[Federal Register Volume 85, Number 60 (Friday, March 27, 2020)]
[Proposed Rules]
[Pages 17382-17431]
[FR Doc No: 2020-05914]

Vol. 85

Friday,

No. 60

March 27, 2020

Part II

Environmental Protection Agency

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40 CFR Part 52

Clean Air Plans; 2006 Fine Particulate Matter Nonattainment Area
Requirements; San Joaquin Valley, California; Proposed Rule

Federal Register / Vol. 85 , No. 60 / Friday, March 27, 2020 /
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2019-0318; FRL-10006-40-Region 9]

Clean Air Plans; 2006 Fine Particulate Matter Nonattainment Area
Requirements; San Joaquin Valley, California

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: The Environmental Protection Agency (EPA or ``Agency'')
proposes to approve portions of two state implementation plan (SIP)
revisions submitted by the State of California to meet Clean Air Act
(CAA or ``Act'') requirements for the 2006 fine particulate matter
(PM2.5) national ambient air quality standards (NAAQS or
``standards'') in the San Joaquin Valley (SJV) Serious nonattainment
area. Specifically, the EPA proposes to approve 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 and address CAA requirements for Serious
PM2.5 nonattainment areas. The EPA also proposes to approve
inter-pollutant trading ratios for use in transportation conformity
analyses for the 2006 PM2.5 NAAQS. As part of this action,
the EPA proposes to grant an extension of the Serious area attainment
date for the 2006 PM2.5 NAAQS in the San Joaquin Valley from
December 31, 2019, to December 31, 2024 based on a proposed
determination that the State has satisfied the statutory criteria for
this extension. We may, however, reconsider this proposal or deny
California's request for extension of the attainment date if, based on
new information or public comments, we find that the State has not
satisfied the statutory criteria for this extension.

DATES: Any comments must arrive by April 27, 2020.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R09-
OAR-2019-0318, at https://www.regulations.gov. For comments submitted
at Regulations.gov, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
Regulations.gov. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, please contact the person identified in
the FOR FURTHER INFORMATION CONTACT section. For the full EPA public
comment policy, information about CBI or multimedia submissions, and
general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.

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

Table of Contents

I. Background
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
    A. Requirements for PM2.5 Serious Area Plans
    B. Requirements for Extension of a Serious Area Attainment Date
IV. Review of the San Joaquin Valley PM2.5 Serious Area
Plan and Extension Application
    A. Emissions Inventory
    B. PM2.5 Precursors
    C. Best Available Control Measures and Most Stringent Measures
    D. Extension of Serious Area Attainment Date Under CAA Section
188(e)
    E. Reasonable Further Progress and Quantitative Milestones
    F. Motor Vehicle Emission Budgets
    G. Major Stationary Source Control Requirements Under CAA
Section 189(e)
V. Summary of Proposed Actions and Request for Public Comment
VI. Statutory and Executive Order Reviews

I. Background

    On October 17, 2006, the EPA strengthened the 24-hour (daily) NAAQS
for particles less than or equal to 2.5 micrometers ([micro]m) in
diameter (PM2.5) by lowering the level from 65 micrograms
([micro]g) per cubic meter (m\3\) to 35 [micro]g/m\3\.\1\ The 24-hour
standards are based on a three-year average of 98th percentile 24-hour
PM2.5 concentrations. The EPA established these standards
after considering substantial evidence from numerous health studies
demonstrating that serious health effects are associated with exposures
to PM2.5 concentrations above these levels.
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    \1\ 71 Federal Register (FR) 61144 (October 17, 2006) and 40 CFR
50.13. In promulgating the 2006 PM2.5 NAAQS, the EPA
retained the level of the 1997 annual average PM2.5 NAAQS
of 15.0 [micro]g/m\3\. 62 FR 36852 (July 18, 1997) and 40 CFR 50.7.
Subsequently, the EPA strengthened the primary annual
PM2.5 NAAQS by lowering the level to 12.0 [micro]g/m\3\
while retaining the secondary annual PM2.5 NAAQS at the
level of 15.0 [micro]g/m\3\. 78 FR 3086 (January 15, 2013) and 40
CFR 50.18. In this preamble, all references to the PM2.5
NAAQS, unless otherwise specified, are to the 2006 24-hour standards
(35 [micro]g/m\3\) as codified in 40 CFR 50.13.
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    Epidemiological studies have shown statistically significant
correlations between elevated PM2.5 levels and premature
mortality. Other important health effects associated with
PM2.5 exposure include aggravation of respiratory and
cardiovascular disease (as indicated by increased hospital admissions,
emergency room visits, absences from school or work, and restricted
activity days), changes in lung function and increased respiratory
symptoms, 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.\2\
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    \2\ 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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    PM2.5 can be emitted directly into the atmosphere as a
solid or liquid particle (primary PM2.5 or direct
PM2.5) or can be formed in the atmosphere as a result of
various chemical reactions from precursor emissions of nitrogen oxides,
sulfur oxides, volatile organic compounds, and ammonia (secondary
PM2.5).\3\
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    \3\ 81 FR 58010, 58011 (August 24, 2016).
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    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 December 14,
2009, the EPA finalized initial air quality designations for the 2006
PM2.5 NAAQS, using air quality monitoring data for the
three-year periods of 2005-2007 and 2006-2008.\4\ The EPA designated
the San Joaquin Valley as a nonattainment area for the 2006
PM2.5 NAAQS.\5\ On June 2, 2014, the EPA classified the San
Joaquin Valley as a Moderate nonattainment area for these NAAQS,
thereby establishing December 31, 2015 as the

latest permissible attainment date for the area under section 188(c)(1)
of the CAA.\6\ Effective February 19, 2016, the EPA reclassified the
San Joaquin Valley as a Serious nonattainment area for these NAAQS.\7\
Shortly thereafter, the EPA approved the State's demonstration that it
was impracticable to attain the 2006 PM2.5 NAAQS by the
December 31, 2015 Moderate area attainment date and related plan
elements addressing the Moderate area requirements for the 2006
PM2.5 NAAQS.\8\
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    \4\ 74 FR 58688 (November 13, 2009).
    \5\ Id. (codified at 40 CFR 81.305). The most recent 24-hour
design value (2016-2018) for the San Joaquin Valley is 65 [micro]g/
m\3\. EPA design value workbook dated July 18, 2019, worksheet
``Table 1b.''
    \6\ 79 FR 31566 (June 2, 2014). The EPA promulgated these
PM2.5 nonattainment area classifications in response to a
2013 decision of the Court of Appeals for the D.C. Circuit remanding
the EPA's prior implementation rule for the PM2.5 NAAQS
and directing the EPA to repromulgate implementation rules pursuant
to subpart 4 of part D, title I of the Act. Natural Resources
Defense Council v. EPA, 706 F.3d 428 (D.C. Cir. 2013).
    \7\ 81 FR 2993 (January 20, 2016).
    \8\ 81 FR 59876 (August 31, 2016).
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    Upon reclassification as a Serious PM2.5 nonattainment
area, the San Joaquin Valley became subject to a new statutory
attainment date no later than the end of the tenth calendar year
following designation (i.e., December 31, 2019) and the requirement to
submit a Serious area plan satisfying the requirements of CAA Title I,
part D, including the requirements of subpart 4, for the 2006
PM2.5 NAAQS.\9\ As explained in the EPA's final
reclassification action, the Serious area plan for the San Joaquin
Valley must include, among other things, provisions to assure that,
under CAA section 189(b)(1)(B), the best available control measures
(BACM) for the control of direct PM2.5 and PM2.5
precursors shall be implemented no later than four years after the area
is reclassified and a demonstration (including air quality modeling)
that the plan provides for attainment as expeditiously as practicable
and no later than the applicable attainment date. The EPA established
an August 21, 2017 deadline for California to adopt and submit a SIP
submission addressing the Serious nonattainment area requirements for
the 2006 PM2.5 NAAQS.\10\ The EPA also noted that California
may choose to submit a request for an extension of the December 31,
2019, Serious area attainment date pursuant to CAA section 188(e)
simultaneously with its submission of a Serious area plan for the
area.\11\
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    \9\ 81 FR 2993, 2998.
    \10\ Id. at 3000 and 81 FR 42263 (June 29, 2016) (codified at 40
CFR 52.247(f)).
    \11\ 81 FR 2993, 2998.
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    As described further in section III.B of this preamble, CAA section
188(e) allows the EPA to extend the attainment date for a Serious area
by up to five years if attainment by the Serious area attainment date
is impracticable. However, before the Agency may grant an extension of
the attainment date, the State must first:
    (1) Apply to the EPA for an extension of the PM2.5
attainment date beyond 2019,
    (2) demonstrate that attainment by 2019 is impracticable,
    (3) have complied with all requirements and commitments applying to
the area in its implementation plan,
    (4) demonstrate to the Administrator's satisfaction that its
Serious area plan includes the most stringent measures that are
achieved in practice in any state and are feasible for the area, and
    (5) submit SIP revisions containing a demonstration of attainment
by the most expeditious alternative date practicable.
    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.\12\ The area is home to four
million people and is the nation's leading agricultural region.
Stretching over 250 miles from north to south and averaging 80 miles
wide, it is partially enclosed by the Coast Mountain range to the west,
the Tehachapi Mountains to the south, and the Sierra Nevada range to
the east. The 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 between the
District, which has responsibility for regulating stationary and most
area sources, and CARB, which has responsibility for regulating most
mobile sources.
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    \12\ For a precise description of the geographic boundaries of
the San Joaquin Valley PM2.5 nonattainment area, see 40
CFR 81.305.
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    On November 16, 2018, CARB submitted to the EPA substantial
portions of the Serious area plan for the 2006 PM2.5 NAAQS
following CARB's adoption of one component of the plan on October 25,
2018 and the SJVUAPCD's adoption of a second component of it on
November 15, 2018.\13\ Because CARB had not yet adopted this submission
in its entirety, the EPA determined that it did not meet the EPA's
completeness requirements for SIP submissions under 40 CFR part 51,
Appendix V, section 2.1.\14\ The EPA's incompleteness findings became
effective on January 7, 2019, and triggered clocks for the application
of emissions offset sanctions for new or modified major stationary
sources in the San Joaquin Valley 18 months after the effective date of
the findings and highway funding sanctions six months thereafter,
unless the EPA affirmatively determines that the State has submitted a
complete SIP addressing the deficiency that was the basis for these
findings, consistent with CAA section 179(b) and the EPA's sanctions
sequencing rule in 40 CFR 52.31.\15\ These findings also triggered the
obligation under CAA section 110(c) on the EPA to promulgate a federal
implementation plan no later than two years after the effective date of
the findings, unless the State has submitted, and the EPA has approved,
the required SIP submittal.\16\
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    \13\ Letter dated November 16, 2018, from Kurt Karperos, Deputy
Executive Officer, CARB, to Mike Stoker, Regional Administrator, EPA
Region IX.
    \14\ 83 FR 62720 (December 6, 2018). The EPA made these findings
in response to a court order issued in Committee for a Better Arvin,
et al., v. Andrew Wheeler, et al., Case No. 18-cv-05700-RS (N.D.
Cal., October 24, 2018).
    \15\ 83 FR 62720, 62723.
    \16\ Id.
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II. Summary and Completeness Review of the San Joaquin Valley PM2.5
Plan

    The EPA is proposing action on portions of two SIP revisions
submitted by CARB to meet the Serious nonattainment area requirements
for the 2006 24-hour PM2.5 NAAQS in the San Joaquin Valley.
Specifically, the EPA is proposing to act on those portions of the
following two plan submissions that pertain to the 2006 24-hour
PM2.5 NAAQS: The ``2018 Plan for the 1997, 2006, and 2012
PM2.5 Standards,'' adopted by the SJVUAPCD on November 15,
2018, and by CARB on January 24, 2019 (``2018 PM2.5 Plan'')
\17\; and the ``San Joaquin Valley Supplement to the 2016 State
Strategy for the State Implementation Plan,'' adopted by CARB on
October 25, 2018 (``Valley State SIP Strategy''). We refer to the
relevant portions of these SIP submissions collectively as the ``SJV
PM2.5 Plan'' or ``Plan.'' The SJV PM2.5 Plan
addresses the Serious area attainment plan requirements for the 2006
24-hour PM2.5 NAAQS in the San Joaquin Valley and includes a
request under CAA section 188(e) for an extension of the Serious area
attainment date for the area for this NAAQS. CARB submitted the SJV
PM2.5 Plan to the EPA

as a revision to the SIP on May 10, 2019.\18\
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    \17\ The 2018 PM2.5 Plan was developed jointly by
CARB and the District.
    \18\ Letter dated May 9, 2019, from Richard Corey, Executive
Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region 9.
The EPA is not, at this time, proposing to act on those portions of
the ``2018 Plan for the 1997, 2006, and 2012 PM2.5
Standards'' or the ``San Joaquin Valley Supplement to the 2016 State
Strategy for the State Implementation Plan'' that pertain to the
1997 PM2.5 NAAQS, the 2012 PM2.5 NAAQS, or
Serious area contingency measures. We intend to act on these
portions of the submitted SIP revisions in subsequent rulemakings.
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    CAA sections 110(a)(1) and (2) and 110(l) require each state to
provide reasonable public notice and opportunity for public hearing
prior to the adoption and submission of a SIP or SIP revision to the
EPA. To meet this requirement, every SIP submission should include
evidence that adequate public notice was given and that an opportunity
for a public hearing was provided consistent with the EPA's
implementing regulations in 40 CFR 51.102.
    CAA section 110(k)(1)(B) requires the EPA to determine whether a
SIP submission is complete within 60 days of receipt. This section also
provides that any plan that the EPA has not affirmatively determined to
be complete or incomplete will become complete by operation of law six
months after the date of submission. The EPA's SIP completeness
criteria are found in 40 CFR part 51, Appendix V.

A. 2018 PM2.5 Plan

    The following portions of the 2018 PM2.5 Plan and
related support documents address the Serious area requirements for the
2006 PM2.5 NAAQS in the San Joaquin Valley: (i) Chapter 4
(``Attainment Strategy for PM2.5''); (ii) Chapter 6
(``Demonstration of Federal Requirements for the 2006 PM2.5
Standard: Serious Plan and Extension Request''); \19\ (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''); \20\ 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).\21\ The
SJVUAPCD Governing Board Resolution 18-11-16 includes emission
reduction commitments on which the SJV PM2.5 Plan
relies.\22\
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    \19\ Chapter 5 (``Demonstration of Federal Requirements for the
1997 PM2.5 Standard'') and Chapter 7 (``Demonstration of
Federal Requirements for the 2012 PM2.5 Standard'') of
the 2018 PM2.5 Plan pertain to the 1997 PM2.5
NAAQS and 2012 PM2.5 NAAQS, respectively. The EPA intends
to act on these portions of the 2018 PM2.5 Plan in
separate rulemakings.
    \20\ The CARB Staff Report includes CARB's review of, among
other things, the 2018 PM2.5 Plan's control strategy and
attainment demonstration. Letter dated December 11, 2019 from
Richard Corey, Executive Officer, CARB to Mike Stoker, Regional
Administrator, EPA Region IX, transmitting the CARB Staff Report [on
the 2018 PM2.5 Plan].
    \21\ 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.
    \22\ SJVUAPCD Governing Board Resolution 18-11-16, paragraph 6,
10-11.
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    The appendices to the 2018 PM2.5 Plan, in order of their
evaluation in this preamble, include: (i) App. B (``Emissions
Inventory''); (ii) App. A (``Ambient PM2.5 Data Analysis'');
(iii) a plan precursor demonstration and clarifications, including App.
G (``Precursor Demonstration'') and Attachment A (``Clarifying
information for the San Joaquin Valley 2018 Plan regarding model
sensitivity related to ammonia and ammonia controls'') to the CARB
Staff Report; (iv) control strategy appendices, including App. C
(``Stationary Source Control Measure Analyses''), App. D (``Mobile
Source Control Measures Analyses''), and App. E (``Incentive-Based
Strategy''); (v) modeling appendices, including App. J (``Modeling
Emission Inventory''), App. K (``Modeling Attainment Demonstration''),
and App. L (``Modeling Protocol''); (vi) App. H (``RFP, Quantitative
Milestones, and Contingency''); and (vii) App. I (``New Source Review
and Emission Reduction Credits''). The 2018 PM2.5 Plan
addresses motor vehicle emission budget (MVEB) requirements in the
``Transportation Conformity'' section of App. D (pages D-119 to D-131).
The 2018 PM2.5 Plan also includes an Executive Summary,
Introduction (Ch. 1), chapters on ``Air Quality Challenges and Trends''
(Ch. 2) and ``Health Impacts and Health Risk Reduction Strategy'' (Ch.
3), and an appendix on ``Public Education and Technology Advancement''
(App. F).
    The District provided public notice and opportunity for public
comment prior to its November 15, 2018 public hearing on and adoption
of the 2018 PM2.5 Plan.\23\ 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.\24\ 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.\25\ 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. The sanctions clocks that were triggered
by our December 6, 2018 findings that the State had failed to submit
complete SIP submissions addressing the statutory requirements that
apply to areas designated nonattainment for the PM2.5 NAAQS,
however, will continue to run until the EPA affirmatively determines,
by letter to the Governor of California, that CARB has submitted a
complete SIP submission addressing the identified deficiencies.\26\
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    \23\ 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.
    \24\ 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.
    \25\ CARB, ``Board Meeting Comments Log,'' March 29, 2019; J&K
Court Reporting, LLC, ``Meeting, State of California Air Resources
Board,'' January 24, 2019 (transcript of CARB's public hearing), and
2018 PM2.5 Plan, App. M (``Summary of Significant
Comments and Responses'').
    \26\ 83 FR 62720 (citing required process for termination of
sanctions clocks in 40 CFR 52.31(d)(5)).
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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.\27\ In its
resolution adopting the 2016 State Strategy (CARB Resolution 17-7), the
Board found that the 2016 State Strategy would achieve 6 tons per day
(tpd) of NOX emission reductions and 0.1 tpd of direct
PM2.5 emission reductions in the 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 the PM2.5
standards for the San Joaquin Valley and to return to the Board with a
commitment to achieve additional emission reductions from mobile
sources.\28\
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    \27\ 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).
    \28\ CARB Resolution 17-7, ``2016 State Strategy for the State
Implementation Plan,'' March 23, 2017, 6-7.

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    CARB responded to this resolution by developing and adopting the
``San Joaquin Valley Supplement to the 2016 State Strategy for the
State Implementation Plan'' (``Valley State SIP Strategy'') to support
the 2018 PM2.5 Plan. The State's May 10, 2019 SIP submission
incorporates by reference the Valley State SIP Strategy as adopted by
CARB on October 25, 2018 and submitted to the EPA on November 16,
2018.\29\
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    \29\ Letter dated May 9, 2019, from Richard Corey, Executive
Officer, CARB, to Mike Stoker, Regional Administrator, EPA Region 9,
2.
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    The Valley State SIP Strategy includes an Introduction (Ch. 1), a
chapter on ``Measures'' (Ch. 2), and a ``Supplemental State Commitment
from the Proposed State Measures for the Valley'' (Ch. 3). Much of the
content of the Valley State SIP Strategy is reproduced in Chapter 4
(``Attainment Strategy for PM2.5'') of the 2018
PM2.5 Plan.\30\ The Valley State SIP Strategy also includes
CARB Resolution 18-49, which, among other things, commits CARB to
achieve specific amounts of NOX and PM2.5
emission reductions by specific years, for purposes of attaining the
PM2.5 NAAQS in the San Joaquin Valley.\31\
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    \30\ 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.
    \31\ CARB Resolution 18-49, ``San Joaquin Valley Supplement to
the 2016 State Strategy for the State Implementation Plan,'' October
25, 2018, 5.
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    CARB provided the required public notice and opportunity for public
comment prior to its October 25, 2018 public hearing on and adoption of
the Valley State SIP Strategy.\32\ 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.\33\
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.
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    \32\ 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.
    \33\ CARB, ``Board Meeting Comments Log,'' November 2, 2018 and
compilation of written comments; and J&K Court Reporting, LLC,
``Meeting, State of California Air Resources Board,'' October 25,
2018 (transcript of CARB's public hearing).
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    The Valley State SIP Strategy became complete by operation of law
on November 10, 2019. The sanctions clocks that were triggered by our
December 6, 2018 findings that the State had failed to submit complete
SIP submissions addressing the statutory requirements that apply to
areas designated nonattainment for the PM2.5 NAAQS, however,
will continue to run until the EPA affirmatively determines, by letter
to the Governor of California, that CARB has submitted a complete SIP
submission addressing the identified deficiencies.\34\
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    \34\ 83 FR 62720 (citing required process for termination of
sanctions clocks in 40 CFR 52.31(d)(5)).
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III. Clean Air Act Requirements for PM2.5 Serious Area Plans

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: \35\
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    \35\ 81 FR 58010, 58074-58075.
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    (1) A comprehensive, accurate, current inventory of actual
emissions from all sources of PM2.5 and PM2.5
precursors in the area (CAA section 172(c)(3));
    (2) Provisions to assure that the best available control measures
(BACM), including best available control technology (BACT), for the
control of direct PM2.5 and 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, 2019, for the San Joaquin Valley
for the 2006 PM2.5 NAAQS), or where the state is seeking an
extension of the attainment date under section 188(e), a demonstration
that attainment by such date is impracticable and that the plan
provides for attainment by the most expeditious alternative date
practicable that is no more than five years later (CAA sections
188(c)(2) and 189(b)(1)(A));
    (4) Plan provisions that require reasonable further progress (RFP)
(CAA section 172(c)(2));
    (5) Quantitative milestones which are to be achieved every three
years until the area is redesignated attainment and which demonstrate
RFP toward attainment by the applicable date (CAA section 189(c));
    (6) Provisions to assure that control requirements applicable to
major stationary sources of PM2.5 also apply to major
stationary sources of PM2.5 precursors, except where the
state demonstrates to the EPA's satisfaction that such sources do not
contribute significantly to PM2.5 levels that exceed the
standard in the area (CAA section 189(e));
    (7) Contingency measures to be implemented if the area fails to
meet RFP or to attain by the applicable attainment date (CAA section
172(c)(9)); and
    (8) A revision to the nonattainment new source review (NSR) program
to lower the applicable ``major stationary source'' \36\ thresholds
from 100 tons per year (tpy) to 70 tpy (CAA section 189(b)(3)).
---------------------------------------------------------------------------

    \36\ 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. 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).
    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''); \37\ (2) ``State
Implementation Plans; General Preamble for the Implementation of Title
I of the Clean Air Act Amendments of 1990; Supplemental'' (``General
Preamble Supplement''); \38\ 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'').\39\

More recently, in an August 24, 2016 final rule entitled, ``Fine
Particulate Matter National Ambient Air Quality Standards: State
Implementation Plan Requirements'' (``PM2.5 SIP Requirements
Rule''), the EPA established regulatory requirements and provided
further interpretive guidance on the statutory SIP requirements that
apply to areas designated nonattainment for the PM2.5
standards.\40\ We discuss these regulatory requirements and
interpretations of the Act as appropriate in our evaluation of the SJV
PM2.5 Plan below.
---------------------------------------------------------------------------

    \37\ 57 FR 13498 (April 16, 1992).
    \38\ 57 FR 18070 (April 28, 1992).
    \39\ 59 FR 41998 (August 16, 1994).
    \40\ 81 FR 58010 (August 24, 2016).
---------------------------------------------------------------------------

B. Requirements for Extension of a Serious Area Attainment Date

    Under section 188(e) of the Act, a state may apply to the EPA for a
single extension of the Serious area attainment date by up to five
years, which the EPA may grant if the state satisfies certain
conditions. Before the EPA may extend the attainment date for a Serious
area under section 188(e), the state must:
    (1) Apply for an extension of the attainment date beyond the
statutory attainment date;
    (2) demonstrate that attainment by the statutory attainment date is
impracticable;
    (3) demonstrate that it has complied with all requirements and
commitments pertaining to the area in the implementation plan;
    (4) demonstrate to the satisfaction of the Administrator that the
plan for the area includes the ``most stringent measures'' that are
included in the implementation plan of any state or are achieved in
practice in any state, and can feasibly be implemented in the area; and
    (5) submit a demonstration of attainment by the most expeditious
alternative date practicable.\41\
---------------------------------------------------------------------------

    \41\ CAA section 188(e) and 40 CFR 51.1005(b). For a discussion
of EPA's interpretation of the requirements of section 188(e), see
the preamble to the PM2.5 SIP Requirements Rule, 81 FR
58010, 58094-58097, and the General Preamble Addendum, 59 FR 41998,
42002.
---------------------------------------------------------------------------

    A state must seek an extension of the Serious area attainment date
at the same time it submits the Serious area attainment plan, if the
state cannot demonstrate attainment by the otherwise applicable
statutory attainment date.\42\
---------------------------------------------------------------------------

    \42\ 40 CFR 51.1005(b)(2).
---------------------------------------------------------------------------

    Under the PM2.5 SIP Requirements Rule, a state seeking
an extension of the Serious area attainment date under section 188(e)
must submit a Serious area attainment plan that meets the following
requirements:
    (1) Base year and attainment projected emissions inventory
requirements in 40 CFR 51.1008(b);
    (2) the most stringent measure requirement in 40 CFR
51.1005(b)(1)(iii) and 51.1010(b), and best available control measures
not previously submitted;
    (3) attainment demonstration and modeling requirements in 40 CFR
51.1011 and 40 CFR 51.1005(b)(1)(i);
    (4) reasonable further progress requirements in 40 CFR 51.1012;
    (5) quantitative milestone requirements in 40 CFR 51.1013;
    (6) contingency measure requirements in 40 CFR 51.1014; and
    (7) nonattainment new source review plan requirements pursuant to
40 CFR 51.165.\43\
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    \43\ 40 CFR 51.1005(b)(2). With respect to contingency measures
and nonattainment new source review plan provisions, the EPA
interprets section 51.1005(b)(2) to require submission of complete
plan provisions addressing these requirements but not to require the
EPA to approve such provisions before granting a section 188(e)
extension request. 81 FR 58010, 58094-58095.
---------------------------------------------------------------------------

    In addition to establishing specific preconditions for an extension
of the Serious area attainment date, section 188(e) provides that the
EPA may consider a number of factors in determining whether to grant an
extension and the appropriate length of time for any such extension.
These factors are: (1) The nature and extent of nonattainment in the
area, (2) the types and numbers of sources or other emitting activities
in the area (including the influence of uncontrollable natural sources
and trans-boundary emissions from foreign countries), (3) the
population exposed to concentrations in excess of the standard in the
area, (4) the presence and concentrations of potentially toxic
substances in the mix of particulate emissions in the area, and (5) the
technological and economic feasibility of various control measures.\44\
Notably, neither the statutory requirements nor the discretionary
factors identified in section 188(e) include the specific ambient air
quality conditions in section 188(d)(2), which must be met for an area
to qualify for an extension of a Moderate area attainment date.
---------------------------------------------------------------------------

    \44\ CAA section 188(e).
---------------------------------------------------------------------------

    We evaluate the state's request for an extension of the Serious
area attainment date in accordance with these statutory criteria and
regulatory requirements, as described below.
    Step 1: Demonstrate that attainment by the statutory Serious area
attainment date is impracticable.
    Section 188(e) authorizes the EPA to grant a state request for an
extension of the Serious area attainment date if, among other things,
attainment by the date established under section 188(c) would be
impracticable. In order to demonstrate impracticability, the plan must
show that the implementation of BACM and BACT (and additional feasible
measures) on relevant source categories will not bring the area into
attainment by the statutory Serious area attainment date.\45\ For the
San Joaquin Valley, the Serious area attainment date for the 2006
PM2.5 NAAQS under section 188(c)(2) was December 31,
2019.\46\ BACM, including BACT, is the required level of control for a
Serious area that must be in place before the Serious area attainment
date. Therefore, we interpret the Act as requiring that a state provide
for at least the implementation of BACM, including BACT, before it can
claim that is impracticable to attain by the statutory deadline. The
statutory provision for demonstrating impracticability requires that
the demonstration be based on air quality modeling.\47\
---------------------------------------------------------------------------

    \45\ 81 FR 58010, 58094.
    \46\ Under CAA section 188(c)(2), the attainment date for a
Serious area ``shall be as expeditiously as practicable but no later
than the end of the tenth calendar year beginning after the area's
designation as nonattainment. . . .'' The EPA designated the San
Joaquin Valley as nonattainment for the 2006 PM2.5 NAAQS
effective December 14, 2009. 74 FR 58688. Therefore, the latest
permissible attainment date under section 188(c)(2), for purposes of
the 2006 PM2.5 NAAQS in this area, is December 31, 2019.
    \47\ CAA section 189(b)(1)(A).
---------------------------------------------------------------------------

    Step 2: Comply with all requirements and commitments in the
applicable implementation plan.
    A second precondition for an extension of the Serious area
attainment under section 188(e) is a showing that the state has
complied with all requirements and commitments pertaining to that area
in the implementation plan. We interpret this criterion to mean that
the state has implemented the control measures and commitments in the
SIP revisions it has submitted to address the applicable requirements
in CAA sections 172 and 189 for PM2.5 nonattainment areas.
For a Serious area attainment date extension request being submitted
simultaneously with the initial Serious area attainment plan for the
area, the EPA interprets section 188(e) not to require the area to have
a fully approved Moderate area attainment plan, and to allow for
extension of the attainment date if the area has complied with all
Moderate area requirements and commitments pertaining to that area in
the state's submitted Moderate area implementation plan.\48\ This

interpretation is based on the plain language of section 188(e), which
requires the state to comply with all requirements and commitments
pertaining to the area in the implementation plan.\49\
---------------------------------------------------------------------------

    \48\ 81 FR 58010, 58095.
    \49\ The Ninth Circuit Court of Appeals upheld this
interpretation of section 188(e) in Vigil v. Leavitt, 366 F.3d 1025,
amended at 381 F.3d 826 (9th Cir. 2004).
---------------------------------------------------------------------------

    Step 3: Demonstrate the inclusion of the most stringent measures.
    A third precondition for an extension of the Serious area
attainment under section 188(e) is for the state to demonstrate to the
satisfaction of the Administrator that the plan for the area includes
the most stringent measures that are included in the implementation
plan of any state, or are achieved in practice in any state, and can
feasibly be implemented in the area. The EPA has defined the term
``most stringent measure'' (MSM) as ``any permanent and enforceable
control measure that achieves the most stringent emissions reductions
in direct PM2.5 emissions and/or emissions of
PM2.5 plan precursors from among those control measures
which are either included in the SIP for any other NAAQS, or have been
achieved in practice in any state, and that can feasibly be implemented
in the relevant PM2.5 NAAQS nonattainment area.'' \50\ The
Act does not specify an implementation deadline for MSM, but because
the clear intent of section 188(e) is to minimize the length of any
attainment date extension, the EPA has interpreted the Act to require
implementation of MSM as expeditiously as practicable and no later than
one year before the extended Serious area attainment date identified by
the state in its extension request.\51\
---------------------------------------------------------------------------

    \50\ 40 CFR 51.1000 and 81 FR 58010, 58096-58097; see also
General Preamble Addendum, 42010 and 65 FR 19964, 19968 (April 13,
2000).
    \51\ 81 FR 58010, 58097.
---------------------------------------------------------------------------

    An MSM demonstration must satisfy the requirements of the
PM2.5 SIP Requirements Rule as described in the preamble to
the rule, as follows: \52\
---------------------------------------------------------------------------

    \52\ 40 CFR 51.1010(b) and 81 FR 58010, 58095-58097.
---------------------------------------------------------------------------

    (1) Update the emission inventory to identify all sources of direct
PM2.5 and all PM2.5 precursor emissions in the
nonattainment area;
    (2) Identify all potential MSM to reduce emissions from sources of
direct PM2.5 and PM2.5 plan precursors that are
approved into any state implementation plan or used in practice in any
state;
    (3) Compare the potential MSM for each relevant source category to
the measures, if any, already adopted for that source category in the
nonattainment area to determine whether such potential MSM would
further reduce emissions and, where the state chooses to reject a
measure from further consideration, demonstrate that it is not
technologically or economically feasible to implement the measure in
whole or in part within five years after the applicable attainment date
for the area; and
    (4) Adopt and implement all potential MSM identified through this
process that collectively will achieve attainment as expeditiously as
practicable and no later than five years after the applicable
attainment date, except those measures for which the state has provided
reasoned justification for rejection, based on technological or
economic feasibility.
    The level of control required under the MSM standard may depend on
how well other areas have chosen to control their sources. If a source
category has not been well controlled in other areas, MSM could
theoretically result in a low level of control. This contrasts with
BACM and BACT, which represent the ``best'' level of control feasible
for an area, regardless of whether it has been implemented elsewhere.
Thus, in some cases the MSM requirement may result in no more controls
or emission reductions than those that result from implementing BACM
and BACT. However, given the strategy in the nonattainment provisions
of the Act to offset longer attainment timeframes with more stringent
emission control requirements, we interpret the MSM provision so as to
increase the potential that it will result in additional controls
beyond the set of measures adopted as BACM and BACT. Accordingly,
states are required to reanalyze any measures that were rejected during
the state's BACM and BACT analysis to see if they have become feasible
in the area given the longer attainment date sought under CAA section
188(e) and changes that have occurred in the interim that improve the
feasibility of such measures.\53\ MSM may also involve increasing the
coverage of measures that were previously adopted as BACM and BACT.\54\
---------------------------------------------------------------------------

    \53\ Id.
    \54\ Id. at 58096.
---------------------------------------------------------------------------

    Notably, the ``to the satisfaction of the Administrator'' qualifier
on the MSM requirement indicates that Congress granted the EPA
considerable discretion in determining whether a plan in fact includes
MSM, recognizing that the overall intent of section 188(e) is that the
Agency grant as short an extension as practicable, consistent with the
objective of expeditious attainment of the NAAQS. For this reason, the
EPA will apply greater scrutiny to the evaluation of MSM for source
categories that contribute the most to the PM2.5 problem in
the SJV and less scrutiny to source categories that contribute less to
the PM2.5 problem.
    Step 4: Demonstrate attainment by the most expeditious alternative
date practicable.
    Section 189(b)(1)(A) requires that the Serious area plan
demonstrate attainment, using air quality modeling, by the most
expeditious date practicable after the statutory Serious area
attainment date.\55\ Evaluation of a modeled attainment demonstration
consists of two parts: Evaluation of the technical adequacy of the
modeling itself and evaluation of the control measures that are relied
on to demonstrate attainment. The EPA's determination of whether the
plan provides for attainment by the most expeditious date practicable
depends on whether the plan provides for implementation of BACM and
BACT no later than the statutory implementation deadline, MSM as
expeditiously as practicable and no later than one year before the
extended attainment date requested by the state, and any other
technologically and economically feasible measures that will result in
attainment as expeditiously as practicable.
---------------------------------------------------------------------------

    \55\ Id. at 58097.
---------------------------------------------------------------------------

    Step 5: Apply for an attainment date extension.
    Finally, the state must apply in writing to the EPA for an
extension of a Serious area attainment date, and this request must
accompany the modeled attainment demonstration showing attainment by
the most expeditious alternative date practicable. Additionally, the
state must provide the public reasonable notice and opportunity for a
public hearing on the attainment date extension request before
submitting it to the EPA, in accordance with the requirements for SIP
revisions in CAA section 110.

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

A. Emissions Inventory

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,

including Serious area requirements, in the PM2.5 SIP
Requirements Rule and codified these requirements in 40 CFR
51.1008.\56\ The EPA has also issued guidance concerning emissions
inventories for PM2.5 nonattainment areas.\57\
---------------------------------------------------------------------------

    \56\ 81 FR 58010, 58078-58079.
    \57\ ``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 should provide a state's best
estimate of actual emissions from all sources of the relevant
pollutants in the area, i.e., all emissions that contribute to the
formation of a particular NAAQS pollutant. For the PM2.5
NAAQS, the base year inventory must include direct PM2.5
emissions, separately reported filterable and condensable
PM2.5 emissions,\58\ and emissions of all chemical
precursors to the formation of secondary PM2.5: nitrogen
oxides (NOX), sulfur dioxide (SO2), volatile
organic compounds (VOC), and ammonia (NH3).\59\ In addition,
the emissions inventory base year for a Serious PM2.5
nonattainment area must be one of the three years for which monitored
data were used to reclassify the area to Serious, or another
technically appropriate year justified by the state in its Serious area
SIP submission.\60\
---------------------------------------------------------------------------

    \58\ The Emissions Inventory Guidance identifies the types of
sources for which the EPA expects states to provide condensable PM
emission inventories. Emissions Inventory Guidance, section 4.2.1
(``Condensable PM Emissions''), 63-65.
    \59\ 40 CFR 51.1008.
    \60\ 40 CFR 51.1008(b)(1).
---------------------------------------------------------------------------

    A state's SIP submission must include documentation explaining how
it calculated emissions data for the inventory. In estimating mobile
source emissions, a state should use the latest emissions models and
planning assumptions available at the time 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.\61\ Following CARB's submission of the Plan, the EPA
approved EMFAC2017, the latest revision to this mobile source emissions
model, and established grace periods during which EMFAC2014 may
continue to be used for transportation conformity purposes (i.e., new
regional emissions analyses and CO, PM10, and
PM2.5 hot-spot analyses).\62\ 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.63 64
---------------------------------------------------------------------------

    \61\ 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.
    \62\ 84 FR 41717 (August 15, 2019). The grace period for new
regional emissions analyses begins on August 15, 2019 and ends on
August 16, 2021, while the grace period for hot-spot analyses begins
on August 15, 2019 and ends on August 17, 2020. 84 FR 41717, 41720.
    \63\ The EPA released an update to AP-42 in January 2011 that
revised the equation for estimating paved road dust emissions based
on an updated data regression that included new emission tests
results. 76 FR 6328 (February 4, 2011). CARB used the revised 2011
AP-42 methodology in developing on-road mobile source emissions; see
https://www.arb.ca.gov/ei/areasrc/fullpdf/full7-9_2016.pdf.
    \64\ AP-42 has been published since 1972 as the primary source
of the EPA's emission factor information. 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.\65\ These future emissions projections are
necessary components of the attainment demonstration required under CAA
section 189(a)(1) and (b)(1) and the demonstration of RFP required
under section 172(c)(2).\66\ Emissions projections for future years
(which are referred to in the Plan as ``forecasted inventories'')
should account for, among other things, the ongoing effects of economic
growth and adopted emissions control requirements. The state's SIP
submission should include documentation to explain how the emissions
projections were calculated. Where a state chooses to allow new major
stationary sources or major modifications to use emission reductions
credits (ERCs) that were generated through shutdown or curtailed
emissions units occuring before the base year of an attainment plan,
the projected emissions inventory used to develop the attainment
demonstration must explicitly include the emissions from such
previously shutdown or curtailed emissions units.\67\
---------------------------------------------------------------------------

    \65\ 40 CFR 51.1008 and 51.1012. Also, see Emissions Inventory
Guidance, section 3 (``SIP Inventory Requirements and
Recommendations'').
    \66\ 40 CFR 51.1004, 51.1008, 51.1011, and 51.1012.
    \67\ 40 CFR 51.165(a)(3)(ii)(C)(1).
---------------------------------------------------------------------------

2. Summary of State's Submission
    Summaries of the planning emissions inventories for direct
PM2.5 and PM2.5 precursors (NOX,
SOX,\68\ VOC,\69\ and ammonia) and the documentation for the
inventories for the San Joaquin Valley PM2.5 nonattainment
area are located in Appendix B (``Emissions Inventory'') and Appendix I
(``New Source Review and Emission Reduction Credits'') of the 2018
PM2.5 Plan.
---------------------------------------------------------------------------

    \68\ The SJV PM2.5 Plan generally uses ``sulfur
oxides'' or ``SOX'' in reference to SO2 as a
precursor to the formation of PM2.5. We use
SOX and SO2 interchangeably throughout this
notice.
    \69\ The SJV PM2.5 Plan generally uses ``reactive
organic gasses'' or ``ROG'' in reference to VOC as a precursor to
the formation of PM2.5. We use ROG and VOC
interchangeably throughout this notice.
---------------------------------------------------------------------------

    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 estimates for the 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.\70\
---------------------------------------------------------------------------

    \70\ 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
planning inventories for the 2013 base year, which were modeled 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.\71\ Today we are
proposing action on those winter average and annual average emissions
inventories necessary to support the attainment plan and section 188(e)
extension

request for the 2006 PM2.5 NAAQS--i.e., the 2013 base year
inventory, forecasted inventories for the RFP milestone years of 2017,
2020, 2023, and 2026, and the forecasted 2024 attainment year
inventory. Each inventory includes emissions from stationary, area, on-
road, and non-road sources.
---------------------------------------------------------------------------

    \71\ 2018 PM2.5 Plan, App. 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 (CEIDARS) and future year inventories were estimated using
the California Emission Projection Analysis Model (CEPAM), 2016 SIP
Baseline Emission Projections, version 1.05.
---------------------------------------------------------------------------

    The base year inventories for stationary sources were developed
using actual emissions reports made by facility operators. The State
developed the base year emissions inventory for area sources using the
most recent models and methodologies available at the time the State
was developing the Plan.\72\ 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.\73\ 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.\74\ Re-entrained paved
road dust emissions were calculated using a CARB methodology consistent
with the EPA's AP-42 road dust methodology.\75\
---------------------------------------------------------------------------

    \72\ 2018 PM2.5 Plan, App. B, section B.2
(``Emissions Inventory Summary and Methodology'').
    \73\ Id. at B-42 to B-44.
    \74\ Id. at B-37.
    \75\ 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.\76\
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.\77\ 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.\78\
---------------------------------------------------------------------------

    \76\ Id. at B-18, B-19.
    \77\ 2018 PM2.5 Plan, App. I, I-1 through I-5.
    \78\ Id. at App. I, Tables I-1 through I-5.
---------------------------------------------------------------------------

    Table 1 provides a summary of the winter (24-hour) average
inventories in tons per day (tpd) of direct PM2.5 and
NOX emissions for the 2013 base year. Table 2 provides a
summary of annual average inventories of direct PM2.5 and
NOX emissions 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]
----------------------------------------------------------------------------------------------------------------
                                   Direct PM2.5
            Category                                    NOX             SOX             VOC           Ammonia
----------------------------------------------------------------------------------------------------------------
Stationary Sources..............             8.5            35.0             6.9            86.6            13.9
Area Sources....................            41.4            11.5             0.5           156.8           291.5
On-Road Mobile Sources..........             6.4           188.7             0.6            51.1             4.4
Non-Road Mobile Sources.........             4.4            65.3             0.3            27.4             0.0
                                 -------------------------------------------------------------------------------
    Totals \a\..................            60.8           300.5             8.4           321.9           309.8
----------------------------------------------------------------------------------------------------------------
Source: 2018 PM2.5 Plan, Appendix B, Tables B-1 through B-5.
\a\ Totals reflect disaggregated emissions and may not add exactly as shown here due to rounding.

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

3. EPA's Evaluation and Proposed Action
    The inventories in the 2018 PM2.5 Plan 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 for which monitored data were used for reclassifying
the San Joaquin Valley to Serious for the 2006 PM2.5
NAAQS,\79\ and it represents actual annual average emissions of all
sources within the nonattainment area. Direct PM2.5 and
PM2.5 precursors are included in the inventories, and
filterable and condensable direct PM2.5 emissions are
identified separately.
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    \79\ 81 FR 2993, 2994.
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    With respect to future year baseline projections, we have reviewed
the growth and control factors and find them acceptable and thus
conclude that

the future baseline emissions projections in the 2018 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. See the EPA's
``Technical Support Document, General Evaluation, San Joaquin Valley
PM2.5 Plan for the 2006 PM2.5 NAAQS,'' February
2020 (``EPA's General Evaluation TSD''). Table III-A of EPA's General
Evaluation 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 2018 PM2.5 Plan are properly supported by
SIP-approved stationary and mobile source measures.\80\
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    \80\ The future year emissions projections in the SJV
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 issued a notice of final rulemaking for the Safer Affordable
Fuel-Efficient (SAFE) Vehicles Rule Part One: One National Program
that, among other things, withdrew the EPA's 2013 waiver of
preemption for the ZEV sales mandate and GHG standards. 84 FR 51310.
See also proposed SAFE rule at 83 FR 42986 (August 24, 2018).
However, the agencies' final rule withdrawing the 2013 waiver did
not include final action on the federal fuel economy and GHG vehicle
emissions standards from the SAFE proposal. If the fuel economy and
GHG standards are finalized prior to our final rulemaking on the SJV
PM2.5 Plan, we will evaluate and address, as appropriate,
the impact of the SAFE action on our proposed action.
---------------------------------------------------------------------------

    For these reasons, we are proposing to approve the 2013 base year
emissions inventory in the 2018 PM2.5 Plan as meeting the
requirements of CAA section 172(c)(3) and 40 CFR 51.1008. We are also
proposing to find that the forecasted inventories in the Plan provide
an adequate basis for the BACM, MSM, RFP, and attainment demonstrations
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
SO2, NOX, VOC, and ammonia to PM2.5,
making them precursors to PM2.5.\81\ 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.\82\
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    \81\ ``Air Quality Criteria for Particulate Matter'' (EPA/600/P-
99/002aF), EPA, October 2004, Ch. 3.
    \82\ ``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.\83\ 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.'' \84\ The EPA has identified SO2,
NOX, VOC, and ammonia as precursors to the formation of
PM2.5.\85\ 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)).
---------------------------------------------------------------------------

    \83\ 81 FR 58010, 58017-58020.
    \84\ CAA section 302(g).
    \85\ 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 reasonably
available control measures (RACM) and reasonably available control
technology (RACT), BACM and BACT, MSM, and NSR] for sources of direct
PM2.5 and PM2.5 precursor emissions. Although
section 189(e) explicitly addresses only major stationary sources, the
EPA interprets the Act as authorizing it also to determine, under
appropriate circumstances, that regulation of specific PM2.5
precursors from other source categories in a given nonattainment area
is not necessary.\86\ 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,\87\ a
state may demonstrate in a SIP submission that control of a certain
precursor pollutant is not necessary in light of its insignificant
contribution to ambient PM10 levels in the nonattainment
area.\88\
---------------------------------------------------------------------------

    \86\ Id. at 58018-58019.
    \87\ General Preamble, 57 FR 13498, 13539-42.
    \88\ 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.\89\ If the EPA determines that the
contribution of the precursor to PM2.5 levels in the area is
not significant and approves the demonstration, the state is not
required to control emissions of the relevant precursor from existing
sources in the attainment plan.\90\
---------------------------------------------------------------------------

    \89\ 40 CFR 51.1006(a)(1).
    \90\ Id.
---------------------------------------------------------------------------

    In addition, in May 2019, the EPA issued the ``PM2.5
Precursor Demonstration Guidance'' (``PM2.5 Precursor
Guidance''), which provides recommendations to states for analyzing
nonattainment area PM2.5 emissions and developing such
optional precursor demonstrations, consistent with the PM2.5
SIP Requirements Rule.\91\ 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.\92\ 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.
---------------------------------------------------------------------------

    \91\ ``PM2.5 Precursor Demonstration Guidance,'' EPA-
454/R-19-004, May 2019, including Memo dated May 30, 2019 from Scott
Mathias, Acting Director, Air Quality Policy Division and Richard
Wayland, Director, Air Quality Assessment Division, Office of Air
Quality Planning and Standards (OAQPS), EPA to Regional Air Division
Directors, Regions 1-10, EPA.
    \92\ ``PM2.5 Precursor Demonstration Guidance, Draft
for Public Review and Comments,'' EPA-454/P-16-001, November 17,
2016, including Memo dated November 17, 2016 from Stephen D. Page,
Director, OAQPS, EPA to Regional Air Division Directors, Regions 1-
10, EPA.
---------------------------------------------------------------------------

    We are evaluating the SJV PM2.5 Plan in accordance with
the presumption embodied within subpart 4 that all PM2.5
precursors must be addressed in the State's evaluation of potential
control measures, unless the State adequately demonstrates that
emissions of a particular precursor or precursors do not contribute
significantly to ambient PM2.5 levels that exceed the
PM2.5 NAAQS in the nonattainment area. In reviewing any
determination by the State to exclude a PM2.5 precursor from
the required evaluation of potential control measures, we consider both
the magnitude of the precursor's contribution to ambient
PM2.5 concentrations in the nonattainment area and the
sensitivity of ambient PM2.5 concentrations in the area to
reductions in emissions of that precursor.\93\
---------------------------------------------------------------------------

    \93\ 40 CFR 51.1006(a)(1)(i) and (ii).
---------------------------------------------------------------------------

2. Summary of State's Submission
    The State presents a brief summary of its PM2.5
precursor analysis in Chapter 6 of the 2018 PM2.5 Plan and
the full precursor demonstration in Appendix G of the 2018
PM2.5 Plan.\94\ CARB also provided clarifying information on
its precursor assessment, including an Attachment A to its letter
transmitting the SJV PM2.5 Plan to the EPA \95\ and further
clarifications in three email transmittals.\96\
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    \94\ A copy of the contents of App. G appears in the CARB Staff
Report, App. C4 (``Precursor Demonstrations for Ammonia,
SOX, and ROG'').
    \95\ Letter dated May 9, 2019, from Richard Corey, Executive
Officer, CARB, to Michael Stoker, Regional Administrator, EPA Region
IX, Attachment A (``Clarifying information for the San Joaquin
Valley 2018 Plan regarding model sensitivity related to ammonia and
ammonia controls'').
    \96\ Email dated June 20, 2019, ``RE: SJV model disbenefit from
SOX reduction,'' from Jeremy Avise, CARB, to Scott
Bohning, EPA Region IX, with attachment (``CARB's June 2019
Precursor Clarification''); email dated September 19, 2019, ``FW:
SJV species responses,'' from Jeremy Avise, CARB, to Scott Bohning,
EPA Region IX, with attachments (``CARB's September 2019 Precursor
Clarification''); and email dated October 18, 2019, from Laura Carr,
CARB to Scott Bohning, Jeanhee Hong, and Rory Mays, EPA Region IX,
with attachment ``Clarifying Information on Ammonia'' (``CARB's
October 2019 Precursor Clarification'').
---------------------------------------------------------------------------

    The Plan provides both concentration-based and sensitivity-based
analyses of precursor contributions to ambient PM2.5
concentrations in the San Joaquin Valley. These analyses led the State
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, as discussed below.\97\ 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 PM2.5
Precursor TSD'').
---------------------------------------------------------------------------

    \97\ 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, the State 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.\98\ The State concluded that direct
PM2.5 and NOX emissions reductions will continue
to have a significant impact on annual and 24-hour PM2.5
design values in the San Joaquin Valley, with NOX reductions
being particularly important.\99\ Consistent with this conclusion, the
State focused the control strategy and attainment demonstration on
these two pollutants, as described in section IV.D of this preamble.
---------------------------------------------------------------------------

    \98\ SJV PM2.5 Plan, Ch. 6, 6-11 to 6-12. CARB
modeled the impacts of both NOX reductions and direct
PM2.5 reductions but the direct PM2.5 results
were used only as a point of comparison, as direct PM2.5
emissions must be regulated in all PM2.5 nonattainment
areas.
    \99\ Id. Ch. 6, 6-12; and 2018 PM2.5 Plan, App. G, 2.
CARB presents its sensitivity analysis for emission reductions in
direct PM2.5 and NOX in the Plan's attainment
demonstration appendix. 2018 PM2.5 Plan, App. K, Table 46
(annual average design values) and Table 50 (24-hour average design
values).
---------------------------------------------------------------------------

    For ammonia, SOX, and VOC, CARB assessed the 2015 annual
average concentration of each precursor in ambient PM2.5 at
Bakersfield, for which the necessary speciated PM2.5 data is
available and where the highest PM2.5 design values have
been recorded in most years, and 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.\100\ 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.
---------------------------------------------------------------------------

    \100\ SJV PM2.5 Plan, App. 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 emission 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. SJV PM2.5 Plan, Ch. 3, 3-3 to 3-4.
---------------------------------------------------------------------------

    Given that these levels are well above the EPA's recommended
contribution threshold in the Draft PM2.5 Precursor
Guidance, CARB then modeled the sensitivity of ambient PM2.5
in the San Joaquin Valley to 30% and 70% reductions in anthropogenic
emissions of each precursor pollutant in 2013 (the Plan's base year),
2020 (the modeled attainment year for the 1997 PM2.5 NAAQS),
and 2024 (the modeled attainment year for the 2006 PM2.5
NAAQS).\101\ CARB supplemented the sensitivity analysis with
consideration of additional information, including factors identified
in the Draft PM2.5 Precursor Guidance, such as emission
trends, the appropriateness of future year versus base year
sensitivity, available emission controls, and the severity of
nonattainment.\102\ The final version of the PM2.5 Precursor
Guidance confirms the relevance of these factors in a sensitivity
analysis.\103\
---------------------------------------------------------------------------

    \101\ SJV PM2.5 Plan, Ch. 6, 6-11 to 6-12.
    \102\ Id. at App. G, 5.
    \103\ PM2.5 Precursor Guidance, 18-19 (consideration
of additional information), 31 (available emission controls), and
35-36 (appropriateness of future year versus base year sensitivity).
---------------------------------------------------------------------------

    The State's sensitivity-based analysis used the same modeling
platform as that used for the Plan's attainment demonstration. The
State modeled the sensitivity of ambient PM2.5
concentrations in San Joaquin Valley to 30% and 70% emission reductions
in 2013, 2020, and 2024 for each of ammonia, SOX, and VOC.
The State estimated base case (2013, 2020, and 2024) design values for
PM2.5 using Relative Response Factors and

calculated the ammonia precursor contribution for a given year and for
each sensitivity scenario (30% and 70% emissions reductions) as the
difference between its base case design value and the design value for
each sensitivity scenario.\104\
---------------------------------------------------------------------------

    \104\ 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% ammonia
emission 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), whereas the
PM2.5 responses in 2024 were all below both recommended
thresholds. For a modeled 70% ammonia emission 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), 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 PM2.5 Precursor TSD, Table 2, and the 2018
PM2.5 Plan, Appendix G, Tables 2, 3, 5, and 7.
    The State bases its ammonia precursor determination on the
sensitivity analysis for the 2024 attainment year with a 30% ammonia
emission reduction. These respectively reflect its assessment of
research studies and the Plan's projected emission reductions, and on
its assessment of available emission controls. As explained in the
PM2.5 Precursor Guidance, precursor responses may be above
the recommend 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 consider whether its identified PM2.5
responses constituted a significant contribution to ambient
PM2.5 in the San Joaquin Valley. The additional information
included research studies, emission trends, and information to support
the State's conclusion that a 30% ammonia emission reduction
represented a reasonable upper bound on the ammonia emission 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 PM2.5 Precursor TSD.
    The State describes previous research that supports its finding
that ammonium nitrate PM2.5 formation in the San Joaquin
Valley is NOX-limited rather than ammonia-limited.\105\
Essentially, ammonia is so abundant that even with large ammonia
emission 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 (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. Hence, the area is considered NOX-
limited. The State points to the conclusions of Lurmann et al. based on
ambient measurements during the winter 2000-2001 CRPAQS (California
Regional Particulate Air Quality Study) intensive field study.\106\
That study found that most areas of the San Joaquin Valley were
NOX-limited with respect to ammonium nitrate formation. And
since that time, large additional NOX emission 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,\107\ 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.\108\ The CARB Staff
Report describes these conclusions in more detail and lists results
from multiple other recent studies with similar conclusions.\109\
---------------------------------------------------------------------------

    \105\ 2018 PM2.5 Plan, App. G, G-9 to G-10; CARB
Staff Report, App. C, 12-15; and Attachment A to CARB's submittal
letter of May 9, 2019.
    \106\ 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.
    \107\ ``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.
    \108\ 2018 PM2.5 Plan, App. G, Figure 2.
    \109\ CARB Staff Report, App. C, 12.
---------------------------------------------------------------------------

    Regarding emission trends, the CARB Staff Report presents an
emission inventory-based argument on the relative insensitivity of
PM2.5 to ammonia reductions.\110\ CARB compared the size of
the ammonia and NOX emission 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).\111\ 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 emission
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 2024 future modeled
case compared to the 2013 base year).
---------------------------------------------------------------------------

    \110\ Id. App. C, 15.
    \111\ Annual average ammonia emissions are projected to decrease
4.6 tpd (1.4%) from 2013 to 2024. 2018 PM2.5 Plan, App.
B, Table B-5.
---------------------------------------------------------------------------

    The State finds that NOX emissions in the San Joaquin
Valley are projected to decrease by 53% from 2013 to 2024 while ammonia
emissions are projected to remain relatively flat, thereby increasing
the relative abundance of ammonia.\112\ Based on the Plan's emission
reduction projections combined with the research study conclusions, the
State relies on the modeled responses for the 2024 future year, rather
than the 2013 base year, stating that the future year NOX
emissions are more representative of San Joaquin Valley emission
conditions.\113\ 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 states that this in

fact applies to the San Joaquin Valley.\114\
---------------------------------------------------------------------------

    \112\ 2018 PM2.5 Plan, App. G, 8-9.
    \113\ Id. App. G, 9.
    \114\ Id (referencing Draft PM2.5 Precursor Guidance,
33). See also PM2.5 Precursor Guidance, 35.
---------------------------------------------------------------------------

    With respect to the State's selection of 30% 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.\115\ 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.\116\
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 a number of scientific studies that address the correlation
between VOC and ammonia emissions from these emission sources.\117\
Based on these evaluations, the State concludes that ammonia control
measures achieving even the low end of the range (30%) are not feasible
for implementation in the San Joaquin Valley and that it is therefore
reasonable to treat a 30% ammonia reduction as an upper bound for
modeling in the precursor demonstration.
---------------------------------------------------------------------------

    \115\ 2018 PM2.5 Plan, App. G, 13 and App. C, section
C-25 and email dated October 18, 2019, from Laura Carr, CARB to
Scott Bohning, EPA Region IX, attaching document entitled
``Clarifying Information on Ammonia.''
    \116\ 2018 PM2.5 Plan, App. C, section C-25.
    \117\ Id. at C-314 and following.
---------------------------------------------------------------------------

    In sum, the State's sensitivity analysis presents a range of
PM2.5 responses to ammonia emission reductions depending on
base year versus future year and depending on the scale of emission
reductions that may be possible. The Plan provides the State's bases
for finding that the sensitivity result for 2024 better represents
conditions in the San Joaquin Valley than the 2013 base year and for
finding a 30% ammonia reduction to be a reasonable upper bound for
modeled ammonia emission reductions in assessing the ammonia
contribution. Based on these analyses, the State concludes that ammonia
does not contribute significantly to levels above the 2006
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 emission reductions of 30% and 70%, 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. The response was below zero at
most monitoring sites, indicating an increase, rather than decrease, in
ambient PM2.5 in response to SOX emission
reductions (i.e., a disbenefit). Only the Stockton and Manteca sites
had slightly positive responses to 30 and 70% emission reductions, and
the Tranquillity site also had a slightly positive response only to a
30% reduction. For 2024, the response ranged from -0.3 [micro]g/m\3\ to
+0.3 [micro]g/m\3\; these are also all below the contribution
threshold, with most sites showing a disbenefit from SOX
reductions. For further detail, please see EPA's PM2.5
Precursor TSD, Table 3, and the 2018 PM2.5 Plan, Appendix G,
Tables 8 and 9.
    CARB also included additional information regarding emission trends
and an evaluation of the SOX emission reduction disbenefit.
We summarize this additional information below and provide a more
detailed evaluation in the EPA's PM2.5 Precursor TSD.
    In terms of emission trends, the State found that SOX
emissions decreased from 2013 to 2014 and then very gradually rise to
8.0 tpd in 2024.\118\ On the basis of SOX emissions being
very similar in 2020 and 2024 (7.8 tpd and 8.0 tpd, respectively), 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 more positive in 2024, but still no more than
0.6 [micro]g/m\3\ in response to a 70% SOX emission
reduction. This supports the State's conclusion as to the overall
disbenefit of reducing SOX emissions.
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    \118\ 2018 PM2.5 Plan, App. G, Figure 4.
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    To explain the SOX emission reduction disbenefit, CARB
refers to the non-linearity of inorganic aerosol thermodynamics, as
described in a study by West et al.\119\ 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 Community Multiscale Air Quality (CMAQ) model and provided
clarifications to the EPA.\120\ 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 is it a well-known and
widely used chemical model.
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    \119\ 2018 PM2.5 Plan, App. 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.
    \120\ CARB's June 2019 Precursor Clarification.
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    Based on the small and mostly negative modeled response of ambient
PM2.5 to SOX emission 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 2006 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% VOC emission 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.\121\ The PM2.5 responses to a 70%
VOC emission reduction in 2013 ranged from 0.2 [micro]g/m\3\ to 4.8
[micro]g/m\3\, including responses above the 1.3 [micro]g/m\3\ draft
contribution threshold at a majority of sites. For a modeled 30% VOC
emission reduction, the ambient PM2.5 responses in 2024
ranged from -0.4 to 0.0 [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 the PM2.5 SIP
Requirements Rule. The PM2.5 responses to a 70% VOC emission
reduction in 2024 ranged from -1.0 to 0.0 [micro]g/m\3\, with all
monitoring sites below the 1.3 [micro]g/m\3\ draft contribution
threshold. In other words, CARB models a decrease in ambient
PM2.5 levels in 2013 in response to either a 30% or 70% VOC
emission reduction, whereas CARB models an increase in ambient
PM2.5 levels in 2024 in response to either a 30% or 70%
reduction in VOC emissions, i.e., a disbenefit. For further detail,
please see EPA's PM2.5 Precursor TSD, Table 4, and the 2018
PM2.5 Plan, Appendix G, Tables 10, 11, 13, and 15.
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    \121\ 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 consider whether
these PM2.5 responses constituted a significant contribution
to ambient PM2.5 in the San Joaquin Valley, including
emission trends and an assessment of the modeled disbenefit of VOC
emission reductions in 2024. CARB bases its precursor determination on
sensitivity analysis for the 2024 attainment year, reflecting its
assessment of the Plan's projected emission reductions. We summarize
this additional information below and present greater detail in the
EPA's PM2.5 Precursor TSD.
    Regarding emission trends, CARB found that VOC emissions would
decrease approximately 30 tpd (or 9%) from 2013 to 2024.\122\ 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.
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    \122\ 2018 PM2.5 Plan, App. G, 19 and Figure 5.
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    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.\123\ 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.\124\
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    \123\ 2018 PM2.5 Plan, App. 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).
    \124\ 2016 PM2.5 Plan, App. A, A-57. See also 2018
PM2.5 Plan, App. K, section 5.6 (``PM2.5
Precursor Sensitivity Analysis''), 71-72.
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    Based on its sensitivity-based analysis of VOC emission reductions
in the 2013 base and 2024 future years, VOC emission trends, and the
scientific understanding of atmospheric VOC chemistry in the San
Joaquin Valley, CARB concludes that VOC emissions do not contribute
significantly to PM2.5 levels that exceed the 2006
PM2.5 NAAQS in the San Joaquin Valley.
3. EPA's Evaluation and Proposed Action
    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 2006 PM2.5 NAAQS in the San Joaquin Valley and that
NOX emission sources, therefore, remain subject to control
requirements under subparts 1 and 4 of 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 2006 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 an acceptable progression of
analyses under the PM2.5 SIP Requirements Rule.\125\
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    \125\ For further discussion of the EPA's evaluation of the
State's concentration-based analysis, see EPA's PM2.5
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 in a straightforward application of the
EPA's recommended approach--i.e., for each modeled year and percent
precursor emission 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 Modeling TSD''). The State considered the EPA's
recommended range of emission reductions (30% to 70%) for the 2013 base
year, an interim year (2020), and the projected 2024 attainment year
for the 2006 PM2.5 NAAQS, and quantified the estimated
response of ambient PM2.5 concentrations to precursor
emission 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 2006
PM2.5 NAAQS in the San Joaquin Valley. Therefore, we turn to
our evaluation of the State's determination for each of these three
precursor pollutants.
a. Ammonia
    For ammonia, as detailed above, CARB estimated the ambient
PM2.5 response to both a 30% and a 70% emission 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. We have evaluated CARB's determination
that the projected 2024 attainment year is more representative of
conditions in the San Joaquin Valley for sensitivity-based analyses and
that 30% is a reasonable upper bound for ammonia emission 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

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 is likely to
be insensitive to ammonia emission reductions.
    We note that the model response to precursor reductions may be
unrealistically large. There is some 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
PM2.5 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. The ammonia contribution to
PM2.5 levels above the standard may therefore be less than
estimated by the State modeling. The 2024 year modeling incorporates
lower NOX emissions and so has a larger abundance of ammonia
relative to nitrate, more similar to the studies' ambient measurements.
The 2024 response to ammonia reductions may thus be more reliable than
the 2013 and 2020 responses, and may be more representative of current
atmospheric conditions despite its use of emission projections for a
future year.
    The relative sizes of the ammonia and NOX precursor
emission inventories after accounting for their differing molecular
weights are a rough indicator of which is the limiting pollutant for
production of ammonium nitrate, because it 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 the various processes mentioned above; it just assumes
all the emitted molecules find each other and fully react. The State
found ammonia to be roughly three times as abundant as NOX
currently after accounting for their differing molecular weights, and
even more so in the future. The EPA repeated the exercise to account
for SOX as well, and found that the ratio of total ammonia
to that needed to react with both nitrate and sulfate ranged from 2.7
in 2013 to 5.6 in 2028. These are about the same as the CARB
NOX-only results, because SOX emissions are very
small relative to those of NOX and ammonia (e.g., in 2013,
winter daily emissions were 8.4 tpd SOX, vs. 300.5 tpd for
NOX and 309.8 tpd for ammonia).\126\ These observations
support the State's finding that PM2.5 is expected to be
relatively insensitive to ammonia reductions, though it is not
definitive.
---------------------------------------------------------------------------

    \126\ 2018 PM2.5 Plan, App. B, Tables B-2, B-3, and
B-4.
---------------------------------------------------------------------------

    The State also concludes that there are continuing large decreases
in NOX emissions in the San Joaquin Valley from 2013 to
2024, including 53% reductions from baseline measures and 10-11%
reductions from additional new measures, while ammonia emissions are
projected to remain roughly constant (i.e., decreasing 1-2%).\127\ In
conjunction with the ambient evidence that ammonia is already
chemically overabundant relative to NOX in the San Joaquin
Valley, this shows that in the future the overabundance will become
even greater, and thus ambient PM2.5 would be even less
responsive to ammonia reductions. This adds conservatism to the State's
conclusions about ammonia insensitivity based on the scientific
studies.
---------------------------------------------------------------------------

    \127\ For further discussion of the SJV PM2.5 Plan's
control strategy, see section IV.D.4.b of this preamble.
---------------------------------------------------------------------------

    While the base year for an attainment plan for a given
nonattainment area is generally more representative of current
conditions, the EPA believes that either a base year or a future year
may be used for modeling an ambient PM2.5 response to
precursor emission reductions, provided the state explains how the
choice of analysis year and associated assumptions are
appropriate.\128\ The State relied on 2024 model responses mainly on
the grounds that large NOX emissions reductions will occur
during 2013-2024, so that the 2024 results will continue to be
representative, unlike earlier model years. These reductions are the
result of regulations put in place by past air quality planning
decisions, and they will occur regardless of decisions about additional
NOX or ammonia controls in the SJV PM2.5 Plan. In
assessing the effect of potential ammonia reductions, the EPA believes
it is reasonable to account for these NOX reductions and the
effect that ammonia reductions would have in the attainment year and
after. 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, and may make the 2024 responses 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 emission trends, including
the projected large amount of NOX emission reductions
through the attainment period, the EPA agrees that the modeled 2024
year is acceptable and representative of conditions in the San Joaquin
Valley.
---------------------------------------------------------------------------

    \128\ PM2.5 Precursor Guidance, 35-36.
---------------------------------------------------------------------------

    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%
reduction as a reasonable upper bound on the ammonia emission
reductions to model in estimating the precursor contribution. As the
State correctly notes, the 30% to 70% range recommended by the EPA is
based on historical NOX and SOX emission
reductions, and changes in ammonia emission levels nationally from 2011
to 2017 ranged from a 9% decrease to a 6% increase.\129\ The State's
descriptions of both the past research relied upon to develop existing
rules that apply to ammonia emission sources and ongoing research show
that it has considered the availability of ammonia controls both in the
past and in the present context, and that the State has a basis for its
conclusion that 30% is a reasonable upper bound on achievable
reductions for ammonia.
---------------------------------------------------------------------------

    \129\ PM2.5 Precursor Guidance, Table 2, page 30.
---------------------------------------------------------------------------

    In sum, we find that the State quantified the sensitivity of
ambient PM2.5 levels to reductions in ammonia using
appropriate modeling techniques, which performed well, and that the
State's choice of 2024 as the reference point for purposes of
evaluating the sensitivity of ambient PM2.5 levels to
ammonia emission reductions is well-supported. We also find that the
State adequately documented its bases for using a 30% reduction in
ammonia emissions as an upper bound in the modeling to assess ambient
sensitivity to ammonia emission reductions. Based on all of these
considerations, the EPA proposes to approve the State's demonstration
that ammonia emissions do not contribute significantly to ambient
PM2.5 levels that exceed the 2006 PM2.5 NAAQS in
the San Joaquin Valley.

b. SOX
    For SOX, the State found that the ambient
PM2.5 responses to SOX emission reductions were
below the EPA's recommended contribution threshold of 1.3 [micro]g/m\3\
in the Draft PM2.5 Precursor Guidance (and below the EPA's
recommended threshold of 1.5 [micro]g/m\3\ in the (final)
PM2.5 Precursor Guidance) and, indeed, that for most sites
there would be an increase in ambient PM2.5 levels in
response to such reductions (i.e., a disbenefit). The EPA has evaluated
the State's determination as to this disbenefit and the State's
resulting conclusion as to the precursor's significance.
    Because the results of the sensitivity analysis were all below the
EPA's recommended 24-hour contribution thresholds at both the 30% and
70% emission reductions, and in both the 2013 base year and 2024
attainment year, it is not necessary to distinguish between the timing
and scale of emission reductions with respect to the response of
ambient PM2.5 levels, as in the ammonia evaluation where the
results diverged according to scale and timing of modeled emission
reductions. The EPA's PM2.5 Precursor TSD contains
additional detail on the EPA's evaluation of SOX as a
PM2.5 precursor, including the unexpected disbenefit of
reducing SOX emissions. Accordingly, we find that the
State's decision to rely on the 2013 sensitivity modeling results for a
30% SOX reduction is acceptable.
    Therefore, on the basis of the modeled ambient PM2.5
response to both a 30% and 70% reduction in SOX emissions in
2013, and the facts and circumstances of the area, the EPA proposes to
approve the State's demonstration that SOX emissions do not
contribute significantly to ambient PM2.5 levels that exceed
the 2006 PM2.5 NAAQS in the San Joaquin Valley.
c. VOC
    For VOC, the State found that the ambient PM2.5 response
to VOC emission reductions were generally below the EPA's recommended
contribution threshold of 1.3 [micro]g/m\3\ in the Draft
PM2.5 Precursor Guidance (and below the EPA's recommended
threshold of 1.5 [micro]g/m\3\ in the final PM2.5 Precursor
Guidance), and often predicted an increase in ambient PM2.5
levels in response to such reductions (i.e., a disbenefit), except for
a 70% emission reduction for the 2013 base year, where the State
predicted the ambient PM2.5 response to be above both
recommended thresholds at a majority of sites. The EPA has evaluated
and agrees with the State's determination that the projected 2024
attainment year is more representative of conditions in the San Joaquin
Valley for sensitivity-based analyses and that VOC reductions in 2024
would mostly result in a disbenefit to ambient PM2.5 levels,
as well as the State's resulting conclusion as to whether VOC's
contribution is significant.
    Regarding emission trends, the EPA agrees that the 9% VOC emissions
decrease from 2013 to 2024 favors reliance on the 2024 modeling
results. Furthermore, there is a large decrease in NOX
emissions over this period, as discussed in the EPA's evaluation of
ammonia in section IV.B.3.a of this preamble, which affects the
atmospheric chemistry with respect to ambient PM2.5
formation from VOC emissions. The 9% VOC emission reductions and the
vast majority of NOX emissions will result from baseline
measures that are projected to occur, even absent any further action by
the State. We therefore find it reasonable to rely on future year 2024
modeled responses to VOC reductions. The EPA also finds that the State
provided a reasonable explanation for the VOC reduction disbenefit and
evidence that it occurs in the San Joaquin Valley.
    For all of these reasons, we propose to approve the State's
demonstration that VOC emissions do not contribute significantly to
ambient PM2.5 levels that exceed the 2006 PM2.5
NAAQS in the San Joaquin Valley.

C. Best Available Control Measures and Most Stringent Measures

1. Statutory and Regulatory Requirements
    Section 189(b)(1)(B) of the Act requires for any serious
PM2.5 nonattainment area that the state submit provisions to
assure that the best available control measures (BACM) for the control
of PM2.5 and PM2.5 precursors shall be
implemented no later than four years after the date the area is
reclassified as a serious area. The EPA has defined BACM in the
PM2.5 SIP Requirements Rule to mean ``any technologically
and economically feasible control measure that can be implemented in
whole or in part within 4 years after the date of reclassification of a
Moderate PM2.5 nonattainment area to Serious and that
generally can achieve greater permanent and enforceable emissions
reductions in direct PM2.5 emissions and/or emissions of
PM2.5 plan precursors from sources in the area than can be
achieved through the implementation of RACM on the same source(s). BACM
includes best available control technology (BACT).'' \130\
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    \130\ 40 CFR 51.1000 (definitions). In longstanding guidance,
the EPA has similarly defined BACM to mean, ``among other things,
the maximum degree of emissions reduction achievable for a source or
source category, which is determined on a case-by-case basis
considering energy, environmental, and economic impacts.'' General
Preamble Addendum, 42010, 42013.
---------------------------------------------------------------------------

    The EPA generally considers BACM a control level that goes beyond
existing RACM-level controls, for example by expanding the use of RACM
controls or by requiring preventative measures instead of
remediation.\131\ Indeed, as implementation of BACM and BACT is
required when a Moderate nonattainment area is reclassified as Serious
due to its inability to attain the NAAQS through implementation of
``reasonable'' measures, it is logical that ``best'' control measures
should represent a more stringent and potentially more costly level of
control.\132\ If RACM and RACT level controls of emissions have been
insufficient to reach attainment, the CAA contemplates the
implementation of more stringent controls, controls on more sources, or
other adjustments to the control strategy necessary to attain the NAAQS
in the area.
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    \131\ 81 FR 58010, 58081 and General Preamble Addendum, 42011,
42013.
    \132\ Id. and General Preamble Addendum, 42009-42010.
---------------------------------------------------------------------------

    Consistent with longstanding guidance provided in the General
Preamble Addendum, the preamble to the PM2.5 SIP
Requirements Rule discusses the following steps for determining BACM
and BACT:
    (1) Develop a comprehensive emission inventory of the sources of
PM2.5 and PM2.5 precursors;
    (2) Identify potential control measures;
    (3) Determine whether an available control measure or technology is
technologically feasible;
    (4) Determine whether an available control measure or technology is
economically feasible; and
    (5) Determine the earliest date by which a control measure or
technology can be implemented in whole or in part.\133\
---------------------------------------------------------------------------

    \133\ 81 FR 58010, 58083-58085.
---------------------------------------------------------------------------

    The EPA allows consideration of factors such as physical plant
layout, energy requirements, needed infrastructure, and workforce type
and habits when considering technological feasibility. For purposes of
evaluating economic feasibility, the EPA allows consideration of
factors such as the capital costs, operating and maintenance costs, and
cost effectiveness (i.e., cost per ton of

pollutant reduced by a measure or technology) associated with the
measure or control.\134\
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    \134\ 40 CFR 51.1010(a)(3) and 81 FR 58010, 58041-58042.