
[Federal Register Volume 77, Number 124 (Wednesday, June 27, 2012)]
[Proposed Rules]
[Pages 38399-38420]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2012-15544]



[[Page 38399]]

Vol. 77

Wednesday,

No. 124

June 27, 2012

Part II





Environmental Protection Agency





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40 CFR Part 52





Approval and Promulgation of Implementation Plans; Arizona; Nogales 
PM10 Nonattainment Area Plan; Proposed Rule

  Federal Register / Vol. 77 , No. 124 / Wednesday, June 27, 2012 / 
Proposed Rules  

[[Page 38400]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2012-0458; FRL-9693-6]


Approval and Promulgation of Implementation Plans; Arizona; 
Nogales PM10 Nonattainment Area Plan

AGENCY: Environmental Protection Agency.

ACTION: Proposed rule.

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SUMMARY: EPA is proposing to approve a state implementation plan 
revision submitted by the Arizona Department of Environmental Quality 
to address the moderate area PM10, particulate matter with 
an aerodynamic diameter of less than or equal to a nominal ten 
micrometers, planning requirements for the Nogales nonattainment area. 
Consistent with this proposal, EPA is also proposing to approve the 
following plan elements as meeting the requirements of the Clean Air 
Act: the Nogales nonattainment area 2008 and 2011 emission inventories; 
the demonstration that the Nogales nonattainment area is attaining the 
National Ambient Air Quality Standard for PM10, but for 
international emissions sources in Nogales, Mexico; the demonstration 
that reasonably available control measures sufficient to meet the 
standard have been implemented in the nonattainment area; the 
reasonable further progress demonstration; the demonstration that 
implementation of measures beyond those needed for attainment meet the 
contingency measure requirement; and, the motor vehicle emissions 
budget for the purposes of determining the conformity of transportation 
plans, programs, and projects with this PM10 plan.

DATES: Written comments must be received on or before July 27, 2012.

ADDRESSES: Submit comments, identified by docket number EPA-R09-OAR-
2012-0458, using one of the following methods: Via the Federal 
eRulemaking Portal, at www.regulations.gov, please follow the on-line 
instructions; via Email to wamsley.jerry@epa.gov; via mail or delivery 
to Jerry Wamsley, Air Planning Office, AIR-2, Environmental Protection 
Agency (EPA) Region IX, 75 Hawthorne Street, San Francisco, CA 94105-
3901.
    Instructions: All comments will be included in the public docket 
without change and may be made available online at www.regulations.gov, 
including any personal information provided, unless the comment 
includes Confidential Business Information (CBI) or other information 
whose disclosure is restricted by statute. Information you consider to 
be CBI or otherwise protected should be clearly identified as such and 
should not be submitted through www.regulations.gov or email. 
www.regulations.gov is an ``anonymous access'' system, and EPA will not 
know your identity or contact information unless you provide it in the 
body of your comment. If you send an email directly to EPA, your email 
address will be automatically captured and included as part of the 
public comment. 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.
    Docket: The index to the docket for this action is available 
electronically at www.regulations.gov and in hard copy at EPA Region 
IX, 75 Hawthorne Street, San Francisco, California. While all documents 
in the docket are listed in the index, some information may be publicly 
available only at the hard copy location (e.g., copyrighted material), 
and some may not be publicly available at either location (e.g., CBI). 
To inspect the hard copy materials, please schedule an appointment 
during normal business hours with the contact listed in the FOR FURTHER 
INFORMATION CONTACT section.

FOR FURTHER INFORMATION CONTACT: Jerry Wamsley, Air Planning Office, 
AIR-2, EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105-
3901, telephone number: (415) 947-4111, or email address, 
wamsley.jerry@epa.gov.

SUPPLEMENTARY INFORMATION: Throughout this document, wherever ``we'', 
``us'' or ``our'' are used, we mean EPA. We are providing the following 
outline to help locate information in this proposal.

Table of Contents

I. The PM10 National Ambient Air Quality Standard and the 
Nogales PM10 Nonattainment Area
    A. PM10 National Ambient Air Quality Standard
    B. Designation and Classification of PM10 Nonattainment Areas, 
Including the Nogales Nonattainment Area
    C. Clean Air Act Plan Requirements for Moderate PM10 
Nonattainment Areas
II. Arizona's State Implementation Plan Submittal To Address PM10 
Attainment in the Nogales Nonattainment Area
    A. Arizona's Submittal and Clean Air Act Procedural Requirements
    B. Description of the Nogales Nonattainment Area
III. CAA and Regulatory Requirements for Moderate Area 
PM10 Attainment Plans and Nonattainment Areas Influenced 
by International Transport
    A. Moderate PM10 Area Planning Requirements
    B. Clean Air Act Provisions and EPA Guidance Concerning 
International Border Areas
    1. Section 179B of the Clean Air Act
    2. The 1994 General Preamble Addendum
    3. Statutory Requirements and Guidance for Determining 
Attainment of the PM10 NAAQS
IV. Review of the Nogales 2012 Plan
    A. Emissions Inventories
    1. Requirements for Emissions Inventories
    2. Review of the Nogales Nonattainment Area Emissions Inventory
    3. Proposed Action on the Nogales Nonattainment Area 2008 and 
2011 Emissions Inventories
    B. Section 179B Analysis and Demonstration of Attainment but for 
International Sources of PM10 Emissions
    1. Review of Statute and Guidance Applied to the Nogales Section 
179B Analysis and Demonstration of Attainment but for International 
Sources of PM10 Emissions
    2. Review of Arizona's Section 179B Analysis and Demonstration 
of Attainment but for International Sources of PM10 
Emissions
    a. Population Growth in the Ambos Nogales Region
    b. Review and Comparison of U.S./Mexico Emission Inventories
    c. Review and Analysis of Regional Meteorology, Topography and 
Ambient PM10 Monitoring Data
    (i) Ambos Nogales Regional Meteorology and Topography
    (ii) Ambient PM10 Monitoring Network, Data, Analyses, 
and Findings
    d. Findings From Reviews of Emission Inventories, and Studies of 
Ambient PM10 Data, and Meteorological Data
    e. Arizona's Demonstration of Attainment for the Nogales 
Nonattainment Area but for International Sources of PM10 
Emissions
    (i) Daily Analysis To Demonstrate Attainment but for 
International Sources of PM10 Emissions
    (ii) Hourly Analysis To Demonstrate Attainment but for 
International Sources of PM10 Emissions
    3. Proposed Action on the Nogales Nonattainment Area Section 
179B Analysis and Demonstration of Attainment but for International 
Sources of PM10 Emissions
    C. Reasonably Available Control Measures (RACM)/Reasonably 
Available Control Technology (RACT) and Adopted Control Strategy
    1. Requirement for RACM/RACT
    2. RACM/RACT in the Nogales Nonattainment Area
    D. Reasonable Further Progress Demonstration and Contingency 
Measures in the Nogales Nonattainment Area

[[Page 38401]]

    1. Reasonable Further Progress
    2. Contingency Measures
    E. Motor Vehicle Emissions Budgets for Transportation Conformity
    1. Requirements for Transportation Conformity
    2. Motor Vehicle Emissions Budget for the Nogales Nonattainment 
Area
    3. Proposed Action on the Motor Vehicle Emissions Budget for the 
Nogales Nonattainment Area
VI. EPA's Proposed Action and Request for Comment
VII. Statutory and Executive Order Reviews

I. The PM10 National Ambient Air Quality Standard and the 
Nogales PM10 Nonattainment Area

A. PM10 National Ambient Air Quality Standard

    The EPA sets the National Ambient Air Quality Standard (NAAQS) for 
certain ambient air pollutants at levels required to protect human 
health and the environment. Particulate matter with an aerodynamic 
diameter less than or equal to a nominal ten micrometers, or 
PM10, is one of these ambient air pollutants for which EPA 
has established health-based standards. On July 1, 1987, EPA 
promulgated two primary standards for PM10: A 24-hour 
standard of 150 micrograms per cubic meter ([micro]g/m\3\); and, an 
annual PM10 standard of 50 [micro]g/m\3\. EPA also 
promulgated secondary PM10 standards that were identical to 
the primary standards. 52 FR 24634; (July 1, 1987). Because they are 
identical, we refer to the primary and secondary standards using the 
singular term, ``standard.'' Effective December 18, 2006, EPA revoked 
the annual PM10 standard but retained the 24-hour 
PM10 standard. 71 FR 61144; (October 17, 2006).
    An area attains the 24-hour PM10 standard when the 
expected number of days per calendar year with a 24-hour concentration 
in excess of the standard (referred to herein as an ``exceedance''), is 
equal to or less than one,\1\ as determined in accordance with 40 CFR 
part 50, appendix K. See 40 CFR 50.6 and 40 CFR part 50, appendix K. 
Conversely, a violation of the PM10 NAAQS occurs when the 
number of expected annual exceedances of the 24-hour standard is 
greater than one.
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    \1\ An exceedance is defined as a daily value that is above the 
level of the 24-hour standard, 150 [micro]g/m\3\, after rounding to 
the nearest 10 [micro]g/m\3\ (i.e., values ending in five or greater 
are to be rounded up). Thus, a recorded value of 154 [micro]g/m\3\ 
would not be an exceedance since it would be rounded to 150 
[micro]g/m\3\; whereas, a recorded value of 155 [micro]g/m\3\ would 
be an exceedance since it would be rounded to 160 [micro]g/m\3\. See 
40 CFR part 50, appendix K, section 1.0.
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B. Designation and Classification of PM10 Nonattainment Areas, 
Including the Nogales Nonattainment Area

    Areas meeting the requirements of section 107(d)(4)(B) of the Clean 
Air Act (CAA or ``Act'') were designated nonattainment for 
PM10 by operation of law and classified ``moderate'' upon 
enactment of the 1990 Clean Air Act Amendments. These areas included 
all former Group I PM10 planning areas identified in 52 FR 
29383, (August 7, 1987), as further clarified in 55 FR 45799, (October 
31, 1990), and any other areas violating the NAAQS for PM10 
prior to January 1, 1989. A Federal Register notice announcing the 
areas designated nonattainment for PM10 upon enactment of 
the 1990 Amendments, known as ``initial'' PM10 nonattainment 
areas, was published on March 15, 1991, (56 FR 11101); and, a 
subsequent Federal Register document correcting the description of some 
of these areas was published on August 8, 1991, (56 FR 37654).
    As a former ``Group I'' area, the Nogales nonattainment area (NA) 
was included in the March 1991 list of initial moderate PM10 
nonattainment areas. Later, we codified the PM10 
nonattainment designations and moderate area classifications in 40 CFR 
part 81 (56 FR 56694; November 6, 1991). For ``moderate'' nonattainment 
areas, such as the Nogales NA, CAA section 188(c) of the 1990 Amended 
Act established an attainment date of December 31, 1994. On January 11, 
2011, pursuant to section 188(b)(2) of the CAA, we determined that the 
Nogales NA met the PM10 NAAQS as of the applicable 
attainment date, December 31, 1994. See 76 FR 1532; (January 11, 2011). 
The designation, classification, and boundaries of the Nogales NA are 
codified at 40 CFR 81.303.

C. Clean Air Act Plan Requirements for Moderate PM10 Nonattainment 
Areas

    Along with the new designations, classifications, and attainment 
dates, the CAA as amended in 1990 also established new planning 
requirements. States were required to develop and submit state 
implementation plan (SIP) revisions providing for, among other 
elements, implementation of reasonably available control measures 
(RACM) for control of PM10, a demonstration that the plan 
would provide for attainment by the applicable attainment date 
(``attainment demonstration''), and contingency measures, for all 
moderate PM10 nonattainment areas. See CAA sections 172(c) 
and 189(a). As discussed later, CAA section 179B(a) allows a State to 
submit a demonstration that the plan would be adequate to attain and 
maintain the standard but for emissions emanating from outside the 
United States in lieu of an attainment demonstration. CAA section 
179B(a) does not, however, relieve qualifying moderate PM10 
nonattainment areas of the other SIP requirements, including but not 
limited to RACM and contingency measures.
    In response, on June 14, 1993, the Arizona Department of 
Environmental Quality (referred to herein as ``ADEQ,'' ``Arizona,'' or 
``the State'') submitted the ``Final State Implementation Plan for the 
Nogales PM10 Nonattainment Area,'' June 1993 (``1993 Nogales 
PM10 Plan''). The 1993 Nogales PM10 Plan 
identifies emissions sources located in Mexico as the principal sources 
affecting ambient PM10 concentrations in the area. EPA has 
not taken action on the 1993 Nogales PM10 Plan. Today's 
action relates to an updated plan for the Nogales PM10 
nonattainment area that is intended by ADEQ, once submitted in final 
form, to supersede the 1993 Nogales PM10 Plan.

II. Arizona's State Implementation Plan Submittal To Address 
PM10 Attainment in the Nogales Nonattainment Area

A. Arizona's Submittal and Clean Air Act Procedural Requirements

    Today's proposed action concerns the Proposed State Implementation 
Plan for the Nogales PM10 Nonattainment Area (``Nogales 2012 Plan''), 
submitted by ADEQ on May 29, 2012. ADEQ concurrently requested that EPA 
``parallel process'' our review and proposed action on the Nogales 2012 
Plan addressing the CAA's PM10 moderate area requirements 
for the Nogales NA.2 3 We have agreed to parallel process 
the Nogales 2012 Plan concurrently with the ADEQ's public hearing and 
submittal process using our authority under 40 CFR part 51, appendix V. 
ADEQ's parallel processing request and the Nogales 2012 Plan consist of 
the following documents:

[[Page 38402]]

``Proposed State Implementation Plan for the Nogales PM10 
Nonattainment Area'' with Appendices A-J, May 17, 2012. The Nogales 
2012 Plan, supporting documents, and public hearing information can 
also be found at ADEQ's Web site, http://www.azdeq.gov/environ/air/plan/notmeet.html#nog.
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    \2\ Under EPA's ``parallel processing'' procedure, EPA proposes 
rulemaking action on a proposed SIP revision concurrently with the 
State's public review process. If the State's proposed SIP revision 
is changed, EPA will evaluate that subsequent change and may publish 
another notice of proposed rulemaking. If no significant change is 
made, EPA will propose a final rulemaking on the SIP revision after 
responding to any submitted comments. Final rulemaking action by EPA 
will occur only after the final SIP revision has been fully adopted 
by ADEQ and submitted formally to EPA for approval as part of the 
Arizona SIP. See 40 CFR part 51, appendix V.
    \3\ Letter from Eric Massey, Director, Air Quality Division, 
Arizona Department of Environmental Quality, to Jared Blumenfeld, 
Regional Administrator, EPA, dated May 29, 2012.
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    We have reviewed the ADEQ's May 29, 2012 parallel processing 
submittal against the completeness criteria at 40 CFR part 51, appendix 
V, section 2.3.1. and find that the submittal is complete. These 
completeness criteria are used specifically for parallel processing 
submittals. Once we have received ADEQ's supplemental submittal after 
the State concludes their public hearing process, we will use the 
general completeness criteria at 40 CFR part 51, appendix V, 2.0 to 
determine completeness of that submittal. Our completeness finding on 
this supplemental submittal will be made as part of our final action on 
this proposal.

B. Description of the Nogales Nonattainment Area

    Covering 76.1 square miles, the Nogales NA is located within Santa 
Cruz County, Arizona, with the southernmost boundary of the Nogales NA 
and Santa Cruz County being the United States (U.S.)/Mexico border. 
Adjacent to the U.S./Mexico border, the city of Nogales, Arizona is 60 
miles south of Tucson, Arizona. The city of Nogales, Arizona is the 
largest city and population center in the Nogales NA.
    The Nogales NA is located within the Sonoran Desert. This desert 
covers 120,000 square miles with a minimum elevation of 2,500 feet 
above sea level and is in the Basin and Range topographic province. 
This topography is characterized by north-south elongated valleys 
surrounded by mountain ranges. Nogales is located in such a north-south 
valley created by the Nogales Wash running north to the Santa Cruz 
River. The mean elevation in Nogales, Arizona is 3,865 feet above sea 
level. Major highways in the Nogales, Arizona area are U.S. Interstate 
19 which connects Tucson, Arizona to Nogales, Arizona and continues 
south into Mexico, where it becomes Federal Highway 15, and Arizona 
State Route 82, which connects Nogales, Arizona with Patagonia, Arizona 
(19 miles) and Sonoita (31 miles) to the northeast.
    Nogales, Mexico lies directly south of Nogales, Arizona across the 
U.S./Mexico border. Taken together and referred to as Ambos Nogales, 
the communities of Nogales, Arizona and Nogales, Mexico comprise the 
largest international border community in Arizona, with a combined 
population of 232,550 inhabitants in 2010, approximately 91 percent of 
whom live in Nogales, Mexico.\4\ The mean elevation in Nogales, Mexico 
is 4,265 feet above sea level.\5\
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    \4\ In 2010, Nogales, Arizona had 20,017 inhabitants and 
Nogales, Mexico had 212,533 inhabitants. U.S. Census Bureau 2010 and 
Instituto Nacional de Estadistica Geografia e Informatica, (INEGI) 
2010.
    \5\ ``Statistical Municipal Workbook for Nogales, Sonora,'' 2005 
edition, INEGI.
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III. CAA and Regulatory Requirements for Moderate Area PM10 
Attainment Plans and Nonattainment Areas Influenced by International 
Transport

A. Moderate PM10 Area Planning Requirements

    The air quality planning requirements for moderate PM10 
nonattainment areas are set out in subparts 1 and 4 of the CAA, 
including sections 110, 172, and 189 of the statute. These sections 
will be discussed further during the review for each plan element, 
later in this proposal. Also, we have issued guidance in a General 
Preamble describing how we will review state submittals under Title I 
of the CAA, including moderate PM10 nonattainment areas. See 
57 FR 13498; (April 16, 1992) and 57 FR 18070; (April 28, 1992). In 
general, moderate area PM10 plans must include the following 
elements: a current, comprehensive emissions inventory of emissions 
sources in the nonattainment area; provisions to ensure that reasonably 
available control measures and/or reasonably available control 
technologies (RACM/RACT) have been implemented in the nonattainment 
area; provisions demonstrating attainment of the PM10 NAAQS 
with quantitative milestones which show reasonable further progress 
(RFP) towards attainment of the NAAQS as expeditiously as practicable; 
contingency measures for RFP and attainment; and, a motor vehicle 
emissions budget for the purpose of determining the conformity of 
transportation programs and plans developed by State transportation 
agencies.\6\ Because the Nogales NA lies along the international border 
with Mexico, the CAA allows Arizona to submit a demonstration that the 
area would have attained the PM10 NAAQS but for 
international transport from Mexico in lieu of a demonstration that the 
area has attained the PM10 NAAQS. The statutory requirements 
and guidance for such a demonstration under section 179B of the CAA are 
discussed next. Under CAA section 179B, however, other SIP 
requirements, such as RACM and contingency measures, among other 
requirements, continue to apply to PM10 nonattainment areas 
even if they quality for relief from the attainment demonstration 
requirement.
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    \6\ The Nogales PM10 nonattainment area is subject to 
the ``moderate'' area, not the ``serious'' area, SIP planning 
requirements under the CAA. This is because the mandatory ``bump-
up'' from ``moderate'' to ``serious'' under CAA section 188(b)(2) is 
only triggered if any area fails to attain the standard by the 
applicable attainment date (in this case, 1994), and the Nogales 
area, which was originally designated nonattainment for 
PM10 based on exceedances measured in the late 1980's, 
attained the standard by 1994. Several years after 1994, the Nogales 
area once again began to experience exceedances but such post-
attainment date exceedances do not trigger the mandatory ``bump-up'' 
provision in CAA section 188(b)(2). The issue of the applicability 
of the ``bump-up'' provision in CAA section 188(b)(2) to the Nogales 
area was addressed fully in EPA's final determination that the 
Nogales area attained the PM10 standard by the applicable 
attainment date. See 76 FR 1532; (January 11, 2011).
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B. Clean Air Act Provisions and EPA Guidance Concerning International 
Border Areas

    Because the southern boundary of the Nogales NA lies along the 
international border with Mexico and transport of PM10 
emissions from Mexico affects air quality in Nogales, Arizona, there 
are specific statutory requirements in the CAA that apply to the 
Nogales NA. With a demonstration from Arizona showing that the Nogales 
NA would have attained the PM10 NAAQS, but for international 
sources of PM10, EPA may approve an attainment plan provided 
by the State, even if the attainment plan does not demonstrate 
attainment of the NAAQS. The PM10 attainment plan, however, 
must meet other requirements of the CAA, contingent upon meeting the 
NAAQS but for international transport. Such a ``but for'' attainment 
demonstration, however, must be consistent with statutory and 
regulatory requirements. First, we will review the statutory basis for 
a ``but for'' attainment demonstration. Secondly, we will review EPA's 
published guidance on how such an analysis may be structured. Lastly, 
we will review how EPA determines whether an area's air quality is 
meeting the PM10 NAAQS using air quality data gathered at 
monitoring sites in the nonattainment area and our application of 40 
CFR part 50, appendix K.
1. Section 179B of the Clean Air Act
    For international border areas like the Nogales NA, CAA section 
179B(a) provides that notwithstanding any other provision of law, an 
implementation plan or plan revision shall be approved by the 
Administrator if such plan or

[[Page 38403]]

revision meets all the requirements applicable to it other than a 
requirement that such plan or revision demonstrate attainment and 
maintenance of the relevant national ambient air quality standards by 
the attainment date specified under the applicable provision, or in a 
regulation promulgated under such provision, and the submitting State 
establishes to the satisfaction of the Administrator that the 
implementation plan of such State would be adequate to attain and 
maintain the relevant national ambient air quality standards by the 
attainment date specified under the applicable provision, or in a 
regulation promulgated under such provision, but for emissions 
emanating from outside of the United States.
    As stated above, notwithstanding any other provision of law, should 
Arizona establish to the satisfaction of the EPA Administrator that the 
Nogales NA would have attained the PM10 NAAQS by the 
applicable attainment date but for emissions emanating from outside the 
U.S., then the Nogales NA is not subject to the provisions of CAA 
section 189(a)(1)(b), requiring a demonstration of attainment of the 
PM10 standards by the applicable attainment date.\7\ The 
underlying purpose of section 179B is to balance the requirements of 
the CAA in nonattainment areas adjacent to international borders 
affected by transport of pollution from foreign sources with the 
consideration that the State does not have the jurisdiction to control 
these foreign sources of pollution affecting attainment of the NAAQS in 
that State.
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    \7\ As discussed earlier, we determined that the Nogales NA met 
the PM10 NAAQS as of the applicable attainment date for 
moderate nonattainment areas, December 31, 1994; consequently, we 
did not reclassify the area to ``serious.'' See 76 FR 1532; (January 
11, 2011).
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2. The 1994 General Preamble Addendum
    As part of guidance relating to serious PM10 
nonattainment areas (General Preamble Addendum), EPA included a 
discussion of the requirements applicable to international border 
areas.\8\ The General Preamble Addendum reviews the information and 
methods that may be used to determine if an international border area 
qualifies for treatment under CAA section 179B and to demonstrate that 
the area would attain the relevant NAAQS but for emissions emanating 
from outside the U.S.
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    \8\ ``State Implementation Plans for Serious PM10 
Nonattainment Areas, and Attainment Date Waivers for PM10 
Nonattainment Areas Generally; Addendum to the General Preamble for 
the Implementation of Title I of the Clean Air Act Amendments of 
1990,''; 59 FR 41998, August 16, 1994.
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    The General Preamble Addendum provides that ``several types of 
information may be used to evaluate the impact of emissions emanating 
from outside the U.S.'' The EPA will consider the information ``for 
individual nonattainment areas on a case-by-case basis in determining 
whether an area may qualify for treatment under section 179B.'' See 59 
FR 42001; (August 16, 1994). The General Preamble Addendum suggests 
five methods that may be used to determine the impact of emissions 
emanating from outside the U.S. Below, we describe the five methods in 
general terms and later, when reviewing Arizona's section 179B analysis 
and demonstration, we will discuss the particular applicability of 
these five methods to the analysis done for the Nogales NA.
    Method 1. Place several ambient PM10 monitors and a 
meteorological station measuring wind speed and direction in the U.S. 
nonattainment area near the international border. Evaluate and quantify 
any changes in monitored PM10 concentrations with a change 
in the predominant wind direction.
    Method 2. Comprehensively inventory PM10 emissions 
within the U.S. in the vicinity of the nonattainment area and 
demonstrate that those sources, after application of reasonably 
available controls, do not cause the NAAQS to be exceeded. This 
analysis must include an influx of background PM10 in the 
area. Background PM10 levels could be based on 
concentrations measured in a similar area not influenced by emissions 
from outside the U.S.
    Method 3. Analyze ambient sample filters for specific types of 
particles emanating from across the border. Although not required, 
characteristics of emissions from sources may be helpful so as to 
better demonstrate the causal relationship with and contribution to 
exceedances in the U.S. nonattainment area due to domestic and 
international emissions.
    Method 4. Inventory the sources on both sides of the border and 
compare the magnitude of PM10 emissions originating within 
the U.S. to those emanating from outside the U.S.
    Method 5. Perform air dispersion and/or receptor modeling to 
quantify the relative impacts on the nonattainment area of sources 
located within the U.S., and of foreign sources of PM10 
emissions.
    As stated in the General Preamble Addendum, the EPA will consider 
the information ``for individual nonattainment areas on a case-by-case 
basis in determining whether an area may qualify for treatment under 
section 179B.'' Because the individual circumstances surrounding a 
nonattainment area may differ widely whether by data, resources, or 
emissions sources, EPA anticipates that ``the State may use one or more 
of these types of information or other techniques, depending on their 
feasibility and applicability, to evaluate the impact of emissions 
emanating from outside the U.S. on the nonattainment area.'' See 59 FR 
42001; (August 16, 1994). Therefore, the analysis Arizona has provided 
for the Nogales NA is specific to this nonattainment area only and the 
timeframe, data, and circumstances therein, and EPA is evaluating the 
analysis as such.
    As explained earlier, the underlying purpose of section 179B is to 
balance the requirements of the CAA in nonattainment areas adjacent to 
international borders affected by transport of pollution from foreign 
sources with the consideration that the State does not have the 
jurisdiction to control these foreign sources of pollution affecting 
attainment of the NAAQS in that State. In this light, the General 
Preamble Addendum discusses several attainment plan requirements as 
applied to nonattainment areas affected by international transport.
    The 1994 General Preamble Addendum discusses the requirements for 
RACM as applied to nonattainment areas affected by international 
transport. In international border areas, ``RACM/RACT must be 
implemented to the extent necessary to demonstrate attainment by the 
applicable attainment date if emissions emanating from outside the U.S. 
were not included in the analysis.'' See 59 FR 42001; (August 16, 
1994). As set forth in section 179B(a)(2), a State's moderate area 
PM10 plan must be ``adequate'' to attain and maintain the 
PM10 NAAQS, but for emissions from outside the U.S. 
Therefore, nothing in section 179B relieves a State from the 
requirement to address and implement RACM. Nonetheless, States are not 
required to implement control measures that go beyond what the plan 
demonstrates would otherwise be adequate for timely attainment and 
maintenance of the PM10 NAAQS but for emissions from outside 
the U.S. Furthermore, to the degree that the State can satisfactorily 
demonstrate that implementation of a control measure clearly would not 
advance the area's attainment date, EPA may conclude that these control 
measures are unreasonable and do not constitute RACM for the 
nonattainment area. See 59 FR 42001; (August 16, 1994).

[[Page 38404]]

    The 1994 General Preamble Addendum also discusses the requirements 
for reasonable further progress (RFP) and contingency measures as 
applied to nonattainment areas affected by international transport. 
Section 179B(a)(1) does not relieve a nonattainment area of the CAA 
requirements for RFP and contingency measures. In international border 
areas, however, ``EPA will not require the contingency measures for 
PM10 to be implemented after the area fails to attain if EPA 
determines that the area would have attained the NAAQS, but for 
emissions emanating from outside the U.S.'' Conversely, to the degree 
that contingency measures are needed to control U.S. sources of 
PM10 to meet RFP or attainment contingency measure 
requirements but for PM10 emissions emanating from outside 
of the U.S., then the statutory requirements for RFP and contingency 
measures still apply. See 59 FR 42001, 42002; (August 16, 1994).
3. Statutory Requirements and Guidance for Determining Attainment of 
the PM10 NAAQS
    EPA determines whether an area's air quality is meeting the 
PM10 NAAQS based upon air quality data gathered at 
monitoring sites in the nonattainment area. Then, EPA reviews the data 
to determine the area's air quality status according to 40 CFR part 50, 
appendix K. Three consecutive years of clean air quality data (i.e., no 
more than one expected exceedance per year) is generally needed to show 
attainment of the 24-hour PM10 standard. As defined by 40 
CFR part 50, appendix K, a complete year of air quality data is 
composed of all four calendar quarters with each quarter containing 
data from at least 75 percent of the scheduled sampling days.
    Under 40 CFR part 50, appendix K, a nonattainment area meets the 
24-hour PM10 NAAQS when the expected number of days per 
calendar year with a 24-hour average concentration above 150 micrograms 
per cubic meter ([mu]g/m\3\) is equal to or less than one. In general, 
the number of expected exceedances at a site which samples every day is 
determined by recording the number of exceedances in each calendar year 
and then averaging them over the most recent three calendar years. For 
sites which do not sample every day, EPA requires adjusting the 
observed exceedances to account for days not sampled. The procedures 
for making this data adjustment are specified in 40 CFR part 50, 
appendix K.
    For this review of the Nogales NA and the contribution of 
international emissions, the standard we will use to demonstrate 
attainment of the PM10 NAAQS, ``but for'' international 
emissions, is similar to the one described above: The expected number 
of days per calendar year with a 24-hour average concentration above 
150 [mu]g/m\3\ must be equal to or less than one. To demonstrate that 
the Nogales NA has met the PM10 standard ``but for'' 
emissions from Mexico, the State's analysis must show that no more than 
three exceedances, based on data completeness and every day sampling, 
over the specific three-year analysis period, would have occurred on 
the U.S. side of the border, setting aside any contributions from 
Mexican sources of PM10.

IV. Review of the Nogales 2012 Plan

    In this section, according to the statutory requirements and 
guidance discussed above in section III, we will review Arizona's 
submitted Nogales 2012 Plan and section 179B analysis and demonstration 
that the Nogales NA is attaining the PM10 NAAQS but for 
international emissions sources from Nogales, Mexico.

A. Emissions Inventories

1. Requirements for Emissions Inventories
    Section 172(c)(3) of the CAA requires plan submittals to include a 
comprehensive, accurate, and current inventory of actual emissions from 
all sources in the nonattainment area.
2. Review of the Nogales Nonattainment Area Emissions Inventories
    Arizona submitted emissions inventories for the Nogales NA for the 
years 2008 and 2011. These emissions inventories were calculated using 
information from version 1.5 of EPA's 2008 National Emission Inventory 
(NEI) and the NEI emissions estimates for Santa Cruz County, Arizona. A 
Nogales NA 2008 emissions inventory was scaled from the larger Santa 
Cruz County emissions inventory using a combination of population and 
land allocation ratios. A specific point source's location was the 
basis for assigning point sources to the Nogales NA emissions 
inventory. On-road motor vehicle PM10 emissions for 2008 and 
2011 were calculated using County-level data for 2008 and 2011 and the 
MOVES2010a model.\9\ The larger and remaining portions of the 2011 
emissions inventory, particularly area sources, were calculated from 
the 2008 emissions inventory according to estimates of population and 
economic growth. An overview of the Nogales NA 2008 and 2011 emissions 
inventories is provided here; for detailed results and a complete 
discussion of the methodology used to produce the emission inventories, 
see ``PM10 Emission Inventories for 2008 and 2011, Nogales 
Non-Attainment Area, Santa Cruz County, Arizona'', in Appendix B of the 
Nogales 2012 Plan.
---------------------------------------------------------------------------

    \9\ On March 2, 2010, EPA approved the availability of the Motor 
Vehicle Emissions Simulator model (MOVES2010a) in official SIP 
submissions to EPA regarding air quality and for certain 
transportation conformity analyses outside the state of California; 
see 75 FR 9411. Also see EPA's Web site for more information, http://www.epa.gov/otaq/models/moves/index.htm.
---------------------------------------------------------------------------

    EPA's NEI database contains information about sources that emit 
criteria air pollutants and their precursors, and hazardous air 
pollutants. The database includes estimates of annual air pollutant 
emissions, including PM10, from point, nonpoint, and mobile 
sources in the 50 states, including Arizona, and specifically Santa 
Cruz County. Collaborating with the states, EPA develops the emissions 
inventory and releases an updated version of the NEI database every 
three years. A complete description of the development of the 2008 NEI 
may be found at the following URL: http://www.epa.gov/ttn/chief/net/2008inventory.html.
    In calculating PM10 emissions from on-road mobile 
sources in Santa Cruz County, Arizona used the MOVES2010a version dated 
September 23, 2010 (hereafter referred to as ``MOVES''). This is the 
current version of the MOVES model. MOVES allows the use of county-
specific data concerning factors such as the average speed distribution 
of on-road vehicles, daily vehicle miles traveled, and road types among 
others in place of national default values. The MOVES model requires 
the use of county-specific data for SIP purposes. In this instance, the 
MOVES calculation was performed using input data from the 2008 NEI for 
Santa Cruz County. Similar MOVES model runs were completed to estimate 
2011 on-road mobile source PM10 emissions.
    Although EPA has no specific guidance on assigning emissions 
sources from a county level of analysis to a smaller area within that 
county, for the Nogales NA emissions inventory, Arizona used a 
combination of population ratios, land area ratios, and point source 
locations within the Nogales NA to determine the appropriate allocation 
of county-wide emissions to the Nogales NA. See Table

[[Page 38405]]

1 for the specific population and land allocation ratios used to scale 
PM10 emissions from the County to the Nogales NA level.

                       Table 1--Summary of Land Area and 2008 Population Allocation Ratios
----------------------------------------------------------------------------------------------------------------
                                                                                                    Allocation
                                                                   Santa Cruz       Nogales NA         ratio
                                                                     County                          (percent)
----------------------------------------------------------------------------------------------------------------
Land Area (square miles)......................................     \10\ 1,237.6             76.1            6.15
2008 Population...............................................    \11\ 43,091      \12\ 23,735             55.1
----------------------------------------------------------------------------------------------------------------

    The State used data from the U.S. Census Bureau to estimate the 
2008 population of the Nogales NA population and Santa Cruz County. A 
land area-weighted emission ratio was developed using U.S. Census 
geographic data and confirmed with Arizona Commerce Authority data.\13\ 
Some source categories, such as agricultural emissions, are likely to 
be proportional to land area; consequently, they are logically 
allocated by the land area ratio. To confirm whether specific point 
sources in the Santa Cruz County emissions inventory should be included 
in the Nogales NA emissions inventory, ADEQ and EPA used visual 
inspections with location information, such as satellite photography 
using Google Earth.
---------------------------------------------------------------------------

    \10\ U.S. Census, Quickfacts, Santa Cruz County, Arizona.
    \11\ 2010 U.S. Census population estimates.
    \12\ Ibid.
    \13\ Arizona Department of Commerce Profile: Santa Cruz County 
Arizona, May 10, 2011, http://www.azcommerce.com/doclib/commune/SantaCruzpercent20county.pdf.
---------------------------------------------------------------------------

    As shown in Table 2, in 2008, the majority of PM10 
emissions in the Nogales NA came from fugitive dust from four source 
categories: Unpaved road dust, road construction, commercial/
industrial/institutional construction, and paved road dust. The 
estimated emissions inventory for 2011 only differed slightly as total 
emissions decreased from 1,524 tons per year (tpy) in 2008 to 1,521 tpy 
in 2011, due primarily to implementation of new and cleaner engine 
standards for diesel engines. Little or no growth in population or 
economic activity occurred from 2008 to 2011. From 2008 to 2011, the 
emissions estimated for five of the top six source categories remain 
unchanged, except for residential wood burning which increased by two 
tons per year. Again, in 2011 as in 2008, these six source categories 
account for approximately 95 percent of all PM10 emissions 
in the Nogales NA.

                          Table 2--2008 and 2011 Nogales NA PM10 Emissions Inventories
                                                 [Tons per year]
----------------------------------------------------------------------------------------------------------------
                               Source category                                      2008              2011
----------------------------------------------------------------------------------------------------------------
Dust--Unpaved Road Dust.....................................................               865               865
Dust--Road Construction.....................................................               267               267
Dust--Commercial/Industrial/Institutional Construction......................               143               143
Dust--Paved Road Dust.......................................................               121               121
Fuel Combustion--Residential--Wood..........................................                24                26
Dust--Residential Construction..............................................                24                24
Waste Disposal--Residential Garbage Burning.................................                23                25
All other sources...........................................................                57                50
                                                                             -----------------------------------
    Total...................................................................             1,524             1,521
----------------------------------------------------------------------------------------------------------------
Note: All other sources include emissions from source categories such as all on-road mobile and off-road mobile,
  all commercial and industrial fuel combustion, agriculture, land clearing and burning activities.
Source: Table 5 in ``PM10 Emission Inventories for 2008 and 2011, Nogales Non-Attainment Area, Santa Cruz
  County, Arizona,'' Appendix B of the Nogales 2012 Plan. Table 5 also provides a detailed listing of all source
  categories. Due to rounding, totals may not reflect exactly the sum of each source category.

3. Proposed Action on the Nogales Nonattainment Area 2008 and 2011 
Emissions Inventories
    We propose to find that the Nogales NA emissions inventories for 
2008 and 2011 are comprehensive, accurate, and current inventories of 
actual emissions from all sources in the nonattainment area and that 
they meet the requirements of section 172(c)(3) of the CAA. The State 
has provided a 2008 base year and 2011 future year emissions inventory 
comprehensively addressing all source categories in the Nogales NA. The 
State also used the most recent iteration of mobile source emissions 
modeling tool, MOVES2010a, in developing its emissions inventories. 
Consequently, we are proposing to find that the emissions inventories 
provided by Arizona meet the requirements of section 172(c)(3) and 
provide an adequate basis for the attainment demonstration under 
section 179B, and the State's RACM/RACT and RFP demonstrations.

B. Section 179B Analysis and Demonstration of Attainment but for 
International Sources of PM10 Emissions

1. Review of Statute and Guidance Applied to the Nogales Section 179B 
Analysis and Demonstration of Attainment but for International Sources 
of PM10 Emissions
    As discussed earlier, the General Preamble Addendum provides that 
``several types of information may be used to evaluate the impact of 
emissions emanating from outside the U.S.'' The EPA will consider the 
information ``for individual nonattainment areas on a case-by-case 
basis in determining

[[Page 38406]]

whether an area may qualify for treatment under section 179B.'' See 59 
FR 42001; (August 16, 1994). The General Preamble Addendum suggests 
five methods that may be used to determine the impact of emissions 
emanating from outside the U.S. and explains that ``the State may use 
one or more of these types of information or other techniques, 
depending on their feasibility and applicability, to evaluate the 
impact of emissions emanating from outside the U.S. on the 
nonattainment area.'' See 59 FR 42001; (August 16, 1994). Below, we 
discuss these five methods for evaluating the effects from transport of 
international pollution and the applicability of these methods to the 
Nogales NA, as presented in the Nogales 2012 Plan.
    Method 1. Place several ambient PM10 monitors and a 
meteorological station measuring wind speed and direction in the U.S. 
nonattainment area near the international border. Evaluate and quantify 
any changes in monitored PM10 concentrations with a change 
in the predominant wind direction.
    The State reviewed the ambient PM10 data, meteorology, 
and topography in the Ambos Nogales area. Arizona maintains a monitor 
in Nogales, Mexico, as well as three monitors in Nogales, Arizona. The 
Nogales, Arizona monitors are divided as follows: Two monitors measure 
ambient PM10 levels; and one monitor measures ambient 
PM2.5 levels.\14\ Arizona also has two reference monitors at 
increasing distances from the Nogales NA. Arizona's complete analysis 
of the ambient data, meteorology, and topography is provided in 
Appendix D of the Nogales 2012 Plan and is discussed below in section 
IV.B.2.c of this proposal. This method provided useful information to 
understand emissions sources and PM10 concentrations in the 
Nogales NA.
---------------------------------------------------------------------------

    \14\ PM2.5, also called fine particulate, refers to 
particulate matter with an aerodynamic diameter less than or equal 
to 2.5 micrometers. PM10 includes both PM2.5 
and the particulates with aerodynamic diameter between 2.5 and 10 
micrometers, which is referred to as PM10-2.5. This 
larger fraction is called ``coarse'' particulate. While fine 
particles originate mostly from combustion sources and secondary 
aerosol generation processes, coarse particles usually originate 
from mechanical activities and fugitive source categories.
---------------------------------------------------------------------------

    Method 2. Comprehensively inventory PM10 emissions 
within the U.S. in the vicinity of the nonattainment area and 
demonstrate that those sources, after application of reasonably 
available controls, do not cause the NAAQS to be exceeded. This 
analysis must include an influx of background PM10 in the 
area. Background PM10 levels could be based on 
concentrations measured in a similar area not influenced by emissions 
from outside the U.S.
    This method implies the use of an air quality model to demonstrate 
that emissions within the U.S. do not create a violation of the NAAQS. 
Although a comprehensive, area-wide inventory of PM10 
emissions is available for Nogales, Arizona, information about the 
spatial and temporal distribution of those emissions required to 
support air quality modeling is not readily available and would require 
significant effort to develop. Furthermore, given the complex 
topography of the Ambos Nogales area, it is not feasible to develop an 
adequate demonstration using available modeling tools.
    Method 3. Analyze ambient sample filters for specific types of 
particles emanating from across the border. Although not required, 
characteristics of emissions from foreign sources may be helpful so as 
to better demonstrate the causal relationship with and contribution to 
exceedances in the U.S. nonattainment area due to international 
emissions.
    This method is unlikely to produce useful information for the 
Nogales NA because the large proportion of crustal PM sources on either 
side of the international border far outweigh any specific stationary 
or combustion-based PM source that could be identified by a filter-
based analysis, and differentiating between Arizona and Mexican sources 
of crustal material is not feasible. Also, specific local and 
international point source emissions information, such as source-
specific signature emissions compounds, was not available with which to 
correlate the filter analyses results.
    Method 4. Inventory the sources on both sides of the border and 
compare the magnitude of PM10 emissions originating within 
the U.S. to those emanating from outside the U.S.
    Arizona provided two emissions inventories: The first emissions 
inventory, discussed above, describes the PM10 sources and 
estimates PM10 emissions in and around the Nogales NA, 
Arizona; and, the second inventory describes the PM10 
sources and estimates PM10 emissions in and around Nogales, 
Mexico. The Nogales NA PM10 emissions inventory is provided 
in Appendix B and the Nogales Municipality, Mexico emissions inventory 
is provided in Appendix C of the Nogales 2012 Plan. The results of both 
inventories are discussed below in section IV.B.2.b. of this proposal. 
Also, as a basis for these analyses, Arizona reviewed population 
estimates and relative population differences for these areas, which is 
further discussed in section IV.B.2.a. of this proposal.
    Method 5. Perform air dispersion and/or receptor modeling to 
quantify the relative impacts on the nonattainment area of U.S. and 
foreign sources of PM10 emissions.
    As discussed above, the information necessary to support air 
dispersion or receptor modeling is not readily available for the 
Nogales, Arizona area, nor is it available for the Nogales, Mexico 
area. For example, neither ADEQ, nor EPA, had available a gridded 
emissions inventory or a data set from an extensive monitoring array of 
ambient PM10 values and meteorological data derived from 
observations on multiple exceedance days.
    Backward wind trajectory analysis using the HYSPLIT model was 
considered, based on Eta Data Assimilation System (EDAS) gridded 
meteorological data, but again, neither Arizona nor EPA pursued this 
analysis.\15\ Previously, EPA performed such an analysis for the 
Nogales, Arizona area and found the resulting wind trajectories to be 
inconclusive. The EDAS has a 40-kilometer grid resolution; in contrast, 
the valley containing Nogales is 20 kilometers wide at its widest 
point. As a result, the EDAS data were not of a fine enough resolution 
to portray the south-to-north valley air drainage flows that are a key 
feature of local Nogales meteorology; consequently, further use of 
HYSPLIT model results for purposes of this section 179B analysis was 
rejected by the State and EPA.
---------------------------------------------------------------------------

    \15\ HYSPLIT is the ``Hybrid Single Particle Lagrangian 
Integrated Trajectory'' Model, developed and maintained by the 
National Oceanic and Atmospheric Administration; see 
www.arl.noaa.gov/HYSPLIT_info.php for more information.
---------------------------------------------------------------------------

    To summarize, the State analyzed ambient PM10 levels in 
and around the Nogales NA, the local meteorology associated with 
exceedances of the PM10 standards, and sources of 
PM10 emissions on either side of the international border. 
These analyses are consistent with Methods 1 and 4 described by the 
General Preamble Addendum. The State examined method 3, but did not 
pursue this avenue of investigation because it was unlikely that 
definitive results could be produced given the large crustal source 
emissions on either side of the international border.
    Initially, the State did not pursue Methods 2 and 5 because it did 
not have the data and the models required for this type of analysis. 
Instead, the State used the available information consistent with 
methods 1 and 4, to

[[Page 38407]]

demonstrate if the Nogales NA would have attained the standard, but for 
international emissions.
    As stated in the General Preamble Addendum, EPA will consider the 
information ``for individual nonattainment areas on a case-by-case 
basis in determining whether an area may qualify for treatment under 
section 179B.'' See 59 FR 42001; (August 16, 1994). Because the 
individual circumstances surrounding a nonattainment area may differ 
widely whether by data, resources, or emissions sources, EPA 
anticipates that ``the State may use one or more of these types of 
information or other techniques, depending on their feasibility and 
applicability, to evaluate the impact of emissions emanating from 
outside the U.S. on the nonattainment area.'' See 59 FR 42001; (August 
16, 1994). The analysis the State has provided for the Nogales NA is 
specific to this nonattainment area only and the timeframe, data, and 
circumstances therein, and EPA evaluated the analysis as such.
2. Review of Arizona's Section 179B Analysis and Demonstration of 
Attainment but for International Sources of PM10 Emissions
a. Population Growth in the Ambos Nogales Region
    In producing emissions inventories, Arizona reviewed recent 2010 
population information from the U.S. Census Bureau and Mexican Census 
data from the Instituto Nacional de Estadistica Geografia e Informatica 
(INEGI). While population estimates, by themselves, are not direct 
indicators of emissions activity, they provide an indication of 
relative human activity and resulting PM10 emissions on 
either side of the international border. Table 3 provides a comparison 
of the populations residing in the Nogales NA and the Nogales 
Municipality, Mexico. The Nogales NA population estimate includes 
persons residing in the city of Nogales, Arizona, and the surrounding 
community of Rio Rico within the Santa Cruz County portion of the 
nonattainment area.

 Table 3--2010 Population: Nogales NA, Arizona and Nogales Municipality,
                                 Mexico
------------------------------------------------------------------------
                  Area                      Population        Percent
------------------------------------------------------------------------
Nogales NA, Arizona.....................          24,059             9.8
Nogales Municipality, Mexico............         220,292            90.2
                                         -------------------------------
    Total...............................         244,351             100
------------------------------------------------------------------------
Source: INEGI & U.S. Census.

    Although the Nogales Municipality is a larger land area than the 
Nogales NA, a large proportion of the Municipality's population is 
concentrated within the city of Nogales, Mexico and the surrounding 
area. In sum, 90.2 percent of the 2010 population in the Ambos Nogales 
area can be attributed to the Mexican side of the international border.
    It is also instructive to examine population change since 1995, 
when the Nogales NA met the PM10 NAAQS along with the 
subsequent observed exceedances of the PM10 NAAQS.\16\ Table 
4 shows population estimates for 1995, 2000, 2005, and 2010, while 
Table 5 shows the annual number of expected exceedances of the 
PM10 NAAQS since 1998, the first year the Nogales NA 
recorded exceedances after meeting the PM10 standard in 
1994. The Nogales NA did not record exceedances of the PM10 
standard from 1995 to 1997.
---------------------------------------------------------------------------

    \16\ See 76 FR 1532; (January 11, 2011) for our determination 
that the Nogales NA attained the PM10 NAAQS by December 
31, 1994.

     Table 4--Nogales, Arizona and Nogales Municipality, Mexico Populations: 1995, 2000, 2005 and 2010 \17\
----------------------------------------------------------------------------------------------------------------
                                                       1995            2000            2005            2010
----------------------------------------------------------------------------------------------------------------
Nogales, Arizona................................          20,184          20,878          20,421          20,837
Nogales Municipality, Mexico....................         133,491         159,787         193,517         220,292
----------------------------------------------------------------------------------------------------------------
Source: INEGI & U.S. Census.

    Between  1995 and 2010, Nogales, Arizona population increased 
approximately three percent, and has fallen slightly since 2000. The 
2010 Nogales NA population at 24,059 persons is marginally larger than 
the city of Nogales because the nonattainment area estimate includes 
portions of the Rio Rico communities in the northernmost portion of the 
nonattainment area. In contrast, the Nogales Municipality, Mexico 
population has increased 65 percent in the 1995 to 2010 timeframe. With 
the exceptions of 2000 and 2004, exceedances of the PM10 
standard have been recorded since 1998 in the Nogales NA. The largest 
number of expected exceedances, 47.9, was recorded in 2006. See Table 
5.
---------------------------------------------------------------------------

    \17\ The 1995 Nogales, Arizona population estimate was 
interpolated from 1990 and 2000 U.S. Census figures; the 1990 
population estimate was 19,489.

                                   Table 5--Nogales, Arizona Expected Exceedances of 24-Hour PM10 NAAQS From 1998-2010
--------------------------------------------------------------------------------------------------------------------------------------------------------
                Monitor frequency                  1998    1999    2000    2001    2002    2003    2004    2005    2006    2007    2008    2009    2010
--------------------------------------------------------------------------------------------------------------------------------------------------------
1 in 6 day......................................    13.5    15.5     0.0     6.9     6.1    12.3     0.0    17.9    20.0     6.1     6.6     0.0     0.0
Continuous......................................  ......  ......  ......  ......  ......  ......  ......    29.6    47.9    14.0    13.2     2.0   * 8.5
--------------------------------------------------------------------------------------------------------------------------------------------------------
* There were no quarters in 2010 where there was a complete data set per 40 CFR part 50, appendix K; see section IV.B.2.c. for a discussion of 2010
  data.
Source for expected exceedance data: EPA Air Quality System Database.


[[Page 38408]]

    To summarize, population estimates since 1995 show the Nogales NA 
population remaining relatively constant while the Nogales 
Municipality, Mexico population has steadily increased to the present 
where 9 of 10 people in the Ambos Nogales area reside in Mexico. Over 
the same timeframe, after attaining the PM10 NAAQS in 1994 
through 1997, expected exceedances of the PM10 NAAQS in the 
Nogales NA increased to a high of 47.9 in 2006 and the area does not 
meet the NAAQS today. The dramatic differential population increase in 
Nogales, Mexico compared to Nogales, Arizona and the surrounding 
nonattainment area supports the inference that a large and growing 
proportion of PM10 emissions in the Ambos Nogales area 
emanates from outside of the Nogales NA and the U.S.
b. Review and Comparison of U.S./Mexico Emissions Inventories
    Both the Nogales NA and the Nogales Municipality, Mexico have 
similar contributing sources of PM10, primarily fugitive 
dust from unpaved and paved roads, as well as combustion sources and 
construction. The Nogales NA emissions inventories were presented above 
in section IV.A.2 of this proposal. While less detailed than the 
Nogales NA emissions inventories, the Nogales Municipality, Mexico 
emissions inventories shows that the largest contributing sources of 
PM10 emissions are from unpaved and paved road dust followed 
by residential wood combustion and other area sources. Because Nogales 
Municipality, Mexico specific data could not be found to calculate 
unpaved and paved road emissions, the State reviewed other U.S./Mexico 
border emissions inventories to identify data for use in these 
calculations. Given the range of data generated and used by these U.S./
Mexico border emissions inventories, low and high estimates were 
calculated for the unpaved and paved road source categories. Much of 
the difference between the low and high estimates of Nogales 
Municipality emissions is attributed to the low and high estimates of 
unpaved and paved road emissions. A high estimate for point sources was 
included because the State did not have readily available source-
specific information providing a precise estimate for stationary point 
sources of PM10 in the Nogales Municipality, Mexico.\18\ The 
methods for calculating these estimates are discussed in ``2008 and 
2011 PM10 Emission Inventories, Nogales Municipality, 
Sonora, Mexico'' in Appendix C of the Nogales 2012 Plan. The Nogales 
Municipality, Mexico emissions inventories for 2008 and 2011 are 
presented in Table 6.
---------------------------------------------------------------------------

    \18\ Two methods were used to scale point source emissions from 
1999 to 2008 and 2011 generating the high and low estimates for 
point source PM10: For the low estimate, National point 
source emissions growth; and, for the high estimate, population 
based allocation ratio. The starting 1999 baseline for point source 
emission was 0.9 tpy and the high estimate, therefore, assumes an 
increase of three orders of magnitude compared to the low estimate. 
No point sources in the Nogales Municipality, Mexico have been 
identified as operating at a level of emissions consistent with the 
high estimate, but lacking source specific data to adjudicate the 
difference in estimates, the high estimate was reported as an upper 
bound. See Appendix C of the Nogales 2012 Plan for the Nogales 
Municipality Emissions Inventory for a complete discussion.

             Table 6--PM10 Emissions Inventories for Nogales Municipality, Mexico for 2008 and 2011
                                                 [Tons per year]
----------------------------------------------------------------------------------------------------------------
 
----------------------------------------------------------------------------------------------------------------
Source category                                                        Range              2008          2011
----------------------------------------------------------------------------------------------------------------
Point Sources.......................  ......................  Low Estimate..........           1.1           1.1
                                                              High Estimate.........           305           390
Area Sources........................  Unpaved Road..........  Low Estimate..........         2,144         2,308
                                                              High Estimate.........         5,521         5,944
                                      Paved Road............  Low Estimate..........            53            57
                                                              High Estimate.........           646           696
                                      Agricultural Tilling..  ......................           0.8           0.8
                                      Agricultural Burning..  ......................           1.6           1.6
                                      Residential Wood        ......................           176            47
                                       Combustion.
                                      Open Burning of Waste.  ......................            55            56
                                      Construction            ......................            23            24
                                       Activities.
                                      Remaining Area Sources  ......................           159           150
Mobile Sources......................  ......................  ......................            80            85
Nonroad Sources.....................  ......................  ......................            20            27
                                                                                     ---------------------------
    Total...........................  ......................  Low Estimate..........         2,713         2,757
                                                                                     ---------------------------
    Total...........................  ......................  High Estimate.........         6,987         7,420
----------------------------------------------------------------------------------------------------------------
Emissions are rounded to the nearest ton/year, or to the nearest tenth of a ton/year for emissions less than 10
  tons/year.
Source: Table 18 from ``2008 and 2011 p.m.10 Emission Inventories, Nogales Municipality, Sonora, Mexico'' in
  Appendix C of the Nogales 2012 Plan.

    A review of the emissions inventory data by relative percentage and 
relative ratio provides two ways of considering the data. A comparison 
of 2008 and 2011 Nogales Municipality, Mexico low emission inventory 
estimates with the Nogales NA 2008 and 2011 emission inventory 
estimates shows a 36/64 percent split in total combined U.S./Mexico 
emissions inventories between emissions from the Nogales NA, Arizona 
and Nogales Municipality, Mexico areas, respectively. To characterize 
the relative difference by ratio using the low emissions estimate for 
the Nogales Municipality, Mexico, for every one ton of PM10 
emissions produced annually in Nogales NA, there is an estimated 1.8 
tons produced in Nogales Municipality. Similarly, a comparison of 2008 
and 2011 Nogales Municipality high emission inventory estimates 
suggests that there is an 18/82 percent split in total combined U.S./
Mexico emissions inventories between emissions from the Nogales NA, 
Arizona and Nogales Municipality, Mexico areas,

[[Page 38409]]

respectively. Again, to characterize the relative difference by ratio 
using the high emissions estimate for the Nogales Municipality, Mexico, 
for every one ton of PM10 emissions produced annually in 
Nogales NA, there is an estimated 4.6 tons produced in Nogales 
Municipality, Mexico.\19\
---------------------------------------------------------------------------

    \19\ See Tables 6-9 from ``Clean Air Act, Section 179B 
Attainment Determination for the Nogales, Arizona PM10 
Nonattainment Area'' in Appendix A of the Nogales 2012 Plan for the 
presentation of the data underlying this relative percentage and 
relative ratio presentation.
---------------------------------------------------------------------------

    In summary, a comparison of the State's 2008 and 2011 emissions 
inventory data shows for every one ton of PM10 produced in 
the Nogales NA, there was between 1.8 and 4.6 tons of PM10 
emissions produced annually in the Nogales Municipality, Mexico, 
depending on the choice of either the low or the high estimate of 
Nogales Municipality, Mexico emissions. The emission sources appear to 
be similar, with the majority of emissions from fugitive dust sources, 
such as reentrained unpaved and paved road dust.
c. Review and Analysis of Regional Meteorology, Topography and Ambient 
PM10 Monitoring Data
    In its review of the ambient PM10 data, meteorological 
data, and through its analyses, Arizona found that the Ambos Nogales 
area's meteorology and topography influence the observed exceedances of 
PM10 NAAQS and there is a definite south-to-north 
directional component to the ambient air quality data underlying the 
exceedances of the PM10 NAAQS. Over the 2007-2009 timeframe, 
there were 29 exceedances at the Nogales, Arizona Post Office (Model: 
Met One BAM 1020) monitor.\20\
---------------------------------------------------------------------------

    \20\ For a listing of the 29 exceedance days by year and 
observed 24-hour concentrations, see Tables 1-3 in ``Analysis of 
Ambient PM10 Levels, Topography, and Meteorological Data 
in Nogales, Arizona: 2007-2009'' in Appendix D of the Nogales 2012 
Plan.
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(i) Ambos Nogales Regional Meteorology and Topography
    The State's analysis of ambient concentration and meteorological 
data identified 26 of the 29 exceedances as having nearly identical 
diurnal patterns; the three exceptions were January 1, 2007, May 22, 
2008, and January 1, 2009.\21\ For each of the 26 days, there is a 
strong pattern of decreasing PM10 concentrations in the 
early morning. Generally, the wind speeds are low and variable 
overnight and wind direction starts southerly but becomes increasingly 
variable into the daylight morning hours. The majority of days have a 
pronounced PM10 increase and drop-off between 6:00 a.m. and 
9:00 a.m., suggesting a reproducible direct PM10 source, 
noting the times correspond to a morning commute pattern. The 
PM10 concentrations reach their lowest points between 10:00 
a.m. and 4:00 p.m., with corresponding increases in ambient temperature 
and wind speed observed during those times. Usually, northerly winds 
accompany these increases in temperature and wind speed. As 
temperatures and wind speeds drop in the evening hours, a pronounced 
spike in PM10 concentration is then observed beginning 
between 4:00 p.m. and 6:00 p.m., with concentrations remaining high for 
several hours and gradually dropping off towards midnight. The 
afternoon spike in PM10 concentrations correlates with a 
significant drop in temperature and wind speed, and generally a shift 
to low and variable southerly (from the south) winds.
---------------------------------------------------------------------------

    \21\ See, in particular, Section 3 of ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'', in Appendix D of the Nogales 2012 
Plan.
---------------------------------------------------------------------------

    Looking at the topography from south to north, the highest 
elevation of a primary roadway transect is at 4,331 feet above sea 
level at the southern edge of Nogales, Mexico, falling to the 
international border at 3,933 feet, continuing to the northern edge of 
the Nogales NA at 3,425 feet, and elevation continues to fall along the 
Santa Cruz River watershed to the north to approximately 3,100 
feet.\22\ Across this largest 48.5-mile local transect, the elevation 
falls approximately 1,200 feet from south to north, i.e., from Nogales, 
Mexico, through the Nogales NA, and to the north towards Tucson, 
Arizona.
---------------------------------------------------------------------------

    \22\ See Figure 18, Long Aerial and Elevation Transect of 
Nogales Arizona and Nogales, Sonora, in ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'', in Appendix D of the Nogales 2012 
Plan.
---------------------------------------------------------------------------

    In examining a smaller 14.8-mile transect along a similar primary 
roadway route, the State found that elevation declines on a south-to-
north axis across two sub-transects centering on the international 
border. The Nogales, Mexico sub-transect shows an elevation drop of 201 
feet over 4.8 miles to the international border where there is a slight 
leveling; starting at 4,134 feet above sea level at the Nogales, Mexico 
urban boundary and dropping to 3,933 feet at the international border. 
The Nogales, Arizona sub-transect shows an elevation drop of 508 feet 
over 10 miles, from the international border to the northern boundary 
of the Nogales NA; starting at 3,933 feet and dropping to 3,425 
feet.\23\ In sum, looking at a south-to-north transect along the 
Nogales Wash, elevations fall from south to north with the highest 
elevations occurring in the Nogales, Mexico area. Looking at the 
general topography of the Ambos Nogales area from a northwest 
perspective in Arizona to the southeast into Mexico, there is a funnel 
created as the Nogales Wash falls from higher southern elevations to 
the international border along the route of the Alvaro Obreg[oacute]n 
Boulevard and into Nogales, Arizona.\24\ Small side canyons extend off 
of the Nogales Wash bottom and into the surrounding hills between the 
international border and south of the Nogales, Mexico city center, and 
to a lesser extent into Nogales, Arizona as elevations drop moving to 
the north.
---------------------------------------------------------------------------

    \23\ See Figure 19, Short Aerial and Elevation Transect of 
Nogales, Arizona and Nogales, Sonora, from ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'', in Appendix D of the Nogales 2012 
Plan.
    \24\ See Figure 17, Elevated Topographical View of Ambos Nogales 
Area from Northwest Perspective with Nogales, Sonora Highlighted and 
International Border in Red Line, from ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'', in Appendix D of the Nogales 2012 
Plan.
---------------------------------------------------------------------------

(ii) Ambient PM10 Monitoring Network, Data, Analyses, and 
Findings
    As suggested by method 1 from the General Preamble Addendum, the 
State analyzed hourly observations of PM10 concentrations, 
wind direction, wind speed and temperature.\25\ First, we will provide 
an overview and review of the Nogales, Arizona monitoring network. 
Second, we will examine the State's review of the ambient 
PM10 data for 2007-2009. Finally, we will review the 
findings from the State's analyses of the ambient PM10 and 
meteorological data.
---------------------------------------------------------------------------

    \25\ Observations of PM10 concentrations, wind 
direction, wind speed and temperature were taken at the Nogales, 
Arizona Post Office site; hourly temperature observations were taken 
at the Nogales International Airport, 7.6 miles from the Nogales 
Post Office monitoring site and within the Nogales NA.
---------------------------------------------------------------------------

    Ambient PM10 and Meteorological Monitoring Network. There are five 
ambient air monitors in the vicinity of Ambos Nogales that the State 
considered for this analysis.\26\ Within the nonattainment area, the 
Nogales, Arizona Post Office is the primary violating monitor location 
for PM10. Arizona operates two PM10 monitors 
there, along with a PM2.5 monitor. The Nogales, Arizona Post 
Office monitoring site is 0.3 miles north of the border and this 
monitoring site is 0.9 miles northeast of the Nogales, Mexico Fire

[[Page 38410]]

Station monitoring site. The Green Valley and Corona de Tucson 
monitoring sites are approximately 35 and 45 miles away from the U.S./
Mexico border, respectively. The Nogales Post Office and the Nogales, 
Mexico Fire Station monitors are operated by ADEQ. The Corona de Tucson 
and the Green Valley monitors, located near Tucson, Arizona, are 
operated by the Pima County Department of Environmental Quality (PDEQ).
---------------------------------------------------------------------------

    \26\ These monitors are described in detail in Section 2 of 
``Analysis of Ambient PM10 Levels, Topography, and 
Meteorological Data in Nogales, Arizona: 2007-2009'', in Appendix D 
of the Nogales 2012 Plan. Also, see Figure 2 of the same document 
for a map of their locations.
---------------------------------------------------------------------------

    Also, Arizona operates a meteorological data collection station at 
the Nogales, Arizona Post Office monitoring site. Wind speed 
observations discussed in its analyses were collected at that location. 
Temperature observations were collected at the Nogales International 
Airport, located approximately six miles northeast of the Nogales, 
Arizona Post Office monitoring site and within the nonattainment area.
    EPA performed independent Technical System Audits (TSAs) of ADEQ's 
ambient air monitoring program in December 2004, September 2009, and 
April 2012 and TSAs of PDEQ's ambient monitoring program in June 2008 
and September 2011, per requirements in 40 CFR part 58, appendix A, 
section 2.5.\27\ We assessed ADEQ and PDEQ's compliance with 
established regulations governing the collection, analysis, validation, 
and reporting of ambient air quality data and concluded that ADEQ and 
PDEQ have a robust ambient air monitoring program, with an appropriate 
quality system in place for collecting ambient air monitoring data. EPA 
reviewed and subsequently approved the 2011 ADEQ annual monitoring 
network plan on December 1, 2011.\28\ We found that ADEQ's 2011 
monitoring network plan was complete and met the requirements for 
annual network plans described in 40 CFR 58.10.
---------------------------------------------------------------------------

    \27\ See EPA's ``Arizona Department of Environmental Quality 
Technical System Audit'' final October 2005; ``Technical System 
Audit Report, Arizona Department of Environmental Quality, Air 
Quality Division, Ambient Air Quality Monitoring Program,'' final 
September 2010; and ``Pima County Department of Environmental 
Quality, Technical System Audit'' final February 2009. Final reports 
for the April 2012 TSA of ADEQ and September 2011 TSA of PDEQ are 
not yet complete.
    \28\ See ADEQ's ``State of Arizona Air Monitoring Network Plan 
For the Year 2011, Final Report'' dated August 2, 2011 and EPA's 
approval letter from Matthew Lakin, Manager of EPA Region 9's Air 
Quality Analysis Office, to Eric Massey, Director of the Air Quality 
Division of Arizona Department of Environmental Quality, dated 
December 1, 2011.
---------------------------------------------------------------------------

    Ambient PM10 Data for 2007-2009. The 24-hour PM10 NAAQS 
is based on the number of expected exceedances greater than 150 [mu]g/
m\3\ averaged over three years.\29\ For this analysis, the State 
considered the most recent and most complete three-year data range 
available: 2007-2009. There was a large period of missing data at the 
Nogales, Arizona Post Office PM10 federal equivalency method 
(FEM)/special purpose monitor between March 16 and October 27, 2010. 
Consequently, we concur with the State that 2007 to 2009 is the most 
appropriate timeframe for this section 179B analysis and attainment 
demonstration. At the Nogales, Arizona Post Office monitors, 
PM10 data completeness for each quarter within the 2007-2009 
timeframe is greater than 75 percent.
---------------------------------------------------------------------------

    \29\ The NAAQS for all pollutants can be found at www.epa.gov/air/criteria.html.
---------------------------------------------------------------------------

    In the 2007-2009 period, there were 29 exceedances at the Nogales, 
Arizona Post Office, FEM/special purpose monitor.\30\ \31\ Of those 
exceedances, 14 occurred in 2007, 13 in 2008, and two in 2009. Twenty-
seven of the twenty-nine exceedances were observed in the October 
through March annual timeframe. Twenty-four hour PM10 
concentrations on exceedance days varied between 155 and 238 [mu]g/
m\3\, with some hourly measurements reaching 900 [mu]g/m\3\. Arizona 
has not flagged any of these 2007, 2008, or 2009 exceedance days for 
potential exclusion from air quality planning considerations under 
EPA's Exceptional Events Rule.\32\ The State focused on the data from 
the Nogales, Arizona Post Office FEM/Met One BAM 1020 monitor for the 
following reasons: it is comparable to the NAAQS; it has recorded all 
the exceedances in the area; it has recorded hourly ambient values; 
and, it has a sufficiently complete dataset for comparison to the 
NAAQS.
---------------------------------------------------------------------------

    \30\ This monitor is formally designated as AQS ID: 04-023-0004, 
POC 3.
    \31\ For a list of the 29 exceedance days by year and observed 
24-hour concentrations at all five Nogales area monitors, see Tables 
1-3 in ``Analysis of Ambient PM10 Levels, Topography, and 
Meteorological Data in Nogales, Arizona: 2007-2009'' in Appendix D 
of the Nogales 2012 Plan.
    \32\ For the Exceptional Events Rule see ``Treatment of air 
quality monitoring data influenced by exceptional events''; 40 CFR 
50.14.
---------------------------------------------------------------------------

    The State did not use 2010 and 2011 data for its detailed 
meteorological analysis and attainment demonstration for two reasons. 
First, the 2010 dataset did not meet the completeness criteria 
specified in 40 CFR part 50, appendix K; no quarter in 2010 had 
complete data. This was due to a large data gap from March 16 to 
October 27 resulting from poor quality assurance and control results. 
Second, at the time of this analysis, the 2011 dataset had yet to be 
entered completely into the EPA's Air Quality System (AQS) database and 
certified by Arizona. As stated earlier, a complete year of air quality 
data, as defined by 40 CFR part 50, appendix K, comprises all four 
calendar quarters with each quarter containing data from at least 75 
percent of the scheduled sampling days. While the 2010 and 2011 ambient 
data do not provide the basis for the State's attainment demonstration, 
the State examined this data and found no information to contradict its 
conclusions using the 2007-2009 data set.\33\
---------------------------------------------------------------------------

    \33\ See Section 4.5 in ``Analysis of Ambient PM10 
Levels, Topography, and Meteorological Data in Nogales, Arizona: 
2007-2009'', in Appendix D of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    The State reviewed the 2010 and 2011 data to see how ambient 
PM10 levels compared to the 2007-2009 dataset. In 2010, the 
Nogales, Arizona Post Office (FRM/Met One BAM 1020) monitor recorded 
six exceedances of the 24-hour PM10 NAAQS; these 24-hour 
average ambient values ranged from 159 [mu]g/m\3\ to 191 [mu]g/m\3\. 
There was one exceedance of the PM10 standard in 2011. 
Arizona has not flagged any of these 2010 or 2011 exceedances for 
potential exclusion from air quality planning considerations under 
EPA's Exceptional Events Rule.
    Analyses of 2007-2009 Ambient PM10 Data, Meteorological Data and 
Findings. To understand and characterize the ambient PM10 
data and meteorological data from the Nogales NA on the 29 exceedance 
days chosen for this analysis, the State conducted two initial studies: 
an examination of hourly ambient PM10 concentrations, hourly 
wind speed observations, and hourly temperatures; and, several analyses 
of hourly wind direction observations and hourly ambient 
PM10 concentrations.
    The first study of hourly observations of ambient PM10 
concentrations, wind speeds, and temperatures on the 29 exceedance days 
involved line plots of these three variables over the 24 hour 
exceedance day.\34\ These line plots showed a relatively tight grouping 
among the three subject variables across 29 exceedance days except for 
three days that were distinct from the rest. The line plot of hourly 
PM10 concentrations versus time of day for all exceedance 
days identified January 1, 2007, May 22, 2008, and January 1, 2009 as 
having a significantly different diurnal pattern.\35\ The remaining 26 
of

[[Page 38411]]

the 29 observed exceedances have nearly identical diurnal patterns.\36\ 
Line plots of hourly wind speed versus time of day for all exceedance 
days show wind speeds were eight miles per hour (mph) or below for all 
exceedance days, with the exception of May 22, 2008, when elevated wind 
speeds were observed.\37\ Line plots of hourly temperatures versus time 
of day for all exceedance days show a distinct diurnal heating and 
cooling pattern with no particular day deviating substantially from the 
others.\38\
---------------------------------------------------------------------------

    \34\ See Figures 4, 5, 6, and 7 in ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'', in Appendix D of the Nogales 2012 
Plan.
    \35\ See Figure 4 in ``Analysis of Ambient PM10 
Levels, Topography, and Meteorological Data in Nogales, Arizona: 
2007-2009'', in Appendix D of the Nogales 2012 Plan.
    \36\ See Figure 5 in ``Analysis of Ambient PM10 
Levels, Topography, and Meteorological Data in Nogales, Arizona: 
2007-2009'', in Appendix D of the Nogales 2012 Plan.
    \37\ See Figure 6 in ``Analysis of Ambient PM10 
Levels, Topography, and Meteorological Data in Nogales, Arizona: 
2007-2009'', in Appendix D of the Nogales 2012 Plan.
    \38\ See Figure 7 in ``Analysis of Ambient PM10 
Levels, Topography, and Meteorological Data in Nogales, Arizona: 
2007-2009'', in Appendix D of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    In a second set of analyses of ambient PM10 
concentrations and wind direction on exceedance days, the State found 
that high PM10 concentrations are associated with wind 
direction from a southerly quadrant, or southerly air flows, more often 
than what is typically observed on non-exceedance days. Also, the State 
found that the largest number of hourly ambient values above 150 [mu]g/
m\3\ and the highest ambient values, including those markedly above 150 
[mu]g/m\3\, originated from a southerly wind direction quadrant.\39\ 
These observations suggest a greater influence on ambient 
PM10 concentrations from sources in Mexico during these 
hours of southerly wind direction.
---------------------------------------------------------------------------

    \39\ Throughout these analyses and this document, the term 
``southerly wind direction quadrant'' refers to wind originating 
from between 135 and 224 degrees on a compass rose. Similarly, the 
term ``all other wind direction quadrants'' refers to the remaining 
270 degrees of wind direction between 225 and 134 degrees on a 
compass rose.
---------------------------------------------------------------------------

    Beginning with wind rose analyses, the State determined that the 
prevailing wind direction was from the south, and to a lesser degree, 
from the west southwest directions on non-exceedance days, but almost 
primarily from the south on exceedance days.\40\ Following with 
pollution rose studies that link hourly ambient PM10 
concentration and wind direction observations, these studies showed a 
significant percentage of values greater than 150 [mu]g/m\3\ 
originating from the southerly wind direction quadrant.\41\ A 
presentation of the Figure 11 pollution rose data in tabular form is 
provided in Table 7. The largest proportion of hourly values above 150 
[mu]g/m\3\ and the highest hourly concentrations were found in the 
southerly wind direction quadrant. When ambient PM10 values 
above 150 [mu]g/m\3\ were sorted by 100 [mu]g/m\3\ increments to 550 
[mu]g/m\3\ and greater, the analysis showed that within each increment 
above 150 [mu]g/m\3\, 71 to 92 percent of the ambient PM10 
observations were from the southerly wind quadrant. Again, these 
observations suggest a greater influence on ambient PM10 
concentrations from sources in Mexico during these hours of southerly 
wind direction.
---------------------------------------------------------------------------

    \40\ See Figures 8 and 9 in ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'', in Appendix D of the Nogales 2012 
Plan.
    \41\ See Figures 11 and 12 in ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'', in Appendix D of the Nogales 2012 
Plan.

                    Table 7--Hourly Ambient PM10 Concentrations Sorted by Concentration and Wind Direction, 2007-2009 Exceedance Days
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               Range of ambient concentration values (microgram/m\3\)
                                                          ----------------------------------------------------------------------------------------------
                 Wind direction quadrant                                                                                                   Share of all
                                                               <150       150-250      250-350      350-450      450-550       >=550      wind direction
                                                            (percent)    (percent)    (percent)    (percent)    (percent)    (percent)     observations
--------------------------------------------------------------------------------------------------------------------------------------------------------
Northerly NW to NNE......................................           27            6            3            3            3            0               17
Easterly NE to ESE.......................................           15           16           16           11            3            8               14
Southerly SE to WSW......................................           41           71           72           84           92           92               57
Westerly SW to WNW.......................................           18            6            8            3            3            0               12
                                                          ----------------------------------------------------------------------------------------------
    Total................................................          100          100          100          100          100          100              100
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: Table 11 in ``Clean Air Act, Section 179B Attainment Determination for the Nogales PM10 Nonattainment Area'' in Appendix A of the Nogales 2012
  Plan.

    Finally, in a third analysis, the State examined the wind direction 
and hourly PM10 concentrations on each exceedance day to 
determine two average ambient values for each exceedance day: one value 
for the southerly wind quadrant and a second value representing all 
other wind direction quadrants.\42\ The results showed that two of the 
29 exceedance days, January 1, 2007 and January 26, 2008, have an 
average ambient concentration greater than 150 [mu]g/m\3\ for the ``all 
other wind direction'' quadrants. The ratio of the southerly quadrant 
concentration to the ``all other direction'' quadrant concentration 
ranges from 0.86 to one to 11 to one, with an average ratio value of 
3.83 to one. Only one day, January 1, 2007, has a ratio value less than 
1.0 to one; i.e., the ``all other direction'' quadrants' share exceeds 
the southerly quadrant share. This analysis also suggests a greater 
influence on ambient PM10 concentrations from sources in 
Mexico during these hours of southerly wind direction.
---------------------------------------------------------------------------

    \42\ See Table 12 for all estimated values on all exceedance 
days in ``Clean Air Act, Section 179B Attainment Determination for 
the Nogales PM10 Nonattainment Area'' in Appendix A of 
the Nogales 2012 Plan.
---------------------------------------------------------------------------

    To summarize, the State analyzed hourly ambient concentrations on 
exceedance days and found that high PM10 concentrations are 
associated with wind direction from a southerly quadrant, or southerly 
air flows, more often than what is typically observed on non-exceedance 
days. The State found that the largest number of hourly ambient values 
above 150 [mu]g/m\3\ and the highest ambient values, including those 
markedly above 150 [mu]g/m\3\, originated from a southerly wind 
direction quadrant. These studies of hourly ambient data confirm these 
general findings; however, the January 1, 2007 and January 26, 2008 
exceedance days may be exceptions. Also, due to the differing 
meteorology exhibited on May 22, 2008 and January 1, 2009, these days 
are marked for further study. All four of these exceedance days are 
reviewed and discussed further, below.

[[Page 38412]]

d. Findings From Reviews of Emission Inventories, and Studies of 
Ambient PM10 Data, and Meteorological Data
    From the State's analyses, the Nogales NA emissions inventories, 
the Nogales Municipality, Mexico emissions inventories, and the 2007-
2009 ambient data and meteorological analyses, the State made the 
findings listed below.
     The majority of exceedances, 79 percent, occurred in the 
October to January timeframe, mostly in November.\43\ Also, given the 
high desert environment and winter light regime, temperatures usually 
drop dramatically, 20 degrees Fahrenheit over the 3-4 hours after 
sunset.\44\
---------------------------------------------------------------------------

    \43\ See Figure 3 in ``Analysis of Ambient PM10 
Levels, Topography, and Meteorological Data in Nogales, Arizona: 
2007-2009'' in Appendix D of the Nogales 2012 Plan.
    \44\ See Figures 7 and 14 in ``Analysis of Ambient 
PM10 Levels, Topography, and Meteorological Data in 
Nogales, Arizona: 2007-2009'' in Appendix D of the Nogales 2012 
Plan.
---------------------------------------------------------------------------

     From the Nogales NA and Nogales Municipality, Mexico 
emission inventories, the State estimated pollution loads may differ by 
a ratio of 1.8 (low estimate)--4.6 (high estimate) to one on a south-
to-north basis in relation to the international border.
     The largest sources of PM10 emissions in the 
Ambos Nogales area are reentrained dust from unpaved and paved roads.
     Overall, elevations drop approximately 709 feet across the 
entire south-to-north local transect, from the southernmost edge of the 
Nogales, Mexico urban boundary to the Nogales NA northern boundary 
line.
     Of the 29 exceedance days in 2007-2009, 26 of those days 
showed a similar pattern of ambient PM10 concentrations, 
wind speeds, wind direction, and temperature variation over a 24-hour 
period; the three exceptions were January 1, 2007, May 22, 2008, and 
January 1, 2009.
     On exceedance days, the largest proportions, 71-92 
percent, of hourly values exceeding 150 [mu]g/m\3\ and almost all of 
the highest observed PM10 concentrations of observations 
above 450 [mu]g/m\3\, 92 percent, are associated with a southerly wind 
direction quadrant.\45\
---------------------------------------------------------------------------

    \45\ See Table 11 above. For a visual representation of this 
data, see the pollution roses in Figures 11 and 12, ``Analysis of 
Ambient PM10 Levels, Topography, and Meteorological Data 
in Nogales, Arizona: 2007-2009'' in Appendix D of the Nogales 2012 
Plan.
---------------------------------------------------------------------------

     The ambient PM10 concentration attributed to 
the southerly wind quadrant exceeds 150 [mu]g/m\3\ on all 29 exceedance 
days. In contrast, two exceedance days from the ``all other wind 
direction'' quadrants show a value greater than 150 [mu]g/m\3\: January 
1, 2007, and January 26, 2008.
     Only one of 29 exceedance days shows the concentration 
attributed to the ``all other wind direction'' quadrants greater than 
that of the concentration attributed to the southerly wind quadrant: 
January 1, 2007.
     On exceedance days, the average ratio of the southerly 
wind quadrant share of 24-hour ambient PM10 values to all 
other wind quadrants share of ambient values is 3.83 to one. This ratio 
is relatively consistent with the estimated pollution loads ratio of 
1.8-4.6 to one, from south-to-north across the international border. 
This comparison of the hourly ambient PM10 value/wind 
direction ratio and the pollution load ratios suggests that the 
pollution load ratios and the low and high emissions inventory 
estimates are both conservatively low and high estimates of ambient 
conditions.

Upon review of the ambient PM10 data, meteorology, and the 
State's analyses, we concur with the State's findings listed above.
e. Arizona's Demonstration of Attainment for the Nogales Nonattainment 
Area but for International Sources of PM10 Emissions
(i) Daily Analysis to Demonstrate Attainment but for International 
Sources of PM10 Emissions
    As described above, 26 of the 29 2007-2009 exceedances showed a 
similar pattern of ambient PM10 concentrations, wind speeds, 
wind direction, and temperature variation over a 24-hour period; the 
exceptions were January 1, 2007, May 22, 2008, and January 1, 2009. Two 
of these days, January 1, 2007, and January 1, 2009, with higher early 
morning PM10 concentrations, only vary from the diurnal 
profile of PM10 concentrations observed for the other 
exceedances, but have similar meteorological and concentration patterns 
throughout the rest of the day. Two of the 29 exceedance days, January 
1, 2007, and January 26, 2008, had high average ambient concentrations 
during hours when the wind was out of directions other than the south. 
Thus, there are 25 exceedance days that are equivalent and can be 
considered as a group, setting aside the dissimilar exceedance days 
listed above, January 1, 2007, January 26, 2008, May 22, 2008, and 
January 1, 2009.
    A Conceptual Model of 2007-2009 Exceedance Days. Considering these 
25 similar exceedance days, the State explained how the elements of 
pollution loads and sources, temperature changes, and wind direction 
may contribute to producing the majority of observed ambient 
PM10 values exceeding the NAAQS in Nogales, Arizona.\46\ The 
data concerning January 1, 2007, January 26, 2008, May 22, 2008, and 
January 1, 2009 are reviewed later in more detail in this daily 
analysis.
---------------------------------------------------------------------------

    \46\ For a graphical depiction of the interplay between ambient 
PM10 concentrations, wind speed, and temperatures 
described by the conceptual model, see Figure 3 in ``Clean Air Act, 
Section 179B Attainment Determination for the Nogales 
PM10 Nonattainment Area'' in Appendix A of the Nogales 
2012 Plan. As explained in the footnote to Figure 3, although the 
diurnal emissions pattern of the January 26, 2008 exceedance day is 
very similar to the 25 exceedance days summarized by the conceptual 
model other parts of the discussion may not be consistent with the 
observed data from January 26, 2008.
---------------------------------------------------------------------------

    Within the cited Figure 3, the State shows the average 
PM10 concentration, wind speed, and temperature across 26 
similar exceedance days and including 25 of those days in the 
conceptual model. The 24-hour pattern of these variables on these 25 
days is similar. Beginning at midnight, the data indicate that there is 
a strong pattern of decreasing PM10 concentrations from the 
previous day's high values into the early morning hours. Then, there is 
a pronounced PM10 increase and drop-off between 6:00 a.m. 
and 9:00 a.m., suggesting a regularly occurring direct PM10 
source, such as reentrained road dust from the morning commute. As 
morning temperatures rise, so does wind speed as wind direction changes 
from south to north dispersing the spike in morning PM10 
concentrations. The PM10 concentrations continue to fall 
through the afternoon and reach their lowest points between 10:00 a.m. 
and 4:00 p.m. The morning and afternoon increases in ambient 
temperature and wind speed can be attributed to the heating portion of 
a diurnal heating and cooling cycle where heated air flows from lower 
elevations in the north to the higher elevations in the south.
    On the 25 days, the meteorological and ambient concentration data 
also provide an explanation for regularly occurring increases in 
PM10 concentrations during the evening hours. As sunset 
approaches and night falls, the diurnal cooling cycle begins. Ambient 
temperatures drop and lower elevation air masses no longer rise with 
convection, causing wind speed to drop and wind direction to be 
variable. As temperatures continue to drop after sunset, wind speeds 
drop and cold air masses flow downslope from higher elevations, causing 
wind direction to shift from a variable/northerly direction to a 
southerly direction. A pronounced spike in PM10 
concentration is then

[[Page 38413]]

observed beginning between 4:00 p.m. and 6:00 p.m.; roughly 
corresponding with the evening commute hours. Concentrations remain 
high for several hours into the evening and gradually begin to decrease 
as midnight approaches. The highest concentrations of PM10 
occur in these evening hours when reentrained dust from unpaved and 
paved roads may be captured by cold air flows moving south to north 
from higher to lower elevations (later in the discussion this 
phenomenon is referred to as ``downslope air flows''). Also, home 
heating combustion may add a component to the evening PM10 
load and also be captured in the evening southerly and downslope air 
flows from Nogales, Mexico into Nogales, Arizona.
    This pattern of exceedances is usually observed during times when 
the general weather pattern allows for stagnation and a relatively 
still air mass subject to movement by the diurnal cooling and heating 
cycle. At other times of the year, frontal systems move through often 
enough and with enough energy to prevent a stagnant air mass in the 
Ambos Nogales region and this diurnal heating and cooling cycle exerts 
less influence on the local meteorology.
    The conceptual model the State has presented to explain the 
exceedances in the Nogales NA is consistent with the study by Arizona 
State University, ``Atmospheric, Hydroclimatic, and Anthropogenic 
Causes of Fugitive Dust in the Nogales, Arizona-Nogales, Sonora 
Airshed.'' \47\ In this study--based on a regression analysis of 815 
daily PM10 observations at Nogales, Arizona, and 457 daily 
PM10 observations at Nogales, Mexico, and other 
information--the authors conclude that stagnant atmospheric conditions 
over a large scale (i.e., a stagnant synoptic atmosphere) is the most 
important factor in predicting high daily PM10 
concentrations.
---------------------------------------------------------------------------

    \47\ Completed in 2002 by A.W. Ellis, the final report is 
available through The Southwest Center for Environmental Research 
and Policy at http://scerpfiles.org/cont_mgt/doc_files/A-02-2.pdf.
---------------------------------------------------------------------------

    For the 25 similar days examined by ADEQ, the ambient 
PM10 concentration attributed to the southerly wind 
direction quadrant always exceeds the 150 [mu]g/m\3\ level, in most 
cases markedly.\48\ Conversely, the ambient concentration attributed to 
the ``all other wind direction'' quadrants never exceeds the 150 [mu]g/
m\3\ level. Across all 25 days, the average of the hourly monitored 
PM10 concentration values for the hours with a southerly 
wind direction ranges from 163 to 369 [mu]g/m\3\ for each of the days, 
with an average value across the 25 days of 264 [mu]g/m\3\. In 
comparison, the average of the hourly concentration values for all 
other wind direction quadrants ranges from 38 to 148 [mu]g/m\3\ for 
each of the days, with an average value across the 25 days of 80 [mu]g/
m\3\. This suggests that emissions sources to the south in Mexico are 
contributing significantly to those hourly ambient concentrations and 
the resulting 24-hour average concentrations.
---------------------------------------------------------------------------

    \48\ For the estimated values providing the basis for the 
conceptual model's 25 exceedance day values discussed in this 
paragraph, see Table 12 in ``Clean Air Act, Section 179B Attainment 
Determination for the Nogales PM10 Nonattainment Area'' 
in Appendix A of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    In sum, for 25 of the 29 exceedance days, the State provided a 
conceptual model explaining how exceedances of the PM10 
NAAQS occur in the Nogales NA. Moreover, for all of these 25 days, the 
origin and contribution of PM10 to exceedances of the 
standard at the Nogales, Arizona Post Office monitor has a very large 
southerly component. Given the wind direction, the proximity of the 
monitor to the border, and the comparison of the magnitude of emissions 
on either side of the border, the majority of the emissions that result 
in these 25 exceedances most likely originate from the Nogales, Mexico 
side of the international border.
    Analysis of Four Days Differing From Conceptual Model: January 1, 
2007; January 26, 2008; May 22, 2008; and, January 1, 2009. The 
conceptual model of Mexican influence on Nogales NA PM10 
concentrations described above fits the observations on 25 of the 29 
exceedance days in 2007-2009. The State identified four specific 
exceedance days that differ in one or more ways from the 25-day 
conceptual model of PM10 exceedances in the Nogales NA: 
January 1, 2007, May 22, 2008, January 26, 2008, and January 1, 2009. 
See Table 8 for more information.

Table 8--24-hour PM10 Concentration ([mu]g/m\3\) and Hourly Concentration Averages ([mu]g/m\3\) Disaggregated by
              Southerly Wind Direction Quadrant for Exceedance Days Differing From Conceptual Model
----------------------------------------------------------------------------------------------------------------
                                                             Southerly wind quadrant    All other wind direction
                  Date                        24-hour         (135 to 224 degrees)        (225 to 134 degrees)
                                           concentration      average concentration      average concentration
----------------------------------------------------------------------------------------------------------------
January 1, 2007........................               210  199 (15 of 24 values).....  231 (9 of 24 values).
January 26, 2008.......................               204  257 (7 of 24 values)......  182 (17 of 24 values).
May 22, 2008...........................               217  217 (24 of 24 values).....  No Observed Values.
January 1, 2009........................               238  323 (14 of 24 values).....  119 (10 of 24 values).
----------------------------------------------------------------------------------------------------------------
Data Source: Air Quality System database; and, Table 4.2 in Nogales 2012 Plan.

    The State examined each of these days in further detail to evaluate 
the influences on the high ambient PM10 values that occurred 
on those days and to determine whether the four remaining exceedance 
days--January 1, 2007, January 26, 2008, May 22, 2008, and January 1, 
2009--should be assigned to the category of exceedance days having a 
significant contribution from emission sources originating from the 
Nogales, Mexico side of the international border. The State's analysis 
is summarized below.
    January 1, 2007 Exceedance Day Review. Considering the January 1, 
2007 exceedance day, it differs from the conceptual model average 
exceedance day in the timing and distribution of observed ambient 
PM10 values and high PM2.5 component most likely 
caused by a combustion source.\49\ The PM10: 
PM2.5 ratio for January 1, 2007 is the lowest in the 29-day 
sample (1.49 to 1). What differs in the case of the January 1, 2007 
exceedance is that the 270 degree wind direction quadrants contain 
enough high values to contribute disproportionately to the overall 24-
hour average concentration. Although more detailed and different field 
studies might prove otherwise, with the information available, the 
State's analysis is inconclusive as to whether this exceedance is 
attributable to a disproportionate international

[[Page 38414]]

contribution and the Nogales NA would not have exceeded the 24-hour 
PM10 standard but for Mexican emissions.\50\
---------------------------------------------------------------------------

    \49\ For the complete discussion of coarse versus fine 
particulate matter on all exceedance days, see Section 4.4 and Table 
8 in ``Analysis of Ambient PM10 Levels, Topography, and 
Meteorological Data in Nogales, Arizona: 2007-2009'' in Appendix D 
of the Nogales 2012 Plan.
    \50\ For a detailed review of the January 1, 2007 exceedance 
day, see Section 4.2.1 of ``Clean Air Act, Section 179B Attainment 
Determination for the Nogales PM10 Nonattainment Area'' 
in Appendix A of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    January 26, 2008 Exceedance Day Review. The State's review of the 
January 26, 2008 exceedance day suggests that this day is most like the 
conceptual model average exceedance day in the timing and distribution 
of observed ambient PM10 values. While the southerly wind 
direction quadrant contains enough high values to contribute 
disproportionately to the overall 24-hour average concentration, there 
are enough remaining high values in the 17 of 24 hourly observations 
from the 270 degree wind direction quadrants to be above the 150 [mu]g/
m\3\ level. Again, while specifically designed field studies might help 
clarify the relative contributions to this exceedance, with the 
information available, the State's analysis is inconclusive as to 
whether this exceedance is attributable to a disproportionate 
international contribution and the Nogales NA would not have exceeded 
the 24-hour PM10 standard but for Mexican emissions.\51\
---------------------------------------------------------------------------

    \51\ For a detailed review of the January 26, 2008 exceedance 
day, see Section 4.2.2 of ``Clean Air Act, Section 179B Attainment 
Determination for the Nogales PM10 Nonattainment Area'' 
in Appendix A of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    May 22, 2008 Exceedance Day Review. The May 22, 2008 exceedance day 
is wholly different from the State's conceptual model exceedance day 
given the relative high wind speeds, a 17 mph high observation, and 
higher than usual coarse PM component likely from disturbed 
surfaces.\52\ The PM10:PM2.5 ratio for May 22, 
2008 is the highest in the 29-day sample (10.96 to 1), well beyond the 
sample average of 6.24 to 1. As with total PM10 emissions, 
emissions of coarse PM (e.g., unpaved roads) are higher from Nogales, 
Mexico, than they are from the Nogales NA. The wind direction is from a 
southerly quadrant in all hourly observations. See Table 8. Given this 
information, we concur that the day should be placed with the 25 other 
exceedance days in the conceptual model, because it is likely that the 
sources of PM10 causing the exceedance originated from the 
Nogales, Mexico side of the international border.\53\
---------------------------------------------------------------------------

    \52\ See Figure 6 in ``Clean Air Act, Section 179B Attainment 
Determination for the Nogales PM10 Nonattainment Area'' 
in Appendix A of the Nogales 2012 Plan.
    \53\ For a detailed review of the May 22, 2008 exceedance day, 
see Section 4.2.3 of ``Clean Air Act, Section 179B Attainment 
Determination for the Nogales PM10 Nonattainment Area'' 
in Appendix A of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    January 1, 2009 Exceedance Day Review. Like the January 1, 2007 
exceedance, the January 1, 2009 exceedance day is different from the 
conceptual model exceedance day in the timing and distribution of 
observed ambient PM10 values and high PM2.5 
component most likely caused by a combustion source. As with total 
PM10 emissions, emissions of fine PM (e.g., combustion 
sources) are higher from Nogales, Mexico, than they are from the 
Nogales NA. For example, a comparison of the 2008 Nogales Municipality, 
Mexico and Nogales NA emissions inventories for the residential 
woodburning source category shows 176 tpy compared to 24 tpy, 
respectively (see Tables 2 and 6, above). The key factor for assigning 
this day is the contribution of high hourly ambient concentrations with 
a southerly wind direction quadrant compared to the remaining 270 
degree wind direction quadrants. See Table 8. Consequently, we concur 
that the day should be placed with the 25 other exceedance days in the 
conceptual model, because it is likely that the sources of 
PM10 causing the exceedance originated from the Nogales, 
Mexico side of the international border.\54\
---------------------------------------------------------------------------

    \54\ For a detailed review of the January 1, 2009 exceedance 
day, see Section 4.2.4 of ``Clean Air Act, Section 179B Attainment 
Determination for the Nogales PM10 Nonattainment Area'' 
in Appendix A of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    To summarize, the State concludes that two exceedance days, May 22, 
2008 and January 1, 2009, should be categorized with the 25 exceedance 
days where the State found that there was a high likelihood of a large 
contribution of PM10 from sources on the Nogales, Mexico 
side of the international border such that the Nogales NA would likely 
have attained the PM10 standard but for emissions from 
Mexico. The two remaining exceedance days, January 1, 2007 and January 
26, 2008, have contributions from PM10 sources on the 
Nogales NA side of the international border such that it cannot be 
determined that there is a similarly high likelihood that the Nogales 
NA would not have exceeded the PM10 standard but for 
PM10 emissions originating from the Mexican side of the 
international border. Therefore, according to this daily analysis, the 
State found that at least 27 of 29 exceedances of the PM10 
NAAQS observed in the Nogales NA during 2007-2009 can be attributed 
primarily to sources of PM10 from across the international 
border. Based on these two exceedances and on data completeness and 
every day sampling for the 2007-2009 timeframe, the State calculated a 
maximum expected annual exceedance rate of 0.7 exceedances per year.
    (ii) Hourly Analysis to Demonstrate Attainment But For 
International Sources of PM10 Emissions
    In a second analysis, the State classified each hourly 
PM10 concentration value from the 29 exceedance days based 
on the likely influence of emissions from Mexico and then recalculated 
the 24-hour average concentration that would have occurred but for 
international transport of PM10 emissions from Nogales, 
Mexico. An hourly concentration was classified as influenced by 
international transport if it met one of four criteria, or decision 
rules, related to hourly observations of wind direction, wind speed, 
and temperature change:
    (1) Hours with sustained (more than one hour consecutively) 
southerly winds greater than 4.5 mph (2 meters/second (m/s)), 
suggesting the primary influence of wind-blown PM10 from 
across the international border;
    (2) hours with southerly winds or air flow and decreasing or stable 
temperatures preceded by or followed by hours with similar conditions, 
suggesting sustained downslope air flows from higher elevations south 
of the international border;
    (3) any hour preceded by and followed by hours with southerly wind 
or air flow and decreasing or stable temperatures, suggesting continued 
influence of downslope air flow from higher elevations south of the 
international border; and,
    (4) surface wind speed less than or equal to 1.1 mph (0.5 m/s), 
preceded by or followed by hours with similar conditions, suggesting 
sustained air mass stagnation where PM10 emissions suspended 
in previous hours remain suspended in the stagnant air mass.

The first decision rule identifies periods consistent with sustained 
high winds from the south carrying wind-blown PM10, as 
discussed earlier concerning the May 22, 2008 exceedance day. The 
second and third decision rules identify periods influenced by 
downslope wind flow conditions described in the conceptual model as 
usually occurring in the late afternoon and evening and transporting 
PM10 from higher elevations in Nogales, Mexico to lower 
elevations in the Nogales NA. The fourth decision rule identifies 
periods of sustained air mass stagnation usually found in the late 
night and early morning hours after the early evening downslope wind or 
air flow has ebbed and before sunrise, after which wind speeds begin to 
increase from their overnight low values.

[[Page 38415]]

    Using the low estimate of total Nogales Municipality, Mexico 
PM10 emissions, the analysis of emissions inventories 
discussed earlier showed that U.S. sources are responsible for a 
maximum of 36 percent of PM10 emissions in the Ambos Nogales 
region; see Table 9. Conversely, using the high estimate of total 
Nogales Municipality, Mexico emissions, U.S. sources are responsible 
for a minimum of 17 to 18 percent of PM10 emissions in the 
Ambos Nogales region in 2008 and 2011, respectively.

   Table 9--2008 and 2011 Total PM10 Emission Inventories: Nogales NA, Arizona and Nogales Municipality, Mexico
                                          [Low estimate, tons per year]
----------------------------------------------------------------------------------------------------------------
                                                                  2008              2011             Percent
----------------------------------------------------------------------------------------------------------------
Nogales NA, Arizona.......................................             1,524             1,521                36
Nogales Municipality, Mexico..............................             2,713             2,757                64
                                                           -----------------------------------------------------
    Total Ambos Nogales Region............................             4,237             4,278               100
----------------------------------------------------------------------------------------------------------------
Source: Tables 6-7 from ``Clean Air Act, Section 179B Attainment Determination for the Nogales, Arizona PM10
  Nonattainment Area'' in Appendix A of the Nogales 2012 Plan.

    Therefore, for each hour that meets one of the four criteria listed 
above, instead of assuming that the concentration is entirely due to 
Mexican sources, a more conservative assumption is that up to 36 
percent of the hourly concentrations may be due to contributions from 
U.S. emission sources. Therefore, in this next step, the observed 
hourly concentrations were weighted by 0.36 for each hour that meets 
any one of the four criteria listed above and used this weighted 
concentration to estimate the 24-hour average concentration that would 
have occurred in the Nogales NA but for international transport from 
Mexico.
    To show the effects of each decision rule, an estimated 24-hour 
concentration was calculated after the application of Rule 1, Rules 2 
and 3, Rules 1-3, and Rules 1-4. The results are summarized below.\55\
---------------------------------------------------------------------------

    \55\ The observed concentrations and meteorological data for 
each hour of each exceedance day, the classification based on the 
criteria listed above, and the re-calculation of the estimated 24-
hour average concentrations but for international transport are 
provided in Section 3.7 of ``Analysis of Ambient PM10 
Levels, Topography, and Meteorological Data in Nogales, Arizona: 
2007-2009'' in Appendix D of the Nogales 2012 Plan.
---------------------------------------------------------------------------

     The application of Rule 1 only removes one day, May 22, 
2008, leaving 28 days showing a concentration value greater than 150 
[mu]g/m\3\.
     The application of Rules 2 and 3 removes 27 days, leaving 
January 1, 2007 and January 26, 2008 showing a concentration value 
greater than 150 [mu]g/m\3\; 196 [mu]g/m\3\ and 244 [mu]g/m\3\, 
respectively.
     The application of Rules 1, 2, and 3 again removes 27 
days, leaving January 1, 2007 and January 26, 2008 showing a 
concentration value greater than 150 [mu]g/m\3\; 196 [mu]g/m\3\ and 244 
[mu]g/m\3\, respectively.
     The application of Rules 1, 2, 3, and 4 removes 29 days, 
leaving no estimated days with a value greater than 150 [mu]g/m\3\. The 
highest 24-hour average concentration estimated was 107 [mu]g/m\3\.

In sum, based on this analysis apportioning hourly concentration data 
using the four criteria to produce an estimated 24-hour average 
concentration but for international emissions, no exceedance days would 
have been expected to occur in the Nogales NA, but for transport from 
Mexico.
    Considering the relatively large differences in emissions 
inventories between the Nogales NA and Nogales Municipality, Mexico and 
the meteorology described by the conceptual model, it is likely that 
observed pollution during southerly downslope wind flows originating 
from Nogales, Mexico also contributed to observed pollution during 
following hours of sustained stagnation. With the wind direction 
varying under low wind speeds and stable temperatures, it remains 
possible, however, that a greater proportion of PM10 
pollution during hours of sustained stagnation may be coming from U.S. 
sources. Therefore, a slightly more conservative approach would be to 
relax the decision rules by not considering sustained stagnation (Rule 
4) and assign PM10 levels during these hours entirely to the 
Nogales NA. Consequently, when considering Mexican influence to only 
occur under conditions of relative high wind speeds (Rule 1) and 
sustained downslope wind flows from the south (Rules 2 and 3), two 
exceedance days would have been expected to occur but for international 
transport: January 1, 2007 and January 26, 2008. Given the finding that 
no more than two exceedance days would have occurred applying criteria 
one through three, as determined by this hourly analysis of 
concentration data, the maximum expected number of annual exceedances 
is 0.7.
3. Proposed Action on the Nogales Nonattainment Area Section 179B 
Analysis and Demonstration of Attainment but for International Sources 
of PM10 Emissions
    We propose to approve Arizona's section 179B analysis and 
demonstration of attainment but for international sources of 
PM10 emissions. After meeting the PM10 NAAQS from 
1994-1997, an increasing number of exceedances occurred in the Nogales 
NA. While population in the Nogales NA has grown slightly since 1995, 
the Nogales Municipality population has increased 65 percent, such that 
in 2010, 90 percent of the Ambos Nogales regional population is the 
Nogales Municipality, Mexico area. This difference in relative 
population and population growth over time supports the inference that 
a much larger proportion of PM10 in the Nogales NA comes 
from emissions sources on the Nogales, Mexico side of the international 
border.
    A comparison of 2008 and 2011 emission inventories between the 
Nogales Municipality and the Nogales NA shows that pollution loads may 
differ by a ratio of 1.8-4.6 to one on a south-to-north basis relative 
to the international border. The Nogales NA contributes 17 to 36 
percent of PM10 emissions in the Ambos Nogales region, 
depending on the emissions inventory estimate chosen for the Nogales 
Municipality, Mexico. Conversely, the Nogales Municipality, Mexico 
contributes 83 to 64 percent of PM10 emissions in the Ambos 
Nogales region.
    In its review of the ambient PM10 data, meteorological 
data, and through its analyses, Arizona found that the Ambos Nogales 
area's meteorology and topography influence the observed exceedances of 
PM10 NAAQS and there is a definite south-to-north 
directional component to the ambient air quality

[[Page 38416]]

data underlying the exceedances of the PM10 NAAQS. Finally, 
daily and hourly analyses of the most recent three years of quality 
assured and State certified ambient PM10 and meteorological 
data from 2007-2009 show that no more than two, and likely none, of the 
29 exceedances would have occurred in the Nogales NA, but for 
PM10 emissions from Mexico.
    Based on these two exceedances, data completeness, and every day 
sampling for the 2007-2009 timeframe, the calculated maximum expected 
annual exceedance rate is 0.7 exceedances per year. The standard we use 
to demonstrate attainment of the PM10 NAAQS, ``but for'' 
international emissions, is that the expected number of days per 
calendar year with a 24-hour average concentration above 150 [mu]g/m\3\ 
must be equal to or less than one. To conclude, we propose to determine 
that Arizona has met this standard and to approve their section 179B 
Analysis and demonstration of attainment but for international 
emissions for the Nogales NA.
    Even if a nonattainment area would have attained the 
PM10 NAAQS but for international transport of emissions from 
outside the U.S., section 179B still requires the area to meet the 
statutory requirements for a nonattainment plan. Section 179B suspends 
the obligation to provide an attainment demonstration showing actual 
attainment of the NAAQS, but a nonattainment area still has to meet 
basic requirements such as RACM/RACT, RFP and contingency measures. We 
will discuss how the 2012 Nogales PM10 Plan addressed these 
requirements in the following sections of this proposed rule.

C. Reasonably Available Control Measures (RACM)/Reasonably Available 
Control Technology (RACT) and Adopted Control Strategy

1. Requirement for RACM/RACT
    CAA section 172(c)(1) requires that an attainment plan ``provide 
for the implementation of all reasonably available control measures as 
expeditiously as practicable (including such reductions in emissions 
from existing sources in the area as may be obtained through the 
adoption, at a minimum, of reasonably available control technology), 
and shall provide for attainment of the national primary ambient air 
quality standards.'' EPA defines RACM as measures that a State finds 
are both reasonably available and contribute to attainment as 
expeditiously as practicable in its nonattainment area. See also the 
General Preamble, 57 FR 13560; (April 16, 1992).
    The General Preamble also discusses the moderate area 
PM10 requirements for RACM/RACT at section 189(a)(1)(C). As 
a starting point, a State should review the list of available control 
measures provided with the General Preamble and provide a reasoned 
judgment for rejecting any of these available control measures. A State 
may show that one or more control measures are unreasonable because 
emissions from those sources are insignificant within the nonattainment 
area; as such, those control measures would not be considered RACM for 
the nonattainment area. Any remaining control measures from the General 
Preamble list should then be evaluated for reasonableness according to 
their technological feasibility and cost of control. See 57 FR 13540-
13541; (April 16, 1992).
    The 1994 General Preamble Addendum also discusses the requirements 
for RACM as applied to nonattainment areas affected by international 
transport. In international border areas, ``RACM/RACT must be 
implemented to the extent necessary to demonstrate attainment by the 
applicable attainment date if emissions emanating from outside the U.S. 
were not included in the analysis.'' As set forth in section 
179B(a)(2), a State's moderate area PM10 plan must be 
``adequate'' to attain and maintain the PM10 NAAQS, but for 
emissions from outside the U.S. Therefore, nothing in section 179B 
relieves a State from the requirement to address and implement RACM. 
Nonetheless, States are not required to implement control measures that 
go beyond what the plan demonstrates would otherwise be adequate for 
attainment and maintenance of the PM10 NAAQS but for 
emissions from outside the U.S. See 59 FR 42001; (August 16, 1994). For 
a nonattainment area making a showing under section 179B, the area is 
required to implement RACM/RACT sufficient to attain the standard by 
the applicable attainment date, but for emissions from outside the 
U.S., and to maintain the level of emissions from U.S. sources 
sufficient to provide for continued attainment of the NAAQS, but for 
the emissions from outside the U.S.
2. RACM/RACT in the Nogales Nonattainment Area
    For the Nogales 2012 Plan, ADEQ reviewed the RACM/RACT 
demonstration from the 1993 Nogales PM10 Plan in light of 
the updated emissions inventories and section 179B demonstration and 
concluded that no additional RACM beyond that already implemented is 
required. In support of this conclusion, ADEQ describes the status of 
implementation of the RACM adopted as part of the 1993 Nogales 
PM10 Plan. Based on our review of both the 1993 plan and the 
current 2012 plan, and for the reasons given below, we agree with 
ADEQ's conclusion that no further RACM is required.
    First, we note that, based on the emissions inventories from the 
1993 and 2012 plans, entrainment of PM10 by vehicle travel 
over unpaved surfaces, primarily roads, remains the most significant 
source of PM10 emissions generated within the Nogales NA, 
and while PM10 emissions from this source are certainly 
lower than they would have been without additional paving, they still 
account for more than 50 percent of the overall PM10 
inventory in the Nogales NA.
    In the late 1980s, ADEQ, Santa Cruz County, and the city of Nogales 
recognized the importance of PM10 emissions from entrainment 
by vehicle travel over unpaved surfaces. To reduce such emissions, the 
city of Nogales undertook a program to pave the unpaved roads in the 
city, paving an average of two miles of unpaved roads per year from 
1989 through 1992,\56\ to chip-seal the city's equipment yard, and to 
pave the unpaved parking areas of Memorial Park and Neighborhood 
Center. Over this same period, within the unincorporated area of the 
Nogales NA, Santa Cruz County undertook a program to chip-seal unpaved 
county roads and chip-sealed approximately 2-3 miles of previously 
unpaved roads per year.\57\
---------------------------------------------------------------------------

    \56\ To put a rate of two miles of paving per year into context, 
we note that, by 1993, there remained approximately 10 miles of 
unpaved public roads within the city of Nogales.
    \57\ For perspective on the county's rate of paving/chip sealing 
of unpaved roads, we note that as of 2011 there were approximately 
40 to 50 miles of unpaved roads remaining in the unincorporated area 
of the Nogales NA.
---------------------------------------------------------------------------

    Through the 1993 Nogales PM10 Plan, the city of Nogales 
committed to paving the remainder of its unpaved streets by 1998, and 
Santa Cruz County committed to chip-seal at least one mile of unpaved 
road per year over 1993 and 1994 within the Nogales NA.\58\
---------------------------------------------------------------------------

    \58\ See 1993 Nogales PM10 Plan, pages 31 and 46.
---------------------------------------------------------------------------

    The 1993 Nogales PM10 Plan also cited diesel-powered 
truck idling at two ports of entry (DeConcini and Mariposa) along the 
U.S. Mexico border in Nogales as a source of PM10 emissions 
within the Nogales NA and identified the reduction of idling time by 
such trucks as a RACM for implementation by the U.S. Customs Service. 
In response, the U.S. Customs Service committed to complete certain

[[Page 38417]]

capital improvements, including the addition of four north-bound lanes 
at the DeConcini Port of Entry (central business district within 
Nogales) and three north-bound lanes at the Mariposa Port of Entry 
(west of the central business district).
    Third, in the late 1980s and early 1990s, the dragging of the 
unpaved border road by the U.S. Border Patrol (to detect fresh 
footprints) was considered another source of PM10 emissions 
contributing to ambient PM10 concentrations in Nogales. The 
1993 Nogales PM10 Plan does not identify RACM for this 
source. However, the 1993 Nogales PM10 Plan notes that, in 
1992, the U.S. Border Patrol discontinued the practice of dragging a 
1.5-mile stretch of border road within the Nogales NA.\59\ The Border 
Patrol discontinued the practice over this stretch of road because it 
was ineffective. The road was also wired for movement sensors to detect 
human movement. These changes reduced this source of PM10 
emissions within the Nogales NA.
---------------------------------------------------------------------------

    \59\ See 1993 Nogales PM10 Plan, page 30.
---------------------------------------------------------------------------

    By the end of 1994, which was the applicable attainment date for 
the Nogales PM10 nonattainment area, the city of Nogales had 
paved an additional four miles of unpaved roads (beyond that completed 
through 1992); Santa Cruz County had paved an additional four miles of 
South River Road; and the U.S. Customs Service had completed the 
capital improvements described above at the DeConcini and Mariposa 
Ports of Entry. Together, these measures, in addition to those 
PM10-reducing measures completed in the late 1980s and early 
1990s and certain other measures implemented outside of the SIP process 
(i.e., the discontinuance of dragging the border road), were sufficient 
to reduce PM10 concentrations in the Nogales NA such that 
maximum 24-hour PM10 concentrations decreased from greater 
than 200 [mu]g/m\3\ in the late 1980s to less than 120 [mu]g/m\3\ by 
1994.
    Based on the data collected during the 1992-1994 period, EPA 
determined that the Nogales area had attained the PM10 
standard by the 1994 area's statutory attainment date. See 76 FR 1532; 
(January 11, 2011). Thus, the measures implemented by the city of 
Nogales, Santa Cruz County, and U.S. Customs Service provided for 
attainment by the applicable attainment date and thereby met the RACM 
requirement. The Nogales 2012 Plan did not include the RACM commitments 
contained in the 1993 Nogales PM10 Plan but, given their 
prior completion and permanent nature, we do not believe that the 
commitments need be made a part of the SIP.
    EPA does recognize that violations of the PM10 standard 
began to occur once again in Nogales beginning in 1998 and that such 
violations continue to the present, but, based on the section 179B 
demonstration contained in the 2012 Nogales Plan, and evaluated in 
section IV.B herein, we do not believe that additional RACM are 
required to be implemented within the Nogales NA because we believe 
that the violations that have occurred since 1998 would not have 
occurred but for emissions from Mexico.
    Our conclusion in this regard recognizes that PM10 
emissions in various important PM10 source categories are 
affected by changes in population, and whereas the population in the 
Nogales NA increased by approximately 5,000 persons during the 20-year 
period from 1990 to 2010, the population in Nogales, Mexico increased 
by approximately 118,000 persons during that same period. Moreover, the 
passage of the North American Fair Trade Agreement (NAFTA) in 1994 has 
continued to fuel the already high level of industrial (Maquiladoras) 
development on the Mexican side of the border. Most significantly, 
however, we note ADEQ's detailed evaluation, as part of the section 
179B demonstration, of the 29 exceedances measured during the 2007-2009 
period and determination that the highest 24-hour PM10 
concentration in Nogales, but for emissions from Mexico, was 107 
[micro]g/m\3\, i.e., well below the 150 [micro]g/m\3\ standard.\60\ 
ADEQ's section 179B demonstration, which we are proposing to approve, 
thus provides support for the conclusion that the violations that have 
occurred since 1998 would not have occurred but for the emissions from 
Mexico and thus no additional RACM need be implemented within the 
Nogales NA.
---------------------------------------------------------------------------

    \60\ The estimated 24-hour average concentrations but for 
international transport for the 29 exceedance days are provided in 
Section 3.7 of ``Analysis of Ambient PM10 Levels, 
Topography, and Meteorological Data in Nogales, Arizona: 2007-2009'' 
in Appendix D of the Nogales 2012 Plan.
---------------------------------------------------------------------------

D. Reasonable Further Progress Demonstration and Contingency Measures 
in the Nogales Nonattainment Area

1. Reasonable Further Progress
    CAA section 172(c)(2) requires that plans for nonattainment areas 
shall provide for reasonable further progress (RFP). RFP is defined in 
section 171(1) as ``such annual incremental reductions in emissions of 
the relevant air pollutant as are required by this part or may 
reasonably be required by the Administrator for the purpose of ensuring 
attainment of the applicable [NAAQS] by the applicable date.''
    The Nogales 2012 Plan cites EPA's determination that the area 
attained the PM10 standard by the applicable attainment date 
as affirming that RFP requirements have been met. We agree that the RFP 
requirement was met in the Nogales NA by 1994 through the various 
paving projects and other measures implemented by the city of Nogales, 
Santa Cruz County, and U.S. Customs Service because the measures in 
fact provided the incremental reductions needed by the area to attain 
by the applicable attainment date (1994). In addition, for the same 
reasons that no additional RACM need be implemented in the Nogales NA, 
notwithstanding the advent of violations of the PM10 
standard once again in 1998, we believe that no additional RFP 
demonstration must be submitted by ADEQ for this area.
2. Contingency Measures
    Regarding contingency measures, under CAA section 172(c)(9), all 
attainment plans must include contingency measures to be implemented if 
an area fails to meet RFP (RFP contingency measures) and contingency 
measures to be implemented if an area fails to attain the 
PM10 NAAQS by the applicable attainment date (attainment 
contingency measures). These contingency measures must be fully adopted 
rules or control measures that are ready to be implemented quickly 
without significant additional action by the State. They must also be 
measures not relied on in the plan to demonstrate RFP or attainment and 
should provide SIP-creditable emissions reductions equivalent to one 
year of RFP. Finally, the SIP should contain trigger mechanisms for the 
contingency measures and specify a schedule for their implementation.
    EPA guidance also provides that contingency measures could be 
implemented early, i.e., prior to the milestone or attainment date.\61\ 
Consistent with this policy, states are allowed to use excess 
reductions from already adopted measures to meet the CAA section 
172(c)(9) contingency measure requirement. This is because the purpose 
of contingency measures is to provide extra reductions that are not

[[Page 38418]]

relied on for RFP or attainment that will provide for continued 
progress while the plan is being revised to fully address the failure 
to meet the required milestone or failure to meet the standard by the 
applicable attainment date. Nothing in the CAA precludes a State from 
implementing such measures before they are triggered. This approach has 
been approved in numerous SIPs. See 62 FR 15844; (April 3, 1997), 
(approval of the Indiana portion of the Chicago area 15 percent Rate of 
Progress plan); 66 FR 30811; (June 8, 2001), (proposed approval of the 
Rhode Island post-1996 ROP plan); and 66 FR 586 and 66 FR 634; (January 
3, 2001), (approval of the Massachusetts and Connecticut 1-hour ozone 
attainment demonstrations). In the only adjudicated challenge to this 
approach, the court upheld it. See Louisiana Environmental Action 
Network v. EPA, 382 F.3d 575 (5th Cir. 2004). The Nogales 2012 Plan 
points to the paving projects that have been implemented since 1994 as 
meeting the contingency measure requirement for the Nogales NA and as 
the justification for not including any additional contingency measures 
in the 2012 Nogales Plan. In assessing the extent of road paving in the 
Nogales NA, ADEQ consulted with officials in the city of Nogales and 
Santa Cruz County to determine the extent of road paving since 1992, 
when the Nogales NA began to record ambient PM10 levels 
below the NAAQS.
---------------------------------------------------------------------------

    \61\ Memorandum, G.T. Helms, Chief, Ozone/Carbon Monoxide 
Programs Branch to Air Directors, ``Contingency Measures for Ozone 
and Carbon Monoxide Redesignations,'' June 1, 1992.
---------------------------------------------------------------------------

    As noted above, in the 1993 Nogales PM10 Plan, the city 
of Nogales committed to paving all public roads in the city by 1998. 
For the purposes of the Nogales 2012 Plan, ADEQ reviewed the status of 
implementation of the city's paving program, and using aerial 
photography, ADEQ identified 11 unpaved roads that were paved between 
1993 and 1996 totaling 8.4 miles.\62\ Among these 11 roads, ADEQ could 
locate traffic data for only nine of them (totaling 7.7 miles) from 
which to estimate the associated reduction in PM10 
emissions. Based on the control effectiveness of paving and available 
traffic data, ADEQ estimated that paving of the nine roads between 1993 
and 1996 reduced PM10 emissions by approximately 80 tons per 
year. See Table 5.3 from the Nogales 2012 Plan.\63\ Assuming that half 
that reduction occurred after 1994, the resulting reduction that was 
surplus to the attainment needs for the Nogales NA was approximately 40 
tons per year, although the actual reduction was greater than 40 tons 
per year because two specific roadways that were paved (but for which 
no traffic data was available) were not included in the calculation. 
ADEQ also checked on the status of the paving program with officials 
from the city of Nogales who reported that all of the unpaved public 
roads in Nogales have been paved and accepted into the City's Street 
Maintenance Program.\64\
---------------------------------------------------------------------------

    \62\ See Appendix E.4 of the Nogales 2012 Plan for aerial 
photography used in implementation review.
    \63\ See Appendix E of the Nogales 2012 Plan for the Technical 
Support Document concerning the calculation of these emission 
reduction estimates.
    \64\ Correspondence from Juan Guerra, City Engineer, City of 
Nogales, Arizona to James Wagner, ADEQ; April 11, 2012; see Appendix 
F.3 of Nogales 2012 Plan.
---------------------------------------------------------------------------

    In a similar implementation review using aerial photography and 
data provided by Santa Cruz County, ADEQ estimated that Santa Cruz 
County paved/chip-sealed 40 miles of unpaved roads between 1994 and 
2001 and an additional 40 miles of unpaved roads between 2002 and 2008. 
Traffic data was available, however, for only approximately 10 miles of 
the total 80 miles of paving/chip-sealing in the post-attainment era, 
but ADEQ estimates that paving/chip-sealing this subset of the larger 
amount reduced PM10 emissions in the Nogales NA by 
approximately 110 tons per year. See Table 5.4 in the 2012 Nogales 
Plan.65 66 Overall, Santa Cruz County and ADEQ provided 
different estimates of the number and extent of paved/chip-sealed roads 
and unpaved roads in the unincorporated area of the Nogales NA, but 
both sets of estimates indicate that more than 70 percent of the roads 
in the unincorporated area within the Nogales NA are paved/chip-sealed 
at the present time.
---------------------------------------------------------------------------

    \65\ See appendix E.4 of the Nogales 2012 Plan for aerial 
photography used in implementation review.
    \66\ See Appendix E.2 of the Nogales 2012 Plan for supporting 
information from Santa Cruz County concerning paving/chip-sealing 
projects completed by the County.
---------------------------------------------------------------------------

    Based on our review of the data collected by ADEQ and presented in 
the Nogales 2012 Plan, we agree with ADEQ that post-1994 paving 
projects in the Nogales NA have provided PM10 emissions 
reductions beyond those relied upon by RFP or attainment and have also 
served to ensure that emissions generated within the Nogales NA do not 
cause a violation of the PM10 standard. The city of Nogales 
and Santa Cruz County did not wait until a triggering event to 
implement the paving projects but continued the paving programs that 
began in the late 1980s and that helped the Nogales NA attain the 
standard by the applicable attainment date (1994). These projects have 
provided significant PM10 emissions reductions, i.e., 
greater than 150 tons per year if all of the unpaved roads that were 
paved/chip-sealed were included, beyond that required for attainment by 
the applicable attainment date.
    We consider such ``early'' implementation of contingency measures 
to be acceptable in this instance because the associated emissions 
reductions provide extra reductions that are not relied upon for RFP or 
attainment and that provide extra assurance that no violations would 
occur in the Nogales NA but for emissions from Mexico. The 
effectiveness of implementation of the contingency measures is 
supported by the conclusion in ADEQ's section 179B demonstration that 
estimates that the highest 24-hour PM10 concentration in 
Nogales, but for emissions from Mexico, during the 2007-2009 period was 
107 [micro]g/m\3\, i.e., well below the 150 [micro]g/m\3\ standard. 
Therefore, we conclude that implementation of the post-1994 paving 
projects in the Nogales NA meets the contingency measure requirement of 
section 172(c)(9).

E. Motor Vehicle Emissions Budgets for Transportation Conformity

1. Requirements for Transportation Conformity
    Transportation conformity is required by section 176(c) of the CAA. 
Actions involving Federal Highway Administration (FHWA) or Federal 
Transit Administration (FTA) funding or approval are subject to the 
EPA's transportation conformity rule, codified at 40 CFR part 93, 
subpart A. Our transportation conformity rule requires that 
transportation plans, programs, and projects developed by Metropolitan 
Planning Organizations (MPOs) in nonattainment and maintenance areas 
conform to SIPs and establishes the criteria and procedures for 
determining whether or not they do so. Conformity to the SIP means that 
transportation activities will not cause or contribute to new air 
quality violations, worsen existing violations, or delay timely 
attainment of the national ambient air quality standards or any interim 
milestone.
    Control strategy SIP submittals (such as RFP and attainment SIP 
submittals) must specify the maximum emissions of transportation-
related emissions from existing and planned highway and transit systems 
allowed in the appropriate years, i.e., the motor vehicle emissions 
budgets (MVEB or ``budgets''). The submittal must also demonstrate that 
these transportation-related emissions levels, when considered with 
emissions from all

[[Page 38419]]

other sources, are consistent with RFP or attainment of the NAAQS, 
whichever is applicable. MPOs cannot use the budgets and the U.S. 
Department of Transportation (USDOT) cannot approve a Regional 
Transportation Plan (RTP) or Transportation Improvement Program (TIP) 
conformity analysis using the budgets until EPA had made an affirmative 
adequacy finding based on a preliminary review of the SIP. MPOs must 
use budgets in a submitted but not yet approved SIP, after EPA has 
determined that the budgets are adequate. For EPA to find these 
emissions levels or ``budgets'' adequate and/or approvable, the 
submittal must meet the conformity adequacy provisions of 40 CFR 
93.118(e)(4) and (5). Also, motor vehicle emissions budgets cannot be 
approved until EPA completes a detailed review of the entire SIP and 
determines that the SIP and the budgets will achieve their intended 
purpose (i.e., RFP, attainment or maintenance). For more information on 
the transportation conformity requirement and applicable policies on 
budgets, please visit our transportation conformity Web site at: http://www.epa.gov/otaq/stateresources/transconf/index.htm.
    PM10 attainment and RFP plans should identify budgets 
for direct PM10 and PM10 attainment plan 
precursors. Direct PM10 budgets should include 
PM10 motor vehicle emissions from tailpipe, brake wear, and 
tire wear. States must also consider whether reentrained paved and 
unpaved road dust or highway and transit construction dust are 
significant contributors and should be included in the direct 
PM10 budget. (See 40 CFR 93.102(b) and 93.122(e) and the 
conformity rule preamble at 69 FR 40004, 40031-40036; (July 1, 2004)). 
The applicability of emission trading between conformity budgets for 
conformity purposes is described in 40 CFR 93.124(c).
2. Motor Vehicle Emissions Budget for the Nogales Nonattainment Area
    Usually, States are required to consult with local metropolitan 
planning organizations (MPOs) when developing a MVEB. The Nogales NA 
does not have an MPO. To develop the MVEB, ADEQ consulted with EPA and 
the Arizona Department of Transportation (ADOT). The Federal Highway 
Administration's Highway Statistics statewide series data on Arizona 
shows a decline in vehicle miles traveled (VMT) between 2007 and 2008, 
and no change in VMT between 2008 and 2009. Emission inventory 
estimates for 2011 show a slight decrease in VMT. This trend is 
consistent with economic conditions. As discussed earlier in this 
proposed rule, the section 179B demonstration shows attainment of the 
PM10 standard in the Nogales NA, but for emissions from 
Mexico. The section 179B demonstration, proposed for approval herein, 
relies on a detailed analysis of PM10 exceedances that 
occurred during a specific three-year period (2007-2009), but assuming 
the 2007-2009 period is representative of the post-attainment date 
(1994) period, the conclusion that no violations would occur in Nogales 
but for emissions from Mexico can be applied throughout the post-
attainment period. As such, there are several different years which are 
consistent with the applicable requirements for reasonable further 
progress and attainment, and which could be used for development of a 
MVEB.\67\ The State chose 2011 as the year for the MVEB. The MVEB was 
determined using information from the emissions inventories described 
in Chapter 3 and included in Appendix B of the Nogales 2012 Plan.
---------------------------------------------------------------------------

    \67\ 40 CFR 93.118(e)(4)(iv) requires motor vehicle emissions 
budget(s), when considered together with all other emissions 
sources, to be consistent with applicable requirements for 
reasonable further progress, attainment, or maintenance (whichever 
is relevant to the given implementation plan submission).
---------------------------------------------------------------------------

    The State's estimated MVEB for the Nogales NA includes 
PM10 emissions from all on-road vehicle emissions source, 
and reentrained fugitive dust from unpaved and paved roads. EPA's 
current MOVES (MOVES2010a) emissions model for on-road mobile sources 
was used to estimate the on-road motor vehicle portion of the 2011 
MVEB. MOVES estimates tailpipe emissions from cars, trucks, 
motorcycles, buses, as well as brake and tire wear. Secondary 
PM10 derived from PM10 precursors are not 
identified as sources of PM10 contributing to exceedances of 
the PM10 NAAQS in the Nogales NA, either in the emissions 
inventories or in the plan, in general.
    Fugitive emissions from paved and unpaved roads are affected by the 
number of VMT, silt volume on paved roads, and other local factors. 
Emissions estimates for these source categories were based on data 
obtained from State and federal agencies for the 2008 NEI. Estimates 
for Santa Cruz County were then apportioned to the Nogales NA based on 
population. The 2011 p.m.10 motor vehicle emissions budget for the 
Nogales NA was estimated at 1,000.3 tons per year. See Table 10.

      Table 10--2011 Nogales NA PM10 Motor Vehicle Emissions Budget
                                 [Tons]
------------------------------------------------------------------------
                       Source category                            PM10
------------------------------------------------------------------------
Unpaved Road Dust............................................      864.9
Paved Road Dust..............................................      121.4
On-road Motor Vehicle--Gasoline..............................        2.6
On-road Motor Vehicle--Diesel................................       11.4
                                                              ----------
    Total....................................................    1,000.3
------------------------------------------------------------------------
Source: Table 7.1 of the Nogales 2012 Plan and ``2008 and 2011 PM10
  Emissions Inventories for the Nogales NA, Santa Cruz County, Arizona''
  in Appendix B of the Nogales 2012 Plan.

3. Proposed Action on the Motor Vehicle Emissions Budget for the 
Nogales Nonattainment Area
    We propose to approve the MVEB for the Nogales NA as submitted by 
ADEQ contingent upon ADEQ's inclusion of road construction 
PM10 in the MVEB. Road construction PM10 should 
be included because, as the second largest source of PM10 
emissions generated within the Nogales NA, road construction 
PM10 is a significant contributor to the overall Nogales NA 
PM10 inventory. See 40 CFR 93.122(e). As revised to include 
road construction PM10, we propose to approve the MVEB for 
three reasons. First, we find that the MVEB is derived from a 
comprehensive, accurate, and current emissions inventory that we 
believe meets the requirements of section 172(c)(3) of the CAA. Second, 
the MVEB includes all on-road sources of PM10 including 
fugitive dust emissions from unpaved and paved roads and will include 
road construction PM10, and was estimated using the latest 
motor vehicle emissions model available at the time of the emissions 
inventory was composed, the MOVES2010a model. Third, the MVEB are 
derived from emissions estimates used by ADEQ in the section 179B 
demonstration to show that the Nogales area would attain the 
PM10 standard, but for emissions from Mexico.

VI. EPA's Proposed Action and Request for Comment

    Based on our review, EPA proposes to approve this moderate area 
plan submitted by Arizona to attain the PM10 NAAQS for the 
Nogales nonattainment area. Specifically, under CAA section 110(k)(3), 
EPA proposes to approve the following elements of the Nogales 2012 
p.m.10 attainment plan:
    (1) The 2008 base year and 2011 emissions inventories as meeting 
the requirements of CAA section 172(c)(3);
    (2) the demonstration of attainment but for international emissions 
as

[[Page 38420]]

meeting the requirements of CAA section 179B(a)(1);
    (3) the implementation of paving projects and capital improvement 
projects at the Ports of Entry within the Nogales NA prior to the 
attainment deadline (1994) as meeting the RACM/RACT requirements of CAA 
sections 172(c)(1), 179B(a)(2), and 189(c)(1)(C);
    (4) the implementation of paving projects and capital improvement 
projects at the Ports of Entry to meet the RFP demonstration 
requirement of CAA sections 172(c)(2) and 179B(a)(2);
    (5) the implementation of post-1994 paving projects as meeting the 
contingency measure requirements of CAA sections 172(c)(9) and 
179B(a)(2); and,
    (6) the 2011 attainment year motor vehicle emissions budget if 
revised to include road construction PM10, because, as 
revised, it is derived from the section 179B demonstration and meets 
the requirements of CAA section 176(c) and of 40 CFR 93, subpart A.
    Even with our proposed approval of Arizona's demonstration that the 
Nogales NA is attaining the PM10 NAAQS but for international 
transport from Mexico, any final action resulting from this proposal 
would not constitute a redesignation to attainment under CAA section 
107(d)(3) because we have not determined that the area has met the 
other CAA requirements for redesignation to attainment of the 
PM10 NAAQS. The classification and designation status in 40 
CFR part 81 would remain moderate nonattainment for the Nogales NA 
until such time as EPA determines that Arizona has met the CAA 
requirements for redesignating the Nogales NA to attainment for the 
PM10 NAAQS. EPA is soliciting public comments on the issues 
discussed in this Federal Register Notice. We will accept comments from 
the public on this proposal for the 30 days after publication of this 
proposed rule in the Federal Register. We will consider these comments 
before taking final action.

VII. Statutory and Executive Order Reviews

    With this action, we propose to approve the moderate area 
PM10 plan submitted by Arizona for the Nogales NA and, if 
finalized, this proposed action would not impose additional 
requirements beyond those imposed by State law or by the CAA. For that 
reason, this proposed action:
     Is not a ``significant regulatory action'' subject to 
review by the Office of Management and Budget under Executive Order 
12866 (58 FR 51735, October 4, 1993);
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have Federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based 
on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Is not subject to requirements of section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the Clean Air Act; and
     Does not provide EPA with the discretionary authority to 
address disproportionate human health or environmental effects with 
practical, appropriate, and legally permissible methods under Executive 
Order 12898 (59 FR 7629, February 16, 1994).
    In addition, this proposed action does not have Tribal implications 
as specified by Executive Order 13175 (65 FR 67249; November 9, 2000), 
because the SIP obligations discussed herein do not apply to Indian 
Tribes and thus will not impose substantial direct costs on Tribal 
governments or preempt Tribal law.

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Intergovernmental 
relations, Particulate matter, Reporting and recordkeeping 
requirements.

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

    Dated: June 20, 2012.
Jared Blumenfeld,
Regional Administrator, EPA Region IX.
[FR Doc. 2012-15544 Filed 6-26-12; 8:45 am]
BILLING CODE 6560-50-P


