[Federal Register Volume 86, Number 167 (Wednesday, September 1, 2021)]
[Proposed Rules]
[Pages 49100-49137]
[FR Doc No: 2021-18764]

Vol. 86

Wednesday,

No. 167

September 1, 2021

Part II

Environmental Protection Agency

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40 CFR Parts 52 and 81

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Clean Air Plans; California; San Joaquin Valley Moderate Area Plan and
Reclassification as Serious Nonattainment for the 2012 PM2.5 NAAQS;
Contingency Measures for the 2006 PM2.5 NAAQS; Proposed Rules

Federal Register / Vol. 86, No. 167 / Wednesday, September 1, 2021 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 52 and 81

[EPA-R09-OAR-2021-0543; FRL-8846-01-R9]

Clean Air Plans; California; San Joaquin Valley Moderate Area
Plan and Reclassification as Serious Nonattainment for the 2012 PM2.5
NAAQS; Contingency Measures for the 2006 PM2.5 NAAQS

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) proposes to take
action on portions of four state implementation plan (SIP) revisions
submitted by California to address Clean Air Act (CAA or ``Act'')
requirements for the 2012 fine particulate matter (PM2.5)
national ambient air quality standards (NAAQS or ``standards'') and for
the 2006 PM2.5 NAAQS in the San Joaquin Valley (SJV)
PM2.5 nonattainment area. Specifically, the EPA proposes to
approve all but the contingency measure element of the submitted
Moderate area plan for the 2012 PM2.5 NAAQS, as updated by
the submitted Serious area plan and related Valley State SIP Strategy,
as meeting all applicable Moderate area plan requirements for the 2012
PM2.5 NAAQS and to approve 2022 motor vehicle emissions
budgets for use in transportation conformity analyses for the 2012
PM2.5 NAAQS. The EPA proposes to disapprove the contingency
measure element with respect to the ``Moderate'' area requirements for
the 2012 PM2.5 NAAQS. The EPA also proposes to reclassify
the SJV PM2.5 nonattainment area, including reservation
areas of Indian country and any other area of Indian country within it
where the EPA or a tribe has demonstrated that the tribe has
jurisdiction, as a ``Serious'' nonattainment area for the 2012
PM2.5 NAAQS based on the EPA's determination that the area
cannot practicably attain the standard by the applicable Moderate area
attainment date of December 31, 2021. Upon final reclassification of
the SJV as a Serious area for this NAAQS, California would be required
to submit a Serious area plan for the area that includes a
demonstration of attainment by the applicable Serious area attainment
date, which is no later than December 31, 2025, or by the most
expeditious alternative date practicable. However, we note that
California has already submitted such Serious area plan that the EPA
will address in a separate rulemaking. Lastly, the EPA is proposing to
disapprove the contingency measure element in the Serious area plan for
the 2006 PM2.5 NAAQS.

DATES: Any comments on this proposal must be received by October 1,
2021.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2021-0543 at https://www.regulations.gov, or via email to
<EMAIL_ADDRESS>For comments submitted at Regulations.gov, follow
the online instructions for submitting comments. Once submitted,
comments cannot be edited or removed from Regulations.gov. For either
manner of submission, 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 (e.g., audio or video) must be accompanied by a written
comment. The written comment is considered the official comment and
should include discussion of all points you wish to make. The EPA will
generally not consider comments or comment contents located outside of
the primary submission (i.e., on the web, cloud, or other file sharing
system). For additional submission methods, please contact the person
identified in the FOR FURTHER INFORMATION CONTACT section. For the full
EPA public comment policy, information about CBI or multimedia
submissions, and general guidance on making effective comments, please
visit https://www.epa.gov/dockets/commenting-epa-dockets. If you need
assistance in a language other than English or if you are a person with
disabilities who needs a reasonable accommodation at no cost to you,
please contact the person identified in the FOR FURTHER INFORMATION
CONTACT section.

FOR FURTHER INFORMATION CONTACT: Rory Mays, Air Planning Office (AIR-
2), EPA Region IX, by phone at<PHONE_NUMBER> or email at
<EMAIL_ADDRESS>
SUPPLEMENTARY INFORMATION: Throughout this document, ``we,'' ``us,'' or
``our'' refer to the EPA.

Table of Contents

I. Background for Proposed Action
II. Summary of San Joaquin Valley 2016 and 2018 PM2.5
Plans
    A. 2016 PM2.5 Plan Summary
    B. 2018 PM2.5 Plan Summary
    C. Procedural Requirements for SIPs and SIP Revisions
III. Clean Air Act Requirements for Moderate PM2.5
Nonattainment Area Plans
IV. Review of San Joaquin Valley Plans for Moderate Area
Requirements
    A. Emissions Inventory
    B. PM2.5 Precursors
    C. Air Quality Modeling
    D. Reasonably Available Control Measures and Control Strategy
    E. Nonattainment New Source Review Requirements Under CAA
Section 189(e)
    F. Demonstration That Attainment by Moderate Area Attainment
Date Is Impracticable
    G. Reasonable Further Progress and Quantitative Milestones
    H. Contingency Measures
    I. Motor Vehicle Emissions Budgets
V. Reclassification as Serious Nonattainment and Serious Area SIP
Requirements
    A. Reclassification as Serious and Applicable Attainment Date
    B. Clean Air Act Requirements for Serious Area Plans
    C. Statutory Deadline for Submission of Serious Area Plan
VI. Reclassification of Areas of Indian Country
VII. Review of Contingency Measure Element for the 2006
PM2.5 NAAQS
    A. Requirements for Contingency Measures
    B. Summary of State's Contingency Measure Element for 2006
PM2.5 NAAQS
    C. EPA Evaluation and Proposed Action
VIII. Summary of Proposed Actions and Request for Public Comment
IX. 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 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 PM2.5 NAAQS'').
71 FR 61144 and 40 CFR 50.13. Unless otherwise noted, all references
to the PM2.5 standards in this notice are to the 2012
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\
PM2.5 can be emitted directly into the atmosphere as a solid
or liquid particle (``primary PM2.5'' or ``direct
PM2.5'') or can be formed 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. Under subpart 4 of part D of
title I of the CAA and applicable implementing regulations, the EPA
designates areas found to be violating the PM2.5 NAAQS, and
areas with emissions that contribute to such violations, as
nonattainment and classifies them initially as Moderate.\4\ States with
Moderate areas have to attain the NAAQS as expeditiously as
practicable, but not later than the end of the sixth calendar year
after the date of designation.\5\ The EPA reclassifies as Serious those
Moderate areas that cannot practicably attain the NAAQS by the latest
statutory attainment date and those areas that fail to attain the NAAQS
by the applicable attainment date. States with Serious areas are
subject to more stringent SIP revision requirements and must attain the
NAAQS as expeditiously as practicable, but not later than the end of
the tenth calendar year after designation.
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    \4\ CAA section 188(a) and 40 CFR 51.1002(a).
    \5\ CAA section 188(c)(1) and 40 CFR 51.1004(a)(1)(i).
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    On January 15, 2015, the EPA designated and classified the SJV as
Moderate nonattainment for the 2012 PM2.5 NAAQS.\6\ With
respect to the 1997 PM2.5 NAAQS and the 2006
PM2.5 NAAQS, the SJV is designated nonattainment and is
classified as Serious.\7\ 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.\8\ 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. Under State law, the San Joaquin Valley Unified Air Pollution
Control District (SJVUAPCD or ``District'') has primary responsibility
for developing plans to provide for attainment of the NAAQS in this
area. The District works cooperatively with the California Air
Resources Board (CARB) in preparing these 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 and some categories of consumer products.
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    \6\ 80 FR 2206 (codified at 40 CFR 81.305).
    \7\ See the tables of area designations for the 1997 and 2006
PM2.5 NAAQS in 40 CFR 81.305.
    \8\ For a precise description of the geographic boundaries of
the SJV PM2.5 nonattainment area, see 40 CFR 81.305.
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    States with areas designated as nonattainment are required to
submit SIP revisions that address various requirements, including the
requirement to demonstrate attainment of the NAAQS as expeditiously as
practicable but no later than the maximum attainment date established
in the CAA or EPA's implementing regulations. However, states with
Moderate PM2.5 nonattainment areas may submit an
impracticability demonstration, in lieu of a modeled attainment
demonstration, if the state can establish that the area cannot
practicably attain a particular PM2.5 NAAQS by the outermost
statutory Moderate area attainment date.\9\
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    \9\ 40 CFR 51.1002(b)(1).
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    On May 10, 2019, CARB made two SIP submissions intended to address
the attainment plan requirements for areas designated as nonattainment
for the 2012 PM2.5 NAAQS.\10\ First, the ``2016 Moderate
Area Plan for the 2012 PM2.5 Standard'' (``2016
PM2.5 Plan'') addresses the Moderate area attainment plan
requirements and includes a demonstration of impracticability of
attaining the 2012 PM2.5 NAAQS in the SJV by the latest
permissible Moderate area attainment date of December 31, 2021. In this
document, the EPA is proposing action on all portions of the 2016
PM2.5 Plan. Second, the ``2018 Plan for the 1997, 2006, and
2012 PM2.5 Standards'' (``2018 PM2.5 Plan'')
addresses the Serious area attainment plan requirements for the 2012
PM2.5 NAAQS, in anticipation of the reclassification of SJV
from Moderate to Serious for that PM2.5 NAAQS. The 2018
PM2.5 Plan incorporates by reference the ``San Joaquin
Valley Supplement to the 2016 State Strategy for the State
Implementation Plan'' (``Valley State SIP Strategy''), a related plan
adopted by CARB on October 25, 2018, and submitted to the EPA with the
2018 PM2.5 Plan on May 10, 2019. For the purposes of this
action, the relevant portion of the Valley State SIP Strategy includes
the control measure commitments associated with the quantitative
milestones for 2019 and 2022.
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    \10\ CARB submitted the two plans electronically on May 10,
2019, as an attachment to a letter dated May 9, 2019, from Richard
W. Corey, Executive Officer, CARB, to Mike Stoker, Regional
Administrator, EPA Region IX.
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    The 2018 PM2.5 Plan updates several elements in the 2016
PM2.5 Plan, including the base year emissions inventory,
plan precursor demonstration, controls analysis, reasonable further
progress (RFP) and quantitative milestones, and motor vehicle emission
budgets (MVEBs or ``budgets''). In this document, the EPA is proposing
action on those portions of the 2018 PM2.5 Plan that apply
to the Moderate area plan requirements for the 2012 PM2.5
NAAQS. However, the EPA is not, at this time, proposing to act on those
portions of the 2018 PM2.5 Plan that are not relevant to our
evaluation of compliance with Moderate area plan requirements for 2012
PM2.5 NAAQS, such as the best available control measures
(BACM) demonstration, control strategy commitments, attainment
demonstration, RFP demonstration and quantitative milestones for later
years, and MVEBs for later years.
    The 2018 PM2.5 Plan also addresses attainment plan
requirements for areas classified as Serious for the 2006
PM2.5 NAAQS. In 2020, we approved those portions of the 2018
PM2.5 Plan that pertain to the 2006 PM2.5 NAAQS,
excluding the contingency measures element for the 2006
PM2.5 NAAQS.\11\ In this document, we are proposing action
on the portion of the 2018 PM2.5 Plan that addresses the
contingency measure requirement for the 2006 PM2.5 NAAQS.
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    \11\ 85 FR 44192 (July 22, 2020).
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    Lastly, the 2018 PM2.5 Plan addresses the contingency
measure requirement for the 2006 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.\12\ 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 requirement in the rule with a trigger that would activate
the requirement should the EPA issue a final rulemaking that SJV failed
to meet a regulatory requirement necessitating implementation of a
contingency measure.
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    \12\ 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 a contingency measure. On July 19, 2019, CARB submitted
the amended rule to the EPA for approval.\13\ We have already taken
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.\14\
Rather, we approved the new provision (section 5.7.3) into the SIP as
part of our approval of the entire amended rule 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. 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 2016 PM2.5 Plan for the 2012 PM2.5
NAAQS and the contingency measure element in the 2018 PM2.5
Plan for the 2006 PM2.5 NAAQS.
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    \13\ Letter dated July 19, 2019, from Richard W. Corey,
Executive Officer, CARB, to Mike Stoker, Regional Administrator, EPA
Region IX.
    \14\ 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).
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II. Summary of San Joaquin Valley 2016 and 2018 PM2.5 Plans

A. 2016 PM2.5 Plan Summary

    The SJVUAPCD Governing Board adopted the 2016 PM2.5 Plan
on September 15, 2016, and CARB adopted the plan on January 24,
2019.\15\ CARB submitted the plan to the EPA on May 10, 2019.
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    \15\ SJVUAPCD Governing Board Resolution 16-9-10, September 15,
2016, and CARB Resolution 19-1, January 24, 2019.
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    The 2016 PM2.5 Plan is organized into three chapters,
five appendices, and two attachments. Chapter 1 (``Introduction'')
provides general background, including discussion of the federal
PM2.5 standards, PM2.5 pollution and health
effects in the SJV, challenges to attaining the standards, and the
District's public process. Chapter 2 (``Impracticability Demonstration
and Request for Reclassification'') presents CARB and the District's
demonstration, based on air quality modeling, that attaining the 2012
PM2.5 NAAQS by the latest permissible attainment date of
December 31, 2021, is impracticable, and a request for reclassification
to Serious. Chapter 3 (``Demonstration of Federal Clean Air Act
Requirements'') describes how the 2016 PM2.5 Plan addresses
the federal requirements for Moderate PM2.5 nonattainment
areas, including a plan precursor demonstration, reasonably available
control measures, RFP, quantitative milestones, contingency measures,
stationary source permitting, and transportation conformity. The 2016
PM2.5 Plan includes the following five technical appendices:
     Appendix A (``Air Quality Modeling'') provides the State's
photochemical air quality modeling in support of the plan's
impracticability demonstration and precursor demonstration;
     Appendix B (``Emissions Inventory'') presents the base
year and future year emissions inventory for direct PM2.5,
NOX, ammonia, SOX, and VOC;
     Appendix C (``SIP Creditable Incentive-Based Emission
Reductions'') provides a demonstration of NOX emission
reductions from heavy-duty off-road vehicle engine vehicle replacements
under the 2011 Carl Moyer Guidelines in support of the plan's Moderate
contingency measure element;
     Appendix D (``New Source Review and Emission Reduction
Credits'') discusses the use of emission reduction credits (ERCs) in
the context of the plan; and
     Appendix E (``Summary of Significant Comments and
Responses'') summarizes significant comments received during the
District's 2016 public review period and the District's responses
thereto.
    In addition, the 2016 PM2.5 Plan includes Attachment 1
(``Stationary and Area Source Control Measure Analyses'') and
Attachment 2 (``Mobile Source Control Measure Analyses''), which
together resubmit the State's 2015 analyses that the District's
stationary and area source control measures and CARB's mobile source
control measures represent BACM and most stringent measures (MSM).
    Lastly, on December 13, 2019, CARB submitted the following two
additional documents that CARB had prepared for the 2016
PM2.5 Plan and made available for public review along with
the plan, but had inadvertently omitted them from the May 10, 2019 SIP
submission to the EPA: \16\ (i) The ``Staff Report, ARB Review of the
San Joaquin Valley 2016 Moderate Area Plan for the 2012
PM2.5 Standard,'' released September 16, 2016 (``CARB 2016
Staff Report''), that provides CARB's staff review of the 2016
PM2.5 Plan, including brief summaries for each of the
Moderate area plan requirements; and (ii) the ``Modeling Emission
Inventory for the PM2.5 State Implementation Plan in the San
Joaquin Valley,'' August 23, 2016 (``2016 Modeling Emissions
Inventory'') that describes the development of the 2016
PM2.5 Plan's modeling emissions inventory, estimation of the
2013 base year emissions inventory, the methodology used to develop the
base year and baseline emissions inventory, and quality assurance of
the modeling emissions inventory.
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    \16\ Letter dated December 11, 2019, from Richard W. Corey,
Executive Officer, CARB, to Mike Stoker, Regional Administrator, EPA
Region IX, with enclosures.
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B. 2018 PM2.5 Plan Summary

    The SJVUAPCD Governing Board adopted the 2018 PM2.5 Plan
on November 15, 2018, and CARB adopted the plan on January 24,
2019.\17\ CARB submitted the 2018 PM2.5 Plan to the EPA on
May 10, 2019, concurrently with the 2016 PM2.5 Plan.
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    \17\ SJVUAPCD Governing Board Resolution 18-11-16, November 15,
2018, and CARB Resolution 19-1, January 24, 2019.
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    The following portions of the 2018 PM2.5 Plan and
related support documents apply to the Moderate area attainment plan
requirements for the 2012 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''); \18\ (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 2018 Staff Report''); \19\ and (v) the State's and District's
board resolutions adopting the 2018 PM2.5 Plan.\20\
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    \18\ 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 PM2.5 NAAQS, respectively. The EPA has
acted on Chapter 6 in our rulemaking for the 2006 PM2.5
NAAQS. See 80 FR 44192 (July 22, 2020). The EPA has proposed to act
on Chapter 5 as part of a separate rulemaking on the 1997 annual
PM2.5 NAAQS. See 86 FR 38652 (July 22, 2021).
    \19\ The CARB 2018 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 2018 Staff
Report [on the 2018 PM2.5 Plan].
    \20\ 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.
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    The appendices to the 2018 PM2.5 Plan, in order of their
evaluation in this proposal, include the following: (i) Appendix
(``App.'') B (``Emissions Inventory''); (ii) 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 2018 Staff Report; (iii) control
strategy appendices, including App. C (``Stationary Source Control
Measure Analyses'') and App. D (``Mobile Source Control Measures
Analyses''); and (iv) App. H (``RFP, Quantitative Milestones, and
Contingency''). The 2018 PM2.5 Plan addresses requirements
for MVEBs in the ``Transportation Conformity'' section of App. D.\21\
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    \21\ See D-119 to D-131.
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    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 appendices on ``Public Education and Technology Advancement''
(App. F), ``Ambient PM2.5 Data Analysis'' (App. A), ``New
Source Review and Emission Reduction Credits'' (App. I) and ``Summary
of Significant Comments and Responses'' (App. M), as well other
chapters and appendices that are primarily relevant to the Serious area
plan requirements, including App. E (``Incentive-Based Strategy''),
App. J (``Modeling Emission Inventory''), App. K (``Modeling Attainment
Demonstration''), and App. L (``Modeling Protocol'').
    Lastly, on February 11, 2020, CARB submitted, via the EPA State
Planning Electronic Collaboration System, a revised version of App. H
(``RFP, Quantitative Milestones, and Contingency'') that replaces the
version submitted with the 2018 PM2.5 Plan on May 10, 2019.
All references to App. H of the 2018 PM2.5 Plan in this
proposed rule are to the revised version of Appendix H submitted
February 11, 2020.

C. Procedural Requirements for SIPs and SIP Revisions

    Sections 110(a)(1) and (2) and 110(l) of the CAA require each state
to provide reasonable public notice and an opportunity for a public
hearing prior to the adoption and submittal 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 an opportunity for a
public hearing was provided consistent with the EPA's implementing
regulations in 40 CFR 51.102.
    Both the District and CARB satisfied applicable statutory and
regulatory requirements for reasonable public notice and hearing prior
to adoption and submission of the 2016 PM2.5 Plan and the
2018 PM2.5 Plan. The District provided public notice and
opportunity for public comment prior to its September 15, 2016 public
hearing on and adoption of the 2016 PM2.5 Plan.\22\ CARB
also provided public notice and opportunity for public comment prior to
its October 20, 2016 public hearing,\23\ where the 2016
PM2.5 Plan was tabled.
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    \22\ SJVUAPCD, ``Notice of Public Hearing, Adopt the Proposed
2016 Moderate Area Plan for the 2012 PM2.5 Standard,''
August 16, 2016, and SJVUAPCD Governing Board Resolution 16-9-10.
    \23\ CARB, ``Notice of Public Meeting to Consider the 2016
PM2.5 State Implementation Plan for the San Joaquin
Valley,'' September 20, 2016.
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    Subsequently, 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.\24\ CARB also provided
public notice and opportunity for public comment prior to its January
24, 2019 public hearing,\25\ when CARB adopted the 2016
PM2.5 Plan and the 2018 PM2.5 Plan.\26\ 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.27 28
Therefore, we find that the 2016 PM2.5 Plan and the 2018
PM2.5 Plan meet the procedural requirements for public
notice and hearing in CAA sections 110(a) and 110(l) and 40 CFR 51.102.
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    \24\ 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.
    \25\ CARB, ``Notice of Public Meeting to Consider the 2018
PM2.5 State Implementation Plan for the San Joaquin
Valley,'' December 21, 2018.
    \26\ CARB Resolution 19-1. See also J&K Court Reporting, LLC,
``Meeting, State of California Air Resources Board,'' October 20,
2016 (transcript of CARB's public hearing), 186-190.
    \27\ For the 2016 PM2.5 Plan: CARB, ``Board Meeting
Comments Log,'' available at https://www.arb.ca.gov/lispub/comm/bccommlog.php?listname=sjvpmplan2016 (accessed August 20, 2021); J&K
Court Reporting, LLC, ``Meeting, State of California Air Resources
Board,'' October 16, 2016 (transcript of CARB's public hearing),
available at https://ww3.arb.ca.gov/board/mt/2016/mt102016.pdf
(accessed December 29, 2020); and 2016 PM2.5 Plan, App. E
(``Summary of Significant Comments and Responses''), noting that no
comments were received during the District's 2016 public review.
    \28\ For the 2018 PM2.5 Plan: 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'').
---------------------------------------------------------------------------

    We present our evaluation of the 2016 PM2.5 Plan (and
2018 PM2.5 Plan as applicable to the Moderate area
attainment plan requirements for the 2012 PM2.5 NAAQS) in
Section IV of this proposed rule. We present our evaluation of the 2018
PM2.5 Plan as applicable to the contingency measure
requirements for the 2006 PM2.5 NAAQS in section VII of this
proposed rule.

III. Clean Air Act Requirements for Moderate PM2.5
Nonattainment Area Plans

    With respect to the statutory requirements for particulate matter
(PM) attainment plans, the general nonattainment area planning
requirements of title I, part D of the CAA are found in subpart 1, and
the attainment planning requirements specifically for PM are found in
subpart 4.
    The EPA has a longstanding general guidance document that
interprets the 1990 amendments to the CAA, commonly referred to as the
General Preamble for the Implementation of Title I of the Clean Air Act
Amendments of 1990 (``General Preamble'').\29\ The General Preamble
addresses the relationship between the subpart 1 and subpart 4
requirements and provides recommendations to states for meeting certain
statutory requirements for PM attainment plans. As explained in the
General Preamble, specific requirements applicable to Moderate area
attainment plan SIP submissions for the PM NAAQS are set forth in
subpart 4 of part

D, title I of the Act, but such SIP submissions must also meet the
general attainment planning provisions in subpart 1 of part D, title I
of the Act, to the extent these provisions ``are not otherwise subsumed
by, or integrally related to,'' the more specific subpart 4
requirements.\30\ The EPA provided further guidance to States on PM
plan submissions in the Addendum to the General Preamble (``General
Preamble Addendum'').\31\
---------------------------------------------------------------------------

    \29\ General Preamble, 57 FR 13498 (April 16, 1992).
    \30\ Id. at 13538.
    \31\ 59 FR 41998 (August 16, 1994).
---------------------------------------------------------------------------

    To implement the PM2.5 NAAQS, the EPA has also
promulgated the ``Fine Particle Matter National Ambient Air Quality
Standard: State Implementation Plan Requirements; Final Rule''
(``PM2.5 SIP Requirements Rule'').\32\ The PM2.5
SIP Requirements Rule establishes regulatory requirements and provides
additional guidance applicable to attainment plan submissions for the
PM2.5 NAAQS, including the 2012 annual PM2.5
NAAQS and the 2006 24-hour PM2.5 NAAQS, addressed in this
section and section VII, respectively, of this proposed rule.
---------------------------------------------------------------------------

    \32\ 81 FR 58010 (August 24, 2016).
---------------------------------------------------------------------------

    The general subpart 1 statutory requirements for attainment plans
include the following: (i) The section 172(c)(1) requirement for
reasonably available control measures (RACM)/reasonably available
control technology (RACT) and attainment demonstrations; (ii) the
section 172(c)(2) requirement to RFP; (iii) the section 172(c)(3)
requirement for emissions inventories; (iv) the section 172(c)(5)
requirement for a nonattainment new source review (NNSR) permitting
program; and (v) the section 172(c)(9) requirement for contingency
measures.
    The more specific subpart 4 statutory requirements for Moderate
PM2.5 nonattainment areas include the following: (i) The
section 189(a)(1)(A) and 189(e) NNSR permit program requirements; (ii)
the section 189(a)(1)(B) requirement for attainment demonstrations;
(iii) the section 189(a)(1)(C) requirement for RACM; and (iv) the
section 189(c) requirements for RFP and quantitative milestones. Under
subpart 4, states with Moderate PM2.5 nonattainment areas
must provide for attainment in the area as expeditiously as practicable
but no later than the latest permissible attainment date under CAA
section 188(c), i.e., December 31, 2021, for the 2012 PM2.5
NAAQS in the SJV, unless the EPA determines, per section 188(b)(1),
that the area cannot practicably attain the NAAQS by the Moderate area
attainment date.\33\ In addition, under subpart 4, direct
PM2.5 and all precursors to the formation of
PM2.5 are subject to control unless the EPA approves a
demonstration from the state establishing that a given precursor does
not contribute significantly to PM2.5 levels that exceed the
PM2.5 NAAQS in the area.\34\
---------------------------------------------------------------------------

    \33\ Generally, under CAA section 188(c), the latest permissible
attainment date for a Moderate nonattainment area is the end of the
sixth calendar year after the area's designation as nonattainment.
Because the EPA designated and classified the San Joaquin Valley as
a Moderate nonattainment area for the 2012 PM2.5 NAAQS
effective April 15, 2015 (80 FR 2206, 2217-2218), the latest
permissible attainment date for these NAAQS in the San Joaquin
Valley is December 31, 2021.
    \34\ 40 CFR 51.1006 and 51.1009.
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IV. Review of San Joaquin Valley Plans for Moderate Area Requirements

A. Emissions Inventory

1. Requirements for Emissions Inventories
    Section 172(c)(3) of the CAA 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. We refer to this inventory as the ``base year inventory.'' The
EPA has established regulatory requirements for base year and other
emissions inventories in the PM2.5 SIP Requirements Rule
\35\ and issued guidance concerning emissions inventories for
PM2.5 nonattainment areas.\36\
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    \35\ 40 CFR 51.1008.
    \36\ 81 FR 58010, 58078-58079 and ``Emissions Inventory Guidance
for Implementation of Ozone and Particulate Matter National Ambient
Air Quality Standards (NAAQS) and Regional Haze Regulations,'' EPA,
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 emissions inventory must include direct
PM2.5 emissions, separately reported filterable and
condensable PM2.5 emissions,\37\ and emissions of all
chemical precursors to the formation of secondary PM2.5:
NOX, SO2, VOC, and ammonia.\38\ In addition, the
emissions inventory base year for a Moderate PM2.5
nonattainment area must be one of the three years (i.e., 2011-2013) for
which monitored data were used to designate the area as nonattainment,
or another technically appropriate year justified by the state in its
Moderate area attainment plan submission.\39\
---------------------------------------------------------------------------

    \37\ The Emissions Inventory Guidance identifies the types of
sources for which the EPA expects states to provide condensable PM
emissions inventories. Emissions Inventory Guidance, section 4.2.1
(``Condensable PM Emissions''), 63-65.
    \38\ 40 CFR 51.1008.
    \39\ 40 CFR 51.1008(a)(1)(i).
---------------------------------------------------------------------------

    In its SIP submission, a state must include documentation
explaining how it calculated emissions data. In estimating mobile
source emissions, a state should use the latest emissions models and
planning assumptions available at the time it develops the SIP
submission. 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.40 41 At the time the 2016 PM2.5 Plan and
2018 PM2.5 Plan were developed, California was required to
use EMFAC2014 to estimate tailpipe and brake and tire wear emissions of
PM2.5, NOX, SO2, and VOC from on-road
mobile sources.\42\
---------------------------------------------------------------------------

    \40\ 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 emissions tests
results. (76 FR 6328, February 4, 2011). CARB used the revised 2011
AP-42 methodology in developing on-road mobile source emissions.
    \41\ AP-42 has been published since 1972 as the primary source
of the EPA's emission factor information. It contains emission
factors and process information for more than 200 air pollution
source categories. A source category is a specific industry sector
or group of similar emitting sources. The emission factors have been
developed and compiled from source test data, material balance
studies, and engineering estimates.
    \42\ The EMFAC model (short for EMission FACtor) is a computer
model developed by CARB. The EPA approved and announced the
availability of EMFAC2014 for use in SIP development and
transportation conformity in California on December 14, 2015 (80 FR
77337). The EPA's approval of the EMFAC2014 emissions model for SIP
and conformity purposes was effective on the date of publication in
the Federal Register. On August 15, 2019, the EPA approved and
announced the availability of EMFAC2017, the latest update to the
EMFAC model for use by state and local governments to meet CAA
requirements (84 FR 41717). EMFAC2017 was not available to the State
and District at the time they were developing the 2016
PM2.5 Plan and had only recently been submitted to the
EPA on July 20, 2018, prior to the adoption of the 2018
PM2.5 Plan.
---------------------------------------------------------------------------

    In addition to the base year inventory submitted to meet the
requirements of CAA section 172(c)(3), a state must also submit future
``baseline inventories'' for the projected attainment year, each RFP
milestone year, and any other year of significance for meeting
applicable CAA requirements.\43\ By baseline inventories we mean
projected emissions inventories for future years that account for,
among other things, the ongoing

effects of economic growth and adopted emission control requirements.
The SIP submission should include documentation to explain how the
state calculated the emissions projections.
---------------------------------------------------------------------------

    \43\ 40 CFR 51.1008(a)(2) and 51.1012(a)(2); see also Emissions
Inventory Guidance.
---------------------------------------------------------------------------

2. Summary of State's Emissions Inventories
    Within the 2016 PM2.5 Plan, the annual average planning
inventories for direct PM2.5 and all PM2.5
precursors (NOX, ammonia, SOX,\44\ and VOC) for
the SJV PM2.5 nonattainment area, together with
documentation for the inventories, are found in Appendix B (``Emissions
Inventory''). In addition, Appendix A (``Air Quality Modeling'')
contains inventory documentation specific to the air quality modeling
inventories. These portions of the 2016 PM2.5 Plan contain
annual average daily emission inventories for 2013 thru 2022 projected
from the 2012 actual emissions inventory,\45\ including the 2013 base
year, the 2019 RFP baseline year, the 2021 Moderate area attainment
year, and the 2022 post-attainment RFP year. The winter average daily
inventory is used to evaluate sources of emissions for attainment of
the 2012 PM2.5 NAAQS in the 2016 PM2.5 Plan.\46\
---------------------------------------------------------------------------

    \44\ The 2016 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.
    \45\ 2016 PM2.5 Plan, App. B, B-18.
    \46\ The 2016 PM2.5 Plan includes annual average and
winter day average inventories for PM2.5 planning
purposes. The winter average daily planning inventory corresponds to
the months of November through April, when daily, ambient
PM2.5 concentrations are typically highest. 2016
PM2.5 Plan, App. B, B-19. The base year inventory is from
the California Emissions Inventory Development and Reporting System
(CEIDARS) and future year inventories were estimated using the
California Emission Projection Analysis Model (CEPAM) version 1.04.
---------------------------------------------------------------------------

    Similarly, within the 2018 PM2.5 Plan, the annual
average planning inventories for direct PM2.5 and all
PM2.5 precursors, together with documentation for the
inventories, are found in Appendix B (``Emissions Inventory''). 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 thru 2028 projected
from the 2012 actual emissions inventory, \47\ including the 2013 base
year, the 2019 and 2022 RFP baseline years, the 2025 Serious area
attainment year, and the 2028 post-attainment RFP year. Both the annual
average and the winter average daily inventories are used to evaluate
sources of emissions for attainment of the 2012 PM2.5 NAAQS
in the 2018 PM2.5 Plan.\48\
---------------------------------------------------------------------------

    \47\ 2018 PM2.5 Plan, App. B, B-18.
    \48\ 2018 PM2.5 Plan, App. B, B-19. The base year
inventory is from CEIDARS and future year inventories were estimated
using CEPAM, version 1.05.
---------------------------------------------------------------------------

    The base year inventories for stationary sources were developed
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 2016 PM2.5 Plan and 2018
PM2.5 Plan.\49\ Importantly, CARB and the District updated
the emissions inventory in the 2018 PM2.5 Plan using the
latest available activity data and emission methodologies available at
the time of plan development. The 2013 base year, annual average
emissions inventories for most source categories did not change or only
changed plus or minus 0.1 tons per day (tpd) between the two plans.\50\
However, the base year emissions inventory from several important
source categories were smaller in the 2018 PM2.5 Plan
relative to the 2016 PM2.5 Plan based on the latest
information. These include a 1.2 tpd decrease in direct
PM2.5 emissions from residential fuel combustion based on a
2016 emissions inventory methodology update,\51\ a 0.4 tpd decrease in
direct PM2.5 emissions from farming operations based on
updated estimates by the California Department of Conservation of
harvested acreage in 2010-2020 rather than 2000-2009,\52\ and a 0.9 tpd
decrease in NOX emissions from trains based on updated
locomotive data from 2016 on Class I and Class II railroads.\53\
Overall, for the 2013 base year, total emissions of both direct
PM2.5 and NOX were 0.9 tpd smaller in the 2018
PM2.5 Plan relative to the 2016 PM2.5 Plan.
---------------------------------------------------------------------------

    \49\ 2016 PM2.5 Plan, App. B, section B.3
(``Emissions Inventory Summary and Methodology''), and 2018
PM2.5 Plan, App. B, section B.2 (``Emissions Inventory
Summary and Methodology'').
    \50\ For example, paved road dust direct PM2.5
emissions decreased 0.1 tpd while off-road equipment NOX
emissions increased by 0.1 tpd between the 2016 and 2018
PM2.5 Plans.
    \51\ 2018 PM2.5 Plan, App. B, B-26.
    \52\ 2018 PM2.5 Plan, App. B, B-27.
    \53\ 2018 PM2.5 Plan, App. B, B-34.
---------------------------------------------------------------------------

    Furthermore, the 2016 PM2.5 Plan's emissions inventory
does not separately report filterable and condensable PM2.5
emissions. However, 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.\54\ 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
applicable to the Moderate area timeframe, including the 2013 base
year, the 2019 RFP year, the 2021 Moderate area attainment year, and
the 2022 post-attainment RFP year, as well as subsequent years.
---------------------------------------------------------------------------

    \54\ 2018 PM2.5 Plan, App. B, B-42 to B-44. The EPA
has approved the emissions inventory submission for the 2006
PM2.5 NAAQS in the SJV, including the filterable and
condensable PM2.5 inventories. 85 FR 44192 (July 22,
2020) (final rule); and 85 FR 17382, 17389 (March 27, 2020)
(proposed rule).
---------------------------------------------------------------------------

    CARB used EMFAC2014 to estimate on-road motor vehicle emissions
based on transportation activity data from the 2014 Regional
Transportation Plan adopted by the transportation planning agencies in
the SJV.\55\ Re-entrained paved road dust emissions were calculated
using a CARB methodology consistent with the EPA's AP-42 road dust
methodology.\56\ CARB also provided emissions inventories for off-road
equipment, including aircraft, trains, recreational boats, construction
equipment, and farming equipment, among others. CARB uses a suite of
category-specific models to estimate off-road emissions for many
categories and, where a new model was not available, used the
OFFROAD2007 model.\57\
---------------------------------------------------------------------------

    \55\ 2016 PM2.5 Plan, App. B, B-33; and 2018
PM2.5 Plan, 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.
    \56\ 2016 PM2.5 Plan, App. B, B-26; and 2018
PM2.5 Plan, App. B, B-28.
    \57\ 2016 PM2.5 Plan, App. B, B-33 through B-35; and
2018 PM2.5 Plan, App. B, B-38 through B-40.
---------------------------------------------------------------------------

    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.\58\
In the 2016 PM2.5 Plan and 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
2022 RFP year and the projected 2025 attainment year, respectively.\59\
The plans identify growth factors, control factors, and estimated
offset use between 2013 and 2022, and 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,\60\ NOX,
SOX, and VOC emissions, by facility.\61\
---------------------------------------------------------------------------

    \58\ 2016 PM2.5 Plan, App. B, B-19; and 2018
PM2.5 Plan, App. B, B-19.
    \59\ 2016 PM2.5 Plan, App. D, D-1 through D-5; and
2018 PM2.5 Plan, App. I, I-1 through I-5.
    \60\ Particulate matter with a diameter of 10 microns or less.
    \61\ 2016 PM2.5 Plan, App. D, tables D-1 through D-5;
and 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 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,
impracticability demonstration, RFP demonstration, and MVEBs in the
2018 PM2.5 Plan with respect the Moderate area requirements.

  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.

3. EPA Evaluation and Proposed Action
    Consistent with the requirement that inventories be based on the
most current and accurate information available to the State and
District at the time they were developing the plans and inventories,
our evaluation for the SJV for the 2012 PM2.5 NAAQS relies
primarily on the emissions inventories in the 2018 PM2.5
Plan. The inventories in the 2018 PM2.5 Plan include the
latest version of California's mobile source emissions model,
EMFAC2014, that had been approved by the EPA at the time, 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(a), the 2013 base year is one of
the three years for which monitored data were used for designating the
area, and it represents 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 and find them acceptable and thus
conclude that the future baseline emissions projections in the 2016
PM2.5 Plan and 2018 PM2.5 Plan reflect
appropriate calculation methods and the latest planning assumptions at
the time the State and District were developing the plans and
inventories. 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.
    Given the State's impracticability demonstration for attaining the
2012 PM2.5 NAAQS in the SJV by the outermost Moderate area
attainment date, the 2016 PM2.5 Plan describes the District
rules achieving post-2013 emission reductions that contribute towards
attaining the NAAQS.\62\ In our rulemaking on the State's attainment
plan for the 2006 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
have been submitted and approved as part of the California SIP.\63\
That set of 2018 PM2.5 Plan baseline measures includes all

those baseline measures identified in the 2016 PM2.5 Plan's
RFP demonstration as achieving emission reductions post-2013. Based on
that review, we confirm that the stationary and area source baseline
measures in the 2016 PM2.5 Plan and 2018 PM2.5
Plan are approved into the SIP and support the emissions reductions for
future years in the SJV. 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.\64\ We therefore find
that the future year baseline projections in the 2016 PM2.5
Plan and 2018 PM2.5 Plan are properly supported by SIP-
approved stationary, area, and mobile source measures.\65\
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    \62\ 2016 PM2.5 Plan, Table 3-2. This includes
District rules for open burning; boilers, steam generators, and
process heaters; flares; glass melting furnaces; stationary internal
combustion engines; and residential wood burning.
    \63\ EPA, ``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.
    \64\ See, e.g., 81 FR 39424 (June 16, 2016), 82 FR 14447 (March
21, 2017), and 83 FR 23232 (May 18, 2018).
    \65\ The baseline emissions projections in the 2016
PM2.5 Plan assume implementation of CARB's zero emissions
vehicle (ZEV) sales mandate and greenhouse gas (GHG) standards,
based on the approved EMFAC2014 model and assumptions that were
available at the time of the SIP's development. On September 27,
2019, the U.S. Department of Transportation and the EPA (the
Agencies) issued a notice of final rulemaking for 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). In response to
SAFE I, CARB developed EMFAC off-model adjustment factors to account
for anticipated changes in on-road emissions. On March 12, 2020, the
EPA informed CARB that the EPA considers these adjustment factors to
be acceptable for future use. See letter dated March 12, 2020, from
Elizabeth J. Adams, EPA Region IX, to Steven Cliff, CARB. 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
that it is impracticable for the SJV 2012 PM2.5 Moderate
area to attain by the Moderate area attainment date of December 31,
2021.
---------------------------------------------------------------------------

    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 2016
PM2.5 Plan and 2018 PM2.5 Plan satisfy the
requirements of 40 CFR 51.1008(a)(2) and 51.1012(a)(2) and provide an
adequate basis for the control measure, RFP, and impracticability
demonstrations in the 2016 PM2.5 Plan and 2018
PM2.5 Plan, respectively.

B. PM2.5 Precursors

1. 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. 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)).
    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 RACM, RACT, BACM, best available control
technology (BACT), MSM, and NNSR) for sources of direct
PM2.5 and PM2.5 precursor emissions. 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,\66\ 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.\67\
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    \66\ General Preamble, 13539-13542.
    \67\ 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.\68\ 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.\69\
---------------------------------------------------------------------------

    \68\ 40 CFR 51.1006(a)(1).
    \69\ Id.
---------------------------------------------------------------------------

    We are evaluating the 2016 PM2.5 Plan and 2018
PM2.5 Plan with respect to the Moderate area requirements in
accordance with the presumption embodied within subpart 4 that all
PM2.5 precursors must be addressed in the State's 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.
2. Summary of State's Precursor Demonstrations
    The State presents analyses of PM2.5 precursors in both
the 2016 PM2.5 Plan and the 2018 PM2.5 Plan and
primarily relies on sensitivity-based contribution analyses to
determine whether each PM2.5 plan precursor contributes
significantly to ambient PM2.5 levels that exceed the 2012
PM2.5 NAAQS. We summarize below key points from the State's
analyses and conclusions for each pollutant, focusing on the three
precursors (ammonia, SOX, and VOC) that the State concludes
do not contribute significantly to PM2.5 levels that exceed
the 2012 PM2.5 NAAQS in the SJV.
    In the 2016 PM2.5 Plan, the State's precursor
demonstration and conclusions are found in section 2.3 (``Summary of
Modeling Results''), section 3.3 (``Precursor

Demonstration''), and Appendix A (``Air Quality Modeling''). The State
estimates that baseline anthropogenic emissions of NOX,
ammonia, SOX, and VOC will decrease by 38 percent (%), 1%,
2%, and 8%, respectively, between 2013 and 2021.\70\ The State does not
present a concentration-based analysis of the contribution of each
precursor to ambient PM2.5 concentrations, but does estimate
PM2.5 component concentrations in the 2013 base year across
all SJV monitoring sites.\71\ The concentrations indicate that each
precursor may have a significant impact on PM2.5 levels.\72\
The State presents a sensitivity-based precursor analysis using the
modeled response of ambient PM2.5 concentrations to a 15%
increase or decrease in the future baseline emissions of each precursor
in 2025 (the latest permissible attainment year if the area is
reclassified to Serious for the 2012 PM2.5 NAAQS).\73\ For
each precursor, the State then takes the difference between the
PM2.5 concentrations from the 15% increase and the 15%
decrease to estimate the ambient PM2.5 response to a 30%
change in the precursor, and reviews the resulting change at each
monitor to see whether any response exceeds a threshold of 0.2
[micro]g/m\3\.\74\
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    \70\ 2016 PM2.5 Plan, 2-4 and Table 2-1.
    \71\ Id. at Table 2-4.
    \72\ Using the species assignments recommended in the Draft
Precursor Demonstration Guidance (on page 21) the relevant
concentrations are as follows: For NOX, the nitrate and
associated ammonium is up to 7.1 [micro]g/m\3\; for SO2,
sulfate is up to 1.7 [micro]g/m\3\; for ammonia, the sum of ammonium
and nitrate is up to 7.1 [micro]g/m\3\; for VOC the only available
concentration is for ``OM'' (organic matter), which is up to 8.7
[micro]g/m\3\, and is likely much higher than the secondary organic
aerosol that is relevant for VOC as a PM2.5 precursor.
All these values are well above the 0.2 [micro]g/m\3\ threshold.
    \73\ 2016 PM2.5 Plan, App. A, section 5.4
(``Precursor Sensitivity Analysis'').
    \74\ For the annual PM2.5 NAAQS, the EPA generally
expects that a precursor demonstration showing that the air quality
impact of a given precursor at all relevant locations does not
exceed a contribution threshold of 0.2 [mu]g/m\3\ will be adequate
to exempt sources of that precursor from control requirements.
PM2.5 Precursor Guidance, 17.
---------------------------------------------------------------------------

    The responses range from 0.5 [micro]g/m\3\ to 1.5 [micro]g/m\3\ for
NOX; from 0.1 [micro]g/m\3\ to 0.2 [micro]g/m\3\ for
ammonia; from 0.1 [micro]g/m\3\ to 0.2 [micro]g/m\3\ for
SOX; and from -0.1 [micro]g/m\3\ to 0.1 [micro]g/m\3\ for
VOC.\75\ 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 but
ammonia, SOX, and VOC do not contribute significantly to
such exceedances.\76\ The 2016 PM2.5 Plan, Appendix A,
section 5.5 (``Discussion of Precursor Sensitivity'') includes
additional discussion of ammonia's and VOC's role in the formation of
ammonium nitrate and VOC's role in the formation of secondary organic
aerosols.
---------------------------------------------------------------------------

    \75\ 2016 PM2.5 Plan, App. A, tables 24, 26, 28, and
27, respectively.
    \76\ Id. at 2-6 and 3-3, and App. A, A-52. We note that direct
PM2.5 emissions are considered a primary source of
ambient PM2.5 (i.e., no further formation in the
atmosphere is required), and therefore is not considered a precursor
pollutant under subpart 4, which may differ from a more generalized
understanding of what contributes to ambient PM2.5.
---------------------------------------------------------------------------

    In the 2018 PM2.5 Plan, 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''). 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 four 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''); 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%, 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.
Notably, the estimated 64% reduction in NOX from 2013 to
2025 (per the 2018 PM2.5 Plan) is much larger than the
estimated 38% reduction in NOX from 2013 to 2021 (per the
2016 PM2.5 Plan), reflecting both additional years of
reductions and additional reductions anticipated from the 2018
PM2.5 Plan control strategy. We also note that a copy of
the contents of the 2018 PM2.5 Plan, App. G appears in
the CARB 2018 Staff Report, App. C4 (``Precursor Demonstrations for
Ammonia, SOX, and ROG'').
---------------------------------------------------------------------------

    While these analyses are primarily designed to evaluate the role of
precursors in attaining the 2006 24-hour PM2.5 NAAQS by 2024
and the 2012 annual PM2.5 NAAQS by 2025, they are important
to the consideration of precursors for the State's Moderate area plan
because they are based on updated data (e.g., updated emissions
inventories, as discussed in section IV.A of this proposed rule), use
an updated methodology to evaluate the sensitivity of ambient
PM2.5 to a range of precursor emission reductions,
consistent with the EPA's guidance, and best reflect the State's
understanding of the control strategies being implemented in the SJV.
    We summarize the State's analyses and conclusions in the following
paragraphs. 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 is 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 [micro]g/m\3\ from the EPA's ``Draft
PM2.5 Precursor Guidance'' \80\ available at the time the
State developed the SIP.\81\ The 2015 annual average contributions of
ammonia, SOX, and VOC are 5.2 [micro]g/m\3\, 1.6 [micro]g/
m\3\ and 6.2 [micro]g/m\3\, respectively.
---------------------------------------------------------------------------

    \80\ ``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.
    \81\ 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.
---------------------------------------------------------------------------

    Given that these levels are well above the EPA's recommended
contribution threshold in the Draft PM2.5 Precursor
Guidance, the State models the sensitivity of ambient PM2.5
in the SJV to reductions in each precursor pollutant. For direct
PM2.5 and NOX, the State models the sensitivity
of ambient PM2.5 in the SJV to a 30% reduction in
anthropogenic emissions of each pollutant in 2013, 2020, and 2024.\82\
The State concludes that direct PM2.5 and NOX
emissions reductions will continue to have a significant impact on
annual

and 24-hour PM2.5 design values in the SJV, with
NOX reductions being particularly important.\83\
---------------------------------------------------------------------------

    \82\ 2018 PM2.5 Plan, Ch. 7, 7-7. The sensitivity-
based analysis used the same modeling platform as that used for the
2018 PM2.5 Plan's attainment and RFP demonstrations. CARB
modeled the impacts of both NOX reductions and direct
PM2.5 reductions, but the direct PM2.5 results
were used only as a point of comparison, as direct PM2.5
emissions must be regulated in all PM2.5 nonattainment
areas.
    \83\ Id. Ch. 7, 7-7; and 2018 PM2.5 Plan, App. G, 2.
CARB presents its sensitivity analysis for emission reductions in
direct PM2.5 and NOX in the plan's attainment
demonstration appendix. 2018 PM2.5 Plan, App. K, Table 46
(annual average design values) and Table 50 (24-hour average design
values).
---------------------------------------------------------------------------

    For ammonia, SOX, and VOC, the State then models the
sensitivity of ambient PM2.5 to 30% and 70% reductions in
anthropogenic emissions of each precursor pollutant in 2013 (the 2018
PM2.5 Plan's base year), 2020 (the modeled attainment year
for the 1997 PM2.5 NAAQS), and 2024 (the modeled attainment
year for the 2006 PM2.5 NAAQS, and proxy for the modeled
attainment year of 2025 for the 2012 PM2.5 NAAQS).\84\
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 [micro]g/m\3\ to
2.30 [micro]g/m\3\ for ammonia; from -0.05 [micro]g/m\3\ to 0.15
[micro]g/m\3\ for SOX; and from -0.50 [micro]g/m\3\ to 0.40
[micro]g/m\3\ for VOC.\85\
---------------------------------------------------------------------------

    \84\ 2018 PM2.5 Plan, Ch. 7, 7-7. The 2018
PM2.5 Plan precursor demonstration assumes that 2025
attainment year sensitivities are very similar to those modeled in
2024. 2018 PM2.5 Plan, App. G, 10. We note that the State
only modeled 30% and 70% reductions in SOX for 2013,
finding that the sensitivity of ambient PM2.5 to such
changes were below the EPA's recommended threshold.
    \85\ 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 exceed 0.2 [micro]g/m\3\ in
certain years at specific monitoring sites. We provide a detailed
summary of these modeling results and our evaluations thereof in the
``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''). 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 [micro]g/m\3\, including a
disbenefit at certain monitoring sites (i.e., ambient PM2.5
level increase), in all scenarios except one. For 2013, the State's
modeling shows an ambient PM2.5 change greater than 0.2
[micro]g/m\3\ in response to a 70% VOC emission reduction. According to
the State, however, such sensitivity results do not reflect the
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.\86\
---------------------------------------------------------------------------

    \86\ For a more detailed summary of the State's precursor
demonstration in the 2018 PM2.5 Plan for the 2006 24-hour
PM2.5 NAAQS, see 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 24-hour PM2.5 Precursor
TSD'').
---------------------------------------------------------------------------

    The State supplements the sensitivity analysis, particularly for
ammonia, with consideration of additional information, including
factors identified in the Draft PM2.5 Precursor Guidance,
such as emission trends, the appropriateness of future year versus base
year sensitivity, available emission controls, and the severity of
nonattainment.\87\ The PM2.5 Precursor Guidance confirms
that these factors may be relevant to a sensitivity-based contribution
analysis.\88\
---------------------------------------------------------------------------

    \87\ 2018 PM2.5 Plan, App. G, 5.
    \88\ 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).
---------------------------------------------------------------------------

    For ammonia, the State notes that a 53% reduction in (baseline)
NOX emissions is projected to occur between 2013 and
2024,\89\ so the conditions in the early years will not persist and the
future year (2024) 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, beyond that presented in the 2016
PM2.5 Plan's precursor demonstration.
---------------------------------------------------------------------------

    \89\ 2018 Plan, App. G, 8.
---------------------------------------------------------------------------

3. EPA Evaluation and Proposed Action
    The EPA has evaluated the State's precursor demonstrations in the
2016 PM2.5 Plan, as supplemented and updated by the
precursor demonstrations 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 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 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 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 in a straightforward application of the EPA's recommended
approach--i.e., for each modeled year and level of 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.\90\ The EPA finds that the performance of the
photochemical models were adequate for use in estimating the ambient
PM2.5 responses.\91\ In particular, for the 2018
PM2.5 Plan precursor demonstration, the State considered the
EPA's recommended range of emission reductions (30% to 70%) for the
2013 base year, 2020 (an interim year), and 2024 (as a proxy for the
projected 2025 attainment year for the 2012 PM2.5 NAAQS),
and quantified

the estimated response of ambient PM2.5 concentrations to
precursor emission changes in the SJV.
---------------------------------------------------------------------------

    \90\ For the 2016 PM2.5 Plan precursor demonstration,
CARB modeled a 15% increase and 15% decrease in a precursor and took
the difference between the resulting PM2.5 concentrations
to estimate the ambient PM2.5 response to a 30% change in
the precursor, rather than a straight 30% reduction, which would be
expected to slightly understate the response, as described in the
EPA's Ammonia Precursor TSD. Nevertheless, this is a reasonable
approach and the State consulted with the EPA on whether this
approach using then-available modeling runs would be acceptable.
    \91\ For the 2018 PM2.5 Plan, the model performance
is discussed further in section J (``Air Quality Model
Performance'') of 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 Modeling TSD''). See further discussion in
section IV.C of this proposed rule.
---------------------------------------------------------------------------

    The State's emissions projections in the 2016 PM2.5 Plan
and the 2018 PM2.5 Plan show that baseline emissions of each
of these precursors will decrease from the 2013 base year to 2021 and
2025, respectively (i.e., none of these pollutants is projected to
increase). 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.\92\
---------------------------------------------------------------------------

    \92\ PM2.5 Precursor Guidance, 35.
---------------------------------------------------------------------------

    In the subsections that follow, we summarize below our evaluation
of the State's precursor demonstrations for ammonia, SOX,
and VOC for purposes of the 2012 PM2.5 NAAQS in the SJV.
a. Ammonia Precursor Demonstration
    In the 2016 PM2.5 Plan, CARB estimates the ambient
PM2.5 response to a 30% reduction in emissions in 2025 and,
in the 2018 PM2.5 Plan, CARB estimates the ambient
PM2.5 response to both a 30% and a 70% emission 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 for 2025 (in the 2016 PM2.5
Plan), and CARB's determination that 2024, as a proxy for the projected
attainment year of 2025, is more representative of conditions in the
SJV for purposes of a sensitivity-based analysis, as discussed in the
following paragraphs. We find it appropriate for the State to consider
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. We provide a detailed evaluation of the State's precursor
demonstration for ammonia emissions in the EPA's Ammonia Precursor TSD.
    As part of its analysis in the 2016 PM2.5 Plan, CARB
estimates that the ambient PM2.5 response to a 30% reduction
in ammonia emissions would range from 0.1 [micro]g/m\3\ to 0.2
[micro]g/m\3\ in 2025 with 3 of 16 monitoring sites having a response
of 0.2 [micro]g/m\3\. However, 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 [micro]g/m\3\ at a number of monitoring
sites, primarily in the 2013 and 2020 analysis years. For example, the
sensitivity results for a 30% reduction in ammonia emission reductions
in 2020 (the closest analysis year to 2021), show that the ambient
PM2.5 response at 9 of 15 monitoring sites would exceed the
0.2 [micro]g/m\3\ threshold. We consider two lines of reasoning
provided by the State to support its conclusion that ammonia emissions
do not contribute significantly to ambient PM2.5 levels that
exceed the 2012 PM2.5 NAAQS in the SJV.
    First, multiple researchers have suggested that ammonia emissions
are underestimated in the SJV by a factor of two to five or more.\93\
This conclusion is based on comparing ambient and satellite
measurements to model results that incorporate estimates of ammonia
emissions and comparing monitoring or modeling results to what would be
expected based on the size(s) of the ammonia and other precursor (e.g.,
NOX) emission inventories. In a supplemental
transmittal,\94\ CARB described the results of two analyses confirming
the likely underestimation of ammonia emissions. CARB compared
Community Multiscale Air Quality (CMAQ) model predictions of ammonia
with the 2013 DISCOVER-AQ \95\ aircraft measurements and found that
ammonia was underpredicted, and noted that this would result in the
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. As a result of the likely
ammonia emissions underestimation, the modeled response to ammonia
precursor reductions in the 2018 PM2.5 Plan's precursor
demonstration may be unrealistically large.
---------------------------------------------------------------------------

    \93\ See, e.g., Parrish, D., ``Synthesis of Policy Relevant
Findings from the CalNex 2010 Field Study, Final Report to the
Research Division of the California Air Resources Board,'' 2014, 63,
https://www.esrl.noaa.gov/csd/projects/calnex/; and 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 4731. See also the EPA's Ammonia Precursor
TSD for further discussion of ammonia research studies.
    \94\ CARB's April 26, 2021, Precursor Clarification.
    \95\ NASA, ``Deriving Information on Surface conditions from
COlumn and VERtically Resolved Observations Relevant to Air
Quality,'' available at https://www.nasa.gov/mission_pages/discover-aq/index.html.
---------------------------------------------------------------------------

    If ammonia emissions were increased in the modeling to correct the
likely underestimation, then modeled ammonia would be more abundant
relative to nitrate; particulate nitrate formation would be more
NOX-limited, and less responsive to ammonia reductions; and
the modeled response to ammonia reductions would be lower than is
reported in the 2018 PM2.5 Plan's precursor demonstration
and likely below the EPA's recommended contribution threshold at most
monitors in 2021.
    In addition, an upward revision in the ammonia emission estimate
would make the model response more consistent with the ambient
measurement studies discussed in the submittal.\96\ The relevant
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.\97\ 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.
---------------------------------------------------------------------------

    \96\ 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.
    \97\ Lurmann et al. 2006, ``Processes Influencing Secondary
Aerosol Formation in the San Joaquin Valley during Winter,'' Journal
of the Air & Waste Management Association (1995) 56(12):1679-93,
https://doi.org/10.1080/10473289.2006.10464573; Markovic et al.,
2014, ``Measurements and modeling of the inorganic chemical
composition of fine particulate matter and associated precursor
gases in California's San Joaquin Valley during CalNex 2010,''
Journal of Geophysical Research--Atmospheres, 119, 6853-6866,
https://doi.org/10.1002/2013JD021408. CalNex, or California Research
at the Nexus of Air Quality and Climate Change, was a NOAA-sponsored
field study during summer 2010. https://www.esrl.noaa.gov/csd/projects/calnex/.
---------------------------------------------------------------------------

    Based on these evaluations, we find that a correction to the likely
underestimation of the ammonia emission inventory would likely result
in a modeled response to ammonia reductions below the 0.2 [micro]g/m\3\
contribution threshold in 2021.
    Second, the air quality benefit of ammonia emission reductions is
projected to decline steeply over time and both the Moderate and
Serious area plans for the 2012 PM2.5 NAAQS for the SJV have
been submitted to the EPA. While a concentration-based analysis is the
initial step for a precursor demonstration under the PM2.5
SIP Requirements Rule,\98\ a precursor

demonstration may then proceed to a sensitivity-based contribution
analysis \99\ to consider how sensitive ambient PM2.5 levels
would be to emissions reductions. Precursor concentration alone does
not account for complications of meteorology and chemistry; ambient
PM2.5 may be relatively insensitive to emissions reductions
and, in some circumstances, emissions reductions may even result in
increased ambient PM2.5, i.e., show a ``disbenefit.'' \100\
---------------------------------------------------------------------------

    \98\ 40 CFR 51.1006 (a)(1)(i).
    \99\ 40 CFR 51.1006 (a)(1)(ii).
    \100\ An example of a disbenefit is ``sulfate replacement,''
which can occur at intermediate ammonia levels when there is not
enough ammonia to fully react with the SOX and
NOX present. Reducing SOX emissions reduces
ambient particulate ammonium sulfate. For each ammonium sulfate, two
ammonium ions are freed; both can combine with a nitrate, forming
two particulate ammonium nitrate molecules. The net result of the
SOX emissions decrease is then an increase in ambient
PM2.5 concentration. See also the EPA's 24-hour
PM2.5 Precursor TSD, 17-18; and West, J.J., Ansari, A.S.,
Pandis, S.N., 1999, ``Marginal PM2.5: Nonlinear aerosol
mass response to sulfate reductions in the eastern United States,''
Journal of the Air & Waste Management Association, 49, 1415-1424.
https://doi.org/10.1080/10473289.1999.10463973.
---------------------------------------------------------------------------

    In selecting the analysis year for a precursor demonstration, we
find it 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. Based on these considerations,
we find 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 PM2.5 NAAQS.
We consider the precursor demonstration in the 2018 PM2.5
Plan as part of this evaluation, because the 2018 PM2.5 Plan
contains a Serious area attainment plan for the 2012 PM2.5
NAAQS based on modeled emissions projections for 2024 and 2025 that are
relevant to our evaluation of the ammonia precursor demonstration in
the 2016 PM2.5 Plan. The 2018 PM2.5 Plan provides
updated analyses with comprehensive modeling and additional information
beyond that provided in the 2016 PM2.5 Plan, and the 2024
model results in the 2018 PM2.5 Plan corroborate the 2025
model results in the 2016 PM2.5 Plan.
    The State's precursor demonstrations in the 2016 PM2.5
Plan and the 2018 PM2.5 Plan show 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. In absolute terms, the ambient
PM2.5 response declines from 0.24 [micro]g/m\3\ in 2020 to
0.12 [micro]g/m\3\ in 2024 at Bakersfield-Planz, and from 0.23
[micro]g/m\3\ to 0.14 [micro]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
[micro]g/m\3\ threshold declines from 9 of 15 to 1 or 2 of
15.101 102 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 attainment year 2024 gives a more
realistic assessment of the potential effect of ammonia controls than
past or current conditions.
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    \101\ 2018 PM2.5 Plan, App. G, tables 4 & 5, G-11.
The result for the Madera site is unclear since its monitored
concentrations are biased high.
    \102\ For 2025, the 2016 PM2.5 Plan states there are
no sites are above the contribution threshold. The sensitivities
show similar declines from 2020 to 2025 of 58% for the monitoring
site with the highest projected PM2.5 level and 46%
averaged over all monitoring sites. Because only a single decimal
place is provided for 2025, the percent declines are more
approximate. Extrapolating the 2018 PM2.5 Plan results to
2025, the percent declines are 55% and 40%, respectively, which are
comparable to those for 2024.
---------------------------------------------------------------------------

    Moreover, given the likely underestimate in ammonia emissions in
the SJV, 2024 modeling results may be more representative even of
current conditions than 2020 modeling results. For example, if 2013
ammonia emissions are underestimated by a factor of three, as suggested
by the CalNex summary report,\103\ then the 2013 ratio of ammonia to
NOX emissions of 1.04 should be about 3.1, instead. The
emissions ratio of ammonia to NOX in 2024 is 2.2, which is
closer to 3.1 than the emissions ratio of ammonia to NOX in
2020, which is 1.6.\104\ Using 2024 modeling results partly compensates
for the likely ammonia emissions underestimation.
---------------------------------------------------------------------------

    \103\ Parrish, D., ``Synthesis of Policy Relevant Findings from
the CalNex 2010 Field Study, Final Report to the Research Division
of the California Air Resources Board,'' 2014, 63, https://www.esrl.noaa.gov/csd/projects/calnex/.
    \104\ 2018 PM2.5 Plan, App. B, tables B-2
(``NOX'') and B-5 (``Ammonia''), annual average tpd,
Grand Total for San Joaquin Valley, B-7 and B-16. The ammonia to
NOX ratio is 329.2/317.2 = 1.04 in 2013; 325.9/203.3 =
1.6 in 2020; and 324.6/148.9 = 2.2 in 2024.
---------------------------------------------------------------------------

    Finally, the decision on whether to control ammonia does not affect
the attainment year for the 2012 annual PM2.5 NAAQS. From
the 2020 sensitivity results,\105\ a 30% reduction in ammonia emissions
would reduce the projected PM2.5 level in 2021 \106\ by 0.24
[micro]g/m\3\. The design value would decrease from a 2020 baseline
value of 14.6 [micro]g/m\3\ down to 14.3 [micro]g/m\3\. The State uses
a 30% ammonia emission reduction as an upper bound in the modeling but
shows that even a 70% ammonia emission reduction would reduce the
design value to only 13.8 [micro]g/m\3\. The result of a 30% or even a
70% ammonia emission reduction, if those were possible, would still be
well above the NAAQS level of 12.0 [micro]g/m\3\. Attainment would
remain impracticable in 2021. A decision to evaluate and possibly adopt
additional ammonia controls in the 2016 PM2.5 Plan would not
remove the need for a Serious area plan identifying a later attainment
year for the 2012 PM2.5 NAAQS.
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    \105\ 2018 PM2.5 Plan, App. G, tables 4 and 6.
    \106\ Sensitivity for the year 2021 is being represented by
model results for 2020. Given the declining NOX emissions
and corresponding decline in ammonia sensitivity, the actual
PM2.5 response to ammonia reductions for 2021 would be
lower than stated.
---------------------------------------------------------------------------

    Such reductions would also have little effect in 2025. Based on the
2024 sensitivity results,\107\ if ammonia emissions were reduced by
30%, the area's 12.0 [micro]g/m\3\ design value would be reduced by
0.12 [micro]g/m\3\, which would not be considered significant (it is
below the EPA's recommended threshold of 0.2 [micro]g/m\3\). A 70%
reduction might lower the design value by 0.36 [micro]g/m\3\ to 11.7
[micro]g/m\3\. Conceivably that could result in attainment of the 2012
PM2.5 NAAQS in 2024 rather than 2025, but it is not clear
whether reductions of that magnitude are feasible.
---------------------------------------------------------------------------

    \107\ 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 find that the State quantified the sensitivity of
ambient PM2.5 levels to reductions in ammonia emissions
using appropriate modeling techniques that performed well; there is
likely an underestimation of ammonia emissions in the SJV and, if
corrected, the modeled response to ammonia reductions would be 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 PM2.5 NAAQS in the SJV.
b. SOX Precursor Demonstration0.05
    As described in section IV.B.2 of this proposed rule, in the 2016
PM2.5 Plan, CARB estimated the ambient PM2.5
response to a 30% reduction in SOX emissions in 2025 to
range from 0.1 [micro]g/m\3\ to 0.2 [micro]g/m\3\, with half the
monitoring sites having a response of 0.2 [micro]g/m\3\. 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
[micro]g/m\3\ to 0.07 [micro]g/m\3\ and estimated the ambient
PM2.5 response to a 70% SOX emission reduction to
range from -0.05 [micro]g/m\3\ to 0.15 [micro]g/m\3\.\108\ 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 SOX and ammonia emissions
over that timeframe remain similar, the State concludes that the 2013
sensitivities are also representative of future years.\109\ 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 [micro]g/m\3\ contribution threshold.\110\
---------------------------------------------------------------------------

    \108\ 2018 PM2.5 Plan, App. G, 15-16, tables 8 and 9.
    \109\ 2018 PM2.5 Plan, App. G, 15.
    \110\ CARB's September 2019 Precursor Clarification.
---------------------------------------------------------------------------

    We note that the 2016 PM2.5 Plan's sensitivity estimates
for 2025 are at or below the EPA's recommended contribution threshold
of 0.2 [micro]g/m\3\, and 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 that the latter precursor demonstration
was based on updated data and an updated methodology, 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
PM2.5 NAAQS in the SJV.
c. VOC Precursor Demonstration
    In the 2016 PM2.5 Plan, CARB estimated the ambient
PM2.5 response to a 30% difference in VOC emissions in 2025
to range from -0.1 [micro]g/m\3\ to 0.1 [micro]g/m\3\. 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 [micro]g/
m\3\, and often predicted an increase in ambient PM2.5
levels in response to such reductions (i.e., a disbenefit), except for
a 70% emission reduction for the 2013 base year, where the State
predicted the ambient PM2.5 response to be above both
recommended thresholds at a majority of sites.\111\
---------------------------------------------------------------------------

    \111\ 2018 PM2.5 Plan, App. G, 18-19, tables 10 and
11.
---------------------------------------------------------------------------

    We note that the 2016 PM2.5 Plan's sensitivity estimates
for 2025 are at or below the EPA's recommended contribution threshold
of 0.2 [micro]g/m\3\, and 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.\112\ Finally, the State concludes that VOC
emissions do not contribute significantly to PM2.5 levels
that exceed the 2012 PM2.5 NAAQS.
---------------------------------------------------------------------------

    \112\ 2018 PM2.5 Plan, 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 attainment 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. The EPA agrees that the
9% VOC emissions decrease from 2013 to 2024 supports reliance on the
2024 modeling results. Furthermore, there is 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 find it reasonable to rely on future
year 2024 modeled responses to VOC reductions. The EPA also finds 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 ``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 2006 NAAQS
Precursor TSD''), VOC reductions led to less peroxyacetyl nitrate
formation, and greater availability of nitrate to form particulate
ammonium nitrate.\113\
---------------------------------------------------------------------------

    \113\ EPA's 2006 NAAQS 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 PM2.5 NAAQS in
the SJV.

C. Air Quality Modeling

1. Requirements for Air Quality Modeling
    Section 189(a)(1)(B) of the CAA requires each state in which a
Moderate area is located to submit a plan that includes a demonstration
(including air quality modeling) of either (i) attainment of the
PM2.5 NAAQS by the applicable attainment date, or (ii)
attainment by that date is impracticable. The 2016 PM2.5
Plan includes a demonstration that attainment by the Moderate
attainment date is impracticable.
    The EPA's PM2.5 modeling guidance \114\ (``Modeling
Guidance'' and ``Modeling Guidance Update'') recommends that a
photochemical model, such as the Comprehensive Air Quality Model with
Extensions or CMAQ, be used to simulate a base case, with
meteorological and emissions inputs reflecting a base case year, to
replicate concentrations monitored in that year. The model application
to the base year undergoes a performance evaluation to ensure that it
satisfactorily corroborates the concentrations monitored in that year.
The model may then be used to simulate emissions occurring in other
years required for a

plan, namely the base year (which may differ from the base case year)
and future year.\115\ The modeled response to the emission changes
between those years is used to calculate relative response factors
(RRFs) that are applied to the design value in the base year to
estimate the projected design value in the future year for comparison
against the NAAQS. Separate RRFs are estimated 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 design value must be speciated
using available chemical species measurements--that is, each day's
measured PM2.5 concentration must be split into its species
components. The Modeling Guidance provides additional detail on the
recommended approach.\116\
---------------------------------------------------------------------------

    \114\ Memorandum dated November 29, 2018, from Richard Wayland,
Air Quality Assessment Division, Office of Air Quality Planning and
Standards (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'').
    \115\ 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.''
    \116\ Modeling Guidance, section 4.4, ``What is the Modeled
Attainment Tests for the Annual Average PM2.5 NAAQS.''
---------------------------------------------------------------------------

    The EPA has not issued modeling guidance specific to
impracticability demonstrations but believes that a state seeking to
make such a demonstration generally should provide air quality modeling
similar to that required for an attainment demonstration.\117\ The main
difference is that for an impracticability demonstration, the
implementation of the SIP control strategy (including RACM) does not
result in attainment of the standard by the Moderate area attainment
date.
---------------------------------------------------------------------------

    \117\ 81 FR 58010, 58048.
---------------------------------------------------------------------------

    For an attainment demonstration, a thorough review of all modeling
inputs and assumptions (including consistency with EPA guidance) is
especially important because the modeling must ultimately support a
conclusion that the plan (including its control strategy) will provide
for timely attainment of the applicable NAAQS. In contrast, for an
impracticability demonstration, the end point is a reclassification to
Serious, which triggers the requirement for a new Serious area
attainment plan with a new air quality modeling analysis, and a new
control strategy.\118\ Thus, the Serious area planning process would
provide an opportunity to refine the modeling analysis and/or correct
any technical shortcomings in the impracticability demonstration.
Therefore, the burden of proof will generally be lower for an
impracticability demonstration compared to an attainment
demonstration.\119\
---------------------------------------------------------------------------

    \118\ CAA section 189(b)(1).
    \119\ 81 FR 58010, 58049.
---------------------------------------------------------------------------

2. Summary of State's Air Quality Modeling
    In the 2016 PM2.5 Plan, the State discussed its air
quality modeling in section 2.3 (``Summary of Modeling Results'') and
Appendix A (``Air Quality Modeling'') and concludes that it is not
practicable to attain the 2012 PM2.5 NAAQS in the SJV by
December 31, 2021. The State used CMAQ (version 5.02) to model three
simulations: A 2013 base year to demonstrate that the model reasonably
reproduced observed PM2.5 concentrations, a 2013 reference
base year simulation that excluded exceptional events such as
wildfires, and a 2021 future year based on the reference year but using
projected 2021 emissions. For the base year simulation, CARB conducted
photochemical modeling with the CMAQ model using inputs developed from
routinely available meteorological and air quality data, as well as
more detailed and extensive data from the DISCOVER-AQ field study
conducted in January to February 2013.
    The State then generated site- and species-specific RRFs for the
ammonium ion, nitrate ion, sulfate ion, organic carbon, elemental
carbon, and a combined grouping of other primary PM2.5
material for the 2021 future year simulation and calculated future year
design values by multiplying the species- and site-specific RRFs by the
corresponding quarterly mean component concentrations. The State summed
the quarterly mean components to determine quarterly mean
PM2.5 concentrations, which it subsequently averaged to
determine the annual design values. The future year design values
reflect the weighted quarterly average concentration from the
projections of five years of data. The State projected future year
annual PM2.5 design values for the 2021 Moderate area
attainment year for the 2012 PM2.5 NAAQS.
    The 2021 baseline simulation used emission levels projected from
the 2013 base year that reflect all control measures adopted by the
time of the 2016 PM2.5 Plan's development that would be
implemented by December 31, 2021. This simulation indicates that the
2012 annual PM2.5 standard will not be met in the SJV in
2021. The projected 2021 control scenario design value is 14.8
[micro]g/m\3\ at Bakersfield-Planz, which is typically the monitoring
site that records the highest PM2.5 levels in the SJV.
    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. It also includes a modeled demonstration
projecting attainment of the 1997 annual PM2.5 NAAQS by
December 31, 2020, with a design value of 14.6 [micro]g/m\3\ at
Bakersfield-Planz. While the plan does not explicitly have a
demonstration of impracticability of attaining the 2012
PM2.5 NAAQS by 2021, the latter projections of annual
PM2.5 concentrations in 2020 provides additional information
on which to judge the practicability of attaining by 2021 in that it is
the closest analysis year available and represents modeling based on
updated data. These projections lend support for the 2016
PM2.5 Plan indication that the 2012 annual PM2.5
standard will not be met in the SJV in 2021.
    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 6.4 (``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 both Appendix A of the 2016 PM2.5 Plan and
Appendix K of the 2018 PM2.5 Plan included statistical and
graphical measures of model performance.
    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.\120\ The
conclusions in the EPA's 2006 NAAQS Modeling TSD focused on the 24-hour
PM2.5 NAAQS; in this notice we extend the evaluation with
information specific to the annual PM2.5 NAAQS. Unless
otherwise noted, the discussion applies to both the modeling in both
the 2016 PM2.5 Plan (Appendix A) and 2018 PM2.5
Plan (Appendix K), since they followed the same model platform
development procedures, and had identical meteorological inputs, very
similar emissions inputs, and very similar model performance.
---------------------------------------------------------------------------

    \120\ 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 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
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. The EPA previously found that the procedures used
in the 2018 PM2.5 Plan for the 24-hour PM2.5
NAAQS generally followed the EPA's recommendations and were adequate.
For the current action, the EPA finds that State procedures \121\ for
estimating future design values for the annual PM2.5 NAAQS
generally followed the EPA's recommendations and are adequate.
---------------------------------------------------------------------------

    \121\ 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, since calculation of
the design value for the 24-hour PM2.5 NAAQS uses the 98th
percentile concentrations, i.e., the top 2%. For the annual average,
peak concentrations continue to be important, but lower concentration
days are also important since 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); and applying the RRF to
monitored base year concentration anchors the final model prediction to
unbiased real-world concentrations. Further, RRFs are calculated on a
quarterly basis, so the bias correction can better account for
emissions sources and atmospheric chemistry that differ between the
seasons.
    The 2018 PM2.5 Plan did not have a separate model
performance evaluation for the 24-hour and annual PM2.5
averaging times; it used statistical and graphical analyses applicable
to both. For the most part, the EPA's 2006 NAAQS Modeling TSD did not
distinguish between the two averaging times either but drew conclusions
for the 24-hour averaging time rather than the annual averaging time.
It did note a large negative bias (underprediction) in the ammonium and
nitrate performance statistics \122\ for the 2nd quarters for
monitoring sites in Bakersfield, Fresno, and Visalia; and we add here
that the 3rd quarter has similar negative bias. The negative model bias
in the 2016 PM2.5 Plan was slightly better than in the 2018
PM2.5 Plan, i.e., the underprediction was slightly less.
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.\123\ The EPA's
2006 NAAQS Modeling TSD noted that since those quarters have
concentrations that are less than half of those in the 1st and 4th,
this may not be much of a concern for the annual average. (It is of
less concern for the 24-hour average, since peak 24-hour concentrations
occur in winter, i.e., in the 1st and 4th quarters.) As noted above,
the RRF procedure removes much of this bias, so the underprediction in
the model performance evaluation does not directly translate into an
underpredicted 2020 design value. In addition, the 2018
PM2.5 Plan shows that annual model performance for each
PM2.5 species is quite good relative to that seen in other
modeling studies, for multiple performance statistics.\124\
---------------------------------------------------------------------------

    \122\ 2016 PM2.5 Plan, App. A 48ff, tables 15 through