[Federal Register Volume 86, Number 183 (Friday, September 24, 2021)]
[Proposed Rules]
[Pages 53150-53184]
[FR Doc No: 2021-20613]

Vol. 86

Friday,

No. 183

September 24, 2021

Part II

 Environmental Protection Agency

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40 CFR Part 52

Partial Approval and Partial Disapproval of Air Quality Implementation
Plans and Determination of Attainment by the Attainment Date;
California; San Joaquin Valley Serious Area and Section 189(d) Plan for
Attainment of the 1997 24-Hour PM2.5 NAAQS; Proposed Rule

Federal Register / Vol. 86 , No. 183 / Friday, September 24, 2021 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2021-0261; FRL-8969-01-R9]

Partial Approval and Partial Disapproval of Air Quality
Implementation Plans and Determination of Attainment by the Attainment
Date; California; San Joaquin Valley Serious Area and Section 189(d)
Plan for Attainment of the 1997 24-Hour PM2.5 NAAQS

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
approve in part and disapprove in part portions of a state
implementation plan (SIP) revision submitted by the State of California
to meet Clean Air Act (CAA or ``Act'') requirements for the 1997 24-
hour fine particulate matter (PM2.5) national ambient air
quality standards (NAAQS) in the San Joaquin Valley nonattainment area.
Specifically, the EPA is proposing to approve all but the contingency
measure element of the submitted SIP revision as meeting all applicable
Serious area and CAA section 189(d) requirements for the 1997 24-hour
PM2.5 NAAQS and is proposing disapproval of the contingency
measure element. The EPA is also proposing to determine that the San
Joaquin Valley air quality planning area has attained the 1997 24-hour
PM2.5 NAAQS. This determination is based on sufficient,
quality-assured, and certified data for 2018-2020. Based on our
proposed finding that the San Joaquin Valley nonattainment area has
attained the 1997 24-hour PM2.5 NAAQS, we are proposing to
determine that the requirement for contingency measures will no longer
apply to the San Joaquin Valley nonattainment area for these NAAQS.
Thus, the EPA is proposing to issue a protective finding for
transportation conformity determinations for this proposed disapproval.

DATES: Any comments on this proposal must be received by October 25,
2021.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2021-0261 at https://www.regulations.gov. For comments submitted at
Regulations.gov, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
Regulations.gov. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (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: Ashley Graham, Air Planning Office
(ARD-2), EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105,
(415) 972-3877, or by 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
    A. PM2.5 NAAQS
    B. San Joaquin Valley PM2.5 Designations,
Classifications, and SIP Revisions
II. Summary and Completeness Review of the San Joaquin Valley
PM2.5 Plan
    A. 2018 PM2.5 Plan
    B. Valley State SIP Strategy
III. Clean Air Act Requirements for PM2.5 Serious Area
Plans and for Serious PM2.5 Areas That Fail To Attain
    A. Requirements for PM2.5 Serious Area Plans
    B. Requirements for Serious PM2.5 Areas That Fail To
Attain
IV. Review of the San Joaquin Valley PM2.5 Plan for the
1997 24-Hour PM2.5 NAAQS
    A. Emissions Inventories
    B. PM2.5 Precursors
    C. Attainment Plan Control Strategy
    D. Attainment Demonstration and Modeling
    E. Reasonable Further Progress and Quantitative Milestones
    F. Contingency Measures
    G. Motor Vehicle Emission Budgets
    H. Nonattainment New Source Review Requirements Under CAA
Section 189(e)
V. Determination of Attainment by the Attainment Date
    A. Requirements for Attainment Determinations
    B. Monitoring Network Considerations
    C. Data Considerations and Proposed Determination
VI. Summary of Proposed Action and Request for Public Comment
VII. Statutory and Executive Order Reviews

I. Background for Proposed Action

A. PM2.5 NAAQS

    Under section 109 of the CAA, the EPA has established NAAQS for
certain pervasive air pollutants (referred to as ``criteria
pollutants'') and conducts periodic reviews of the NAAQS to determine
whether they should be revised or whether new NAAQS should be
established.
    On July 18, 1997, the EPA revised the NAAQS for particulate matter
by establishing new NAAQS for particles with an aerodynamic diameter
less than or equal to a nominal 2.5 micrometers (PM2.5).\1\
The EPA established primary and secondary annual and 24-hour standards
for PM2.5.\2\ The annual primary and secondary standards
were set at 15.0 micrograms per cubic meter ([mu]g/m\3\), based on a
three-year average of annual mean PM2.5 concentrations, and
the 24-hour primary and secondary standards were set at 65 [mu]g/m\3\,
based on the three-year average of the 98th percentile of 24-hour
PM2.5 concentrations at each monitoring site within an
area.\3\ Collectively, we refer herein to the 1997 24-hour and annual
PM2.5 NAAQS as the ``1997 PM2.5 NAAQS'' or ``1997
PM2.5 standards.''
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    \1\ 62 FR 38652.
    \2\ For a given air pollutant, ``primary'' NAAQS are those
determined by the EPA as requisite to protect the public health,
allowing an adequate margin of safety, and ``secondary'' standards
are those determined by the EPA as requisite to protect the public
welfare from any known or anticipated adverse effects associated
with the presence of such air pollutant in the ambient air. See CAA
section 109(b).
    \3\ 40 CFR 50.7.
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    On October 17, 2006, the EPA revised the level of the 24-hour
PM2.5 NAAQS to 35 [mu]g/m\3\,\4\ and on January 15, 2013,
the EPA revised the level of the primary annual PM2.5 NAAQS
to 12.0 [mu]g/m\3\.\5\ Even though the EPA lowered the 24-hour and
annual PM2.5 NAAQS, the 1997 24-hour PM2.5 NAAQS
remain in effect and the 1997 primary annual PM2.5 NAAQS
remains in effect in areas designated nonattainment for that NAAQS.\6\
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    \4\ 71 FR 61144.
    \5\ 78 FR 3086.
    \6\ 40 CFR 50.13(d).
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    The EPA established the 1997 PM2.5 NAAQS after
considering substantial

evidence from numerous health studies demonstrating that serious health
effects are associated with exposures to PM2.5
concentrations above these levels. 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 dates), changes in lung function and
increased respiratory symptoms, and new evidence for more subtle
indicators of cardiovascular health. Individuals particularly sensitive
to PM2.5 exposure include older adults, people with heart
and lung disease, and children.\7\
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    \7\ 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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    Sources can emit PM2.5 directly into the atmosphere as a
solid or liquid particle (primary PM2.5 or direct
PM2.5), or PM2.5 can form in the atmosphere
(secondary PM2.5) as a result of various chemical reactions
from precursor emissions of nitrogen oxides (NOX), sulfur
oxides (SOX), volatile organic compounds, and ammonia.\8\
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    \8\ For example, see 72 FR 20586, 20589 (April 25, 2007).
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B. San Joaquin Valley PM2.5 Designations, Classifications, and SIP
Revisions

    Following promulgation of a new or revised NAAQS, the EPA is
required under CAA section 107(d) to designate areas throughout the
nation as attaining or not attaining the NAAQS. Effective April 5,
2005, the EPA established the initial air quality designations for the
1997 24-hour and annual PM2.5 NAAQS, using air quality
monitoring data for the three-year periods of 2001-2003 and 2002-
2004.\9\ The EPA designated the San Joaquin Valley as nonattainment for
both the 1997 24-hour PM2.5 NAAQS (65 [mu]g/m\3\) and the
1997 annual PM2.5 NAAQS (15.0 [mu]g/m\3\).\10\
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    \9\ 70 FR 944 (January 5, 2005).
    \10\ 40 CFR 81.305.
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    The San Joaquin Valley 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.\11\ The area is home to four
million people and is one of the nation's leading agricultural regions.
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 attainment plans. Authority for
regulating sources under state jurisdiction in the San Joaquin Valley
is split under State law between the District, which generally has
responsibility for regulating stationary and area sources, and CARB,
which generally has responsibility for regulating mobile sources.
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    \11\ For a precise description of the geographic boundaries of
the San Joaquin Valley nonattainment area, see 40 CFR 81.305.
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    At the time of the initial designations for the 1997
PM2.5 NAAQS, the EPA interpreted the CAA to require
implementation of the NAAQS under the general nonattainment plan
requirements of subpart 1.\12\ Under subpart 1, states were required to
submit nonattainment plan SIP submissions within three years of the
effective date of designations, that, among other things, provided for
implementation of reasonably available control measures (RACM),
reasonable further progress (RFP), contingency measures, and a modeled
attainment demonstration showing attainment of the NAAQS as
expeditiously as practicable but no later than five years from the
designation (in this instance, no later than April 5, 2010) unless the
state justified an attainment date extension of up to five years.\13\
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    \12\ 72 FR 20586.
    \13\ CAA sections 172(a)(2), 172(c)(1), 172(c)(2), and
172(c)(9).
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    Between 2007 and 2011, California submitted six SIP revisions to
address nonattainment area planning requirements for the 1997 24-hour
and annual PM2.5 NAAQS in the San Joaquin Valley,\14\ which
we refer to collectively as the ``2008 PM2.5 Plan.'' On
November 9, 2011, the EPA approved the portions of the 2008
PM2.5 Plan, as revised in 2009 and 2011, that addressed
attainment of the 1997 24-hour and annual PM2.5 NAAQS in the
San Joaquin Valley PM2.5 nonattainment area, except for the
attainment contingency measures, which we disapproved.\15\ We also
granted the State's request to extend the attainment deadline for the
1997 PM2.5 NAAQS in the San Joaquin Valley to April 5,
2015.\16\
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    \14\ 76 FR 69896, n. 2 (November 9, 2011).
    \15\ Id. at 69924.
    \16\ Id.
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    Following a January 4, 2013 decision of the U.S. Court of Appeals
for the D.C. Circuit (``D.C. Circuit'') remanding the EPA's 2007
implementation rule for the 1997 PM2.5 NAAQS,\17\ the EPA
published a final rule on June 2, 2014, classifying the San Joaquin
Valley as a Moderate nonattainment area for the 1997 24-hour and annual
PM2.5 NAAQS under subpart 4, part D of title I of the
Act.\18\ In this action, the EPA acknowledged that states must meet
both subpart 1 and subpart 4 requirements in nonattainment plan SIP
submissions for the 1997 24-hour and annual PM2.5 NAAQS and
provided states with additional time to supplement or withdraw and
resubmit any pending nonattainment plan SIP submissions.
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    \17\ Natural Resources Defense Council v. EPA, 706 F.3d. 428
(D.C. Cir. 2013) (``NRDC''). In NRDC, the court held that the EPA
erred in implementing the 1997 PM2.5 standards solely
pursuant to the general implementation requirements of subpart 1,
without also considering the requirements specific to nonattainment
areas for particles less than or equal to 10 [micro]m in diameter
(PM10) in subpart 4, part D of title I of the CAA. The
court reasoned that the plain meaning of the CAA requires
implementation of the 1997 PM2.5 standards under subpart
4 because PM2.5 falls within the statutory definition of
PM10 and is thus subject to the same statutory
requirements as PM10. The court remanded the rule,
without vacatur, and instructed the EPA ``to repromulgate these
rules pursuant to Subpart 4 consistent with this opinion.''
    \18\ 79 FR 31566.
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    Effective May 7, 2015, the EPA reclassified the San Joaquin Valley
as a Serious nonattainment area for the 1997 PM2.5 NAAQS
based on the determination that the State could not practicably attain
these NAAQS in the San Joaquin Valley nonattainment area by the latest
statutory Moderate area attainment date, i.e., April 5, 2015.\19\ Upon
reclassification as a Serious area, the State became subject to the
requirement of CAA section 188(c)(2) to attain the 1997
PM2.5 NAAQS, as expeditiously as practicable but no later
than ten years after designation, i.e., by no later than December 31,
2015. California submitted its 1997 PM2.5 Serious area plan
for the San Joaquin Valley in two submissions dated June 25, 2015 and
August 13, 2015, including a request under section 188(e) to extend the
attainment date for the 1997 24-hour PM2.5 NAAQS by three
years (to December 31, 2018) and to extend the attainment date for the
1997 annual PM2.5 NAAQS by five years (to December 31,
2020). On February 9, 2016, the EPA proposed to approve most of the
Serious area plan and to

grant the State's request for extensions of the December 31, 2015
attainment date.\20\ However, on October 6, 2016, after considering
public comments, the EPA denied California's request for these
extensions of the attainment dates.\21\ Consequently, on November 23,
2016, the EPA determined that the San Joaquin Valley had failed to
attain the 1997 24-hour and annual PM2.5 NAAQS by the
December 31, 2015 Serious area attainment date.\22\ This determination
triggered a requirement for California to submit a new SIP submission
for the 1997 24-hour and annual PM2.5 NAAQS for the San
Joaquin Valley that satisfies the requirements of CAA section 189(d).
The statutory deadline for this additional SIP submission was December
31, 2016. The EPA did not finalize the actions proposed on February 9,
2016, with respect to the submitted Serious area plan.\23\
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    \19\ 80 FR 18528 (April 7, 2015).
    \20\ 81 FR 6936. California's request for extension of the
Serious Area attainment date for the San Joaquin Valley accompanied
its Serious Area attainment plan for the 1997 PM2.5 NAAQS
and related motor vehicle emission budgets, submitted June 25, 2015
and August 13, 2015, respectively.
    \21\ 81 FR 69396.
    \22\ 81 FR 84481.
    \23\ 81 FR 69396, 69400.
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    On December 6, 2018, the EPA determined that California had failed
to submit a complete section 189(d) attainment plan for the 1997 24-
hour and annual PM2.5 NAAQS, among other required SIP
submissions for the San Joaquin Valley, by the statutory deadlines.\24\
This finding, which became effective on January 7, 2019, triggered
clocks under CAA section 179(a) for the application of emissions offset
sanctions 18 months after the finding, and highway funding sanctions 6
months thereafter, unless the EPA affirmatively determined that the
State has made a complete SIP submission addressing the identified
failure to submit deficiencies.\25\ The finding also triggered the
obligation under CAA section 110(c) for the EPA to promulgate a federal
implementation plan no later than two years after the finding, unless
the State has submitted, and the EPA has approved, the required SIP
submission.\26\
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    \24\ 83 FR 62720.
    \25\ Id. at 62723.
    \26\ Id.
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    On May 10, 2019, CARB made SIP submissions intended to address the
Serious area nonattainment plan and CAA section 189(d) requirements for
the 1997 24-hour and annual PM2.5 NAAQS, among other
requirements for the 2006 and 2012 PM2.5 NAAQS.\27\ CARB
clarified in its May 10, 2019 letter that these new SIP submissions
superseded past submissions to the EPA that the agency had not yet
acted on for the 1997 PM2.5 NAAQS, including the 2015
Serious area attainment plan submissions. On June 24, 2020, the EPA
issued a letter finding these submissions complete and terminating the
sanctions clocks under CAA section 179(a).\28\ The portions of these
SIP submissions that pertain to the 1997 24-hour PM2.5 NAAQS
are the subject of this proposal.
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    \27\ Letter dated May 9, 2019, from Richard Corey, Executive
Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region 9.
The letter clarifies that the 2018 PM2.5 Plan supersedes
past submittals to the EPA that the agency has not yet acted on for
the 1997 PM2.5 standards, including the 2015 Plan for the
1997 Standard (submitted by CARB on June 25, 2015) and motor vehicle
emission budgets (submitted by CARB August 13, 2015).
    \28\ Letter dated June 24, 2020, from Elizabeth J. Adams,
Director, Air and Radiation Division, EPA Region IX, to Richard
Corey, Executive Officer, CARB, Subject: ``RE: Completeness Finding
for State Implementation Plan (SIP) Submissions for San Joaquin
Valley for the 1997, 2006, and 2012 Fine Particulate Matter
(PM2.5) National Ambient Air Quality Standards (NAAQS)
and Termination of Clean Air Act (CAA) Sanction Clocks.''
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II. Summary and Completeness Review of the San Joaquin Valley
PM[bdi2].[bdi5] Plan

    The EPA is proposing action on portions of two SIP submissions made
by CARB to address nonattainment plan requirements for the 1997 24-hour
PM2.5 NAAQS in the San Joaquin Valley. Specifically, the EPA
is proposing to act on those portions of the following two SIP
submissions that pertain to the 1997 24-hour PM2.5 NAAQS:
(i) The ``2018 Plan for the 1997, 2006, and 2012 PM2.5
Standards,'' adopted by the SJVUAPCD on November 15, 2018, and by CARB
on January 24, 2019 (``2018 PM2.5 Plan''); \29\ and (ii) the
``San Joaquin Valley Supplement to the 2016 State Strategy for the
State Implementation Plan,'' adopted by CARB on October 25, 2018
(``Valley State SIP Strategy''). CARB submitted the 2018
PM2.5 Plan and Valley State SIP Strategy to the EPA as a
revision to the California SIP on May 10, 2019.\30\ We refer to these
two SIP submissions collectively as the ``SJV PM2.5 Plan''
or ``Plan.''
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    \29\ The 2018 PM2.5 Plan was developed jointly by
CARB and the District.
    \30\ Letter dated May 9, 2019, from Richard Corey, Executive
Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region 9.
The EPA previously acted on those portions of the ``2018 Plan for
the 1997, 2006, and 2012 PM2.5 Standards'' and the ``San
Joaquin Valley Supplement to the 2016 State Strategy for the State
Implementation Plan'' that pertain to the 2006 PM2.5
NAAQS (85 FR 44192, July 22, 2020), and proposed action on those
portions pertaining to the 1997 annual PM2.5 NAAQS (86 FR
38652, July 22, 2021) and 2012 annual PM2.5 NAAQS (86 FR
49100, September 1, 2021). The EPA is not, at this time, taking any
action on those portions that pertain to the 1997 annual
PM2.5 NAAQS or the 2012 annual PM2.5 NAAQS. We
intend to act on these portions of the submitted SIP revisions in
subsequent rulemakings.
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    The SJV PM2.5 Plan addresses the Serious area
nonattainment plan and CAA section 189(d) requirements for the 1997 24-
hour and annual PM2.5 NAAQS in the San Joaquin Valley,
including the State's demonstration that the area would attain the 1997
24-hour PM2.5 NAAQS by December 31, 2020. In this proposal,
the EPA is proposing action only on those portions of the SJV
PM2.5 Plan that pertain to the 1997 24-hour PM2.5
NAAQS. The EPA is acting on the portions of the SJV PM2.5
Plan that pertain to the 1997 annual PM2.5 NAAQS and
subsequent PM2.5 NAAQS in separate rulemakings.
    CAA sections 110(a)(1) and (2) and 110(l) require each state to
provide reasonable public notice and opportunity for public hearing
prior to the adoption and submission of a SIP or SIP revision to the
EPA. To meet this requirement, every SIP submission must include
evidence that the state provided adequate public notice and an
opportunity for a public hearing consistent with the EPA's implementing
regulations in 40 CFR 51.102.
    CAA section 110(k)(1)(B) requires the EPA to determine whether a
SIP submission is complete within 60 days of receipt. This section also
provides that any plan that the EPA has not affirmatively determined to
be complete or incomplete will become complete by operation of law six
months after the date of submission. The EPA's SIP completeness
criteria are found in 40 CFR part 51, Appendix V.

A. 2018 PM2.5 Plan

    The following portions of the 2018 PM2.5 Plan and
related support documents address both the Serious area nonattainment
plan requirements in CAA section 189(b) and the CAA section 189(d)
requirements for the 1997 24-hour PM2.5 NAAQS in the San
Joaquin Valley: (i) Chapter 4 (``Attainment Strategy for
PM2.5''); (ii) Chapter 5 (``Demonstration of Federal
Requirements for 1997 PM2.5 Standards''); \31\ (iii)
numerous appendices to the 2018 PM2.5 Plan; (iv)

CARB's ``Staff Report, Review of the San Joaquin Valley 2018 Plan for
the 1997, 2006, and 2012 PM2.5 Standards,'' release date
December 21, 2018 (``CARB Staff Report''); \32\ and (v) the State's and
District's board resolutions adopting the 2018 PM2.5 Plan
(CARB Resolution 19-1 and SJVUAPCD Governing Board Resolution 18-11-
16).\33\
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    \31\ Chapter 6 (``Demonstration of Federal Requirements for the
2006 PM2.5 Standard: Serious Plan and Extension
Request'') and Chapter 7 (``Demonstration of Federal Requirements
for the 2012 PM2.5 Standard'') of the 2018
PM2.5 Plan pertain to the 2006 PM2.5 NAAQS and
the 2012 PM2.5 NAAQS, respectively. The EPA previously
acted on those portions of the Plan that pertain to the 2006
PM2.5 NAAQS (85 FR 44192), and proposed action on those
portions pertaining to the 2012 annual PM2.5 NAAQS (86 FR
49100). The EPA intends to take further action on those portions
that pertain to the 2012 annual PM2.5 NAAQS in separate
rulemakings.
    \32\ Letter dated December 11, 2019, from Richard Corey,
Executive Officer, CARB, to Mike Stoker, Regional Administrator, EPA
Region 9, transmitting the CARB Staff Report [on the 2018
PM2.5 Plan]. The CARB Staff Report includes CARB's review
of, among other things, the 2018 PM2.5 Plan's control
strategy and attainment demonstration.
    \33\ 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 that address the
requirements for the 1997 24-hour PM2.5 NAAQS include: (i)
Appendix A (``Ambient PM2.5 Data Analysis''); (ii) Appendix
B (``Emissions Inventory''); (iii) Appendix C (``Stationary Source
Control Measure Analyses''); (iv) Appendix D (``Mobile Source Control
Measure Analyses''); (v) Appendix G (``Precursor Demonstration''); (vi)
Appendix H (``RFP, Quantitative Milestones, and Contingency''); \34\
(vii) Appendix I (``New Source Review and Emission Reduction
Credits''); (viii) Appendix J (``Modeling Emission Inventory''); (ix)
Appendix K (``Modeling Attainment Demonstration''); and (x) Appendix L
(``Modeling Protocol'').
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    \34\ Appendix H to 2018 PM2.5 Plan, submitted
February 11, 2020 via the EPA State Planning Electronic
Collaboration System. Following the identification of a
transcription error in the RFP tables of Appendix H, on February 11,
2020, the State submitted a revised version of Appendix H that
corrects the transcription error and provides additional information
on the RFP demonstration. All references to Appendix H in this
proposed rule are to the revised version submitted on February 11,
2020, which replaces the version submitted with the 2018
PM2.5 Plan on May 10, 2019.
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    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.\35\ CARB also provided public notice
and opportunity for public comment prior to its January 24, 2019 public
hearing on and adoption of the 2018 PM2.5 Plan.\36\ 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.\37\ Therefore, we find
that the 2018 PM2.5 Plan meets the procedural requirements
for public notice and hearing in CAA sections 110(a) and 110(l) and 40
CFR 51.102. The 2018 PM2.5 Plan became complete by operation
of law on November 10, 2019.
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    \35\ 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.
    \36\ CARB, ``Notice of Public Meeting to Consider the 2018
PM2.5 State Implementation Plan for the San Joaquin
Valley,'' December 21, 2018, and CARB Resolution 19-1.
    \37\ 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, Appendix M (``Summary of Significant
Comments and Responses'').
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B. Valley State SIP Strategy

    CARB developed the ``Revised Proposed 2016 State Strategy for the
State Implementation Plan'' (``2016 State Strategy'') to support
attainment planning in the San Joaquin Valley and Los Angeles-South
Coast Air Basin (``South Coast'') ozone nonattainment areas.\38\ In its
resolution adopting the 2016 State Strategy (CARB Resolution 17-7), the
Board found that the 2016 State Strategy would achieve 6 tons per day
(tpd) of NOX emissions reductions and 0.1 tpd of direct
PM2.5 emissions reductions in the San Joaquin Valley by 2025
and directed CARB staff to work with the SJVUAPCD to identify
additional reductions from sources under District regulatory authority
as part of a comprehensive plan to attain all of the PM2.5
NAAQS in the San Joaquin Valley and to return to the Board with a
commitment to achieve additional emissions reductions from mobile
sources.\39\
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    \38\ The EPA has approved certain commitments made by CARB in
the 2016 State Strategy for purposes of attaining the ozone NAAQS in
the San Joaquin Valley and South Coast ozone nonattainment areas
(see, e.g., 84 FR 3302 (February 12, 2019) and 84 FR 52005 (October
1, 2019)) and for attaining the 2006 PM2.5 NAAQS in the
San Joaquin Valley (85 FR 44192).
    \39\ CARB Resolution 17-7, ``2016 State Strategy for the State
Implementation Plan,'' March 23, 2017, 6-7.
---------------------------------------------------------------------------

    CARB responded to this resolution by developing and adopting the
``San Joaquin Valley Supplement to the 2016 State Strategy for the
State Implementation Plan'' (``Valley State SIP Strategy'') to support
the 2018 PM2.5 Plan. The State's May 10, 2019 SIP submission
incorporates by reference the Valley State SIP Strategy as adopted by
CARB on October 25, 2018 and submitted to the EPA on November 16,
2018.\40\
---------------------------------------------------------------------------

    \40\ Letter dated May 9, 2019, from Richard Corey, Executive
Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region 9.
---------------------------------------------------------------------------

    The Valley State SIP Strategy includes an ``Introduction'' (Chapter
1), a chapter on ``Measures'' (Chapter 2), and a ``Supplemental State
Commitment from the Proposed State Measures for the Valley'' (Chapter
3). Much of the content of the Valley State SIP Strategy is reproduced
in Chapter 4 (``Attainment Strategy for PM2.5'') of the 2018
PM2.5 Plan.\41\ The Valley State SIP Strategy also includes
CARB Resolution 18-49, which, among other things, commits CARB to
achieve specific amounts of NOX and PM2.5
emissions reductions by specific years, for purposes of attaining the
PM2.5 NAAQS in the San Joaquin Valley.\42\
---------------------------------------------------------------------------

    \41\ For example, Table 2 (proposed mobile source measures and
schedule), Table 3 (emissions reductions from proposed mobile source
measures), and Table 4 (summary of emission reduction measures) of
the Valley State SIP Strategy correspond to tables 4-8, 4-9, and 4-
7, respectively, of the 2018 PM2.5 Plan, Chapter 4.
    \42\ CARB Resolution 18-49, ``San Joaquin Valley Supplement to
the 2016 State Strategy for the State Implementation Plan,'' October
25, 2018, 5.
---------------------------------------------------------------------------

    CARB provided the required public notice and opportunity for public
comment prior to its October 25, 2018 public hearing on and adoption of
the Valley State SIP Strategy.\43\ The SIP submission includes proof of
publication of the public notice for this public hearing. It also
includes copies of the written and oral comments received during the
State's public review process and CARB's responses thereto.\44\
Therefore, we find that the Valley State SIP Strategy meets the
procedural requirements for public notice and hearing in CAA sections
110(a) and 110(l) and 40 CFR 51.102. The Valley State SIP Strategy
became complete by operation of law on November 10, 2019.
---------------------------------------------------------------------------

    \43\ CARB, ``Notice of Public Meeting to Consider the San
Joaquin Valley Supplement to the 2016 State Strategy for the State
Implementation Plan,'' September 21, 2018, and CARB Resolution 18-
49.
    \44\ CARB, ``Board Meeting Comments Log,'' November 2, 2018 and
compilation of written comments; and J&K Court Reporting, LLC,
``Meeting, State of California Air Resources Board,'' October 25,
2018 (transcript of CARB's public hearing).
---------------------------------------------------------------------------

III. Clean Air Act Requirements for PM[bdi2].[bdi5] Serious
Area Plans and for Serious PM[bdi2].[bdi5] Areas That Fail
To Attain

A. Requirements for PM2.5 Serious Area Plans

    Upon reclassification of a Moderate nonattainment area as a Serious
nonattainment area under subpart 4 of part D, title I of the CAA, the
Act requires the state to make a SIP submission that addresses the
following Serious nonattainment area requirements: \45\
---------------------------------------------------------------------------

    \45\ 40 CFR 51.1003(b)(1); 81 FR 58010, 58074-58075 (August 24,
2016).
---------------------------------------------------------------------------

    1. A comprehensive, accurate, current inventory of actual emissions
from all sources of PM2.5 and PM2.5 precursors in
the area (CAA section 172(c)(3));

    2. Provisions to assure that the best available control measures
(BACM), including best available control technology (BACT), for the
control of direct PM2.5 and PM2.5 precursors
shall be implemented no later than four years after the area is
reclassified (CAA section 189(b)(1)(B));
    3. A demonstration (including air quality modeling) that the plan
provides for attainment as expeditiously as practicable but no later
than the end of the tenth calendar year after designation as a
nonattainment area (i.e., December 31, 2015, for the San Joaquin Valley
for the 1997 PM2.5 NAAQS);
    4. Plan provisions that require RFP (CAA section 172(c)(2));
    5. Quantitative milestones that are to be achieved every three
years until the area is redesignated attainment and that demonstrate
RFP toward attainment by the applicable date (CAA section 189(c));
    6. Provisions to assure that control requirements applicable to
major stationary sources of PM2.5 also apply to major
stationary sources of PM2.5 precursors, except where the
state demonstrates to the EPA's satisfaction that such sources do not
contribute significantly to PM2.5 levels that exceed the
standard in the area (CAA section 189(e)); \46\
---------------------------------------------------------------------------

    \46\ As discussed in section IV.H, California submitted
nonattainment NSR SIP revisions to address the subpart 4
requirements for the San Joaquin Valley Serious PM2.5
nonattainment area on November 20, 2019. We are not proposing any
action on this submission at this time. We will act on this
submission through a separate rulemaking, as appropriate.
---------------------------------------------------------------------------

    7. Contingency measures to be implemented if the area fails to meet
RFP or to attain by the applicable attainment date (CAA section
172(c)(9)); and
    8. A revision to the nonattainment new source review (NSR) program
to lower the applicable ``major stationary source'' \47\ thresholds
from 100 tons per year (tpy) to 70 tpy (CAA section 189(b)(3)).
---------------------------------------------------------------------------

    \47\ For any Serious area, the terms ``major source'' and
``major stationary source'' include any stationary source that emits
or has the potential to emit at least 70 tons per year of
PM2.5. CAA section 189(b)(3) and 40 CFR
51.165(a)(1)(iv)(A)(1)(vii) and (viii) (defining ``major stationary
source'' in serious PM2.5 nonattainment areas).
---------------------------------------------------------------------------

    Serious area plans must also satisfy the requirements for Moderate
area plans in CAA section 189(a), to the extent the state has not
already met those requirements in the Moderate area plan submitted for
the area.\48\ In addition, the Serious area plan must meet the general
requirements applicable to all SIP submissions under section 110 of the
CAA, including the requirement to provide necessary assurances that the
implementing agencies have adequate personnel, funding, and authority
under section 110(a)(2)(E); and the requirements concerning enforcement
provisions in section 110(a)(2)(C).
---------------------------------------------------------------------------

    \48\ Because the EPA has not previously approved a SIP
submission for the San Joaquin Valley as meeting the subpart 4 RACM
Moderate area planning requirement under CAA section 189 for the
1997 24-hour PM2.5 NAAQS, the EPA is evaluating relevant
portions of the SJV PM2.5 Plan for compliance with these
requirements, in addition to the requirements of CAA sections 189(b)
and 189(d).
---------------------------------------------------------------------------

B. Requirements for Serious PM2.5 Areas That Fail To Attain

    In the event that a Serious area fails to attain the
PM2.5 NAAQS by the applicable attainment date, CAA section
189(d) requires that ``the State in which such area is located shall,
after notice and opportunity for public comment, submit within 12
months after the applicable attainment date, plan revisions which
provide for attainment of the . . . standard . . .'' An attainment plan
under section 189(d) must, among other things, demonstrate expeditious
attainment of the NAAQS within the time period provided under CAA
section 179(d)(3) and provide for annual reductions in emissions of
direct PM2.5 or a PM2.5 plan precursor pollutant
within the area of not less than five percent per year from the most
recent emissions inventory for the area until attainment.\49\ In
addition to the requirement to submit control measures providing for a
five percent reduction in emissions of certain pollutants on an annual
basis, the EPA interprets CAA section 189(d) as requiring a state to
submit an attainment plan that includes the same basic statutory plan
elements that are required for other attainment plans.\50\
---------------------------------------------------------------------------

    \49\ CAA section 189(d), 40 CFR 51.1004(a)(3), 40 CFR
51.1010(c).
    \50\ 81 FR 58010, 58098.
---------------------------------------------------------------------------

    Specifically, a state must submit to the EPA its plan to meet the
requirements of CAA section 189(d) in the form of a complete attainment
plan submission that includes the following elements: \51\
---------------------------------------------------------------------------

    \51\ 40 CFR 51.1003(c)(1).
---------------------------------------------------------------------------

    1. A comprehensive, accurate, current inventory of actual emissions
from all sources of PM2.5 and PM2.5 precursors in
the area;
    2. A Serious area plan control strategy that ensures that BACM,
including BACT, for the control of direct PM2.5 and
PM2.5 precursors are implemented in the area;
    3. Additional measures (beyond those already adopted in previous
nonattainment plan SIP submissions for the area as RACM/RACT, BACM/
BACT, and most stringent measures (MSM) (if applicable)) \52\ that
provide for attainment of the NAAQS as expeditiously as practicable
and, from the date of such submission until attainment, demonstrate
that the plan will at a minimum achieve an annual five percent
reduction in emissions of direct PM2.5 or any
PM2.5 plan precursor;
---------------------------------------------------------------------------

    \52\ MSM is applicable if the EPA has previously granted an
extension of the attainment date under CAA section 188(e) for the
nonattainment area and NAAQS at issue.
---------------------------------------------------------------------------

    4. A demonstration (including air quality modeling) that the plan
provides for attainment of the NAAQS at issue as expeditiously as
practicable;
    5. Plan provisions that require RFP;
    6. Quantitative milestones that the state is to meet every three
years until the area is redesignated attainment and that demonstrate
RFP toward attainment by the applicable date;
    7. Contingency measures to be implemented if the state fails to
meet any requirement concerning RFP or quantitative milestones or to
attain the NAAQS at issue by the applicable attainment date; and
    8. Provisions to assure that control requirements applicable to
major stationary sources of PM2.5, also apply to major
stationary sources of PM2.5 precursors, except where the
state demonstrates to the EPA's satisfaction that such sources do not
contribute significantly to PM2.5 levels that exceed the
NAAQS at issue in the area.\53\
---------------------------------------------------------------------------

    \53\ As discussed in section IV.H, California submitted
nonattainment NSR SIP revisions to address the subpart 4
requirements for the San Joaquin Valley Serious PM2.5
nonattainment area on November 20, 2019. We are not proposing any
action on this submission at this time. We will act on this
submission through a separate rulemaking, as appropriate.
---------------------------------------------------------------------------

    A state's section 189(d) plan submission must demonstrate
attainment as expeditiously as practicable, and no later than five
years from the date of the EPA's determination that the area failed to
attain, consistent with sections 179(d)(3) and 172(a)(2) of the
CAA.\54\
---------------------------------------------------------------------------

    \54\ 81 FR 84481, 84482.
---------------------------------------------------------------------------

    A state with a Serious PM2.5 nonattainment area that
fails to attain the NAAQS by the applicable Serious area attainment
date must also address any statutory requirements applicable to
Moderate and Serious nonattainment area plans under CAA sections 172
and 189 of the CAA to the extent that those requirements have not
already been met.\55\ Because the EPA has not previously approved a SIP
submission

for the San Joaquin Valley as meeting the subpart 4 RACM Moderate area
planning requirements under CAA section 189 for the 1997 24-hour
PM2.5 NAAQS, the EPA is evaluating relevant portions of the
SJV PM2.5 Plan for compliance with this requirement. In
addition, as discussed above, the EPA has not previously approved a SIP
submission for the San Joaquin Valley as meeting the Serious area
planning requirements under CAA section 189(b)(1) for the 1997 24-hour
PM2.5 NAAQS. Some Serious area planning requirements operate
on a timeline that is based on the outermost statutory Serious area
attainment date of the end of the tenth calendar year following the
area's designation to nonattainment. Because section 189(d) requires a
state to address any applicable Serious area requirements that the
state has not already met in the area, and the section 189(d)
obligations do not come into effect until an area has failed to attain
the NAAQS by the Serious area attainment date, the EPA proposes that it
should evaluate any previously unmet Serious area planning obligations
based on the current, applicable attainment date appropriate under
section 189(d), and not the original Serious area attainment date.
---------------------------------------------------------------------------

    \55\ 81 FR 58010, 58098.
---------------------------------------------------------------------------

    The EPA provided its preliminary views on the CAA's requirements
for particulate matter plans under part D, title I of the Act in the
following guidance documents: (1) ``State Implementation Plans; General
Preamble for the Implementation of Title I of the Clean Air Act
Amendments of 1990'' (``General Preamble''); \56\ (2) ``State
Implementation Plans; General Preamble for the Implementation of Title
I of the Clean Air Act Amendments of 1990; Supplemental'' (``General
Preamble Supplement''); \57\ and (3) ``State Implementation Plans for
Serious PM-10 Nonattainment Areas, and Attainment Date Waivers for PM-
10 Nonattainment Areas Generally; Addendum to the General Preamble for
the Implementation of Title I of the Clean Air Act Amendments of 1990''
(``General Preamble Addendum'').\58\ More recently, in an August 24,
2016 final rule entitled, ``Fine Particulate Matter National Ambient
Air Quality Standards: State Implementation Plan Requirements''
(``PM2.5 SIP Requirements Rule''), the EPA established
regulatory requirements and provided further interpretive guidance on
the statutory SIP requirements that apply to areas designated
nonattainment for the PM2.5 NAAQS.\59\ We discuss these
regulatory requirements and interpretations of the Act as appropriate
in our evaluation of the SJV PM2.5 Plan that follows.
---------------------------------------------------------------------------

    \56\ 57 FR 13498 (April 16, 1992).
    \57\ 57 FR 18070 (April 28, 1992).
    \58\ 59 FR 41998 (August 16, 1994).
    \59\ 81 FR 58010.
---------------------------------------------------------------------------

IV. Review of the San Joaquin Valley PM[bdi2].[bdi5] Plan
for the 1997 24-Hour PM[bdi2].[bdi5] NAAQS

    The EPA is evaluating the SJV PM2.5 Plan against the
Serious area requirements for the 1997 24-hour PM2.5 NAAQS
and the section 189(d) requirements for the 1997 24-hour
PM2.5 NAAQS, as laid out in section III of this proposal.
Many requirements for both a Serious area plan and a section 189(d)
plan are structured around the relevant statutory attainment date. The
latest statutory Serious area attainment date for the San Joaquin
Valley area was December 31, 2015.\60\ On November 23, 2016, the EPA
determined that the area failed to attain by the Serious area
attainment date.
---------------------------------------------------------------------------

    \60\ As discussed in section I.B, California submitted its
Serious area plan for the 1997 24-hour PM2.5 NAAQS in two
submissions dated June 25, 2015 and August 13, 2015, including a
request under section 188(e) to extend the attainment date for the
1997 24-hour PM2.5 NAAQS by three years (to December 31,
2018). On October 6, 2016, the EPA denied the request for an
extension, but did not finalize action on the Serious area plan
submissions. Accordingly, the Serious area attainment date remained
unchanged: As expeditiously as practicable but no later than
December 31, 2015.
---------------------------------------------------------------------------

    For the purposes of the section 189(d) requirements, the attainment
date is the date by which a state can attain the NAAQS as expeditiously
as practicable, but no later than five years from the publication date
of the final determination of failure to attain.\61\ As discussed in
section IV.D, the SJV PM2.5 Plan projected that attainment
could be achieved in fewer than five years, i.e., by December 31, 2020.
---------------------------------------------------------------------------

    \61\ CAA section 179(d)(3); 81 FR 84481, 84482. The
determination of failure to attain published on November 23, 2016.
---------------------------------------------------------------------------

    When the State submitted the SJV PM2.5 Plan in 2019, the
State withdrew its previous Serious area plan that it had developed to
meet the December 31, 2015 Serious area attainment date. Because the
State submitted the SJV PM2.5 Plan after the EPA's finding
that the area had failed to attain by the applicable Serious area
attainment date, the State could not demonstrate in the SJV
PM2.5 Plan that the area would attain by the Serious area
attainment date, nor could it address other requirements based on this
attainment date, such as RFP and quantitative milestones, because many
of the relevant dates had already passed. As described in section III
of this document, in a section 189(d) plan, a state must address any
statutory requirements applicable to Moderate and Serious nonattainment
area plans to the extent that it has not already met those
requirements, but the EPA believes that it should base this evaluation
on the current applicable attainment date under section 189(d). For
example, it would be illogical to require a state to submit a Serious
area modeled attainment demonstration that provided for attainment by
December 31, 2015, after the EPA has already determined based on
monitoring data that the state failed to attain by such date.
    For the purposes of our evaluation of the Serious area plan
requirements, although the State is required to submit a Serious area
plan, and it must structure such a plan based on the Serious area
attainment date, it would serve no purpose to evaluate the SJV
PM2.5 Plan against the now-passed Serious area attainment
date by which the area has already failed to attain. For example, RFP
and quantitative milestones normally are dependent upon the attainment
date. Accordingly, because the State must still meet all Serious area
plan requirements, even if doing so later in conjunction with the
section 189(d) plan and its later attainment date, we will evaluate the
State's compliance with the Serious area plan requirements in light of
the later section 189(d) attainment date, as appropriate. Where the
State in the SJV PM2.5 Plan applies the section 189(d)
attainment date to a Serious area requirement, we will note the
statutory Serious area timeline and accept the submission in
fulfillment of the State's Serious area plan obligation, but evaluate
the submission in light of the section 189(d) attainment date.

A. Emissions Inventories

1. Statutory and Regulatory Requirements
    CAA section 172(c)(3) requires that each SIP include a
comprehensive, accurate, current inventory of actual emissions from all
sources of the relevant pollutant or pollutants in the nonattainment
area. The EPA discussed the emissions inventory requirements that apply
to PM2.5 nonattainment areas in the PM2.5 SIP
Requirements Rule and codified these requirements in 40 CFR
51.1008.\62\ The EPA has also issued guidance concerning emissions

inventories for PM2.5 nonattainment areas.\63\
---------------------------------------------------------------------------

    \62\ Id. at 58098-58099.
    \63\ ``Emissions Inventory Guidance for Implementation of Ozone
and Particulate Matter National Ambient Air Quality Standards
(NAAQS) and Regional Haze Regulations,'' U.S. 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 for a Serious area attainment
plan or a CAA section 189(d) plan must provide a state's best estimate
of actual emissions from all sources of the relevant pollutants in the
area, i.e., all emissions that contribute to the formation of a
particular NAAQS pollutant. For the PM2.5 NAAQS, the base
year inventory must include direct PM2.5 emissions,
separately reported filterable and condensable PM2.5
emissions,\64\ and emissions of all chemical precursors to the
formation of secondary PM2.5, i.e., nitrogen oxides
(NOX), sulfur dioxide (SO2), volatile organic
compounds (VOC), and ammonia.\65\
---------------------------------------------------------------------------

    \64\ 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.
    \65\ 40 CFR 51.1008(b)(1) and (c)(1).
---------------------------------------------------------------------------

    The emissions inventory base year for a Serious area attainment
plan must be one of the three years for which monitoring data were used
to reclassify the area to Serious, or another technically appropriate
year justified by the state in its Serious area SIP submission.\66\ The
emissions inventory base year for a Serious PM2.5
nonattainment area subject to CAA section 189(d) must be one of the
three years for which the EPA used monitored data to determine that the
area failed to attain the PM2.5 NAAQS by the applicable
Serious area attainment date, or another technically appropriate year
justified by the state in its Serious area SIP submission.\67\
---------------------------------------------------------------------------

    \66\ 40 CFR 51.1008(b)(1).
    \67\ 40 CFR 51.1008(c)(1).
---------------------------------------------------------------------------

    A state's SIP submission must include documentation explaining how
it calculated emissions data for the inventory. In estimating mobile
source emissions, a state should use the latest emissions models and
planning assumptions available at the time the SIP is developed. The
latest EPA-approved version of California's mobile source emission
factor model for estimating tailpipe, brake, and tire wear emissions
from on-road mobile sources that was available during the State's and
District's development of the SJV PM2.5 Plan was
EMFAC2014.\68\ Following CARB's submission of the Plan, the EPA
approved EMFAC2017, the latest revision to this mobile source emissions
model. 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.\69\ \70\
---------------------------------------------------------------------------

    \68\ 80 FR 77337 (December 14, 2015). EMFAC is short for
EMission FACtor. The EPA announced the availability of the EMFAC2014
model, effective on the date of publication in the Federal Register,
for use in state implementation plan development and transportation
conformity in California. Upon that action, EMFAC2014 was required
to be used for all new regional emissions analyses and CO,
PM10, and PM2.5 hot-spot analyses that were
started on or after December 14, 2017, which was the end of the
grace period for using the prior mobile source emissions model,
EMFAC2011.
    \69\ 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; see
https://www.arb.ca.gov/ei/areasrc/fullpdf/full7-9_2016.pdf.
    \70\ AP-42 has been published since 1972 as the primary source
of the EPA's emission factor information and is available at https://www.epa.gov/air-emissions-factors-and-quantification/ap-42-compilation-air-emissions-factors. 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.
---------------------------------------------------------------------------

    In addition to the base year inventory submitted to meet the
requirements of CAA section 172(c)(3), the state must also submit a
projected attainment year inventory and emissions projections for each
RFP milestone year.\71\ These future emissions projections are
necessary components of the attainment demonstrations required under
CAA sections 189(b)(1) and 189(d) and the demonstration of RFP required
under section 172(c)(2).\72\ Emissions projections for future years
(referred to in the Plan as ``forecasted inventories'') should account
for, among other things, the ongoing effects of economic growth and
adopted emissions control requirements. The state's SIP submission
should include documentation to explain how the state calculated the
emissions projections. Where a state chooses to allow new major
stationary sources or major modifications to use emissions reduction
credits (ERCs) that were generated through shutdown or curtailed
emissions units occuring before the base year of an attainment plan,
the projected emissions inventory used to develop the attainment
demonstration must explicitly include the emissions from such
previously shutdown or curtailed emissions units.\73\
---------------------------------------------------------------------------

    \71\ 40 CFR 51.1008 and 51.1012. See also Emissions Inventory
Guidance, section 3 (``SIP Inventory Requirements and
Recommendations'').
    \72\ 40 CFR 51.1004, 51.1008, 51.1011, and 51.1012.
    \73\ 40 CFR 51.165(a)(3)(ii)(C)(1).
---------------------------------------------------------------------------

2. Summary of the State's Submission
    The State included summaries of the planning emissions inventories
for direct PM2.5 and PM2.5 precursors
(NOX, SOX,\74\ VOC,\75\ and ammonia) and the
documentation for the inventories for the San Joaquin Valley
PM2.5 nonattainment area in Appendix B (``Emissions
Inventory'') and Appendix I (``New Source Review and Emission Reduction
Credits'') of the 2018 PM2.5 Plan.
---------------------------------------------------------------------------

    \74\ The SJV PM2.5 Plan generally uses ``sulfur
oxides'' or ``SOX'' in reference to SO2 as a
precursor to the formation of PM2.5. We use
SOX and SO2 interchangeably throughout this
document.
    \75\ The SJV PM2.5 Plan generally uses ``reactive
organic gasses'' or ``ROG'' in reference to VOC as a precursor to
the formation of PM2.5. We use ROG and VOC
interchangeably throughout this document.
---------------------------------------------------------------------------

    CARB and District staff worked together to develop the emissions
inventories for the San Joaquin Valley PM2.5 nonattainment
area. The District worked with operators of the stationary facilities
in the nonattainment area to develop the stationary source emissions
estimates. The responsibility for developing emissions estimates for
area sources such as agricultural burning and paved road dust was
shared by the District and CARB. CARB staff developed the emissions
inventories for both on-road and non-road mobile sources.\76\
---------------------------------------------------------------------------

    \76\ The EPA regulations refer to ``non-road'' vehicles and
engines whereas CARB regulations refer to ``Other Mobile Sources''
or ``off-road'' vehicles and engines. These terms refer to the same
types of vehicles and engines. We refer herein to such vehicles and
engines as ``non-road'' sources.
---------------------------------------------------------------------------

    The Plan includes winter (24-hour) average and annual average daily
emissions inventories for the 2013 base year, which CARB derived from
the 2012 emissions inventory, and estimated emissions for forecasted
years from 2017 through 2028 for the attainment and RFP demonstrations
for the 1997, 2006, and 2012 PM2.5 NAAQS.\77\ In this
proposal, we are proposing action on those winter average and annual
average emissions inventories necessary to support the Serious area and
CAA section 189(d) nonattainment plans for the 1997 24-

hour PM2.5 NAAQS, i.e., the 2013 base year inventory,
forecasted inventories for the RFP milestone years of 2017, 2020
(attainment year), and 2023 (post-attainment milestone year), and
additional forecasted emissions inventories for 2018 and 2019 to
support the five percent annual emissions reduction demonstration as
required by CAA section 189(d). Each inventory includes emissions from
stationary, area, on-road, and non-road sources.
---------------------------------------------------------------------------

    \77\ 2018 PM2.5 Plan, Appendix B, B-18 to B-19. The
winter average daily planning inventory corresponds to the months of
November through April, when daily, ambient PM2.5
concentrations are typically highest. The base year inventory is
from the California Emissions Inventory Development and Reporting
System and future year inventories were estimated using the
California Emission Projection Analysis Model (CEPAM), 2016 SIP
Baseline Emission Projections, version 1.05.
---------------------------------------------------------------------------

    CARB developed the base year inventories for stationary sources
using actual emissions reports from facility operators. The State
developed the base year emissions inventory for area sources using the
most recent models and methodologies available at the time the State
was developing the Plan.\78\ The Plan also 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.\79\ CARB used EMFAC2014 to estimate on-road motor
vehicle emissions based on transportation activity data from the 2014
Regional Transportation Plan (2014 RTP) adopted by the transportation
planning agencies in the San Joaquin Valley.\80\ Re-entrained paved
road dust emissions were calculated using a CARB methodology consistent
with the EPA's AP-42 road dust methodology.\81\
---------------------------------------------------------------------------

    \78\ 2018 PM2.5 Plan, Appendix B, section B.2
(``Emissions Inventory Summary and Methodology'').
    \79\ Id. at B-42 to B-44.
    \80\ Id. at B-37.
    \81\ Id. at B-28.
---------------------------------------------------------------------------

    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.\82\
In addition, the Plan states that the District is providing for use of
pre-base year ERCs as offsets by accounting for such ERCs in the
projected 2025 emissions inventory.\83\ The 2018 PM2.5 Plan
identifies growth factors, control factors, and estimated offset use
between 2013 and 2025 for direct PM2.5, NOX,
SOX, and VOC emissions by source category and lists all pre-
base year ERCs issued by the District for PM10,
NOX, SOX, and VOC emissions, by facility.\84\
---------------------------------------------------------------------------

    \82\ Id. at B-18 and B-19.
    \83\ 2018 PM2.5 Plan, Appendix I, I-1 to I-5.
    \84\ Id. at tables I-1 to I-5.
---------------------------------------------------------------------------

    Table 1 provides a summary of the winter (24-hour) average
inventories in tons per day (tpd) of direct PM2.5 and
PM2.5 precursors for the 2013 base year. Table 2 provides a
summary of annual average inventories of direct PM2.5 and
PM2.5 precursors for the 2013 base year. These annual
average inventories provide the basis for the control measure analysis
and the RFP and attainment demonstrations in the SJV PM2.5
Plan.

  Table 1--San Joaquin Valley Winter Average Emissions Inventory for Direct PM2.5 and PM2.5 Precursors for the
                                              2013 Base Year (tpd)
----------------------------------------------------------------------------------------------------------------
            Category               Direct PM2.5         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 to 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 to B-5.
a Totals reflect disaggregated emissions and may not add exactly as shown here due to rounding.

3. The EPA's Review of the State's Submission
    We have reviewed the emissions inventories in the SJV
PM2.5 Plan that pertain to the 1997 24-hour PM2.5
NAAQS and the emissions inventory estimation methodologies used by
California for consistency with CAA requirements and the EPA's
guidance. We find that the inventories are based on the most current
and accurate information available to the State and District at the
time they were developing the Plan and inventories, including the
latest version of California's mobile source emissions model that had
been approved by the EPA at the time, EMFAC2014. The inventories
comprehensively address all source categories in the San Joaquin Valley
PM2.5 nonattainment area and are consistent with the EPA's
inventory guidance.
    In accordance with 40 CFR 51.1008(b)(1), the 2013 base year is one
of the three years of monitored data with which the EPA reclassified
the San Joaquin Valley area to Serious. Furthermore, in accordance with
40 CFR 51.1008(c)(1), the 2013 base year is one of the three years of
monitored data with which the EPA determined that the San Joaquin
Valley area failed to attain the PM2.5 NAAQS by the
applicable Serious area attainment date for the

1997 24-hour PM2.5 NAAQS.\85\ The 2013 base year emissions
inventories represent actual annual average emissions of all sources
within the nonattainment area, direct PM2.5 and
PM2.5 precursors are included in the inventories, and
filterable and condensable direct PM2.5 emissions are
identified separately.
---------------------------------------------------------------------------

    \85\ 81 FR 84481, 84482.
---------------------------------------------------------------------------

    With respect to future year emissions projections, we have reviewed
the growth and control factors and find them acceptable and thus
conclude that the future baseline emissions projections, which reflect
ongoing emissions reductions from existing (i.e., ``baseline'') control
measures as discussed in section IV.C.2.a, in the SJV PM2.5
Plan reflect appropriate calculation methods and the latest planning
assumptions. 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 sources, the related
rules must be approved by the EPA into the SIP. Table 1 of the EPA's
``Technical Support Document, San Joaquin Valley PM2.5 Plan
for the 1997 24-hour PM2.5 NAAQS,'' August 2021 (``EPA's
1997 24-hour PM2.5 TSD'') shows District rules with post-
2013 compliance dates that are reflected in the future year baseline
inventories, along with information on the EPA's approval of these
rules, and shows that stationary source emissions reductions assumed by
the SJV PM2.5 Plan for future years are supported by rules
approved as part of the California SIP for the San Joaquin Valley. With
respect to mobile sources, the EPA has taken action in recent years to
approve CARB mobile source regulations into the state-wide portion of
the California SIP. We therefore find that the future year baseline
projections in the SJV PM2.5 Plan are properly supported by
SIP-approved stationary and mobile source measures.\86\
---------------------------------------------------------------------------

    \86\ The baseline emissions projections in the 2018
PM2.5 Plan assume implementation of CARB's Zero Emissions
Vehicle (ZEV) sales mandate and greenhouse gas (GHG) standards. 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 for the ZEV sales mandate and
vehicle GHG standards. 84 FR 51310. 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 titled: 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 San Joaquin Valley 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
attainment, RFP, or five percent reductions demonstrations for the
1997 24-hour PM2.5 NAAQS in the SJV PM2.5
Plan.
---------------------------------------------------------------------------

    For these reasons, we are proposing to approve the 2013 base year
emissions inventories in the SJV PM2.5 Plan for the 1997 24-
hour PM2.5 NAAQS as meeting the requirements of CAA section
172(c)(3) and 40 CFR 51.1008 for purposes of both the Serious area and
the CAA section 189(d) attainment plans. We are also proposing to find
that the forecasted inventories in the Plan for the years 2017, 2018,
2019, 2020, and 2023 provide an adequate basis for the BACM, RFP, and
the modeled attainment demonstration analyses in the SJV
PM2.5 Plan.

B. PM2.5 Precursors

1. Statutory and Regulatory Requirements
    The composition of PM2.5 is complex and highly variable
due in part to the large contribution of secondary PM2.5 to
total fine particle mass in most locations, and to the complexity of
secondary particle formation processes. A large number of possible
chemical reactions, often non-linear in nature, can convert gaseous
NOX, SO2, VOC, and ammonia to PM2.5,
making them precursors to PM2.5.\87\ Formation of secondary
PM2.5 may also depend on atmospheric conditions, including
solar radiation, temperature, and relative humidity, and the
interactions of precursors with preexisting particles and with cloud or
fog droplets.\88\
---------------------------------------------------------------------------

    \87\ ``Air Quality Criteria for Particulate Matter'' (EPA/600/P-
99/002aF), EPA, October 2004, Chapter 3.
    \88\ ``Regulatory Impact Analysis for the Final Revisions to the
National Ambient Air Quality Standards for Particulate Matter''
(EPA/452/R-12-005), EPA, December 2012), 2-1.
---------------------------------------------------------------------------

    Under subpart 4 of part D, title I of the CAA and the
PM2.5 SIP Requirements Rule, each state containing a
PM2.5 nonattainment area must evaluate all PM2.5
precursors for regulation unless, for any given PM2.5
precursor, the state demonstrates to the Administrator's satisfaction
that such precursor does not contribute significantly to
PM2.5 levels that exceed the NAAQS in the nonattainment
area.\89\ The provisions of subpart 4 do not define the term
``precursor'' for purposes of PM2.5, nor do they explicitly
require the control of any specifically identified PM2.5
precursor. The statutory definition of ``air pollutant,'' 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.'' \90\ The EPA has identified NOX,
SO2, VOC, and ammonia as precursors to the formation of
PM2.5.\91\ 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., CAA section
189(e)).
---------------------------------------------------------------------------

    \89\ 81 FR 58010, 58017-58020.
    \90\ CAA section 302(g).
    \91\ 81 FR 58010, 58015.
---------------------------------------------------------------------------

    Section 189(e) of the Act requires that the control requirements
for major stationary sources of direct PM10 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 and RACT,
BACM and BACT, MSM, and new source review (NSR)). Although section
189(e) explicitly addresses only major stationary sources, the EPA
interprets the Act as authorizing it also to determine, under
appropriate circumstances, that regulation of specific PM2.5
precursors from other source categories in a given nonattainment area
is not necessary.\92\ For example, under the EPA's longstanding
interpretation of the control requirements that apply to stationary,
area, and mobile sources of PM10 precursors in the
nonattainment area under CAA section 172(c)(1) and subpart 4,\93\ a
state may demonstrate in a SIP submission that control of a certain
precursor pollutant is not necessary because it does not contribute
significantly to ambient PM10 levels in the nonattainment
area and is not needed for attainment.\94\
---------------------------------------------------------------------------

    \92\ Id. at 58018-58019.
    \93\ General Preamble, 13539-13542.
    \94\ 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.\95\ If the EPA determines that the contribution
of the precursor to PM2.5 levels in the area is not
significant and approves the demonstration, then the state is not
required to control emissions of the relevant precursor from sources in
the attainment plan.\96\
---------------------------------------------------------------------------

    \95\ 40 CFR 51.1006(a)(1).
    \96\ Id.
---------------------------------------------------------------------------

    In addition, in May 2019, the EPA issued the ``Fine Particulate
Matter (PM2.5) Precursor Demonstration Guidance''
(``PM2.5 Precursor Guidance''),\97\ which provides
recommendations to states for analyzing nonattainment area
PM2.5 emissions and developing such optional precursor
demonstrations, consistent with the PM2.5 SIP Requirements
Rule. The PM2.5 Precursor Guidance builds upon the draft
version of the guidance, released on November 17, 2016 (``Draft
PM2.5 Precursor Guidance''), which CARB referenced in
developing its precursor demonstration in the SJV PM2.5
Plan.\98\ The EPA's recommendations in the PM2.5 Precursor
Guidance are generally consistent with those in the Draft
PM2.5 Precursor Guidance, with some exceptions, including
that the EPA's recommended contribution threshold for the 24-hour
PM2.5 NAAQS changed from 1.3 [micro]g/m\3\ in the draft
guidance to 1.5 [micro]g/m\3\ in the final guidance.\99\
---------------------------------------------------------------------------

    \97\ ``PM2.5 Precursor Demonstration Guidance,'' EPA-
454/R-19-004, May 2019, including memorandum dated May 30, 2019 from
Scott Mathias, Acting Director, Air Quality Policy Division and
Richard Wayland, Director, Air Quality Assessment Division, Office
of Air Quality Planning and Standards (OAQPS), EPA to Regional Air
Division Directors, Regions 1-10, EPA.
    \98\ ``PM2.5 Precursor Demonstration Guidance, Draft
for Public Review and Comments,'' EPA-454/P-16-001, November 17,
2016, including memorandum dated November 17, 2016 from Stephen D.
Page, Director, OAQPS, EPA to Regional Air Division Directors,
Regions 1-10, EPA.
    \99\ For the 24-hour 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 1.5 [mu]g/m\3\ will be adequate
to exempt sources of that precursor from control requirements.
PM2.5 Precursor Guidance, 17.
---------------------------------------------------------------------------

    We are evaluating the 1997 24-hour PM2.5 NAAQS portion
of the SJV PM2.5 Plan in accordance with the presumption
embodied within subpart 4, that states address all PM2.5
precursors in the 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 and are not necessary for attainment. In reviewing
any determination by a 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 the State's Submission
    The State presents a brief summary of its PM2.5
precursor analysis in Chapter 5 of the 2018 PM2.5 Plan and
the full precursor demonstration in Appendix G (``Precursor
Demonstration'') of the 2018 PM2.5 Plan.\100\ CARB presents
additional modeling results in Appendix K (``Modeling Attainment
Demonstration''), section 5.6 (``PM2.5 Precursor Sensitivity
Analysis''). CARB also provided clarifying information on its precursor
assessment, including an Attachment A to its letter transmitting the
2018 PM2.5 Plan to the EPA \101\ and further clarifications
in five email transmittals.\102\ The CARB Staff Report contains
additional discussion of the role of ammonia in the formation of
ammonium nitrate and the role of VOC in the formation of ammonium
nitrate and secondary organic aerosol.\103\
---------------------------------------------------------------------------

    \100\ A copy of the contents of Appendix G appears in the CARB
Staff Report, Appendix C4 (``Precursor Demonstrations for Ammonia,
SOX, and ROG'').
    \101\ Letter dated May 9, 2019, from Richard Corey, Executive
Officer, CARB, to Michael Stoker, Regional Administrator, EPA Region
9, Attachment A (``Clarifying information for the San Joaquin Valley
2018 Plan regarding model sensitivity related to ammonia and ammonia
controls'').
    \102\ Email dated June 20, 2019, from Jeremy Avise, CARB, to
Scott Bohning, EPA Region IX, Subject: ``RE: SJV model disbenefit
from SOX reduction,'' with attachment (``CARB's June 2019
Precursor Clarification''); email dated September 19, 2019, from
Jeremy Avise, CARB, to Scott Bohning, EPA Region IX, Subject: ``FW:
SJV species responses,'' 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, Subject: ``Clarifying information on ammonia,'' with
attachment ``Clarifying Information on Ammonia'' (``CARB's October
2019 Precursor Clarification''); email dated April 19, 2021, from
Laura Carr, CARB, to Rory Mays, EPA Region IX, Subject: ``Ammonia
update,'' with attachment ``Update on Ammonia in the San Joaquin
Valley'' (``CARB's April 19, 2021 Precursor Clarification''); and
email dated April 26, 2021, from Laura Carr, CARB, to Scott Bohning,
EPA Region IX, Subject: ``RE: Ammonia update,'' with attachment
``Ammonia in San Joaquin Valley'' (``CARB's April 26, 2021 Precursor
Clarification'').
    \103\ CARB Staff Report, Appendix C, 9-16. The CARB Staff
Report, Appendix C4 (``Precursor Demonstrations for Ammonia,
SOX, and ROG'') is very similar to the contents of
Appendix G of the 2018 PM2.5 Plan.
---------------------------------------------------------------------------

    The 2018 PM2.5 Plan provides both concentration-based
and sensitivity-based analyses of precursor contributions to ambient
PM2.5 concentrations in the San Joaquin Valley. The State
supplemented the sensitivity analysis, particularly for ammonia, with
additional information, including factors identified in the
PM2.5 Precursor Guidance, such as emissions trends, the
appropriateness of future year versus base year sensitivity, available
emissions controls, and the severity of nonattainment.\104\ These
analyses led CARB to conclude that direct PM2.5 and
NOX emissions contribute significantly to ambient
PM2.5 levels that exceed the PM2.5 NAAQS in the
San Joaquin Valley while ammonia, SOX, and VOC do not
contribute significantly to such exceedances.\105\ We summarize the
State's analysis and conclusions below. For a more detailed summary of
the precursor demonstration in the Plan, please refer to 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 February 2020
Precursor TSD'').
---------------------------------------------------------------------------

    \104\ PM2.5 Precursor Guidance, 18-19 (consideration
of additional information), 31 (available emissions controls), and
35-36 (appropriateness of future year versus base year sensitivity).
    \105\ 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.
---------------------------------------------------------------------------

    For direct PM2.5 and NOX, CARB modeled the
sensitivity of ambient PM2.5 in the San Joaquin Valley to a
30 percent reduction in anthropogenic emissions of each pollutant in
2013, 2020, and 2024.\106\ The State concluded that direct
PM2.5 and NOX emissions reductions will continue
to have a significant impact on 24-hour PM2.5 design values
in the San Joaquin Valley, with NOX reductions being
particularly important.\107\ Consistent with this conclusion, the State
focused the control strategy and attainment demonstration on these two
pollutants,

as described in section IV.C of this preamble.
---------------------------------------------------------------------------

    \106\ 2018 PM2.5 Plan, Chapter 5, 5-7 to 5-8. CARB
modeled the effects 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.
    \107\ Id. at 5-8; and 2018 PM2.5 Plan, Appendix G, 2.
CARB presents its sensitivity analysis for emissions reductions in
direct PM2.5 and NOX in the Plan's attainment
demonstration appendix. 2018 PM2.5 Plan, Appendix K,
Table 47 (annual average design values) and Table 48 (24-hour
average design values).
---------------------------------------------------------------------------

    For ammonia, SOX, and VOC, CARB assessed the 2015 annual
average concentration of each precursor in ambient PM2.5 at
Bakersfield, for which the necessary speciated PM2.5 data
are available and where the highest PM2.5 design values have
been recorded in most years, and compared those concentrations to the
recommended annual average contribution threshold of 0.2 [micro]g/m\3\
from the Draft PM2.5 Precursor Guidance, which was available
at the time the State developed the SIP.\108\ The contributions of
ammonia, SOX, and VOC were 5.2 [micro]g/m\3\, 1.6 [micro]g/
m\3\, and 6.2 [micro]g/m\3\, respectively. Given that these levels are
well above the EPA's 0.2 [micro]g/m\3\ recommended contribution
threshold, the State proceeded with a sensitivity-based analysis.
---------------------------------------------------------------------------

    \108\ 2018 PM2.5 Plan, Appendix G, 3. The Plan does
not present a concentration-based analysis for the 24-hour average
concentrations in the San Joaquin Valley. Instead, CARB relied on
the annual average concentration-based analysis as an interim step
to the sensitivity-based analysis, for which CARB assessed the
sensitivity of both 24-hour average and annual average ambient
PM2.5 concentrations to precursor emissions reductions.
Separately, the 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, Chapter 3, 3-3 to
3-4.
---------------------------------------------------------------------------

    CARB's sensitivity-based analysis used the same Community
Multiscale Air Quality (CMAQ) modeling platform as that used for the
Plan's attainment demonstration. The State modeled the sensitivity of
ambient PM2.5 concentration in the San Joaquin Valley to 30
percent and 70 percent emissions reductions in 2013, 2020, and 2024 for
each of ammonia, SOX, and VOC. The State estimated baseline
(2013, 2020, and 2024) design values for PM2.5 using
relative response factors (RRFs) and calculated the ammonia,
SOX, and VOC precursor contribution for a given year and for
each sensitivity scenario (30 percent and 70 percent emissions
reductions) as the difference between its baseline design value and the
design value for each sensitivity scenario.\109\
---------------------------------------------------------------------------

    \109\ This procedure is the procedure recommended by the EPA.
PM2.5 Precursor Guidance, 37.
---------------------------------------------------------------------------

    We summarize the State's sensitivity-based analysis and additional
information in the sections that follow for ammonia, SOX,
and VOC.
a. Ammonia
    For ammonia, the State compared the 24-hour precursor contributions
to 1.3 [micro]g/m\3\, the recommended contribution threshold in the
Draft PM2.5 Precursor Guidance. For a modeled 30 percent
ammonia emissions reduction, the ambient PM2.5 responses in
2013 ranged from 0.9 to 3.3 [micro]g/m\3\ across 15 monitoring sites,
with a majority of sites above the 1.3 [micro]g/m\3\ contribution
threshold (and also above the 1.5 [micro]g/m\3\ contribution threshold
in the final PM2.5 Precursor Guidance). PM2.5
responses in 2020 ranged from 0.5 to 1.9 [micro]g/m\3\, with four sites
at or above the 1.3 [micro]g/m\3\ contribution threshold, including one
site above the 1.5 [micro]g/m\3\ contribution threshold in the final
PM2.5 Precursor Guidance. In 2024, all modeled responses
were below both recommended contribution thresholds. For a modeled 70
percent ammonia emissions reduction, the ambient PM2.5
responses in 2013 ranged from 3.5 to 12.4 [micro]g/m\3\, with all
monitoring sites above the 1.3 [micro]g/m\3\ threshold (and above the
1.5 [micro]g/m\3\ threshold), the PM2.5 responses in 2020
ranged from 1.6 to 6.4 [micro]g/m\3\, and the PM2.5
responses in 2024 ranged from 1.2 to 3.0 [micro]g/m\3\, with most sites
above both recommended thresholds. For further detail, please see the
EPA's February 2020 Precursor TSD, Table 2, and the 2018
PM2.5 Plan, Appendix G, tables 2 through 7. In summary, for
a 30 percent ammonia reduction, a majority of sites have
PM2.5 responses above the contribution threshold in the 2013
modeling, decreasing to a single site above the contribution threshold
for 2020, and no sites above the contribution threshold for 2024. For a
70 percent reduction, all sites are above the contribution threshold in
the 2013 and 2020 modeling, and a majority of sites are above the
contribution threshold in 2024.
    The State based its ammonia precursor determination on the
sensitivity analysis for the future years, using a 30 percent ammonia
emissions reduction. These choices respectively reflect its assessment
of research studies and the Plan's projected emissions reductions, and
on its assessment of available emissions controls. As explained in the
PM2.5 Precursor Guidance, precursor responses may be above
the recommended contribution threshold and yet not contribute
significantly to levels that exceed the standard in the area.
Therefore, as recommended by the EPA, the State considered additional
information to examine whether the identified PM2.5
responses constituted a significant contribution to ambient
PM2.5 in the San Joaquin Valley. The additional information
included research studies, emissions trends, and information to support
the State's conclusion that a 30 percent ammonia emissions reduction
represented a reasonable upper bound on the ammonia emissions
reductions to model in estimating its contribution to ambient
PM2.5 levels. We summarize this additional information below
and provide a more detailed evaluation in the EPA's February 2020
Precursor TSD.
    The State describes previous research that supports its finding
that ammonium nitrate PM2.5 formation is the San Joaquin
Valley is NOX-limited rather than ammonia-limited.\110\
Essentially, ammonia is so abundant in the San Joaquin Valley that even
with large ammonia emissions reductions there would still be enough
ammonia to combine with the available NOX to readily form
particulate ammonium nitrate. Therefore, ammonia emissions reductions
would lead to only small decreases in PM2.5 concentrations.
In contrast, because emissions of NOX are less abundant in
the San Joaquin Valley (i.e., more limited relative to emissions of
ammonia after normalizing for their differing molecular weights), the
PM2.5 concentrations in the atmosphere are more responsive
to reductions in NOX than to reductions of ammonia. Thus,
these analyses indicate that the area is NOX-limited.
---------------------------------------------------------------------------

    \110\ 2018 PM2.5 Plan, Appendix G, 9-10; CARB Staff
Report, Appendix C, 12-15; and Attachment A to CARB's May 9, 2019
submittal letter.
---------------------------------------------------------------------------

    The State also points to the conclusions of a study conducted by
Lurmann et al., based on ambient measurements during the winter 2000-
2001 California Regional Particulate Air Quality Study intensive field
study.\111\ That study found that most areas of the San Joaquin Valley
were NOX-limited with respect to ammonium nitrate formation.
Since that time, large additional NOX emissions reductions
have occurred, which would increase the degree to which ammonium
nitrate formation in the San Joaquin Valley is NOX-limited.
Based on more recent aircraft-borne measurements during the 2013
DISCOVER-AQ campaign,\112\ the State similarly concluded that ammonium
nitrate formation is NOX-limited based on the large amount
of ``excess ammonia,'' which is defined as the amount of measured
ammonia left over if all the nitrate and sulfate present

were to combine with available ammonia to form particulate.\113\ The
CARB Staff Report describes these conclusions in more detail and lists
results from multiple other recent studies with similar
conclusions.\114\ Finally, in a supplemental submittal, CARB described
the results of two analyses confirming the likely underestimation of
ammonia emissions in the modeled emissions inventory inputs.\115\ CARB
compared CMAQ model predictions of ammonia with the 2013 DISCOVER-AQ
aircraft measurements and found 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 valley-wide average was about 25
percent less than observed. Because the modeling performs well for the
various PM2.5 components, as well as for ozone and
NO2,\116\ the CARB finding of CMAQ model underpredictions
for ammonia is consistent with an underestimation of ammonia emissions
inventory input to the model.
---------------------------------------------------------------------------

    \111\ Frederick W. Lurmann, Steven G. Brown, Michael C.
McCarthy, and Paul T. Roberts, ``Processes Influencing Secondary
Aerosol Formation in the San Joaquin Valley during Winter,'' Journal
of the Air & Waste Management Association, (2006), 56:12, 1679-1693,
DOI: 10.1080/10473289.2006.10464573.
    \112\ Deriving Information on Surface conditions from COlumn and
VERtically Resolved Observations Relevant to Air Quality,'' https://www.nasa.gov/mission_pages/discover-aq/index.html.
    \113\ 2018 PM2.5 Plan, Appendix G, Figure 2.
    \114\ CARB Staff Report, Appendix C, 12.
    \115\ CARB's April 26, 2021 Precursor Clarification.
    \116\ EPA's February 2020 Modeling TSD, 21.
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    Regarding emissions trends, the CARB Staff Report presents an
emissions inventory-based argument on the relative insensitivity of
PM2.5 to ammonia reductions.\117\ CARB compared the size of
the ammonia and NOX emissions inventories in tons per day,
after normalizing for their differing molecular weights, and found that
ammonia was roughly three times as abundant as NOX in 2013
and is projected to be about six times as abundant in 2025, due to the
continuing decline in NOX emissions (while ammonia emissions
are generally constant into the future).\118\ While the State
recognized that this is only a ``first-level assessment,'' it provides
additional support for the State's conclusion that NOX, and
not ammonia, is the limiting precursor for ammonium nitrate formation,
and that the ammonium nitrate portion of ambient PM2.5 would
be expected to be relatively insensitive to ammonia emissions
reductions. This is also consistent with the ammonia sensitivity
modeling for the San Joaquin Valley, which showed that PM2.5
concentrations will be less sensitive to ammonia reductions as
NOX emissions go down in the future (i.e., the
PM2.5 impacts were much smaller in the 2020 and 2024 future
modeled cases compared to the 2013 base year).
---------------------------------------------------------------------------

    \117\ CARB Staff Report, Appendix C, 15.
    \118\ Annual average ammonia emissions are projected to decrease
4.6 tpd (1.4 percent) from 2013 to 2024. 2018 PM2.5 Plan,
Appendix B, Table B-5.
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    The State projected that NOX emissions in the San
Joaquin Valley would decrease by 36 percent from 2013 to 2020, and by
53 percent from 2013 to 2024, while ammonia emissions would remain
relatively flat, thereby increasing the relative abundance of
ammonia.\119\ Based on the Plan's emissions reduction projections
combined with the research study conclusions, the State relies on the
modeled responses for the future years, rather than the 2013 base year,
stating that the future year NOX emissions are more
representative of San Joaquin Valley emissions conditions.\120\ The
State references the Draft PM2.5 Precursor Guidance, which
notes that it may be appropriate to model future conditions that are
more representative of current atmospheric conditions and those
conditions expected closer to the attainment date. The State concludes
that this in fact applies to the San Joaquin Valley.\121\
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    \119\ 2018 PM2.5 Plan, Appendix G, 8-9.
    \120\ Id. at 9.
    \121\ Id (referencing Draft PM2.5 Precursor Guidance,
33). See also PM2.5 Precursor Guidance, 35.
---------------------------------------------------------------------------

    With respect to the State's selection of 30 percent as an upper
bound on the ammonia reductions to model, the State described its
review of the most important ammonia source categories in the San
Joaquin Valley, existing control measures that affect ammonia emissions
from these sources, additional mitigation options for these sources,
and information provided in the PM2.5 Precursor Guidance
about ammonia reductions achieved nationwide from 2011 to 2017.\122\
The primary sources of ammonia emissions identified in the 2018
PM2.5 Plan are: (1) Confined animal facilities (CAFs); (2)
agricultural fertilizer; (3) biosolids, animal manure, and poultry
litter operations; and (4) organic material composting operations.\123\
CAFs are subject to District Rule 4570; biosolids, animal manure, and
poultry litter operations are subject to District Rule 4565; and
organic material composting operations are subject to District Rule
4566. Although these District rules explicitly apply only to VOC
emissions from these sources, the State concludes that these rules also
reduce ammonia emissions. Appendix C of the 2018 PM2.5 Plan
cites several scientific studies that address the correlation between
VOC and ammonia emissions from these emissions sources.\124\ Based on
these evaluations, the State concludes that ammonia control measures
achieving even the low end of the range (30 percent) are not feasible
for implementation in the San Joaquin Valley and that it is therefore
reasonable to treat a 30 percent ammonia reduction as an upper bound
for modeling in the precursor demonstration.
---------------------------------------------------------------------------

    \122\ 2018 PM2.5 Plan, Appendix G and Appendix C,
section C-25, and CARB's October 2019 Precursor Clarification.
    \123\ 2018 PM2.5 Plan, Appendix C, section C-25.
    \124\ Id. at C-314 and following.
---------------------------------------------------------------------------

    In summary, the State's sensitivity analysis presents a range of
PM2.5 responses to ammonia emissions reductions depending on
base year versus future year, and on the scale of emissions reductions
that may be possible. The Plan provides the State's bases for finding
that the future year sensitivity results better represent conditions in
the San Joaquin Valley than the 2013 base year and for finding a 30
percent ammonia reduction to be a reasonable upper bound for modeled
ammonia emissions reductions in assessing the ammonia contribution.
Based on these analyses, the State concludes that ammonia does not
contribute significantly to ambient PM2.5 levels above the
1997 24-hour PM2.5 NAAQS in the San Joaquin Valley.
b. SOX
    For SOX, the State compared the 24-hour precursor
contributions to the recommended draft contribution threshold of 1.3
[micro]g/m\3\ in the Draft PM2.5 Precursor Guidance. For
modeled SOX emissions reductions of 30 percent and 70
percent, the ambient PM2.5 responses in 2013 ranged from -
1.4 to 0.5 [micro]g/m\3\ across 15 monitoring sites, which all fall
below the 1.3 [micro]g/m\3\ draft contribution threshold, and hence
also below the contribution threshold of 1.5 [micro]g/m\3\ in the final
version of the PM2.5 Precursor Guidance.\125\ The response
was below zero at most monitoring sites, indicating an increase, rather
than a decrease, in ambient PM2.5 in response to
SOX emissions reductions (i.e., a disbenefit). Only the
Stockton and Manteca sites had slightly positive responses to 30
percent and 70 percent emissions reductions, and the Tranquillity site
also had a slightly positive response only to a 30 percent reduction.
For the 15 sites, in 2020, the responses to 30 percent and 70 percent
emissions reductions ranged from -1.3 [micro]g/m\3\ to

0.5 [micro]g/m\3\ while for 2024, the responses ranged from -1.1
[micro]g/m\3\ to 0.6 [micro]g/m\3\; these are also all below the
contribution threshold, with most sites showing a disbenefit from
SOX reductions.\126\ The Stockton, Manteca, and Tranquillity
sites showed the same pattern of slight benefits as for 2013.\127\ For
further detail, please see the EPA's February 2020 Precursor TSD, Table
3 and the 2018 PM2.5 Plan, Appendix G, tables 8 and 9 and
Appendix K, tables 46, 48, and 50.
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    \125\ 2018 PM2.5 Plan, Appendix G, Table 8 and Table
9.
    \126\ CARB's September 2019 Precursor Clarification, 2020
analysis tables 15 and 16, and 2024 analysis tables 15 and 16.
    \127\ 2018 PM2.5 Plan, Appendix K, Table 48 and Table
50.
---------------------------------------------------------------------------

    CARB also included additional information regarding emissions
trends and an evaluation of the SOX emissions reduction
disbenefit. We summarize this additional information below and provide
a more detailed evaluation in the EPA's February 2020 Precursor TSD.
    In terms of emissions trends, the State found that SOX
emissions decreased from 2013 to 2014 and then were expected to very
gradually rise to 7.8 tpd in 2020 and 8.0 tpd in 2024.\128\ Given that
projected SOX emissions are very similar in 2020 and 2024,
the State concluded that the 2020 and 2024 sensitivity results were
redundant. Comparing the ambient responses in 2013 and 2024, the State
found that the responses were slightly less negative or, for a small
number of sites, slightly higher in 2024, but still no more than 0.6
[micro]g/m\3\ in response to a 70 percent SOX emissions
reduction.\129\ This supports the State's conclusion as to the overall
disbenefit of reducing SOX emissions.
---------------------------------------------------------------------------

    \128\ 2018 PM2.5 Plan, Appendix G, Figure 4.
    \129\ CARB's September 2019 Precursor Clarification, 2013
analysis Table 16 and 2024 analysis Table 16.
---------------------------------------------------------------------------

    To explain the SOX emissions reduction disbenefit that
is observed in some cases, CARB refers to the non-linearity of
inorganic aerosol thermodynamics, as described in a study by West et
al.\130\ That paper discusses how, under certain conditions, reducing
SOX could free ammonia to combine with nitrate, increasing
overall PM2.5 mass. To investigate this issue further, CARB
conducted simulations with the ISORROPIA inorganic aerosol
thermodynamic equilibrium model used within the CMAQ model and provided
clarifications to the EPA.\131\ In essence, CARB states that for some
conditions typical of San Joaquin Valley, ISORROPIA switches to a
different chemical regime in which the disbenefit occurs. CARB states
that it is not known how well this model behavior reflects the actual
atmosphere, but CARB accepts the results because it is a well-known and
widely used chemical model.
---------------------------------------------------------------------------

    \130\ 2018 PM2.5 Plan, Appendix K, section 5.6
(``PM2.5 Precursor Sensitivity Analysis''); 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.
    \131\ CARB's June 2019 Precursor Clarification.
---------------------------------------------------------------------------

    Based on the small and mostly negative modeled response of ambient
PM2.5 to SOX emissions reductions, and based on
its scientific understanding of sulfate interactions with other
molecules in the air, the State concludes that SOX does not
contribute significantly to ambient PM2.5 levels that exceed
the 1997 24-hour PM2.5 NAAQS in the San Joaquin Valley.
c. VOC
    For VOC, CARB compared the 24-hour precursor contributions to the
EPA's recommended draft contribution threshold of 1.3 [micro]g/m\3\.
For a modeled 30 percent VOC emissions reduction, the ambient
PM2.5 responses in 2013 ranged from 0.1 to 1.9 [micro]g/m\3\
across 15 monitoring sites, with two sites above the 1.3 [micro]g/m\3\
draft contribution threshold.\132\ \133\ The 2020 responses ranged from
-0.1 to 0.6 [micro]g/m\3\, with all monitoring sites below the 1.3
[micro]g/m\3\ draft contribution threshold, and hence also below the
contribution threshold of 1.5 [micro]g/m\3\ that was finalized in the
final PM2.5 Precursor Guidance. The 2024 responses ranged
from -0.4 to 0.0 [micro]g/m\3\, with all monitoring sites below both
the draft and final contribution thresholds. For a 70 percent VOC
emissions reduction, the PM2.5 responses in 2013 ranged from
0.2 to 4.8 [micro]g/m\3\, including responses above both contribution
thresholds at a majority of sites. The 2020 response ranged from -0.2
to 1.5 [micro]g/m\3\, with one site at the final contribution
threshold. The 2024 response ranged from -1.0 to 0.0 [micro]g/m\3\ with
monitoring sites below both the contribution thresholds. In other
words, in response to either a 30 percent or a 70 percent reduction in
VOC emissions, CARB models a decrease in ambient PM2.5
levels at all sites for 2013, whereas for 2020, there were just small
decreases in ambient PM2.5 levels at most sites and an
increase at one site, and for 2024 there were increases in
PM2.5 at all sites, i.e., a disbenefit. For further detail,
please see the EPA's February 2020 Precursor TSD, Table 4, and the 2018
PM2.5 Plan, Appendix G, tables 10 through 15.
---------------------------------------------------------------------------

    \132\ 2018 PM2.5 Plan, Appendix G, Table 10.
    \133\ We note that one site (Visalia) has a modeled response
above the EPA's final recommended contribution threshold of 1.5
[micro]g/m\3\ and one additional site (Bakersfield-California
Avenue) has a modeled response below the 1.5 [micro]g/m\3\ threshold
but above the EPA's draft threshold of 1.3 [micro]g/m\3\.
---------------------------------------------------------------------------

    CARB then considered additional information to assess whether these
PM2.5 responses constituted a significant contribution to
ambient PM2.5 in the San Joaquin Valley, including emissions
trends and an assessment of the modeled disbenefit of VOC emissions
reductions. Regarding emissions trends, CARB found that VOC emissions
would decrease approximately 30 tpd (or 9 percent) from 2013 to 2024,
with approximately 28 out of the 30 tpd reduction taking place by
2020.\134\ The State concludes that the formation of ambient
PM2.5 from VOC may therefore differ in base and future years
and that the sensitivity analysis for 2013 is not representative of
current or future conditions.
---------------------------------------------------------------------------

    \134\ 2018 PM2.5 Plan, Appendix G, 19 and Figure 5.
---------------------------------------------------------------------------

    CARB explained the modeled disbenefit of VOC reductions as follows:
Emissions of VOC and NOX react in the atmosphere to form
organic nitrate species, such as peroxyacetyl nitrate (PAN), meaning
that some portion of the NOX emissions is not available to
react with ammonia to form ammonium nitrate. In other words, VOC
emissions are a ``sink'' for NOX emissions. Reducing VOC
emissions therefore reduces the formation of organic nitrates, so the
sink is smaller and nitrate molecules are freed to react with ammonia
to form particulate ammonium nitrate.\135\ The State further explored
the VOC disbenefit based on a 2016 CARB modeling assessment provided in
Appendix A (``Air Quality Modeling'') of the ``2016 Moderate Area Plan
for the 2012 PM2.5 Standard'' for the San Joaquin Valley
(``2016 PM2.5 Plan''), which CARB submitted to the EPA as a
SIP revision on May 10, 2019.\136\
---------------------------------------------------------------------------

    \135\ 2018 PM2.5 Plan, Appendix K, 72 (citing Meng,
Z., D. Dabdub, D., Seinfeld, J.H., Chemical Coupling Between
Atmospheric Ozone and Particulate Matter, Science 277, 116 (1997).
DOI: 10.1126/science.277.5322.116).
    \136\ 2016 PM2.5 Plan, Appendix A, A-57. See also
2018 PM2.5 Plan, Appendix K, section 5.6
(``PM2.5 Precursor Sensitivity Analysis''), 71-72.
---------------------------------------------------------------------------

    Based on its sensitivity-based analysis of VOC emissions
reductions, VOC emissions trends, and the scientific understanding of
VOC chemistry in the San Joaquin Valley, CARB concludes that VOC
emissions do not contribute significantly to PM2.5 levels
that exceed the 1997 24-hour PM2.5 NAAQS in the San Joaquin
Valley.

3. The EPA's Review of the State's Submission
    The EPA has evaluated the State's precursor demonstration
consistent with the PM2.5 SIP Requirements Rule and the
recommendations in the PM2.5 Precursor Guidance. Based on
this evaluation, the EPA agrees that NOX emissions
contribute significantly to ambient PM2.5 levels that exceed
the 1997 24-hour PM2.5 NAAQS in the San Joaquin Valley and
that NOX emissions sources, therefore, remain subject to
control requirements under subparts 1 and 4 of the part D, title I of
the Act. For the reasons provided below, the EPA proposes to approve
the State's demonstration that ammonia, SOX, and VOC
emissions do not contribute significantly to ambient PM2.5
levels that exceed the 1997 24-hour PM2.5 NAAQS in the San
Joaquin Valley.
    Regarding the State's analytical approach, the EPA finds that the
State based its analyses on the latest available data and studies
concerning ambient PM2.5 formation in the San Joaquin Valley
from precursor emissions. Regarding the required concentration-based
analysis, the EPA finds that the State assessed the absolute annual
average contribution of each precursor in ambient PM2.5
(i.e., in 2015). On the basis of the absolute concentrations being well
above the EPA's recommended contribution thresholds for both the 24-
hour and annual average NAAQS, the State proceeded with its
sensitivity-based analysis, which is the recommended sequence under the
final PM2.5 Precursor Guidance.\137\
---------------------------------------------------------------------------

    \137\ For further discussion of the EPA's evaluation of the
State's concentration-based analysis, see the EPA's February 2020
Precursor TSD, sections entitled ``Concentration-based analysis''
within the EPA's evaluation for each of ammonia, SOX, and
VOC.
---------------------------------------------------------------------------

    With respect to the sensitivity-based analysis, we find that the
State performed its analyses following the steps of the EPA's
recommended approach--i.e., for each modeled year and percent precursor
emissions reduction, the State estimated the ambient PM2.5
response using the procedure recommended in the PM2.5
Precursor Guidance and compared the result to the recommended
contribution threshold. The EPA also finds that the performance of the
photochemical model was adequate for use in estimating the ambient
PM2.5 responses, as discussed 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
February 2020 Modeling TSD''). The State considered the EPA's
recommended range of emissions reductions (30 percent to 70 percent)
for the 2013 base year, the projected 2020 attainment year for the 1997
24-hour PM2.5 NAAQS, and the projected 2024 attainment year
for the 2006 PM2.5 NAAQS, and quantified the estimated
response of ambient PM2.5 concentrations to precursor
emissions changes for the first time in a PM2.5 SIP
submission for the San Joaquin Valley. The EPA finds that such
quantification and CARB's consideration of additional information
provide an informed basis on which to make a determination as to
whether ammonia, SOX, and VOC do or do not contribute
significantly to ambient PM2.5 levels that exceed the 1997
24-hour PM2.5 NAAQS in the San Joaquin Valley.\138\
Therefore, we turn to our evaluation of the State's determination for
each of these three precursor pollutants.
---------------------------------------------------------------------------

    \138\ The State did not evaluate the 2015 Serious area
attainment year. Because the year has passed and the area failed to
attain by the Serious area attainment date, we will evaluate the
precursor analysis for the Serious area plan based on the current
section 189(d) projected attainment date of December 31, 2020.
---------------------------------------------------------------------------

a. Ammonia
    For ammonia, as detailed above, CARB estimated the ambient
PM2.5 response to both a 30 percent and a 70 percent
emissions reduction. We find that it was appropriate for the State to
consider additional information to interpret those results to determine
whether the ammonia contribution is significant. The primary conclusion
demonstrated by the State's analysis of additional information is that
ammonium nitrate formation is NOX-limited. As discussed in
more detail below, we agree with this conclusion. We have evaluated
CARB's determination that a projected future year is more
representative of conditions in the San Joaquin Valley for sensitivity-
based analyses and that 30 percent is a reasonable upper bound for
ammonia emissions reductions to assess the precursor contribution, as
discussed below.
    The State provided ample information from scientific studies based
on ambient measurements to help assess the estimated sensitivity of
ambient PM2.5 to ammonia reductions. Conclusions based on
ambient data are particularly relevant because they provide direct
evidence of the chemical state of the atmosphere and are not dependent
on modeled estimates of emissions or modeled ambient PM2.5
concentrations. Measurements represent the ``real world'' result of the
pollutants' differing geographic distributions, the various
meteorological and chemical factors influencing their conversion to
particulate, and their removal from the atmosphere by deposition and
other processes. The observed abundance of ammonia relative to nitric
acid, and the positive amount of chemically excess ammonia, both
provide strong evidence that ammonia is not the limiting pollutant for
particulate ammonium nitrate formation. They also support the State's
conclusion that PM2.5 concentrations are insensitive to
ammonia emissions reductions.
    The relative amount of ammonia and NOX emissions is one
of the most critical factors in determining the sensitivity of ambient
PM2.5 to ammonia reductions. We note that the model response
to precursor reductions may be unrealistically large due to the
underestimation of ammonia emissions and therefore of the ratio of
ammonia to NOX emissions. There is evidence that ammonia
emissions may be underestimated based on direct measurements of ammonia
emissions flux during two measurement campaigns, as discussed in the
EPA's February 2020 Precursor TSD. If ammonia emissions were higher in
the modeling, then ammonia would be more abundant relative to nitrate
and particulate nitrate formation would be more NOX-limited
and less sensitive to ammonia reductions. This would make the model
response more consistent with the ambient measurement studies, which
suggest a very low sensitivity to ammonia. This evidence indicates that
ammonia contribution to PM2.5 levels above the standard is
likely to be less than estimated by the State's modeling in each of the
three years. In comparison to the 2013 and 2020 modeling, the modeling
for the year 2024 incorporates lower NOX emissions and so
has a larger abundance of ammonia relative to nitrate, more similar to
the studies' ambient measurements. Thus, the 2024 response to ammonia
reductions is likely to be more reliable than the 2013 and 2020
responses and appears to be more representative of current atmospheric
conditions despite the use of emissions projections for a future year.
    The relative sizes of the ammonia and NOX precursor
emissions inventories after accounting for their differing molecular
weights are a rough indicator of which pollutant is the limiting
pollutant for production of ammonium nitrate because ammonium nitrate
forms from a one-to-one ratio of molecules derived from each precursor
(i.e., one ammonium nitrate forms from one

ammonium and one nitrate). However, unlike measurements and
photochemical modeling, a simple emissions ratio does not account for
various processes mentioned above; it assumes all the emitted molecules
find one another and react. The State found ammonia to be roughly three
times as abundant as NOX in 2013 after accounting for their
differing molecular weights, and even more abundant in future years.
The EPA repeated the exercise to account for SOX and found
that the ratio of total ammonia to the ammonia needed to react with
both nitrate and sulfate ranged from 2.7 in 2013 to 5.6 in 2028. These
results are approximately the same as the CARB NOX-only
results because SOX emissions are very small relative to
NOX and ammonia emissions (e.g., in 2013, winter daily
emissions were 8.4 tpd of SOX versus 300.5 tpd of
NOX and 309.8 tpd of ammonia).\139\ These observations
support the State's finding that PM2.5 is expected to be
relatively insensitive to ammonia reductions, though they are not
definitive on their own.
---------------------------------------------------------------------------

    \139\ 2018 PM2.5 Plan, Appendix B, tables B-2, B-3,
and B-4.
---------------------------------------------------------------------------

    The State also points to large decreases or projected decreases in
NOX emissions in the San Joaquin Valley from 2013 to 2024,
including a 36 percent reduction from baseline measures by 2020, and a
53 percent reduction by 2024, while CARB projects that ammonia
emissions will remain roughly constant (i.e., decreasing 1-2 percent).
In conjunction with the ambient evidence that ammonia is already
chemically overabundant relative to NOX in the San Joaquin
Valley, this indicates that the overabundance will become even greater
in the future, and thus ambient PM2.5 is expected to be even
less responsive to ammonia reductions. This adds conservatism to the
State's conclusions about ammonia sensitivity based on the scientific
studies.
    While the base year for an attainment plan for a given
nonattainment area is generally more representative of current
conditions, there can be situations in which is it more appropriate to
use future conditions representative of when sources will operate, and
the EPA believes that states may use either a base year or a future
year for modeling an ambient PM2.5 response to precursor
emissions reductions, provided the state explains how the choice of
analysis year and associated assumptions are appropriate.\140\ The 2013
modeled responses cannot be considered current at the present time, in
comparison to the 2020 results. Large NOX emissions
reductions have occurred from 2013-2020 and are projected to continue
to occur on through 2024, continuing to decrease the ratio of
NOX to ammonia. In light of this ongoing trend, and the
ambient data indicating that models underestimate ammonia, the EPA
believes that future year results, which more accurately reflect the
expected NOX to ammonia ratio, will continue to be
representative, unlike the 2013 base year. These reductions are the
result of regulations put in place by past air quality planning
decisions and they will occur regardless of the actions that are being
proposed herein. In assessing the effect of potential ammonia
reductions, the EPA believes it is reasonable to account for these
NOX reductions. In addition, as noted above, the greater
abundance of ammonia relative to NOX in the 2024 year
modeling is more consistent with recent ambient measurements, which
suggest that the 2024 responses are more representative of current
atmospheric conditions than the other model years for assessing
sensitivity to ammonia reductions. Therefore, in consideration of the
scientific studies and emissions trends, including the projected large
amount of NOX emissions reductions through the attainment
period, the EPA agrees that use of a future year is appropriate. Given
the available research and ambient data, we conclude that the modeled
2024 year is the most representative of conditions in the San Joaquin
Valley.
---------------------------------------------------------------------------

    \140\ PM2.5 Precursor Guidance, 35-36.
---------------------------------------------------------------------------

    Even if we were to set aside the more representative 2024 modeling,
in the 2020 modeled responses, only the Bakersfield-Planz site is above
the contribution threshold, at 1.9 [micro]g/m\3\. A single value above
the threshold is not determinative, particularly in light of the
additional information provided above, indicating that the modeled
values overestimate the contribution of ammonia to ambient
PM2.5 levels, and that the trend continues toward less
contribution in the future as the ratio of NOX to ammonia
continues to drop. Moreover, the monitored 2020 design value is
attaining the 1997 24-hour PM2.5 NAAQS because, as discussed
above and in section V of this proposal, at the current time there are
not PM2.5 levels above the NAAQS. This is further evidence
that the single 2020 modeled response above the contribution threshold
is not a significant contribution to PM2.5 levels in excess
of the NAAQS, even if the 2020 modeling were considered representative.
    In the context of interpreting the full set of modeling results for
ammonia emissions reductions, the EPA also considered the State's
conclusion that the absence of available ammonia controls for sources
in the San Joaquin Valley supports its decision to treat a 30 percent
reduction as a reasonable upper bound on the ammonia emissions
reductions to model in estimating the precursor contribution. As the