[Federal Register Volume 86, Number 247 (Wednesday, December 29, 2021)]
[Proposed Rules]
[Pages 74310-74352]
[FR Doc No: 2021-27796]

Vol. 86

Wednesday,

No. 247

December 29, 2021

Part IV

Environmental Protection Agency

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40 CFR Part 52

Clean Air Plans; 2012 Fine Particulate Matter Serious Nonattainment
Area Requirements; San Joaquin Valley, California; Proposed Rule

Federal Register / Vol. 86 , No. 247 / Wednesday, December 29, 2021 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2021-0884; FRL-9292-01-R9]

Clean Air Plans; 2012 Fine Particulate Matter Serious
Nonattainment Area Requirements; San Joaquin Valley, California

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA or ``Agency'')
proposes to approve portions of two state implementation plan (SIP)
revisions submitted by the State of California to meet Clean Air Act
(CAA or ``Act'') requirements for the 2012 annual fine particulate
matter (PM2.5) national ambient air quality standards (NAAQS
or ``standards'') in the San Joaquin Valley (SJV) Serious nonattainment
area. Specifically, the EPA proposes to approve the State's Serious
area plan for the 2012 annual PM2.5 NAAQS, submitted May 10,
2019, for all Serious PM2.5 area requirements (except
contingency measures), including emissions inventories, best available
control measures, demonstrations of attainment and reasonable further
progress, quantitative milestones, and motor vehicle emission budgets.
We may, however, reconsider this proposal if, based on new information
or public comments, we find that the State has not satisfied the
statutory criteria for a Serious area PM2.5 attainment plan.
The EPA also proposes to disapprove the portions of the State's Serious
area plan, and the contingency provisions of a third SIP submission
regarding residential wood burning, that pertain to the Serious area
contingency measurement requirements for the 2012 annual
PM2.5 NAAQS.

DATES: Any comments must arrive by January 28, 2022.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2021-0884, 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.

FOR FURTHER INFORMATION CONTACT: Rory Mays, Air Planning Office (AIR-
2), EPA Region IX,<PHONE_NUMBER>, [email protected].

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

Table of Contents

I. Background for Proposed Action
II. Summary and Completeness Review of Applicable SIP Submissions
    A. San Joaquin Valley 2018 PM2.5 Plan
    B. Valley State SIP Strategy
    C. Rule 4901 Contingency Provision
III. Clean Air Act Requirements for PM2.5 Serious Area
Plans
IV. Review of the San Joaquin Valley PM2.5 Serious Area
Plan
    A. Emissions Inventory
    B. PM2.5 Precursors
    C. Air Quality Modeling
    D. Best Available Control Measures
    E. Nonattainment New Source Review Requirements Under CAA
Section 189(e)
    F. Attainment Demonstration
    G. Reasonable Further Progress and Quantitative Milestones
    H. Contingency Measures
    I. Motor Vehicle Emission Budgets
V. Summary of Proposed Actions and Request for Public Comment
VI. Statutory and Executive Order Reviews

I. Background for Proposed Action

    On January 15, 2013, the EPA strengthened the primary annual NAAQS
for particulate matter with a diameter of 2.5 microns or less
(PM2.5) by lowering the level from 15.0 micrograms per cubic
meter ([micro]g/m\3\) to 12.0 [micro]g/m\3\ (``2012 annual
PM2.5 NAAQS'').\1\ The EPA established these standards after
considering substantial evidence from numerous health studies
demonstrating that serious health effects are associated with exposures
to PM2.5 concentrations above these levels.
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    \1\ 78 FR 3086 and 40 CFR 50.18. The EPA first established NAAQS
for PM2.5 on July 18, 1997 (62 FR 38652), including
annual standards of 15.0 [micro]g/m\3\ based on a 3-year average of
annual mean concentrations and 24-hour (daily) standards of 65
[micro]g/m\3\ based on a 3-year average of 98th percentile 24-hour
concentrations (40 CFR 50.7) (``1997 PM2.5 NAAQS''). In
addition, on October 17, 2006, the EPA strengthened the 24-hour
(daily) NAAQS for PM2.5 by lowering the level from 65
[micro]g/m\3\ to 35 [micro]g/m\3\ (``2006 24-hour PM2.5
NAAQS''). 71 FR 61144 and 40 CFR 50.13. Unless otherwise noted, all
references to the PM2.5 standards in this notice,
including all instances of ``2012 annual PM2.5 NAAQS,''
are to the 2012 primary annual NAAQS of 12.0 [micro]g/m\3\ codified
at 40 CFR 50.18.
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    Epidemiological studies have shown statistically significant
correlations between elevated PM2.5 levels and premature
mortality. Other important health effects associated with
PM2.5 exposure include aggravation of respiratory and
cardiovascular disease (as indicated by increased hospital admissions,
emergency room visits, absences from school or work, and restricted
activity days), changes in lung function, and increased respiratory
symptoms. Individuals particularly sensitive to PM2.5
exposure include older adults, people with heart and lung disease, and
children.\2\ Sources can emit PM2.5 directly into the
atmosphere as a solid or liquid particle (``primary PM2.5''
or ``direct PM2.5'') or it can form in the atmosphere
(``secondary PM2.5'') as a result of various chemical
reactions among precursor pollutants such as nitrogen oxides
(NOX), sulfur oxides (SOX), volatile organic
compounds (VOC), and ammonia (NH3).\3\
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    \2\ 78 FR 3086, 3088.
    \3\ EPA, Air Quality Criteria for Particulate Matter, No. EPA/
600/P-99/002aF and EPA/600/P-99/002bF, October 2004.
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    Following promulgation of a new or revised NAAQS, the EPA is
required by CAA section 107(d) to designate areas throughout the nation
as attaining or not attaining the NAAQS. On January 15, 2015, the EPA
designated and classified the SJV as Moderate nonattainment for the
2012 annual PM2.5 NAAQS.\4\ The EPA has approved the State's
demonstration that it was impracticable to attain the 2012 annual
PM2.5 NAAQS by the outermost December 31, 2021 Moderate area
attainment date and related plan elements addressing the Moderate area
requirements for the 2012 annual PM2.5 NAAQS, except for the
contingency measure element, which the EPA disapproved.\5\ In that same
action, the EPA reclassified the SJV as a Serious nonattainment area
for these NAAQS.
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    \4\ 80 FR 2206 (codified at 40 CFR 81.305).
    \5\ 86 FR 67343 (November 26, 2021).
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    On December 27, 2021, the effective date of the SJV's
reclassification as a Serious PM2.5 nonattainment area, the
SJV will become subject to a new statutory attainment date no later
than the end of the tenth calendar year following designation (i.e.,
December

31, 2025) and the requirement to submit a Serious area plan satisfying
the requirements of CAA Title I, part D, including the requirements of
subpart 4, for the 2012 annual PM2.5 NAAQS.\6\ As explained
in the EPA's final reclassification action, the Serious area plan for
the SJV must include, among other things, provisions to assure that,
under CAA section 189(b)(1)(B), the best available control measures
(BACM) for the control of direct PM2.5 and PM2.5
precursors shall be implemented no later than four years after the area
is reclassified and a demonstration (including air quality modeling)
that the plan provides for attainment as expeditiously as practicable
but no later than December 31, 2025, or by the most expeditious
alternative date practicable and no later than December 31, 2030, in
accordance with the requirements of CAA sections 189(b) and 188(e). As
described in our final action reclassifying the SJV as a Serious
PM2.5 nonattainment area, California must adopt and submit a
SIP submission addressing the Serious nonattainment area requirements
for the 2012 annual PM2.5 NAAQS within 18 months (i.e., by
June 27, 2023), for emissions inventories, BACM, and nonattainment new
source review (NSR), and by December 31, 2023, for the attainment
demonstration and related planning requirements.
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    \6\ Id. at 67347.
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    The SJV PM2.5 nonattainment area encompasses over 23,000
square miles and includes all or part of eight counties: San Joaquin,
Stanislaus, Merced, Madera, Fresno, Tulare, Kings, and the valley
portion of Kern.\7\ The area is home to four million people and is the
nation's leading agricultural region. Stretching over 250 miles from
north to south and averaging 80 miles wide, it is partially enclosed by
the Coast Mountain range to the west, the Tehachapi Mountains to the
south, and the Sierra Nevada range to the east. The CAA assigns primary
responsibility to the state for developing plans to attain the NAAQS.
Under State law, California divides this responsibility between the San
Joaquin Valley Unified Air Pollution Control District (SJVUAPCD or
District) and the California Air Resources Board (CARB) in preparing
attainment plans. Authority for regulating sources under state
jurisdiction in the SJV is split between the District, which has
responsibility for regulating stationary and most area sources, and
CARB, which has responsibility for regulating most mobile sources.
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    \7\ For a precise description of the geographic boundaries of
the SJV PM2.5 nonattainment area, see 40 CFR 81.305.
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II. Summary and Completeness Review of Applicable SIP Submissions

    The EPA is proposing action on portions of three SIP revisions
submitted by CARB to meet the Serious nonattainment area requirements
for the 2012 annual PM2.5 NAAQS in the SJV. Specifically,
the EPA is proposing to act on those portions of the following two plan
submissions that pertain to the Serious area requirements for the 2012
annual PM2.5 NAAQS: The ``2018 Plan for the 1997, 2006, and
2012 PM2.5 Standards,'' adopted by the SJVUAPCD on November
15, 2018, and by CARB on January 24, 2019 (``2018 PM2.5
Plan''); \8\ and the ``San Joaquin Valley Supplement to the 2016 State
Strategy for the State Implementation Plan,'' adopted by CARB on
October 25, 2018 (``Valley State SIP Strategy'').
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    \8\ The 2018 PM2.5 Plan was developed jointly by CARB
and the District.
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    We refer to the relevant portions of these SIP submissions
collectively in this proposal as the ``SJV PM2.5 Plan'' or
``Plan.'' The SJV PM2.5 Plan addresses attainment plan
requirements for multiple PM2.5 NAAQS in the SJV, including
the Serious area attainment plan requirements for the 2012 annual
PM2.5 NAAQS. CARB submitted the SJV PM2.5 Plan to
the EPA as a revision to the California SIP on May 10, 2019.\9\ It
became complete by operation of law on November 10, 2019.\10\
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    \9\ Letter dated May 9, 2019, from Richard W. Corey, Executive
Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region
IX. Previously, in separate rulemakings, the EPA has finalized
action on the portions of the SJV PM2.5 Plan that pertain
to the 1997 annual PM2.5 NAAQS, the 2006 24-hour
PM2.5 NAAQS, and the Moderate area plan for the 2012
annual PM2.5 NAAQS. See 86 FR 67329 (November 26, 2021)
(final rule regarding the 1997 annual PM2.5 NAAQS); 85 FR
44192 (July 22, 2020) (final rule regarding the 2006 24-hour
PM2.5 NAAQS, except contingency measures); and 86 FR
67343 (final rule regarding the Moderate area plan for the 2012
annual PM2.5 NAAQS and contingency measures for the 2006
24-hour PM2.5 NAAQS). The EPA has also separately
proposed action on the portions of the SJV PM2.5 Plan
that pertain to the 1997 24-hour PM2.5 NAAQS. 86 FR 53150
(September 24, 2021).
    \10\ We note that, with respect to plans previously required for
the 1997, 2006, and 2012 PM2.5 NAAQS, including the
Moderate area plan only for the 2012 annual PM2.5 NAAQS,
the EPA had made findings of failure to submit effective January 7,
2019, that triggered sanctions clocks. 83 FR 62720 (December 6,
2018). Following the May 10, 2019 submission of the 2018
PM2.5 Plan and Valley State SIP Strategy, the EPA
affirmatively determined that the SIP submissions addressed the
deficiency that was the basis for such findings, resulting in the
termination of the associated sanctions clocks. Letter dated June
24, 2020, from Elizabeth Adams, Director, Air and Radiation
Division, EPA Region IX, to Richard W. Corey, Executive Officer,
CARB. However, neither the findings nor completeness determination
applied to the Serious area plan for the 2012 annual
PM2.5 NAAQS as it was not yet required.
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    In addition, the EPA is proposing action on the portion of a third
SIP submission that pertains to SJVUAPCD Rule 4901, as amended by the
District on June 20, 2019, and submitted to the EPA on July 19, 2019
(``Rule 4901 Contingency Provision''). The EPA has already taken final
action on the rule modification for this submission.\11\ In this action
we are evaluating the submission for purposes of addressing the
contingency measures requirement in the SJV for the 2012 annual
PM2.5 NAAQS.
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    \11\ 85 FR 44206 (July 22, 2020) (final approval of District
Rule 4901); 85 FR 1131, 1132-33 (January 9, 2020) (proposed approval
of District Rule 4901). Completeness review for this submission was
conducted and described in that action. See also 86 FR 67329
(removing the contingency provision from the SIP).
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    CAA sections 110(a)(1) and (2) and 110(l) require each state to
provide reasonable public notice and opportunity for public hearing
prior to the adoption and submission of a SIP or SIP revision to the
EPA. To meet this requirement, every SIP submission should include
evidence that adequate public notice was given and that an opportunity
for a public hearing was provided consistent with the EPA's
implementing regulations in 40 CFR 51.102.
    CAA section 110(k)(1)(B) requires the EPA to determine whether a
SIP submission is complete within 60 days of receipt. This section also
provides that any plan that the EPA has not affirmatively determined to
be complete or incomplete will become complete by operation of law six
months after the date of submission. The EPA's SIP completeness
criteria are found in 40 CFR part 51, Appendix V.

A. San Joaquin Valley 2018 PM2.5 Plan

    The following portions of the 2018 PM2.5 Plan and
related support documents address the Serious area requirements for the
2012 annual PM2.5 NAAQS in the SJV: (i) Chapter 4
(``Attainment Strategy for PM2.5''); (ii) Chapter 7
(``Demonstration of Federal Requirements for the 2012 PM2.5
Standard''); \12\ (iii) numerous appendices to the 2018
PM2.5 Plan; (iv) CARB's ``Staff Report, Review of the San
Joaquin Valley 2018 Plan for the 1997, 2006, and 2012 PM2.5
Standards,'' release date December 21, 2018 (``CARB

Staff Report''); \13\ and (v) the State's and District's board
resolutions adopting the 2018 PM2.5 Plan (CARB Resolution
19-1 and SJVUAPCD Governing Board Resolution 18-11-16).\14\ The
SJVUAPCD Governing Board Resolution 18-11-16 includes emission
reduction commitments on which the SJV PM2.5 Plan
relies.\15\
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    \12\ Chapter 5 (``Demonstration of Federal Requirements for the
1997 PM2.5 Standard'') and Chapter 6 (``Demonstration of
Federal Requirements for the 2006 PM2.5 Standard'') of
the 2018 PM2.5 Plan pertain to the 1997 PM2.5
NAAQS and 2006 24-hour PM2.5 NAAQS, respectively.
    \13\ The CARB Staff Report includes CARB's review of, among
other things, the 2018 PM2.5 Plan's control strategy and
attainment demonstration. Letter dated December 11, 2019, from
Richard W. Corey, Executive Officer, CARB to Mike Stoker, Regional
Administrator, EPA Region IX, transmitting the CARB Staff Report.
    \14\ CARB Resolution 19-1, ``2018 PM2.5 State
Implementation Plan for the San Joaquin Valley,'' January 24, 2019,
and SJVUAPCD Governing Board Resolution 18-11-16, ``Adopting the
[SJVUAPCD] 2018 Plan for the 1997, 2006, and 2012 PM2.5
Standards,'' November 15, 2018.
    \15\ SJVUAPCD Governing Board Resolution 18-11-16, paragraph 6,
10-11.
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    The appendices to the 2018 PM2.5 Plan, in order of their
evaluation in this proposed rule, include: (i) App. B (``Emissions
Inventory''); (ii) App. A (``Ambient PM2.5 Data Analysis'');
(iii) a plan precursor demonstration and clarifications, including App.
G (``Precursor Demonstration'') and Attachment A (``Clarifying
information for the San Joaquin Valley 2018 Plan regarding model
sensitivity related to ammonia and ammonia controls'') to the CARB
Staff Report; (iv) control strategy appendices, including App. C
(``Stationary Source Control Measure Analyses''), App. D (``Mobile
Source Control Measures Analyses''), and App. E (``Incentive-Based
Strategy''); (v) modeling appendices, including App. J (``Modeling
Emission Inventory''), App. K (``Modeling Attainment Demonstration''),
and App. L (``Modeling Protocol''); (vi) App. H (``RFP, Quantitative
Milestones, and Contingency''); and (vii) App. I (``New Source Review
and Emission Reduction Credits''). The 2018 PM2.5 Plan
addresses motor vehicle emission budget requirements in the
``Transportation Conformity'' section of App. D (pages D-119 to D-131).
The 2018 PM2.5 Plan also includes an Executive Summary,
Introduction (Ch. 1), chapters on ``Air Quality Challenges and Trends''
(Ch. 2) and ``Health Impacts and Health Risk Reduction Strategy'' (Ch.
3), and an appendix on ``Public Education and Technology Advancement''
(App. F).
    The District provided public notice and opportunity for public
comment prior to its November 15, 2018 public hearing on and adoption
of the 2018 PM2.5 Plan.\16\ CARB also provided public notice
and opportunity for public comment prior to its January 24, 2019 public
hearing on and adoption of the 2018 PM2.5 Plan.\17\ The SIP
submission includes proof of publication of notices for the respective
public hearings. It also includes copies of the written and oral
comments received during the State's and District's public review
processes and the agencies' responses thereto.\18\ Therefore, we
reaffirm that the 2018 PM2.5 Plan meets the procedural
requirements for public notice and hearing in CAA sections 110(a) and
110(l) and 40 CFR 51.102. The 2018 PM2.5 Plan became
complete by operation of law on November 10, 2019, pursuant to CAA
section 110(k)(1)(B).
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    \16\ SJVUAPCD, ``Notice of Public Hearing for Adoption of
Proposed 2018 PM2.5 Plan for the 1997, 2006, and 2012
Standards,'' October 16, 2018, and SJVUAPCD Governing Board
Resolution 18-11-16.
    \17\ CARB, ``Notice of Public Meeting to Consider the 2018
PM2.5 State Implementation Plan for the San Joaquin
Valley,'' December 21, 2018, and CARB Resolution 19-1.
    \18\ CARB, ``Board Meeting Comments Log,'' March 29, 2019; J&K
Court Reporting, LLC, ``Meeting, State of California Air Resources
Board,'' January 24, 2019 (transcript of CARB's public hearing), and
2018 PM2.5 Plan, App. M (``Summary of Significant
Comments and Responses'').
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B. Valley State SIP Strategy

    CARB developed the ``Revised Proposed 2016 State Strategy for the
State Implementation Plan'' (``2016 State Strategy'') to support
attainment planning in the SJV and Los Angeles-South Coast Air Basin
(``South Coast'') ozone nonattainment areas.\19\ In its resolution
adopting the 2016 State Strategy (CARB Resolution 17-7), the Board
found that the 2016 State Strategy would achieve 6 tons per day (tpd)
of NOX emission reductions and 0.1 tpd of direct
PM2.5 emission reductions in the SJV by 2025 from source
categories under the regulatory authority of CARB. The resolution
directed CARB staff to work with the SJVUAPCD to identify additional
reductions from sources under District regulatory authority as part of
a comprehensive plan to attain all of the PM2.5 NAAQS for
the SJV and to return to the Board with a commitment to achieve
additional emission reductions from mobile sources.\20\
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    \19\ The EPA has approved certain commitments made by CARB in
the 2016 State Strategy for purposes of attaining the ozone NAAQS in
the SJV and South Coast ozone nonattainment areas. See, e.g., 84 FR
3302 (February 12, 2019) and 84 FR 52005 (October 1, 2019).
    \20\ CARB Resolution 17-7, ``2016 State Strategy for the State
Implementation Plan,'' March 23, 2017, 6-7.
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    CARB responded to this resolution by developing and adopting the
``San Joaquin Valley Supplement to the 2016 State Strategy for the
State Implementation Plan'' (``Valley State SIP Strategy'') to support
the 2018 PM2.5 Plan. The State's May 10, 2019 SIP submission
incorporates by reference the Valley State SIP Strategy as adopted by
CARB on October 25, 2018, and submitted to the EPA on November 16,
2018.\21\
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    \21\ Letter dated May 9, 2019, from Richard W. Corey, Executive
Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region
IX, 2.
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    The Valley State SIP Strategy includes an Introduction (Ch. 1), a
chapter on ``Measures'' (Ch. 2), and a ``Supplemental State Commitment
from the Proposed State Measures for the Valley'' (Ch. 3). Much of the
content of the Valley State SIP Strategy is reproduced in Chapter 4
(``Attainment Strategy for PM2.5'') of the 2018
PM2.5 Plan.\22\ The Valley State SIP Strategy also includes
CARB Resolution 18-49, which, among other things, commits CARB to
achieve specific amounts of NOX and PM2.5
emission reductions by specific years, for purposes of attaining the
PM2.5 NAAQS in the SJV.\23\
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    \22\ For example, Table 2 (proposed mobile source measures and
schedule), Table 3 (emissions reductions from proposed mobile source
measures), and Table 4 (summary of emission reduction measures) of
the Valley State SIP Strategy correspond to tables 4-8, 4-9, and 4-
7, respectively, of the 2018 PM2.5 Plan, Chapter 4.
    \23\ CARB Resolution 18-49, ``San Joaquin Valley Supplement to
the 2016 State Strategy for the State Implementation Plan,'' October
25, 2018, 5.
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    CARB provided the required public notice and opportunity for public
comment prior to its October 25, 2018 public hearing on and adoption of
the Valley State SIP Strategy.\24\ The SIP submission includes proof of
publication of the public notice for this public hearing. It also
includes copies of the written and oral comments received during the
State's public review process and CARB's responses thereto.\25\
Therefore, we reaffirm that the Valley State SIP Strategy meets the
procedural requirements for public notice and hearing in CAA sections
110(a) and 110(l) and 40 CFR 51.102. The Valley State SIP Strategy
became complete by operation of law on November 10, 2019, pursuant to
CAA section 110(k)(1)(B).
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    \24\ CARB, ``Notice of Public Meeting to Consider the San
Joaquin Valley Supplement to the 2016 State Strategy for the State
Implementation Plan,'' September 21, 2018, and CARB Resolution 18-
49.
    \25\ CARB, ``Board Meeting Comments Log,'' November 2, 2018 and
compilation of written comments; and J&K Court Reporting, LLC,
``Meeting, State of California Air Resources Board,'' October 25,
2018 (transcript of CARB's public hearing).
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C. Rule 4901 Contingency Provision

    Lastly, the 2018 PM2.5 Plan addresses the contingency
measure requirements for the 2012 annual PM2.5 NAAQS by
reference to, among other things, a District contingency measure, and

emissions estimates for the year following the attainment year for use
in evaluating whether the emissions reductions from the contingency
measure are sufficient.\26\ With respect to the District contingency
measure, the 2018 PM2.5 Plan calls for the District to amend
District Rule 4901 (``Wood Burning Fireplaces and Wood Burning
Heaters'') to include a provision in the rule with a trigger that would
activate the requirements of the contingency measure should the EPA
issue a determination or final rulemaking that the SJV failed to meet a
regulatory requirement necessitating implementation of a contingency
measure.
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    \26\ 2018 PM2.5 Plan, App. H (revised February 11,
2020), H-24 to H-26.
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    In response to the commitment made in the 2018 PM2.5
Plan, in June 2019 the District adopted amendments to Rule 4901,
including a new provision (codified as section 5.7.3 of the amended
rule) that is structured to function as a contingency measure. On July
19, 2019, CARB submitted the amended rule to the EPA for approval.\27\
The EPA took final action to approve the amended Rule 4901 (including
the new section 5.7.3) into the California SIP, but in our approval we
noted that we were not evaluating the contingency measure in section
5.7.3 of revised Rule 4901 for compliance with all requirements of the
CAA and the EPA's implementing regulations that apply to such
measures.\28\ Rather, we approved the new provision (section 5.7.3)
into the SIP as part of our approval of the entire amended rule as SIP
strengthening because the provision strengthens the rule by providing a
possibility of additional curtailment days and thus potentially
additional emissions reductions. We indicated that we would evaluate
whether section 5.7.3, in conjunction with other submitted provisions,
meets the statutory and regulatory requirements for contingency
measures in a future action.\29\ In this document, we are evaluating
District Rule 4901, and in particular section 5.7.3, in the context of
our action on the contingency measure element in the 2018
PM2.5 Plan for the 2012 annual PM2.5 NAAQS.
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    \27\ Letter dated July 19, 2019, from Richard W. Corey,
Executive Officer, CARB, to Mike Stoker, Regional Administrator, EPA
Region IX.
    \28\ 85 FR 44206 (July 22, 2020) (final approval of District
Rule 4901); 85 FR 1131, 1132-33 (January 9, 2020) (proposed approval
of District Rule 4901).
    \29\ The EPA subsequently removed section 5.7.3 of Rule 4901
from the California SIP. 86 FR 67329 (final rule on 1997 annual
PM2.5 NAAQS portion of the SJV PM2.5 Plan,
including final disapproval of the contingency measures element for
those NAAQS).
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III. Clean Air Act Requirements for PM2.5 Serious Area Plans

    Upon reclassification of a Moderate nonattainment area as a Serious
nonattainment area under subpart 4 of part D, title I of the CAA, the
Act requires the state to make a SIP submission that addresses the
following Serious nonattainment area requirements: \30\
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    \30\ 81 FR 58010, 58074-58075 (August 24, 2016).
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    (1) A comprehensive, accurate, current inventory of actual
emissions from all sources of PM2.5 and PM2.5
precursors in the area (CAA section 172(c)(3));
    (2) Provisions to assure that the best available control measures
(BACM), including best available control technology (BACT), for the
control of direct PM2.5 and all PM2.5 precursors
shall be implemented no later than four years after the area is
reclassified (CAA section 189(b)(1)(B)), unless the state elects to
make an optional precursor demonstration that the EPA approves
authorizing the state not to regulate one or more of these pollutants;
    (3) A demonstration (including air quality modeling) that the plan
provides for attainment as expeditiously as practicable but no later
than the end of the tenth calendar year after designation as a
nonattainment area (i.e., December 31, 2025, for the SJV for the 2012
annual PM2.5 NAAQS) (CAA sections 188(c)(2) and
189(b)(1)(A)(i));
    (4) Plan provisions that require reasonable further progress (RFP)
(CAA section 172(c)(2));
    (5) Quantitative milestones which are to be achieved every three
years until the area is redesignated attainment and which demonstrate
RFP toward attainment by the applicable date (CAA section 189(c));
    (6) Provisions to assure that control requirements applicable to
major stationary sources of PM2.5 also apply to major
stationary sources of PM2.5 precursors, except where the
state demonstrates to the EPA's satisfaction that such sources do not
contribute significantly to PM2.5 levels that exceed the
standard in the area (CAA section 189(e));
    (7) Contingency measures to be implemented if the area fails to
meet RFP or to attain by the applicable attainment date (CAA section
172(c)(9)); and
    (8) A revision to the nonattainment new source review (NSR) program
to lower the applicable ``major stationary source'' \31\ thresholds
from 100 tons per year (tpy) to 70 tpy (CAA section 189(b)(3)).
---------------------------------------------------------------------------

    \31\ For any Serious area, the terms ``major source'' and
``major stationary source'' include any stationary source that emits
or has the potential to emit at least 70 tons per year of
PM2.5. CAA section 189(b)(3) and 40 CFR
51.165(a)(1)(iv)(A)(1)(vii) and (viii) (defining ``major stationary
source'' in serious PM2.5 nonattainment areas).
---------------------------------------------------------------------------

    A state's Serious area plan must also satisfy the requirements for
Moderate area plans in CAA section 189(a), to the extent the state has
not already met those requirements in the Moderate area plan submitted
for the area. In addition, the state's Serious area plan must meet the
general requirements applicable to all SIP submissions under section
110 of the CAA, including the requirement to provide necessary
assurances that the implementing agencies have adequate personnel,
funding, and authority under section 110(a)(2)(E); and the requirements
concerning enforcement provisions in section 110(a)(2)(C).
    The EPA provided its preliminary views on the CAA's requirements
for particulate matter plans under part D, title I of the Act in the
following guidance documents: (1) ``State Implementation Plans; General
Preamble for the Implementation of Title I of the Clean Air Act
Amendments of 1990'' (``General Preamble''); \32\ (2) ``State
Implementation Plans; General Preamble for the Implementation of Title
I of the Clean Air Act Amendments of 1990; Supplemental'' (``General
Preamble Supplement''); \33\ and (3) ``State Implementation Plans for
Serious PM-10 Nonattainment Areas, and Attainment Date Waivers for PM-
10 Nonattainment Areas Generally; Addendum to the General Preamble for
the Implementation of Title I of the Clean Air Act Amendments of 1990''
(``General Preamble Addendum'').\34\ More recently, in an August 24,
2016 final rule entitled, ``Fine Particulate Matter National Ambient
Air Quality Standards: State Implementation Plan Requirements''
(``PM2.5 SIP Requirements Rule''), the EPA established
regulatory requirements and provided further interpretive guidance on
the statutory SIP requirements that apply to areas designated
nonattainment for the PM2.5 standards.\35\ We discuss these
regulatory requirements and interpretations of the Act as appropriate
in our evaluation of the State's submissions below.
---------------------------------------------------------------------------

    \32\ 57 FR 13498 (April 16, 1992).
    \33\ 57 FR 18070 (April 28, 1992).
    \34\ 59 FR 41998 (August 16, 1994).
    \35\ 81 FR 58010.

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IV. Review of the San Joaquin Valley PM2.5 Serious Area Plan

A. Emissions Inventory

1. Requirements for Emissions Inventories
    CAA section 172(c)(3) requires that each SIP include a
comprehensive, accurate, current inventory of actual emissions from all
sources of the relevant pollutant or pollutants in the nonattainment
area. The EPA discussed the emissions inventory requirements that apply
to PM2.5 nonattainment areas, including Serious area
requirements, in the PM2.5 SIP Requirements Rule and
codified these requirements in 40 CFR 51.1008.\36\ The EPA has also
issued guidance concerning emissions inventories for PM2.5
nonattainment areas.\37\
---------------------------------------------------------------------------

    \36\ Id. at 58078-58079.
    \37\ EPA, ``Emissions Inventory Guidance for Implementation of
Ozone and Particulate Matter National Ambient Air Quality Standards
(NAAQS) and Regional Haze Regulations,'' May 2017 (``Emissions
Inventory Guidance''), available at https://www.epa.gov/air-emissions-inventories/air-emissions-inventory-guidance-implementation-ozone-and-particulate.
---------------------------------------------------------------------------

    The base year emissions inventory should provide a state's best
estimate of actual emissions from all sources of the relevant
pollutants in the area, i.e., all emissions that contribute to the
formation of a particular NAAQS pollutant. For the PM2.5
NAAQS, the base year inventory must include direct PM2.5
emissions, separately reported filterable and condensable
PM2.5 emissions,\38\ and emissions of all chemical
precursors to the formation of secondary PM2.5: Nitrogen
oxides (NOX), sulfur dioxide (SO2), volatile
organic compounds (VOC), and ammonia (NH3).\39\ In addition,
the emissions inventory base year for a Serious PM2.5
nonattainment area must be one of the three years for which monitored
data were used to reclassify the area to Serious, or another
technically appropriate year justified by the state in its Serious area
plan submission.\40\
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    \38\ The Emissions Inventory Guidance identifies the types of
sources for which the EPA expects states to provide condensable PM
emission inventories. Emissions Inventory Guidance, section 4.2.1
(``Condensable PM Emissions''), 63-65.
    \39\ 40 CFR 51.1008.
    \40\ 40 CFR 51.1008(b)(1).
---------------------------------------------------------------------------

    A state's SIP submission must include documentation explaining how
it calculated emissions data for the inventory. In estimating mobile
source emissions, a state should use the latest emissions models and
planning assumptions available at the time it developed the submission.
The latest EPA-approved version of California's mobile source emission
factor model for estimating tailpipe, brake, and tire wear emissions
from on-road mobile sources that was available during the State's and
District's development of the SJV PM2.5 Plan was
EMFAC2014.\41\ Following CARB's submission of the Plan, the EPA
approved EMFAC2017, the latest revision to this motor vehicle emissions
model for SIP purposes.\42\ States are also required to use the EPA's
``Compilation of Air Pollutant Emission Factors'' (``AP-42'') road dust
method for calculating re-entrained road dust emissions from paved
roads.\43\
---------------------------------------------------------------------------

    \41\ 80 FR 77337 (December 14, 2015). EMFAC is short for
EMission FACtor. The EPA announced the availability of the EMFAC2014
motor vehicle emissions model, effective on the date of publication
in the Federal Register, for use in state implementation plan
development and transportation conformity in California. We note
that CARB's use of EMFAC2014 in developing the emission inventories
for the Serious area plan for the 2012 annual PM2.5 NAAQS
preceded the requirement to adopt and submit such Serious area plan.
    \42\ 84 FR 41717 (August 15, 2019).
    \43\ The EPA released an update to AP-42 in January 2011 that
revised the equation for estimating paved road dust emissions based
on an updated data regression that included new emission tests
results. 76 FR 6328 (February 4, 2011). CARB used the revised 2011
AP-42 methodology in developing on-road mobile source emissions.
``Miscellaneous Process Methodology 7.9 Entrained Road Travel, Paved
Road Dust,'' CARB, November 2016.
---------------------------------------------------------------------------

    In addition to the base year inventory submitted to meet the
requirements of CAA section 172(c)(3), the state must also submit a
projected attainment year inventory and emissions projections for each
RFP milestone year.\44\ These future emissions projections are
necessary components of the attainment demonstration required under CAA
section 189(b)(1) and the demonstration of RFP required under section
172(c)(2).\45\ Emissions projections for future years (which are
referred to in the Plan as ``forecasted inventories'') should account
for, among other things, the ongoing effects of economic growth and
adopted emissions control requirements. The state's SIP submission
should include documentation to explain how it calculated the emissions
projections. Where a state chooses to allow new major stationary
sources or major modifications to use emission reductions credits
(ERCs) that were generated through shutdown or curtailed emissions
units occuring before the base year of an attainment plan, the
projected emissions inventory used to develop the attainment
demonstration must explicitly include the emissions from such
previously shutdown or curtailed emissions units.\46\
---------------------------------------------------------------------------

    \44\ 40 CFR 51.1008 and 51.1012. Also, see Emissions Inventory
Guidance, section 3 (``SIP Inventory Requirements and
Recommendations'').
    \45\ 40 CFR 51.1004, 51.1008, 51.1011, and 51.1012.
    \46\ 40 CFR 51.165(a)(3)(ii)(C)(1).
---------------------------------------------------------------------------

Summary of State's Submission
    The State included summaries of the planning emissions inventories
for direct PM2.5 and all PM2.5 precursors
(NOX, SOX,\47\ VOC,\48\ and ammonia) and the
documentation for the inventories for the SJV PM2.5
nonattainment area in Appendix B (``Emissions Inventory'') and Appendix
I (``New Source Review and Emission Reduction Credits'') of the 2018
PM2.5 Plan. In addition, Appendix J (``Modeling Emission
Inventory'') contains inventory documentation specific to the air
quality modeling inventories. These portions of the 2018
PM2.5 Plan contain annual average daily emission inventories
for 2013 through 2028 projected from the 2012 actual emissions
inventory,\49\ including the 2013 base year, the 2019 and 2022 RFP
milestone years, the 2025 Serious area attainment year, and a 2028
post-attainment RFP year. The State used both the annual average and
the winter average daily inventories to evaluate emission sources for
the 2012 annual PM2.5 NAAQS in the 2018 PM2.5
Plan.\50\
---------------------------------------------------------------------------

    \47\ The SJV PM2.5 Plan generally uses ``sulfur
oxides'' or ``SOX'' in reference to SO2 as a
precursor to the formation of PM2.5. We use
SOX and SO2 interchangeably throughout this
notice.
    \48\ The SJV PM2.5 Plan generally uses ``reactive
organic gasses'' or ``ROG'' in reference to VOC as a precursor to
the formation of PM2.5. We use ROG and VOC
interchangeably throughout this notice.
    \49\ 2018 PM2.5 Plan, App. B, B-18.
    \50\ Id. at App. B, B-19. The base year inventory is from
CEIDARS and future year inventories were estimated using CEPAM,
version 1.05.
---------------------------------------------------------------------------

    The State selected 2013 for the base year emission inventory,
building on the 2012 actual emissions inventory and considering
available air quality data, trends, and field studies.\51\
Specifically, the State worked with local air districts and selected
2012 for the actual emissions inventory as it aligned with the 2012
data collection year of the Multiple Air Toxics Exposure Study IV
(MATES IV) \52\ of the South Coast Air Quality Management District
(SCAQMD) and to maintain consistency across various California air
quality plans.\53\ The State then projected the

2013 base year emissions inventory (also referred to as the planning
emissions inventory), presented in Appendix B of the Plan, from that
2012 actual emission inventory. Regarding the modeling emissions
inventory, developed from the base year emissions inventory, the State
conducted its base case modeling using 2013 for several reasons:
Analysis of air quality trends, adjusted for meteorology, that
indicated 2013 as a year conducive to ozone and PM2.5
formation; availability of research-grade measurements of two
significant pollution episodes in the DISCOVER-AQ field study of
January to February 2013; and the relatively high design values for
2013, making it a conservative choice for attainment modeling.\54\
---------------------------------------------------------------------------

    \51\ Id. at App. L, 11-12.
    \52\ Additional information on the MATES IV study performed in
2012 is available at: https://www.aqmd.gov/home/air-quality/air-quality-studies/health-studies/mates-iv. SCAQMD performed the
subsequent MATES V study in 2018 and issued the MATES V final report
in August 2021. See https://www.aqmd.gov/home/air-quality/air-quality-studies/health-studies/mates-v, and ``MATES V, Multiple Air
Toxics Exposure Study in the South Coast AQMD, Final Report,''
SCAQMD, August 2021.
    \53\ 2018 PM2.5 Plan, App. B, B-18.
    \54\ Id. at App. L, 12. The State presents further information
in the ``APPENDIX: San Joaquin Valley PM2.5 SIP (2018)''
of Appendix L, and highlights that 2013 was one of the worst years
in the decade preceding 2018 for PM2.5 pollution in the
SJV, underscoring its use as a conservative base year for modeling
attainment of the 2012 annual PM2.5 NAAQS. 2018
PM2.5 Plan, Ch. 7, 7-6.
---------------------------------------------------------------------------

    In addition, simultaneously with submission of the 2018
PM2.5 Plan, the State submitted the Moderate area plan for
the SJV for the 2012 annual PM2.5 NAAQS, adopted by the
District in 2016, that similarly used 2013 for the base year emissions
inventory (``2016 PM2.5 Plan''). In that plan, the State
included a modeling demonstration that it would be impracticable for
the SJV to attain the 2012 annual PM2.5 NAAQS by the
outermost Moderate area attainment date of December 31, 2021.\55\ The
modeling demonstration used three overlapping design value periods
covering 2010-2014 and the 2013 base year emissions inventory to model
the ambient air quality in 2021.
---------------------------------------------------------------------------

    \55\ 2016 PM2.5 Plan, Ch. 2, section 2.3 (``Summary
of Modeling Results'') and App. A (``Air Quality Modeling''). The
EPA has summarized the State's impracticability demonstration in
greater detail in our proposed rule on the 2016 PM2.5
Plan. 86 FR 49100, 49113 (September 1, 2021).
---------------------------------------------------------------------------

    The State developed base year inventories in the 2018
PM2.5 Plan for stationary sources using actual emissions
reports made by facility operators. The State developed the base year
emissions inventories for area sources using the most recent models and
methodologies available at the time the State was developing the 2018
PM2.5 Plan.\56\ The 2018 PM2.5 Plan includes
background, methodology, and inventories of condensable and filterable
PM2.5 emissions from stationary point and non-point
combustion sources that are expected to generate condensable
PM2.5.\57\ It provides filterable and condensable emissions
estimates, expressed as annual PM2.5 emissions (tons per
year), for all of the identified source categories for the years
relevant for the 2012 annual PM2.5 NAAQS Serious area plan
requirements, including the 2013 base year, the 2019 and 2022 RFP
years, the 2025 Serious area attainment year, and a 2028 post-
attainment RFP year.
---------------------------------------------------------------------------

    \56\ 2018 PM2.5 Plan, App. B, section B.2
(``Emissions Inventory Summary and Methodology'').
    \57\ Id. at App. B, B-42 to B-44.
---------------------------------------------------------------------------

    CARB used EMFAC2014, which was the EPA-approved model at the time
CARB developed and submitted the inventories, to estimate on-road motor
vehicle emissions based on transportation activity data from the 2014
Regional Transportation Plans adopted by the transportation planning
agencies in the SJV.\58\ Re-entrained paved road dust emissions were
calculated using a CARB methodology consistent with the EPA's AP-42
road dust methodology.\59\ CARB also provided emissions inventories for
non-road equipment, including aircraft, trains, recreational boats,
construction equipment, and farming equipment, among others. CARB uses
a suite of category-specific models to estimate non-road emissions for
many categories and, where a new model was not available, used the
OFFROAD2007 model.\60\
---------------------------------------------------------------------------

    \58\ Id. at App. B, B-37. We note that the vehicle miles
traveled data used in the 2018 PM2.5 Plan's emissions
inventory is from the final 2017 Federal Transportation Improvement
Program from each of the SJV's eight metropolitan planning
organizations.
    \59\ Id. at App. B, B-28.
    \60\ Id. at App. B, B-38 through B-40. The EPA regulations refer
to ``non-road'' vehicles and engines whereas CARB regulations refer
to ``Other Mobile Sources'' or ``off-road'' vehicles and engines.
These terms refer to the same types of vehicles and engines. We
refer herein to such vehicles and engines as ``non-road'' sources.
---------------------------------------------------------------------------

    CARB developed the emissions forecasts by applying growth and
control profiles to the base year inventory. CARB's mobile source
emissions projections take into account predicted activity rates and
vehicle fleet turnover by vehicle model year and adopted controls.\61\
In the 2018 PM2.5 Plan, the District provides for use of
pre-base year ERCs as offsets by accounting for such ERCs in the
projected emissions inventory for the 2025 attainment year.\62\ The
Plan identifies growth factors, control factors, and estimated offset
use between 2013 and 2025, for direct PM2.5, NOX,
SOX, and VOC emissions by source category and lists all pre-
base year ERCs issued by the District for PM10,\63\
NOX, SOX, and VOC emissions by facility.\64\
---------------------------------------------------------------------------

    \61\ Id. at App. B, B-19.
    \62\ Id. at App. I, I-1 through I-5.
    \63\ Particulate matter with a diameter of 10 microns or less.
    \64\ 2018 PM2.5 Plan, App. I, tables I-1 through I-5.
---------------------------------------------------------------------------

    Table 1 provides a summary of the 2018 PM2.5 Plan's
winter (24-hour) average inventories in tpd of direct PM2.5
and PM2.5 precursor emissions for the 2013 base year. Table
2 provides a summary of the 2018 PM2.5 Plan's annual average
inventories of direct PM2.5 and PM2.5 precursor
emissions for the 2013 base year. For purposes of this proposal, these
annual average inventories provide bases primarily for our evaluation
of the precursor demonstration, control measure analysis, attainment
demonstration, RFP demonstration, and motor vehicle emissions budgets
(``budgets'') in the 2018 PM2.5 Plan with respect to the
Serious area attainment plan requirements for the 2012 annual
PM2.5 NAAQS.

  Table 1--San Joaquin Valley Winter Average Emissions Inventory for Direct PM2.5 and PM2.5 Precursors for the
                                                 2013 Base Year
                                                      [tpd]
----------------------------------------------------------------------------------------------------------------
                                   Direct PM2.5
            Category                                    NOX             SOX             VOC           Ammonia
----------------------------------------------------------------------------------------------------------------
Stationary Sources..............             8.5            35.0             6.9            86.6            13.9
Area Sources....................            41.4            11.5             0.5           156.8           291.5
On-Road Mobile Sources..........             6.4           188.7             0.6            51.1             4.4
Non-Road Mobile Sources.........             4.4            65.3             0.3            27.4             0.0
                                 -------------------------------------------------------------------------------
    Totals \a\..................            60.8           300.5             8.4           321.9           309.8
----------------------------------------------------------------------------------------------------------------
Source: 2018 PM2.5 Plan, Appendix B, tables B-1 through B-5.

\a\ Totals reflect disaggregated emissions and may not add exactly as shown here due to rounding.

  Table 2--San Joaquin Valley Annual Average Emissions Inventory for Direct PM2.5 and PM2.5 Precursors for the
                                                 2013 Base Year
                                                      [tpd]
----------------------------------------------------------------------------------------------------------------
                                   Direct PM2.5
            Category                                    NOX             SOX             VOC           Ammonia
----------------------------------------------------------------------------------------------------------------
Stationary Sources..............             8.8            38.6             7.2            87.1            13.9
Area Sources....................            41.5             8.1             0.3           153.4           310.9
On-Road Mobile Sources..........             6.4           183.1             0.6            49.8             4.4
Non-Road Mobile Sources.........             5.8            87.4             0.3            33.8             0.0
                                 -------------------------------------------------------------------------------
    Totals \a\..................            62.5           317.2             8.5           324.1           329.2
----------------------------------------------------------------------------------------------------------------
Source: 2018 PM2.5 Plan, Appendix B, tables B-1 through B-5.
\a\ Totals reflect disaggregated emissions and may not add exactly as shown here due to rounding.

EPA Evaluation and Proposed Action
    The inventories in the 2018 PM2.5 Plan include the
latest version of California's mobile source emissions model,
EMFAC2014, that the EPA had approved at the time the State made the SIP
submissions, and the EPA's most recent AP-42 methodology for paved road
dust. The inventories comprehensively address all source categories in
the SJV PM2.5 nonattainment area and are consistent with the
EPA's inventory guidance.
    In accordance with 40 CFR 51.1008(b)(1), the EPA has evaluated the
State's justification for using 2013 for the base year emissions
inventory as a technically appropriate inventory year for the 2012
annual PM2.5 NAAQS Serious area plan for the SJV. In
particular, the State describes the technical bases for the selection
of 2013 for the modeling emissions inventory, explaining that 2013 was
conducive to PM2.5 formation in the SJV; the important
DISCOVER-AQ field study measured two significant pollution episodes in
the SJV in January to February 2013; and the 2013 design values (across
monitoring sites) were relatively high in comparison to other recent
years,\65\ making it a conservative choice for future air quality
projections for RFP and attainment of the 2012 annual PM2.5
NAAQS. We agree that these points make 2013 both a conservative year
for modeling future air quality and one that aligns the comprehensive,
accurate, and recent emissions inventory at the time the State
developed and submitted the 2018 PM2.5 Plan with empirical
data from the DISCOVER-AQ field study.
---------------------------------------------------------------------------

    \65\ EPA design value workbook dated May 24, 2021,
``pm25_designvalues_2018_2020_final_05_24_21.xlsx,'' worksheets
``Table3a.''
---------------------------------------------------------------------------

    The EPA's approval of the State's demonstration that it was
impracticable to attain the 2012 annual PM2.5 NAAQS by 2021
and reclassification of the SJV to Serious for the 2012 annual
PM2.5 NAAQS was based foremost on the State's modeled
demonstration.\66\ While we also considered the 2018-2020 design values
(across monitoring sites) as part of our evaluation, such ambient air
quality data was not available in 2017-2018 when CARB and the District
were developing the 2018 PM2.5 Plan.
---------------------------------------------------------------------------

    \66\ 86 FR 67343, 67345. See also, 86 FR 49100, 49117-49118
(proposed rule on State's Moderate area plan).
---------------------------------------------------------------------------

    Therefore, the EPA proposes to find the State's justification for
selecting 2013 for the base year emissions inventory to be technically
appropriate, consistent with 40 CFR 51.1008(b)(1). Furthermore, the
2013 base year represents actual annual average emissions of all
sources within the nonattainment area. Direct PM2.5 and
PM2.5 precursors are included in the inventories, and
filterable and condensable direct PM2.5 emissions are
identified separately.
    With respect to future year baseline projections, we have reviewed
the growth and control factors estimated by the State and propose to
find them acceptable and thus conclude that the future baseline
emissions projections in the 2018 PM2.5 Plan reflect
appropriate calculation methods and the latest planning assumptions at
the time the State and District were developing the Plan and its
emissions inventory. Also, as a general matter, the EPA will approve a
SIP submission that takes emissions reduction credit for a control
measure only where the EPA has approved the measure as part of the SIP.
Thus, for example, to take credit for the emissions reductions from
newly adopted or amended District rules for stationary and area
sources, the related rules must be approved by the EPA into the SIP.
    In our rulemaking on the State's attainment plan for the 2006 24-
hour PM2.5 NAAQS in the SJV, we reviewed the baseline
measures identified as 2018 PM2.5 Plan baseline controls to
ensure that the measures that are relied upon in the plan are submitted
and approved as part of the California SIP.\67\ We reaffirm that the
stationary and area source baseline measures in the 2018
PM2.5 Plan are approved into the SIP and support the
emissions reductions for future years in the SJV, with two exceptions
discussed in section IV.F.3.a of the proposed rule that would not
materially affect the attainment demonstration in the Plan. With
respect to mobile sources, the EPA has acted in recent years to approve
CARB mobile source regulations into the state-wide portion of the
California SIP.\68\ We therefore propose to find that the future year
baseline projections in the 2018 PM2.5 Plan are properly
supported by SIP-approved stationary, area, and mobile source
measures.\69\
---------------------------------------------------------------------------

    \67\ EPA Region IX, ``Technical Support Document, General
Evaluation, San Joaquin Valley PM2.5 Plan for the 2006
PM2.5 NAAQS,'' February 2020 (``EPA's General Evaluation
TSD''). Table V-A of EPA's General Evaluation TSD shows District
rules with post-2013 compliance dates that are reflected in the
future year baseline inventories of the 2018 PM2.5 Plan,
along with information on the EPA's approval of these rules.
    \68\ See, e.g., 81 FR 39424 (June 16, 2016), 82 FR 14447 (March
21, 2017), and 83 FR 23232 (May 18, 2018).
    \69\ The baseline emissions projections in the 2018
PM2.5 Plan assume implementation of CARB's zero emissions
vehicle (ZEV) sales mandate and greenhouse gas (GHG) standards,
based on the EMFAC2014 model that was the current EPA-approved model
available at the time of the SIP's development and the assumptions
that were available at that time. On September 27, 2019, the U.S.
Department of Transportation and the EPA (the Agencies) issued the
joint action known as the ``Safer Affordable Fuel-Efficient (SAFE)
Vehicles Rule Part One: One National Program'' (``SAFE I'') that,
among other things, withdrew the EPA's 2013 waiver of preemption of
CARB's ZEV sales mandate and vehicle GHG standards. 84 FR 51310
(September 27, 2019). See also proposed SAFE rule at 83 FR 42986
(August 24, 2018). On April 30, 2020 (85 FR 24174), the Agencies
issued a notice of final rulemaking for the ``The Safer Affordable
Fuel-Efficient (SAFE) Vehicles Rule for Model Years 2021-2026
Passenger Cars and Light Trucks'' (``SAFE II''), establishing the
federal fuel economy and GHG vehicle emissions standards based on
the August 2018 SAFE proposal. The effect of both SAFE final rules
(SAFE I and SAFE II) on the on-road vehicle mix in the SJV
nonattainment area and on the resulting vehicular emissions is
expected to be minimal during the timeframe addressed in this SIP
revision. Therefore, we anticipate the SAFE final rules would not
materially change the demonstration of attainment of the 2012 annual
PM2.5 NAAQS in the SJV by the Serious area attainment
date of December 31, 2025.

---------------------------------------------------------------------------

    For these reasons, we are proposing to approve the 2013 base year
emissions inventory in the 2018 PM2.5 Plan as meeting the
requirements of CAA section 172(c)(3) and 40 CFR 51.1008. We are also
proposing to find that the future year baseline inventories in the 2018
PM2.5 Plan satisfy the requirements of 40 CFR 51.1008(b)(2)
and 51.1012(a)(2) and provide an adequate basis for the control
measure, attainment, and RFP demonstrations for the 2012 annual
PM2.5 NAAQS in the 2018 PM2.5 Plan.

B. PM2.5 Precursors

Requirements for Control of PM2.5 Precursors
    The provisions of subpart 4 of part D, title I of the CAA do not
define the term ``precursor'' for purposes of PM2.5, nor do
they explicitly require the control of any specifically identified PM
precursor. The statutory definition of ``air pollutant'' in CAA section
302(g), however, provides that the term ``includes any precursors to
the formation of any air pollutant, to the extent the Administrator has
identified such precursor or precursors for the particular purpose for
which the term `air pollutant' is used.'' The EPA has identified
NOX, SO2, VOC, and ammonia as precursors to the
formation of PM2.5.\70\ Accordingly, the attainment plan
requirements of subpart 4 apply to emissions of all four precursor
pollutants and direct PM2.5 from all types of stationary,
area, and mobile sources, except as otherwise provided in the Act
(e.g., in CAA section 189(e)).
---------------------------------------------------------------------------

    \70\ 81 FR 58010, 58018.
---------------------------------------------------------------------------

    Section 189(e) of the Act requires that the control requirements
for major stationary sources of direct PM10 (which includes
PM2.5) also apply to major stationary sources of
PM10 precursors, except where the Administrator determines
that such sources do not contribute significantly to PM10
levels that exceed the standard in the area. Section 189(e) contains
the only express exception to the control requirements under subpart 4
(e.g., requirements for reasonably available control measures (RACM),
reasonably available control technology (RACT), BACM, BACT, most
stringent measures (MSM), and nonattainment NSR). Although section
189(e) explicitly addresses only major stationary sources, the EPA
interprets the Act as authorizing it also to determine, under
appropriate circumstances, that regulation of specific PM2.5
precursors from other source categories in a given nonattainment area
is not necessary. For example, under the EPA's longstanding
interpretation of the control requirements that apply to stationary and
mobile sources of PM10 precursors in the nonattainment area
under CAA section 172(c)(1) and subpart 4,\71\ a state may demonstrate
in a SIP submission that control of a certain precursor pollutant is
not necessary in light of its insignificant contribution to ambient
PM10 levels in the nonattainment area.\72\
---------------------------------------------------------------------------

    \71\ General Preamble, 13539-13542.
    \72\ Courts have upheld this approach to the requirements of
subpart 4 for PM10. See, e.g., Assoc. of Irritated
Residents v. EPA, et al., 423 F.3d 989 (9th Cir. 2005).
---------------------------------------------------------------------------

    Under the PM2.5 SIP Requirements Rule, a state may elect
to submit to the EPA a ``comprehensive precursor demonstration'' for a
specific nonattainment area to show that emissions of a particular
precursor from all existing sources located in the nonattainment area
do not contribute significantly to PM2.5 levels that exceed
the standard in the area.\73\ If the EPA determines that the
contribution of the precursor to PM2.5 levels in the area is
not significant and approves the demonstration, the state is not
required to control emissions of the relevant precursor from existing
sources in the attainment plan.\74\
---------------------------------------------------------------------------

    \73\ 40 CFR 51.1006(a)(1).
    \74\ Id.
---------------------------------------------------------------------------

    In addition, in May 2019, the EPA issued the ``PM2.5
Precursor Demonstration Guidance'' (``PM2.5 Precursor
Guidance''), which provides recommendations to states for analyzing
nonattainment area PM2.5 emissions and developing such
optional precursor demonstrations, consistent with the PM2.5
SIP Requirements Rule.\75\ The EPA developed recommended contribution
thresholds to help assess whether a precursor significantly contributes
to PM2.5 levels above the NAAQS. The thresholds are based on
the size of PM2.5 differences that are distinguishable
statistically in monitored data. If the chemical component of
PM2.5 ambient concentrations corresponding to emissions of a
precursor (e.g., the concentration of sulfate, which corresponds to
SO2 emissions) is below the threshold, that is evidence that
the precursor does not significantly contribute. If the precursor fails
this concentration-based test, the State can use a sensitivity-based
test, in which the modeled sensitivity or response of ambient
PM2.5 concentrations to changes in emissions of the
precursor is estimated and then compared to the threshold. In addition
to comparing the concentration or modeled response to the threshold,
the State can consider other information in assessing whether the
precursor significantly contributes. The EPA's recommended annual
average contribution threshold for the annual PM2.5 NAAQS is
0.2 [mu]g/m\3\.\76\
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    \75\ ``PM2.5 Precursor Demonstration Guidance,'' EPA-
454/R-19-004, May 2019, including Memo dated May 30, 2019, from
Scott Mathias, Acting Director, Air Quality Policy Division and
Richard Wayland, Director, Air Quality Assessment Division, Office
of Air Quality Planning and Standards (OAQPS), EPA to Regional Air
Division Directors, Regions 1-10, EPA. The PM2.5
Precursor Guidance builds upon the draft version of the guidance,
released on November 17, 2016 (``Draft PM2.5 Precursor
Guidance''), which CARB referenced in developing its precursor
demonstration in the SJV PM2.5 Plan. ``PM2.5
Precursor Demonstration Guidance, Draft for Public Review and
Comments,'' EPA-454/P-16-001, November 17, 2016, including Memo
dated November 17, 2016, from Stephen D. Page, Director, OAQPS, EPA
to Regional Air Division Directors, Regions 1-10, EPA.
    \76\ PM2.5 Precursor Guidance, 17.
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    We are evaluating the 2018 PM2.5 Plan with respect to
the Serious area attainment plan requirements in accordance with the
presumption embodied within subpart 4 that the State must address all
PM2.5 precursors in its evaluation of potential control
measures, unless the State adequately demonstrates that emissions of a
particular precursor or precursors do not contribute significantly to
ambient PM2.5 levels that exceed the PM2.5 NAAQS
in the nonattainment area. In reviewing any determination by the State
to exclude a PM2.5 precursor from the required evaluation of
potential control measures, we consider both the magnitude of the
precursor's contribution to ambient PM2.5 concentrations in
the nonattainment area and the sensitivity of ambient PM2.5
concentrations in the area to reductions in emissions of that precursor
in accordance with the PM2.5 Precursor Guidance.
Summary of State's Submission
    The State's precursor demonstration and conclusions are found in
Chapter 7 (``Demonstration of Federal Requirements for 2012
PM2.5 Standard'') and Appendix G (``Precursor
Demonstration'') of the 2018 PM2.5 Plan. CARB also provides
clarifying information on its precursor assessment, including an
Attachment A to its letter transmitting the 2018 PM2.5 Plan
to the

EPA \77\ and further clarifications in five email transmittals.\78\
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    \77\ Letter dated May 9, 2019, from Richard W. Corey, Executive
Officer, CARB, to Michael Stoker, Regional Administrator, EPA Region
IX, Attachment A (``Clarifying information for the San Joaquin
Valley 2018 Plan regarding model sensitivity related to ammonia and
ammonia controls'').
    \78\ Email dated June 20, 2019, ``RE: SJV model disbenefit from
SOX reduction,'' from Jeremy Avise, CARB, to Scott
Bohning, EPA Region IX, with attachment (``CARB's June 2019
Precursor Clarification''); email dated September 19, 2019, ``FW:
SJV species responses,'' from Jeremy Avise, CARB, to Scott Bohning,
EPA Region IX, with attachments (``CARB's September 2019 Precursor
Clarification''); email dated October 18, 2019, from Laura Carr,
CARB, to Scott Bohning, Jeanhee Hong, and Rory Mays, EPA Region IX,
with attachment ``Clarifying Information on Ammonia'' (``CARB's
October 2019 Precursor Clarification''); email dated April 19, 2021,
from Laura Carr, CARB, to Rory Mays, EPA Region IX, Subject:
``Ammonia update,'' with attachment ``Update on Ammonia in the San
Joaquin Valley'' (``CARB's April 19, 2021 Precursor
Clarification''); and email dated April 26, 2021, from Laura Carr,
CARB, to Scott Bohning, EPA Region IX, Subject: ``RE: Ammonia
update,'' with attachment ``Ammonia in San Joaquin Valley''
(``CARB's April 26, 2021, Precursor Clarification'').
---------------------------------------------------------------------------

    The State estimates that anthropogenic emissions of NOX,
ammonia, SOX, and VOC will decrease by 64 percent (%), 1%,
6%, and 9%, respectively, between 2013 and 2025.\79\ The 2018
PM2.5 Plan provides both concentration-based and
sensitivity-based analyses of precursor contributions to ambient
PM2.5 concentrations in the SJV. Based on these analyses,
the State concludes that emissions of NOX (as well as direct
PM2.5) contribute significantly to ambient PM2.5
levels that exceed the PM2.5 NAAQS in the SJV but ammonia,
SOX, and VOC do not contribute significantly to such
exceedances.
---------------------------------------------------------------------------

    \79\ 2018 PM2.5 Plan, Ch. 7, 7-5 and Table 7-2. We
also note that a copy of the contents of the 2018 PM2.5
Plan, App. G appears in the CARB Staff Report, App. C4 (``Precursor
Demonstrations for Ammonia, SOX, and ROG'').
---------------------------------------------------------------------------

    We summarize the State's analyses and conclusions for ammonia,
SOX, and VOC in the following paragraphs. For a more
detailed summary of the precursor demonstration in the Plan, please
refer to two EPA technical support documents (TSDs): The first covers
all the precursors and the second one specifically addresses ammonia.
The first TSD is the EPA's ``Technical Support Document, EPA Evaluation
of PM2.5 Precursor Demonstration, San Joaquin Valley
PM2.5 Plan for the 2006 PM2.5 NAAQS,'' February
2020 (``EPA's PM2.5 Precursor TSD''), which provides the
EPA's summary of the State's precursor analyses for all four
PM2.5 precursors. Most of our analysis in the EPA's
PM2.5 Precursor TSD is applicable to the portion of the Plan
pertaining to the Serious area plan for the 2012 annual
PM2.5 NAAQS. For example, the State's precursor
demonstration used 2015 annual average concentration data for its
concentration-based analysis, examined both 24-hour and annual average
sensitivities of ambient PM2.5 concentrations to reductions
in each precursor in 2013, 2020, and 2024, and presented information on
research studies and emission trends that are relevant for assessing
the sensitivity of both 24-hour average and annual average ambient
PM2.5 concentrations to emission reductions of each
PM2.5 precursor. Our evaluation of such factors, as
described in the EPA's PM2.5 Precursor TSD, is similarly
applicable for the 2012 annual PM2.5 NAAQS.
    With respect to ammonia emission reductions, the EPA's
PM2.5 Precursor TSD summarizes the State's analysis of 24-
hour average sensitivity of ambient PM2.5 concentrations
across monitoring sites and years (see Table 2 of the EPA's
PM2.5 Precursor TSD). The EPA's second TSD, ``Technical
Support Document, EPA Evaluation of Ammonia Precursor Demonstration,
San Joaquin Valley Moderate Area PM2.5 Plan for the 2012
PM2.5 NAAQS,'' August 2021 (``EPA's Ammonia Precursor
TSD''), summarizes the annual average sensitivity of ambient
PM2.5 concentrations to ammonia emission reductions (see
Table 2 of the EPA's Ammonia Precursor TSD) and provides further
summary and context with respect to the State's ammonia precursor
demonstration for the 2012 annual PM2.5 NAAQS.
    For ammonia, SOX, and VOC, CARB assesses the 2015 annual
average concentration of each precursor in ambient PM2.5 at
Bakersfield, for which the necessary speciated PM2.5 data
was available and where the highest PM2.5 design values have
been recorded in most years, and compares those concentrations to the
recommended annual average contribution threshold of 0.2 [mu]g/
m\3\.\80\ CARB concludes that the 2015 annual average contributions of
ammonia, SOX, and VOC are 5.2 [mu]g/m\3\, 1.6 [mu]g/m\3\ and
6.2 [mu]g/m\3\, respectively.
---------------------------------------------------------------------------

    \80\ 2018 PM2.5 Plan, App. G, 3. The 2018
PM2.5 Plan presents a graphical representation of annual
average ambient PM2.5 components (i.e., crustal
particulate matter, elemental carbon, organic matter, ammonium
sulfate, and ammonium nitrate) for 2011-2013 for Bakersfield,
Fresno, and Modesto. 2018 PM2.5 Plan, Ch. 3, 3-3 to 3-4.
---------------------------------------------------------------------------

    For ammonia, SOX, and VOC, the State modeled the
sensitivity of ambient PM2.5 to 30% and 70% reductions in
anthropogenic emissions of each precursor pollutant for modeled years
2013, 2020, and 2024. The year 2013 is the 2018 PM2.5 Plan's
base year; 2020 is the modeled attainment year for the 1997
PM2.5 NAAQS; and 2024 is the modeled attainment year for the
2006 24-hour PM2.5 NAAQS. For the 2012 annual
PM2.5 NAAQS, the modeled attainment year is 2025, but the
State did not conduct precursor sensitivity modeling for that
additional year. Instead the State assumed that 2024 and 2025 would
have very similar results; \81\ and results for 2024 were used as a
proxy for those of 2025. Emissions totals for those two years are
within 0.2% of each other for all pollutants, except that
NOX emissions are 3% lower in 2025.\82\ Depending on the
analysis year and percentage precursor emission reduction, the
sensitivity of ambient PM2.5 to reductions in annual average
precursor emissions ranges from 0.08 [mu]g/m\3\ to 2.30 [mu]g/m\3\ for
ammonia; from -0.05 [mu]g/m\3\ to 0.15 [mu]g/m\3\ for SOX;
and from -0.50 [mu]g/m\3\ to 0.40 [mu]g/m\3\ for VOC.\83\
---------------------------------------------------------------------------

    \81\ Id. at Ch. 7, 7-7, and App. G, 10.
    \82\ 2018 PM2.5 Plan, App. B. As discussed below, the
lower NOX emissions in 2025 compared to 2024 mean that
the PM2.5 response to ammonia reductions would be lower
than those stated in the Plan's precursor demonstration; using 2024
results is more conservative than using 2025 results.
    \83\ Id. at App. G, tables 2 through 7 for ammonia, tables 8 and
9 for SOX, and tables 10 through 15 for VOC.
---------------------------------------------------------------------------

    For ammonia, the modeled sensitivity of ambient PM2.5
levels to a 30% or 70% emission reduction exceeds 0.2 [mu]g/m\3\ in
certain years at specific monitoring sites. As discussed in section
IV.B.3.a of this proposed rule, for the 30% reduction results for 2024,
upon which the State primarily relied, 2 out of 15 monitoring sites
have responses above the threshold and the ambient PM2.5
response declines substantially from 2020 to 2024, with the decline
being generally larger for the sites with the highest projected
PM2.5 levels. In contrast, for SOX and VOC, the
modeled sensitivity of ambient PM2.5 levels to a 30% or 70%
emission reduction in either precursor is below 0.2 [mu]g/m\3\ in all
model scenarios except one, including a disbenefit (i.e., ambient
PM2.5 levels increase when precursor emissions are reduced)
at some monitoring sites for both precursors. For 2013, the State's
modeling shows an ambient PM2.5 change greater than 0.2
[mu]g/m\3\ at 7 out of 15 monitoring sites in response to a 70% VOC
emission reduction. According to the State, however, such sensitivity
results do not reflect the current atmospheric chemistry in the SJV
given the projected emission reductions from 2013 to 2024 for all four
PM2.5 precursors, especially for VOC and NOX, as
further described in this proposed rule.

    The State supplemented the sensitivity analysis, particularly for
ammonia, with consideration of additional information such as emission
trends, the appropriateness of future year versus base year
sensitivity, available emission controls, and the severity of
nonattainment.\84\ These factors were identified in the then-available
Draft PM2.5 Precursor Guidance, as well as in the final
PM2.5 Precursor Guidance, as factors that may be relevant to
a sensitivity-based contribution analysis.\85\
---------------------------------------------------------------------------

    \84\ Id. at App. G, 5.
    \85\ PM2.5 Precursor Guidance, 18-19 (consideration
of additional information), 31 (available emission controls), and
35-36 (appropriateness of future year versus base year sensitivity).
---------------------------------------------------------------------------

    The State notes that a 53% reduction in (baseline) NOX
emissions is projected to occur between 2013 and 2024,\86\ so the
conditions in the early years will not persist and the future year is
more representative of the Valley's ambient conditions than earlier
years. The 2018 PM2.5 Plan's precursor demonstration also
presents a review of District agricultural rules that control VOC
emissions and also provide ammonia co-benefits. The State concludes
that a 30% reduction is a reasonable upper bound on the ammonia
reductions to model. Finally, the 2018 PM2.5 Plan's
precursor demonstration presents extensive support for the State's
conclusion regarding an ambient excess of ammonia relative to
NOX, i.e., that particulate ammonium nitrate formation is
NOX-limited, and will become increasingly NOX-
limited as NOX reductions increase into the future.
---------------------------------------------------------------------------

    \86\ 2018 PM2.5 Plan, App. G, 8.
---------------------------------------------------------------------------

EPA Evaluation and Proposed Action
    The EPA has evaluated the State's precursor demonstration in the
2018 PM2.5 Plan, as well as other relevant information
available to the EPA, consistent with the PM2.5 SIP
Requirements Rule and the recommendations in the PM2.5
Precursor Guidance. Based on this evaluation, the EPA agrees with the
State's conclusion that NOX emissions contribute
significantly to ambient PM2.5 levels that exceed the 2012
annual PM2.5 NAAQS in the SJV and that NOX
emission sources, therefore, remain subject to control requirements
under subparts 1 and 4 of part D, title I of the Act. Additionally, for
the reasons provided in the following paragraphs, the EPA proposes to
approve the State's comprehensive precursor demonstrations for ammonia,
SOX, and VOC based on a conclusion that emissions of these
precursor pollutants do not contribute significantly to ambient
PM2.5 levels that exceed the 2012 annual PM2.5
NAAQS in the SJV.
    The State based its analyses on the latest available data and
studies concerning ambient PM2.5 formation in the SJV from
precursor emissions. For the required concentration-based analysis, the
State assessed the absolute annual average contribution of each
precursor to ambient PM2.5 (i.e., in 2015). Given that the
absolute concentrations in 2015 were above the EPA's recommended
contribution thresholds for both the 24-hour and annual average
PM2.5 NAAQS, the State proceeded to a sensitivity-based
analysis, consistent with the PM2.5 SIP Requirements Rule.
    For the sensitivity-based analysis, the State performed its
analyses based on the EPA's recommended approach--i.e., for each
modeled year and level of precursor emissions reduction (in
percentages), the State estimated the ambient PM2.5 response
using the procedure recommended in the PM2.5 Precursor
Guidance, and compared the result to the EPA's recommended contribution
threshold. In particular, the State considered the EPA's recommended
range of emission reductions (30% to 70%) for the 2013 base year, 2020
(an interim year), and the 2024 future year, and quantified the
estimated response of ambient PM2.5 concentrations to
precursor emission changes in the SJV.
    The State's emissions projections in the 2018 PM2.5 Plan
show that baseline emissions of each of these precursors will decrease
from the 2013 base year to both 2021 and 2025. These decreases are
included in the State's modeled projections of ambient PM2.5
levels in the SJV for purposes of demonstrating attainment and RFP. The
State's sensitivity analyses are consistent with these projections, in
accordance with the EPA's recommendations in the PM2.5
Precursor Guidance.\87\
---------------------------------------------------------------------------

    \87\ PM2.5 Precursor Guidance, 35.
---------------------------------------------------------------------------

    In the subsections that follow, we summarize our evaluation of the
State's precursor demonstrations for ammonia, SOX, and VOC
for purposes of the 2012 annual PM2.5 NAAQS in the SJV.
(a) Ammonia Precursor Demonstration
    In the 2018 PM2.5 Plan, CARB estimates the ambient
PM2.5 response to both a 30% and a 70% emissions reduction
in 2013, 2020, and 2024. We have evaluated CARB's sensitivity-based
contribution analyses for 2013, 2020, and 2024 (in the 2018
PM2.5 Plan) and CARB's determination that 2024 results are
representative of conditions in the SJV for purposes of a sensitivity-
based analysis, as discussed in the following paragraphs. The EPA's
PM2.5 Precursor Guidance explicitly provides for
consideration of a future year, such as the attainment year.\88\ We
consider it appropriate for the State to take into account additional
information as part of its evaluation of whether the ammonia
contribution is significant and to rely on the responses to the 30%
modeled ammonia emissions reduction in its precursor demonstration for
ammonia. The State primarily relied on the 30% reduction results after
concluding that 30% was a reasonable upper bound on potential ammonia
reductions, based on past research on ammonia emissions and potential
control options for agricultural sources. The EPA agrees that this is a
reasonable upper bound on ammonia emissions reductions to use in the
precursor demonstration, as discussed in EPA's approval of the
precursor demonstration for the 2006 24-hour PM2.5
NAAQS.\89\ We provide a detailed evaluation of the State's precursor
demonstration for ammonia emissions in the EPA's Ammonia Precursor TSD.
---------------------------------------------------------------------------

    \88\ Id.
    \89\ 85 FR 17382 (March 27, 2020), 17395; EPA's PM2.5
Precursor TSD, 13.
---------------------------------------------------------------------------

    The precursor demonstration in the 2018 PM2.5 Plan
indicates that the ambient response to a 30% ammonia emission reduction
would exceed the EPA's recommended contribution threshold of 0.2 [mu]g/
m\3\ for 14 out of 15 monitoring sites in the 2013 analysis year, and
at 9 out of 15 for the 2020 analysis year. For the 2024 analysis year,
2 of the 15 sites would exceed the contribution threshold, Madera and
Hanford. In absolute terms, the ambient PM2.5 response
declines from 0.24 [mu]g/m\3\ in 2020 to 0.12 [mu]g/m\3\ in 2024 at
Bakersfield-Planz, the highest concentration site. The Madera and
Hanford responses decline, respectively, from 0.36 to 0.21 [mu]g/m\3\,
and from 0.42 to 0.26 [mu]g/m\3\. The average response over all
monitoring sites declines from 0.23 [mu]g/m\3\ to 0.14 [mu]g/m\3\, with
the decline being generally larger for the sites with the highest
projected PM2.5 levels.
    While the Madera and Hanford responses to ammonia reductions are
above the contribution threshold, additional information about these
locations leads the EPA to give these responses lower weight in the
overall assessment of whether ammonia contributes significantly to
PM2.5 levels. The State notes that the 2013 base year Madera
monitored concentrations are

biased high,\90\ which would lead to model estimates of the response to
ammonia reductions that are biased high (because for model projections,
relative responses of the model to emissions changes are applied to
monitored concentrations). While the State did not discuss the evidence
for this in detail in its 2018 PM2.5 Plan, it is consistent
with an analysis of Madera measured concentrations that the State
provided in a prior PM2.5 plan for the SJV.\91\ The EPA has
previously discussed that the Madera data for the limited period of
2011 to 2013 are not representative for purposes of an attainment
demonstration.\92\
---------------------------------------------------------------------------

    \90\ 2018 PM2.5 Plan, App. G, 14.
    \91\ ``Assessment of the Representativeness of 2011
PM2.5 Beta Attenuation Monitor Data from Madera,'' in
``Staff Report, ARB Review of San Joaquin Valley PM2.5
State Implementation Plan,'' adopted by CARB on May 21, 2015, App.
A, ``Weight of Evidence Analysis.''
    \92\ 81 FR 6936, 6971 (February 9, 2016). The conclusion that
2011-2013 Madera data was biased high was based on it not fitting
the north-south concentration gradient historically seen in
relations to other monitors, a comparison to data from a second
monitor at the same site, and the return to the historic pattern
after adjustments were made to instrument operation after checking
its zero point. The data is considered valid in the EPA's Air
Quality System (AQS) for purposes of assessing whether the NAAQS is
met. However, the EPA considered it to be anomalously high for that
period, and not representative for use in modeling. Adjusted
substituted data from nearby monitors had concentrations about 10%
lower, and were accepted by the EPA for the demonstration of
attainment of the 1997 annual PM2.5 NAAQS.
---------------------------------------------------------------------------

    For the 2018 PM2.5 Plan precursor demonstration,
Madera's ambient PM2.5 response in 2024 to a 30% ammonia
emissions reduction was 0.21 [mu]g/m\3\, just 5% above EPA's
recommended contribution threshold of 0.2 [mu]g/m\3\. Because the 2024
modeling starting point was a base design value using monitored
concentrations from 2010-2014, if more typical Madera concentrations
were used, it is likely that the 2024 Madera response to ammonia
reductions would be below the contribution threshold. Moreover, given
the NOX emission reductions that are projected to continue
from 2024 to 2025, the EPA expects that PM2.5 sensitivity to
ammonia reductions would decrease from the 0.21 [mu]g/m\3\ unadjusted
value in 2024 to a lower value in 2025, likely decreasing even the
unadjusted, biased-high value to below the threshold.
    There is also information suggesting that the Hanford response to
ammonia reductions may be lower than indicated in the State's 2018
PM2.5 Plan precursor demonstration. An independent study
using aircraft and surface data from the winter 2013 DISCOVER-AQ \93\
campaign, a key period in the 2018 PM2.5 Plan's 2013 base
year, found that the Community Multiscale Air Quality (CMAQ) model
underestimated ammonia at Hanford by roughly a factor of five; Hanford
is just outside a region with high ammonia emissions in the model
(western Tulare County).\94\ If the model's ammonia concentrations were
higher to better match observations, then there would be relatively
more ammonia per NOX; ammonia then would be less of a
limiting factor for particulate ammonium nitrate formation and the
model response to ammonia reductions would be lower. This phenomenon is
described more fully below.
---------------------------------------------------------------------------

    \93\ NASA, ``Deriving Information on Surface conditions from
COlumn and VERtically Resolved Observations Relevant to Air
Quality,'' described at https://www.nasa.gov/mission_pages/discover-aq/index.html.
    \94\ Kelly, J.T. et al. 2018, ``Modeling
NH4NO3 over the San Joaquin Valley during the
2013 DISCOVER-AQ campaign,'' Journal of Geophysical Research:
Atmospheres, 123, 4727-4745, https://doi.org/10.1029/2018JD028290 at
4733. The paper notes that, despite the ammonia underestimation,
model performance was good for particulate ammonium nitrate and the
ammonium nitrate was not sensitive to the ammonia underestimate
since its formation was NOX-limited.
---------------------------------------------------------------------------

    The 2018 PM2.5 Plan did not include an evaluation of
model performance for ammonia per se (just for particulate ammonium),
but in supplemental transmittals \95\ CARB described the results of two
analyses confirming the likely underestimation of ammonia. CARB
compared CMAQ model predictions of ammonia with the 2013 DISCOVER-AQ
aircraft measurements and found that ammonia was underpredicted, and
noted that this would result in the PM2.5 response to
ammonia reductions being overpredicted. CARB also compared 2017
satellite measurements of ammonia with CMAQ model predictions and found
that modeled ammonia concentrations were half of the magnitude of the
satellite observations at some locations, and the modeled average in
the SJV was about 25% less than observed. CARB concluded that the model
tends to overpredict the sensitivity of ammonium nitrate formation to
ammonia emission reductions. CARB also speculated that the
underprediction could be partly be explained by the underestimation of
ammonia emissions using current methodologies.\96\ If modeled ammonia
concentrations were closer to observations, e.g., via increased
emissions in the model, then the modeled response to ammonia precursor
reductions would be lower than shown in the 2018 PM2.5
Plan's precursor demonstration. An increase in modeled ambient ammonia
(such as via a larger emissions estimate) would also make the model
response more consistent with the evidence from the ambient measurement
studies that are discussed next.
---------------------------------------------------------------------------

    \95\ CARB's April 19, 2021, Precursor Clarification and CARB's
April 26, 2021, Precursor Clarification.
    \96\ As discussed in EPA's Ammonia Precursor TSD, there is
evidence that ammonia emisions are underestimated, based on
comparsons between satellite measurements and what would be expected
from emissions inventories.
---------------------------------------------------------------------------

    As additional information for assessing the contribution of ammonia
to PM2.5, the State discussed evidence from multiple ambient
measurement studies.\97\ The studies suggest a very low ambient
sensitivity to ammonia, based on measured excess ammonia relative to
NOX, the abundance of particulate nitrate relative to
gaseous NOX, and the large abundance of ammonia relative to
nitric acid. The studies all conclude that there is a large amount of
ammonia left over after reacting with NOX, so that ammonia
emission reductions would be expected mainly to reduce the amount of
ammonia excess, rather than to reduce the particulate amonium nitrate.
These ambient studies provide strong evidence independent of the
modeling that PM2.5 would respond only weakly to ammonia
emissions reductions.
---------------------------------------------------------------------------

    \97\ 2018 PM2.5 Plan, 6-7, and App. G, G-9 to G-10;
the CARB 2018 Staff Report, App. C, 12-15; and Submittal Letter,
Attachment A. These studies are also discussed in the EPA's
PM2.5 Precursor TSD.
---------------------------------------------------------------------------

    Another consideration is that the PM2.5 benefit of
ammonia emission reductions is projected to decline steeply over time.
In selecting the analysis year for a precursor demonstration, we
believe it is appropriate to consider changes in atmospheric chemistry
that may occur between the base or current year and the attainment year
because the changes may ultimately affect the nonattainment area's
progress toward expeditious attainment. The PM2.5 Precursor
Guidance explicitly states that a future year may be used, and that
there are a multitude of considerations in choosing the analysis
year.\98\ The ``anticipated growth or loss of sources . . . or trends
in ambient speciation data and precursor emissions'' \99\ are among the
``facts and circumstances of the area'' \100\ to consider in
determining the significance of a precursor. The Guidance states that a
future year could be more appropriate if it better represents the
period that sources will operate in. As discussed in more detail below,
the 2024 model results better

represent the period that ammonia sources will operate in, because of
the steep decline in NOX emissions projected to occur by
2024 and 2025. We consider it reasonable for the State to focus on the
ambient PM2.5 response to ammonia emission reductions in
2024, rather than an earlier year, as the modeled response in 2024 in
the SJV better reflects the potential benefit of ammonia control
measures for purposes of expeditious attainment of the 2012 annual
PM2.5 NAAQS.
---------------------------------------------------------------------------

    \98\ PM2.5 Precursor Guidance, 35.
    \99\ Id. at 18.
    \100\ PM2.5 SIP Requirements Rule, 40 CFR
51.1006(a)(1)(ii).
---------------------------------------------------------------------------

    The State's precursor demonstration in the 2018 PM2.5
Plan shows that ambient sensitivity to ammonia emission reductions in
the SJV declines steeply over time. Between 2020 and 2024, the modeled
response to a 30% ammonia emission reduction declines by 50% at the
Bakersfield-Planz monitoring site, which has the highest projected
PM2.5 level, and by 37% averaged over all monitoring
sites.\101\ As noted above, in absolute terms, the ambient
PM2.5 response declines from 0.24 [mu]g/m\3\ in 2020 to 0.12
[mu]g/m\3\ in 2024 at Bakersfield-Planz, which has the highest
projected PM2.5 design value, and from 0.23 [mu]g/m\3\ to
0.14 [mu]g/m\3\ as averaged over all monitoring sites, with the decline
being generally larger for the sites with the highest projected
PM2.5 levels. Thus, between 2020 and 2024, the number of
sites at which modeled sensitivity exceeds the 0.2 [mu]g/m\3\ threshold
declines from 9 out of 15 down to 1 or 2 out of 15.\102\ As discussed
above, ammonia sensitivity declines because of the shifting atmospheric
chemistry caused by NOX emissions decreases. NOX
emissions are projected to decrease 27% between 2020 and 2024 due to
baseline measures (e.g., existing motor vehicle controls). The
decreased NOX emissions will make ammonia more abundant
relative to NOX, and even less of a limiting factor on
PM2.5 formation. In other words, the model response in the
future year 2024 gives a more realistic assessment of the potential
effect of ammonia controls than past or current conditions. Between
2024 and 2025, the attainment year, NOX emissions are
projected to decrease by an additional 3.5% from 2024 levels,\103\ so
that the response to ammonia reductions in the attainment year would be
lower than the 2024 results reported in the Plan.
---------------------------------------------------------------------------

    \101\ Extrapolating the 2018 PM2.5 Plan results to
2025, the percent declines are 55% and 40%, respectively, which are
larger still than those for 2024.
    \102\ 2018 PM2.5 Plan, App. G, tables 4 and 5, G-11.
As discussed above, the response for the Madera site is likely below
the contribution threshold since its monitored concentrations are
biased high.
    \103\ Annual average NOX emissions are projected to
decrease from 148.9 tpd in 2024 to 143.7 tpd in 2025. 2018
PM2.5 Plan, App. B, Table B-2.
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    Finally, based on the 2024 sensitivity results,\104\ if ammonia
emissions were reduced by 30%, the area's projected 12.0 [mu]g/m\3\
design value, occurring at the Bakersfield-Planz monitoring site, would
be reduced by 0.12 [mu]g/m\3\, which would not be considered
significant (it is below the EPA's recommended threshold of 0.2 [mu]g/
m\3\).
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    \104\ 2018 PM2.5 Plan, App. G, tables 5 and 7, 11-12.
The response to 2025 ammonia reductions would be lower than the
values stated in the text, due to the effect of declining
NOX emissions.
---------------------------------------------------------------------------

    In sum, we conclude that the State quantified the sensitivity of
ambient PM2.5 levels to reductions in ammonia emissions
using appropriate modeling technique; the modeled response to ammonia
reductions is likely lower than reported; and the State's choice of
2024 and 2025 as the reference points for purposes of evaluating the
sensitivity of ambient PM2.5 levels to ammonia emission
reductions is well-supported. Based on all of these considerations, the
EPA proposes to approve the State's demonstration that ammonia
emissions do not contribute significantly to ambient PM2.5
levels that exceed the 2012 annual PM2.5 NAAQS in the SJV.
(b) SOX Precursor Demonstration
    In the 2018 PM2.5 Plan, CARB estimated the 2013 ambient
PM2.5 response to a 30% SOX emission reduction to
range from -0.01 [mu]g/m\3\ to 0.07 [mu]g/m\3\ and estimated the
ambient PM2.5 response to a 70% SOX emission
reduction to range from -0.05 [mu]g/m\3\ to 0.15 [mu]g/m\3\.\105\ The
State also provides an emissions trend chart that shows SOX
emissions to be steady at approximately 8 tpd from 2013 through 2024.
Given that the relative levels of estimated SOX and ammonia
emissions over that timeframe remain similar, the State concludes that
the 2013 sensitivities are also representative of future years.\106\
The State also provides the ambient PM2.5 responses in 2013,
2020, and 2024 to 30% and 70% reductions in SOX emissions,
all of which are below the 0.2 [mu]g/m\3\ contribution threshold.\107\
---------------------------------------------------------------------------

    \105\ Id. at App. G, 15-16, tables 8 and 9.
    \106\ 2018 PM2.5 Plan, App. G, 15. The State includes
modeling of 30% and 70% reductions of SOX only for 2013,
finding that the sensitivity of ambient PM2.5 to such
changes were below the EPA's recommended threshold, and that the
2020 and 2024 results would differ little from 2013 due to the
similarity of emissions conditions over time. App. G, 17. CARB's
September 2019 Precursor Clarification provides the 2020 and 2024
sensitivity results, which are indeed very close to those for 2013.
    \107\ CARB's September 2019 Precursor Clarification.
---------------------------------------------------------------------------

    We note that the 2018 PM2.5 Plan's sensitivity estimates
for 2013 are well below that threshold for both the 30% and 70%
emission reduction scenarios and even negative for certain monitoring
sites. Given those results and the steady SOX emission
levels over 2013 to 2025 (as opposed to increases), the EPA agrees with
the State's conclusion that the 2013 modeled sensitivities provide a
sufficient basis for the SOX precursor demonstration. The
supplemental results provided by the State for 2020 and 2024 support
this conclusion.
    Therefore, on the basis of these modeled ambient PM2.5
responses to SOX emission reductions in the SJV, and the
facts and circumstances of the area, the EPA proposes to approve the
State's demonstration that SOX emissions do not contribute
significantly to ambient PM2.5 levels that exceed the 2012
annual PM2.5 NAAQS in the SJV.
(c) VOC Precursor Demonstration
    In the 2018 PM2.5 Plan, the State found that the ambient
PM2.5 response to VOC emission reductions were generally
below the EPA's recommended contribution threshold of 0.2 [mu]g/m\3\,
and predicted an increase in ambient PM2.5 levels in
response to VOC reductions (i.e., a disbenefit) at 2 out of 15
monitoring sites in 2020, and 11 out of 15 sites in 2024. Only for a
70% emission reduction for the 2013 base year did the State predict the
ambient PM2.5 response to be above the threshold at a
majority of sites.\108\
---------------------------------------------------------------------------

    \108\ 2018 PM2.5 Plan, App. G, 18-19, tables 10 and
11.
---------------------------------------------------------------------------

    We note that the 2018 PM2.5 Plan's sensitivity estimates
for 2020 and 2024 are well below that threshold for both the 30% and
70% emission reduction scenarios, and even negative for certain
monitoring sites. The State also provides an emissions trend chart that
shows VOC emissions are projected to decrease by about 30 tpd, or 9%
between 2013 and 2020 as well as between 2013 and 2024, and concludes
that 2013 sensitivity results are not representative into the future
and that the 2020 and 2024 results are representative.\109\ Finally,
the State concludes that VOC emissions do not contribute significantly
to PM2.5 levels that exceed the 2012 annual PM2.5
NAAQS.
---------------------------------------------------------------------------

    \109\ Id. at App. G, 19-20.
---------------------------------------------------------------------------

    The EPA has evaluated and agrees with the State's determination in
the 2018 PM2.5 Plan that the projected 2024 year is more
representative of conditions in the SJV for sensitivity-based analyses
and that VOC reductions in 2024 would mostly result in a

disbenefit to ambient PM2.5 levels, seen at 11 of 15
monitoring sites. The EPA agrees that the 9% VOC emissions decrease
from 2013 to 2024 supports reliance on the 2024 modeling results.
Furthermore, there is projected to be a large decrease in
NOX emissions over this period, as described in section
IV.B.2 of this proposed rule, that affects the atmospheric chemistry
with respect to ambient PM2.5 formation from VOC emissions.
The 9% VOC emission reductions and the vast majority of NOX
emissions reductions are expected to result from baseline measures
already in effect. Therefore, we conclude that it is reasonable to rely
on future year 2024 modeled responses to VOC reductions. The EPA also
concludes that the State provided a reasonable explanation for the VOC
reduction disbenefit and evidence that it occurs in the SJV; as
discussed in the EPA's PM2.5 Precursor TSD, VOC reductions
led to less peroxyacetyl nitrate formation, and so to greater
availability of nitrate to form particulate ammonium nitrate.\110\
---------------------------------------------------------------------------

    \110\ EPA's PM2.5 Precursor TSD, 22.
---------------------------------------------------------------------------

    For these reasons, we propose to approve the State's demonstration
that VOC emissions do not contribute significantly to ambient
PM2.5 levels that exceed the 2012 annual PM2.5
NAAQS in the SJV.

C. Air Quality Modeling

1. Requirements for Air Quality Modeling
    Section 189(b)(1)(A) of the CAA requires that each Serious area
plan include a demonstration (including air quality modeling) that the
plan provides for attainment of the PM2.5 NAAQS by the
applicable attainment date. As noted in sections I and II of this
proposed rule, the outermost statutory Serious area attainment date for
the 2012 annual PM2.5 NAAQS in the SJV is December 31, 2025.
    The PM2.5 SIP Requirements Rule explains that Serious
area plans under CAA section 189(b) must include a demonstration
(including air quality modeling) that the control strategy provides for
attainment of the PM2.5 NAAQS as expeditiously as
practicable.\111\ For purposes of determining the attainment date that
is as expeditious as practicable, the state must conduct future year
modeling that takes into account emissions growth, known controls
(including any controls that were previously determined to be RACM/RACT
or BACM/BACT), and any other emissions controls that are needed for
expeditious attainment of the NAAQS.
---------------------------------------------------------------------------

    \111\ 40 CFR 51.1011(b)(1); 81 FR 58010, 58087.
---------------------------------------------------------------------------

    The EPA's PM2.5 modeling guidance \112\ (``Modeling
Guidance'' and ``Modeling Guidance Update'') recommends that states use
a photochemical model, such as the CMAQ model, to simulate a base case,
with meteorological and emissions inputs reflecting a base case year to
replicate concentrations monitored in that year. The Modeling Guidance
recommends the following procedures for states to use in attainment
demonstrations. The model should undergo a performance evaluation to
ensure that it satisfactorily reproduces the concentrations monitored
in the base case year. The model may then be used to simulate emissions
occurring in other years required for an attainment plan, namely the
base year (which may differ from the base case year) and future
year.\113\ The Modeling Guidance recommends that the modeled response
to the emission changes between the base and future years be used to
calculate relative response factors (RRFs). The modeled RRFs are then
applied to the monitored design value in the base year to estimate the
projected design value in the future year, which can be compared
against the NAAQS. In the recommended procedure, the RRFs are
calculated for each chemical species component of PM2.5, and
for each quarter of the year, to reflect their differing responses to
seasonal meteorological conditions and emissions. Because each species
is handled separately, before applying an RRF, the base year
PM2.5 design value must first be split into its species
components, using available chemical species measurements. The Modeling
Guidance provides additional detail on the recommended approach.\114\
---------------------------------------------------------------------------

    \112\ Memorandum dated November 29, 2018, from Richard Wayland,
Air Quality Assessment Division, OAQPS, EPA, to Regional Air
Division Directors, EPA, Subject: ``Modeling Guidance for
Demonstrating Air Quality Goals for Ozone, PM2.5, and
Regional Haze,'' (``Modeling Guidance''), and Memorandum dated June
28, 2011, from Tyler Fox, Air Quality Modeling Group, OAQPS, EPA, to
Regional Air Program Managers, EPA, Subject: ``Update to the 24 Hour
PM2.5 NAAQS Modeled Attainment Test,'' (``Modeling
Guidance Update'').
    \113\ In this section, we use the terms ``base case,'' ``base
year'' or ``baseline,'' and ``future year'' as described in section
2.3 of the EPA's Modeling Guidance. The ``base case'' modeling
simulates measured concentrations for a given time period, using
emissions and meteorology for that same year. The modeling ``base
year'' (which can be the same as the base case year) is the
emissions starting point for the plan and for projections to the
future year, both of which are modeled for the attainment
demonstration. Modeling Guidance, 37-38. Note that CARB sometimes
uses ``base year'' synonymously with ``base case'' and ``reference
year'' instead of ``base year.''
    \114\ Modeling Guidance, section 4.4, ``What is the Modeled
Attainment Tests for the Annual Average PM2.5 NAAQS.''
---------------------------------------------------------------------------

2. Summary of State's Submission
    The 2018 PM2.5 Plan includes a modeled demonstration
projecting that the SJV will attain the 2012 annual PM2.5
NAAQS by December 31, 2025. The Plan's primary discussion of the
photochemical modeling appears in Appendix K (``Modeling Attainment
Demonstration'') of the 2018 PM2.5 Plan. The State briefly
summarizes the area's air quality problem in Chapter 2.2 (``Air Quality
Challenges and Trends'') and summarizes the modeling results in Chapter
7.4 (``Attainment Demonstration and Modeling'') of the 2018
PM2.5 Plan. The State provides a conceptual model of
PM2.5 formation in the SJV as part of the modeling protocol
in Appendix L (``Modeling Protocol''). Appendix J (``Modeling Emission
Inventory'') describes emission input preparation procedures. The State
presents additional relevant information in Appendix C (``Weight of
Evidence Analysis'') of the CARB 2018 Staff Report, which includes
ambient trends and other data in support of the demonstration of
attainment by 2025.
3. EPA Evaluation and Conclusion
    CARB's air quality modeling approach investigated the many
interconnected facets of modeling ambient PM2.5 in the SJV,
including model input preparation, model performance evaluation, use of
the model output for the numerical NAAQS attainment test, and modeling
documentation. Specifically, this required the development and
evaluation of a conceptual model, modeling protocol, episode (i.e.,
base year) selection, modeling domain, CMAQ model selection, initial
and boundary condition procedures, meteorological model choice and
performance, modeling emissions inventory preparation procedures, model
performance, attainment test procedure, and adjustments to baseline air
quality for modeling. These analyses are generally consistent with the
EPA's recommendations in the Modeling Guidance.
    The model performance evaluation in section 5.2 (``CMAQ Model
Evaluation'') of Appendix K of the 2018 PM2.5 Plan included
statistical and graphical measures of model performance.
    The EPA's evaluation of the modeling for the 2012 annual
PM2.5 NAAQS incorporates the evaluation that the EPA
previously did for other NAAQS in the

2018 PM2.5 Plan. The EPA previously evaluated and approved
the modeling conducted for the 2006 24-hour PM2.5 NAAQS as
part of the 2018 PM2.5 Plan; see the EPA's ``Technical
Support Document, EPA Evaluation of Air Quality Modeling, San Joaquin
Valley PM2.5 Plan for the 2006 PM2.5 NAAQS,''
February 2020 (``EPA's 2006 NAAQS Modeling TSD'') accompanying that
action for details.\115\ The conclusions in the EPA's 2006 NAAQS
Modeling TSD focused on the 2006 24-hour PM2.5 NAAQS; in
this notice we extend the evaluation with information specific to the
2012 annual PM2.5 NAAQS.
---------------------------------------------------------------------------

    \115\ The model performance is discussed further in section J
(``Air Quality Model Performance'') of the EPA's 2006 NAAQS Modeling
TSD.
---------------------------------------------------------------------------

    Most aspects of the 2018 PM2.5 Plan modeling and the
EPA's evaluation of it are the same for the 24-hour and the annual
averaging times, and the EPA has found them adequate. These include the
modeling protocol, choice of model, meteorological modeling, modeling
emissions inventory, choice of model, modeling domain, and procedures
for model performance evaluation. One aspect that differs between the
24-hour and annual averaging times is the specific calculation
procedure for estimating a future design value. In the procedure
recommended in the Modeling Guidance for both averaging times, the
model is used to calculate RRFs, the ratio of modeled future
concentrations to base year concentrations, and the RRF is applied to
monitored base year concentrations; this is done for each monitor,
PM2.5 species, and calendar quarter. But for the 24-hour
averaging time, the recommended procedure uses the highest individual
concentration days in each quarter, whereas for the annual average, it
uses the average of all days in each quarter. For the current action on
the 2018 PM2.5 Plan, the EPA considers that the State
procedures \116\ for estimating future design values for the 2012
annual PM2.5 NAAQS generally followed the EPA's
recommendations and are adequate.
---------------------------------------------------------------------------

    \116\ 2018 PM2.5 Plan, App. K, 18.
---------------------------------------------------------------------------

    Another modeling aspect that can differ between 24-hour and annual
average is the focus of the model performance evaluation on the
respective averaging times. For the 24-hour average, it is especially
important that modeled concentrations on the highest days are
comparable to those on the highest monitored days because calculation
of the design value for the 24-hour PM2.5 NAAQS uses the
98th percentile concentrations. For the annual average, peak
concentrations continue to be important, but lower concentration days
are also important because all days are included in the average. Under-
and over-predictions on non-peak days may average out and have little
overall effect on the modeled annual concentration, but systematic
underprediction on non-peak days could lead to model underprediction of
the annual average concentration. This problem of model bias is
mitigated by the use of the model in a relative sense as recommended in
the Modeling Guidance. In the RRF, model bias ``cancels out'' to a
degree since it would be present in both its numerator (future year)
and its denominator (base year). Applying the RRF to monitored base
year concentration in this way anchors the final model prediction to
real-world concentrations. Further, the Modeling Guidance recommends
that RRFs be calculated on a quarterly basis, to better account for
emissions sources and atmospheric chemistry that differ between the
seasons.
    The 2018 PM2.5 Plan did not include a separate model
performance evaluation for the 24-hour and annual PM2.5
averaging times; the State used statistical and graphical analyses
applicable to both. The EPA evaluated the modeling for the 2012 annual
PM2.5 NAAQS using that same information, much of which has
already been discussed in the EPA's 2006 NAAQS Modeling TSD. For the
most part, in the EPA's 2006 NAAQS Modeling TSD, the EPA did not
distinguish between the two averaging times either, but drew
conclusions for the 24-hour averaging time rather than the annual
averaging time. That TSD did note a relatively large negative
normalized bias (underprediction) in the ammonium and nitrate
performance statistics \117\ for the 2nd quarter for monitoring sites
in Bakersfield, Fresno, and Visalia; and we add here that the 3rd
quarter has similar negative bias. Underprediction of total
PM2.5 in the 2nd and 3rd quarters is also evident in time
series plots for most monitoring sites, though by only a small amount
for several monitoring sites.\118\ The RRF procedure removes much of
this bias, so the underprediction in the model performance evaluation
does not translate into an underpredicted 2025 design value. The EPA's
2006 NAAQS Modeling TSD noted that because those quarters have
projected concentrations that are less than half of those in the 1st
and 4th, this may have a small influence on annual average
concentrations. It has still less influence on the 24-hour average,
because peak 24-hour concentrations typically occur in winter, i.e., in
the 1st and 4th quarters. For example, the worst quarterly
underprediction for nitrate was a for quarter 3, and occurred when
quarterly total PM2.5 concentration was 9.4 [mu]g/m\3\. By
contrast, for quarter 1 nitrate had a small overprediction, and
occurred when quarterly total PM2.5 concentration was 21.1
[mu]g/m\3\. That is, nitrate predictions have more bias during the
quarters with low PM2.5 concentrations. This is apparent
from the Plan's ``bugle'' plot for the four monitors with speciated
data.\119\ Large (negative) values of bias in nitrate predictions occur
for the lowest quarterly nitrate concentrations. For the higher
concentrations that most affect the annual average, nitrate fractional
bias has a mixture of positive and negative values. For total
PM2.5, fractional bias has a similar seasonal pattern to
that of nitrate, with underprediction during quarter 2 and quarter 3
when quarterly PM2.5 concentration values are in the 5-10
[mu]g/m\3\ range, and small bias when quarterly concentrations are in
the 20-30 [mu]g/m\3\ range. For the overall annual average, performance
is good relative to that seen in other modeling studies with lower
values of bias and error for multiple performance statistics for
nitrate, as well as for the other PM2.5 species and total
PM2.5.\120\
---------------------------------------------------------------------------

    \117\ Id. at App. K, 48ff, tables 20 through 23.
    \118\ Id. at App. K, 131ff, Supplemental materials, Figures
S.41-S.52.
    \119\ Id. at App. K, 53, Figure 13.
    \120\ Id. at App. K, 54, Figure 14.
---------------------------------------------------------------------------

    The high PM2.5 concentration days are generally captured
by the model, even though some are underpredicted in December at
certain monitoring sites such as Fresno. Overall, the modeled site
maxima are comparable to the measurements. Also, the frequency of high
and low days generally matches observations so the annual as well as
the daily model performance is acceptable.
    The EPA evaluated, in our rulemaking with respect to the 2006 24-
hour PM2.5 NAAQS in the SJV, the State's choice of model and
the extensive discussion in the 2018 PM2.5 Plan about
modeling procedures, tests, and performance analyses.\121\ We consider
the State's analyses consistent with the EPA's guidance on modeling for
PM2.5 attainment planning purposes. Based on these reviews,
we propose to find that the modeling in the 2018 PM2.5 Plan
is adequate for the purposes of supporting

the State's RFP demonstration and the attainment demonstration.
---------------------------------------------------------------------------

    \121\ For a more detailed summary of the State's air quality
modeling in the 2018 PM2.5 Plan with respect to the 2006
24-hour PM2.5 NAAQS, rather than the 2012 annual
PM2.5 NAAQS, please refer to the EPA's 2006 NAAQS
Modeling TSD.
---------------------------------------------------------------------------

D. Best Available Control Measures

1. Statutory and Regulatory Requirements
    Section 189(b)(1)(B) of the Act requires for any serious
PM2.5 nonattainment area that the state submit provisions to
assure that the best available control measures (BACM) for the control
of PM2.5 and PM2.5 precursors shall be
implemented no later than four years after the date the area is
reclassified as a Serious area. The EPA has defined BACM in the
PM2.5 SIP Requirements Rule to mean ``any technologically
and economically feasible control measure that can be implemented in
whole or in part within 4 years after the date of reclassification of a
Moderate PM2.5 nonattainment area to Serious and that
generally can achieve greater permanent and enforceable emissions
reductions in direct PM2.5 emissions and/or emissions of
PM2.5 plan precursors from sources in the area than can be
achieved through the implementation of RACM on the same source(s). BACM
includes best available control technology (BACT).'' \122\
---------------------------------------------------------------------------

    \122\ 40 CFR 51.1000 (definitions). In longstanding guidance,
the EPA has similarly defined BACM to mean, ``among other things,
the maximum degree of emissions reduction achievable for a source or
source category, which is determined on a case-by-case basis
considering energy, environmental, and economic impacts.'' General
Preamble Addendum, 42010, 42013.
---------------------------------------------------------------------------

    The EPA generally considers BACM a control level that goes beyond
existing RACM-level controls, for example by expanding the use of RACM
controls or by requiring preventative measures instead of
remediation.\123\ Indeed, as implementation of BACM and BACT is
required when a Moderate nonattainment area is reclassified as Serious
due to its inability to attain the NAAQS through implementation of
``reasonable'' measures, it is logical that ``best'' control measures
should represent a more stringent and potentially more costly level of
control.\124\ If RACM and RACT level controls of emissions have been
insufficient to reach attainment, the CAA contemplates the
implementation of more stringent controls, controls on more sources, or
other adjustments to the control strategy necessary to attain the NAAQS
in the area.
---------------------------------------------------------------------------

    \123\ 81 FR 58010, 58081 and General Preamble Addendum, 42011,
42013.
    \124\ Id. and General Preamble Addendum, 42009-42010.
---------------------------------------------------------------------------

    Consistent with longstanding guidance provided in the General
Preamble Addendum, the preamble to the PM2.5 SIP
Requirements Rule discusses the following steps for determining BACM
and BACT:
    1. Develop a comprehensive emission inventory of the sources of
PM2.5 and PM2.5 precursors;
    2. Identify potential control measures;
    3. Determine whether an available control measure or technology is
technologically feasible;
    4. Determine whether an available control measure or technology is
economically feasible; and
    5. Determine the earliest date by which a control measure or
technology can be implemented in whole or in part.\125\
---------------------------------------------------------------------------

    \125\ 81 FR 58010, 58083-58085.
---------------------------------------------------------------------------

    The EPA allows consideration of factors such as physical plant
layout, energy requirements, needed infrastructure, and workforce type
and habits when considering technological feasibility. For purposes of
evaluating economic feasibility, the EPA allows consideration of
factors such as the capital costs, operating and maintenance costs, and
cost effectiveness (i.e., cost per ton of pollutant reduced by a
measure or technology) associated with the measure or control.\126\
---------------------------------------------------------------------------

    \126\ 40 CFR 51.1010(a)(3) and 81 FR 58010, 58041-58042.
---------------------------------------------------------------------------

    Once these analyses are complete, the state must use this
information to develop enforceable control measures and submit them to
the EPA for evaluation as SIP provisions to meet the basic requirements
of CAA section 110 and any other applicable substantive provisions of
the Act. The EPA is using these steps as guidelines in the evaluation
of the BACM and BACT measures and related analyses in the SJV
PM2.5 Plan.
2. Summary of State's Submission
    As discussed in section IV.A of this proposed rule, Appendix B of
the 2018 PM2.5 Plan contains the planning inventories for
direct PM2.5 and all PM2.5 precursors
(NOX, SOX, VOC, and ammonia) for the SJV
nonattainment area together with documentation to support these
inventories. Each inventory includes emissions from stationary, area,
on-road, and non-road emission sources, and the State specifically
identifies the condensable component of direct PM2.5 for
relevant stationary and area source categories. As discussed in section
IV.B of this proposed rule concerning precursors, the State's analysis
indicates that the Plan should control emissions of PM2.5
and NOX in order to reach attainment. Accordingly, the State
evaluated potential controls for those pollutants in the analysis of
what is necessary to meet the BACM (including BACT) requirements.
    For stationary and area sources, the District identifies the
sources of direct PM2.5 and NOX in the SJV that
are subject to District emission control measures and provides its
evaluation of these regulations for compliance with BACM requirements
in Appendix C of the 2018 PM2.5 Plan. As part of its process
for identifying candidate BACM and considering the technical and
economic feasibility of additional control measures, the District
reviewed the EPA's guidance documents on BACM, additional guidance
documents on control measures for direct PM2.5 and
NOX emission sources, and control measures implemented in
other ozone and PM2.5 nonattainment areas in California and
other states.\127\ Based on these analyses, the District concludes that
all best available control measures for stationary and area sources are
in place in the SJV for NOX and directly emitted
PM2.5 for purposes of meeting the BACM/BACT requirement for
the 2012 annual PM2.5 NAAQS.
---------------------------------------------------------------------------

    \127\ 2018 PM2.5 Plan, Ch. 4, section 4.3.1.
---------------------------------------------------------------------------

    For mobile sources, CARB identifies the sources of direct
PM2.5 and NOX in the SJV that are subject to the
State's emission control measures and provides its evaluation of these
regulations for compliance with BACM requirements in Appendix D of the
2018 PM2.5 Plan. Appendix D describes CARB's process for
determining BACM, including identification of the sources of direct