deterioration, is known to result from
exposure to environmental factors such as sunlight, moisture, fungi, and
varying temperatures; however, to the extent that particles may cause or
contribute to physical damage of building materials, such damage is
primarily caused by chemically active—especially particulate nitrates
and sulfates—fine particles or hygroscopic coarse particles.  On the
other hand, particles consisting of carbonaceous compounds are
responsible for soiling of commonly used building materials and
culturally important items (statues, works of art, etc.)  Soiling or
exposure to PM can affect the aesthetic appeal of surfaces by giving
them a dirty appearance, resulting in an increased frequency of
cleaning.  Nevertheless, while the role of ambient PM in specific
adverse effects is well documented in the available studies, the 2004 CD
and 2005 SP also concluded that there remains insufficient evidence 

to establish a quantitative relationship between ambient PM and any of
the various effects described. 

The EPA believes that these observations and the underlying available
evidence continue to support consideration of retaining an appropriate
degree of control on both fine and coarse particles. Lacking any
specific quantitative basis for establishing distinct standards to
protect against PM related to adverse effects on materials, EPA believes
that reductions in fine and coarse particles likely to result from the
current suite of secondary PM standards, or the range of recommended
revisions to the primary PM standards and to the secondary PM2.5
standard to address visibility impairment, would contribute to
protection against PM-related soiling and materials damage.

Climate and solar radiation effects. 

The effects of PM on climate result from either the scattering or
absorption of radiation by ambient particles, resulting in a cooling or
warming effect on climate, respectively.  Studies suggest that global
and regional climate changes could have both positive and negative
effects on human health and welfare, and the environment.  Most
components of ambient PM, especially sulfates, scatter and reflect
incoming solar radiation back into space.  However, some components of
ambient PM, especially black carbon, absorb incoming solar radiation or
outgoing terrestrial radiation.  Sulfate particles indirectly affect
climate by serving as condensation nuclei which alter the size
distribution of cloud droplets (producing more droplets with smaller
sizes), causing the amount of solar radiation that clouds reflect back
to space to increase.

	While substantial qualitative information has shown the important role
that ambient PM plays in both global and regional climatic processes,
that role is presently poorly quantified.  There are considerable
uncertainties and difficulties in projecting likely climate change
impacts.  The 2005 SP indicates that “any complete assessment of the
direct radiative effects of PM would require computationally intensive
calculations that incorporate the spatial and temporal behavior of
particles of varying composition that have been emitted from, or formed
by precursors emitted from, different sources.”  2005 SP at 6-55.  In
addition, calculations of indirect physical effects of particles on
climate are subject to much larger uncertainties than those related to
the direct radiative effects of particles. 

	Exposure to solar radiation may have direct effects on human health and
agricultural and ecological systems; indirect effects on human health
and ecosystems, and effects on materials.  2005 SP at 6-56ff.  Several
studies cited in the 2004 CD reinforce the idea that particles can play
an important role in affecting the transmission of solar UV-B radiation.
 However, none of these studies included measurements of ambient PM
concentrations, so that direct relationships between PM levels and UV-B
radiation transmission could not be determined.  In addition, the
relationships between particles and UV-B radiation transmission can vary
considerably over location, conditions, and time.  2005 SP at 6-56.  In
summary, the EPA staff concluded that available information is
insufficient to project the extent to which, or even whether,
location-specific changes in ambient PM would indirectly affect human
health or the environment.

Fundamental elements of increments

As we have previously noted, under the model established in the Act and
prior EPA regulations, the function of an increment is not like that of
the NAAQS in that an increment is not intended to set a uniform ambient
pollutant concentration “ceiling” across the U.S.  See 70 FR 59600. 
That is, while both increments and NAAQS generally serve to limit air
pollution levels, increments are designed to allow a uniform degree of
pollutant concentration increase for each area in the U.S. with a
particular classification, with the allowable increase measured against
a baseline air quality level for a particular area.12  Because the
baseline air quality level varies from one location to another, and is
not established until a PSD permit is submitted, it is not possible to
determine what the maximum pollutant concentration attainable is for a
given area (to be used to determine the protection afforded by an
increment against potential adverse environmental effects) until the
specific baseline air quality level is known.

For the reasons described in our increments rule for NOx, our objective
is to establish uniform increments that allow the same level of
deterioration for each area of the country having the same
classification.  70 FR 59601.  Our goal is not to establish increments
to reduce existing air pollutant concentrations below baseline levels in
each area, but rather to define a level of increase in pollutant
concentrations above baseline levels that represents “significant”
deterioration for each area classification.  70 FR 59600. 

Evaluation of the safe harbor increments.

Mindful of the considerations we previously described about the
fundamental characteristics of the increments, we reviewed the
scientific and technical evidence available for the 2005 review of the
NAAQS for PM in order to determine whether, and to what extent, the
“safe harbor” increments might need to be modified in order to
protect air quality values, health and welfare, and parks while ensuring
economic growth consistent with the preservation of clean air resources
in accordance with sections 166(c) and 160 of the Act.  As we did in our
evaluation of the safe harbor NO2 increments, we propose to rely on an
approach that evaluates how protective the safe harbor PM2.5 increments
are by trying to compare the marginal pollutant concentration increases
allowed by the safe harbor increment levels against the pollutant
concentrations at which various environmental responses occur.  We
analyzed the available evidence from both a quantitative and qualitative
perspective to reach a decision about whether we should modify the
contingent safe harbor PM2.5 increments and whether we have sufficient
information to select a specific alternative level, averaging time, or
pollutant indicator for the increments.  

Non-visibility related effects

 

In quantitatively evaluating the adequacy of the contingent safe harbor
increments for PM2.5 for non-visibility related welfare effects, we
experienced difficulties with  identifying the appropriate indicator, as
well as to the level of the increments.  In the most recent evaluation
of the NAAQS for PM, EPA staff concluded that “sufficient information
is not available at this time to recommend consideration of either an
ecologically based indicator or an indicator based distinctly on soiling
and materials damage, in terms of specific chemical components of PM.”
 2005 SP at 7-15.  For consideration of the effects of ambient PM on
vegetation and other ecosystems, the available data indicate that the
chemical species of PM (especially particulate nitrate and sulfate) has
more relevance than the size fraction (coarse or fine).  Acid
precipitation, including particulate sulfate, has been found to be
particularly damaging to foliage, and along with ambient SO2 contributes
significantly to materials damage and soiling.  

	Determining the most effective levels for any indicator for PM from the
available data is difficult because the evidence is insufficient to
provide a quantitative relationship between ambient PM concentrations
and known and observed adverse ecological effects.  

Fundamental areas of uncertainty preclude establishing predictable
relationships between ambient concentrations of particulate nitrogen and
sulfur compounds and associated ecosystem effects.  One source of
uncertainty hampering the characterization of such relationships is the
extreme complexity and variability that exist in estimating particle
deposition rates. These rates are affected by numerous factors,
including particle size and composition, associated atmospheric
conditions, and the properties of the surfaces being impacted.  A
related source of uncertainty is establishing the portion of the total
nitrogen and sulfur deposition occurring at a given site is attributable
to ambient PM.  Though several national deposition monitoring networks
have been successfully measuring wet and dry deposition for several
decades, they often do not distinguish the form (e.g., particle, wet,
and dry gaseous) in which a given chemical species is deposited.
Further, it 

is not clear how well data from monitoring sites may apply to
non-monitored sites with different surface cover, meteorology, or other
deposition related factors.  

	Another fundamental problem that makes it difficult to establish a
meaningful dose-response relationship between ambient PM levels and
specific adverse environmental effects is that ecosystems have different
sensitivities and capacities to buffer or assimilate pollutants. Many of
the documented ecosystem-level effects only became evident after
long-term, chronic exposures to total annual loads of reactive nitrogen
(Nr) or acidifying compounds that eventually exceeded the natural
buffering or assimilative capacity of the system.  In most cases, PM
deposition is not the only contributor to the total load of Nr or
acidifying compounds entering the affected system.  Since it is
difficult to predict the rate of PM deposition, and thus, the PM
contribution to total deposition at a given site, it is difficult to
predict the ambient concentration of PM that would likely lead to the
observed adverse effects within any particular ecosystem. Equally
difficult is the prediction of recovery rates for areas already
affected, if PM deposition rates of various chemical species were to be
reduced.

	In response to our 2005 proposal for NO2 increments, some commenters
expressed the opinion that a better way of identifying acceptable
pollutant loadings, particularly for protection against ecological
effects, is the use of a “critical load” concept.13  70 FR 59612. 
At that time, EPA expressed support for the concept, but indicated that
our current knowledge about critical loads did not “provide a
sufficient basis for establishing a uniform, national standard such as a
PSD increment.”  

	The critical load concept was once again reviewed in the 2005 SP for
PM.  It was noted in that document that the “[k]ey to the
establishment of a critical load is the selection of appropriate
ecological endpoints or indicators that are measurable characteristics
related to the structure, composition, or functioning of ecological
systems (i.e., indicators of condition).”  2005 SP at 6-46.  The EPA
recognized the value of using critical loads and acknowledged that a
number of different groups in the U.S. have begun to use or develop
critical loads.  Nevertheless, while recognizing that current activities
“hold promise,” EPA concluded that “widespread use of [critical
loads] in the U.S. is not yet possible.”  Among other things,
currently available data are insufficient to quantify the contribution
of ambient PM to total Nr or acid deposition, and it is not clear
whether a critical load could be developed just for the portion of the
total N or S input that is contributed by PM.  SP at 4-49.  Research, in
conjunction with the development of improved predictive models, could
help in future consideration within the U.S. of the critical loads
concept, and in determining how much of any given critical load is
contributed by different sources of pollutants.  

As explained earlier, the available scientific and technical data do not
yet enable us to adequately relate ambient concentrations of PM2.5 to
ecosystem responses.  Without such key information, it is difficult to
quantitatively evaluate the effectiveness of the “safe harbor”
increments for protecting air quality values, health and welfare, and
parks while ensuring economic growth consistent with the preservation of
clean air resources.  Alternatively, we must make a qualitative judgment
as to whether the contingent safe harbor increments for PM2.5 or some
alternative increments meet the applicable factors.  

In this situation, we believe that the determination of the increment
levels that satisfy the factors applicable under section 166(c) is
ultimately a policy choice that the Administrator must make, similar to
the policy choice the Administrator must make in setting a primary NAAQS
“with an adequate margin of safety.”  See Lead Industries Ass’n v.
EPA, 647 F.2d 1130, 1147 (D.C. Cir. 1980) (where information is
insufficient to permit fully informed factual determinations, the
Administrator’s decisions rest largely on policy judgments).  Using a
similar approach is warranted because both section 109 and section
160(1) direct the Administrator to use his or her judgment in making
choices regarding an adequate margin of safety or protecting against
effects that may still occur notwithstanding compliance with the NAAQS
-- both areas of inquiry characterized by great uncertainty.  Thus, in
the process for setting NAAQS, the Administrator looks to factors such
as the uncertainty of the science, the seriousness of the health
effects, and the magnitude of the environmental problem (isolated or
commonplace).  E.g., 62 FR 38652 (July 18, 1997) (PM2.5 NAAQS). 

Bearing on this policy decision for increments are various
considerations, based on the available information and the factors
applicable under section 166(c).  The factors establishing particular
environmental objectives (protecting air quality values, health and
welfare, and parks) might suggest that, in some areas, we permit little
or no increase in PM2.5 emissions or establish an increment for another
form of PM because there are data indicating that an effect may be
attributable to PM emissions.  However, as explained in the NOx rule, we
do not believe that Congress intended for the PSD program to eliminate
all negative effects.  Thus, rather than just seeking to eliminate all
negative effects, we must attempt to identify a level of increase at
which any additional effects beyond existing (or baseline) levels would
be “significant” and protect against those “adverse” effects. 
Furthermore, we need to ensure that our increments provide room for some
economic growth.  Congress intended for EPA to weigh these
considerations carefully and establish regulations that balance economic
growth and environmental protection.

Since we are unable to establish a direct, widely applicable,
quantitative relationship between particular levels of PM2.5 and
specific negative effects, we give particular weight to the policy
judgment that Congress made when it set the statutory increments as a
percentage of the NAAQS and created increments for the same pollutant
form and time period that was reflected in the NAAQS.  In section 166 of
the Act, Congress directed that EPA study the establishment of PSD
regulations for other pollutants for which Congress did not wish to set
increments at the time.  

Congress’s own reluctance to set increments to prevent significant
deterioration of air quality due to emissions of NOx, and the provisions
ensuring time for Congressional review and action, suggest that Congress
intended for EPA to avoid speculative judgments about the science where
data are lacking.  Thus, in the absence of specific data showing that an
increment level that of the “safe harbor” level would better protect
health, welfare, parks, and air quality values, while simultaneously
maximizing opportunities for economic growth, we give weight in our
qualitative analysis of the 

factors applicable under section 166(c) to the method that Congress used
to establish the statutory increments.

In making this qualitative judgment, we also consider the overall
regulatory framework that we have established in the PSD regulations for
PM2.5.  This framework includes a case-by-case analysis of each permit
application to identify additional impacts (e.g., soils and vegetation),
a special review by the FLM and State permitting authority of potential
adverse effects on air quality values in parks and special areas, and a
requirement that all new and modified sources install BACT.  In
addition, the area classification system ensures that there will be
economic growth in particular areas that is consistent with the values
of each State and itsit’s individual communities.  Based on this
qualitative analysis, we do not believe it is necessary to adopt more
stringent increments to satisfy section 166(c) of the Act with respect
to non-visibility related effects.  

	Visibility protection

In the case of visibility protection, the available evidence was strong
enough to enable EPA to conclude that PM2.5 is the appropriate indicator
for measuring the effects of ambient PM on visibility impairment. 
Accordingly, using PM2.5 concentrations as the basis for review, EPA
evaluated a range of PM2.5 ambient concentrations, averaging times (24
hours and less), and a range of concentration percentiles (using a
concentration-based form for the standard) in order to establish a
recommendation for setting the secondary NAAQS for PM to address
visibility impairment in urban areas.  As explained in the 2005 SP, EPA
considered, as a lower bound for setting the short-term secondary PM2.5
standard, a PM2.5 concentration of either 20 or 25 μg/m3, averaged over
a 4- to 8-hour averaging time within daylight hours, depending on the
percentile range considered for the form of the standard.  

The Class II, short-term safe harbor increment for PM2.5 is 9 μg/m3. 
This level is well below the lower bound recommended for setting the
secondary PM2.5 standard, but is based on a 24-hour averaging time at
the 98th percentile.  The 2005 SP also notes that the estimated 98th
percentile values in distributions of daily background levels are
below10 μg/m3 in most areas.  Thus, the allowable deterioration from
the safe harbor increment in 

addition to the natural background level generally falls below the
minimum values recommended in the 2005 SP for the secondary short-term
standard for PM2.5.

	With regard to the Class I increments for PM2.5, we note that Congress
explicitly included visibility as an air quality related value (AQRV),
enabling Federal land managers to protect significant attributes of
federal Class I areas.  Act                     section 165(d)(2)(B). 
The FLM, assigned the affirmative responsibility to protect Federal
Class I areas, are to use AQRVs which are separate and distinct from
increments, to address individual Class I areas and the unique
attributes identified for each Class I area.  Congress recognized that
AQRVs and increments were not the same thing and established independent
procedures for the implementation of each.  For example, the Act
authorizes FLM to evaluate the effects of pollutant increases using
AQRVs as the basis regardless of the effect of such pollutant increases
on the increments.  In using the AQRV, FLM are not limited in their
evaluation by the maximum allowable pollutant increase set by the
increment and may identify adverse impacts on visibility pursuant to
AQRVs even when the pollution increase will not cause or contribute to
an exceedance of an increment.  Instead, the pollutant increase is
evaluated against the AQRV which considers the specific conditions
existing in the Class I area of concern.  Thus, regardless of the
increased amount of pollution that an increment may allow, the FLM may
determine that the visibility in the Class I area is adversely affected
by an amount of pollutant increase less than that allowed by the
increment.

	From a qualitative perspective, we believe that visibility protection
in Class I areas is more adequately provided by the AQRV process, where
each area can be addressed on the basis of the local situation and the
FLM’s assessment of potential ambient impacts by a particular source. 
Nevertheless, generally speaking an increment should not be so large
that it routinely results in substantially more pollution in Class I
areas than is generally acceptable under the AQRV approach.  The
contingent Safe harbor PM2.5 increments for Class I areas are 1 μg/m3
and 2 μg/m3 for the annual and 24-hour averaging periods, respectively.
 

	We believe the importance of using distinct PM2.5 increments to protect
against visibility impairment is also lessened by the fact that
Congress, aware of the statutory requirements for prevention of
significant deterioration of air quality, established several visibility
programs that specifically target emissions reductions to achieve the
desired visibility benefits.  Under the regional haze regulations,
promulgated by EPA in 1999, States are required to establish goals for
improving visibility on the 20% most impaired days in each Class I area,
and for allowing no degradation on the 20 % least impaired days.  Each
State must adopt emission reduction strategies which, in combination
with the strategies of contributing States, assure that Class I area
visibility improvement goals are met.  Five multi-state planning
organizations are evaluating the sources of PM2.5 contributing to Class
I area visibility impairment to lay the technical foundation for
developing strategies, coordinated among many States, in order to make
reasonable progress in Class I areas across the U.S.  

	We believe it is also important to consider the fact that some State
and local governments have also developed programs to improve visual air
quality in specific urban areas.  These programs are individually
designed to focus on improving visibility to a visual range defined by
the specific area of concern.  Such local programs can more
appropriately focus on the preferences of individual communities where a
uniform national increment for visibility protection generally cannot.

	In setting the NAAQS for PM, EPA ultimately concluded that a distinct
secondary standard with a different averaging time or form was not
warranted at that time.  Instead, we concluded that a set of secondary
PM2.5 standards set identical to the revised primary PM2.5 standards was
is a reasonable approach when considered in conjunction with the
regional haze program as a means of achieving appropriate levels of
visibility protection in urban, non-urban, and Class I areas across the
U.S.   With regard to evaluating the safe harbor increments for PM2.5,
we had to consider how much weight to give to visibility protection as a
function of the increments.  That is, whether the increments were the
appropriate means of providing the most effective protection against
visibility impairment in urban areas as well as in rural areas,
including Federal Class I areas.  In light of the other more direct
approaches being used to address visibility problems across the U.S., we
believe that the use of distinct PM increments for visibility protection
is not the most effective means of addressing the visibility problem. 
Thus, we do not believe it is necessary to modify the safe harbor
increments for PM2.5 to further protect visibility.  

Proposed baseline dates for PM2.5 increments under option 1.

If we adopt option 1, we propose to require the implementation of the
PM2.5 increment system with new baseline areas, baseline dates and
trigger dates.  Specifically, 

we are proposing that the major source baseline date and trigger date,
both fixed dates, will be defined as the effective date of this rule
after promulgation.  

In light of current and expected trends in PM2.5 concentrations, EPA’s
judgment is that starting with new baseline dates on or after the
effective date of this rule would make the new PSD increments more
effective protective.  Under our proposed approach, any emissions
reductions occurring prior to the effective date of this rule would be
counted toward the baseline concentration rather than expanding the
PM2.5 increment.  If a retroactive baseline date were to apply,
emissions reductions occurring prior to the effective date of this rule
would serve to expand the available increments, enabling more pollution
than would otherwise be allowed to occur.

In addition, we believe starting with new baseline dates to implement
new increments for PM2.5 is appropriate under this option because we
would treat PM2.5 essentially as a “new” pollutant for purposes of
PSD and section 166 of the Act.  We believe that establishing a new
baseline overcomes significant implementation concerns that would
otherwise exist if the existing PM baseline were maintained.  If we were
to require sources and reviewing authorities to conduct PM2.5 increment
analyses based on the minor source baseline dates previously established
under the TSP or PM10 program, they would have to attempt to recreate
the PM2.5 emissions inventory as of the minor source baseline date in
order to determine the baseline PM2.5 concentration for the area.  For
early minor source baseline dates in particular (e.g., 1976 in areas of
the U.S.), establishing the emissions inventory for PM2.5 would be
extremely difficult, cumbersome and potentially inaccurate because
historic emissions inventories did not include PM2.5 emissions.  For all
of these reasons, we are proposing option 1 as our preferred option and
request comment on this contingent safe harbor approach under option 1

Revocation of PM10 annual increments

If we use option 1 to adopt additional increments for PM2.5, we propose
to revoke the annual increments for PM10 based on the same technical
evidence that led us to revoke the annual PM10 NAAQS.  As discussed
earlier, we do not believe EPA is precluded from adopting new particular
matter increments under section 166(a) of the Act because we promulgated
a NAAQS for PM2.5 after 1977.  However, if we read section 166(f) to
address PM10 alone, the interaction of sections 166(a) and 166(f) could
suggest that pollutant-specific PSD regulations for particulate matter
promulgated on the basis of section 166(a) must be limited to
regulations that address fine particulate matter.  However, this view
would create tension with language in section 166(a) that calls for us
to conduct a holistic evaluation to establish a system of PSD
regulations (including numerical and other measures) for each pollutant
covered by this provision.  Since it would be preferable to develop a
system of regulation for particulate matter generally and select the
appropriate indicator for particulate matter increments based on a
comprehensive review of the effects of all forms of particulate matter
(as we did in the recent NAAQS rule), we do not believe Congress could
have intended to constrain EPA’s discretion to consider the
potentially differing effects of coarse and fine particles when
developing pollutant-specific PSD regulations under section 166(a).  

Since EPA recently revised the NAAQS for PM10 and eliminated the annual
PM10 NAAQS, we believe it is permissible for the Agency to interpret the
phrase “pollutants for which national ambient air quality standards
are promulgated after August 7, 1977” to apply to revisions to PM10 as
well.   In our 1989 proposal to adopt PM10 increments, before the
addition of section 166(f) to the Act, we construed the language in
section 166(a) to be broad enough to support adoption of PM10
increments.   Under a holistic approach, considering all forms of
particulate matter, we do not believe the evidence supports retaining an
annual increment for PM10 under the PSD program.  In our   October 17,
2006 action on the PM NAAQS, the Administrator concluded that an annual
coarse particle NAAQS was not warranted at this time.   71 Fed. Reg. at
61198-99.   The Criteria Document concluded that the available evidence
does not suggest an association of adverse health effects with long-term
exposure to coarse particles and the Staff paper concluded there is no
quantitative evidence that directly supports an annual standard.  Id. at
61198.  With respect to welfare effects, the evidence indicated that a
short-term PM2.5 standard was the best approach for addressing
visibility.   Id. at 61280.  For non-visibility welfare effects, the
Administrator concluded that the available evidence was not sufficient
to support an additional indicator, but that a secondary NAAQS identical
to the 

primary NAAQS directionally improves the level of protection afforded
vegetation, ecosystems, and materials.   Id. at 61210.   

When the evidence described in the Criteria Document and Staff Paper is
considered in light of the legal criteria applicable under section
166(c), we believe it supports the conclusion that an annual PM10
increment is no longer needed under the PSD program.  In the absence of
a clear association between long-term exposure to coarse particles and
adverse health effects, we do not see a justification for an annual PM10
increment to protect public health, notwithstanding compliance with the
NAAQS.   In addition, the new increments for PM2.5 that we propose to
adopt, in combination with the existing 24-hour increment for PM10, will
address welfare effects, air quality related values, and air quality in
national parks and other special areas.  As described earlier,
visibility impacts are principally attributable to short-term fine
particle concentrations and thus will be addressed by the new short-term
PM2.5 increment.  The evidence indicates that the non-visibility welfare
effects of concern are primarily attributable to deposition of sulfate
and nitrate particles of any size.  Thus, the combination of the new
PM2.5 increments and the existing 24-hour PM10 increment will address
non-visibility welfare impact attributable to deposition.  Since we
propose to retain the 24-hour PM10 increment and adopt new annual and
24-hour fine particle increments that will target all of these effects,
we do not consider it warranted to require continued tracking of changes
in annual concentrations of PM10 under the PSD program.    

Option 2 – Equivalent Substitution Approach For Annual Increments –
Section 166(f)

	

Under this option, we would recognize PM2.5 as a new indicator for
particulate matter for NSR purposes, and develop annual PM2.5 increments
to replace the annual PM10 increments using the equivalent substitution
approach under the authority of section 166(f) of the Act. 	 

The approach proposed under this option in this proposed rule would be
similar to the one we used in 1993, and discussed earlier to convert
from TSP increments to PM10 increments, to avoid having to implement
increments based on standards that no longer 

existed.  On October 17, 2006, EPA revoked the primary and secondary
annual PM10 standards and retained the primary and secondary 24-hr PM10
standards.  71 FR 61144.  

In this case, we therefore are developing annual PM2.5 increments to
replace the annual PM10 increments.  Also, consistent with our prior
action in 1993, we are proposing to eliminate or revoke the PM10
increments in this notice.  However, for developing the 24-hr PM2.5
increments, we are proposing to use the increment values derived under
the contingent safe harbor approach explained in option 1.  We seek
comment not only on the levels of the proposed “equivalent”
increments, but also on our use of this equivalent increment option for
only the annual PM2.5 increments.  In addition, we seek comment on
whether we should rely on section 166(f) to also propose the 24-hr PM2.5
increments, even though the primary and secondary 24-hr PM10 NAAQS are
not being revoked.

Development of equivalent increments

To establish equivalent PM10 increments in the 1993 rule, EPA compared
the TSP and PM10 impacts of each of the 249 major sources subject to
major NSR in our NSR database.  EPA observed that, in principle, for any
source the equivalent PM10 increments was simply the product of the TSP
increment to the source’s PM10/PM emissions ratio.  58 FR 31627.  

In this rulemaking, EPA proposes to apply the same type of ratio
approach to establish equivalent increments for PM10 under section
166(f) of the Act.  Unlike the 1993 analysis where we evaluated a
database of 249 major sources, for this rulemaking EPA relied on a more
comprehensive analysis of the “2001 National Emissions Estimates by
Source Categories” for PM10 and PM2.514.    SEQ CHAPTER \h \r 1 From
the 2001 National Emissions Inventory, the ratio of emission estimates
from utilities and industrial point source categories were used to find
the PM2.5 to the PM10 emissions ratio.  For purposes of deriving the
ratio, area sources and non-road and mobile sources were not included on
the basis that for NSR permitting virtually all of the permitted sources
fall within the utility and industrial point source categories.  

Utilities and industrial point source emission estimates were combined
and a ratio of 0.8 was calculated as the ratio of emissions of PM2.5 to
PM10.  Hence, the annual increments developed for PM2.5 would be based
on equal to the value 0.8 multiplied by the increment value for PM10. 
Although we believe that this approach is based on a permissible
interpretation of the statute, we believe it results in increment values
for PM2.5 that are much higher than the values Congress envisioned when
it established the original increments for PM & SO2 based on percentages
of the then existing NAAQS. unreasonably high increment values (fFor
example, an annual PM2.5 increment in Class II areas using this approach
would be 13 (g/m3, which is 87% of the annual PM2.5 NAAQS of 15 (g/m3 ).
 In contrast, Congress established the Class II Increments for PM and
SO2 to represent 25% of the NAAQS.  To avoid such an unreasonable
outcome for PM2.5, we rejected this approach and instead are proposing
two variations (options 2A & 2B) of the equivalent increment approach as
the second and third option.  

Proposed annual increments for PM2.5

Option 2A 

In addition to an emissions ratio to reflect the shift in the indicator
from PM10 to PM2.5, we have also considered the shift in the stringency
of the NAAQS that resulted when we changed the pollutant indicator from
PM10 to PM2.5.  Accordingly, the ratio of emissions (0.8) that we
previously calculated would be multiplied by the ratio of the PM2.5
NAAQS over the PM10 NAAQS (15/50 = 0.3 μg/m3 for the annual standard)
to derive an adjustment factor (0.24 for the annual NAAQS) for
calculating the Class I, II, and III annual PM2.5 increments.  Hence,
multiplying the Class I, II, and III annual PM10 increments, 4, 17, and
34 μg/m3, respectively, by the new adjustment factor yields the

 following proposed increment values (rounded to the nearest whole
number) under  option 2A:

Averaging Period	NAAQS

((g/m3)	Increments ((g/m3)



Class I	Class II	Class III

Annual	15	1	4	8

24-hr	35	2	9	18



Coincidentally, this new adjustment based on the PM2.5-to-PM10 NAAQS
ratio results in annual PM2.5 increment values identical to the values
derived using option 1, the percentage-of-NAAQS approach.  As stated
earlier, because the 24-hour PM10 NAAQS have not been revoked, we do not
consider section 166(f) to be the best fit for the development of the
24-hour PM2.5 increments.  Thus, for new 24-hr PM2.5 increments,

 we are proposing to rely on the authority of section 166(a) to derive
24-hour increments as proposed under option 1.

Option 2B

 NAAQS (15/50 = 0.3 μg/m3 for the annual NAAQS).  The values for the
annual PM2.5 increments derived by multiplying the Class I, II, and III
annual PM10 increments, 4, 17, and 34 ug/m3, respectively, by this
adjustment ratio yields the following proposed increment levels (rounded
to the nearest whole number) under option 2B: 

Averaging Period	NAAQS

((g/m3)	Increments ((g/m3)



Class I	Class II	Class III

Annual	15	1	5	10

24-hr	35	2	9	18



As with option 2A, for the 24-hr PM2.5 increments, we are proposing to
use increment values developed via the contingent safe harbor approach
as described in option 1. 

3.	Baseline dates 

Under these options (2A and 2B), since we will be replacing annual PM10
increments with annual PM2.5 increments, we propose to retain the
existing TSP/PM10 baseline and trigger dates and baseline areas for the
PM2.5 program.  Section 166(f) does not address how EPA should handle
baseline dates for a substituted increment.  In 1993, we decided to
retain the existing baseline dates for TSP when we replaced the section 
163 increment with PM10 increments.  We propose the same approach under
this option in this rulemaking because the continuation of the historic
TSP/PM10 baseline dates would ensure that no past case of increment
consumption is abandoned and serve as the closest measure of a
substitute.   However, as discussed earlier, given PM2.5 emissions
trends, our judgment is that establishing baseline dates for PM2.5 after
the effective date of this rule may be more effective at preventing
significant deterioration because the baseline concentrations will
reflect emissions reductions.  We request comment on 

whether this would provide sufficient justification for EPA to establish
new baseline dates under the section 166(f) substitution approach.  

However, in conjunction with the annual PM2.5 increments discussed above
this, we are proposing to use option 1 increment levels for 24-hr PM2.5
increments which would use new baseline areas, trigger and baseline
dates.  Thus, assuming the baseline date for the PM10 increments has
already been triggered, this results in different baseline dates for the
annual and 24-hr PM2.5 increments.  This would also require a PSD
applicant to develop two separate emissions inventories of
increment-consuming sources for evaluating a new source’s cumulative
PM2.5 impacts in the area of concern.  We seek comment on this issue of
multiple inventories under the equivalent increments approach. 

Significant Impact Levels (SILS)  

Background on SILs

Significant Impact Levels or SILs are numeric values derived by EPA that
may be used to evaluate the impact a proposed major source or
modification may have on the NAAQS or PSD increment.  The SILs currently
appear in EPA’s regulations in 40 CFR 51.165(b), which are the
provisions that require States to operate a preconstruction review
permit program for major stationary sources that wish to locate in an
attainment or unclassifiable area but would cause or contribute to a
violation of the NAAQS.  The SILs in that regulation are the level of
ambient impact that is considered to represent a “significant
contribution” to nonattainment. 

Although 40 CFR 51.165 is the regulation that establishes the minimum
requirements for nonattainment NSR programs in SIPs, the provisions of
40 CFR 51.165(b) are actually applicable to sources located in
attainment and unclassifiable areas.  See 40 CFR 51.165(b)(4).  Where a
PSD source located in such areas may have an impact on an adjacent
non-attainment area, the PSD source must still demonstrate that it will
not cause or contribute to a violation of the NAAQS in the adjacent
area.  This demonstration may be made by showing that the emissions from
the PSD source alone are below the significant impact levels set forth
in 40 CFR 51.165(b)(2).  However, where emissions from a proposed PSD
source or modification would have an ambient impact in a non-attainment
area that would exceeding the SILs, the source is considered to cause or
contribute to a violation of the NAAQS and may not be issued a PSD
permit without obtaining emissions reductions to compensate for
itsit’s impact.  40 CFR. 51.165(b)(2)-(3).  

	The EPA has also applied SILs in other analogous circumstances under
the PSD program.  Based on EPA interpretations and guidance, SILs have
also been widely used in the PSD program as a screening tool for
determining when a new major source or major modification that wishes to
locate in an attainment or unclassifiable area must conduct a more
extensive air quality analysis to demonstrate that it will not cause or
contribute to a violation of the NAAQS or PSD increment in the
attainment or unclassifiable area.  SILs are also used to define the
extent of the Significant Impact Area (SIA) where a cumulative air
quality analysis accounting for emissions changes from all sources in
the SIA is performed.  

EPA’s guidance on SILs in the PSD program

The EPA’s historical application of SILs to the analysis of major
source impacts on attainment and unclassifiable areas under the PSD
program has largely been based on interpretations reflected in EPA
guidance memorandum.  The EPA has not previously incorporated the
concept of a SIL into itsour PSD regulations at 40 CFR 51.166 and 40 CFR
52.21.  Nevertheless, EPA has long considered the “significant
contribution” test set forth in 40 CFR 51.165(b)(2) to apply to the
impact of PSD sources on attainment areas as well, since that provision
applies to major new sources and major modifications located in
attainment and unclassifiable areas.  Thus, EPA has also supported the
use of SILs as screening mechanism when analyzing whether a source
located in a PSD area will cause or contribute to a violation of the
NAAQS or PSD increment in attainment or unclassifiable areas.

Although EPA’s current PSD regulations do not contain SILs, EPA
initially developed SILs for TSP and other pollutants under the PSD
program in 1978.  43 FR 26380 (June 19, 1978).  In the preamble to
itsour 1978 regulations, EPA described SILs as a screening technique to
alleviate resource burdens (the costs and time involved in sophisticated
computer modeling of ambient air impacts) where there was little or no
threat to the PSD increments or NAAQS.  45 FR 26398.  However, as the
threat to the increments increased, EPA intended for more sophisticated
techniques to be used.  Id.  Since EPA’s analysis indicated that the
air quality impact of many sources fell off rapidly to insignificant
levels, the Agency did not intend to analyze the impacts beyond the
geographic point where the concentrations from the source fell below
certain levels derived from the class I increments.  Id.  These levels
were interpreted by EPA as representing the minimum amount of ambient
impact that is significant and hence came to be known as the significant
impact levels or SILs.  Id.  

When EPA substantially revised itsour PSD regulations in 1980 to include
significant emissions rates and significant monitoring concentrations,
EPA did not include the SILs in itsour PSD regulations.  At that time,
EPA felt that there was no need for a separate table of SILs because of
the adoption of “a de minimis exclusion for monitoring” otherwise
known as SMCs (described later).  45 FR 52707.  In addition, EPA saw
little value in retaining SILs as an exemption from the air quality
analysis because the demonstration necessary to qualify for the
exemption was itself an air quality analysis.  45 FR 52707.  

Subsequently, in draft guidance for permit writers, EPA advised that
SILs may be used to determine whether a source needs to conduct a
cumulative or “full” impact analysis to demonstrate that in
conjunction with all other increment consuming sources, it will not
cause or contribute to violation of the NAAQS or PSD increment in an
attainment or unclassifiable areas.  New Source Review Workshop Manual,
at C.24-C.25 (Draft 1990); See also 40 CFR 51.166(k); 40 CFR 52.21(k).  
Permitting authorities followed this guidance, and this approach remains
an accepted aspect of PSD program implementation.  If based on a
preliminary impact analysis, a source can show that itsit’s emissions
alone will not increase ambient concentrations by more than the SILs,
EPA  considers this to be a sufficient demonstration that a source will
have not cause or contribute to a violation of the NAAQS or increment.  

In light of the unique air quality considerations in Class I areas, EPA
has drawn a distinction between the use of SILs in Class II areas and
Class I areas.  The EPA’s draft 1990 guidance only identified SILs to
be used in Class II areas under the PSD program.  Workshop Manual at
C.28.  However, in 1991, EPA advised the State of Virginia that the
concept of a SIL might be applied to Class I areas if the levels were
determined in a reasonable manner.  Memorandum from John Calcagni, Air
Quality Management Division, to Thomas J. Maslany, Air, Radiation, and
Toxics Divisions (Sept. 10, 1991).  The EPA did not support the use of
SILs to determine whether a source should conduct an analysis of
itsit’s impact on air-quality related values (AQRVs).  Since there are
currently no Class III areas for PSD in the United States, there has
been no need for EPA to apply SILs in these areas.

Legal Basis for SILs

The concept of a significant impact level is grounded on the de minimis
principles described by the court in Alabama Power Co. v. Costle, 636
F.2d 323, 360 (D.C. Cir. 1980).  In this case reviewing EPA’s 1978 PSD
regulations, the court recognized that “there is likely a basis for an
implication of de minimis authority to provide exemption when the
burdens of regulation yield a gain of trivial or no value.”  636 F.2d
at 360.  Based on this de minimis principle from the court’s opinion,
EPA developed significant emissions rates and significant monitoring
concentrations in itsour 1980s regulations for PSD.  The significant
emission rates reflect levels below which EPA considers an emissions
increase to be de minimis and thus not a major modification that
requires a PSD permit or NA-NSR permit.  45 FR 52676, 52705-07.  See
also 40 CFR 51.166(b)(23); 40 CFR 52.21(b)(23).  As discussed further
later, the significant monitoring concentrations in EPA regulations
define a de minimis level of impact that EPA has concluded does not
justify collecting pre-construction monitoring data for purposes of an
air quality impact analysis.  45 FR 52710.  

Similarly, significant impact levels are intended to identify a level of
ambient impact on air quality concentrations that EPA regards as de
minimis.  The EPA considers a source whose individual impact falls below
a SIL to have a de minimis impact on air quality concentrations.  Thus,
a source that demonstrates itsit’s impact does not exceed a SIL at the
relevant location is not required to conduct more extensive air quality
analysis or modeling to demonstrate that itsit’s emissions, in
combinations with the emissions of other sources in the vicinity, will
not cause or contribute to a violation of the NAAQS at that location. 
In light of insignificance of the ambient impact from the source alone,
EPA considers the conduct of a cumulative air quality analysis and
modeling by such a source to yield information of trivial or no value
with respect to the impact of the proposed source or modification.  The
EPA’s Environment Appeals Board has recently reiterated and affirmed
EPA’s interpretation of the Act to allow EPA to evaluate the
significance of a source’s impact when determining whether it would
“cause or contribute” to a NAAQS or increment violation under
section 165(a)(3) of the Act.  In Re: Prairie State Generating Company,
PSD Appeal No. 05-05, slip op. at 139-144 (Aug. 24, 2006). 

Thus, in developing SILs for this proposal, EPA sought to derive SILs
for PM2.5 utilizing methods that would identify levels representing a de
minimis or insignificant impact on ambient air quality.  In choosing
among the options set forth later, EPA proposes to select an option that
reflects the degree of ambient impact on PM2.5 concentrations that can
be considered truly de minimis and would justify no further analysis or
modeling of the air quality impact of a source in combination with other


sources in the area because the source would not cause or contribute to
an exceedance of the PM2.5 NAAQS or the PM2.5 increments established
elsewhere in this proposal. 

Relationship of SILs to AQRVs

We wish to emphasize that consistent with the original purpose of the
Class I SILs, the Class I SILs for PM2.5 we are proposing are not
intended to serve as thresholds for determining the need for an AQRV
analysis or whether an adverse impact on an AQRV will occur.  An adverse
impact on an AQRV depends upon the sensitivity of the particular AQRV. 
An ambient concentration that is considered insignificant for purposes
of increment consumption should not automatically be considered
inconsequential relative to the inherently fact-specific demonstration
upon which an adverse impact on an AQRV is to be based.  Accordingly,
the fact that a source’s predicted impact is less than the SIL in a
Class I area would neither relieve the source from having to complete an
analysis of impacts on AQRVs nor automatically allow the reviewing
authority to reject the FLM’s demonstration of adverse impact on an
AQRV.  See 61 Fed Reg. at 38292.

Proposed Options for PM2.5 SILs (for PSD and NA-NSR)

We are seeking comment on the relative merits of each of the following
options for setting PM2.5 SILs.

Option 1 - Propose SILs using the approach we proposed for PM10 in 1996 


The first option that we are proposing utilizes the same approach we
proposed for PM10 in the 1996 NSR Reform proposal.  For Class I areas we
would set the SIL to         4 percent of the Class I PM2.5 increment. 
For Class II and Class III areas, we would codify the SIL values of 1.0
(g/m3 for the annual averaging period and 5.0 (g/m3 for the 24-hour
averaging period, that already exist for PM10 in 40 CFR 51.165(b)(2). 
If we adopt this option, we would set the Class I SILs based on the
Class I increments that we elect to adopt under the increment options. 
Based on the Class I increment values proposed in the % of NAAQS
increment option 1, the SILs under this option would be as follows:

Averaging Period	Class I Increment

((g/m3)	SILs ((g/m3)



Class I	Class II	Class III

Annual	1	0.04	1.0	1.0

24-hour	2	0.08	5.0	5.0



As stated earlier, we had proposed this approach for setting PM10 SILs
in our 1996 NSR Reform proposal.  Many commenters supported this
approach and believed that the proposed SIL values would serve as
appropriate de minimis values.  In fact, EPA is aware that many States
have been using these proposed SILs for PM10 as screening tools since
1996.

Regarding the proposal to set the level of Class I SILs at 4 percent of
the Class I increments, we believe that where a proposed source
contributes less than 4 percent to the Class I increment, concentrations
are sufficiently low so as not to warrant a detailed analysis of the
combined effects of the proposed source and all other
increment-consuming emissions.  We previously used a similar rationale
to establish the significant emissions rates for PSD applicability
purposes, concluding in part that emissions rates that resulted in
ambient impacts less than 4 percent of the 24-hour standards for
particulate matter and SO2 were sufficiently small so as to be
considered de minimis.  

The original SIL values of 1.0 and 5.0ug/m3 for TSP and PM10 were
interpreted by EPA as representing the minimum amount of ambient impact
that is significant.  This forms the basis of the proposed PM2.5 SIL
values of 1.0 and 5.0 ug/m3 for the annual and 24-hr standard for Class
II and III areas. 

Option 2.  PM2.5 to PM10 emissions ratio

In our second proposed option for SILs, we would multiply the PM10 SILs
(proposed in 1996) by the emissions ratio of PM2.5 to PM10 for point
sources in the 2001 extrapolation of the final 1999 NEI.  This is very
similar to option 2A for developing increments, and would use the same
PM2.5/PM10 emissions ratio (0.8).  The Class I PM10 SILs that we
proposed in 1996 were 0.2 (g/m3 (annual) and 0.3 (g/m3 (24-hour).  For
Class II and III PM10 SILs, we proposed 1.0 (g/m3 (annual) and 5.0 (g/m3
(24-hour) levels.  The SIL values determined in this option are as
follows:

Averaging Period	SILs ((g/m3)

	Class I	Class II	Class III

Annual	0.16	0.8	0.8

24-hour	0.24	4.0	4.0



The SILs derived under this option are slightly more stringent for Class
II & III areas than those in option 1.  Since PM2.5 emissions are a
subset of PM10 emissions, we believe that an emissions ratio of the PM10
SILs would serve as an appropriate de minimis SIL value and represent
insignificant impact on ambient air quality.  

Option 3.  PM2.5 to PM10 NAAQS ratio

Under the third option that we are proposing, we would multiply the PM10
SILs by the ratio of the PM2.5 NAAQS to the PM10 NAAQS.  This is very
similar to option 32B for developing PM2.5 increments, and would use the
same factors.  We would start with the same values for the PM10 SILs
that we used for option 2 above for SILs..  The PM2.5 SILs determined
using this approach are as follows:

Averaging Period	SILs ((g/m3)

	Class I	Class II	Class III

Annual	0.06	0.3	0.3

24-hour	0.07	1.2	1.2



The SILs derived under this option are very stringent for Class II and
III areas compared to options 1 and 2.  Nevertheless, we believe that
the NAAQS ratio approach is an appropriate alternative to determine
SILs, since it reflects the stringency in the NAAQS for PM2.5 relative
to that of PM10.  We believe that these SIL values would serve as
appropriate de minimis values.  

Significant Monitoring Concentrations (SMCs)

Background on SMCs

Preconstruction monitoring and itsit’s role in NSR program

Under the Act and EPA regulations, an applicant for a PSD permit is
required to gather preconstruction monitoring data in certain
circumstances.  Section 165(a)(7) calls for “such monitoring as may be
necessary to determine the effect which emissions from any such facility
may have, or is having, on air quality in any areas which may be
affected by emissions from such source.”  42 U.S.C. 7475(a)(7).  In
addition, section 165(e) requires an analysis of the air quality in
areas affected by a proposed major facility or major modification and
calls for gathering one year of monitoring data unless the permitting
authority determines that a complete and adequate analysis may be
accomplished in a shorter period.  42 U.S.C. 7575(e)(3).  These
requirements are codified in EPA’s PSD regulations at 40 CFR 51.166(m)
and 40 CFR 52.21(m).  

In accordance with EPA’s Guideline for Air Quality Modeling (40 CFR
part 51, Appendix W), the preconstruction monitoring data is primarily
used to determine background concentrations in modeling conducted to
demonstrate that the proposed source or modification will not cause or
contribute to a violation of the NAAQS.  40 CFR part 51, Appendix W,
section 9.2.  For most areas where multiple sources of air pollution are
present, EPA’s Guideline recommends using monitoring data to identify
the portion of background concentrations attributable to natural
background, minor sources, and distant major sources.  40 CFR part 51,
Appendix W, section 9.2.3.f.  For nearby major sources, EPA recommends
explicitly modeling the emissions of such sources rather than relying on
monitored data as part of the NAAQS compliance demonstrations.  As
described earlier, the compliance demonstration with respect to the PSD
increment compliance focuses on modeling the change in emissions from
sources in the Significant Impact Area. 

History of SMC rules adopted by EPA

In 1980, EPA adopted regulations that exempt sources from
preconstruction monitoring requirements for a pollutant if the source
can demonstrate that itsit’s ambient air impact is less than a value
known as the Significant Monitoring Concentration or SMC.  The
pollutant-specific SMCs are codified at 40 CFR 51.166(i)(5)(i) and 40
CFR 52.21(i)(5)(i).  The EPA developed SMCs as a screening tool for
sources to determine whether they should conduct site-specific
preconstruction ambient monitoring.  At the time they were adopted, EPA
described the SMCs as “air quality concentration de minimis level[s]
for each pollutant… for the purpose of providing a possible exemption
from monitoring requirements.”  45 FR 52676, 52707 (Aug. 7, 1980). 
The EPA explained that it believed there was “little to be gained from
preconstruction monitoring” where a source could show that itsit’s
projected impact on the affected area was below these de minimis levels.
 45 FR 52710. 

In 1980, EPA determined the SMCs based on the current capability of
providing a meaningful measure of the pollutants.  The EPA promulgated
values that represented five times the lowest detectable concentration
in ambient air that could be measured by the instruments available for
monitoring the pollutants.  45 FR 52710.  The EPA chose the factor of
five after reviewing test data for various methods and considering
instrument sensitivity, potential for sampling error, instrument
variability, and the capability to read recorded data.  Id. 

For particulate matter, EPA set the SMCs for TSP at five times the
lowest detectable ambient concentration for TSP (2.0 ug/m3) using the
reference method 5 for ambient sampling at that time.  Memorandum from
Rehme, K. A., EPA/EMSL/QAD/MSB, to Peters, W., EPA/OAQPS/CPDD, on PSD
Monitoring (May 20, 1980).15  We set a SMC only for the 24-hour
averaging period, at a level of 10 (g/m3.  We retained the same
numerical level when we replaced the TSP NAAQS and increments with the
PM10 NAAQS and increments.   

Legal Basis for SMCs 

As with the SMCs adopted by EPA in 1980, the SMCs for PM2.5 proposed in
this action are supported by the de minimis doctrine set forth in the
Alabama Power v. Costle opinion.  Like the other pollutants for which
EPA has promulgated SMCs, EPA believes there is little to be gained from
preconstruction monitoring of PM2.5 concentrations when the increased
emissions of PM2.5 from a proposed source or modification has a de
minimis impact on ambient concentrations of PM2.5.  If a source can show
through modeling of itsit’s emissions alone that itsit’s impacts are
less than the corresponding SMC, there is little to be gained by
requiring that source to collect additional monitoring data on PM2.5
emissions to establish background concentrations for further analysis.  

Therefore, in developing SMCs for this proposal, EPA sought to use
methods that would identify levels representing a de minimis or
insignificant impact on PM2.5 ambient air quality that makes the
collection of additional monitoring data extraneous.  In choosing among
the options set forth later, EPA proposes to select an option that
reflects the degree of ambient impact on PM2.5 concentrations that can
be considered truly de minimis and would not justify the gathering of
monitoring data to establish background concentrations for a
demonstration of compliance with the NAAQS.  

Proposed Options for PM2.5 SMC 

Option 1.  Lowest detectable concentration 

For this approach, we would use the same methodology originally used in
1980 to set the SMC for TSP, i.e. determining the lowest detectable
concentration and multiplying this value by five.  The lowest detectable
24-hr average concentration for PM2.5 is 2.0 (g/m3 (40 CFR 50 App L
section 3).  Thus, applying this methodology for PM2.5 yields an SMC of
10 (g/m3 for the 24-hr averaging period.

As we indicated in 1980 when we originally used this methodology to set
the SMCs for TSP and the other PSD pollutants, the use of five times the
lowest detectable concentration was chosen to realistically reflect
pollutant levels at which low level concentrations or small incremental
changes in pollutant concentrations can reasonably be determined.  The
factor of five takes into account the measurement errors associated with
the monitoring of these low pollutant levels or small incremental
changes in concentration.  These measurement errors arise form various
sources, such as sample collection, analytical measurement, calibration,
and interferences (See Memorandum from Rehme, K. A. mentioned earlier).
We believe this is a reasonable approach, since it has also been used
for PM10 and TSP.  We seek comment on this approach.		

Option 2.  PM2.5 to PM10 emissions ratio

Proposed option 2 establishes the SMC for PM2.5 by multiplying the
existing PM10 SMC (10 (g/m3) by the ratio of PM2.5 emissions to PM10
emissions in the 2001 extrapolation of the final 1999 NEI.  This is the
same methodology used in Increments 

option 2A and SIL option 2, and uses the same emissions ratio (0.8). 
This yields a SMC value of 8.0 (g/m3 for PM2.5 for the 24-hr averaging
period.  

This approach gives a PM2.5 SMC value that is equivalent, in terms of
emissions, to the existing PM10 SMC.  We believe that this approach is
consistent with the approach that Congress set out for increments in
section 166(f) of the Act and is, as such, a reasonable approach for
developing PM2.5 SMCs.  We seek comment on this approach.

Option 3.  PM2.5 to PM10 NAAQS ratio

Under the third option, we propose to multiply the PM10 SMC by the ratio
of the PM2.5 NAAQS to the PM10 NAAQS.  This is the same approach
proposed for Increment option 32B and SIL option 3.  Because the PM10
SMC is for the 24-hour averaging period, we would use the ratio of the
24-hour NAAQS for PM2.5 (35 (g/m3) and PM10 (150 (g/m3).  As noted
previously, tThe resulting factor is 0.233.  Thus, the PM2.5 SMC
developed using this option would be 2.3 (g/m3, for the 24-hour
averaging period. 

The SMC developed using this approach is very stringent compared to
options 1 and 2, since it reflects the stringency in 24 hr NAAQS of
PM2.5 relative to PM10. Nevertheless, we believe this to be also a
reasonable approach and seek comments on it.

Correction of Cross References

In addition to exempting sources that have emissions increases below the
SMCs, EPA also exempts sources from preconstruction monitoring where the
source demonstrates that existing ambient concentrations of a pollutant
in the affected area are currently below the SMCs.  40 CFR
51.166(i)(5)(ii); 52.21(i)(5)(ii).  This aspect of the monitoring
exemption was also adopted in the 1980 rulemaking.  45 FR 52710.  

The EPA also proposes in this rulemaking to correct a cross reference
contained in these parts of the regulations.  Paragraphs (ii) and (iii)
in 40 CFR 51.166(i)(5) and paragraph (ii) in 40 CFR 52.21(i)(5) each
refer to concentrations listed in paragraphs (i)(8)(i).  However, there
is no paragraph (i)(8)(i) in §51.166 and no concentration values are
contained in section (i)(8)(i) of §52.21.  The cross references in
these provisions were intended to reference the SMCs in paragraph
(i)(5)(i), but EPA failed to make this change when the paragraphs were
renumbered in a prior rulemaking.  We propose to correct that oversight
in this rule. 

Effective Date of the Final Rule, SIP Submittal/Approval Deadlines and
PM10 Revocation Deadline. 

This section sets forth EPA’s proposed effective dates for the PM2.5
increments (under different options), SILs and SMC.  In addition, we are
setting forth the proposed deadlines for States to submit revisions to
their SIPs incorporating these changes to the PSD regulations, and for
EPA to approve or disapprove the revised plans. Finally, this section
describes EPA’s proposed schedule for revoking the PM10 annual
increments in conjunction with the commencement of the PM2.5 increment
system under the part 51 and part 52 PSD regulations and we request
comment on establishing a transition period for processing complete
permit applications.  Please see Table 1 in the docket  (Docket ID No.
EPA-HQ-OAR-2006-0605) for a summary of the proposed options and
alternatives on which we seek comment.

Option 1:  Increments promulgated pursuant to section 166(a) of the Act.


Effective date of Final Rule

	As described in section III.E.2.a. of this preamble, section 166(b) of
the Act specifies that new regulations for increments promulgated
pursuant to section 166(a) of the Act  become effective one year after
the date of promulgation.  Accordingly, if we promulgate the new PM2.5
increment under the authority of Section 166(a) following Option 1, we
propose an year’s delay in the effective date.  

	Alternatively, EPA seeks comments on whether we could make the new
increment regulations effective 60 days from promulgation.  Considering
the various timeframes outlined in section 166, it is clear that
Congress envisioned that increments or other measures would become
effective within three years of the promulgation of a NAAQS.  In the
current circumstance, due to prolonged litigation and other
implementation concerns, there has been an extended delay of over ten
years since we established the PM2.5 NAAQS.  Given this extended delay,
we believe that the overall Congressional intent reflected in section
166 may best be met by advancing the effective date of the proposed
regulations.   

States have to submit SIPs by April 5, 2008 to address the NSR
provisions of the final PM2.5 implementation rule after the federal NSR
implementation rule is promulgated later this year.  If EPA decides to
promulgate option 1 for increments and 166(b) timelines, the increments
rule would not be implemented in SIP–approved States until
approximately January 2010 (assuming promulgation of this rule in Spring
2008 and allowing 21 months for SIP submittal).  Thus from April 2008 to
Jan 2010, PSD sources would be subject to a PM2.5 applicability program,
but would need to continue the current   PM10 air quality impacts
analysis,.  Under these circumstances,  we expect that States, affected
industry, and environmental groups will see value in advancing the
effective date of the promulgated increments. 

In addition, the Congressional intent behind section 166(b) may now be
satisfied by the review provided under the Congressional Review Act, 5
U.S.C. 801 et seq., as added by the Small Business Regulatory
Enforcement Fairness Act of 1996.   Legislative history indicates that,
when section 166(b) was first enacted in 1977, Congress established the
delayed effective date in order to allow time for “contrary
Congressional action.” H.R. Conf. Rep. 95-564, at 151 (1977).  The
Congressional Review Act (CRA) provides Congress with an expedited means
of reviewing and potentially disapproving final actions issued by
federal agencies.  Under the CRA, a member of Congress can introduce a
joint resolution to disapprove a particular rule and have that
resolution considered using expedited procedures if the resolution is
introduced within the designated time period (generally 60 days
depending on the Congressional calendar).  Furthermore, an agency rule
meeting the CRA definition of “major” cannot take effect for 60
days.   We request comment on whether, given these procedures under the
CRA, a 60-day delay in the effective date of the proposed rule could
satisfy the Congressional intent reflected in section 166(b).  

State Program

In this action, we propose to establish final PM2.5 increments as
minimal program element for all State Programs.  Accordingly, States
must submit revised SIPs for EPA‘s approval that incorporate the final
PM2.5 increments, or demonstrate that an alternative approach is at
least equivalent to this minimum program element.  Irrespective of
whether we establish an effective date of the final rule that falls one
year after or 60 days after we promulgate the final rule, we propose to
require States to submit revised implementation plans to EPA for
approval within 21 months of promulgation (9 months after the effective
date of such regulations) in accordance with the time frames specified
in Section 166(b) of the Act.  Section 166(b) also specifies that we
must approve or disapprove these revisions within 25 months of
promulgation (4 months from the statutory deadline for SIP submittal). 
We regard these statutory deadlines as maximum allowed timeframes for
action and do not believe that the Act restricts our ability to approve
SIP revisions requested by a State at any time before these deadlines. 
We also propose to change the regulatory provisions at 40 CFR 166(a)(6)
to specifically articulate these deadlines for these State SIP
submittals.

3.	Federal Program

	The EPA must also decide how to apply the procedures set forth in
section 166(b) of the Act to the new PM2.5 increments under our part 52
PSD regulations, which apply for States without approved PSD programs as
well as for Indian lands.  We propose to begin to implement the Part 52
PSD program upon the effective date of the final rule.  Accordingly, if
we delay the effective date for one year after the date of promulgation
in accordance with Section 166(b), then the Part 52 PSD program would
become effective and implemented in the applicable areas, on this date. 
Alternatively, if we establish an 

effective date 60 days after we promulgate the final rules, the Part 52
PSD program would become effective on this same date.  

Alternatively, we request comment on whether we should delay
implementation of the Federal Part 52 PSD program until 25 months after
promulgation, or the outside date by which EPA is required to approve
State SIP revisions.  This is the same approach we took in 1988 to
implement the then new NO2 increments.  53 FR at 40658.  We are not
offering this as our proposed approach because of the significant delay
that has already occurred between the time we promulgated the PM2.5
NAAQS and the time we will finalize this rule.   However, we recognize
that it may not be equitable to begin implementation of the new program
requirements in those few areas where the Federal program applies before
the majority of States are required to implement the program. 
Nonetheless, we seek comment on applying this alternative approach for
the Federal Part 52 PSD program and specifically on the consequences of
potential inequities.

Option 2:  Increments promulgated pursuant to section 166(f) of the Act.
 

Effective date of Final Rule

In contrast to the proposed delay of the effective date of the new PM2.5
increments under option 1, we propose to make the new PM2.5 increments
proposed under option 2 effective 60 days from the date of promulgation,
consistent with the CRA timeframe.  We do not interpret section 166(b)
of the Act to apply to increments promulgated under the authority of
section 166(f) because the first sentence in section 166(b) describes
only “[r]egulations referred to in subsection (a).” 

State Program

We previously stated that we believe that it is appropriate to establish
a deadline for States to submit required SIP revisions analogous to the
deadline that applies to States when we promulgate or revise a NAAQS. 67
FR 80241.  We previously codified, conforming regulatory text at 40 CFR
166(a)(6).  Under Option 2 of this proposal, we propose to follow the
existing regulatory provisions that require a State to adopt and submit
for EPA approval itsit’s PM2.5 plan revisions no later than 3 years
after the date on which we promulgate (i.e., publish in the Federal
Register) the new regulations in the part 51 PSD regulations.  
Alternatively, we request comment on whether we should require a
timeframe shorter than 36 months, such as the statutory maximum of 21
months required under Option 1.  Given the limited nature of the
required changes, we believe that States generally may not need more
than 21 months to adopt and submit revised plans to EPA for approval. 
If we select this alternative approach, we propose to make conforming
regulatory changes to 40 CFR 166(a)(6).

Federal Program 

For the Federal part 52 PSD regulations, we propose under Option 2 to
make the new PM2.5 increments effective 60 days from date we promulgate
the final rules.  However, unlike the proposed 3-year period being
proposed for States to submit their plan revisions to EPA for review and
approval, we propose to implement the new increments under the part 52
PSD regulations upon the effective date of the final rules.   Since it
would be difficult to know when States are planning to revise their own
PSD programs consistent with the new increment regulations, it is not
possible to ensure a consistent implementation date between approved
State programs and programs being implemented under the part 52 PSD
regulations unless we delayed implementation for a full four years (3
years for SIP submission and 1 year for EPA to approve the revision). 
We believe that this delay is excessive and does not accomplish the goal
of expedient implementation of a PM2,5 PSD program.  We request comment
on this approach.  

Revocation of the  PM10 Increment

	While we believe it is appropriate to revoke the annual PM10 increment
as explained earlier in this preamble, we propose to retain the PM10
increments in both part 51 or part 52 PSD regulations until the new
PM2.5 increments are being implemented either by a State through an
approved SIP, or by EPA through the Federal Part 52 PSD program. 
Accordingly, we propose to approve the removal of the annual PM10
increments from any State implementation plan on or after the date we
approve the new PM2.5 increments in the same plan.  We believe that
States should request the removal of the annual PM10 increments from
their PSD programs at the same time they submit plan revisions
containing the new PM2.5 increments, allowing EPA to act on both actions
simultaneously.  

Similarly, we propose to retain the annual PM10 increments in the part
52 PSD regulations until the effective date of the new PM2.5 increments.
 

Transition Period

	We believe that it is appropriate to establish a transition period to
clarify when PSD permit applications must contain an increment analysis
for the new PM2.5 increments following the date they become effective
and are approved as part of any State or Federal PSD program.  In the
past, we have allowed for permit applications submitted before the
implementation date of new increment regulations to continue to be
processed under the existing rules, so long as the permitting authority
has determined  that the application is complete before the
implementation date .  See e.g., existing        40 CFR 51.166(a)(i)(8)
and (9).  Consequently, we are also proposing a new provision in both
the parts 51 and 52 PSD regulations to provide a transition process for
initiating the requirement for analysis of the new PM2.5 increments.  
Under the part 51 regulations, we are proposing that during the
transition period , States have discretion to continue the existing 
PM10 increment program or begin implementing the new PM2.5 increment
program .  For the federally administered programs under part 52 PSD
regulations, the provision would apply to each new PSD permit applicant
upon the effective date of the rule.  However, we are also proposing a
similar transition period in these programs.  See proposed 40 CFR
51.166(i)(10) and 40 CFR 52.21(i)(11), respectively.

Effective Date for SILs and SMCs

	Unlike the approach we propose for PM2.5 increments, we are not
proposing to make SILs and SMCs a minimum element of an approved SIP. 
Accordingly, we are not proposing to establish specific deadlines for
submission of revisions to incorporate the final rules in to SIPs.  We
do not believe that SILs or SMCs are required elements of an approvable
State program because in the absence of these requirements, States can
satisfy the statutory requirements by obtaining pre-construction
monitoring data and conducting a cumulative air quality analysis for
every PSD permit application.

Nonetheless, we believe that availability of SILs and SMCs greatly
improve program implementation by streamlining the permit process and
reducing the labor hours necessary to submit and review a complete
permit application where the projected impact of the proposed source is
de minimis de minimis in the relevant area.  For these reasons, we
request comment on whether we have authority to establish these as
minimum program elements based on the improved efficiency of the permit
process.  If we require States to incorporate SILs and SMCs as mandatory
elements of an approvable program, then we would apply the existing
regulations at 40 CFR 166(a)(6) for establishing the SIP submittal
deadline.  Under either approach, the final rules would become effective
60 days after we promulgate the final rules.

Statutory and Executive Order Reviews

Executive Order 12866:  Regulatory Planning and Review

	Under Executive Order 12866 (58 FR 51735, October 4, 1993), this action
is a significant regulatory action because it raises novel legal or
policy issues arising out of legal mandates, the President’s
priorities, or the principle set forth in the EO.  Accordingly, EPA
submit 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.

Paperwork Reduction Act

The information collection requirements in this rule have been submitted
for approval to the OMB under the Paperwork Reduction Act, 44 U.S.C.
3501 et seq.  The information collection requirements are not
enforceable until OMB approves them.  The Information Collection Request
(ICR) document prepared by EPA has been assigned OMB Control Number
2060-0003 (EPA ICR No. 1230.21). 

Certain records and reports are necessary for the State or local agency
(or the EPA Administrator in non-delegated States), for example, to: (1)
confirm the compliance of status of stationary sources, identify any
stationary sources not subject to the standards, and identify stationary
sources subject to the rules; and (2) ensure that the stationary source
control requirements are being achieved.  The information would be used
by EPA or State enforcement personnel to (1) identify stationary sources
subject to the rules, (2) ensure that appropriate control technology is
being properly applied, and (3) ensure that the emission control devices
are being properly operated and maintained on a continuous basis.  

The proposed rule would increase the burden for owners and operators of
major stationary sources by adding new requirements for the review of
PM2.5 emissions from new and modified major stationary sources,
pertaining to tracking new emissions of PM2.5 against maximum allowable
pollutant concentration increases (increments); collecting ambient air
quality monitoring data for existing PM2.5 concentrations; reviewing the
effects of PM2.5 emissions on soils and vegetation, as well as on air
quality related values in Class I areas, and requiring the application
of best available control technology.  At the same time, there would be
a reduction in burden directly associated with the revocation of the
annual increment for PM10, as proposed in this proposed rule.  Over the
3-year period covered by the ICR, we estimate an average annual burden
increase of about 10,600 hours and $ 694,300 for all industry entities
that would be affected by the proposed rule.  For the same reasons, we
also expect the proposed rule to increase burden for the State and local
authorities reviewing permit applications when fully implemented.  In
addition, there would be additional burden for State and local agencies
to revise their SIPs to incorporate the proposed changes.  We estimate
this one-time burden to be about 1493 annual hours and $65,005 for all
State and local reviewing authorities that would be affected by this
proposed rule.    

Burden means the total time, effort, or financial resources expended by
persons to generate, maintain, retain, or disclose or provide
information to or for a Federal agency.  This includes the time needed
to review instructions; develop, acquire, install, and utilize
technology and systems for the purposes of collecting, validating, and
verifying information, processing and maintaining information, and
disclosing and providing information; adjust the existing ways to comply
with any previously applicable instructions and requirements; train
personnel to be able to respond to a collection of information; search
data sources; complete and review the collection of information; and
transmit or otherwise disclose the information.

Any 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.

To comment on the Agency's need for this information, the accuracy of
the provided burden estimates, and any suggested methods for minimizing
respondent burden, including the use of automated collection techniques,
EPA has established a public docket for this rule, which includes this
ICR, under Docket ID number EPA-HQ-OAR-2003-0605.   Submit any comments
related to the ICR for this proposed rule to EPA and OMB.  See
‘Addresses’ section at the beginning of this notice for where to
submit comments to EPA.  Send comments to OMB at the Office of
Information and Regulatory Affairs, Office of Management and Budget,
725, 17th Street, NW, Washington, DC 20503, Attention: Desk Office for
EPA.  Since OMB is required to make a decision concerning the ICR
between 30 and 60 days after [INSERT DATE OF PUBLICATION IN THE FEDERAL
REGISTER], a comment to OMB is best assured of having itsit’s full
effect if OMB receives it by [INSERT DATE 30 DAYS AFTER DATE OF
PUBLICATION IN THE FEDERAL REGISTER].    The final rule will respond to
any OMB or public comments on the information collection requirements
contained in this proposal.		

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 proposed rule on small
entities, (small entity( is defined as: (1) a small business as defined
by the Small Business Administration’s regulations at 13 CFR 121.201;
(2) a small governmental jurisdiction that is a government or 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 itsit’s field.  .

After considering the economic impacts of this proposed rule on small
entities, I certify that this rule will not have a significant economic
impact on a substantial number of small entities.  The requirements of
this proposed rule apply only to new major stationary sources, based on
their potential to emit at least 250 tons per year (or 100 tons per year
in certain cases) of any air pollutant, or major modifications of
existing major stationary sources.

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.  Under section 202 of the UMRA, we
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
aggregate, or to the private sector, of $100 million or more in any 1
year.  Before promulgating an EPA rule for which a written statement is
needed, section 205 of the UMRA generally requires us to identify and
consider a reasonable number of regulatory alternatives and 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 us 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 we establish any regulatory
requirements that may significantly or uniquely affect small
governments, including tribal governments, we 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 our regulatory proposals with significant
Federal intergovernmental mandates, and 

informing, educating, and advising small governments on compliance with
the regulatory requirements.

We have determined that this proposed 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 1 year. The
proposed rule adds only a relatively small number of new requirements to
the existing permit requirements already in place under the PSD program,
since States are currently implementing a PM10 surrogate program
pursuant to EPA guidance.  Thus, this proposed rulemaking is not subject
to the requirements of sections 202 and 205 of the UMRA.

Executive Order 13132:  Federalism

Executive Order 13132, entitled “Federalism” (64 FR 43255, August
10, 1999), requires us to develop an accountable process to ensure
Ameaningful and timely input by State and local officials in the
development of regulatory policies that have federalism implications.@ 
APolicies that have federalism implications@ is defined in the Executive
Order to include regulations that have Asubstantial 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 proposed rule does not have federalism implications.  It would 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.  Pursuant to the terms of Executive
Order 13132, it has been determined that this proposed rule does not 

have "federalism implications" because it does not meet the necessary
criteria.  Thus, the requirements of section 6 of the Executive Order do
not apply to this proposed rule.

In the spirit of Executive Order 13132, and consistent with our policy
to promote communications between us and State and local governments, we
specifically solicit 

comment on this proposed rule from State and local officials.  

Executive Order 13175:  Consultation and Coordination with Indian Tribal
Governments

Executive Order 13175, entitled “Consultation and Coordination with
Indian Tribal Government” (65 FR 67249, November 6, 2000), requires us
to develop an accountable process to ensure Ameaningful and timely input
by tribal officials in the development of regulatory policies that have
tribal implications.@

This proposed rule does not have "Tribal implications" as defined in
Executive Order 13175.  This rule provides the elements to implement a
PM2.5 PSD program in attainment areas.  The CAA provides for States to
develop plans to regulate emissions of air pollutants within their
jurisdictions.  The Tribal Air Rule (TAR) under the CAA gives Tribes the
opportunity to develop and implement CAA programs such as programs to
attain and maintain the PM2.5 NAAQS, but it leaves to the discretion of
the Tribe the decision of whether to develop these programs and which
programs, or appropriate elements of a program, they will adopt. 

Although Executive Order 13175 does not apply to this rule, EPA did
reach out to national Tribal Organizations in 2006 to provide a forum
for tribal professionals to provide input to the rulemaking.   However,
since this program is being implemented by EPA in Indian country, not
much participation or input was received.  It will neither impose
substantial direct compliance costs on tribal governments, nor preempt
Tribal law.   EPA specifically solicits additional comment on this
proposed rule from tribal officials.

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

Executive Order  13045 “Protection of Children from Environmental
Health Risks and Safety Risks” (62 FR 19885, April 23, 1997) applies
to any rule that:  (1) is determined to be "economically significant" as
defined under Executive Order 12866, and (2) concerns an environmental
health or safety risk that we have reason to believe may have a
disproportionate effect on children.  If the regulatory action meets
both criteria, the Agency must evaluate the environmental health or
safety effects of the planned rule on children, and explain why the
planned regulation is preferable to other potentially effective and
reasonably feasible alternatives considered by the Agency.

	This proposed rule is not subject to the EO because it is not
economically significant as defined in EO 12866, and because the Agency
does not have a reason to believe the environmental health or safety
risks addressed by this action present a disproportionate risk to
children because one of the basic requirements of the PSD program is
that new and modified major stationary sources must demonstrate that any
new emissions do not cause or contribute to air quality in violation of
the national ambient air quality standards.  The public is invited to
submit or identify peer-reviewed studies and data, of which EPA may not
be aware, that assessed resolutions of early life exposure to ambient
concentrations of fine particulate measured as PM2.5.

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

	This rule is not subject to 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 proposed rule adds elements to streamline the PSD
permitting of major sources and hence would reduce the permitting costs
to the sources.  

National Technology Transfer and Advancement Act

Section 12(d) of the National Technology Transfer and Advancement Act of
1995 (NTTAA), Public Law No. 104-113, 12(d) (15 U.S.C. 272 note)
directs us to use voluntary consensus standards (VCS) in our regulatory
and procurement activities unless to do so would be inconsistent with
applicable law or otherwise impractical.  The VCS are technical
standards (e.g., materials specifications, test methods, sampling
procedures, and business practices) developed or adopted by one or more
voluntary consensus bodies.  The NTTAA directs us to provide Congress,
through annual reports to OMB, with explanations when we do not use
available and applicable VCS. This proposed rule does not involve
technical standards.  Therefore, we are not considering the use of any
voluntary consensus standards.

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

Executive Order 12898 (59 FR 7629 (February 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.

The EPA has determined that this proposed rule will not have
disproportionately high and adverse human health environmental effects
on minority or low-income populations because it does not affect the
level of protection provided to human health or the environment.  This
regulation would provide regulatory certainty for implementing the
preconstruction NSR permitting program for PM2.5, requiring sources to
put on Best Available Control Technology.  Consequently, the regulations
should result in some health benefits to persons living in low-income
and minority communities.  

Statutory Authority 

The statutory authority for this proposed action is provided by sections
101, 160, 163, 165, 166, 301, and 307(d) of the Act as amended (42
U.S.C. 7401, 7470, 7473, 7475, 7476, 7601, and 7607(d)).

List of Subjects

40 CFR Part 51

Administrative practices and procedures, Air pollution control,
Environmental protection, Intergovernmental relations.

40 CFR Part 52

Administrative practices and procedures, Air pollution control,
Environmental protection, Intergovernmental relations.



Page 139 42 of 1647 - Prevention of Significant Deterioration (PSD) for
Particulate Matter Less Than 2.5 Micrometers (PM2.5) – Increments,
Significant Impact Levels (SILs) and Significant Monitoring
Concentration (SMC)

  

  ___________________________                                           
                                                             

Dated:

____________________________

Stephen L. Johnson,

Administrator 



  SEQ CHAPTER \h \r 1 For the reasons set out in the preamble, title 40,
chapter I of the Code of Federal Regulations is proposed to be amended
as follows:

PART 51 - [Amended]

	1.  The authority citation for part 51 continues to read as follows:

	Authority: 23 U.S.C. 101; 42 U.S.C. 7401 - 7671q.

Subpart I - [Amended]

	2.  Section 51.165 is amended by revising the table in paragraph (b)(2)
to read as follows:

§51.165  Permit requirements.

* * * * *

	(b)  * * *

	(2)  * * *

Option 1 for the table in paragraph (b)(2):

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 (g/m3	

	

1.0 (g/m3	

1.0 (g/m3	

		5 (g/m3	

5 (g/m3	

5 (g/m3	

	

			

	

	

	

0.5 mg/m3		25 (g/m3	

	

	

	

		

2 mg/m3



Option 2 for the table in paragraph (b)(2):

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 (g/m3	

	

0.8 (g/m3	

1.0 (g/m3	

		5 (g/m3	

5 (g/m3	

4 (g/m3	

	

			

	

	

	

0.5 mg/m3		25 (g/m3	

	

	

	

		

2 mg/m3



Option 3 for the table in paragraph (b)(2):

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 (g/m3	

	

0.3 (g/m3	

1.0 (g/m3	

		5 (g/m3	

5 (g/m3	

1.2 (g/m3	

	

			

	

	

	

0.5 mg/m3		25 (g/m3	

	

	

	

		

2 mg/m3



* * * * *

	3.  Section 51.166 is amended as follows:

  SEQ CHAPTER \h \r 1 	a.  By revising the table in paragraph (c);

	b.  By revising paragraph (i)(5)(i)(c); 

	c.  By revising paragraphs (i)(5)(ii) and (iii);

	d.  By revising paragraphs (i)(8) and (9);

	e.  By adding paragraph (i)(10); 

	f.   By revising paragraph (k); and

	g.  By revising the table in paragraph (p)(4).

	§51.166 Prevention of significant deterioration of air quality.

* * * * *

	(c)  * * * 

Option 1 for the table in paragraph (c):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10: 

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

8

2

5

25

2.5

Class II

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

30

20

91

512

25

Class III

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

PM10, 24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

8

18

60

40

182

700

50



Option 2A for the table in paragraph (c):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

8

2

5

25

2.5

Class II

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

30

20

91

512

25

Class III

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

8

18

60

40

182

700

50



Option 2B for the table in paragraph (c):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

8

2

5

25

2.5

Class II

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

5

9

30

20

91

512

25

Class III

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

10

18

60

40

182

700

50

	

* * * * *

	(i)  * * *

	(5)  * * *

	(i)  * * *

	(c)  Particulate matter:

	(1)  10 (g/m3 of PM10, 24-hour average;

Option 1 for paragraph (i)(5)(i)(c)(2):

	(2)  10 (g/m3 of PM2.5, 24-hour average;

Option 2 for paragraph (i)(5)(i)(c):

	(2)  8.0 (g/m3 of PM2.5, 24-hour average;

Option 3 for paragraph (i)(5)(i)(c):

	(2)  2.3 (g/m3 of PM2.5, 24-hour average;

* * * * *

	(ii)  The concentrations of the pollutant in the area that the source
or modification would affect are less than the concentrations listed in
paragraph (i)(5)(i) of this section; or

	(iii)  The pollutant is not listed in paragraph (i)(5)(i) of this
section.

* * * * *

	(8)  The plan may provide that the permitting requirements equivalent
to those contained in paragraph (k)(1)(b) of this section do not apply
to a stationary source or modification with respect to any maximum
allowable increase for nitrogen oxides if the owner or operator of the
source or modification submitted an application for a permit under the
applicable permit program approved or promulgated under the Act before
the provisions embodying the maximum allowable increase took effect as
part of the plan and the permitting authority subsequently determined
that the application as submitted before that date was complete.

	(9)  The plan may provide that the permitting requirements equivalent
to those contained in paragraph (k)(1)(b) of this section shall not
apply to a stationary source or modification with respect to any maximum
allowable increase for PM10 if (i) the owner or operator of the source
or modification submitted an application for a permit under the
applicable permit program approved under the Act before the provisions
embodying the maximum allowable increases for PM10 took effect as part
of the plan, and (ii) the permitting authority subsequently determined
that the application as submitted before that date was complete. 
Instead, the applicable requirements equivalent to paragraph (k)(1)(b)
shall apply with respect to the maximum allowable increases for TSP as
in effect on the date the application was submitted.

	(10)  The plan may provide that the permitting requirements equivalent
to those contained in paragraph (k)(1)(b) of this section shall not
apply to a stationary source or modification with respect to any maximum
allowable increase for PM2.5 if (i) the owner or operator of the source
or modification submitted an application for a permit under the
applicable permit program approved under the Act before the provisions
embodying the maximum allowable increases for PM2.5 took effect as part
of the plan, and (ii) the permitting authority subsequently determined
that the application as submitted before that date was complete. 
Instead, the applicable requirements equivalent to paragraph (k)(1)(b)
shall apply with respect to the maximum allowable increases for PM10 as
in effect on the date the application was submitted.

* * * * *

	(k)  Source impact analysis.  

(1)  Required demonstration.  The plan shall provide that the owner or
operator of the proposed source or modification shall demonstrate that
allowable emission increases from the proposed source or modification,
in conjunction with all other applicable emissions increases or
reduction (including secondary emissions), would not cause or contribute
to air pollution in violation of:

	(a)  Any national ambient air quality standard in any air quality
control region; or

	(b)  Any applicable maximum allowable increase over the baseline
concentration in any area.

	(2)  Significant impact levels.  The plan shall provide that, for
purposes of PM2.5, the demonstration required in paragraph (k)(1) of
this section is deemed to have been made if the emissions increase of
direct PM2.5 emissions from the new stationary source alone or the net
emissions increase of direct PM2.5 emissions from the modification alone
would cause, in all areas, air quality impacts less than the following
amounts:

Option 1 for the table in paragraph (k)(2):

Averaging time	Class I significant impact levels	Class II significant
impact levels	Class III significant impact levels

Annual		0.04 (g/m3		1.0 (g/m3		1.0 (g/m3

24-hour		0.08 (g/m3		5.0 (g/m3		5.0 (g/m3



Option 2 for the table in paragraph (k)(2):

Averaging time	Class I significant impact levels	Class II significant
impact levels	Class III significant impact levels

Annual		0.16 (g/m3		0.8 (g/m3		0.8 (g/m3

24-hour		0.24 (g/m3		4.0 (g/m3		4.0 (g/m3



Option 3 the table in paragraph (k)(2):

Averaging time	Class I significant impact levels	Class II significant
impact levels	Class III significant impact levels

Annual		0.06 (g/m3		0.3 (g/m3		0.3 (g/m3

24-hour		0.07 (g/m3		1.2 (g/m3		1.2 (g/m3



* * * * *

	(p)  * * *

	(4)  * * *

Option 1 for the table in paragraph (p)(4):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

30

20

91

325

25



Option 2A for the table in paragraph (p)(4):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

30

20

91

325

25



Option 2B for the table in paragraph (p)(4):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

5

9

30

20

91

325

25



* * * * *

	4.  Appendix S to part 51 is amended by revising the table in Section
III.A to read as follows:

Appendix S to Part 51—Emission Offset Interpretative Ruling

* * * * *

	III.  * * *

	A.  * * *

Option 1 for the table in Section III.A:

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 (g/m3	

	

1.0 (g/m3	

1.0 (g/m3	

		5 (g/m3	

5 (g/m3	

5 (g/m3	

	

			

	

	

	

0.5 mg/m3		25 (g/m3	

	

	

	

		

2 mg/m3



Option 2 for the table in Section III.A:

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 (g/m3	

	

0.8 (g/m3	

1.0 (g/m3	

		5 (g/m3	

5 (g/m3	

4 (g/m3	

	

			

	

	

	

0.5 mg/m3		25 (g/m3	

	

	

	

		

2 mg/m3





Option 3 for the table in Section III.A:

Pollutant	Annual	Averaging time (hours)



24	8	3	1

SO2	

PM10	

PM2.5	

NO2	

CO		1.0 (g/m3	

	

0.3 (g/m3	

1.0 (g/m3		5 (g/m3	

5 (g/m3	

1.2 (g/m3	

	

			

	

	

	

0.5 mg/m3		25 (g/m3	

	

	

	

		

2 mg/m3



* * * * *

PART 52 - [Amended]

	5.  The authority citation for part 52 continues to read as follows:

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

Subpart A - [Amended]

	6.  Section 52.21 is amended as follows:

	  SEQ CHAPTER \h \r 1 a.  By revising the table in paragraph (c); 

	b.  By revising the third entry in paragraph (i)(5)(i); 

	c.  By revising paragraphs (i)(5)(ii) and (iii);

	d.  By revising paragraphs (i)(9) and (10);

	e.  By adding paragraph (i)(11); 

	f.  By revising paragraph (k); and

	g.  By revising the table in paragraph (p)(5).

	§52.21  Prevention of significant deterioration of air quality.

* * * * *

	(c)  * * * 

Option 1 for the table in paragraph (c):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

8

2

5

25

2.5

Class II

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

30

20

91

512

25

Class III

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

PM10, 24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

8

18

60

40

182

700

50



Option 2A for the table in paragraph (c):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

8

2

5

25

2.5

Class II

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

30

20

91

512

25

Class III

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

8

18

60

40

182

700

50



Option 2B for the table in paragraph (c):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

Class I

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

1

2

8

2

5

25

2.5

Class II

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

5

9

30

20

91

512

25

Class III

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

10

18

60

40

182

700

50

	

* * * * *

	(i)  * * *

	(5)  * * *

	(i)  * * *

Option 1 for the third entry in paragraph (i)(5)(i):

	Particulate matter:

	(a)  10 (g/m3 of PM10, 24-hour average;

	(b)  10 (g/m3 of PM2.5, 24-hour average;

Option 2 for the third entry in paragraph (i)(5):

	Particulate matter:

	(a)  10 (g/m3 of PM10, 24-hour average;

 	(b)  8.0 (g/m3 of PM2.5, 24-hour average;

Option 3 for the third entry in paragraph (i)(5):

	Particulate matter:

	(a)  10 (g/m3 of PM10, 24-hour average;

 	(b)  2.3 (g/m3 of PM2.5, 24-hour average;

* * * * *

	(ii)  The concentrations of the pollutant in the area that the source
or modification would affect are less than the concentrations listed in
paragraph (i)(5)(i) of this section; or

	(iii)  The pollutant is not listed in paragraph (i)(5)(i) of this
section.

* * * * *

	(9)  The requirements of paragraph (k)(1)(a) of this section shall not
apply to a stationary source or modification with respect to any maximum
allowable increase for nitrogen oxides if the owner or operator of the
source or modification submitted an application for a permit under this
section before the provisions embodying the maximum allowable increase
took effect as part of the applicable implementation plan and the
Administrator subsequently determined that the application as submitted
before that date was complete.

	(10)  The requirements in paragraph (k)(1)(b) of this section shall not
apply to a stationary source or modification with respect to any maximum
allowable increase for PM10 if (i) the owner or operator of the source
or modification submitted an application for a permit under this section
before the provisions embodying the maximum allowable increases for PM10
took effect in an implementation plan to which this section applies, and
(ii) the Administrator subsequently determined that the application as
submitted before that date was otherwise complete.  Instead, the
requirements in paragraph (k)(1)(b) shall apply with respect to the
maximum allowable increases for TSP as in effect on the date the
application was submitted.

	(11)  The requirements in paragraph (k)(1)(b) of this section shall not
apply to a stationary source or modification with respect to any maximum
allowable increase for PM2.5 if (i) the owner or operator of the source
or modification submitted an application for a permit under this section
before the provisions embodying the maximum allowable increases for
PM2.5 took effect in an implementation plan to which this section
applies, and (ii) the Administrator subsequently determined that the
application as submitted before that date was otherwise complete. 
Instead, the requirements in paragraph (k)(1)(b) shall apply with
respect to the maximum allowable increases for PM10 as in effect on the
date the application was submitted.

* * * * *

	(k)  Source impact analysis.  

(1)  Required demonstration.  The owner or operator of the proposed
source or modification shall demonstrate that allowable emission
increases from the proposed source or modification, in conjunction with
all other applicable emissions increases or reductions (including
secondary emissions), would not cause or contribute to air pollution in
violation of:

	(a)  Any national ambient air quality standard in any air quality
control region; or

	(b)  Any applicable maximum allowable increase over the baseline
concentration in any area.

	(2)  Significant impact levels.  For purposes of PM2.5, the
demonstration required in paragraph (k)(1) of this section is deemed to
have been made if the emissions increase of direct PM2.5 emissions from
the new stationary source alone or the net emissions increase of direct
PM2.5 emissions from the modification alone would cause, in all areas,
air quality impacts less than the following amounts:



Option 1 for the table in paragraph (k)(2):

Averaging time	Class I significant impact levels	Class II significant
impact levels	Class III significant impact levels

Annual		0.04 (g/m3		1.0 (g/m3		1.0 (g/m3

24-hour		0.08 (g/m3		5.0 (g/m3		5.0 (g/m3



Option 2 for the table in paragraph (k)(2):

Averaging time	Class I significant impact levels	Class II significant
impact levels	Class III significant impact levels

Annual		0.16 (g/m3		0.8 (g/m3		0.8 (g/m3

24-hour		0.24 (g/m3		4.0 (g/m3		4.0 (g/m3



Option 3 for the table in paragraph (k)(2):

Averaging time	Class I significant impact levels	Class II significant
impact levels	Class III significant impact levels

Annual		0.06 (g/m3		0.3 (g/m3		0.3 (g/m3

24-hour		0.07 (g/m3		1.2 (g/m3		1.2 (g/m3



* * * * *

	(p)  * * *

	(5)  * * *



Option 1 for the table in paragraph (p)(5):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

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ఀ24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

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9

30

20

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325

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Option 2 for the table in paragraph (p)(5):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

4

9

30

20

91

325

25



Option 3 for the table in paragraph (p)(5):

Pollutant	Maximum allowable increase (micrograms per cubic meter)

PM2.5:

Annual arithmetic mean	

24-hr maximum	

PM10:

24-hr maximum	

Sulfur dioxide:

Annual arithmetic mean	

24-hr maximum	

3-hr maximum	

Nitrogen dioxide:  

Annual arithmetic mean		

5

9

30

20

91

325

25



* * * * *

1 In this proposal, the terms “we,” “us,” and “our” refer to
the EPA and the terms “you” and “your” refer to the owners or
operators of stationary sources of air pollution.

2 We have delegated authority to some States to implement the Federal
PSD program.  The EPA remains the permitting authority in non-delegated
States and in Indian country.

3  Baseline dates are pollutant specific.  That is, a complete PSD
application establishes the baseline date only for those regulated NSR
pollutants that are projected to be emitted in significant amounts (as
defined in the regulations) by the applicant’s new source or
modification.  Thus, an area may have different baseline dates for
different pollutants.  Also, the baseline remains triggered even if the
applicant later withdraws the initial permit application.

 We note that on June 6, 2007, we published a notice of proposed
rulemaking proposing to refine several aspects of the increment
calculation process to clarify how States and regulated sources may
calculate increases in pollutant concentrations for purposes of
determining compliance with the PSD increments.  See 72 FR at 31372. 
When final, these revisions will amend the PSD regulations at 40 CFR
51.166 and 52.21.

 See EPA’s “Guideline on Air Quality Models” at 40 CFR part 51,
appendix W.

 The term “air quality related values” is not defined in the Act,
but the legislative history provides that “The term ‘air quality
related values’ of Federal lands designated as class I includes the
fundamental purposes for which such lands have been established and
preserved by the Congress and the responsible Federal agency.  For
example, under the 1916 Organic Act to establish the National Park
Service (16 U.S.C. 1), the purpose of such national park lands ‘is to
conserve the scenery and the natural and historic objects and the
wildlife therein and to provide for the enjoyment of the same in such
manner and by such means as will leave them unimpaired for the enjoyment
of future generations.’” S. Rep. No. 95-127 at 36 (1977)

4 Under the 2005 NOx regulation, States can adopt measures other than
increments as long as they can demonstrate that the measures selected
comply with the same criteria and goals of 166 (c) and (d) of the Act
that must be met for increments.

5 In our review of the PM NAAQS, we concluded that, because the fine and
thoracic coarse components of PM10 generally have different sources,
composition and formation processes, they should be treated as separate
pollutants.  (OAQPS SP, December 2005, page 3-1.)

6 Even if such a waiver of the Class I increment is allowed upon a
finding of no adverse impact, the source must comply with such emissions
limitations as may be necessary to ensure that the Class II increment
for SO2 or PM is not exceeded.  Section 165(d)(2)(C)(iv).  The EPA made
this provision applicable to the PSD provisions for NOx, with a cap of
25 g/m3 - the NO2 Class II increment.  53 FR 3704; 40 CFR 51.166(p)(4)
and 52.21(p)(5).

7 In response to concerns that Class I increment would hinder growth in
areas surrounding the Class I area, Congress established Class I
increments as a means of determining where the burden of proof should
lie for a demonstration of adverse effects on AQRVs.  See Senate Debate,
June 8, 1977 (3 LH at 725).

8 See S. Rep. 95-127, at 12, reprinted at 3 LH at 1386, 1410 (describing
the goal of protecting “air quality values” in “Federal lands -
such as national parks and wilderness areas and international parks,”
and in the next paragraph and subsequent text using the term “air
quality related values” to describe the same goal); id. at 35, 36
(“The bill charges the Federal land manager and the supervisor with a
positive role to protect air quality values associated with the land
areas under the jurisdiction of the [FLM]” and then describing the
statutory term as “air quality related values”).  H.R. Report 95-564
at 532 (describing duty of Administrator to consider “air quality
values” of the tribal and State lands in resolving an appeal of a
tribal or State redesignation, which is described in the final bill as
“air quality related values”).

9 We have paraphrased these factors here and in other sections to
facilitate the explanation of our reasoning.  However, we recognize, as
we did in our regulation for NOx that the statutory language is broader
than the shorthand we use here for convenience.

10 This periodic review of the PM NAAQS updates the last review, which
began in 1994 and resulted in revised standards for PM in 1997. 

11 The form of the 1987 24-hour PM10 standard is based on the expected
number of day per year (averaged over 3 years) on which the level of the
standard is exceeded; thus, attainment with the one-expected exceedance
form is determined by comparing the fourth-highest concentration in 3
years with the level of the standard.

12 It should be noted, however, that an increment does not allow air
pollution levels in an area to increase beyond the ambient concentration
of a pollutant that would exceed the level allowed by the NAAQS.

orb on a sustained basis before it experiences a measurable amount of
degradation.  In contrast to the units for increments, μg/m3, a
critical load is typically expressed as a loading rate in kilograms of a
pollutant per hectare per year.

葞Ũ

 Emissions Estimates by Source Categories

15 Memorandum from Rehme, K. A., EPA/EMSL/QAD/MSB, to Peters, W.,
EPA/OAQPS/CPDD, on PSD Monitoring.  May 20, 1980.

Draft

Do not quote, cite, copy, or distribute.

026/0826/07

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