[Federal Register Volume 88, Number 242 (Tuesday, December 19, 2023)]
[Proposed Rules]
[Pages 87850-87888]
[FR Doc No: 2023-27513]

Vol. 88

Tuesday,

No. 242

December 19, 2023

Part II

Environmental Protection Agency

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40 CFR Part 52

Air Quality Implementation Plans; California; San Diego County; 2008
and 2015 8-Hour Ozone Nonattainment Area Requirements; Proposed Rule

Federal Register / Vol. 88, No. 242 / Tuesday, December 19, 2023 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2021-0135; FRL-9538-02-R9]

Air Quality Implementation Plans; California; San Diego County;
2008 and 2015 8-Hour Ozone Nonattainment Area Requirements

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve portions of two state implementation plan (SIP) revisions
submitted by the State of California to meet Clean Air Act requirements
for the 2008 8-hour ozone national ambient air quality standards (NAAQS
or ``standards'') and the 2015 8-hour ozone NAAQS in the San Diego
County ozone nonattainment area (``San Diego County area'' or
``area''). The first SIP revision, ``2020 Plan for Attaining the
National Ambient Air Quality Standards for Ozone in San Diego County''
(``2020 San Diego County Ozone SIP'' or ``2020 Plan''), addresses most
of the SIP requirements for the area. The second SIP revision, referred
to as the ``Smog Check Certification,'' supplements the motor vehicle
inspection and maintenance program portion of the 2020 Plan. The EPA is
proposing to approve the 2020 Plan, and the San Diego County portion of
the Smog Check Certification, as meeting all the applicable ozone
nonattainment area requirements for the 2008 and 2015 8-hour ozone
NAAQS addressed by the plan except for the emissions statement
requirement that the EPA previously found to have been met and the
contingency measure requirements, for which the EPA is deferring
action.

DATES: Comments must be received on or before January 18, 2024.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2021-0135 at https://www.regulations.gov. For comments submitted at
Regulations.gov, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
Regulations.gov. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, please contact the person identified in
the FOR FURTHER INFORMATION CONTACT section. For the full EPA public
comment policy, information about CBI or multimedia submissions, and
general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets. If you need assistance in a
language other than English or if you are a person with disabilities
who needs a reasonable accommodation at no cost to you, please contact
the person identified in the FOR FURTHER INFORMATION CONTACT section.

FOR FURTHER INFORMATION CONTACT: John J. Kelly, Air Planning Office
(AIR-2-1), EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105.
By phone at<PHONE_NUMBER>, or by email at [email protected].

SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us,''
and ``our'' refer to the EPA.

Table of Contents

I. Regulatory Context
    A. Ozone Standards, Area Designations, and SIPs
    B. The San Diego County Ozone Nonattainment Area
    C. Clean Air Act and Regulatory Requirements for 2008 and 2015
Ozone Nonattainment Area SIPs
II. Submission From the State of California To Address Ozone
Requirements in San Diego County
    A. Summary of State Submissions
    B. Clean Air Act Procedural Requirements for Adoption and
Submission of SIP Revisions
III. Evaluation of the 2020 San Diego County Ozone SIP
    A. Emissions Inventories
    B. Reasonably Available Control Measures Demonstration and
Control Strategy
    C. Attainment Demonstration
    D. Rate of Progress Plan and Reasonable Further Progress
Demonstration
    E. Transportation Control Strategies and Measures To Offset
Emissions Increases From Vehicle Miles Traveled
    F. Contingency Measures
    G. Motor Vehicle Emissions Budgets for Transportation Conformity
    H. General Conformity Budgets
    I. Other Clean Air Act Requirements Applicable to Severe Ozone
Nonattainment Areas
IV. Environmental Justice Considerations
V. Proposed Action
VI. Statutory and Executive Order Reviews

I. Regulatory Context

A. Ozone Standards, Area Designations, and SIPs

    Ground-level ozone pollution is formed from the reaction of
volatile organic compounds (VOC) and oxides of nitrogen
(NOX) in the presence of sunlight.\1\ These two pollutants,
referred to as ozone precursors, are emitted by many types of sources,
including on- and off-road motor vehicles and engines, power plants and
industrial facilities, and smaller area sources such as lawn and garden
equipment and paints.
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    \1\ The State of California refers to reactive organic gases
(ROG) in some of its ozone-related SIP submissions. As a practical
matter, ROG and VOC refer to the same set of chemical constituents,
and for the sake of simplicity, we refer to this set of gases as VOC
in this proposed rule.
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    Scientific evidence indicates that adverse public health effects
occur following exposure to ozone, particularly in children and adults
with lung disease. Breathing air containing ozone can reduce lung
function and inflame airways, which can increase respiratory symptoms
and aggravate asthma or other lung diseases.\2\
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    \2\ ``Fact Sheet--2008 Final Revisions to the National Ambient
Air Quality Standards for Ozone,'' dated March 2008.
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    Under section 109 of the Clean Air Act (CAA or ``the Act''), the
EPA promulgates NAAQS for pervasive air pollutants, such as ozone, to
protect public health and welfare. Under CAA section 110, following
promulgation of a new or revised NAAQS, states are required to adopt
and submit plans that provide for implementation, maintenance, and
enforcement of the NAAQS (referred to as State Implementation Plans or
SIPs). Under CAA section 107(d), the EPA is required to designate areas
throughout the nation as either attaining or not attaining the NAAQS,
and states with designated nonattainment areas are required to submit
SIP revisions to, among other things, provide for attainment as
expeditiously as practicable but not later than the applicable
attainment dates.
    In 1979, the EPA established primary and secondary NAAQS for ozone
at 0.12 parts per million (ppm) averaged over a 1-hour period (``1979
ozone NAAQS'').\3\ In 1997, the EPA revised the primary

and secondary standards for ozone in the ambient air to 0.08 ppm
averaged over an 8-hour period (``1997 ozone NAAQS'').\4\
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    \3\ 44 FR 8202 (February 8, 1979). When the CAA was amended in
1990, each area of the country that was designated nonattainment for
the 1979 ozone NAAQS, including the San Diego area, was classified
by operation of law as nonattainment and classified as Marginal,
Moderate, Serious, Severe, or Extreme depending on the severity of
the area's air quality problem. The EPA redesignated the San Diego
County area from Serious nonattainment to attainment for the 1979
ozone NAAQS, effective July 28, 2003. 68 FR 37976 (June 26, 2003).
    \4\ 62 FR 38856 (July 18, 1997). In 2004, the EPA designated
areas of the country with respect to the 1997 ozone NAAQS. See 69 FR
23858 (April 30, 2004). The EPA redesignated the San Diego County
area from Moderate nonattainment to attainment for the 1997 ozone
NAAQS, effective July 5, 2013. 78 FR 33230 (June 4, 2013).
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    In 2008, the EPA lowered the 8-hour ozone NAAQS to 0.075 ppm
(``2008 ozone NAAQS'').\5\ Then in 2015, the EPA further lowered the 8-
hour ozone NAAQS to 0.070 ppm (``2015 ozone NAAQS'').\6\ On December
31, 2020, the EPA finalized its most recent periodic review of the
ozone NAAQS, retaining the form and level of the standards.\7\ The EPA
has revoked both the 1979 ozone NAAQS and the 1997 ozone NAAQS but not
the 2008 ozone NAAQS.\8\
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    \5\ 73 FR 16436 (March 27, 2008).
    \6\ 80 FR 65292 (October 26, 2015).
    \7\ 85 FR 87256. The SIP revision that is the subject of this
proposed action relates to the requirements for the 2008 and 2015
ozone standards.
    \8\ 40 CFR 50.9(b) and 40 CFR 50.10(c).
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    In 2012, the EPA designated San Diego County as nonattainment for
the 2008 ozone NAAQS and classified the area as ``Marginal.'' \9\ Areas
classified as Marginal must attain the NAAQS within three years of the
effective date of the nonattainment designation.\10\ Following this
initial classification as Marginal, the EPA found in 2016 that the area
did not attain the 2008 ozone standards by the Marginal attainment
deadline of July 20, 2015.\11\ As a result of our finding, the area was
reclassified by operation of law to Moderate nonattainment.\12\
Moderate nonattainment areas have six years to attain the standard.
Following the Moderate attainment deadline of July 20, 2018, the EPA
found that the area did not attain the 2008 ozone standards.\13\ As a
result of our finding, the area was reclassified by operation of law to
Serious nonattainment, with a Serious attainment deadline of July 20,
2021, nine years after the effective date of designation as a
nonattainment area for the 2008 ozone NAAQS. In response to a letter to
the EPA dated January 8, 2021 from the California Air Resources Board
(CARB), the EPA reclassified the area to Severe for the 2008 ozone
NAAQS.\14\ In the same letter, CARB requested that the EPA also
reclassify the area as Severe for the 2015 ozone NAAQS. The EPA's
initial designation for the San Diego County area for the 2015 ozone
NAAQS was nonattainment, with a Moderate classification.\15\ The San
Diego County area is now classified as Severe for both the 2008 and the
2015 ozone NAAQS.\16\
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    \9\ 77 FR 30087 (May 21, 2012), effective July 20, 2012.
    \10\ CAA section 181(a)(1); 40 CFR 51.1102 and 51.1103(a).
    \11\ 81 FR 26697 (May 4, 2016).
    \12\ The State of California submitted the San Diego County
area's 2016 Moderate ozone attainment plan and the 2016 Moderate
ozone RACT demonstration to the EPA as a SIP revision on April 12,
2017. The State withdrew the 2016 Moderate ozone attainment plan by
letter dated December 16, 2021, following submittal of the 2020 plan
and the EPA's grant of the State's request to reclassify San Diego
County to Severe for the 2008 ozone NAAQS. The EPA approved the 2016
Moderate ozone RACT demonstration at 85 FR 77996 (December 3, 2020),
87 FR 38665 (June 29, 2022) and 88 FR 2538 (January 17, 2023).
    \13\ 84 FR 44238 (August 23, 2019).
    \14\ Letter dated January 8, 2021 from Richard Corey, Executive
Officer, California Air Resources Board, to John Busterud, Regional
Administrator, U.S. EPA Region IX; 86 FR 29522 (June 2, 2021),
effective July 2, 2021.
    \15\ 83 FR 25776 (June 4, 2018). Severe areas must attain the
standard as expeditiously as practicable, but not later than 15
years after the effective date of designation. For the 2008 ozone
NAAQS, the Severe attainment deadline is July 20, 2027. However,
note that for attainment modeling purposes we refer to the
attainment year as 2026. For the 2015 ozone NAAQS, the Severe
attainment deadline is August 3, 2033, with a 2032 attainment year.
    \16\ 86 FR 29522 (June 2, 2021), effective July 2, 2021.
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    Designations of nonattainment for a given NAAQS trigger
requirements under the CAA to prepare and submit SIP revisions. The SIP
revision that is the subject of this proposed action addresses the
Severe nonattainment area requirements that apply to the San Diego
County area for the 2008 and the 2015 ozone NAAQS.
    Under California law, CARB is the state agency that is responsible
for the adoption and submission to the EPA of California SIPs and SIP
revisions, and it has broad authority to establish emissions standards
and other requirements for mobile sources and certain area sources,
such as consumer products. Local and regional air pollution control
districts in California are responsible for the regulation of
stationary sources and are generally responsible for the development of
regional air quality management plans (``plans''). In the San Diego
County area, the San Diego County Air Pollution Control District
(SDCAPCD or ``District'') develops and adopts plans to address CAA
planning requirements applicable to that area. Such plans are then
submitted to CARB for adoption and submittal to the EPA as revisions to
the California SIP.

B. The San Diego County Ozone Nonattainment Area

    The San Diego County area is located in the southwestern-most
portion of the State of California, and its boundaries generally align
with those of San Diego County. For a precise description of the
geographic boundaries of the San Diego County area for both the 2008
and 2015 ozone NAAQS, see 40 CFR 81.305.
    Prior plans and state control measures developed by the District
and CARB have produced significant emissions reductions over the years
and improved air quality in the area. For instance, the 8-hour ozone
design value for the San Diego County area decreased from 0.095 ppm to
0.079 ppm from 2002 to 2022,\17\ despite increases in population and
vehicular activity.
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    \17\ Three design value reports (EPA, Air Quality Design Value
Report, July 12, 2011; San Diego 2008 Ozone Trends Report, U.S. EPA
Air Quality System, May 8, 2023; and San Diego 2015 Ozone Trends
Report, U.S. EPA Air Quality System, May 8, 2023), are included in
the docket for this action. For the 2008 and 2015 ozone NAAQS, the
design value at any given monitoring site is the 3-year average of
the annual fourth highest daily maximum 8-hour average ambient air
quality ozone concentration. The maximum design value among the
various ozone monitoring sites is the design value for the area.
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    Under certain weather conditions, the San Diego County area is
downwind from the Los Angeles-South Coast Air Basin (``South Coast'')
and, under certain other weather conditions, from Mexico, and is
subject to transport of ozone from those areas. The South Coast is
regulated by the South Coast Air Quality Management District (SCAQMD).
The 2020 Plan describes ozone transport from these areas as follows:

. . . air pollution from both regions significantly contribute to
ozone levels in the San Diego region under certain weather
conditions. This impact is acknowledged in State documentation and
regulation. Importantly . . . SCAQMD has implemented effective
emissions control programs, resulting in a trend of emission
reductions and air quality improvements in the South Coast region.
Though the region is designated as an Extreme Nonattainment Area for
the 2008 and 2015 ozone NAAQS, SCAQMD predicts continued ozone
reductions through at least 2031 as shown in their SIP for the 2008
ozone NAAQS. In turn, air pollution transported to San Diego County
is expected to decrease as a result of their actions.\18\
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    \18\ 2020 Plan, p. 13.

    Because of the transport from the South Coast into the San Diego
County area, continued progress in the South Coast towards meeting the
2008 and 2015 ozone NAAQS is expected to help the San Diego County area
attain these ozone NAAQS.

C. Clean Air Act and Regulatory Requirements for 2008 and 2015 Ozone
Nonattainment Area SIPs

    States must implement the 2008 and 2015 ozone NAAQS under title I,
part D

of the CAA, including sections 171-179B of subpart 1 (``Nonattainment
Areas in General'') and sections 181-185 of subpart 2 (``Additional
Provisions for Ozone Nonattainment Areas''). To assist states in
developing effective plans to address ozone nonattainment problems, in
2015, the EPA issued a SIP Requirements Rule (SRR) that addresses
implementation of various aspects of the 2008 ozone NAAQS (``2008 Ozone
SRR''), including attainment dates, requirements for emissions
inventories, attainment demonstrations, and reasonable further progress
(RFP) demonstrations, among other SIP elements. The 2008 Ozone SRR also
addresses the transition from the 1997 ozone NAAQS to the 2008 ozone
NAAQS and associated anti-backsliding requirements.\19\ In 2018, the
EPA also issued an SRR for the 2015 ozone NAAQS (``2015 Ozone SRR'')
that addresses implementation of the 2015 standards.\20\ The regulatory
requirements of the 2008 Ozone SRR are codified at 40 CFR part 51,
subpart AA; those for the 2015 Ozone SRR are codified in 40 CFR part
51, subpart CC. We discuss the CAA and regulatory planning requirements
for the elements of 2008 and 2015 ozone plans relevant to this proposed
action in more detail in Section III of this document.
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    \19\ 80 FR 12264 (March 6, 2015). Anti-backsliding requirements
are the provisions applicable to revoked NAAQS (including the 1979
1-hour ozone NAAQS and the 1997 ozone NAAQS).
    \20\ 83 FR 62998 (December 6, 2018).
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II. Submission From the State of California To Address Ozone
Requirements in San Diego County

A. Summary of State Submissions

1. SDCAPCD's 2020 Attainment Plan
    On January 12, 2021, CARB submitted the 2020 Plan to the EPA as a
revision to the California SIP.\21\ The 2020 Plan addresses many of the
nonattainment area requirements for the San Diego County area for both
the 2008 and the 2015 8-hour ozone NAAQS. In this document, we are
proposing action on the 2020 Plan that addresses both the 2008 and 2015
8-hour ozone NAAQS for the San Diego County area.
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    \21\ Letter (with enclosures) dated January 8, 2021, from
Richard Corey, Executive Officer, CARB, to John Busterud, Regional
Administrator, EPA Region IX (submitted electronically January 12,
2021).
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    The 2020 Plan SIP submittal includes the various sections and
attachments of the plan, plus the District's resolution of approval for
the plan (District Resolution 20-166) and CARB's resolution of adoption
of the plan as a revision to the California SIP (CARB Resolution 20-
29).\22\ The 2020 Plan includes a District commitment to achieve
additional emissions reductions beyond those expected to occur from
already-implemented control measures and relies on a similar commitment
by CARB. More specifically, the 2020 Plan includes a commitment by the
District to achieve an additional 1.7 tons per day (tpd) reduction in
NOX by 2032 \23\ and relies on CARB's commitment to achieve
aggregate emissions reductions in San Diego County of 4 tpd of
NOX by 2032.\24\ Both commitments are part of the 2020
Plan's attainment demonstration for the 2015 ozone NAAQS. With respect
to both the 2008 and the 2015 ozone NAAQS, the 2020 Plan addresses the
CAA requirements for emissions inventories, air quality modeling
demonstrating attainment, reasonably available control measures (RACM),
RFP, transportation control strategies and measures, new source review
(NSR), contingency measures for failure to make RFP or to timely attain
the relevant standards, and motor vehicle inspection and maintenance
(I/M) programs (also referred to as ``smog check'' programs), among
other requirements. The 2020 Plan also addresses the emissions
statement requirement, and in separate action, the EPA approved the
emissions statement portion of the 2020 Plan as meeting the applicable
requirements for emissions statements for the 2008 and 2015 ozone
NAAQS.\25\
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    \22\ SDCAPCD Board Resolution 20-166, October 14, 2020; CARB
Board Resolution 20-29, Proposed San Diego 8-Hour Ozone State
Implementation Plan Submittal, November 19, 2020 (``CARB Board
Resolution 20-29'').
    \23\ 2020 Plan, at 58, 81-82.
    \24\ CARB Board Resolution 20-29, at 6.
    \25\ 87 FR 45657 (July 29, 2022).
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    The 2020 Plan is organized into an executive summary, five
sections, and attachments lettered A through Q. Section 1,
``Introduction and Overview,'' introduces the 2020 Plan, including its
purpose, the two ozone NAAQS it addresses, current air quality in the
area in comparison with those NAAQS, historical air quality progress in
San Diego County, and the District's approach to air quality planning.
Section 2, ``General Attainment Plan Requirements,'' addresses CAA
requirements that apply to the area as nonattainment for both the 2008
and the 2015 ozone NAAQS. Section 3, ``2008 Eight Hour Ozone NAAQS
Attainment Plan Requirements,'' addresses CAA requirements that apply
to the area as nonattainment specifically for the 2008 ozone NAAQS,
including anti-backsliding requirements for the revoked 1979 and 1997
ozone standards. Section 4, ``2015 Eight Hour Ozone NAAQS Attainment
Plan Requirements,'' addresses CAA requirements that apply to the area
as nonattainment specifically for the 2015 ozone NAAQS, including anti-
backsliding requirements for revoked standards. Section 5,
``Conclusions,'' presents the District's conclusions regarding whether
the 2020 Plan meets applicable Clean Air Act requirements.
    The 2020 Plan also includes technical attachments:
     Attachment A (``Emissions Inventories and Documentation
for Baseline, RFP, and Attainment Years'') presents tables, analysis,
and documentation for the emissions inventories included in the plan.
     Attachment B (``Planned Military Projects Subject to
General Conformity'') contains annual data compiled by the United
States Marine Corps (USMC) and Department of the Navy (DoN) for
emissions changes resulting from USMC and DoN projects out to year
2037, for the purpose of demonstrating general conformity for USMC and
DoN facilities in the area.
     Attachment C (``Planned San Diego International Airport
Projects Subject to General Conformity'') is a report that provides an
emissions inventory for the San Diego International Airport, for the
purpose of demonstrating general conformity for the airport.
     Attachment D (``CARB Control Measures, 1985 to 2019'') is
a listing of CARB control measures from 1985 to 2019.
     Attachment E (``CARB Analyses of Key Mobile Source
Regulations and Programs Providing Emission Reductions'') describes
CARB's mobile source regulations and programs that provide emissions
reductions in the San Diego County area.
     Attachment F (``Pre-Baseline Banked Emission Reduction
Credits'') describes emission reduction credits that were banked before
the baseline year.
     Attachment G (``Analyses of Potential Additional
Stationary Source Control Measures'') provides the District's analysis
of the feasibility of additional stationary source control measures
that could be pursued in the area.
     Attachment H (``Implementation Status of Transportation
Control Measures'') provides the implementation status of
transportation control measures by the San Diego Association of
Governments (SANDAG) and other transportation agencies.
     Attachment I (``CARB Analyses of Potential Additional
Mobile Source and Consumer Products Control Measures'')

analyzes the potential for further mobile source and consumer products
controls in the area.
     Attachment J (``Calculation of Cumulative Potential
Emission Reductions for Possible Reasonably Available Control Measures
(RACM)'') calculates the cumulative potential emissions reductions in
the area in support of the plan's RACM demonstration.
     Attachment K (``Modeling Protocol & Attainment
Demonstration for the 2020 San Diego Ozone SIP'') provides the modeling
protocol and attainment demonstration for the San Diego County area as
Severe nonattainment for both the 2008 and the 2015 ozone NAAQS.
     Attachment L (``Modeling Emission Inventory for the Ozone
State Implementation Plan in San Diego County'') describes the modeled
or ``gridded'' emissions inventories for the area, in support of the
area's two modeled attainment demonstrations.
     Attachment M (``Weight of Evidence Demonstration for San
Diego County'') provides a weight-of-evidence demonstration for the
area, in support of the area's modeled attainment demonstrations.
     Attachment N (``VMT Offset Demonstration for San Diego
County'') provides the area's VMT offset demonstration.
     Attachment O (``Contingency Measures for San Diego
County'') represents the District's assessment of compliance with the
contingency measure requirements for the area.
     Attachment P (``Federal Clean Air Act Requirements and
References in Attainment Plan'') provides a summary of CAA requirements
that apply to the area with specific citations to locations in the plan
that address those requirements.
     Attachment Q (``Endnotes'') contains the text of all
endnotes found in the plan.
    Attainment of the 2008 and the 2015 ozone NAAQS in the San Diego
County area is dependent on emissions reductions occurring in the
adjacent South Coast nonattainment area. The 2016 South Coast Ozone SIP
documents baseline emissions reductions from already-adopted control
measures and provides for new emissions reductions to be achieved
through fulfillment of SCAQMD and CARB commitments for further
reductions, and through new technology measures.\26\ More specifically,
as discussed in Section III.D, ``Attainment Demonstration,'' of the
EPA's proposed approval of the 2016 South Coast Ozone SIP,\27\ the
ozone attainment demonstrations for South Coast for the 1997 and 2008
ozone NAAQS include emissions reduction commitments made by the SCAQMD
in the 2016 AQMP and by CARB in the ``Revised Proposed 2016 State
Strategy for the State Implementation Plan'' (``2016 State Strategy'').
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    \26\ 84 FR 28132 (June 17, 2019), at 28134-28134, tables 10 and
11. The EPA finalized its approval of the 2016 South Coast Ozone SIP
at 84 FR 52005 (October 1, 2019).
    \27\ 84 FR 28132, 28143-28157 (June 17, 2019),
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    The 2016 State Strategy focuses on two areas: the South Coast and
the San Joaquin Valley. Although it did not include specific emissions
reduction commitments for San Diego County, CARB states that,
``[s]hould additional areas require emission reductions to meet the
current ozone and PM2.5 standards, ARB will quantify area
and year specific reductions as part of individual attainment plans.''
\28\ The 2020 Plan for the 2015 ozone NAAQS relies on CARB's commitment
to achieve 4 tpd of NOX emissions reductions in 2032 from
mobile sources to demonstrate attainment of this standard in San Diego
County.\29\
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    \28\ 2016 State Strategy, 35.
    \29\ CARB Review of the 2020 Plan for Attaining the National
Ambient Air Quality Standards for Ozone in San Diego County, Release
Date: October 16, 2020, at 11; CARB Board Resolution 20-29, at 6.
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2. Smog Check Certification
    On April 26, 2023, CARB submitted the ``California Smog Check
Performance Standard Modeling and Program Certification for the 70
Parts Per Billion (ppb) 8-Hour Ozone Standard'' (``Smog Check
Certification'') to supplement the motor vehicle I/M portion of the
2020 Plan.\30\ The Smog Check Certification includes CARB's evaluation
of the California Smog Check program for compliance with the applicable
I/M performance standard as defined in EPA's regulations for certain
nonattainment areas for the 2008 and 2015 ozone NAAQS, including San
Diego County.
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    \30\ Letter (with enclosures) dated April 26, 2023, from Steven
S. Cliff, Ph.D., Executive Officer, CARB, to Martha Guzman, Regional
Administrator, EPA Region IX (submitted electronically April 26,
2023).
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    CARB's SIP submittal package for the Smog Check Certification
includes CARB Resolution 23-9, through which CARB adopted the Smog
Check Certification as part of the California SIP,\31\ public notice of
CARB's hearing on the proposed SIP revision, public comments and
responses, and MOVES \32\ input and output data sheets. In this
document, we are proposing action on the San Diego County portion of
the Smog Check Certification as a supplement to the vehicle I/M portion
of the 2020 Plan.
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    \31\ CARB Board Resolution 23-9, March 23, 2023.
    \32\ MOVES is the acronym for the EPA's Motor Vehicle Emission
Simulator model.
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B. Clean Air Act Procedural Requirements for Adoption and Submission of
SIP Revisions

    CAA sections 110(a) and 110(l) require a state to provide
reasonable public notice and opportunity for public hearing prior to
the adoption and submission of a SIP or SIP revision. To meet this
requirement, every SIP submittal should include evidence that adequate
public notice was given and an opportunity to submit written comments
and request a public hearing was provided consistent with the EPA's
implementing regulations in 40 CFR 51.102.
    Both the District and CARB have satisfied the applicable statutory
and regulatory requirements for reasonable public notice and hearing
prior to the adoption and submittal of the 2020 Plan. The District held
two public webinars, one in July and another in August, 2020, and held
a hearing on October 14, 2020, to discuss the plan and solicit public
input.\33\ On September 14, 2020, the District published a notice in a
local newspaper of the public hearing to be held on October 14, 2020,
to consider approval of the 2020 Plan.\34\ On October 14, 2020, the
District held the public hearing, and on that same date, through
Resolution 20-166, the District board approved the 2020 Plan and
directed the Air Pollution Control Officer to forward its resolution
and the 2020 Plan to CARB for submittal to the EPA for inclusion in the
California SIP.
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    \33\ Letter dated October 20, 2020,from Robert Reider, Interim
Director, SDCAPCD, to Richard Corey, CARB Executive Officer. See the
letter's response to comments document regarding the two webinars
and its ``Minute Order'' document regarding the public hearing.
    \34\ Id. See the October 20, 2020 letter's proof of publication
document regarding public notice for the October 14, 2020 public
hearing.
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    Upon receipt of the 2020 Plan from the District, CARB also provided
public notice and opportunity for public comment on the plan. On
October 16, 2020, CARB released for public review its staff report for
the 2020 Plan (``CARB Staff Report'') \35\ and published a notice of
public meeting to be held on November 19, 2020, to consider

adoption of the 2020 Plan as a revision to the California SIP.\36\ On
November 19, 2020, CARB held the hearing and adopted the 2020 Plan as a
revision to the California SIP and directed the Executive Officer to
submit the 2020 Plan to the EPA for approval into the California
SIP.\37\ On January 12, 2021, the Executive Officer of CARB submitted
the 2020 Plan to the EPA. Six months after submittal, on July 12, 2021,
the 2020 Plan became complete by operation of law.\38\
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    \35\ CARB Review of the 2020 Plan for Attaining the National
Ambient Air Quality Standards for Ozone in San Diego County, Release
Date: October 16, 2020.
    \36\ Notice of Public Meeting to Consider Approval of the
Proposed San Diego 8-Hour Ozone State Implementation Plan Submittal,
signed by Richard Corey, Executive Officer, CARB, October 16, 2020.
    \37\ CARB Resolution 20-29, 6.
    \38\ CAA section 110(k)(1)(B).
---------------------------------------------------------------------------

    CARB has also satisfied the applicable statutory and regulatory
requirements for reasonable public notice and hearing prior to the
adoption and submittal of the Smog Check Certification. On February 10,
2023, CARB released for public review the draft Smog Check
Certification and published a notice of public meeting to be held on
March 23, 2023, to consider adoption of the Smog Check Certification as
a revision to the California SIP.\39\ On March 23, 2023, CARB held the
hearing and adopted the Smog Check Certification as a revision to the
California SIP and directed the Executive Officer to submit the Smog
Check Certification to the EPA for approval into the California
SIP.\40\ On April 26, 2023, the Executive Officer of CARB submitted the
Smog Check Certification to the EPA.
---------------------------------------------------------------------------

    \39\ Notice of Public Meeting to Consider the Proposed
California Smog Check Performance Standard Modeling and Program
Certification for the 70 parts per billion 8-hour Ozone Standard,
signed by Steven S. Cliff, Ph.D., Executive Officer, CARB, February
10, 2023.
    \40\ CARB Resolution 23-9, 6.
---------------------------------------------------------------------------

    Based on information provided in the SIP revisions submitted on
January 12, 2021 and April 26, 2023, and summarized in Section II.A
this document, the EPA has determined that all hearings were properly
noticed and that a reasonable opportunity to submit written comments
was provided. Therefore, we find that the submittal of the 2020 Plan
and the Smog Check Certification meets the procedural requirements for
public notice and hearing in CAA sections 110(a) and 110(l) and 40 CFR
51.102.

III. Evaluation of the 2020 San Diego County Ozone SIP

A. Emissions Inventories

1. Statutory and Regulatory Requirements
    CAA sections 172(c)(3) and 182(a)(1) require states to submit for
each ozone nonattainment area a ``base year inventory'' that is a
comprehensive, accurate, current inventory of actual emissions from all
sources of the relevant pollutant or pollutants in the area. In
addition, the 2008 Ozone SRR and the 2015 Ozone SRR require that the
inventory year be selected consistent with the baseline year for the
RFP demonstration, which is the most recent calendar year for which a
complete triennial inventory is required to be submitted to the EPA
under the Air Emissions Reporting Requirements (AERR) at the time of
designation for the ozone NAAQS.\41\ For the 2008 ozone NAAQS, the
baseline year for the RFP demonstration is 2011, and for the 2015 ozone
NAAQS, the base year for the RFP demonstration is 2017.
---------------------------------------------------------------------------

    \41\ 2008 Ozone SRR at 40 CFR 51.1115(a) and 40 CFR 51.1110(b),
2015 Ozone SRR at 40 CFR 51.1315(a) and 40 CFR 51.1310(b), and the
Air Emissions Reporting Requirements at 40 CFR part 51, subpart A.
---------------------------------------------------------------------------

    The EPA has issued guidance on the development of base year and
future year emissions inventories for 8-hour ozone and other
pollutants.\42\ Emissions inventories for ozone must include emissions
of VOC and NOX and represent emissions for a typical ozone
season weekday.\43\ States should include documentation explaining how
the emissions data were calculated. In estimating mobile source
emissions, states should use the latest emissions models and planning
assumptions available at the time the SIP is developed.\44\
---------------------------------------------------------------------------

    \42\ ``Emissions Inventory Guidance for Implementation of Ozone
and Particulate Matter National Ambient Air Quality Standards
(NAAQS) and Regional Haze Regulations,'' EPA-454/B-17-002, May 2017,
available in the docket for this action and at https://www.epa.gov/air-emissions-inventories/air-emissions-inventory-guidance-implementation-ozone-and-particulate.
    \43\ For 2008 ozone, 40 CFR 51.1115(a) and (c), and 40 CFR
51.1100(bb) and (cc). For 2015 ozone, 40 CFR 51.1315(a) and (c), and
40 CFR 51.1300(p) and (q).
    \44\ 80 FR 12264, 12290 (March 6, 2015); 83 FR 62998, 63022
(December 6, 2018).
---------------------------------------------------------------------------

    Future baseline emissions inventories must reflect the most recent
population, employment, travel, and congestion estimates for the area.
In this context, ``baseline'' emissions inventories refer to emissions
estimates for a given year and area that reflect rules and regulations
and other measures that are already adopted. Future baseline emissions
inventories are necessary to show the projected effectiveness of SIP
control measures. Both the base year and future year inventories are
necessary for photochemical modeling to demonstrate attainment.
2. Summary of State's Submission
    The 2020 Plan includes three sets of base year and future year
average summer day baseline inventories for NOX and VOC for
the San Diego County area, for both the 2008 and 2015 ozone NAAQS.\45\
One set of base year and future year baseline emissions inventories
reflects emissions within the San Diego County area and includes marine
emissions out to 100 nautical miles (NM) from the coast. A second set
of emissions inventories adds emissions from the South Coast Air Basin
to those generated within the San Diego County area (plus marine
emissions out to 100 NM from the coast) to produce combined
inventories. A third set of emissions inventories reflects San Diego
County area emissions including marine emissions but only out to three
NM from the coast. All three sets of inventories include the years
2011, 2017, 2020, 2023, 2026, 2029 and 2032.
---------------------------------------------------------------------------

    \45\ 2020 Plan, Attachment A.
---------------------------------------------------------------------------

    Documentation for the inventories is found in Sections 3 and 4 of
the 2020 Plan, addressing the 2008 and 2015 ozone NAAQS, respectively,
as well as in the Plan's Attachment A. Because ozone levels in the area
are typically highest during the summer months, the inventories
provided in the 2020 Plan represent average summer day emissions from
May through October. The inventories in the 2020 Plan reflect District
rules adopted through the end of calendar year 2019 and CARB rules
adopted through the end of calendar year 2017. For estimating on-road
motor vehicle emissions, these inventories use EMFAC2017, the EPA-
approved version of California's mobile source emissions model
available at the time the 2020 Plan was developed.\46\
---------------------------------------------------------------------------

    \46\ EMFAC is short for EMission FACtor. The EPA announced the
availability of the EMFAC2017 model for use in state implementation
plan development and transportation conformity in California on
August 15, 2019. 84 FR 41717. The EPA's approval of the EMFAC2017
emissions model for SIP and conformity purposes was effective on the
date of publication of the notice in the Federal Register.
---------------------------------------------------------------------------

    The VOC and NOX emissions estimates are grouped into two
general categories, stationary sources and mobile sources. Stationary
sources are further divided into ``point'' and ``area'' sources. Point
sources typically refer to stationary sources that are permitted
facilities and have one or more identified and fixed pieces of
equipment and emissions points. Area sources consist of widespread and
numerous smaller emissions sources, such as consumer products,
fireplaces and agricultural burning.\47\ The mobile

sources category is divided into two major subcategories, ``on-road''
and ``off-road'' mobile sources. On-road mobile sources include light-
duty automobiles, light-, medium-, and heavy-duty trucks, and
motorcycles. Off-road mobile sources include aircraft, locomotives,
construction equipment, mobile equipment, and recreational vehicles.
---------------------------------------------------------------------------

    \47\ 2020 Plan, p. A-30.
---------------------------------------------------------------------------

    Point source (also referred to as ``stationary source'') emissions
for the 2011 and 2017 base year emissions inventories are calculated
using reported data from facilities using the District's annual
emissions reporting program, which applies under District Rule 19.3 to
stationary sources in the San Diego County area that emit 25 tons per
year (tpy) or more of VOC or NOX. Area sources include
smaller emissions sources distributed across the nonattainment area.
CARB and the District estimate emissions for numerous area source
categories using established inventory methods, including publicly
available emissions factors and activity information. Specific
estimates are included in the 2020 Plan for area source categories:
consumer products, architectural coatings and related process solvent
use, pesticides and fertilizers, asphalt paving and roofing,
residential fuel combustion, farming operations, fires, managed burning
and disposal, and cooking.
    On-road emissions inventories in the 2020 Plan are calculated using
CARB's EMFAC2017 model and the travel activity data provided by SANDAG
in SANDAG's 2018 adopted Regional Transportation Improvement
Program.\48\ CARB provided emissions inventories for off-road
equipment, including construction and mining equipment, industrial and
commercial equipment, lawn and garden equipment, agricultural
equipment, ocean-going vessels, commercial harbor craft, locomotives,
cargo handling equipment, pleasure craft, and recreational vehicles.
CARB used several models to estimate emissions for off-road equipment
categories.\49\ Aircraft emissions inventories are developed in
conjunction with the airports in the region. In particular, an
emissions analysis was included in the 2020 Plan for the San Diego
International Airport.\50\
---------------------------------------------------------------------------

    \48\ Id. at A-35. SANDAG is the metropolitan planning
organization (MPO) for San Diego County.
    \49\ Id. at A-36.
    \50\ Id., Attachment C, ``Planned San Diego International
Airport Projects Subject to General Conformity.''
---------------------------------------------------------------------------

    The 2020 Plan distinguishes between emissions sources within San
Diego County, which includes coastal emissions (including marine vessel
emissions) within three NM of the coastline, and emissions sources
operating outside the county but within 100 NM of the coastline. The
base year emissions inventory reflects only those emissions sources
that operate within the nonattainment area (i.e., within three NM of
the coastline), but offshore emissions sources affect ozone
concentrations in the nonattainment area and thus are included in the
emissions inventories used for the attainment demonstrations in the
2020 Plan.
    The calendar year 2017 is the base year in the 2020 Plan for both
the 2008 and 2015 ozone NAAQS because 2017 the most recent calendar
year for which a complete triennial inventory was required to be
submitted to the EPA under the provisions of 40 CFR part 51, subpart A
at the time of plan development. The 2020 Plan includes an emissions
inventory for an earlier year, i.e., calendar year 2011, because that
year is the RFP baseline year for the 2008 ozone NAAQS. The 2017 base
year inventory was used to forecast all future years for area and
mobile sources and to ``backcast'' such sources for 2011.\51\
---------------------------------------------------------------------------

    \51\ Id. at Q-2, footnote 29.
---------------------------------------------------------------------------

    To develop the 2011 inventory, CARB relied on actual emissions
reported from industrial point sources for 2011 and backcast emissions
from 2017 for smaller stationary and certain area sources.\52\ Area
source emissions from pesticide were developed by CARB based on actual
emissions reported for 2011, while those from agricultural burning were
developed by CARB based on actual emissions reported for 2008 that were
``grown'' (that is, projected forward from 2008, based on estimated
changes in agricultural burning) to 2011. CARB produced 2011 on-road
emissions estimates using EMFAC2017. Non-road emissions were either
backcast from 2017 (commercial aircraft and military ocean-going
vessels) or were estimated using CARB's OFFROAD2007 model.\53\
---------------------------------------------------------------------------

    \52\ Id.
    \53\ Email dated March 21, 2023, from Nick Cormier, SDCAPCD to
John J. Kelly, EPA, Subject: ``FW: 2011 emission inventory in SD's
2020 ozone plan.''
---------------------------------------------------------------------------

    For the 2020 Plan, CARB used the California Emission Projection
Analysis Model (CEPAM), 2019 SIP Baseline Emission Projections, Version
1.00 to develop future year emissions forecasts (i.e., 2020, 2023,
2026, 2029 and 2032).\54\ In doing so, CARB reviewed the growth and
control factors for each category and relevant year along with the
resulting emissions projections.\55\ CARB compared year-to-year trends
to similar and past datasets to ensure general consistency, checked
emissions for specific categories to confirm they reflect the
anticipated effects of applicable control measures, and verified mobile
source categories with CARB mobile source staff for consistency with
the on-road and off-road emission models.\56\
---------------------------------------------------------------------------

    \54\ 2020 Plan, Attachment A, Section A.8.
    \55\ Id.
    \56\ Id.
---------------------------------------------------------------------------

    In developing the 2020 Plan, the District worked with the
Department of the Navy and the United States Marine Corps to identify
specific growth increments from future anticipated actions to include
in the baseline emissions forecasts for use by the military to comply
with the applicable general conformity regulations. The District then
coordinated with CARB to include the growth increments or ``budgets''
in the applicable source categories in the CEPAM model used by CARB to
develop the future year emissions inventories. More specifically, the
CEPAM model runs used for the future year emissions estimates in the
2020 Plan reflect a military growth increment of 1.08 tpd of VOC and
8.34 tpd of NOX for all future years addressed in the
plan.\57\ Similarly, the District worked with the San Diego County
Regional Airport Authority to identify a growth increment for future
anticipated actions at San Diego International Airport (SDIA) for use
in connection with the general conformity regulations. The growth
increment for SDIA for all future year emissions estimates in the 2020
Plan is 0.141 tpd of VOC and 1.756 tpd for NOX.\58\ Section
III.H of this document provides further information on the military and
SDIA growth increments reflected in the 2020 Plan.
---------------------------------------------------------------------------

    \57\ 2020 Plan, Section <IP_ADDRESS> and Attachment B.
    \58\ Id., Section <IP_ADDRESS> and Attachment C.
---------------------------------------------------------------------------

    The future year emissions estimates in the 2020 Plan include two
additional specific adjustments--one to account for pre-base year
emissions reduction credits (ERCs) and one to account for the EPA's
rescission, in a final action referred to as ``SAFE 1,'' of a waiver of
preemption of CARB's light-duty vehicle zero emission vehicle (ZEV)
sales mandate and greenhouse gas (GHG) standards.\59\
---------------------------------------------------------------------------

    \59\ ``The Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule
Part One: One National Program'' (SAFE 1), 84 FR 51310 (September
27, 2019).
---------------------------------------------------------------------------

    Under the EPA's SIP regulations for nonattainment new source review
(NSR) programs, a state may allow new major stationary sources or major
modifications to use as offsets ERCs that were generated through
shutdown or

curtailed emissions units occuring before the base year of an
attainment plan. However, to use such ERCs, the projected emissions
inventories used to develop the RFP and attainment demonstration must
explicitly include the emissions from such previously shutdown or
curtailed emissions units.\60\ The District has elected to provide for
use of pre-base year ERCs as offsets by explicitly including such ERCs
in the future year emissions estimates in the 2020 Plan. The ERC set-
aside in the 2020 Plan amounts to 0.71 tpd of VOC and 0.56 tpd of
NOX.\61\
---------------------------------------------------------------------------

    \60\ 40 CFR part 51, Appendix S, section IV.C.5.
    \61\ 2020 Plan, section <IP_ADDRESS> and Attachment F.
---------------------------------------------------------------------------

    The ``EMFAC2017 Adjustment Factors'' refers to adjustment factors
that CARB developed for EMFAC2017 to account for the EPA's SAFE 1 final
action that, among other things, withdrew the EPA's waiver of
preemption for CARB's Advanced Clean Car (ACC) regulation as it
pertained to CARB's ZEV sales mandate and GHG standards.\62\ EMFAC2017
reflected emissions reductions that were estimated to be achieved
through implementation of the ACC regulation, including the ZEV sales
mandate. In response to the EPA's SAFE 1 action, CARB developed
correction factors to be used to account for the foregone emissions
reductions (EMFAC2017 Adjustment Factors).\63\ In 2020, the EPA
concurred on the use of CARB's EMFAC2017 Adjustment Factors for the
purposes of SIP development in California,\64\ and the 2020 Plan takes
them into account as an adjustment to the EMFAC2017-derived motor
vehicle emissions estimates included in the future year emissions
inventories. For the 2020 Plan, the EMFAC2017 Adjustment Factor is
generally 0.1 tpd or less for VOC and NOX in all future
years expected to be affected by the SAFE 1 action.
---------------------------------------------------------------------------

    \62\ The EPA issued the ACC waiver on January 9, 2013 (78 FR
2112).
    \63\ Letter and enclosures dated March 5, 2020 from Steven S.
Cliff, Ph.D., Deputy Executive Officer, CARB, to Elizabeth Adams,
Director, Air and Radiation Division, EPA Region IX.
    \64\ Letter dated March 12, 2020, from Elizabeth J. Adams,
Director, Air and Radiation Division, EPA Region IX, to Steven S.
Cliff, Ph.D., Deputy Executive Officer, CARB.
---------------------------------------------------------------------------

    Table 1 of this document provides a summary of the baseline
emissions inventories for the base year and future years in tpd
(average summer day) for VOC and NOX for the 2008 ozone
NAAQS.\65\ The inventories summarized in Table 1 distinguish between
emissions generated within the nonattainment area and emissions that
are generated offshore between three NM and 100 NM from the coastline
of San Diego County. Table 1 also shows the adjustments made to account
for ERCs and the EMFAC2017 Adjustment Factors. Table 2 of this document
provides the same type of summary information as Table 1, but presents
the base year and future years that are relevant for the 2015 ozone
NAAQS.
---------------------------------------------------------------------------

    \65\ Tables 1 and 2 summarize anthropogenic emissions sources
only, which is consistent with the EPA's ``Emissions Inventory
Guidance for Implementation of Ozone and Particulate Matter National
Ambient Air Quality Standards (NAAQS) and Regional Haze
Regulations'' (May 2017). Anthropogenic emissions sources are
distinguishable from natural sources, which include biogenic,
geogenic and wildfire emissions sources. Both anthropogenic and
natural sources of emissions are, however, included in emissions
inventories used for attainment demonstration modeling purposes.
---------------------------------------------------------------------------

    Based on the emissions inventory for 2017, stationary, area, and
mobile sources (on-road and off-road) contribute roughly equally to
county-wide VOC emissions, whereas mobile sources (on-road and off-
road) are the predominant sources of NOX emissions. The
inventory for 2017 also shows the magnitude of marine offshore (3 NM to
100 NM) emissions sources relative to those within the nonattainment
area. A comparison of the base years with the future years shows the
significant decrease that is expected to be achieved through CARB's
regulations for new on-road and off-road mobile sources together with
vehicle turnover (i.e., the rate of replacement of older, more
polluting models with new models manufactured to meet tighter emissions
standards). For a more detailed discussion of the methodologies used to
develop the inventories, see Attachment A of the 2020 Plan.

                       Table 1--San Diego County Base Year and Future Year Baseline Emissions Inventories for the 2008 Ozone NAAQS
                                                            [Summer planning inventory, tpd]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                    2011                  2017                  2020                  2023                  2026
                                           -------------------------------------------------------------------------------------------------------------
                                               NOX        VOC        NOX        VOC        NOX        VOC        NOX        VOC        NOX        VOC
--------------------------------------------------------------------------------------------------------------------------------------------------------
Stationary Sources........................        4.4       27.4        4.1       27.6        4.0       26.9        3.9       26.3        4.0       26.3
Area Sources..............................        1.9       36.8        1.7       33.6        1.5       34.3        1.4       34.8        1.2       35.2
On-Road Mobile Sources....................       71.2       34.4       37.7       20.5       28.5       16.5       19.7       13.8       17.5       12.3
Off-Road Mobile Sources...................       33.2       38.0       33.5       31.1       32.6       28.5       31.2       26.7       30.3       25.2
Emission Reduction Credits adjustment.....  .........  .........  .........  .........        0.6        0.7        0.6        0.7        0.6        0.7
EMFAC2017 Adjustment Factor...............  .........  .........  .........  .........  .........  .........       <0.1        0.1       <0.1       <0.1
                                           -------------------------------------------------------------------------------------------------------------
    Total--San Diego County Nonattainment       110.7      136.6       77.0      112.9       67.1      107.0       56.8      102.4       53.6       99.7
     Area.................................
--------------------------------------------------------------------------------------------------------------------------------------------------------
Marine Emissions (3 NM-100 NM)............       15.8        0.8       17.5        1.0       17.5        1.0       18.1        1.0       18.6        1.1
                                           -------------------------------------------------------------------------------------------------------------

    Total--Nonattainment Area plus Marine       126.5      137.5       94.5      113.8       84.7      108.0       74.8      103.4       72.2      100.8
     Emissions (3 NM-100 NM)..............
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: 2020 Plan, Attachment A, Tables A-1 and A-3. The sum of the emissions values may not equal the total due to rounding of the numbers.

                       Table 2--San Diego County Base Year and Future Year Baseline Emissions Inventories for the 2015 Ozone NAAQS
                                                           [summer planning inventory, (tpd)]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                    2017                  2023                  2026                  2029                  2032
                                           -------------------------------------------------------------------------------------------------------------
                                               NOX        VOC        NOX        VOC        NOX        VOC        NOX        VOC        NOX        VOC
--------------------------------------------------------------------------------------------------------------------------------------------------------
Stationary Sources........................        4.1       27.6        3.9       26.3        4.0       26.3        4.0       26.6        4.1       27.2
Area Sources..............................        1.7       33.6        1.4       34.8        1.2       35.2        1.0       35.6        1.0       36.1
On-Road Mobile Sources....................       37.7       20.5       19.7       13.8       17.5       12.3       16.0       11.1       15.1       10.0
Off-Road Mobile Sources...................       33.5       31.1       31.2       26.7       30.3       25.2       29.7       24.2       28.9       23.2
Emission Reduction Credits adjustment.....  .........  .........        0.6        0.7        0.6        0.7        0.6        0.7        0.6        0.7
EMFAC2017 Adjustment Factor...............  .........  .........       <0.1        0.1       <0.1       <0.1       <0.1       <0.1       <0.1        0.1
                                           -------------------------------------------------------------------------------------------------------------
    Total--San Diego County Nonattainment        77.0      112.9       56.8      102.4       53.6       99.7       51.3       98.2       49.7       97.2
     Area.................................
--------------------------------------------------------------------------------------------------------------------------------------------------------
Marine Emissions (3 NM-100 NM)............       17.5        1.0       18.1        1.0       18.6        1.1       19.0        1.0       19.3        1.1
                                           -------------------------------------------------------------------------------------------------------------
    Total--Nonattainment Area plus Marine        94.5      113.8       74.8      103.4       72.2      100.8       70.0       99.3       69.0       98.3
     Emissions (3 NM-100 NM)..............
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: 2020 Plan, Attachment A, Tables A-1 and A-3. The sum of the emissions values may not equal the total due to rounding of the numbers.

3. The EPA's Review of the State's Submission
    The 2020 Plan refers to year 2017 as the base year inventory for
both the 2008 and 2015 ozone NAAQS but also includes an inventory of
actual emissions in calendar year 2011, which we have reviewed for the
purpose of evaluating compliance with the base year emissions inventory
SIP requirement for the 2008 ozone NAAQS. Year 2017 is the appropriate
base year for the emissions inventory SIP requirement for the 2015
ozone NAAQS.
    We have reviewed the 2011 and 2017 base year emissions inventories
in the 2020 Plan and the inventory methodologies used by the District
and CARB for consistency with CAA requirements and EPA guidance. First,
we find that the 2011 and 2017 inventories include estimates for VOC
and NOX for a typical ozone season weekday, and that CARB
has provided adequate documentation explaining how the emissions are
calculated. Second, we find that the 2011 and 2017 base year emissions
inventories in the 2020 Plan reflect appropriate emissions models and
methodologies, and, therefore, represent comprehensive, accurate, and
current inventories of actual emissions during those years in the San
Diego County area. Therefore, the EPA is proposing to approve the 2011
and 2017 emissions inventories in the 2020 Plan as meeting the
requirements for base year inventories for 2008 and 2015 ozone set
forth in CAA sections 172(c)(3) and 182(a)(1), and 40 CFR 51.1115 and
40 CFR 51.1315. In addition, although the requirement for a base year
emissions inventory applies to the nonattainment area, we find that the
District's estimates of marine emissions out to 100 NM (i.e., beyond
the nonattainment area boundary that extends three NM offshore) are
reasonable and appropriate to include in the 2020 Plan given that such
emissions must be accounted for in

the ozone attainment demonstrations for this nonattainment area.
    With respect to the future year emissions baseline projections, we
have reviewed the growth and control factors and find them acceptable
and conclude that the future baseline emissions projections in the 2020
Plan reflect appropriate calculation methods and the latest planning
assumptions. We have also reviewed the documentation concerning the
growth increments for the military and for SDIA and the documentation
for the ERCs and find that they are appropriately accounted for in the
future year baseline emissions inventories or, in the case of the ERCs,
as an off-model adjustment to the inventories.\66\ With respect to the
EMFAC2017 Adjustment Factors, we note that, since adoption of the 2020
Plan, the EPA has rescinded SAFE 1 (the withdrawal of the waiver of
CARB's ZEV sales mandate and GHG standards),\67\ which calls into
question the use of the EMFAC2017 Adjustment Factor, as it may affect
projections, particularly over the long term. However, as shown in
Tables 1 and 2, the EMFAC2017 Adjustment Factor adjustment in the
future year emissions inventories is insignificant (0.1 tpd or less for
both VOC and NOX), and thus the change in circumstances
regarding the status of CARB's ZEV sales mandate does not affect the
emissions projections used for the RFP and attainment demonstrations in
the 2020 Plan.
---------------------------------------------------------------------------

    \66\ See Section III.H of this document for our full evaluation,
and proposed approval, of the growth increments for the military and
SDIA.
    \67\ 87 FR 14332 (March 14, 2022).
---------------------------------------------------------------------------

    Also, as a general matter, the EPA will approve a SIP revision that
takes emissions reduction credit for a control measure only where the
EPA has approved the measure as part of the SIP. Thus, to take credit
for the emissions reductions from District rules for stationary sources
and CARB rules for mobile sources, the related rules must be approved
by the EPA into the SIP.\68\ The EPA performed a review of District
rules relied upon in developing the future baseline emissions
inventories for the 2020 Plan.\69\ Based on our review, we find that,
with only one exception that does not implicate the RFP or attainment
demonstrations of the 2020 Plan,\70\ District rules relied upon in
developing the future baseline emissions inventories are approved as
part of the SIP. With respect to mobile sources, the EPA has taken
action in recent years to approve CARB mobile source regulations into
the California SIP.\71\ We therefore find that the future year baseline
projections in the 2020 Plan are properly supported by SIP-approved
stationary and mobile source measures.
---------------------------------------------------------------------------

    \68\ See generally Committee for a Better Arvin v. EPA, 786 F.3d
1169, 1175-1177 (9th Cir. 2015).
    \69\ The EPA's review of District rules relied upon in
developing the future baseline emissions inventories is presented in
Memorandum to Docket EPA-R09-OAR-2021-0135 from Jeff Wehling, Office
of Regional Counsel, EPA Region IX, August 25, 2023.
    \70\ District Rule 61.4.1 should be submitted for approval as
part of the SIP; however, the related emissions reductions are not
of a magnitude as to implicate the RFP or attainment demonstrations.
    \71\ See 81 FR 39424 (June 16, 2016), 82 FR 14446 (March 21,
2017), and 83 FR 23232 (May 18, 2018).
---------------------------------------------------------------------------

B. Reasonably Available Control Measures Demonstration and Control
Strategy

1. Statutory and Regulatory Requirements
    CAA section 172(c)(1) requires that each attainment plan provide
for the implementation of all RACM as expeditiously as practicable
(including such reductions in emissions from existing sources in the
area as may be obtained through implementation of reasonably available
control technology (RACT)), and to provide for attainment of the NAAQS.
The 2008 Ozone SRR and the 2015 Ozone SRR require that, for each
nonattainment area required to submit an attainment demonstration, the
state concurrently submit a SIP revision demonstrating that it has
adopted all RACM necessary to demonstrate attainment as expeditiously
as practicable and to meet any RFP requirements.\72\
---------------------------------------------------------------------------

    \72\ 40 CFR 51.1112(c); 40 CFR 51.1312(c). The ``San Diego
County area'' is shorthand for two nonattainment areas, one for each
of two ozone NAAQS: the 2008 and the 2015 ozone NAAQS. The boundary
is the same for both areas. Accordingly, the District submitted two
attainment demonstrations in the 2020 Plan, one for each of the two
standards.
---------------------------------------------------------------------------

    The EPA has previously provided guidance interpreting the RACM
requirement, in the General Preamble for the Implementation of the
Clean Air Act Amendments of 1990 (``General Preamble'') and in a
memorandum entitled ``Guidance on the Reasonably Available Control
Measure Requirement and Attainment Demonstration Submissions for Ozone
Nonattainment Areas.'' \73\ In short, to address the requirement to
adopt all RACM, states should consider all potentially reasonable
measures for source categories in the nonattainment area to determine
whether they are reasonably available for implementation in that area
and whether they would, if implemented individually or collectively,
advance the area's attainment date by one year or more.\74\ Any
measures that are necessary to meet these requirements that are not
already either federally promulgated, or part of the state's SIP, must
be submitted in enforceable form as part of the state's attainment plan
for the area.
---------------------------------------------------------------------------

    \73\ See General Preamble, 57 FR 13498, 13560 (April 16, 1992)
and memorandum dated November 30, 1999, from John S. Seitz,
Director, OAQPS, to Regional Air Directors, Subject: ``Guidance on
the Reasonably Available Control Measure Requirement and Attainment
Demonstration Submissions for Ozone Nonattainment Areas.''
    \74\ Id. See also 44 FR 20372 (April 4, 1979), and memorandum
dated December 14, 2000, from John S. Seitz, Director, OAQPS, to
Regional Air Directors, Subject: ``Additional Submission on RACM
From States with Severe One-Hour Ozone Nonattainment Area SIPs.''
---------------------------------------------------------------------------

    For ozone nonattainment areas classified as Moderate or above, CAA
section 182(b)(2) also requires implementation of RACT for all major
sources of VOC and for each VOC source category for which the EPA has
issued a control techniques guideline. CAA section 182(f) requires that
RACT under section 182(b)(2) also apply to major stationary sources of
NOX. In Severe areas, a major source is a stationary source
that emits or has the potential to emit at least 25 tpy of VOC or
NOX (CAA sections 182(d) and (f)). Under the 2008 Ozone SRR
and the 2015 Ozone SRR, states were required to submit SIP revisions
meeting the RACT requirements of CAA sections 182(b)(2) and 182(f) no
later than 24 months after the effective date of designation for the
2008 ozone NAAQS and the 2015 ozone NAAQS, respectively. Implementation
of the required RACT measures is required as expeditiously as
practicable but no later than January 1 of the 5th year after the
effective date of designation for the 2008 ozone NAAQS (see 40 CFR
51.1112(a)) and for the 2015 ozone NAAQS (see 40 CFR 51.1312(a)).\75\
---------------------------------------------------------------------------

    \75\ California submitted the CAA section 182 RACT SIP for the
San Diego County area for both the 2008 and 2015 ozone NAAQS, as a
Severe nonattainment area with a 25 tpy major source threshold, on
December 29, 2020. To date, the EPA has taken several actions on the
San Diego County RACT SIP. We are not taking action on the RACT SIP
in this rulemaking but will be completing action on it in a separate
rulemaking(s).
---------------------------------------------------------------------------

2. Summary of the State's Submission
    The 2020 Plan presents two RACM demonstrations. The first is
included in Section 3.2.1 and addresses the 2008 ozone NAAQS. The
second is presented in Section 4.2.1 for the 2015 ozone NAAQS. Within
each Section, the 2020 Plan presents a RACM analysis organized by
several emissions source groups. The District and CARB each undertook a
process to identify and evaluate potential RACM that could contribute
to expeditious attainment of the 2008 ozone NAAQS and the 2015

ozone NAAQS in the San Diego County area. In addition, the District
presented a ``RACM Cumulative Analysis'' for each standard as an
overarching analysis of all source categories covered by CARB, the
District and SANDAG.\76\
---------------------------------------------------------------------------

    \76\ 2020 Plan, Sections 3.2.1 and 4.2.1.
---------------------------------------------------------------------------

    The 2020 Plan's RACM section for the 2008 ozone NAAQS begins by
determining the magnitude of emissions reductions that would be needed
to advance the area's attainment date by one year. As noted in Section
I.B of this document, air pollutants transported from the South Coast
region contribute to higher ozone levels in San Diego County under
certain weather conditions. Accordingly, the RACM analysis in the 2020
Plan for the 2008 ozone NAAQS accounts for projected emissions from the
San Diego County-South Coast transport couplet.\77\
---------------------------------------------------------------------------

    \77\ 2020 Plan, p. 38. In this context, ``transport couplet''
refers to a ``transport couple,'' a term that refers to two air
basins, one of which has an impact on ambient air pollutant
concentrations in the other air basin due to transport of pollutants
and precursors by prevailing wind patterns. See ``Assessment of the
Impacts of Transported Pollutants on Ozone Concentrations in
California,'' CARB, March 2001.
---------------------------------------------------------------------------

    Using emissions levels of the District's chosen 2026 attainment
demonstration year as a basis for comparison, the District compared
emissions levels from 2026 to what the levels are projected to be one
year earlier, that is, 2025. The lower levels in 2026 were then
subtracted from the higher levels of emissions in 2025, providing a
difference in emissions levels that could then be compared against the
2020 Plan's RACM, that is, emissions reductions from reasonably
available control measures, to determine if enough RACM reductions
would be available to advance the 2026 attainment year to 2025. These
levels are provided in Table 3 of this document.

 Table 3--Emissions Reductions Needed To Advance Attainment by One Year,
                            2008 Ozone NAAQS
------------------------------------------------------------------------
                                                             Emissions
                    Emissions totals                           (tpd)
------------------------------------------------------------------------
2026 VOC Emissions Inventory............................           471.0
2025 VOC Emissions Inventory............................           473.8
VOC Emissions Reductions Needed in 2025 to Demonstrate               2.8
 Attainment.............................................
2026 NOX Emissions Inventory............................           344.0
2025 NOX Emissions Inventory............................           347.4
NOX Emissions Reductions Needed in 2025 to Demonstrate               3.4
 Attainment.............................................
------------------------------------------------------------------------
Source: 2020 Plan, Table 3-2 and Table A-2.

    Because the District's attainment demonstration relies on specific
levels of emissions of both VOC and NOX, the reductions of
emissions to advance that attainment date one year would require
reductions in both VOC and NOX at the levels shown in Table
3, that is, 2.8 tpd of VOC and 3.4 tpd of NOX (``2008 ozone
NAAQS RACM targets''). These amounts of reductions are then viewed as
targets to see if they can be met or exceeded, and if so, then the
attainment year for the 2008 ozone NAAQS would be moved up one year, to
2025. The 2020 Plan groups emissions sources into several large
categories and assesses each one to identify potential RACM and to
determine their potential collectively to provide emissions reductions
equal to or greater than these targets.
a. 2008 Ozone NAAQS, District's RACM Analysis
    The District provides a comprehensive evaluation of its 2008 ozone
NAAQS RACM control strategy in Section 3.2.1 (``Reasonably Available
Control Measures (RACM) Demonstration'') and Attachments A, D, G, H, I
and J of the 2020 Plan. The evaluation includes: source descriptions;
base year and projected baseline year emissions for the source category
affected by the rule; discussion of the current requirements of the
rule; and discussion of potential additional control measures,
including, in many cases, a discussion of the technological and
economic feasibility of the additional control measures. This includes
a comparison of each District rule to analogous control measures
adopted by other agencies.
    The District's RACM demonstration for the 2008 ozone NAAQS begins
with an analysis of stationary source controls, described in Section
<IP_ADDRESS> (``Identifying Potential RACM for Stationary Sources'') of the
2020 Plan. This section of the 2020 Plan identifies potential control
measures and analyzes these measures for emissions reduction
opportunities, as well as economic and technological feasibility. The
District's comprehensive demonstration considers potential control
measures for stationary sources located throughout the area under its
jurisdiction, that is, the entirety of San Diego County.
    As a first step in the RACM analysis, the District prepared a
detailed inventory of emissions sources of VOC and NOX to
identify source categories from which emissions reductions would
effectively contribute to attainment. Details on the methodology and
development of the emissions inventory are discussed in Section 3 and
Attachment A of the 2020 Plan. Because the San Diego County area
airshed is coupled with the South Coast Air Basin, which was used in
the attainment demonstration modeling in the 2020 Plan, the District
prepared a ``couplet'' emissions inventory that includes the two areas'
combined emissions. A total of 75 source categories are included in the
couplet emissions inventory: 45 for stationary and area sources and 30
for mobile sources.\78\ Although the couplet emissions inventory
includes South Coast and is therefore used in calculating the 2008
ozone NAAQS RACM targets (2.8 tpd VOC, 3.4 tpd NOX), only
sources of emissions within San Diego County were evaluated for their
potential to either meet the 2008 ozone NAAQS RACM targets or to
contribute to a collective reduction to meet those targets.
---------------------------------------------------------------------------

    \78\ 2020 Plan, Table A-2.
---------------------------------------------------------------------------

    The District compared the 45 source categories to its rules for
stationary and area sources. This analysis builds upon a foundation of
District rules developed for earlier ozone plans and approved as part
of the SIP. These rules establish emissions limits or other types of
emissions controls for a wide range of sources, including VOC storage
and handling, use of solvents, gasoline storage, gasoline transfer, dry
cleaning with petroleum-based solvent, architectural coatings, surface
coating operations, marine, wood products and aerospace coating
operations, degreasing operations, cutback and emulsified asphalts,
kelp processing and

biopolymer manufacturing operations, pharmaceutical and cosmetic
manufacturing, and bakery ovens, among others. These rules have already
provided significant reductions toward attainment of the 2008 ozone
NAAQS by 2026.
    The District excluded RACT rules from their stationary source RACM
analysis because those rules are already required by federal law to be
included in the SIP and are therefore not ``potential'' RACM control
measures. Likewise, the District excluded stationary and area sources
it regulates under the State's requirement to adopt ``all feasible
measures,'' as these measures are also already implemented and
incorporated into the area's attainment demonstration, and are
therefore also not potential RACM. In addition, California state law
requires ``Best Available Retrofit Control Technology'' or BARCT.\79\
Because BARCT is an ongoing requirement for the District, BARCT rules
are already implemented, would provide no new emissions reductions, and
are therefore not potential RACM.
---------------------------------------------------------------------------

    \79\ California Health & Safety Code sections 40918, 40919,
40920 and 40920.5.
---------------------------------------------------------------------------

    To demonstrate that the SDCAPCD considered all candidate measures
that are available and technologically and economically feasible for
stationary sources, the District conducted several steps in their
analysis.
Step 1. Stakeholder Outreach
    As part of a previous planning effort for the 2008 ozone NAAQS (the
2016 Moderate Plan),\80\ and again as part of the SIP development
effort for the (Severe) 2020 Plan, the District held multiple
stakeholder outreach sessions. These sessions were intended to solicit
stakeholder input on the full array of control measures that might be
available for emissions sources in the area. Two public workshops were
held in July 2020, in addition to other individual stakeholder meetings
that were held for feedback on the entire draft 2020 Plan before and
after each public workshop. These meetings built upon similar outreach
the District conducted for prior federal and state air quality plans,
including the 2016 Moderate Plan.
---------------------------------------------------------------------------

    \80\ The State of California submitted the San Diego County
area's 2016 Moderate ozone attainment plan to the EPA as a SIP
revision on April 12, 2017. At the time, the area was a Moderate
nonattainment area for the 2008 ozone NAAQS. The State withdrew the
2016 Moderate ozone attainment plan by letter dated December 16,
2021 following submittal of the 2020 Plan and the EPA's grant of the
State's request to reclassify San Diego County to Severe for the
2008 ozone NAAQS.
---------------------------------------------------------------------------

Step 2. Reasonably Available Control Technology Analysis
    The District then considered Reasonably Available Control
Technology (RACT) stationary source categories and found 11 existing
District control measures that could be further controlled when
compared to existing rules in other California air districts.\81\ These
11 control measures apply to specific types of emissions sources:
Receiving and Storing Volatile Organic Compounds at Bulk Plants and
Bulk Terminals, Transfer of Organic Compounds into Mobile Transport
Tanks, Metal Parts and Product Coating Operations, Paper, Film, and
Fabric Coatings, Aerospace Coating Operations, Graphic Arts Operations,
Marine Coating Operations, Adhesive Materials Application Operations,
Industrial and Commercial Boilers, Process Heaters and Steam
Generators, Natural Gas-Fired Fan-Type Central Furnaces, and Stationary
Gas Turbine Engines. The SDCAPCD compared its rules to the analogous
rules for the same stationary source types in other California air
districts, as candidate potential measures, and estimated the potential
emissions reductions associated with each control measure if it were
modified to reflect the other district's rule.
---------------------------------------------------------------------------

    \81\ 2020 Plan, Table G-1, items G.1 to G.11.
---------------------------------------------------------------------------

Step 3. EPA Technical Support Documents (TSDs)
    The District researched TSDs from recent EPA rulemakings but did
not find any potential additional stationary source controls beyond
what its RACT analysis found.\82\
---------------------------------------------------------------------------

    \82\ Email dated August 31, 2023, from Nick Cormier, SDCAPCD, to
John J. Kelly, EPA.
---------------------------------------------------------------------------

Step 4. Control Measures in Other Areas
    The District reviewed stationary source control measures in other
areas (i.e., San Francisco Bay Area, Sacramento, San Joaquin Valley,
Santa Barbara, South Coast, and Ventura County) to evaluate whether
control technologies available and cost-effective within other areas
would be available and cost-effective for use in the San Diego County
area.\83\ These include six control measures: Vacuum Truck Operations,
Miscellaneous NOX Sources, Equipment Leaks, Restaurant
Cooking Operations, Food Products Manufacturing/Processing, and
Metalworking Fluids and Direct-Contact Lubricants.
---------------------------------------------------------------------------

    \83\ 2020 Plan, Table G-1, items G.12 to G.17.
---------------------------------------------------------------------------

Step 5. EPA Menu of Control Measures
    The Menu of Control Measures (MCM) \84\ compiled by the EPA's
Office of Air Quality Planning and Standards was created to provide
information useful in the development of emissions reduction strategies
and to identify and evaluate potential control measures. District staff
reviewed the EPA's MCM for stationary source point and nonpoint sources
of NOX and VOC.
---------------------------------------------------------------------------

    \84\ EPA, MCM, April 12, 2012.
---------------------------------------------------------------------------

    Based on its evaluation of all available stationary source control
measures, the District concluded that its existing rules are generally
as stringent as analogous rules in other districts, and where they were
not, quantified the difference. In all, the District estimated that the
total possible emissions reductions from further control of stationary
sources subject to existing District rules and control of additional
source categories would be approximately 0.4 tpd for VOC and 0.4 tpd
for NOX.\85\
---------------------------------------------------------------------------

    \85\ 2020 Plan, Attachment G, Table G-1.
---------------------------------------------------------------------------

b. 2008 Ozone NAAQS, RACM Analysis for Transportation Control Measures
    Attachment H of the 2020 Plan contains the District's
transportation control measure (TCM) RACM evaluation. The implemented
TCMs in Attachment H are applicable in San Diego County. The District
conducted the TCM RACM analysis on behalf of SANDAG and local
jurisdictions in San Diego County, based on SANDAG's regional
transportation plan (RTP), specifically, ``San Diego Forward: The 2019
Federal Regional Transportation Plan'' (``2019 RTP'').\86\ The 2019 RTP
was developed in consultation with federal, state and local
transportation and air quality planning agencies and other
stakeholders.
---------------------------------------------------------------------------

    \86\ The 2019 RTP was adopted by SANDAG's Board on October 25,
2019. The 2019 RTP was approved by the Federal Highway
Administration on November 15, 2019.
---------------------------------------------------------------------------

    As described in Attachment H of the 2020 Plan, for the TCM RACM
analysis, the District listed all TCMs that are included in CAA section
108(f) and their implementation status in San Diego County.\87\ Of the
16 TCMs listed in CAA section 108(f), 13 are implemented in San Diego
County. Of these implemented TCMs, five were included in the area's
1982 SIP.
---------------------------------------------------------------------------

    \87\ 2020 Plan, Attachment H, ``Implementation Status of
Transportation Control Measures,'' Table H-1.
---------------------------------------------------------------------------

    Of the three TCMs that are not implemented in San Diego County, one
(``Trip Reduction Ordinances'') was adopted in 1994, but was then
rescinded in 1995 when federal and State laws were amended eliminating
the mandate

for such measures.\88\ Another (``Programs to limit or restrict vehicle
use in downtown areas or other areas of emission concentration
particularly during periods of peak use'' or ``Peak Use Restriction
Programs'') was found to be infeasible due to San Diego's low-density
land use pattern and accompanying longer transit travel times. However,
the District notes that SANDAG's Smart Growth Incentive Program
provides funding to cities in San Diego County for infrastructure
projects that enhance alternatives to driving in higher density areas.
---------------------------------------------------------------------------

    \88\ As amended in 1990, CAA section 182(d)(1)(B) required
states with Severe ozone nonattainment areas to adopt and submit SIP
revisions requiring employers in such areas to implement programs to
reduce work-related vehicle trips and miles traveled by employees,
commonly referred to as ``trip reduction ordinances.'' Amendments to
the CAA promulgated in 1995 revised CAA section 182(d)(1)(B) such
that trip reduction ordinances are no longer required but may be
adopted and submitted as SIP revisions at the state's discretion.
---------------------------------------------------------------------------

    Finally, one TCM, (``Programs to reduce motor vehicle emissions,
consistent with Title II, which are caused by extreme cold start
conditions'' or ``Cold Weather Start Programs'') was found to be not
applicable to San Diego County due to its mild climate.
    Based on its review of TCM projects implemented in San Diego
County, the District determined that 13 of the 16 TCMs listed in CAA
section 108(f) are being implemented in the county and are therefore
ineligible for consideration as potential RACM. To determine if the
three unimplemented TCMs could be required as RACM, the District
estimated the maximum emissions reductions to be attributed to those
TCMs.
    The 2020 Plan estimates the maximum emissions reduction potential
of the three unimplemented TCMs, citing a 1992 SANDAG study that
estimated maximum emissions reductions for Trip Reduction Ordinances
alone at less than 2 percent of on-road vehicle emissions.\89\ The 1992
SANDAG study also found that potential reductions of all 15 of the
other TCMs combined do not equal the Trip Reduction Ordinances TCM
alone. Therefore, the 2020 Plan estimates the maximum potential
emissions reduction potential of the three unimplemented TCMs as 2
percent of on-road vehicle emissions in a given year. For the modeled
attainment year, 2026, projected on-road motor vehicle emissions in San
Diego County are 12.2 tpd VOC and 17.5 tpd NOX. Two percent
of these projected emissions is 0.2 tpd VOC and 0.4 tpd NOX.
---------------------------------------------------------------------------

    \89\ ``Transportation Control Measures for the Air Quality
Plan,'' SANDAG, 1992.
---------------------------------------------------------------------------

c. 2008 Ozone NAAQS, CARB's RACM Analysis
    CARB's RACM analysis is contained in Attachment I (``CARB Analyses
of Potential Additional Mobile Source and Consumer Products Control
Measures'') (``CARB RACM assessment'') of the 2020 Plan. The CARB RACM
analysis provides a general description of CARB's existing mobile
source programs. In its analysis, CARB includes mobile source control
measures described in CARB's ``2016 State Strategy for the State
Implementation Plan'' (2016 State Strategy).\90\ A more detailed
description of CARB's mobile source control program, including a
comprehensive table listing on- and off-road mobile source regulatory
actions taken by CARB from 1985 to 2019, is contained in Attachment D
of the 2020 Plan (``CARB Control Measures, 1985 to 2019 (March
2020)''). CARB's RACM analysis and 2016 State Strategy collectively
contain CARB's evaluation of mobile source and other statewide control
measures that reduce emissions of NOX and VOC in California,
including San Diego County.
---------------------------------------------------------------------------

    \90\ CARB's 2016 State Strategy is available in the docket for
this action and at https://ww3.arb.ca.gov/planning/sip/2016sip/rev2016statesip.pdf.
---------------------------------------------------------------------------

    Source categories for which CARB has primary responsibility for
reducing emissions in California include most new and existing on- and
off-road engines and vehicles, motor vehicle fuels, and consumer
products. CARB developed its 2016 State Strategy through a multi-step
measure development process, including extensive public consultation,
to develop and evaluate potential strategies for mobile source
categories under CARB's regulatory authority that could contribute to
expeditious attainment of the standard.\91\ Through the process of
developing the 2016 State Strategy, CARB identified certain defined
measures as available to achieve additional VOC and NOX
emissions reductions from sources under CARB jurisdiction, including
tighter requirements for new light- and medium-duty vehicles (referred
to as the ``Advanced Clean Cars 2'' measure), a low-NOX
engine standard for vehicles with new heavy-duty engines, tighter
emissions standards for small off-road engines, and more stringent
requirements for consumer products, among others.\92\ In adopting the
2016 State Strategy, CARB committed to bringing the defined measures to
the CARB Board for action according to the specific schedule included
as part of the strategy.\93\
---------------------------------------------------------------------------

    \91\ 2020 Plan, p. I-2.
    \92\ 2016 State Strategy, Chapter 4 (``State SIP Measures'').
    \93\ CARB Resolution 17-7 (dated March 23, 2017), p. 7. CARB's
resolution is available in the docket for this action and at https://ww3.arb.ca.gov/planning/sip/2016sip/res17-7.pdf.
---------------------------------------------------------------------------

    Given the need for substantial emissions reductions from mobile and
area sources to meet the NAAQS in California nonattainment areas, CARB
established stringent control measures for on-road and off-road mobile
sources and the fuels that power them. California has unique authority
under CAA section 209 (subject to a waiver by the EPA) to adopt and
implement new emission standards for many categories of on-road
vehicles and engines, and new and in-use off-road vehicles and engines.
    CARB's mobile source program extends beyond regulations that are
subject to the waiver or authorization process set forth in CAA section
209 to include standards and other requirements to control emissions
from in-use heavy-duty trucks and buses, gasoline and diesel fuel
specifications, and many other types of mobile sources. Generally,
these regulations have been submitted and approved as revisions to the
California SIP.\94\
---------------------------------------------------------------------------

    \94\ See, e.g., the EPA's approval of standards and other
requirements to control emissions from in-use heavy-duty diesel-
powered trucks, at 77 FR 20308 (April 4, 2012), revisions to the
California on-road reformulated gasoline and diesel fuel regulations
at 75 FR 26653 (May 12, 2010), and revisions to the California motor
vehicle inspection and maintenance program at 75 FR 38023 (July 1,
2010).
---------------------------------------------------------------------------

    In their RACM analysis, CARB concludes that, in light of the
extensive public process culminating in the 2016 State Strategy, with
the current mobile source program and proposed measures included in the
2016 State Strategy, there are no additional mobile source RACM that
would advance attainment of the 2008 ozone NAAQS in San Diego County.
As a result, CARB concludes that California's mobile source programs
fully meet the RACM requirement.\95\
---------------------------------------------------------------------------

    \95\ 2020 Plan, p. I-6.
---------------------------------------------------------------------------

    Attachment I of the 2020 Plan describes CARB's current consumer
products program and commitments in the 2016 State Strategy to achieve
additional VOC reductions from consumer products.\96\ As described in
Attachment I, CARB's current consumer products program limits VOC
emissions from 129 consumer product categories, including product
categories such as

antiperspirants and deodorants and aerosol coatings.\97\ The EPA has
approved these measures into the California SIP as VOC emissions
controls for a wide array of consumer products.\98\
---------------------------------------------------------------------------

    \96\ Id., pp. I-6, I-7. CARB's consumer product measures are
found in the California Code of Regulations, Title 17 (``Public
Health''), Division 3 (``Air Resources''), Chapter 1 (``Air
Resources Board''), Subchapter 8.5 (``Consumer Products'').
    \97\ Id., p. D-34.
    \98\ The compilation of such measures that have been approved
into the California SIP, including Federal Register citations, is
available at: https://www.epa.gov/sips-ca/epa-approved-regulations-california-sip. EPA's most recent approval of amendments to
California's consumer products regulations was in 2020. 85 FR 57703
(September 16, 2020).
---------------------------------------------------------------------------

d. 2008 Ozone NAAQS, the District's RACM Conclusion
    In addition to evaluating a number of stationary, area, and mobile
sources, as well as consumer products, in the separate groups as
described in Section III.B.a. to Section III.B.c. in this document, the
District presents a ``cumulative analysis'' to assess whether all
potential RACM combined could result in advancement of the modeled 2026
attainment year to 2025.\99\ Attachment J (``Calculation of Cumulative
Potential Emission Reductions for Possible Reasonably Available Control
Measures (RACM)'') of the 2020 Plan presents the cumulative potential
RACM.\100\ When taken together, all potential RACM reductions of VOC
and NOX that the District and CARB evaluated amount to
approximately 0.7 tpd VOC and 0.7 tpd NOX. These amounts
fall far short of the 2008 ozone RACM targets of 2.8 tpd VOC and 3.4
tpd NOX.\101\ The District therefore concludes that,
collectively, there are not enough potential RACM reductions to advance
the attainment date.
---------------------------------------------------------------------------

    \99\ 2020 Plan, Section <IP_ADDRESS>, ``RACM Cumulative Analysis,''
pp. 41-42.
    \100\ Id., Table J-1.
    \101\ Although the District based its RACM analysis for the 2008
ozone NAAQS on emissions reductions in the San Diego County-South
Coast transport couplet, the District also analyzed emissions
reductions from the District alone and also concluded that the
attainment year could not be advanced one year with RACM emissions
reductions. See email dated August 9, 2023, from Nick Cormier,
SDCAPCD, to Jefferson Wehling, EPA.
---------------------------------------------------------------------------

e. 2015 Ozone NAAQS, RACM
    In addition to addressing RACM for the 2008 ozone NAAQS, the 2020
Plan addresses RACM for the 2015 NAAQS. Section 4.2.1, ``Reasonably
Available Control Measures (RACM) Demonstration,'' of the 2020 Plan
contains the plan's RACM demonstration for the 2015 ozone NAAQS. The
demonstration reflects much of what the 2020 Plan presents for
demonstrating RACM for the 2008 ozone NAAQS and relies on the same
attachments described in Section III.B.2.a.-d. of this document, that
is, Attachments A (``Emissions Inventories and Documentation for
Baseline, RFP, and Attainment Years''), D (``CARB Control Measures,
1985 to 2019''), G (``Analyses of Potential Additional Stationary
Source Control Measures''), H (``Implementation Status of
Transportation Control Measures''), I (``CARB Analyses of Potential
Additional Mobile Source and Consumer Products Control Measures''), and
J (``Calculation of Cumulative Potential Emission Reductions for
Possible Reasonably Available Control Measures (RACM'').
    In the 2020 Plan, the District compares 2032 projected emissions of
the ozone precursors VOC and NOX to those of the year prior,
2031, to determine the amount of emissions reductions that would be
necessary in order to advance attainment by one year, to 2031,
providing a 2015 ozone NAAQS RACM target. These levels are provided in
Table 4 of this document. Unlike the emissions projections used to
determine the magnitude of emissions reductions that would be necessary
to advance attainment by one year for the RACM demonstration for the
2008 ozone NAAQS, the emissions projections used to determine the
magnitude of emissions reductions necessary to advance attainment by
one year for the RACM demonstration for the 2015 ozone NAAQS reflect
emissions only for San Diego County (i.e., including marine emissions 3
to 100 NM off the County coastline) rather than those for the South
Coast-San Diego couplet. Using this more conservative approach, the
District determined that VOC reductions of 0.1 tpd and NOX
reductions of 5.9 tpd would advance the attainment date for the 2015
ozone NAAQS by one year.\102\
---------------------------------------------------------------------------

    \102\ 2020 Plan, Table 4-2, p. 58.

 Table 4--Emissions Reductions Needed To Advance Attainment by One Year,
                            2015 Ozone NAAQS
------------------------------------------------------------------------
                                                             Emissions
                    Emissions totals                           (tpd)
------------------------------------------------------------------------
2032 VOC Emissions Inventory............................            98.3
2031 VOC Emissions Inventory............................            98.4
VOC Emissions Reductions Needed in 2031 to Demonstrate               0.1
 Attainment.............................................
2032 NOX Emissions Inventory............................          * 63.3
2031 NOX Emissions Inventory............................            69.2
NOX Emissions Reductions Needed in 2025 to Demonstrate               5.9
 Attainment.............................................
------------------------------------------------------------------------
Source: 2020 Plan, Table 4-2, ``Emissions Reductions Required to Advance
  Attainment By One Year, 2015 Ozone NAAQS (tons per day).''
* Adjusted for RACM. The unadjusted 2032 NOX emissions inventory for San
  Diego County is 69.0 tpd. However, for attainment purposes, CARB has
  committed to obtain additional emissions reductions, in the amount of
  4 tpd NOX, as described in Section 4.3.5 of the 2020 Plan, and 1.7 tpd
  NOX, as described in Section 4.3.4 of the 2020 Plan and in Attachment
  L, Section L.3.9. These commitments add up to 5.7 tpd NOX, leaving a
  total emissions inventory of NOX in 2032 of 63.3 tpd.

    Once the District identifies 2015 ozone NAAQS RACM targets (0.1 tpd
VOC, 5.9 tpd NOX) in the 2020 Plan, the District assesses
all potential RACM reductions to determine if, collectively, they could
equal or exceed the targets. The District analyzes these potential RACM
reductions in essentially the same steps as those taken to assess
potential RACM for the 2008 ozone NAAQS, starting with stationary
sources. As described in Section III.B.2.a. of this document, for the
stationary source portion of the RACM demonstration for the 2008 ozone
NAAQS, if all potential stationary source RACM were adopted in the
area, stationary source emissions would be reduced an additional 0.41
tpd for VOC and 0.40 tpd for NOX.\103\ With respect to TCMs,
the District estimates that if all unimplemented TCMs were to be
adopted, transportation-related emissions sources in San Diego County
would be reduced by 2 percent of the on-road motor vehicle emissions
inventory for year 2032, or

approximately 0.2 tpd VOC and 0.3 tpd NOX. For mobile
sources and consumer products, the District concludes in the 2020 Plan
that there are no potential RACM reductions available since all
reasonable rules regulating both are currently being implemented.\104\
In the 2020 Plan, the District bases this conclusion on analysis
performed by CARB in Attachment I, which we describe in Section
III.B.2.c. of this document regarding 2008 ozone NAAQS RACM.
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    \103\ 2020 Plan, Attachment G, Table G-1, ``Stationary Source
Categories for Which More Stringent Control Requirements Have Been
Adopted by Another Air District,'' p. G-1.
    \104\ Id., Section <IP_ADDRESS>, ``Identifying Potential RACM for
Mobile Sources and Consumer Products,'' 61, and Attachment I, ``CARB
Analyses of Potential Additional Mobile Source and Consumer Products
Control Measures.''
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    The District included an additional step in its RACM analysis for
the 2015 ozone NAAQS, which was not performed for the 2008 ozone NAAQS.
The purpose was to determine whether further reductions would be
possible, given that the area's 2032 modeled attainment year was
further in the future for the 2015 ozone NAAQS than for the 2008 ozone
NAAQS (2026). The District assessed the top ten non-mobile source
categories of VOC and NOX in San Diego County's emissions
inventory.\105\
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    \105\ Id., Attachment A-1, Table A-1.
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    For each of these categories, the District estimates the percentage
of the county's 2032 emissions of VOC and NOX.\106\ In each
of two tables in the 2020 Plan (Table 4-3 and Table 4-4), the District
provides, for each category: the numerical ranking from 1 to 10, with 1
representing the category with the highest emissions of all ten
categories; the source category name; the emission inventory code or
EIC; \107\ 2017 base year and 2032 projected attainment year emissions
of VOC or NOX; the percentage of the County's projected 2032
total emissions of VOC or NOX; a description of applicable
regulations for the category; and whether there are potential RACM
reductions, with an accompanying justification. The purpose of this
last item, potential RACM and justification, is to determine first if
there are RACM reductions available. A ``yes'' in this column indicates
that the category has further reductions that are not being
implemented. A ``no'' indicates that the category has no potential RACM
reductions. Justifications for a ``no'' in this column vary. For
example, the number 1 category of VOC non-mobile emissions is Consumer
Products. These were discussed in both the 2008 and 2015 ozone NAAQS
RACM sections in the 2020 Plan. In both instances, the conclusions,
based on the analyses provided, are that there are no further CARB
Consumer Products regulations to put in place.
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    \106\ Id., Table 4-3, ``Top Ten Categories of VOC Emissions in
2032 (Non-Mobile),'' and Table 4-4, ``Top Ten Categories of
NOX Emissions in 2032 (Non-Mobile).''
    \107\ Emissions inventory source categories are represented by a
14-digit emission inventory code (EIC) for area and mobile sources.
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    In the 2020 Plan, text accompanying each of these two tables (that
is, Tables 4-3 and 4-4) provides further assessment of each category.
To continue the example for Consumer Products, the text explains that
CARB has been developing regulations for this category for thirty
years, developing regulations for over 100 consumer product categories.
These regulations have been amended frequently, with increasing levels
of stringency for VOC limits and reactivity limits.
    In each of these two tables, the District demonstrates that the top
ten categories of VOC and NOX are addressed in the 2020
Plan. Where a potential for RACM exists, each category is addressed in
the 2020 Plan in Sections <IP_ADDRESS> and <IP_ADDRESS> regarding RACM for the
2008 and 2015 ozone NAAQS, respectively, and in Attachment G.
f. 2015 Ozone NAAQS, the District's RACM Conclusion
    After evaluating the emissions reduction potentials of stationary,
area, and mobile sources, as well as consumer products, by themselves,
the District presents a ``cumulative analysis'' to assess whether all
potential RACM combined could result in advancement of the modeled 2032
attainment year to 2031.\108\ Attachment J (``Calculation of Cumulative
Potential Emission Reductions for Possible Reasonably Available Control
Measures (RACM)'') of the 2020 Plan presents the cumulative potential
RACM reductions in Table J-1, ``Calculation of Cumulative Potential
Emission Reductions for Possible Reasonably Available Control Measures
(RACM).'' When taken together, all potential RACM reductions of VOC and
NOX that the District and CARB evaluated amount to
approximately 0.6 tpd VOC and 0.7 tpd NOX. The potential
RACM for combined VOC and NOX, 1.3 tpd potential RACM
reduction falls far short of the 2015 ozone RACM target (for combined
VOC and NOX), 6.0 tpd. The District therefore concludes that
collectively, there is not enough potential RACM reductions to advance
the attainment date for the 2015 ozone NAAQS.
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    \108\ 2020 Plan, Section <IP_ADDRESS>, ``RACM Cumulative Analysis,''
p. 74.
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3. The EPA's Review of the State's Submission
    As described in Section III.B.2.a. of this document, the District
already implements many rules to reduce VOC and NOX
emissions from stationary and area sources in the San Diego County
area. For the 2020 Plan, the District evaluated a range of potentially
available measures. We find that the process followed by the District
in the 2020 Plan to identify additional stationary and area source RACM
is generally consistent with the EPA's recommendations in the General
Preamble, that the District's evaluation of potential measures is
appropriate, and that the District has provided reasoned justifications
for rejection of measures deemed not reasonably available.
    With respect to mobile sources, CARB's current program addresses
the full range of mobile sources in the San Diego County area through
regulatory programs for both new and in-use vehicles. With respect to
TCMs, we find that the District's process for identifying additional
TCM RACM and its conclusion that the TCMs being implemented in the San
Diego County area (i.e., the TCMs listed in Attachment H of the 2020
Plan) represents all TCM RACM to be reasonably justified and supported.
Further, we find that the District's cumulative analyses appropriately
sum the various sources of potential RACM, and we agree with the
District's conclusion that, taken together, all potential RACM would
advance neither the 2026 modeled attainment year for the 2008 ozone
NAAQS, nor the 2032 modeled attainment year for the 2015 ozone NAAQS.
Based on our review of these RACM analyses and the District's and
CARB's adopted rules, we propose to find that there are currently no
additional RACM that would advance attainment of either the 2008 ozone
NAAQS or the 2015 ozone NAAQS in the San Diego County area, and that
the 2020 Plan provides for the implementation of all RACM as required
by CAA section 172(c)(1), 40 CFR 51.1112(c) and 40 CFR 51.1312(c).

C. Attainment Demonstration

1. Statutory and Regulatory Requirements
    An attainment demonstration consists of: (1) technical analyses,
such as base year and future year modeling, to locate and identify
sources of emissions that are contributing to violations of the ozone
NAAQS within the nonattainment area (i.e., analyses related to the
emissions inventory for

the nonattainment area and the emissions reductions necessary to attain
the standards); (2) a list of adopted measures (including RACT
controls) with schedules for implementation and other means and
techniques necessary and appropriate for demonstrating RFP and
attainment as expeditiously as practicable but no later than the
outside attainment date for the area's classification; (3) a RACM
analysis; and (4) contingency measures required under sections
172(c)(9) and 182(c)(9) of the CAA that can be implemented without
further action by the state or the EPA to cover emissions shortfalls in
RFP and failures to attain.\109\ In this section, we address the first
two components of the attainment demonstration--the technical analyses
and a list of adopted measures. We address the RACM component of the
2020 Plan attainment demonstration in Section III.B (Reasonably
Available Control Measures Demonstration and Control Strategy) of this
document and the contingency measures component of the attainment
demonstration in Section III.F (Contingency Measures) of this document.
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    \109\ 78 FR 34178, 34184 (June 6, 2013) (proposed rule for
implementing the 2008 ozone NAAQS), codified at 40 CFR 51.1108. For
the 2015 ozone NAAQS, the EPA finalized modeling requirements at 40
CFR 51.1308.
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    With respect to the technical analyses, section 182(c)(2)(A) of the
CAA requires that a plan for an ozone nonattainment area classified
Serious or above include a ``demonstration that the plan . . . will
provide for attainment of the ozone [NAAQS] by the applicable
attainment date. This attainment demonstration must be based on
photochemical grid modeling or any other analytical method determined .
. . to be at least as effective.'' The attainment demonstration
predicts future ambient concentrations for comparison to the NAAQS,
making use of available information on measured concentrations,
meteorology, and current and projected emissions inventories of ozone
precursors, including the effect of control measures in the plan.
    Areas classified Severe for the 2008 and 2015 ozone NAAQS must
demonstrate attainment as expeditiously as practicable, but no later
than 15 years after the effective date of designation to nonattainment.
San Diego County was designated nonattainment for the 2008 ozone NAAQS
effective July 20, 2012, and for the 2015 ozone NAAQS, the area was
designated nonattainment effective August 3, 2018.\110\ Accordingly the
area must demonstrate attainment of the 2008 ozone NAAQS by July 20,
2027; for the 2015 ozone NAAQS, the area must demonstrate attainment by
August 3, 2033.\111\ An attainment demonstration must show attainment
of the standards by the ozone season (for San Diego County, the ozone
season is the entire calendar year) prior to the attainment date, so in
practice, Severe nonattainment areas must demonstrate attainment in
2026 for the 2008 ozone NAAQS and in 2032 for the 2015 ozone NAAQS.
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    \110\ 77 FR 30087 (May 21, 2012) and 83 FR 25776 (June 4, 2018),
respectively.
    \111\ 80 FR 12264 and 83 FR 62998, respectively.
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    The EPA's recommended procedures for modeling ozone as part of an
attainment demonstration are contained in ``Modeling Guidance for
Demonstrating Air Quality Goals for Ozone, PM2.5, and
Regional Haze'' (``Modeling Guidance'').\112\ The Modeling Guidance
includes recommendations for a modeling protocol, model input
preparation, model performance evaluation, use of model output for the
numerical NAAQS attainment test, and modeling documentation. Air
quality modeling is performed using meteorology and emissions from a
base year, and the predicted concentrations from this base case
modeling are compared to air quality monitoring data from that year to
evaluate model performance.
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    \112\ Modeling Guidance, EPA 454/R-18-009, November 2018.
Additional EPA modeling guidance can be found in 40 CFR 51 Appendix
W, ``Guideline on Air Quality Models,'' 82 FR 5182 (January 17,
2017). These documents are available in the docket for this action
and at https://www.epa.gov/sites/default/files/2020-10/documents/o3-pm-rh-modeling_guidance-2018.pdf and https://www.epa.gov/scram/clean-air-act-permit-modeling-guidance, respectively.
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    Once the model performance is determined to be acceptable, future
year emissions are simulated with the model. The relative (or percent)
change in modeled concentration due to future emissions reductions
provides a relative response factor (RRF). Each monitoring site's RRF
is applied to its monitored base year design value to provide the
future design value for comparison to the NAAQS. The Modeling Guidance
also recommends supplemental air quality analyses, which may be used as
part of a weight of evidence analysis. A weight of evidence analysis
corroborates the attainment demonstration by considering evidence other
than the main air quality modeling attainment test, such as trends and
additional monitoring and modeling analyses. Lastly, an unmonitored
area analysis is used to predict areas of high ozone concentrations
where air quality monitoring data is not available. This analysis
utilizes interpolated ambient data with modeled outputs to determine
gradient-adjusted spatial fields. Section 4.7 of the Modeling Guidance
provides guidelines for estimating design values at unmonitored grid
cells.
    The Modeling Guidance does not require a particular year to be used
as the base year for 8-hour ozone plans.\113\ The Modeling Guidance
states that the most recent year of the National Emissions Inventory
\114\ may be appropriate for use as the base year for modeling, but
that other years may be more appropriate when considering meteorology,
transport patterns, exceptional events, or other factors that may vary
from year to year.\115\ Therefore, the base year used for the
attainment demonstration need not be the same year used to meet the
requirements for emissions inventories and RFP.
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    \113\ Modeling Guidance, Section 2.7.1, p. 35.
    \114\ The National Emissions Inventory (NEI) is an electronic
database of criteria pollutant and precursor emissions data for the
United States. State, local and tribal agencies contribute to the
NEI every three years (2011, 2014, 2017, 2020, etc.). For more
information about the NEI, see: https://www.epa.gov/air-emissions-inventories/national-emissions-inventory-nei.
    \115\ Modeling Guidance at Section 2.7.1, p 35.
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    With respect to the list of adopted measures, CAA section 172(c)(6)
requires that nonattainment area plans include enforceable emissions
limitations, and such other control measures, means or techniques
(including economic incentives such as fees, marketable permits, and
auctions of emission rights), as well as schedules and timetables for
compliance, as may be necessary or appropriate to provide for timely
attainment of the NAAQS.\116\ Under the 2008 Ozone SRR and the 2015
Ozone SRR, all control measures needed for attainment must be
implemented no later than the beginning of the attainment year ozone
season.\117\ The attainment year ozone season is defined as the ozone
season immediately preceding a nonattainment area's maximum attainment
date.\118\
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    \116\ See also CAA section 110(a)(2)(A).
    \117\ 40 CFR 51.1108(d) and 40 CFR 51.1308(d), respectively.
    \118\ 40 CFR 51.1100(h) for the 2008 ozone NAAQS and 40 CFR
51.1300(g), for the 2015 ozone NAAQS.
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2. Summary of the State's Submission
a. Photochemical Modeling
    The 2020 San Diego County Ozone SIP includes photochemical modeling
for the 2008 and 2015 ozone NAAQS. CARB performed the air quality
modeling for the 2020 Plan. The modeling relies on a 2017 base year and
demonstrates attainment of the 2008 ozone NAAQS in 2026 and attainment
of the 2015 ozone NAAQS in 2032.

    As a general matter, the modeling for the 2020 Plan represents the
most up-to-date photochemical modeling performed for the area,
accounting for improved chemical gaseous and particulate mechanisms,
improved computational resources and post-processing utilities,
enhanced spatial and temporal allocations of the emissions inventory,
and CARB's latest attainment demonstration methodology. Air quality
modeling included in the 2020 Plan is described briefly in the plan's
Sections 3.3 and 4.3 (for 2008 and 2015 ozone NAAQS, respectively) and
in detail in the plan's Attachment K (``Attachment K'' or ``Modeling
Protocol'').\119\ The 2020 Plan discusses its modeling emissions
inventory in Attachment L, ``Modeling Emissions Inventory,'' while
Attachment M, ``Weight of Evidence Demonstration for San Diego
County,'' supplements the plan's modeling results with a weight of
evidence analysis.
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    \119\ 2020 Plan, Attachment K, ``Modeling Protocol & Attainment
Demonstration for the 2020 San Diego Ozone SIP'' (March 2020).
---------------------------------------------------------------------------

    Attachment K of the 2020 Plan provides a description of model input
preparation procedures, various model configuration options, and model
performance statistics. The Modeling Protocol contains all the elements
recommended in the Modeling Guidance, including: selection of model,
time period to model, modeling domain, and model boundary conditions
and initialization procedures; a discussion of emissions inventory
development and other model input preparation procedures; model
performance evaluation procedures; selection of days; and other details
for calculating Relative Response Factors (RRFs). Attachment K also
provides the coordinates of the modeling domain.
    Attachment L of the 2020 Plan thoroughly describes the development
of the modeling emissions inventory, including its chemical speciation,
its spatial and temporal allocation, its temperature dependence, and
quality assurance procedures.
    The CARB Staff Report for the 2020 Plan provides additional
information about CAA requirements that apply to the San Diego County
area, including an attainment demonstration, emissions reductions
commitments by CARB and the District and the source categories from
which those reductions are expected to come.\120\
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    \120\ Emissions reduction commitments are described in the 2020
Plan (Sections 4.3.4 and 4.3.5; Attachment L, Section 3.9; and Table
4-9), the CARB Staff Report, and the District's and CARB's Board
resolutions.
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    The modeling analysis uses version 5.2.1 of the Community
Multiscale Air Quality (CMAQ) photochemical model, developed by the
EPA. To prepare meteorological input for CMAQ, the Weather Research and
Forecasting model version <IP_ADDRESS> (WRF) from the National Center for
Atmospheric Research was used. CMAQ and WRF are both recognized in the
Modeling Guidance as technically sound, state-of-the-art models. The
areal extent and the horizontal and vertical resolution used in these
models are adequate for modeling San Diego County ozone.
    The WRF meteorological model results and performance statistics are
described in Section K.3.1 (``Meteorological Model Evaluation'') of
Attachment K. The District and CARB evaluated the performance of the
WRF model through a series of simulations and concluded that the daily
WRF simulation for 2017 performed comparably to recent WRF modeling
studies of ozone formation in California. The District's conclusions
are supported by hourly time series, with performance statistics
provided in Table K-7 for wind speed, temperature and relative
humidity.
    Ozone model performance and related statistics are described in the
2020 Plan Attachment K, Section K.3.2 (``Air Quality Model
Evaluation''), which includes tables of statistics recommended in the
Modeling Guidance for ozone for San Diego County. Model performance
metrics provided in the 2020 Plan include mean bias, mean error, mean
fractional bias, mean fractional error, normalized mean bias,
normalized mean error, root mean square error, and correlation
coefficient. In addition, plots were provided in evaluating the
modeling: time-series plots comparing the predictions and observations,
scatter plots for comparing the magnitude of the simulated and observed
mixing ratios, box plots to summarize the time series data across
different regions and averaging times, as well as frequency
distributions.
    After model performance for the 2017 base case was accepted, the
model was applied to develop RRFs for the attainment
demonstration.\121\ This entailed running the model with the same
meteorological inputs as before, but with adjusted emissions
inventories to reflect the expected changes between 2017 and the
attainment years 2026 and 2032. The base year, or ``reference year'' as
referred to by the District and CARB, modeling inventory was the same
as the inventory for the modeling base case, except for the exclusion
of some emissions events that are random or cannot be projected to the
future.\122\ The 2026 and 2032 inventories project the base year into
the future by including the effect of economic growth and emissions
control measures. To develop the RRFs for the 8-hour ozone NAAQS, only
the top 10 modeled days were used, consistent with the Modeling
Guidance.\123\
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    \121\ Modeling TSD, p. 26. Section 4.0 of the Modeling Guidance
focuses on establishing guidelines for analyzing simulated emissions