[Federal Register Volume 88, Number 239 (Thursday, December 14, 2023)]
[Rules and Regulations]
[Pages 86581-86608]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-27088]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2023-0263; FRL-10941-02-R9]


Air Quality State Implementation Plans; Approvals and 
Promulgations: California; 1997 Annual Fine Particulate Matter Serious 
and Clean Air Act Section 189(d) Nonattainment Area Requirements; San 
Joaquin Valley, CA

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA or ``Agency'') is 
taking final action to approve portions of state implementation plan 
(SIP) revisions submitted by the State of California to meet Clean Air 
Act (CAA or ``Act'') requirements for the 1997 annual fine particulate 
matter (PM2.5) national ambient air quality standards (NAAQS 
or ``standards'') in the San Joaquin Valley PM2.5 
nonattainment area. Specifically, the EPA is approving those portions 
of the submitted SIP revisions as they pertain to the Serious 
nonattainment area and CAA section 189(d) requirements for the 1997 
annual PM2.5 NAAQS, except for the requirement for 
contingency measures which will be addressed in a separate rulemaking. 
In addition, the EPA is approving the 2020 and 2023 motor vehicle 
emissions budgets and the trading mechanism for use in transportation 
conformity analyses for the 1997 annual PM2.5 NAAQS.

DATES: This rule is effective on January 16, 2024.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-R09-OAR-2023-0263. All documents in the docket are 
listed on the https://www.regulations.gov website. Although listed in 
the index, some information is not publicly available, e.g., 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Certain other material, such as 
copyrighted material, is not placed on the internet and will be 
publicly available only in hard copy form. Publicly available docket 
materials are available through https://www.regulations.gov, or please 
contact the person identified in the FOR FURTHER INFORMATION CONTACT 
section for additional availability information. If you need assistance 
in a language other than English or if you are a person with a 
disability who needs a reasonable accommodation at no cost to you, 
please contact the person identified in the FOR FURTHER INFORMATION 
CONTACT section.

FOR FURTHER INFORMATION CONTACT: Ashley Graham, Geographic Strategies 
and Modeling Section (AIR-2-2), EPA Region IX, 75 Hawthorne Street, San 
Francisco, CA 94105. By phone: (415) 972-3877 or by email at 
[email protected].

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

Table of Contents

I. Summary of the Proposed Action
II. Public Comments and EPA Responses
    A. Comments From Central California Environmental Justice 
Network (CCEJN)
    B. Comments From Central Valley Air Quality Coalition (CVAQ)
    C. Comments From a Private Individual
III. Motor Vehicle Emissions Budgets and Transportation Conformity
IV. Environmental Justice Considerations
V. Final Action
VI. Statutory and Executive Order Reviews

I. Summary of the Proposed Action

    On July 14, 2023, in accordance with CAA section 110(k)(3), the EPA 
proposed to approve portions of SIP revisions submitted by the 
California Air Resources Board (CARB) to meet CAA requirements for the 
1997 annual PM2.5 NAAQS in the San Joaquin Valley 
PM2.5 nonattainment area.\1\ The San Joaquin Valley is 
classified as a Serious nonattainment area for the 1997 annual 
PM2.5 NAAQS and is also subject to CAA section 189(d) 
requirements because of the failure of the area to attain the 1997 
annual PM2.5 NAAQS by the area's original Serious area 
attainment date (i.e., December 31, 2015). The EPA's determination that 
the area failed to attain by the original December 31, 2015 attainment 
date triggered the requirement for the State to submit the SIP 
revisions on which the EPA is taking final action in this document.\2\
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    \1\ 88 FR 45276.
    \2\ 81 FR 84481 (November 23, 2016).
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    The SIP revisions on which we proposed action are those portions of 
the ``2018 Plan for the 1997, 2006, and 2012 PM2.5 
Standards'' (``2018 PM2.5 Plan'') \3\ and the ``San Joaquin 
Valley Supplement to the 2016 State Strategy for the State 
Implementation Plan'' (``Valley State SIP Strategy'') \4\ that pertain 
to the 1997 annual PM2.5 NAAQS, and the ``Attainment Plan 
Revision for the 1997 Annual PM2.5 Standard'' (``15 
[micro]g/m\3\ SIP Revision'').\5\ CARB submitted the 2018 
PM2.5 Plan and Valley State SIP Strategy to the EPA as a 
revision to the California SIP on May 10, 2019, and submitted the 15 
[micro]g/m\3\ SIP Revision on November 8, 2021. We refer to these three 
submissions collectively as the ``SJV PM2.5 Plan'' or 
``Plan.'' The SJV PM2.5 Plan was developed jointly by the 
San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD or 
``District'') and CARB and addresses Serious area nonattainment plan 
and CAA section 189(d) requirements for the 1997 annual 
PM2.5 NAAQS in the San Joaquin Valley, except for the 
requirement for contingency measures. The Plan includes the State's 
demonstration that the area will attain the 1997 annual 
PM2.5 NAAQS by December 31, 2023.
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    \3\ The 2018 PM2.5 Plan was adopted by the San 
Joaquin Valley Unified Air Pollution Control District on November 
15, 2018, and by CARB on January 24, 2019.
    \4\ The Valley State SIP Strategy was adopted by CARB on October 
25, 2018.
    \5\ The ``15 [micro]g/m\3\ SIP Revision'' was adopted by the San 
Joaquin Valley Unified Air Pollution Control District on August 19, 
2021, and adopted by CARB on September 23, 2021.
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    Following submittal of the SJV PM2.5 Plan, CARB 
transmitted to the EPA two technical supplements providing additional 
information in support of the Plan. The first supplement, submitted on 
March 30, 2023, included documents titled ``Ammonia: Supplemental 
Information for EPA in Support of 15 [micro]g/m\3\ Annual 
PM2.5 Standard, March

[[Page 86582]]

2023'' (``March 2023 Ammonia Supplement'') and ``Building 
Electrification Technical Supplement for the 1997 Annual 
PM2.5 NAAQS'' (``March 2023 Building Heating Supplement''). 
The second supplement was submitted on June 15, 2023, and included 
information on the State's consideration of Title VI of the Civil 
Rights Act of 1964 (``Title VI'') in the context of SIP development to 
provide necessary assurances for purposes of CAA section 
110(a)(2)(E)(i) (``Title VI Supplement'').\6\
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    \6\ Letter dated June 15, 2023, from Steven S. Cliff, Executive 
Officer, CARB, to Martha Guzman, Regional Administrator, EPA Region 
IX, with enclosures titled ``Title VI of the Civil Rights Act of 
1964: CARB Supplemental Information for EPA in Support of 15 
[micro]g/m\3\ Annual PM2.5 Standard'' (``CARB Title VI 
Supplement'') and ``San Joaquin Valley Air Pollution Control 
District Write-Up on Title VI of the Civil Rights Act of 1964: 
Supplemental Information for EPA in Support of 15 [micro]g/m\3\ 
Annual PM2.5 Standard'' (``District Title VI 
Supplement'').
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    The EPA proposed to approve the best available control measures/
best available control technology (BACM/BACT) demonstration,\7\ the 
five percent annual emissions reduction demonstration, the attainment 
demonstration (including air quality modeling), the reasonable further 
progress (RFP) demonstration, and the quantitative milestones 
demonstration in the SJV PM2.5 Plan as meeting the Serious 
nonattainment area and CAA section 189(d) planning requirements for the 
1997 annual PM2.5 NAAQS. We also proposed to find that the 
previously approved \8\ 2013 base year emissions inventories continue 
to satisfy the requirements of CAA section 172(c)(3) and 40 CFR 51.1008 
for purposes of both the Serious area and the CAA section 189(d) 
attainment plans, and to find that the forecasted inventories for the 
years 2017, 2018, 2019, 2020, 2023, and 2026 provide an adequate basis 
for the BACM, RFP, five percent, and modeled attainment demonstration 
analyses. Finally, we proposed to approve the motor vehicle emissions 
budgets for 2020 and 2023 and the trading mechanism provided for use in 
transportation conformity analyses.\9\
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    \7\ As discussed in Section III.B of the proposal, a section 
189(d) plan must address any outstanding Moderate or Serious area 
requirements that have not previously been approved. Because we have 
not previously approved a subpart 4 RACM demonstration for the San 
Joaquin Valley nonattainment area, we also proposed to approve the 
BACM/BACT demonstration in the SJV PM2.5 Plan as meeting 
the subpart 4 RACM/RACT requirement for the area. (88 FR 45276, 
45322).
    \8\ On November 26, 2021, the EPA finalized a partial approval 
and partial disapproval of the 2018 PM2.5 Plan for the 
1997 annual PM2.5 NAAQS, including approval of the 2013 
base year emissions inventory in the Plan. 86 FR 67329.
    \9\ An adequacy finding for the 2020 and 2023 motor vehicle 
emissions budgets was effective on February 25, 2022. (87 FR 7834, 
February 10, 2022).
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    Please see our July 14, 2023 proposed rulemaking for additional 
background and a detailed explanation of the rationale for our proposed 
action.

II. Public Comments and EPA Responses

    The public comment period for the proposed rulemaking opened on 
July 14, 2023, the date of its publication in the Federal Register, and 
closed on August 14, 2023. During this period, the EPA received three 
comment submissions from the following entities: (1) a coalition of six 
environmental and community organizations (collectively referred to 
herein as ``CCEJN''),\10\ (2) a coalition of eight environmental and 
community organizations (collectively referred to herein as 
``CVAQ''),\11\ and (3) a private citizen commenter.\12\ We respond to 
the comments herein.
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    \10\ Comment letter dated and received August 11, 2023, 
including 36 attachments, addressed to Ashley Graham, EPA Region IX. 
The six environmental and community organizations, in order of 
appearance in the letter, are the Central California Environmental 
Justice Network, the Central Valley Air Quality Coalition, 
Earthjustice, the Leadership Counsel for Justice and Accountability, 
the National Parks Conservation Association, and Sierra Club--Kern-
Kaweah Chapter.
    \11\ Comment letter dated and received August 14, 2023, 
addressed to Martha Guzman, Regional Administrator, EPA Region IX. 
The eight environmental and community organizations, in order of 
appearance in the letter, are the Central Valley Air Quality 
Coalition, Earthjustice, Sierra Club--Kern-Kaweah Chapter, the 
National Parks Conservation Association, the Central California 
Environmental Justice Network, Little Manila Rising, and Valley 
Improvement Projects.
    \12\ Comment letter dated and received August 14, 2023, from 
Richard Grow, to Docket ID No. EPA-R09-OAR-2023-0263.
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A. Comments From Central California Environmental Justice Network 
(CCEJN)

1. Necessary Assurances Required by CAA Section 110(a)(2)(E)
    Comment 1.A: CCEJN questioned the EPA's proposed approval of the 
SJV PM2.5 Plan because of concerns about the adequacy of the 
necessary assurances that the State provided in the Title VI 
supplement. The commenter contends that to comply with CAA section 
110(a)(2)(E), a state's necessary assurances must relate to a state's 
nonattainment plan SIP submission itself, not merely the public 
processes carried out while preparing the plan or state laws and 
policies outside of the plan. The commenter claims that the Title VI 
Supplement fails to do this because it ``has nothing to do with'' the 
specific contents of the SJV PM2.5 Plan. As an example, the 
commenter points to the State's lack of a Title VI analysis supporting 
its decision to not regulate ammonia as part of its PM2.5 
reduction strategy and contends that this example indicates that the 
State has failed to provide adequate necessary assurances. 
Additionally, CCEJN asserts that the EPA's analysis of the Plan must 
consider how the Plan itself complies with Title VI and that the EPA 
did not do so in its proposal.
    Response 1.A: The EPA agrees with the commenter that CAA section 
110(a)(2)(E)(i) requires that a state provide necessary assurances that 
implementing the SIP submission at issue would not be prohibited by 
Title VI. However, the EPA disagrees with the commenter that the 
necessary assurances provided by CARB, in conjunction with the 
substantive elements of the Plan itself, are insufficient to show that 
implementation of the Plan is not prohibited by Title VI, consistent 
with CAA section 110(a)(2)(E)(i). The EPA explained its rationale 
regarding its evaluation of the necessary assurances and CAA section 
110(a)(2)(E)(i) in detail in our proposal.\13\
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    \13\ 88 FR 45276, 45319-45321.
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    As a point of clarification, the commenter includes references to 
``compliance with Title VI'' as the relevant inquiry for purposes of 
necessary assurances under CAA section 110(a)(2)(E)(i). The EPA does 
not agree with this characterization of its responsibilities under the 
CAA.\14\ In the proposal action, the EPA clearly noted that ``[t]he 
EPA's proposed SIP approval does not constitute a formal finding of 
compliance with Title VI or 40 CFR part 7.'' \15\ The EPA further noted 
that ``[a]pproval of this SIP submission for purposes of CAA 
110(a)(2)(E)(i) does not affect the EPA's discretion to enforce Title 
VI and/or the EPA's civil rights regulations.'' \16\ Without making a 
formal finding of compliance with Title VI, the EPA believes the 
analysis in the EPA's proposed approval and in this

[[Page 86583]]

final rulemaking is consistent with CAA section 110(a)(2)(E)(i).\17\
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    \14\ See El Comit[eacute] para el Bienestar de Earlimart et al. 
v. EPA, 786 F.3d 688 (9th Cir. 2015) (``El Comit[eacute] effectively 
contends the EPA should have evaluated California's assurances the 
same way the EPA would have to deal with a pending Title VI 
complaint setting forth allegations of a current violation. El 
Comit[eacute]'s argument fails because it misconstrues the EPA's 
burden regarding the `necessary assurances' requirement. The EPA has 
a duty to provide a reasoned judgment as to whether the state has 
provided `necessary assurances,' but what assurances are `necessary' 
is left to the EPA's discretion.'').
    \15\ 88 FR 45276, 45321.
    \16\ Id.
    \17\ See El Comit[eacute] para el Bienestar de Earlimart et al. 
v. EPA, 786 F.3d 688 (9th Cir. 2015) (``Section 110(a)(2)(E) . . . 
does not require a state to `demonstrate' it is not prohibited by 
Federal or State law from implementing its proposed SIP revision. 
Rather, this section requires a state to provide `necessary 
assurances' of this.'')
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    With respect to the substance of the State's submission, the EPA 
disagrees with the commenter that the public processes surrounding the 
development and implementation of an attainment plan have no bearing on 
necessary assurances under CAA section 110(a)(2)(E)(i). As stated in 
the proposal, ``[w]hat is appropriate for purposes of necessary 
assurances can vary depending upon the nature of the issues in a 
particular situation. Thus, the EPA evaluates a state's compliance with 
CAA 110(a)(2)(E)(i) on a case-by-case basis.'' \18\ Further, the EPA 
has discretion to determine what assurances are necessary and may 
require more or different information as needed in other SIP 
actions.\19\ For example, in other contexts, the EPA has identified 
public participation as an established approach for recipients of EPA 
assistance to provide meaningful access to programs and activities.\20\ 
Therefore, the EPA does not agree with the contention that methods of 
providing for public participation are not relevant to the analysis of 
necessary assurances under CAA section 110(a)(2)(E)(i).
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    \18\ 88 FR 45276, 45320.
    \19\ See id.
    \20\ See, e.g., https://www.epa.gov/external-civil-rights/external-civil-rights-guidance. Although information on this website 
is not specific to CAA section 110(a)(2)(E)(i) necessary assurances, 
it provides information regarding public participation and 
information provided to recipients of EPA assistance.
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    In the Title VI Supplement, the State described the early and 
enhanced public engagement processes that CARB and the District 
undertook during the development and approval of the 2016 State SIP 
Strategy, Valley State SIP Strategy, 2018 PM2.5 Plan, and 15 
[micro]g/m\3\ SIP Revision, all of which formed the basis for the SJV 
PM2.5 Plan for the 1997 annual PM2.5 NAAQS. It 
also described steps the State and District took to solicit and respond 
to public input following the local adoption of the Plan and to 
implement the control measures and strategy outlined in the Plan. These 
approaches are beyond minimum public notice and comment requirements 
and provide relevant information and important context of the necessary 
assurances under CAA section 110(a)(2)(E)(i) that the Plan was adopted 
and will be implemented into the future in a manner that is not 
prohibited by Title VI.
    Similarly, the descriptions of State measures like Assembly Bill 
617 (``AB 617'') and the development of community air monitoring 
networks provide relevant context for the regulatory landscape in which 
the State will implement the Plan, as well as the intent of the 
regulators. The EPA believes the State initiatives to prevent or 
diminish potential health-related impacts to communities most impacted 
by air pollution also, in part, provide assurances that the 
implementation of the Plan is not prohibited by Title VI in a manner 
consistent with CAA section 110(a)(2)(E)(i). The State's Civil Rights 
Policy, too, provides additional support for the conclusion that 
implementation of the Plan would not be prohibited by Title VI. For 
example, the policy would allow for members of the public to notify and 
file a formal complaint with the State that an alleged violation of 
Title VI is occurring ``during the administration of [the State's] 
programs.'' \21\ Taken together, these various State processes and 
initiatives support the conclusion that the State provided necessary 
assurances that implementation of the plan would not be prohibited by 
Title VI.
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    \21\ Title VI Supplement, p. 8.
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    The commenter points to one primary substantive deficiency in the 
Plan that they believe indicates the State has not demonstrated 
compliance with CAA section 110(a)(2)(E)(i): The commenter claims that 
ammonia is a major precursor of PM2.5 and that the policy 
decision ``to decline to regulate ammonia implicates disparate 
treatment and/or disparate impact, yet CARB provides no necessary 
assurances that this policy decision does not violate Title VI.'' The 
EPA's proposed and final actions, based upon the State's SIP 
submissions, reflect the EPA's agreement that ammonia is not a 
significant precursor of PM2.5 for the purposes of the 1997 
annual PM2.5 NAAQS in the San Joaquin Valley. As described 
in more detail in Section II.A.3 of this document, this final 
determination comes following the EPA's review of the State's submittal 
and request for additional information to support the State's decision 
not to regulate ammonia for this NAAQS, as well as the EPA's review of 
the exhibits and attachments from the commenter. Included in the 
State's submittal and March 2023 Ammonia Supplement are estimates of 
the level of emissions reductions possible with a suite of potential 
ammonia control measures, justifications for why many of these measures 
are not feasible or are already being implemented in the area, and 
ultimately, why the State has chosen to focus on reducing direct 
PM2.5 and NOX to reduce PM2.5 
concentrations in the San Joaquin Valley air basin. The EPA believes 
the technical information provided by the State to support its decision 
not to regulate ammonia for purposes of the 1997 annual 
PM2.5 NAAQS provides adequate necessary assurances that the 
implementation of this Plan will not be prohibited by Title VI.
    The EPA recognizes that the San Joaquin Valley area has previously 
struggled to attain the 1997 annual PM2.5 NAAQS and that the 
Demographic Index analysis the EPA completed as a part of the proposed 
approval indicates the area includes communities of color and low-
income populations above the national average. However, as explained in 
this response and in our proposal, the EPA believes the information in 
the record contains adequate necessary assurances consistent with CAA 
section 110(a)(2)(E)(i). This analysis is based in part on technical 
analyses such as that the modeling in the State's and District's Plan 
shows attainment for these NAAQS by the applicable attainment date and 
that the control strategy for PM2.5 takes into consideration 
the unique atmospheric conditions in the San Joaquin Valley air basin 
in which the PM2.5 response to reductions in ammonia 
emissions would be relatively small. Thus, based on the existing 
technical record before the EPA, we find that the State has adequately 
provided necessary assurances that the implementation of the Plan is 
consistent with CAA section 110(a)(2)(E)(i).
    Comment 1.B: Next, CCEJN contends that the policies cited by CARB 
in its Title VI supplement to support its necessary assurances, e.g., 
AB 617, community air monitoring networks, and CARB's Civil Rights 
Policy, are not enforceable parts of the submitted Plan (pursuant to 
CAA section 110(a)(2)(A)), cannot lead to credited emissions reductions 
for SIP purposes, and thus cannot be relied upon as necessary 
assurances.
    Response 1.B: The EPA disagrees that necessary assurances must 
themselves be enforceable parts of a plan. While in some instances a 
state may submit additional enforceable measures as a component of 
necessary assurances, the EPA believes that this is not a requirement. 
The commenter cites the CAA section 110(a)(2)(A) requirement that plans 
include enforceable emissions limitations and other control measures as 
a basis for the assertion that necessary assurances must be enforceable 
and part of the plan. The EPA agrees that nonattainment plans

[[Page 86584]]

must contain enforceable emissions limitations and other control 
measures--but this does not mean that CAA section 110(a)(2)(E)(i) 
necessary assurances must themselves be emissions limitations or 
control measures. The EPA interprets section 110(a)(2)(E)(i) as 
allowing an ``assurance'' to include an analysis of the plan. In this 
context, a state providing adequate information to the EPA to provide 
necessary assurances that the state is not prohibited by Title VI from 
carrying out the plan in the SIP submission is sufficient. In the 
proposal action, the EPA explained the rationale for this approach, 
including citing to relevant case law finding that ``what assurances 
are `necessary' is left to the EPA's discretion.'' \22\ This is 
consistent with necessary assurances that the EPA requires when needed 
for other issues related to section 110(a)(2)(E)(i). For example, 
states also provide necessary assurances concerning the adequacy of 
personnel, funding, and state law authority to implement a SIP 
submission, and the EPA generally relies on facts, analyses, and other 
forms of assurances from the state for these purposes--not enforceable 
measures (that is, the EPA generally does not require SIP-approved 
rules that are incorporated by reference into the Code of Federal 
Regulations to provide such necessary assurances). There may be 
circumstances under which the EPA would expect a state to provide a 
state law provision for inclusion into the SIP in order to provide such 
necessary assurances for these other requirements, but this is not 
generally the case.
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    \22\ 88 FR 45276, 45320. See also, El Comit[eacute] para el 
Bienestar de Earlimart et al. v. EPA, 786 F.3d 688 (9th Cir. 2015).
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    Where a necessary assurances analysis concludes that additional 
enforceable measures are needed, a state would also include such new 
measures in the SIP submission, but necessary assurances need not 
necessarily themselves constitute such measures, as the commenter 
suggests. In this case, the EPA has concluded that the information 
provided by the State concerning its existing policies and programs 
provides adequate necessary assurances that the State's implementation 
of the SIP submissions at issue would not be prohibited by Title VI.
2. Emissions Inventory
    Comment 2.A: CCEJN states that the soil NOX emissions 
estimate of approximately 10 tons per day (tpd) used in the modeling 
emissions inventory was dubious when the State submitted the Plan in 
2018 and that the estimate is clearly inaccurate based on more recent 
studies, which the commenter claims suggest soil NOX may 
contribute as much as 100 tpd to total NOX emissions. The 
commenter also asserts that studies suggest that soil NOX 
emissions are likely driven primarily by agriculture and therefore 
should be considered anthropogenic. To support these assertions, the 
commenter references Exhibit A to the letter (``Exhibit A''), which 
summarizes 10 studies from 2015-2023, from which the author concludes 
that 9 of the studies indicate that standard soil NOX 
parameterizations underestimate agricultural soil NOX 
emissions by a factor of 2 to 10.
    CCEJN further states that ``[t]he state has acknowledged that its 
existing inventory may be outdated, and it has begun the process of 
studying NOX emissions from soil in order to update the 
inventory for future submissions to EPA,'' but that its use of the 
existing inventory in the interim ``. . . is unlawful because it is 
based exclusively on inertia, and `the EPA cannot simply recite 
``scientific uncertainty'' to evade its statutory duty to update 
regulations' '' (citing A Cmty. Voice v. EPA, 997 F.3d 983, 994 (9th 
Cir. 2021)). The commenter suggests that ``[i]nstead, the state must 
make an updated good faith estimate--if not a perfect estimate--of 
emissions, taking into account that the Clean Air Act is `preventative' 
and `precautionary' in nature,'' and asserts that such estimate would 
undoubtedly be higher than the estimate in the current inventory and 
would identify significant anthropogenic soil NOX emissions.
    Based on its analysis, CCEJN concludes that the EPA must disapprove 
the inventory because it is neither ``current'' nor ``accurate'' and 
that failure to do so is arbitrary and capricious.
    Response 2.A: The EPA acknowledges the information provided by 
CCEJN in its comments and in the studies described in Exhibit A 
suggesting that soil NOX emissions may be higher than have 
typically been estimated in the past. The studies cited by the 
commenter rely on variants of several emissions estimation approaches, 
including efforts to achieve better agreement between air quality 
models and satellite measurements, and to correlate satellite 
measurements over croplands with the expected soil temperature and 
moisture dependence of soil NOX emissions. While most of the 
studies cited by the commenter were published after the State developed 
the emissions and conducted the modeling for the 2018 PM2.5 
Plan upon which the 15 [micro]g/m\3\ SIP Revision is based, the EPA 
would not characterize the studies as providing ``updated'' emissions 
that would make the estimates in the 2018 PM2.5 Plan 
obsolete, as suggested by the commenter. Rather, as discussed further 
in the remainder of this response, we find that some recent studies 
provide evidence that soils are an important NOX source, and 
several provide alternative estimates of soil NOX emissions 
using various approaches.
    The EPA agrees that there is evidence suggesting soil 
NOX emissions may be higher than previously estimated but 
disagrees with the characterization in Exhibit A that 9 out of the 10 
studies conclude that California soil NOX is underestimated 
by a factor of 2 or more. That was the conclusion of two of the 
studies, those described in Almaraz et al. (2018) \23\ and Sha et al. 
(2021).\24\ Luo et al. (2022) \25\ did not opine on how their estimate 
compares with prior estimates, though the authors did provide an 
estimate that the author of Exhibit A notes implies that prior 
estimates are largely underestimated. The other studies provide 
evidence consistent with soil NOX as an important source or 
suggest a stronger temperature dependence for soil NOX 
emissions compared to previous approaches.
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    \23\ Almaraz et al. (2018), Agriculture is a major source of 
NOX pollution in California, Science Advances, 4(1), 
2018, doi:10.1126/sciadv.aao3477.
    \24\ Sha et al. (2021), Impacts of soil NOX emission 
on O3 air quality in rural California, Environmental 
Science & Technology, 55(10), 7113-7122, doi:10.1021/
acs.est.0c06834.
    \25\ Luo et al. (2022), Integrated Modeling of U.S. Agricultural 
Soil Emissions of Reactive Nitrogen and Associated Impacts on Air 
Pollution, Health, and Climate, Environmental Science & Technology, 
56 (13), 9265-9276. doi:10.1021/acs.est.1c08660.
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    While there is evidence suggesting soil NOX emissions 
may be higher than previously estimated, there are conflicting 
conclusions in the literature. Because the inventories in the SJV 
PM2.5 Plan reflect the State's best estimate based on the 
information available at the time the Plan was developed, the EPA does 
not believe a change in the soil NOX emissions estimation 
approach relied on in the SJV PM2.5 Plan is warranted at 
this time. There is a need to reconcile the disagreement among studies 
by examining the differing assumptions, techniques, data sources, 
locations, and time periods covered. Such further examination may also 
help resolve the substantial uncertainty and variability of the 
proportion of soil NOX emissions that can be attributed to 
anthropogenic sources such as agricultural fertilizer application.
    The EPA further disagrees with CCEJN's assertion that the State 
relies

[[Page 86585]]

on the soil NOX emissions estimates in its existing 
inventory due to ``inertia.'' As noted by the commenter, the State has 
effectively acknowledged that its methodology for estimating soil 
NOX emissions may need to be updated when it shared its 
plans to convene a subject matter expert review panel to assess the 
state of the science on soil NOX emissions and make 
recommendations for future estimates.\26\ These efforts indicate that 
the State is taking the issue seriously and attempting to address it, 
as acknowledged by the commenter. However, in exploring possible 
improvements to its soil NOX estimation approach, the State 
is not disavowing the approach used in the SJV PM2.5 Plan, 
nor is there a widely accepted soil NOX emissions inventory 
approach that the State is willfully refusing to use. Depending on the 
outcomes of the review panel's work, the State may find that its 
current approach provides the best estimate and retain such approach, 
or the State may determine that an alternative approach would provide a 
more accurate estimate and use such approach moving forward.
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    \26\ SJVUAPCD, 2023 PM2.5 Plan for Attainment of the 
Federal 2012 Annual PM2.5 Standard, Public Workshop, 
slide 16, http://www.valleyair.org/Workshops/postings/2023/05-11-23_PM25/presentation.pdf. (A recording of the workshop is also cited 
in the comment letter in fn. 39).
---------------------------------------------------------------------------

    For the SJV PM2.5 Plan, the State used the 
DeNitrification[hyphen]DeComposition model (DNDC) to estimate the 10 
tpd of soil NOX emissions used in the modeling.\27\ The 
approach is supported by research conducted in the same time frame as 
studies cited by the commenter and therefore the EPA does not consider 
the State's approach to be outdated. The emissions inventory in the 
Plan was among the work that led to the paper by Guo et al. (2020),\28\ 
which was cited in Exhibit A as among the recent research on soil 
NOX. Guo et al. (2020) did not find that soil NOX 
emissions are significantly underestimated in the State's emissions 
inventory. Rather, the study examined evidence from satellite 
retrievals and ground-based measurements that indicate that the State's 
approach provides an accurate emissions inventory for the San Joaquin 
Valley. The EPA believes that the DNDC-based soil NOX 
emissions used in the modeling are a good faith estimate consistent 
with the State's current view of the state of the science, and that the 
State's estimate is acceptable for use in the modeling emissions 
inventory in the SJV PM2.5 Plan for the 1997 annual 
PM2.5 NAAQS.
---------------------------------------------------------------------------

    \27\ Email dated May 26, 2020, from Jeremy Avise, CARB, to Scott 
Bohning, EPA Region IX, Subject: ``Soil NOX in ARB's 
modeling'', with attached poster ``Preliminary Assessment of Soil 
NOX Emissions from Agricultural Cropland in the San 
Joaquin Valley''; ``Estimating Nitrogen Emissions from California's 
Agricultural Lands'', March 5, 2019, presentation by Mike 
Fitzgibbon, CARB, at 2019 California Climate & Agriculture Summit, 
https://calclimateag.org/2019summit/.
    \28\ Guo et al. (2020), Assessment of Nitrogen Oxide Emissions 
and San Joaquin Valley PM2.5 Impacts From Soils in 
California, Journal of Geophysical Research: Atmospheres, 125(24), 
doi:10.1029/2020JD033304. Note that a web document with a DOI or 
Digital Object Identifier, such as 10.1029/2020JD033304, may be 
found via prefixing doi.org/ to the doi, as in: https://doi.org/10.1029/2020JD033304.
---------------------------------------------------------------------------

    The EPA acknowledges that there is evidence that soil 
NOX emissions have historically been underestimated, 
including evidence from some studies finding that satellite 
observations of column NO2 (total amount of NO2 
in a vertical column of the atmosphere) indicate that soil 
NOX emissions are higher than predictions by photochemical 
models using emissions estimates from older soil NOX 
parameterizations. The commenter describes some of such evidence in 
Exhibit A. However, the case for soil NOX emissions being 
significantly underestimated in the San Joaquin Valley is not as 
settled as CCEJN's comment implies. The studies cited by the commenter 
differ in the questions they attempt to address, their assumptions and 
analytical approaches, their data analysis techniques and metrics, and 
in the differing environmental conditions in the locations and time 
periods they cover.
    In the remainder of this response, we identify statements from the 
ten research papers listed in Exhibit A to show that their support for 
a substantially greater soil NOX emissions for the San 
Joaquin Valley is not definitive, and that there is not an agreed upon 
method to estimate a missing increment of emissions if one is in fact 
needed. Note that these points are not meant to discredit the work of 
the respective authors but rather to illustrate that there are varying 
factors that require greater investigation to determine the magnitude 
of soil NOX emissions in the San Joaquin Valley. Given these 
complicating factors and uncertainties, the EPA requests that CARB and 
the District continue their work to examine their current methodology 
for estimating soil NOX emissions, and as appropriate, 
revise their methodology based on the findings of the expert review 
panel and the latest available research.
    Oikawa et al. (2015) \29\ measured NOX emissions from 
sorghum plots after applying fertilizer, and explored the effect of 
higher soil NOX emissions on the performance of an air 
quality model by comparing the model results with satellite 
NO2 column observations and surface measurements. The study 
authors concluded that soil NOX emissions would need to be 
10 or more times higher to match observations. However, surface 
measurements were not consistently underestimated in the model, and 
increasing emissions in the model to match the satellite retrievals led 
to overestimates in emissions at the surface derived from measurements 
of soil NOX emissions fluxes. The paper also noted that 
global estimates of soil NOX emissions from other studies 
vary by a factor of three (ranging from 9 to 27 Tg per year), 
indicating a high level of uncertainty. The study conclusions suggest 
that soil NOX emissions are largely underestimated but the 
magnitude of the underestimate is not quantified.
---------------------------------------------------------------------------

    \29\ Oikawa et al. (2015), Unusually high soil nitrogen oxide 
emissions influence air quality in a high-temperature agricultural 
region. Nat. Commun., 6:8753, doi:10.1038/ncomms9753.
---------------------------------------------------------------------------

    Parrish et al. (2017) \30\ focuses on understanding trends in ozone 
design values, noting a difference in the San Joaquin Valley trend in 
comparison with other California air basins. The authors note that the 
difference may partially be accounted for by the higher agricultural 
activity in the Valley, for which controls have not been implemented as 
extensively as for other anthropogenic sources. While this explanation 
could also hold for agricultural soil NOX, that particular 
issue is not explored.
---------------------------------------------------------------------------

    \30\ Parrish et al. (2017), Ozone Design Values in Southern 
California's Air Basins: Temporal Evolution and U.S. Background 
Contribution. J. Geophys. Res. Atmos., 122, 11166-11182, 
doi:10.1002/2016JD026329.
---------------------------------------------------------------------------

    Exhibit A cites Kleeman et al. (2019) \31\ as providing evidence of 
a missing source of NOX emissions that could help correct a 
``consistent underprediction'' in nitrate concentrations. The EPA 
believes this underprediction was overstated. For the January average 
of the three model years reported, there was a modest underprediction 
of nitrate in the model base cases without soil NOX compared 
to a somewhat larger overprediction when soil NOX emissions 
were added; whereas for the 2010 model year, nitrate was overpredicted 
in the base case and the overprediction was worsened in the

[[Page 86586]]

soil NOX case.\32\ In the conclusion, the authors state that 
``further research is required to more accurately estimate winter 
emissions rates of soil NOX and to account for year-to-year 
variations driven by changes in meteorological conditions, fertilizer 
application rates, and irrigation practices,'' and that the tests 
conducted ``do not definitely prove that the missing emissions source 
is indeed fertilized agricultural soils. Future measurements should be 
made in the rural portions of the SJV to further test the hypothesis 
that soil NOX emissions are a significant factor in the air 
quality cycles within the region.'' \33\ The EPA interprets such 
conclusions as an acknowledgement that additional research is needed, 
with a focus on wintertime conditions when San Joaquin Valley 
PM2.5 concentrations are highest.
---------------------------------------------------------------------------

    \31\ Kleeman, M., A. Kumar, and A. Dhiman, ``Investigative 
Modeling of PM2.5 Episodes in the San Joaquin Valley Air 
Basin during Recent Years'' (CARB Contract No. 15-301, 2019), 
available at https://ww2.arb.ca.gov/sites/default/files/classic/research/apr/past/15-301.pdf.
    \32\ Id. at 60 and 63.
    \33\ Id. at 77.
---------------------------------------------------------------------------

    The author of Exhibit A summarizes a result from Chen et al. 
(2020),\34\ noting acceptable PM2.5 model performance 
despite overly low atmospheric mixing heights. But the author goes on 
to suggest that overly low mixing heights should have led to 
PM2.5 overpredictions; the good performance therefore may 
imply that the PM2.5 precursor emissions were too low. The 
study also found that rural site column NO2 was 
underpredicted by 25 percent relative to NO2 columns derived 
from surface-based measurements, suggesting that soil NOX 
emissions are underestimated. Thus, the study authors acknowledge that 
soil NOX emissions may need to be further examined. However, 
they also note good agreement between modeled column NO2 and 
the NO2 columns derived from surface-based measurements at 
the urban sites of Fresno and Bakersfield, where NO2 is 
double that of the rural sites, and state that ``it is unlikely that 
NOX emissions from croplands are comparable to mobile 
sources'' (the main source of NOX emissions). That is, the 
NOX emissions increase that would be needed to increase the 
model predictions by 25 percent for the low-NO2 rural sites 
is unlikely to be comparable to the NOX emissions driving 
the high NO2 urban sites. This finding supports further 
exploration of soil NOX emissions, and a possible 
underestimate, but does not imply a large underestimate in soil 
NOX emissions.
---------------------------------------------------------------------------

    \34\ Chen et al. (2020), Modeling air quality in the San Joaquin 
valley of California during the 2013 Discover-AQ field campaign, 
Atmospheric Environment: X, Volume 5, January 2020, 100067, 
doi:10.1016/j.aeaoa.2020.100067.
---------------------------------------------------------------------------

    Wang et al. (2021) \35\ explored the relatively modest downward 
trend in satellite column NO2 measurements after 2009, as 
compared to the steady decrease in anthropogenic NOX 
emissions, and the role of soil NOX emissions in this 
apparent discrepancy. They found better model agreement with satellite 
column NO2 when they increased the temperature 
responsiveness of their soil NOX emissions estimates, 
especially at high temperatures. This change also improved the 
correlation between modeled column NO2 and satellite column 
NO2 in the central United States. This correlation is an 
important finding, implying soil NOX emissions may be 
underestimated. However, it should be noted that in absolute terms, 
even without soil NOX, the model simulation overpredicted 
the NO2 concentration relative to the satellite retrieval. 
The authors acknowledge that there are many reasons why the predictions 
might not match the observations. The authors cite an uncertainty of 35 
percent in the satellite NO2 columns, and the uncertainty in 
the satellite retrieval encompasses all of the results, from the zero 
soil NOX scenario to the increased soil NOX 
scenario.\36\ The EPA views this as a large enough uncertainty to limit 
confidence in at least some of the study conclusions.
---------------------------------------------------------------------------

    \35\ Wang et al (2021), Improved modelling of soil 
NOX emissions in a high temperature agricultural region: 
role of background emissions on NO2 trend over the US, 
Environ. Res. Lett., 16, doi:10.1088/1748-9326/ac16a3.
    \36\ Id. at Figure 3.
---------------------------------------------------------------------------

    Wang et al. (2021) states that the downward trend in the satellite 
column NO2 is smaller than the downward trend in 
anthropogenic NOX emissions, and that the discrepancy is 
greater for the central U.S. than for the eastern or western U.S. Since 
the San Joaquin Valley is in the west, the EPA interprets this result 
as indicating that there is less of a potential need for increases in 
soil NOX emissions estimates in the San Joaquin Valley 
relative to the central U.S. to resolve the discrepancy. The authors 
also cited another study in which the apparent discrepancy between the 
trends in modeled versus surface-level ambient measurements (as opposed 
to the satellite retrieval) was found to be within the bounds of the 
uncertainty of the ambient measurements. The study provides a strong 
impetus for exploring soil NOX emissions and their potential 
increased rate at higher temperatures but does not provide evidence 
that soil NOX emissions are significantly underestimated in 
the San Joaquin Valley.
    To evaluate the human health and climate benefits of reducing 
reactive nitrogen emissions, Luo et al. (2022) \37\ used the Fertilizer 
Emission Scenario Tool for CMAQ (FEST-C) to generate soil 
NOX emissions estimates for every U.S. county, including 
those counties in the San Joaquin Valley. Exhibit A notes that the 
FEST-C-derived San Joaquin Valley county total emissions of soil 
NOX is 100 tpd compared to CARB's emissions inventory for 
all anthropogenic NOX which amounts to roughly 200 tpd. The 
study used a different emissions model than the model used by CARB, 
underscoring the need to explore why emissions models yield such 
different results. The study did not validate the model-derived 
NO2 predictions using satellite retrievals or ground-based 
measurements, so it does not provide direct evidence that soil 
NOX emissions are underestimated for the San Joaquin Valley.
---------------------------------------------------------------------------

    \37\ Luo et al. (2022), Integrated Modeling of U.S. Agricultural 
Soil Emissions of Reactive Nitrogen and Associated Impacts on Air 
Pollution, Health, and Climate, Environmental Science & Technology, 
2022, 56 (13), 9265-9276. doi:10.1021/acs.est.1c08660.
---------------------------------------------------------------------------

    Wang et al. (2023) \38\ explored trends in satellite column 
NO2 and ground level measurements, and the role of lightning 
and soil NOX in explaining spatial and temporal 
distributions of NO2. Among other results, they found that 
temperature and soil moisture, which are important drivers of soil 
NOX emissions, were highly correlated with satellite column 
NO2 in rural areas of California, including crop lands. This 
suggests soil NOX is an important source of NOX 
near crop lands. The study examined trends in NOX over time 
rather than attempting to quantify soil NOX emissions and 
therefore does not provide direct evidence that soil NOX 
emissions are underestimated for the San Joaquin Valley.
---------------------------------------------------------------------------

    \38\ Wang et al (2023), Satellite NO2 trends reveal 
pervasive impacts of wildfire and soil emissions across California 
landscapes, Environ. Res. Lett., 18, doi:10.1088/1748-9326/acec5f.
---------------------------------------------------------------------------

    Finally, three studies cited in Exhibit A, Almaraz et al. (2018), 
Guo et al. (2020), and Sha et al. (2021), provided estimates of soil 
NOX emissions in California. Almaraz et al. (2018) \39\ 
estimated soil NOX emissions using a top-down approach based 
on aircraft measurements as well as the Integrated Model for the 
Assessment of the Global Environment (IMAGE) soil model. Guo et al. 
(2020) \40\ compared satellite measurements of NO2 with CMAQ 
air quality model predictions using soil

[[Page 86587]]

NOX emissions from the DNDC soil model. Sha et al. (2021) 
\41\ conducted a similar measurement-model comparison but using the 
Weather Research and Forecasting model coupled with Chemistry (WRF-
Chem) air quality model and the Berkeley Dalhousie Iowa Soil NO 
Parameterization (BDISNP) soil model. The IMAGE and BDISNP models are 
empirical or parametric models. They rely on emissions factors that are 
derived from empirical measurements and that may vary by land use, 
precipitation, and temperature, but do not incorporate algorithms that 
reflect the underlying physical principles. The DNDC model used in Guo 
at al. (2020) and in the State's emissions inventory is a 
biogeochemical or mechanistic model. It also uses measurements for 
validation but includes detailed consideration of the individual 
physical and biological processes in soils that lead to NOX 
emissions and their dependence on factors like the soil's various 
nitrogen- and carbon-containing species, moisture, and temperature.
---------------------------------------------------------------------------

    \39\ Almaraz et al. (2018), Agriculture is a major source of 
NOX pollution in California, Science Advances, 4(1), 
2018, doi:10.1126/sciadv.aao3477.
    \40\ Guo et al. (2020), op. cit.
    \41\ Sha et al. (2021), Impacts of soil NOX emission 
on O3 air quality in rural California, Environmental 
Science & Technology, 55(10), 7113-7122, doi:10.1021/
acs.est.0c06834.
---------------------------------------------------------------------------

    Comparisons between the results described in Almaraz et al. (2018), 
Guo et al. (2020), and Sha et al. (2021) show large disagreements.\42\ 
Almaraz et al. (2018) estimated that soil NOX emissions from 
fertilized croplands account for 32 percent of California 
NOX emissions, Sha et al. (2021) estimated soil 
NOX emissions comprise 40.1 percent of California's total 
NOX emissions, while Guo et al. (2020) estimate that soil 
NOX emissions are only 1.1 percent of California 
anthropogenic NOX emissions. (As noted earlier in this 
response, the DNDC model emissions estimation work performed for the 
Guo et al. (2020) study was also the basis for the State's soil 
NOX emissions estimate.) The fraction of nitrogen applied as 
fertilizer released as NOX to the atmosphere was estimated 
by Almaraz et al. (2018) to be 15 percent, while 7 other studies 
reviewed by Guo et al. (2020) estimate it to be 2 percent or less. 
Furthermore, there is an additional possible discrepancy between the 
work described in Wang et al. (2021) \43\ and Wang et al. (2023),\44\ 
and the results in Guo et al. (2020). The former two found correlations 
between satellite-derived column NO2 over agricultural areas 
and modeled soil emissions, suggesting soil NOX as a driver 
of NO2 there. However, using correlations and ratios of 
NOX to CO among monitoring sites, and satellite column 
NO2 retrievals, Guo et al. (2020) found little difference 
between the diurnal and seasonal temporal variation at rural sites 
compared to urban sites, consistent with a larger contribution of 
emissions from urban sources rather than rural soils. Higher soil 
NOX emissions would increase summer emissions more in rural 
areas than in urban areas.
---------------------------------------------------------------------------

    \42\ The EPA also compared these studies in approving 
California's 2020 emissions inventory submittal. 87 FR 59015, 59017-
59019 (February 9, 2022).
    \43\ Wang et al. (2021), op. cit.
    \44\ Wang et al. (2023), op. cit.
---------------------------------------------------------------------------

    Despite widely differing estimates of the relative portion of 
California's NOX emissions inventories attributable to soil 
NOX in Almaraz et al. (2018), Sha et al. (2021), and Guo et 
al. (2020), each study reported high agreement between its modeled and 
its observed soil NOX emissions. Reconciling the differences 
in input data used in the models, such as fertilizer and irrigation 
amounts and timing; other inputs to the air quality models; and data 
analysis techniques would be necessary for a process-based 
understanding of the differences in the contribution and magnitude of 
soil NOX emissions estimates between models. There is also a 
need for additional measurements of soil NOX emissions 
fluxes for various locations and conditions to help develop and 
validate soil models.
    The various authors acknowledge considerable uncertainty in their 
work. While Almaraz et al. (2018) suggest that soil NOX 
emissions may be significantly underestimated using current techniques, 
the study acknowledges the limited number of surface measurements that 
were available for purposes of validating the model results and that, 
where observations exist, there is a large range in observed values due 
to varying soil conditions (e.g., relating to temperature, moisture, 
and fertilizer application). The ``top-down'' NOX emissions 
estimates derived from aircraft measurements relied upon in the study 
also reflect a significant degree of uncertainty, reported at 190 tpd 
plus or minus 130 tpd, i.e., plus or minus 68 percent. The authors 
acknowledge the limited number of surface measurements that were 
available for purposes of comparing with the model results, the 
difficulty in comparing the model results with the observations, and 
the need for more field measurements. Guo et al. (2020) stated that 
obtaining an emissions factor correlating NOX emissions to 
fertilizer application from the presently available data in various 
studies (including Almaraz et al. (2018)) would be ``difficult or 
impossible'' due to the sparseness of data collected in terms of 
sampling length, sampling frequency, and the episodic nature of 
nitrogen gases from soil.
    Most of the discussion herein concerns the varying estimates of 
overall total soil NOX emissions. However, how those 
emissions are distributed in time and space are also of great 
importance for understanding the effect of NOX emissions on 
ambient PM2.5 concentrations. PM2.5 
concentrations in the San Joaquin Valley are highest in the cool, moist 
winter, whereas soil NOX emissions are highest in the warm, 
dry summer. For modeling PM2.5 concentrations, it is 
especially important that the soil NOX approach that is used 
performs well under wintertime conditions. Also important is how the 
approach reflects soil composition, soil management practices, and 
fertilizer application, each of which vary in time and space. Adopting 
a different soil NOX emissions estimation approach is not a 
matter of simply replacing one estimate of total soil NOX 
with another. Rather, it requires ensuring that the approach accurately 
reflects the spatial and temporal variation of the many factors 
affecting emissions and of the emissions themselves.
    In light of the uncertainties and disagreements among studies, the 
EPA does not believe that the available research provides sufficient 
certainty about the magnitude and proportion of soil NOX 
emissions to warrant a revision to the State's inventory for purposes 
of the SJV PM2.5 Plan.\45\ The EPA is not convinced that any 
revised estimate developed by the State at this time would be 
verifiably more accurate than the inventory in the Plan. A revision to 
the State's inventory approach may be warranted in the future pending 
the State's ongoing work in this area and the most up-to-date 
understanding of soil NOX emissions, as discussed earlier in 
this response. The EPA encourages the State to continue its ongoing 
work to convene a subject matter expert review panel to assess the 
state of the science on soil NOX emissions, to keep abreast 
of the latest research, and to update its estimation methodologies, as 
appropriate. However, for purposes of the SJV PM2.5 Plan for 
the 1997 annual PM2.5 NAAQS that is the subject of this 
action, we find that the State relied on a reasonable methodology that 
is supported by the research literature. Thus, we conclude that the 
State

[[Page 86588]]

provided an accurate, up-to-date emissions inventory for 
NOX.
---------------------------------------------------------------------------

    \45\ The EPA reached a similar conclusion in approving 
California's 2020 emissions inventory submittal. 87 FR 59015, 59017-
59019 (February 9, 2022).
---------------------------------------------------------------------------

    Comment 2.B: Regarding the motor vehicle emissions modeling, CCEJN 
points to a previous statement from the EPA, saying that ``it could 
approve an outdated inventory so long as the inventory was built using 
the `latest EPA-approved' emission model `at the time [the State] 
developed the submission.' '' The commenter asserts that the EPA now 
``proposes to abandon both the statutory text and the already-lax 
requirement to use the most recent EPA-approved model,'' by allowing 
the State to rely on a model that is a decade old when two more recent 
models are available, one of which (EMFAC2017) shows higher attainment-
year emissions of both NOX and PM2.5. CCEJN 
contends that the State and the EPA speculate that the higher values 
would not affect the attainment demonstration. However, CCEJN asserts 
that the effect on the attainment demonstration is unknown and that it 
is also unknown what the effects would be on the precursor 
demonstration, which the commenter claims relies on low estimates of 
NOX in 2023 to conclude that the State need not regulate 
ammonia.
    Finally, the commenter states that the ``EPA's decision to abandon 
its recently adopted standard that inventories should be built using 
the `latest EPA-approved' emission model is arbitrary and capricious,'' 
asserting that the EPA is ``simply resistant to the idea that a current 
inventory must be used'' and has lost litigation over this issue 
(citing Sierra Club v. EPA, 671 F.3d 955 (9th Cir. 2012)), and claiming 
that ``. . .the agency is therefore bending over backwards to adopt 
whatever standard will allow the state to continue to use the outdated 
inventory.''
    Response 2.B: The EPA disagrees with CCEJN's claims that we are 
resistant to require, or have changed our position, that inventories 
must be developed using the latest EPA-approved emissions model 
available at the time the State developed the SIP submission and that 
our proposed action to reaffirm the base year inventory is arbitrary 
and capricious. As discussed in our proposal, the SJV PM2.5 
Plan relies on much of the same technical information and analyses from 
the 2018 PM2.5 Plan, including the emissions 
inventories.\46\ The EPA previously found, for purposes of the 1997 
annual PM2.5 NAAQS as well as other PM2.5 
standards, that these inventories were based on the most current and 
accurate information available to the State and District at the time 
they were developing the 2018 PM2.5 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.\47\ 
Thus, as part of our prior action on the 2018 PM2.5 Plan for 
the 1997 annual PM2.5 NAAQS, we approved the emissions 
inventories as meeting the Serious area and CAA section 189(d) 
requirements for the 1997 annual PM2.5 NAAQS.\48\
---------------------------------------------------------------------------

    \46\ 88 FR 45276, 45279.
    \47\ The EPA previously approved the emissions inventories in 
the 2018 PM2.5 Plan as they pertain to the Serious area 
and 189(d) requirements for the 1997 annual PM2.5 NAAQS 
(86 FR 67329, November 26, 2021), the Serious area and 189(d) 
requirements for the 1997 24-hour PM2.5 NAAQS (87 FR 
4503, January 28, 2022), the Serious area requirements for the 2006 
24-hour PM2.5 NAAQS (85 FR 44192, July 22, 2020), and the 
Moderate area planning requirements for the 2012 annual 
PM2.5 NAAQS (86 FR 67343, November 26, 2021).
    \48\ 86 FR 67329.
---------------------------------------------------------------------------

    In the EPA's final action approving the base year inventories in 
the 2018 PM2.5 Plan for the 1997 annual PM2.5 
NAAQS, the EPA addressed concerns raised by a commenter about the use 
of EMFAC2014.\49\ The EPA discussed the timeline for the State's 
submittal of the emissions inventories in the 2018 PM2.5 
Plan relative to the EPA's approval of EMFAC2014 and EMFAC2017, 
explaining that EMFAC2014 was the most current mobile source model 
available for emissions inventory development purposes at the time the 
State was developing the plan. Nevertheless, at that time, we 
considered comparisons between EMFAC2014 and EMFAC2017 in the 2013 base 
year as provided by CARB in its ``Staff Report, Proposed SIP Revision 
for the 15 [micro]g/m\3\ Annual PM2.5 Standard for the San 
Joaquin Valley'' (``CARB Staff Report'').\50\ Based on our review of 
the State's analysis, we concluded that the 2013 base year emissions 
inventories in the 2018 PM2.5 Plan were comprehensive, 
accurate, and current, consistent with the requirements of CAA section 
172(c)(3) and 40 CFR 51.1008.
---------------------------------------------------------------------------

    \49\ Id. at 67332-67334.
    \50\ CARB, ``Staff Report, Proposed SIP Revision for the 15 
[micro]g/m\3\ Annual PM2.5 Standard for the San Joaquin 
Valley,'' release date August 13, 2021.
---------------------------------------------------------------------------

    Given that the 15 [micro]g/m\3\ SIP Revision was submitted to the 
EPA by the State as an ``administrative revision'' to the 2018 
PM2.5 Plan and relies on much of the same technical 
information that was developed for the 2018 PM2.5 Plan, the 
State continued to rely on the previously approved emissions 
inventories from the 2018 PM2.5 Plan. However, to address 
the most up-to-date information available, in addition to the EMFAC2017 
model results noted earlier in this response, the State provided to the 
EPA comparisons between the estimated annual NOX and 
PM2.5 emissions developed for the 2018 PM2.5 Plan 
using EMFAC2014 with those developed using the most recent EPA-approved 
version of EMFAC, EMFAC2021.\51\ CARB's analysis included comparisons 
between all three EMFAC models for both the 2020 RFP year and the 2023 
attainment year.\52\ As the commenter correctly notes, model results 
from EMFAC2017 indicate higher NOX and PM2.5 
emissions in the 2023 attainment year than those derived for the same 
year using EMFAC2014. However, EMFAC2021, which was the most recent 
EPA-approved model at the time of the EPA's proposal,\53\ indicates 
that NOX and PM2.5 emissions in the 2023 
attainment year are lower than those derived for the same year using 
EMFAC2014.
---------------------------------------------------------------------------

    \51\ 88 FR 45276, 45284-45285.
    \52\ Id.
    \53\ The EPA approved the use of EMFAC2021 for use in SIP 
development on November 15, 2022 (87 FR 68483).
---------------------------------------------------------------------------

    As discussed in the EPA's technical support document (TSD) for our 
proposal,\54\ the differences in emissions estimates for mobile sources 
between the three EMFAC model versions correspond to differences of 
approximately two percent or less of the regional emissions inventories 
for PM2.5 and NOX for the 2023 attainment 
year.\55\ Using the sensitivity of the PM2.5 design value 
per tpd of emissions modeled by the State, the EPA assessed the effects 
of the various EMFAC model version results on the attainment 
demonstration in the Plan.\56\ Based on our technical analysis, we 
determined that although the NOX and PM2.5 
emissions estimates in the 2023 attainment year are higher in EMFAC2017 
than in EMFAC2014, the effect on the PM2.5 concentrations of 
0.07 [micro]g/m\3\ is sufficiently small that the attainment 
demonstration remains valid.\57\ Furthermore, more up-to-date emissions 
data from EMFAC2021 show lower emissions of NOX and 
PM2.5 in the attainment year, indicating that the attainment 
modeling results in the Plan derived using EMFAC2014 are conservative. 
The same is true for the modeling for the precursor demonstration--the 
lower NOX estimates derived using EMFAC2021 would produce 
lower sensitivities of PM2.5 to ammonia, since they would 
increase the abundance of ammonia

[[Page 86589]]

relative to NOX (since particulate ammonium nitrate 
formation would be less limited by, and so less sensitive to, the 
amount of ammonia). Therefore, the State's conclusions based 
on their use of EMFAC2014 are conservative relative to if it had used 
the most up-to-date EPA-approved model, EMFAC2021. Thus, we disagree 
with the assertions that the effects of the various EMFAC versions on 
the attainment demonstration and precursor demonstration are unknown 
and find that reliance on the previously approved emissions inventories 
is acceptable.
---------------------------------------------------------------------------

    \54\ EPA, ``Technical Support Document, San Joaquin Valley 
PM2.5 Plan Revision for the 1997 Annual PM2.5 
NAAQS,'' April 2023.
    \55\ Id. at 53.
    \56\ Spreadsheet ``EMFAC update effect on annual 1997 p.m.2.5 
NAAQS attainment demonstration.xlsx,'' EPA Region IX, May 1, 2023.
    \57\ Id.
---------------------------------------------------------------------------

    Finally, we also disagree with the commenter's assertion (citing 
Sierra Club) \58\ that the EPA has lost litigation over the issue that 
a current inventory must be used. In Sierra Club, the Ninth Circuit 
remanded the EPA's March 2010 approval of an ozone attainment plan for 
the San Joaquin Valley submitted in 2004, holding that the EPA's 
failure to consider new emissions data that the State had submitted in 
2007 as part of a separate ozone plan rendered the EPA's action 
arbitrary and capricious under the Administrative Procedure Act.\59\ 
The decision in that case rested on the unreasonableness of the EPA's 
failure to address the new emissions data. The court found the EPA's 
action arbitrary and capricious because of its ``reliance on old data 
without meaningful comment on the significance of more current compiled 
data'' and concluded that ``it was unreasonable for EPA summarily to 
rely on the point of view taken [in longstanding policy] without 
advancing an explanation for its action based on `the facts found and 
the choice made.' '' \60\
---------------------------------------------------------------------------

    \58\ Sierra Club v. EPA, 671 F.3d 955 (9th Cir. 2012).
    \59\ Id. The court also noted that the EPA's action was 
inconsistent with the court's holding in Ass'n of Irritated 
Residents (AIR) v. EPA, 632 F.3d 584 (9th Cir. 2011) (amended and 
superseded by Ass'n of Irritated Residents v. U.S. EPA, 686 F.3d 
668, 671 (9th Cir. 2012)), which ``supports the proposition that if 
new information indicates to EPA that an existing SIP or SIP 
awaiting approval is inaccurate or not current, then, viewing air 
quality and scope of emissions with public interest in mind, EPA 
should properly evaluate the new information and may not simply 
ignore it without reasoned explanation of its choice.'' Id. at 967.
    \60\ Id. at 968 (citing Burlington Truck Lines v. United States, 
371 U.S. 156, 168 (1962)).
---------------------------------------------------------------------------

    For purposes of this action, the EPA has reviewed the emissions 
data derived using more recent versions of the EMFAC model provided by 
CARB, consistent with the holding in Sierra Club. Based on our 
technical analysis of the latest information available described 
earlier in this response, we determined that the precursor and 
attainment demonstrations are valid. Thus, we continue to find that the 
2013 base year inventories in the SJV PM2.5 Plan for the 
1997 annual PM2.5 NAAQS satisfy the requirements of CAA 
section 172(c)(3) and 40 CFR 51.1008 for purposes of both the Serious 
area and the CAA section 189(d) attainment plan requirements, and to 
find that the forecasted inventories provide an adequate basis for the 
BACM, RFP, and the modeled attainment demonstration analyses in the 
Plan.
3. Ammonia Precursor Demonstration
    Comment 3: CCEJN states that the EPA must disapprove the ammonia 
precursor demonstration based on considerations outlined in several 
specific comments (summarized in Comments 3.A through 3.D that follow), 
but also in several introductory remarks. In the introductory remarks, 
the commenter appears to refer to the precursor demonstration's modeled 
PM2.5 responses to ammonia reductions for the 2020 analysis 
year, some of which are above the 0.2 [micro]g/m\3\ EPA-recommended 
contribution threshold for the 2012 annual PM2.5 NAAQS in 
the EPA's ``PM2.5 Precursor Demonstration Guidance'' 
(``PM2.5 Precursor Demonstration Guidance'').\61\ Based on 
these model results, the commenter asserts that the State tacitly 
acknowledges that ammonia assessments in previous PM2.5 
plans, finding that ammonia does not contribute significantly to 
PM2.5 levels that exceed the 1997 annual PM2.5 
NAAQS, were incorrect. The commenter concludes that these results 
indicate that the State should have been regulating ammonia in the 
recent past, and also that the State should err on the side of caution 
and regulate ammonia now. Finally, CCEJN contends that not regulating 
ammonia has led to greater ammonium nitrate PM2.5, thereby 
implicating disparate treatment and disparate impacts, and that the 
State has failed to provide necessary assurances that the policy 
decision not to regulate ammonia complies with Title VI.
---------------------------------------------------------------------------

    \61\ ``PM2.5 Precursor Demonstration Guidance,'' EPA-
454/R-19-004, May 2019, including memorandum dated May 30, 2019, 
from Scott Mathias, Acting Director, Air Quality Policy Division and 
Richard Wayland, Director, Air Quality Assessment Division, Office 
of Air Quality Planning and Standards (OAQPS), EPA, to Regional Air 
Division Directors, Regions 1-10, EPA.
---------------------------------------------------------------------------

    Response 3: The EPA disagrees with the commenter's premise that the 
modeled PM2.5 responses for the 2020 analysis year indicate 
that ammonia contributed significantly to PM2.5 levels in 
the past. Under the EPA's PM2.5 Precursor Demonstration 
Guidance, a response above the recommended contribution threshold 
indicates a ``contribution,'' but additional information can be 
considered in determining whether that response ``contributes 
significantly.'' \62\ Such information may include, but is not limited 
to, the amount by which the threshold is exceeded, studies to evaluate 
specific atmospheric chemistry in the area, trends in ambient 
speciation data and precursor emissions,\63\ and the general facts and 
circumstances of the nonattainment area.\64\ In concluding that ammonia 
does not contribute significantly, the State considered model responses 
for the 2024 analysis year in addition to 2020, as well as other 
additional information, as summarized in the EPA's February 2020 
Precursor Technical Support Document.\65\ We do not believe that 
viewing modeled responses to ammonia for specific years in isolation or 
out of context is an adequate method for determining whether a 
precursor contributes significantly to PM2.5 levels.
---------------------------------------------------------------------------

    \62\ PM2.5 Precursor Demonstration Guidance, pp. 17-
19.
    \63\ Id.
    \64\ Id. at 14; 40 CFR 51.1006(a)(1)(ii).
    \65\ ``Technical Support Document, EPA Evaluation of 
PM2.5 Precursor Demonstration, San Joaquin Valley 
PM2.5 Plan for the 2006 PM2.5 NAAQS,'' 
February 2020.
---------------------------------------------------------------------------

    Additionally, the EPA does not agree that prior precursor 
assessments should be considered erroneous based on the analysis in a 
newer plan, particularly when the more recent plan uses different 
criteria for assessing precursor significance. Previous plans for the 
1997 annual PM2.5 NAAQS in the San Joaquin Valley, like the 
ones mentioned by the commenter, predated the 2016 ``Fine Particulate 
Matter National Ambient Air Quality Standards: State Implementation 
Plan Requirements'' (``PM2.5 SIP Requirements Rule'') \66\ 
and the 2019 PM2.5 Precursor Demonstration Guidance; 
therefore, they did not assess a modeled ammonia response relative to a 
contribution threshold but rather relied on the conclusions from 
modeling performed at the time and from past studies indicating that 
ammonium nitrate PM2.5 is far more responsive to 
NOX reductions than to ammonia reductions. Following 
promulgation of the PM2.5 SIP Requirements Rule, the EPA now 
requires that each precursor be evaluated individually by comparing 
modeled responses to the contribution threshold and considering 
additional information.\67\ The State conducted its precursor analysis 
for the SJV PM2.5

[[Page 86590]]

Plan in accordance with these requirements.
---------------------------------------------------------------------------

    \66\ 81 FR 58010 (August 24, 2016).
    \67\ 40 CFR 51.1006; EPA's PM2.5 Precursor 
Demonstration Guidance.
---------------------------------------------------------------------------

    Regarding CCEJN's Title VI-related concerns, we address the 
comments regarding Title VI in Responses 1.A, 1.B, 5, and 7, which rely 
on supporting information discussed in Responses 3.A, 3.B.1 through 
3.B.4, 3.C, and 3.D.
    Comment 3.A: CCEJN's first specific stated concern with the 
precursor demonstration is that the State's conclusion that the San 
Joaquin Valley is NOX-limited relies on low NOX 
estimates based on soil NOX emissions that are biased low. 
The commenter asserts that ``. . .the state's estimates of soil 
NOX emissions are on the extreme low-end of those reported 
in the academic literature, and the state has acknowledged that it is 
unsure how much NOX is actually emitted from soil in the 
Valley.'' The commenter asserts that the State's only rationale for 
maintaining the current estimate is that it will take time to develop a 
new estimate, even though including anthropogenic soil NOX 
emissions has been a longstanding request by Valley advocates.
    Additionally, CCEJN asserts that ``[t]he state's reliance on very 
low estimates of soil NOX emissions is contrary to the 
presumption that precursors should be regulated and to the overall 
`preventative' and `precautionary' tenor of the Act.'' The commenter 
asserts that even if there was not sufficient time to fully evaluate 
the scientific literature, a key question is what assumptions the State 
should rely on in the interim. The commenter proposes that the State 
should base its decision of whether to regulate ammonia on a median 
reasonable estimate of soil NOX emissions, if not the high-
end estimate.
    Response 3.A: We do not agree that the information provided by the 
commenter on soil NOX emissions undermines the State's 
conclusion that PM2.5 formation in the San Joaquin Valley is 
NOX-limited (i.e., much more sensitive to NOX 
emissions reductions than to ammonia emissions reductions). Three lines 
of evidence support the EPA's agreement with the State's conclusion. 
First, at this time, it is not clear that soil NOX emissions 
estimates are largely underestimated as the commenter suggests. Second, 
ammonia emissions are likely underestimated and so the response to an 
ammonia reduction is likely overestimated in the modeling. Third, 
ambient measurements strongly suggest that PM2.5 
concentrations would respond relatively little to ammonia emissions 
reductions. We discuss each of these lines of evidence in the 
paragraphs that follow.
    We do not dispute that increasing NOX emissions in the 
model would be expected to decrease the modeled amount of ammonia 
relative to NOX and increase the modeled sensitivity of 
PM2.5 concentrations to ammonia reductions. However, as 
discussed in detail in Response 2.A, further investigation is needed 
and merited regarding whether soil NOX emissions are 
underestimated or the magnitude of such underestimation. The magnitude 
of the difference, if any, could have an important effect on whether 
the model responses to ammonia reductions would be above the 
contribution threshold. Additionally, even if it is determined that 
soil NOX emissions are underestimated, proper updating of 
the model emissions inventory to address the relative abundance of 
ammonia and NOX could require updates to both the 
NOX and ammonia emissions inventories, and there is ample 
evidence that ammonia emissions are underestimated. Furthermore, 
independent of any emissions estimates or modeling, evidence from 
ambient measurements imply that PM2.5 concentrations would 
respond very little to ammonia reductions, and that the model responses 
in the precursor demonstration may be overestimated, as discussed 
further in the remainder of this response. Thus, the EPA disagrees with 
the commenter's assertions that the State's conclusion that the San 
Joaquin Valley is NOX-limited (in the sense that it is much 
more sensitive to NOX reductions than to ammonia reductions) 
is based on biased soil NOX emissions estimates that compel 
the EPA to disapprove the ammonia precursor demonstration.
    A second line of evidence is that multiple studies have suggested 
that ammonia emissions are underestimated in the San Joaquin Valley. 
These studies reached this conclusion by comparing ambient measurements 
and satellite retrievals to model results that incorporate estimates of 
ammonia emissions, and by comparing monitoring or modeling results to 
what would be expected based on the size(s) of the ammonia and 
NOX emissions inventories. For example, in a summary report 
for the CalNex air quality study, the authors concluded based on direct 
measurements of ammonia emissions flux that ``[p]reliminary results 
indicate that within the San Joaquin Valley, [ammonia] emissions could 
be underestimated in inventories by about a factor of three.'' \68\ 
This finding was confirmed in later modeling using monitored data from 
the DISCOVER-AQ field study.\69\ Other studies identified in a 
literature search also suggest that ammonia emissions are 
underestimated, as discussed in the remainder of this response. If 
higher ammonia emissions were used in the modeling to correct the 
underestimation, then modeled ammonia would be more abundant relative 
to nitrate, and particulate nitrate formation would be more 
NOX-limited. Thus, the modeled response to ammonia 
reductions would be lower than reported in the precursor demonstration 
in the SJV PM2.5 Plan, and below the contribution threshold.
---------------------------------------------------------------------------

    \68\ Parrish, D. (2014), Synthesis of Policy Relevant Findings 
from the CalNex 2010 Field Study, Final Report to the Research 
Division of the California Air Resources Board, 2014, p. 63; 
available at https://csl.noaa.gov/projects/calnex/synthesisreport.pdf.
    \69\ Kelly, J.T. et al. (2018), Modeling 
NH4NO3 over the San Joaquin Valley during the 
2013 DISCOVER-AQ campaign, Journal of Geophysical Research: 
Atmospheres, 123, 4727-4745, doi:10.1029/2018JD028290.
---------------------------------------------------------------------------

    A literature search conducted by the EPA found ample evidence that 
ammonia emissions may be underestimated in the San Joaquin Valley.\70\ 
Most studies compared air quality model results with satellite 
retrievals; a few compared model results to measurements from aircraft. 
All of the studies reviewed concluded that ammonia emissions are 
underestimated by a factor of two to five. A factor of two is greater 
than the 20-51 percent increase in total NOX emissions 
estimated by Almaraz et al. (2018) and would more than offset the 
effect of an increase in soil NOX on the sensitivity of 
PM2.5 concentrations to ammonia reductions. These studies 
collectively suggest that ammonia emissions are underestimated in the 
San Joaquin Valley. In turn, that implies that model estimates of the 
sensitivity in the precursor demonstration may be overestimated.
---------------------------------------------------------------------------

    \70\ Memorandum dated October 12, 2023, from Scott Bohning, EPA 
Region IX, to Docket EPA-R09-OAR-2023-0263, Subject: ``Literature 
search finds evidence that ammonia emissions are underestimated.''
---------------------------------------------------------------------------

    Note that such an underestimate does not imply that the emissions 
inventories in the SJV PM2.5 Plan do not meet the 
requirements of CAA section 172(c)(3); rather it reflects that more 
work is needed to continue to improve ammonia emissions estimates. 
Studies may deduce that there is underestimation using a ``top down'' 
approach relying on ambient measurements or satellite observations; the 
measurements reflect the atmospheric sum of the contribution of many 
sources, possibly over an extended area. On the other hand, an 
emissions inventory developed for regulatory purposes is typically a 
``bottom-up'' estimate, derived from

[[Page 86591]]

compiling an inventory of stationary, area, mobile, and biogenic 
sources, with their associated emissions factors and activity rates. 
The emissions inventory is based on detailed knowledge and measurements 
of specific source types under particular conditions. It is impractical 
to measure every source under all environmental conditions or under all 
possible variations, and to know the exact mix of source types and of 
management practices in place. Thus, the emissions inventory depends on 
the basic assumption that information compiled for the subset of 
sources that it is practical to measure can be generalized to the full 
population of sources in an area. Characterizing ammonia emissions from 
the bottom up requires spatially and temporally resolved data, such as 
detailed farming practices including irrigation and fertilizer 
application, and how they affect emissions, which may vary depending on 
multiple factors. Such detailed data may not be available except at an 
enormous, impractical cost. A bottom-up emissions inventory may use the 
best available data and techniques, yet not match estimates made via 
top-down approaches. The discrepancy between the estimates from top-
down and bottom-up approaches indicates the need for further research 
to better characterize the specific source types that contribute to the 
total.
    In 2021, CARB reported comparisons between its own model 
predictions of ammonia to ambient data.\71\ The SJV PM2.5 
Plan did not include an evaluation of model performance for ammonia per 
se (just for particulate ammonium), but in a supplemental transmittal, 
CARB described the results of two analyses confirming the likely 
underestimation of ammonia. CARB compared CMAQ model predictions of 
ammonia with the 2013 DISCOVER-AQ \72\ aircraft measurements and found 
that near-ground ammonia was underpredicted by 50 percent at Fresno and 
200 percent at Porterville. CARB also compared 2017 satellite 
observations of ammonia from the Infrared Atmospheric Sounding 
Interferometer to CMAQ model predictions and found that modeled ammonia 
concentrations were half of the magnitude of the satellite retrievals 
at some locations, and that the modeled average in the San Joaquin 
Valley was about 25 percent less than observed. CARB also noted that 
underprediction of ammonia would result in the modeled PM2.5 
response to ammonia reductions being overpredicted.
---------------------------------------------------------------------------

    \71\ Email dated April 26, 2021, from Laura Carr, CARB, to Scott 
Bohning, EPA Region IX, Subject: ``RE: Ammonia update,'' with 
attachment ``Ammonia in San Joaquin Valley''.
    \72\ DISCOVER-AQ: ``Deriving Information on Surface conditions 
from COlumn and VERtically Resolved Observations Relevant to Air 
Quality,'' https://science.nasa.gov/mission/discover-aq.
---------------------------------------------------------------------------

    Finally, a third line of evidence supports the conclusion that 
PM2.5 in the San Joaquin Valley is relatively insensitive to 
ammonia reductions. Evidence from ambient data is especially strong 
since it is independent of uncertainties in the emissions estimates and 
the modeling exercises. Appendix G (``Precursor Demonstration'') of the 
2018 PM2.5 Plan and Appendix C (``Weight of Evidence 
Analysis'') of the CARB Staff Report on the 2018 PM2.5 Plan 
\73\ describe previous research in support of the claim that ammonium 
nitrate PM2.5 formation is NOX-limited rather 
than ammonia-limited. That is, PM2.5 concentrations in the 
San Joaquin Valley are expected to be sensitive to reductions in 
NOX emissions but much less sensitive to reductions in 
ammonia. Essentially, due to the abundance of ammonia, even with 
ammonia emissions reductions there would still be enough available 
ammonia to combine with NOX (in the form of nitric acid) to 
form about the same amount of particulate ammonium nitrate. This was 
the conclusion of Lurmann et al. (2006) \74\ based on ambient 
measurements during the California Regional Particulate Air Quality 
Study (CRPAQS), an intensive field study during winter 2000-2001. 
Ammonia was almost always abundant relative to the amount of nitric 
acid \75\ (derived from NOX and the immediate precursor to 
particulate nitrate), so the authors concluded that ammonium nitrate 
formation in the San Joaquin Valley was NOX-limited. This 
conclusion was based on ambient data collected before the additional 60 
percent reduction in NOX emissions that has occurred in the 
interim, which would be expected to have increased the degree of 
NOX-limitation (i.e., particulate ammonium nitrate formation 
would be more limited by, and so more sensitive to, the amount of 
NOX).
---------------------------------------------------------------------------

    \73\ 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.
    \74\ Lurmann et al. (2006) Processes Influencing Secondary 
Aerosol Formation in the San Joaquin Valley during Winter, Journal 
of the Air & Waste Management Association, 56(12):1679-1693, doi: 
10.1080/10473289.2006.10464573.
    \75\ Nitric acid (HNO3) is formed from NOX 
emissions; it combines with ammonium to form particulate ammonium 
nitrate. The relative amounts of nitric acid and ammonium indicate 
which is the limiting factor in ammonium nitrate formation.
---------------------------------------------------------------------------

    Consistent with CRPAQS, aircraft-borne measurements during the more 
recent 2013 DISCOVER-AQ \76\ study led CARB to a similar conclusion, 
based on the large amount of ``excess ammonia''. This is defined as the 
amount of measured ammonia left over if all the nitrate and sulfate 
present combined with available ammonia to form particulate. The CARB 
December 2018 Staff Report describes this in more detail,\77\ and also 
lists results from multiple other recent studies with similar 
conclusions. Two studies with chemical modeling,78 79 at 
temperature and humidity levels typical for the San Joaquin Valley and 
with ammonia and nitrate concentrations observed during DISCOVER-AQ, 
showed that over 90 percent of the nitrate is present as particulate 
rather than gas, consistent with abundance of ammonia and with low 
sensitivity to ammonia changes. Two other studies, one using data from 
DISCOVER-AQ \80\ and one using data from the 2010 CalNex field 
campaign, \81\ found measured ammonia to be 50-100 times as abundant as 
nitric acid, implying low sensitivity to ammonia emissions changes.\82\ 
In summary, the

[[Page 86592]]

ambient field study data that the EPA is aware of is consistent with a 
conclusion that PM2.5 concentrations in the Valley are much 
more sensitive to NOX emissions reductions than to ammonia 
emissions reductions. This evidence is independent of the State's soil 
NOX emissions estimate and is an important basis for the 
EPA's determination that the responses to ammonia reductions for the 
1997 annual PM2.5 NAAQS that are slightly above the 
recommended contribution threshold are likely overestimated. Thus, the 
ambient evidence supports the EPA's determination that ammonia does not 
contribute significantly to PM2.5 levels above the 1997 
annual PM2.5 NAAQS.
---------------------------------------------------------------------------

    \76\ DISCOVER-AQ: ``Deriving Information on Surface conditions 
from COlumn and VERtically Resolved Observations Relevant to Air 
Quality,'' https://science.nasa.gov/mission/discover-aq.
    \77\ CARB, ``Staff Report: Review of the San Joaquin Valley 2018 
Plan for the 1997, 2006, and 2012 PM2.5 Standards,'' 
December 21, 2018, Appendix C, 12ff.; available at https://ww2.arb.ca.gov/resources/documents/2018-san-joaquin-valley-pm25-plan.
    \78\ Id. at 12 (presenting CARB analysis of ammonia impacts in 
the San Joaquin Valley).
    \79\ Prabhakar et al. (2017) Observational assessment of the 
role of nocturnal residual-layer chemistry in determining daytime 
surface particulate nitrate concentrations, Atmospheric Chemistry 
Physics, 17, 14747-14770. doi:10.5194/acp-17-14747-2017.
    \80\ Parworth et al. (2017) Wintertime water-soluble aerosol 
composition and particle water content in Fresno, California, 
Journal of Geophysical Research, Atmosphere., 122, 3155-3170. doi: 
10.1002/2016JD026173, p. 3165. (noting that ``The average mixing 
ratio of NH3 was 49 times greater than HNO3 . 
. . . These results highlight that NH3 was in excess, and 
NH4NO3 [ammonium nitrate] formation is likely 
limited by HNO3 availability in Fresno,'' i.e., about a 
factor of 50).
    \81\ CalNex, or California Research at the Nexus of Air Quality 
and Climate Change, was a NOAA-sponsored field study during summer 
2010; https://www.esrl.noaa.gov/csd/projects/calnex/. Markovic et 
al., (2014), Measurements and modeling of the inorganic chemical 
composition of fine particulate matter and associated precursor 
gases in California's San Joaquin Valley during CalNex 2010, Journal 
of Geophysical Research--Atmospheres, 119, 6853-6866, doi:10.1002/
2013JD021408, p. 6863 (noting that `` . . . the observed 
NH3 (g) mixing ratios were elevated . . . the observed 
HNO3 (g) mixing ratios were 2 orders of magnitude 
lower,'' i.e., about a factor of 100).
    \82\ The CARB December 2018 Staff Report explains (in Appendix 
C, p. 14) that NOX is the limiting pollutant as shown by 
this relative abundance of ammonia, but that the expected low 
sensitivity to ammonia reductions does not mean zero response; the 
reduction necessarily shifts nitrate from particulate to gas to 
maintain chemical equilibrium. Thus, NOX being the 
limited pollutant does not contradict the modeled responses to 30-70 
percent reductions.
---------------------------------------------------------------------------

    Comment 3.B.1: CCEJN's second concern with the precursor 
demonstration relates to the State's conclusions regarding the level of 
ammonia reductions that could be achieved through potential control 
measures. The commenter asserts that ``. . . the state repeatedly uses 
a lack of certainty about emission reduction potential to justify no 
regulation at all.'' As an example, they argue that the State 
acknowledges that research shows that ammonia emissions from manure-
based fertilizer can be reduced by 50-90 percent through quick mixing 
or injection but that it declines to consider the measure feasible for 
synthetic fertilizers merely because the State does not know how 
effective it will be.
    Response 3.B.1: We disagree with CCEJN's claim that the State 
relies primarily on a lack of certainty about potential emissions 
reductions to justify not regulating ammonia in the San Joaquin Valley. 
Rather, the State based its decision not to regulate ammonia for 
purposes of meeting the 1997 annual PM2.5 NAAQS on the 
technical analyses it performed indicating that ammonia does not 
contribute significantly to PM2.5 concentrations that exceed 
the 1997 annual PM2.5 NAAQS.
    Where the State identifies uncertainties about potential ammonia 
emissions reductions, it does so in the context of its controls 
analysis to support the ammonia precursor demonstration, which it 
conducted at the request of the EPA and in accordance with EPA 
guidance. As acknowledged by the commenter, under the PM2.5 
SIP Requirements Rule, a state may submit an optional precursor 
demonstration showing that a particular PM2.5 precursor 
chemical species does not contribute significantly to PM2.5 
levels above the standard in the area.\83\ If the EPA approves a 
precursor demonstration for a particular chemical species, the state is 
not required to control emissions of that precursor from existing 
sources in the relevant attainment plan.\84\
---------------------------------------------------------------------------

    \83\ 81 FR 58010, 58021 (August 24, 2016); 40 CFR 51.1006 
(``Optional PM2.5 precursor demonstrations'').
    \84\ 40 CFR 51.1006(a)(1)(iii) and 51.1010(a)(2)(ii).
---------------------------------------------------------------------------

    The EPA's July 2023 proposal includes a detailed summary of the 
precursor demonstration in the SJV PM2.5 Plan and supporting 
March 2023 Ammonia Supplement, and of the EPA's evaluation. We will not 
reiterate all of the State's conclusions herein except to highlight the 
key finding that modeled sensitivities for the 1997 annual 
PM2.5 NAAQS of PM2.5 concentrations to a 30 
percent ammonia reduction are approximately at or below the 
contribution threshold used to determine significance. The 
PM2.5 Precursor Guidance explains that in cases where the 
PM2.5 response to a 30 percent reduction in precursor 
emissions is close to the contribution threshold, the EPA may require 
air agencies to identify and evaluate potential emissions controls in 
support of a precursor demonstration that relies on a sensitivity 
analysis. The response of ambient PM2.5 to an actual 
assessment of the benefit from potential controls can be used to 
determine whether controlling ammonia would significantly affect 
PM2.5 levels. In accordance with 40 CFR 51.1010(a)(2)(ii), 
the EPA required the State to provide an analysis of potential controls 
to aid the EPA in its evaluation of the precursor demonstration. The 
State provided such controls analysis in the March 2023 Ammonia 
Supplement, which built upon information previously provided in the 
2018 PM2.5 Plan.
    As discussed in our proposal, the State's controls analysis 
included a review of ammonia emissions reductions achieved nationwide 
from 2011 to 2017, an evaluation of the main ammonia source categories 
in the San Joaquin Valley, a summary of existing control measures in 
the San Joaquin Valley that affect ammonia from these sources, a review 
of existing control measures implemented by other air districts, and an 
evaluation of additional mitigation options for ammonia sources in the 
Valley.\85\ Based on the State's and District's analyses, they 
determined that significant ammonia emissions reductions are already 
being achieved by measures targeting VOC emissions and that the ammonia 
reductions achievable from additional controls are well below 30 
percent.
---------------------------------------------------------------------------

    \85\ 88 FR 45276, 45288-45290.
---------------------------------------------------------------------------

    In this action, we are finalizing our determination that the State 
has provided adequate support for its conclusion that available 
additional ammonia controls would yield less than a 30 percent 
reduction in ammonia emissions. We are finding that the District made a 
convincing case that significant ammonia reductions have already been 
achieved through District Rule 4570 and that few additional mitigation 
measures could provide only modest further reductions from confined 
animal facilities (CAFs), which account for 58 percent of the total 
ammonia inventory. Similarly, the State has provided support for its 
assertion that additional reductions are not feasible from the 
fertilizer, composting, and other smaller source categories through its 
analysis of potential fertilizer controls and information regarding 
controls that are already in place for these source categories. As 
discussed in our proposal, we acknowledge the uncertainty in the 
reductions that are currently being achieved from the fertilizer source 
category but are finalizing our determination that even if ammonia 
reductions could be reduced by a very high percentage, such reductions 
added to the potential reductions from CAFs would amount to less than a 
30 percent reduction in total ammonia emissions.
    Given that the State's modeled sensitivities of PM2.5 
concentrations to a 30 percent ammonia reduction are approximately at 
or below the threshold used for identifying an impact that is 
significant for the 1997 annual PM2.5 NAAQS, and that the 
potential additional reductions would be well below 30 percent, the 
response of PM2.5 to an ammonia reduction of a percentage 
smaller than 30 percent would be below the contribution threshold, 
indicating that ammonia does not contribute significantly to ambient 
PM2.5 concentrations for purposes of the SJV 
PM2.5 Plan for the 1997 annual PM2.5 NAAQS. Based 
on these results, the State excluded ammonia controls from the SIP 
submission. Because the EPA is finalizing approval of the State's 
precursor demonstration as proposed, the State is not required to 
regulate ammonia for purposes of meeting the CAA requirements for the 
1997 annual PM2.5 NAAQS.
    Regarding the example cited by the commenter of quickly mixing or 
injecting fertilizer into the soil, we do not disagree that research 
literature indicates that quick mixing or injection

[[Page 86593]]

can reduce ammonia emissions from manure-based fertilizer. The State 
acknowledges in the March 2023 Technical Supplement that applying 
manure to the soil surface without incorporation can lead to 
significant ammonia emissions and includes an extensive discussion of 
the various methods of incorporation as well as the related 
requirements for injection and incorporation of manure-based fertilizer 
in District Rule 4570. We disagree, however, with the commenter's 
assertions that because the measure is effective at reducing ammonia 
from manure-based fertilizers, the State should infer a similar 
magnitude of effectiveness for synthetic fertilizers. The studies cited 
by the commenter acknowledge uncertainties and highlight the importance 
of additional research to adapt a potential measure to local 
conditions.\86\ For example, Ti et al. (2019), in a global meta-
analysis of measures to reduce ammonia emissions from livestock and 
cropping systems, found that the effects of fertilizer application 
processes are highly dependent on crop type.\87\ The paper further 
concludes that mitigation needs to be carefully planned and adapted to 
local conditions because ammonia emissions are dependent on 
environmental factors such as weather and soil conditions, that the 
applicability of measures depends strongly on farm structures, and that 
studies examining economic feasibility and the effects of combinations 
of measures are needed.\88\ The State's March 2023 Ammonia Supplement 
draws similar conclusions about the need for additional research to 
assess the potential for ammonia emissions reductions, specifically as 
they relate to quick mixing and injection, under conditions 
representative of those in the San Joaquin Valley.\89\ Given these 
uncertainties, we agree with the State's conclusion that additional 
research is needed and find that the State's decision not to assign 
ammonia reductions to such measure at this time to be reasonable.
---------------------------------------------------------------------------

    \86\ Pan, B. et al. (2016). Ammonia volatilization from 
synthetic fertilizers and its mitigation strategies: A global 
synthesis. Agriculture, Ecosystems & Environment, Vol. 232, 283-289, 
doi:10.1016/j.agee.2016.08.019; Ti, C. et al. (2019). Potential for 
mitigating global agricultural ammonia emission: A meta-analysis. 
Environmental Pollution, Vol. 245, 141-148, doi:10.1016/
j.envpol.2018.10.124.
    \87\ Ti et al. (2019) op cit., p. 146. For example, the paper 
notes that the effects of fertilizer application practices on 
reducing ammonia emissions from vegetable production are lower than 
in wheat and fruit production due in part to the smaller reduction 
in ammonia emissions from vegetable fields associated with more 
intensive irrigation.
    \88\ Id. at 147.
    \89\ March 2023 Ammonia Supplement, p. 94.
---------------------------------------------------------------------------

    In addition to helping to resolve the uncertainties related to the 
effectiveness of mitigation measures, additional research would also be 
beneficial for improving understanding of any potential disbenefits 
that may be specific to the area. The commenter appears to acknowledge 
the potential for disbenefits in a footnote to their comment, which 
notes that CCEJN does not endorse any specific approach for reducing 
ammonia emissions, including quick mixing or injection, and that 
``regulation of ammonia emissions cannot be permitted to exacerbate 
degradation of groundwater quality.'' These expressed concerns about 
the potential for adverse effects on water quality seem to align with 
the State's position that more research is needed. Such research may 
also inform other important considerations, such as the effects on 
greenhouse gas emissions.
    Comment 3.B.2: CCEJN asserts that the State's evaluation of 
emissions from fertilizers is limited in that it is seemingly based on 
just two studies, and does not consider additional mitigation options 
identified in the literature such as using non-urea based fertilizers; 
using controlled release fertilizers; using fertilizers with 
nitrification inhibitors; irrigating immediately after fertilizer 
placement; or adding amendments to fertilizers, such as zeolite, 
pyrite, or organic acids. The commenter also points to a study on the 
field of precision agriculture as a resource on mechanisms to minimize 
fertilizer use,\90\ as well as two studies examining how modeling can 
be used to predict ammonia volatilization, claiming that such studies 
undermine the State's position that emissions reductions cannot be 
calculated.\91\
---------------------------------------------------------------------------

    \90\ Association of Equipment Manufacturers, The Environmental 
Benefits of Precision Agriculture in the United States, https://newsroom.aem.org/download/977839/environmentalbenefitsofprecisionagriculture-2.pdf.
    \91\ Gurung, R.B. et al. (2021) Modeling ammonia volatilization 
from urea application to agricultural soils in the DayCent model. 
Nutr Cycl Agroecosyst, 119, 259-273. doi:10.1007/s10705-021-10122-z; 
Yang, Y. et al. (2022) Comprehensive quantification of global 
cropland ammonia emissions and potential abatement. Science of The 
Total Environment, 812, 151450, doi:10.1016/j.scitotenv.2021.151450.
---------------------------------------------------------------------------

    Response 3.B.2: We disagree with CCEJN's characterization of the 
State's analysis of emissions from fertilizer as ``extremely narrow.'' 
We infer that the commenter is referring to the State's analyses for 
synthetic fertilizer specifically, based on the numerous studies cited 
in the State's discussion of manure application-related measures,\92\ 
and the commenter's assertion that the State's evaluation of 
fertilizers is seemingly based on the findings from just two studies 
and that Table 13 of the March 2023 Ammonia Supplement lists references 
for Guthrie et al. (2018) \93\ and Eory et al. (2016) only.\94\ 
However, we note that both Guthrie et al. (2018) and Eory et al. (2016) 
are compilation studies covering a range of mitigation options for 
organic and synthetic fertilizer application and that the State's March 
2023 Ammonia Supplement cites numerous studies in addition to these two 
compilation studies. Furthermore, the State turned to the research 
literature only after reviewing how other California State agencies are 
engaged in fertilizer use and attempting to identify any existing rules 
or regulations in the nation controlling ammonia emissions from this 
source category.
---------------------------------------------------------------------------

    \92\ E.g., see March 2023 Ammonia Supplement pp. 74-75.
    \93\ Guthrie, S. et al. (2018). Impact of ammonia emissions from 
agriculture on biodiversity: An evidence synthesis. Rand Europe, The 
Royal Society. https://www.rand.org/pubs/research_reports/RR2695.html.
    \94\ Eory, V. et al. (2016) ClimateXChange, On-farm technologies 
for the reduction of greenhouse gas emissions in Scotland. https://www.climatexchange.org.uk/media/1927/on-farm_technology_report.pdf.
---------------------------------------------------------------------------

    Regarding the additional mitigation options identified by CCEJN, we 
appreciate that the commenter raises these potential strategies. We 
acknowledge the studies cited by the commenter finding that 
implementation of some of these strategies may help minimize ammonia 
emissions from agricultural systems around the globe. We encourage CARB 
and the District to keep abreast of research examining mitigation 
options for minimizing ammonia emissions from fertilizer application in 
support of future policy and management decisions, particularly as they 
may relate to reducing PM2.5 exposure in the San Joaquin 
Valley. However, as discussed in the following paragraphs, in light of 
the absence of any SIP-approved requirements elsewhere in the nation, 
the regulations adopted by other California State agencies to control 
fertilizer application, and the uncertainties discussed in the studies 
cited by CARB and the commenters, the EPA continues to agree with the 
State's overall conclusions that more research is needed on potential 
mitigation measures to reduce ammonia emissions from fertilizer 
application in the San Joaquin Valley. We also agree that based on the 
information currently available, the additional reductions achievable 
are sufficiently low that the PM2.5 response to such 
reduction would

[[Page 86594]]

be below the contribution threshold, indicating that ammonia does not 
contribute significantly to ambient PM2.5 concentrations for 
purposes of the SJV PM2.5 Plan for the 1997 annual 
PM2.5 NAAQS. As we emphasized in our proposal, this finding 
is specific to the facts and circumstances of this particular plan and 
does not pre-determine the outcome of significance determinations of 
precursors in the future.
    In the March 2023 Ammonia Supplement, the State describes its 
efforts to identify any SIP-approved requirements limiting ammonia 
emissions from fertilizers that are being implemented in any other 
areas of the United States and explains that it has not identified any 
rules or regulations being implemented elsewhere. Thus, it describes 
regulations in place adopted by other California State agencies to 
control fertilizer application and its review of research studies 
examining techniques for reducing ammonia emissions from synthetic 
fertilizer application.
    The State describes in Appendix C (``Stationary Source Control 
Measure Analyses'') of the 2018 PM2.5 Plan and in the March 
2023 Ammonia Supplement the various State agencies responsible for 
ensuring environmentally safe use of fertilizer material. It describes 
requirements for commercial irrigated lands in the San Joaquin Valley 
to prepare a farm management plan (including an irrigation nitrogen 
management plan) that complies with waste discharge requirements in 
accordance with the Central Valley Irrigated Lands Regulatory Program 
established by the California State Water Resources Control Board. The 
nitrogen management plan is designed to ensure that the amount of 
nitrogen applied to agricultural lands is in reasonable balance with 
the needs of crops that are being grown. The State explains that the 
``4 R's'' of nitrogen management (``Right source'' of nitrogen at the 
``right rate,'' ``right time,'' and ``right place'') \95\ serve as 
guiding nitrogen efficiencies principles that growers are recommended 
to follow when developing their management plans, and that growers are 
required to employ enhanced strategies if it is determined that they 
are not optimizing fertilizer use, as determined by the fraction of 
nitrogen applied to nitrogen used.
---------------------------------------------------------------------------

    \95\ March 2023 Ammonia Supplement, p. 92.
---------------------------------------------------------------------------

    Next, CARB discusses measures identified in the literature for 
reducing ammonia emissions from fertilizer application, which include 
optimizing fertilizer use, adding a urease inhibitor, mixing and 
injecting fertilizer into the soil quickly, and applying fertilizer 
during optimal weather conditions. Based on its review, the State finds 
that several of the strategies align with the 4 R's of nitrogen 
management but that more research is needed to determine the 
feasibility and effectiveness of such strategies in California due to 
the unique climate conditions and farming practices in the San Joaquin 
Valley, and to explore any potential adverse consequences. CARB cites 
studies linking weather conditions with ammonia emissions,\96\ and 
states that it is unclear which environmental factors are the most 
important for different fertilizer types.
---------------------------------------------------------------------------

    \96\ Venterea, R.T. et al. (2012) Challenges and opportunities 
for mitigating nitrous oxide emissions from fertilized cropping 
systems. Frontiers in Ecology and the Environment, 10:10, 562-570. 
doi:10.1890/120062; Grahmann, K., et al. (2013) Nitrogen use 
efficiency and optimization of nitrogen fertilization in 
conservation agriculture. Cabi Reviews, 8:053. doi:10.1079/
PAVSNNR20138053.
---------------------------------------------------------------------------

    As discussed in Response 3.B.1, the studies cited by CCEJN 
similarly highlight the need for additional research to examine how the 
potential for ammonia emissions reductions varies with local 
conditions. These studies largely focused on the United Kingdom or were 
global in scale and none of them appear to address mitigation 
potentials in the western United States or San Joaquin Valley 
specifically. Thus, none of the studies reflect climate conditions or 
farming practices in the San Joaquin Valley, and likely also do not 
reflect efficiencies already achieved through local regulations in the 
Valley. Furthermore, several of the studies suggest that some of the 
measures have already been adopted in many areas, adding to the 
uncertainty about whether and where there are opportunities for 
significant reductions in ammonia. For example, Pan et al. (2016), 
notes that ``[e]nhanced efficiency fertilizers have been widely adopted 
to minimize N[itrogen] loss, including NH3 volatilization 
from agricultural systems.'' \97\ Similarly, Gu et al. (2023), in a 
study examining the potential to mitigate nitrogen pollution from 
global cropland, concluded that the largest reduction of reactive 
nitrogen input and losses available were in East and South Asia and 
Southeast Asia, which they attribute to an overuse of fertilizer in 
those areas.\98\ They calculated a much lower reduction potential in 
the European Union, Australia, and North America, where they concluded 
that nitrogen use in croplands is ``closer to the estimated optimal 
level.''
---------------------------------------------------------------------------

    \97\ Pan et al. (2016) op. cit., p. 288.
    \98\ Gu, B. et al. (2023) Cost-effective mitigation of nitrogen 
pollution from global croplands. Nature, Vol. 613, pp. 77-84.
---------------------------------------------------------------------------

    In addition to the uncertainty in emissions reduction potentials, 
we note that studies suggest that one of the five mitigation options 
identified by CCEJN, using fertilizers with nitrification inhibitors, 
may lead to an increase in ammonia emissions. For example, Pan et al. 
(2016) noted that ``[a]lthough nitrification inhibitors are designed to 
target N2O emissions, the use of these inhibitors may 
prolong the retention of NH4 in the soil resulting in 
[ammonia] volatilization (Kim et al., 2012; Lam et al., 2016; Ni et 
al., 2014).'' \99\ Pan et al. (2016) concluded that nitrification 
inhibitors increase ammonia volatilization by 38.0 percent.\100\ 
Similarly, Ti et al. (2019) found that nitrification inhibitors 
increased ammonia emissions by 42.6 percent,\101\ whereas Newell Price 
et al. (2011) found that ``[ammonia] emissions to air and ammonium/
nitrite losses to water may be increased by a small amount.'' \102\ 
While studies specific the San Joaquin Valley may show different 
results, based on the studies cited by the commenter, the research 
currently available does not indicate that use of fertilizers with 
nitrification inhibitors would reduce ammonia emissions in the San 
Joaquin Valley.
---------------------------------------------------------------------------

    \99\ Pan et al. (2016) op. cit., p. 284.
    \100\ Id. at p. 286.
    \101\ Ti et al. (2019) op. cit., p. 143.
    \102\ J. Newell Price, et al., (2011) An inventory of mitigation 
methods and guide to their effects on diffuse water pollution, 
greenhouse gas emissions and ammonia emissions from agriculture 
(Defra Project WQ0106). http://randd.defra.gov.uk/Document.aspx?Document=MitigationMethodsUserGuideDecember2011FINAL.pdf, p. 52.
---------------------------------------------------------------------------

    The studies that CCEJN points to on precision agriculture also note 
wide adoption of such practices while acknowledging some potential for 
additional environmental benefits. For example, in a 2021 report on the 
benefits of precision agriculture in the United States, the Association 
of Equipment Manufacturers discusses environmental improvements that 
have already been achieved through adoption of precision agriculture 
technologies.\103\ Whitmore (2019) notes that larger farms have been 
quicker to adopt precision agriculture techniques due to greater 
resources,\104\ and Lowenberg-Deboer

[[Page 86595]]

and Erickson (2019) note that ``[t]he biggest gap in [precision 
agriculture] adoption is for medium and small farms in the developing 
world that do not use motorized mechanization,'' which they attribute 
to cost-effectiveness challenges.\105\ Lowenberg-Deboer and Erickson 
(2019) also highlight the perception that adoption of precision 
agriculture has been slow, but state that ``[s]ome aspects of 
[precision agriculture] were adopted as quickly and as widely as any 
technology in history, while others have lagged behind for technical 
and economic reasons.'' \106\
---------------------------------------------------------------------------

    \103\ Association of Equipment Manufacturers, The Environmental 
Benefits of Precision Agriculture in the United States, https://newsroom.aem.org/download/977839/environmentalbenefitsofprecisionagriculture-2.pdf.
    \104\ Whitmore J. (2019) Precision Farming Comes into Its Own, 
Mich. St. Univ., https://www.canr.msu.edu/news/precision-farming-comes-into-its-own.
    \105\ Lowenberg-DeBoer, J. and Erickson, B. (2019) Setting the 
Record Straight on Precision Agriculture Adoption, Agronomy J., p. 
1565.
    \106\ Id. at 1552.
---------------------------------------------------------------------------

    Taken together, the EPA finds that the studies cited by CCEJN 
highlight the uncertainties in the feasibility of the measures 
identified in its comment letter and suggest that more research is 
needed to estimate the additional reductions achievable in the San 
Joaquin Valley. Furthermore, while several studies suggest that there 
may be the potential for additional ammonia reductions from synthetic 
fertilizer application, they also indicate that such potential is not 
quantifiable with the information available at this time and may be 
lower in the San Joaquin Valley than in other locations around the 
globe.
    Finally, regarding CCEJN's comment about the availability of 
modeling to predict ammonia volatilization, we acknowledge these 
additional studies \107\ identified by the commenter describing models 
for estimating ammonia emissions. However, we disagree with the 
commenter that the output from these models compel certain policy 
decisions in the San Joaquin Valley at this time. Here again the 
commenter cites large-scale studies that do not reflect model 
performance under conditions representative of those in the Valley. 
Both studies cited by the commenter note uncertainties due to crop 
type, meteorological conditions, and other factors, suggesting that 
research specific to the climate and farming practices in the Valley is 
needed. Furthermore, it is not clear that the models discussed in the 
studies are ripe for application in a regulatory context. For example, 
Gurung et al. (2021) concludes that additional research is needed 
before the models could be used to evaluate policy decisions for 
mitigating ammonia emissions from soils:
---------------------------------------------------------------------------

    \107\ Gurung et al. (2021) op. cit.; Yang et al. (2022) op. cit.

    In future research, DayCent can also be used to test ``what if'' 
scenarios for identifying best management practices (BMPs) given 
variation in the soil and climatic conditions. These scenarios could 
focus on adopting the 4R nutrient stewardship principles and 
identifying regional level BMPs associated with the addition of urea 
fertilization. Further model improvement would also allow for a 
broader set of options to be evaluated in support of policy and 
management decisions associated with mitigating of NH3 
---------------------------------------------------------------------------
volatilization from agricultural soils.

    Thus, based on our review, we find the State's conclusions that 
further research is needed to explore ammonia reduction potentials in 
the San Joaquin Valley to be reasonable. We encourage the State and 
District to perform and keep abreast of research on quantifying the 
effects of mitigation measures on ammonia emissions and their 
implications for policy and management decisions.
    Comment 3.B.3: CCEJN asserts that the State dismisses controls for 
fertilizers on the basis that there is no published literature on 
control effectiveness in the San Joaquin Valley specifically. The 
commenter contends that such justification is ``sometimes absurd'' and 
that it cannot be true that studies specific to the Valley are 
necessary to determine that minimizing the use of fertilizer will 
decrease ammonia emissions. The commenter asserts that ``this bar for 
effectiveness makes meaningful regulation impossible, particularly when 
the state disincentivizes research in the Central Valley by insisting 
that ammonia need not be regulated.'' The commenter further notes that 
it is unfortunate that the State never mentions conducting any studies 
in the San Joaquin Valley.
    Response 3.B.3: We disagree with CCEJN that the State claims that 
studies specific to the Valley are needed to discern that reducing 
fertilizer use will reduce ammonia emissions. In the 2018 
PM2.5 Plan, the State discusses the link between fertilizer 
application and both ammonia emissions and nitrate contamination in 
groundwater, and describes current State regulations aimed at 
optimizing fertilizer use to minimize emissions of ammonia to the 
atmosphere.\108\ Additionally, in its discussion of optimizing or 
minimizing fertilizer use in the 2023 Ammonia Supplement, the State 
discuss the ``4 R's'' of nitrogen management (i.e., ``applying the 
`Right source' of nitrogen at the `Right rate,' `Right time,' and 
`Right place' '') and that minimizing fertilizer use is consistent with 
the right rate principle. CARB also notes that Guthrie et al. (2018) 
describes that minimizing the application of fertilizer to a level 
commensurate with optimal crop production can reduce ammonia 
emissions.\109\ Thus, the State does acknowledge the potential benefits 
of minimizing fertilizer use on ammonia emissions. Where the State 
concludes that additional research is needed is in the context of how 
optimal fertilizer use can be achieved, which it notes is ``not well 
described by both Guthrie et al. (2018) and the publications they 
referenced, nor were any specific regulations identified.'' Given that 
some level of reduction is already being achieved through existing 
regulations and current practices, and the importance of careful 
consideration of environmental factors for optimizing fertilizer use, 
we find the State's conclusion that additional research specific to the 
warm, dry climate conditions of the San Joaquin Valley is needed to 
determine whether additional strategies could further optimize 
fertilizer use and reduce ammonia emissions to be reasonable.
---------------------------------------------------------------------------

    \108\ 2018 PM2.5 Plan, Appendix C, pp. C-339 to C-
341.
    \109\ March 2023 Ammonia Supplement, p. 92.
---------------------------------------------------------------------------

    Regarding CCEJN's statement that the State dismisses controls for 
fertilizers based on a lack of information on control effectiveness in 
the Valley, as discussed in Responses 3.B.1 and 3.B.2, studies reviewed 
by the State, as well as studies cited by the commenter, emphasize that 
strategies to reduce ammonia emissions are highly dependent on local 
environmental factors and farm structures, and that more research is 
needed to examine these factors, as well as the effects of combinations 
of measures. The State concludes that specific mitigation strategies 
identified in the literature, such as optimizing fertilizer use, are 
already being implemented in the San Joaquin Valley because of 
regulations adopted by other California State agencies and co-benefits 
such as reduced cost to farmers. Based on the literature study findings 
regarding the importance of local information and the need to examine 
combinations of measures, the absence of existing rules or regulations 
in other areas controlling ammonia emissions directly, and the State's 
evaluation of the mitigation strategies already implemented through 
regulation by other State agencies, we maintain that it is reasonable 
that the State concludes that more research specific to the Valley is 
needed to assess the feasibility and effectiveness of additional 
measures for synthetic fertilizers.
    We also disagree with CCEJN's assertions that needing additional 
studies specific to the conditions in the

[[Page 86596]]

Valley makes meaningful regulation impossible and that the State 
disincentivizes research by concluding ammonia does not need to be 
regulated. Contrary to the commenter's claim that the State does not 
discuss any studies that it is conducting to assess the effectiveness 
of ammonia controls in the Valley, the State does include a discussion 
of recent and ongoing and research in Section 4 of the March 2023 
Ammonia Supplement. CARB's work includes the development of a mobile 
measurement platform equipped with an ammonia monitor and other 
instrumentation to examine ammonia sources. The State notes that in 
fall 2018, CARB collaborated with researchers from the University of 
California, Davis to measure ammonia and other air pollutants near 
dairies in the San Joaquin Valley to evaluate the effectiveness of 
alternative manure management practices.\110\ The State also mentions 
additional research to evaluate emissions from dairies, to use 
satellite and remote sensing data to evaluate ammonia emissions sources 
across the Valley, and to identify opportunities to reduce ammonia and 
other pollutant emissions from dairy manure lagoons specifically. These 
efforts may inform future decision-making regarding the regulation of 
ammonia in the San Joaquin Valley.
---------------------------------------------------------------------------

    \110\ March 2023 Ammonia Supplement, Figure 5 (showing that 
dairy cattle account for an estimated 67.2 percent of ammonia 
emissions from CAFs).
---------------------------------------------------------------------------

    Moreover, the EPA's action herein to approve the precursor 
demonstration in the SJV PM2.5 Plan for the 1997 annual 
PM2.5 NAAQS does not preclude the State from adopting 
controls for ammonia in the future. As discussed in our proposal, a 
consequence of this final action to approve the State's ammonia 
precursor demonstration is that the State is not required to implement 
BACM/BACT level controls for sources of ammonia for purposes of the SJV 
PM2.5 Plan for 1997 annual PM2.5 NAAQS. Under 40 
CFR 51.1006(b), such precursor demonstration approval applies only to 
the SJV PM2.5 Plan that is the subject of this final action. 
For any new PM2.5 attainment plan that the State is required 
to submit in accordance with 40 CFR 51.1003 for purposes of any 
PM2.5 NAAQS, the EPA may determine that ammonia contributes 
significantly to PM2.5 levels that exceed the NAAQS and that 
the State is required to implement controls for sources of ammonia for 
purposes of such attainment plan.
    Comment 3.B.4: Regarding the District's current rules, CCEJN 
asserts that the State assumes that farmers are already adopting the 
most efficient practices (e.g., feeding the most efficient amount of 
protein, incorporating manure quickly) but ``provides little support 
for these assumptions, even though it is well established that farmers 
do not always adopt the most efficient practices.'' The commenter 
proposes that the precursor analysis should err on maintaining the 
presumption that precursors should be regulated and thereby err on the 
side of high estimates of potential effectiveness and that because the 
State does not do so, its analysis is arbitrary and capricious. The 
commenter asserts that the State relies on ``biased assumptions,'' 
assuming low potential effectiveness from measures not being 
implemented, high reductions from Rule 4570, and that making optional 
measures mandatory would have no impact. The commenter further contends 
that if Rule 4570 is effective, the State should make its most 
effective requirements mandatory where feasible and possibly increase 
the stringency, and that the EPA should require the State to conduct 
further analysis of the rule.
    Response 3.B.4: We disagree with CCEJN's assertions that the State 
provides little support for its estimates of ammonia reductions that 
have been achieved by existing regulations and that the assumptions it 
makes to arrive at those estimates are biased. As discussed in our 
proposal, the District discusses in detail in Appendix C of the 2018 
PM2.5 Plan how Rule 4570 is structured, the control menu 
requirements for each of the CAF operations/sources, and research 
papers that support its estimates of ammonia emissions reductions from 
the measures.\111\ As the District explains, some of the measures in 
Rule 4570 are required to be implemented but the rule also requires 
that additional measures be selected from a menu of options. The menu-
based approach was developed to allow facilities flexibility to select 
measures that are the most practical and effective for their design and 
operation.\112\
---------------------------------------------------------------------------

    \111\ 2018 PM2.5 Plan, Appendix C, pp. C-312 to C-
323.
    \112\ Id.; March 2023 Ammonia Supplement, pp. 25-26.
---------------------------------------------------------------------------

    For those measures that are required to be selected from a menu of 
options, the District presents its rationale in Appendix C of the 2018 
PM2.5 Plan and Appendix F of the staff report for Rule 4570 
for its assumptions about which measure a farmer will select and the 
resulting effects on ammonia emissions.\113\ The District references 
research studies to support many of its assumptions, and where there is 
greater uncertainty about which measures may be selected or the 
corresponding ammonia reductions that can be achieved, the District 
explains how its assumptions are conservative. CCEJN has not provided 
any evidence to refute the District's analysis or conclusions. 
Therefore, based on the information presented, the EPA believes that 
the District relied on its expertise and the best information available 
and applied that information reasonably.
---------------------------------------------------------------------------

    \113\ 2018 PM2.5 Plan, Appendix C, pp. C-311 to C-
323; SJVUAPCD, ``Final Draft Staff Report, Proposed Re-Adoption of 
Rule 4570 (Confined Animal Facilities),'' June 18, 2009, at Appendix 
F, ``Ammonia Reductions Analysis for Proposed Rule 4570 (Confined 
Animal Facilities),'' June 15, 2006 (discussing various assumptions 
underlying the District's calculation of ammonia emissions factors).
---------------------------------------------------------------------------

    Regarding CCEJN's statement that the State should err on the side 
of high estimates of potential reductions from additional measures, 
given the uncertainties discussed in Responses 3.B.1 and 3.B.2, we find 
that the potential emissions reductions achievable in the San Joaquin 
Valley from many of the measures are not quantifiable at this time and 
that the State drew reasonable conclusions based on the information it 
evaluated. While the EPA appreciates that the commenter raises 
additional research studies not identified by the State in its 
analysis, as discussed in Responses 3.B.1 and 3.B.2, we have reviewed 
the studies and find that they do not contradict the State's 
conclusions. Thus, we find that the State's analysis of potential 
ammonia emissions reductions is neither arbitrary nor capricious.
    We also find that CCEJN's claim that it is well-established that 
farmers do not adopt the most efficient practices is not well 
supported. To back this claim, the commenter cites two studies 
discussing the rates of adoption of precision agriculture 
technologies.\114\ However, these studies do not appear to indicate any 
reluctance on the part of farmers to adopt the most efficient 
practices. As discussed in Response 3.B.2, these papers discuss 
widespread adoption of precision agriculture technology while also 
acknowledging areas where there are opportunities for increased 
adoption, such as for specific crop types or farm sizes and for 
specific precision agriculture technologies, such as variable rate 
technology.\115\ Where

[[Page 86597]]

adoption has been slower, the studies point to feasibility constraints 
and the need for more research. For example, Lowenberg-DeBoer and 
Erickson (2019) emphasize that precision agriculture has been widely 
adopted and that in cases where technologies have been adopted at a 
slower pace, the authors attribute it to technological and economic 
feasibility challenges.\116\ The study authors also note that the 
studies they reviewed hypothesize that more reliable decision rules 
that account for the effects of moisture, temperature, soil organic 
matter, and other factors on nitrogen response may be needed to 
increase variable rate technology adoption.\117\ Whitmore (2019) 
similarly notes the complexity and high cost of new equipment as 
barriers to wider adoption of precision technology.\118\ CCEJN does not 
provide any evidence related to other measures in its letter or other 
measures in the State's analysis to support its claim.
---------------------------------------------------------------------------

    \114\ Whitmore (2019) op. cit.; Lowenberg-DeBoer and Erickson 
(2019) op. cit.
    \115\ Variable rate technology refers to the use of data and 
automation to optimize application of fertilizer, soil amendments, 
seed, or plant protection chemicals to optimize crop performance, 
save time and money, and reduce environmental impacts.
    \116\ Lowenberg-DeBoer and Erickson (2019) op. cit., p. 1552.
    \117\ Id. at 1564-1565.
    \118\ Whitmore (2019) op. cit.
---------------------------------------------------------------------------

    Finally, we disagree with CCEJN's assertion that if Rule 4570 is 
effective, the State must consider making its optional requirements 
mandatory. As discussed earlier in this response, if the EPA approves a 
state's precursor demonstration showing that a particular 
PM2.5 precursor chemical species does not contribute 
significantly to PM2.5 levels above the standard in the 
area, the state is relieved of the obligation to control emissions of 
that precursor from existing sources in the relevant attainment plan.
    Comment 3.C: Regarding the State's reliance on 2024 modeling 
results for its precursor analysis, CCEJN asserts that the State should 
not have relied on modeling of 2024, which is after the 2023 attainment 
deadline, and which nevertheless shows ammonia contributions that are 
above the contribution threshold. CCEJN further asserts that the use of 
2024 modeling ``violates the Act in three ways.''
    First, the commenter asserts that the approach ignores the 
requirement to demonstrate attainment as expeditiously as practicable 
because it does not consider ammonia reductions that may have resulted 
in attainment before 2023. They note that the State claimed it was 
close to attaining in 2020 and that meaningful reductions in ammonia 
would have most likely resulted in attainment earlier (i.e., in 2021 or 
2022).
    Second, the commenter notes that the State relies not only on a 
future year but a year after the attainment deadline. Because 
NOX emissions are expected to be lower in 2024 than 2023, 
the commenter suggests that the impacts of ammonia reductions would be 
less in 2024 than in 2023 and that the impacts of ammonia reductions in 
2023 are unknown. The commenter also claims that the EPA makes 
assumptions about how the State conducted its analysis and recommends 
that the EPA seek clarification from the State about whether the 
analysis relied on emissions projected from baseline (i.e., existing) 
control measures or baseline measures plus measures committed to in the 
plan. If the State did not conduct the analysis ``with numbers that are 
comparable to what are expected in 2023,'' the commenter contends that 
the EPA must require the State to redo the analysis.
    Third, CCEJN asserts that the State's model indicating a design 
value of 12.03 [micro]g/m\3\ cannot accurately describe 2023 conditions 
given that 2022 data show a design value well above 16 [micro]g/m\3\. 
They conclude that the ``EPA's approval of a precursor analysis that 
relies on such unrealistic modeling is therefore arbitrary and 
capricious and contrary to law.''
    Response 3.C: While the State relied on 2024 modeled sensitivities 
of PM2.5 to ammonia reductions, it is important to note that 
the EPA also considered the 2023 model responses via a NOX-
based interpolation between the State's model results for 2020 and 
2024. The highest estimated response was at the Hanford site, 0.26 
[micro]g/m\3\ for 2024 and 0.27 [micro]g/m\3\ for 2023, and did not 
change the EPA's conclusions regarding the ammonia precursor 
demonstration.\119\ In determining that ammonia does not contribute 
significantly in the San Joaquin Valley despite the Hanford response 
being above the 0.25 [micro]g/m\3\ contribution threshold that the 
State derived for the 1997 annual PM2.5 NAAQS, we continue 
to rely on the abundant ambient evidence of excess ammonia relative to 
NOX. This evidence includes evidence specific to the Hanford 
area, where mobile laboratory observations during the DISCOVER-AQ study 
showed ambient concentrations of ammonia that were approximately five 
times higher than those that were modeled.\120\ These factors led the 
EPA to conclude that the model responses were likely overestimated and 
did not represent a significant contribution of ammonia to 
PM2.5 levels.
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    \119\ 88 FR 45276, 45293, fn. 184.
    \120\ Kelly, J.T. et al. (2018), op. cit.
---------------------------------------------------------------------------

    We further disagree with the commenter's assertion that the State's 
approach ignores the requirement for expeditious attainment. The CAA 
requirement for expeditious attainment is not directly relevant for 
evaluating a precursor demonstration, which is mainly concerned with 
whether PM2.5 in the atmosphere is sensitive to emissions 
reductions of the precursor. For that purpose, the PM2.5 
Precursor Demonstration Guidance provides for the use of modeled 
sensitivities of PM2.5 to a reduction in precursor emissions 
evaluated in the base year or a future year, noting that there are many 
considerations in choosing the appropriate year to model.\121\ The key 
factor for the State's use of a future year was the fact that sizable 
NOX emissions reductions were projected to occur over time 
and would change the atmospheric chemistry in the San Joaquin Valley. 
The reductions are mainly due to the existing motor vehicle control 
program and would occur independent of any controls in, or EPA action 
on, the Plan.\122\ The sensitivity of PM2.5 concentrations 
to ammonia reductions decreases with decreasing NOX 
emissions. Between 2020 and 2024, the modeled response to a 30 percent 
ammonia emissions reduction declines by 50 percent at the design value 
monitoring site, Bakersfield-Planz, from 0.24 [micro]g/m\3\ down to 
0.12 [micro]g/m\3\. (The corresponding decline is 37 percent for the 
average over all monitoring sites.) Thus, much of the benefit of 
ammonia controls applied in 2020 would be lost by 2023 and 2024.
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    \121\ PM2.5 Precursor Demonstration Guidance, p. 36.
    \122\ 2018 PM2.5 Plan, Appendix B. NOX 
emissions decrease 27 percent between 2020 and 2024 due to baseline 
measures.
---------------------------------------------------------------------------

    With regard to whether ammonia emissions reductions could have 
resulted in earlier attainment, the EPA used results from the Plan's 
attainment demonstration to assess the effect of a 30 percent ammonia 
reduction in 2022 and found that it would not have resulted in 
attainment in that year.\123\ We estimated the 2022 design value as 
15.4 [micro]g/m\3\ by using a NOX emissions-based 
interpolation between the Plan's 2018 and 2023 design values, 16.3 and 
14.7 [micro]g/m\3\, respectively.\124\ Similarly we estimated the 2022 
sensitivity to ammonia from the State's modeled sensitivities for 2020 
and 2024. Applying a 30 percent ammonia reduction for 2022 resulted in 
a design value of 15.2 [micro]g/m\3\, which is above the level of the 
1997 annual PM2.5 NAAQS

[[Page 86598]]

(i.e., 15.0 [micro]g/m\3\). Thus, we conclude that ammonia emissions 
reductions would not have resulted in attainment before the Plan's 
projected 2023 attainment date.
---------------------------------------------------------------------------

    \123\ Spreadsheet ``Estimated 2023 annual PM2.5 
ammonia sensitivity and 2022 DV.xlsx,'' ``2023 vs. 2024 response to 
30% ammonia reduction,'' EPA Region IX, October 20, 2023.
    \124\ 15 [micro]g/m\3\ SIP Revision, Appendix K, Table 33.
---------------------------------------------------------------------------

    Regarding the use of 2024 modeled sensitivities in lieu of modeled 
sensitivities for 2023, the EPA finds that our conclusions would be the 
same for the purposes of our evaluation of the precursor demonstration. 
We estimated 2023 responses to ammonia emissions reductions by 
interpolating between the responses for available 2020 and 2024 
modeling; the interpolation used projected NOX emissions for 
2020, 2023, and 2024 and found the estimated 2023 response to be only 
0.01 [micro]g/m\3\ higher than in 2024.\125\ While there are several 
differences between 2020 and 2024 modeled emissions for the various 
PM2.5 precursors and direct PM2.5, the key 
difference for assessing the change in the sensitivity of 
PM2.5 to ammonia reductions is NOX emissions 
levels. The modeling for 2020 and 2024 represent PM2.5 
design values for the NOX emissions levels in 2020 and 2024, 
and their respective responses to a 30 percent ammonia emissions 
reduction. To estimate the PM2.5 response to ammonia 
reductions in other years or for other control scenarios, only the 
NOX emissions level is needed. The estimate does not depend 
on NOX emissions differences between 2023 and 2024 
calculated for baseline, controlled, or other scenarios, only on the 
resulting 2023 emissions level being evaluated.
---------------------------------------------------------------------------

    \125\ Spreadsheet ``Estimated 2023 annual PM2.5 
ammonia sensitivity and 2022 DV.xlsx,'' ``Whether 30% ammonia 
reduction could attain early,'' EPA Region IX, October 20, 2023.
---------------------------------------------------------------------------

    The commenter states that it is unclear whether the precursor 
demonstration analysis relied on a baseline emissions inventory, or an 
inventory considering the controls in the plan. While this is not 
documented prominently in the submittal materials, the precursor 
demonstration modeling performed by the State used baseline 
projections,\126\ that is, emissions expected with existing control 
measures and without new control measures from the 2018 
PM2.5 Plan or the 15 [micro]g/m\3\ SIP Revision.\127\ 
Notably, the EPA's conclusions for the precursor demonstration do not 
depend on which of the two inventories is used. For the interpolation 
to 2023, the EPA relied on controlled NOX emissions levels 
(150.6 tpd) to estimate the 2023 response to 30 percent reduction to be 
0.265 [micro]g/m\3\ (reported as 0.27 [micro]g/m\3\). Using baseline 
NOX emissions (153.6 tpd), the estimated 2023 response is 
0.275 [micro]g/m\3\, which is about 0.01 [micro]g/m\3\ higher. Thus, 
the difference between using the baseline or controlled emissions for 
assessing the sensitivity to ammonia emissions reductions is 
negligible.
---------------------------------------------------------------------------

    \126\ 2018 PM2.5 Plan, Appendix K, Section 5.6 
``PM2.5 Precursor Sensitivity Analysis'', p. 70: ``To 
evaluate the impact of reducing emissions of different 
PM2.5 precursors on PM2.5 DVs, a series of 
model sensitivity simulations were performed, for which 
anthropogenic emissions of the precursor species were reduced by a 
certain percentage from the baseline emissions;'' email dated 
September 19, 2019, from Jeremy Avise, CARB, to Scott Bohning, EPA 
Region IX, Subject: ``FW: SJV species responses,'' with attachments, 
in which the attached tables have titles like ``Difference in Annual 
PM2.5 mass and species between the 2024 baseline run and 
the 30% PM reduction precursor run.''
    \127\ In comparison to potential modeling of controlled 
emissions, the NOX emissions for projected baseline years 
2020 and 2024 are higher, ammonia would be less abundant relative to 
NOX, and the responses to ammonia reductions would be 
higher. Relying on baseline rather than controlled NOX 
emissions levels was therefore conservative for purposes of the 
ammonia precursor demonstration.
---------------------------------------------------------------------------

    Finally, the EPA disagrees that a monitored 2022 design value being 
``well above'' the modeled 2023 design value invalidates the modeling 
for purposes of the precursor demonstration. As discussed in the EPA's 
modeling TSD for the 2018 PM2.5 Plan,\128\ the State 
determined that the model performance was excellent, and the EPA found 
the results to be adequate for attainment demonstration modeling. The 
modeling used a 2013 base year, i.e., the specific meteorological and 
emissions conditions of 2013, not those of 2022 (nor of the 2018 
monitored value used in scaling the modeling results from the 2018 
PM2.5 Plan). Even when the modeling itself is valid, the 
model-predicted design value can differ from a recent monitored design 
value due to different meteorological conditions than in 2013 base 
case, emissions variability, and atypical events that affect the 
monitored value, but that are not necessarily reflected in the modeling 
because they are inherently unpredictable.\129\ The greater uncertainty 
in the precursor demonstration, which supports the EPA's conclusion in 
this final action, is that the modeling seems to conservatively 
overestimate the sensitivity of PM2.5 concentrations to 
ammonia reductions compared to what would be expected based on ambient 
measurements of ammonia and nitrate, as discussed in Response 3A.
---------------------------------------------------------------------------

    \128\ EPA, ``Technical Support Document, EPA Evaluation of Air 
Quality Modeling, San Joaquin Valley PM2.5 Plan for the 
2006 PM2.5 NAAQS,'' February 2020.
    \129\ The issue of how model predictions may not match monitor 
observations despite a well-performing model, and how that does not 
in itself invalidate the precursor demonstration is discussed in 
more detail in the EPA's proposed disapproval of the 2018 
PM2.5 Plan portion addressing the 1997 annual 
PM2.5 NAAQS. 86 FR 67329, 67335 (November 26, 2021).
---------------------------------------------------------------------------

    Comment 3.D: CCEJN's fourth concern with the precursor analysis is 
that it believes that ``[t]he State improperly adopts a lax 
contribution threshold of 0.25 [micro]g/m\3\.'' The commenter 
acknowledges that the State's approach of using a 0.25 [micro]g/m\3\ 
threshold is consistent with the EPA's guidance but contends that the 
guidance is arbitrary and capricious and that the EPA should reject it 
in this rulemaking. To support their assertion, the commenter reasons 
that

    [t]he result of the state's approach is that an area, like the 
San Joaquin Valley, that is failing to meet multiple successively 
rigorous standards for the same measurement of the same pollutant, 
may need to regulate a precursor only for purposes of the more 
rigorous standard. This is a senseless result because the failure to 
meet an already-outdated standard only highlights the necessity of 
taking all feasible regulatory steps, including regulating relevant 
precursors.

    The commenter concludes that there is no advantage of two distinct 
thresholds because the area will need to apply the lower threshold 
eventually, and states that the ``EPA's failure to grapple with this 
arbitrary result means that it has failed to provide a reasoned 
explanation for its guidance, and the guidance--or at least its 
application in this case--is arbitrary and capricious.'' For areas not 
meeting both the 1997 and 2012 annual PM2.5 NAAQS, the 
commenter proposes that the EPA should require states to apply the 
threshold for the 2012 NAAQS for purposes of evaluating a precursor 
contribution for both NAAQS.
    Response 3.D: The EPA disagrees that the same contribution 
threshold must be used regardless of the level of the NAAQS being 
examined. The EPA believes that applying a threshold that is 
proportional to the level of the NAAQS is appropriate and consistent 
with the Act; i.e., 0.2 [micro]g/m\3\ is appropriate for the 2012 
annual PM2.5 NAAQS of 12.0 [micro]g/m\3\, and 0.25 [micro]g/
m\3\ is appropriate for the 1997 annual PM2.5 NAAQS of 15.0 
[micro]g/m\3\.
    The contribution thresholds the EPA derived in the PM2.5 
Precursor Demonstration Guidance represent a change in air quality that 
is statistically indistinguishable from the inherent variability in the 
measured atmospheric concentrations. A contribution threshold that is 
proportional to, or scales with, the level of the NAAQS may also be 
termed a ``relative'' approach, since the size of the threshold is 
relative to the level of the NAAQS. The contribution thresholds in the 
PM2.5

[[Page 86599]]

Precursor Demonstration Guidance were derived from a relative 
variability estimate multiplied by the NAAQS level for the 2006 24-hour 
PM2.5 NAAQS and 2012 annual PM2.5 NAAQS. Notably, 
the PM2.5 Precursor Demonstration Guidance states: \130\
---------------------------------------------------------------------------

    \130\ PM2.5 Precursor Demonstration Guidance, p. 17, 
fn. 20.

    As described in the Technical Basis Document, the monitoring 
site variability is first calculated as a percentage of the measured 
PM2.5. Then the median percent variability from all sites 
is multiplied by the level of the NAAQS to get the threshold 
concentrations. Therefore, these thresholds represent a percentage 
of the 2006 24-hour NAAQS (35 [mu]g/m\3\) and the 2012 annual NAAQS 
(12 [mu]g/m\3\). Different thresholds may be applicable to other 
---------------------------------------------------------------------------
levels and/or forms of the NAAQS (either past or future).

    The Technical Basis Document \131\ referred to in the guidance 
explains that relative variability (concentration changes as a fraction 
of total concentration) was found to be more stable than absolute 
variability (concentration changes in [micro]g/m\3\), and notes that 
this ``indicates that a central tendency value for the relative 
variability in the DV [design value]. Therefore, a representative value 
can be multiplied by the level of that NAAQS to obtain a value in 
concentration units ([micro]g/m\3\ for PM2.5) that is 
appropriately used to characterize variability.'' \132\ The Technical 
Basis Document also explains that the ``relative variability was fairly 
consistent across the range of design values, suggesting a commonality 
in the relative variability across a wide range of geographic regions, 
chemical regimes, and baseline air quality levels.'' \133\ Thus, a 
concentration amount that is relative, or proportional, to the NAAQS 
level is a better basis than a fixed concentration number for 
determining the size of a concentration change that is within the 
inherent variability of monitored concentrations. The superiority of 
the relative variability approach that was the basis of the 
PM2.5 Precursor Demonstration Guidance contribution 
threshold of 0.2 [micro]g/m\3\ for the 2012 annual PM2.5 
NAAQS makes it appropriate to scale that value according to the NAAQS 
level to arrive at 0.25 [micro]g/m\3\ for the 1997 annual 
PM2.5 NAAQS.
---------------------------------------------------------------------------

    \131\ EPA, ``Technical Basis for the EPA's Development of the 
Significant Impact Thresholds for PM2.5 and Ozone,'' EPA-
454/R-18-001R-18-001, EPA OAQPS, April 2018, available at https://www.epa.gov/nsr/significant-impact-levels-ozone-and-fine-particles, 
https://www.epa.gov/sites/default/files/2018-04/documents/ozone_pm2.5_sils_technical_document_final_4-17-18.pdf.
    \132\ Technical Basis Document, p. 26.
    \133\ Id. at 39.
---------------------------------------------------------------------------

    Moreover, the EPA does not agree that it is arbitrary or contrary 
to the Act to apply a lower contribution threshold or to potentially 
regulate a precursor only for a more stringent NAAQS--it is reasonable 
to expect that achieving lower PM2.5 concentrations may 
require regulation of additional sources of direct PM2.5 
and/or PM2.5 precursors. This is true even if an area is 
nonattainment for both the higher and lower NAAQS and the EPA will 
ultimately be applying the lower contribution threshold for a 
subsequent plan to attain the more stringent NAAQS. Indeed, the 
PM2.5 SIP Requirements Rule at 40 CFR 51.1000 defines a 
precursor demonstration to mean analyses showing that precursor 
emissions do not contribute significantly to PM2.5 levels 
that exceed the relevant PM2.5 standard'' [emphasis added]. Applying a 
lower threshold for the 1997 annual PM2.5 NAAQS because the 
area is in nonattainment for a more stringent NAAQS could presume that 
the modeling and precursor demonstration in a future plan will show 
responses to ammonia reductions above the lower threshold and that 
ammonia will be determined to be significant, such that ammonia would 
need to be controlled. The EPA does not believe it is appropriate to 
prejudge the analyses for a potential future plan.
4. BACM/MSM Demonstration
    Comment 4: Regarding the BACM demonstration, CCEJN notes that the 
EPA's proposed approval does not address the CAA requirement for most 
stringent measures (MSM), asserting that such analysis is required for 
a 189(d) plan under 40 CFR 51.1010(c)(2)(i) and (c)(4), and 88 FR 
45280, 45297, 45322. The commenter claims that it appears that the 
State acknowledges that the MSM requirement applies in its submittal 
and asserts that the EPA cannot approve the Plan until it reviews the 
State's control measures under the MSM standard.
    The commenter also states that ``[t]he state's control measures 
meet neither the BACM nor MSM standards.'' They note that in previous 
letters to the EPA (as summarized in a previous letter attachment 
included as Exhibit B), Valley groups have identified numerous 
weaknesses and presented ways the District could strengthen its 
regulations. The commenter asserts that the EPA's technical support 
document accompanying the proposed action addresses few of these 
weaknesses, and advises that ``[t]o the extent EPA has not considered 
whether the suggestions in the letter constitute BACM or MSM for 
purposes of the 1997 annual standard, it should do so.'' Specifically, 
the commenter notes that ``[o]ne particularly glaring shortfall in the 
state's submission is its failure to contain any analysis of potential 
control measures to minimize soil NOX emissions,'' and 
suggests that the EPA must require the State to analyze the measures in 
Exhibit A to CCEJN's comment letter (citing control measures described 
on pages 5 and 6), including measures to reduce soil NOX 
emissions from fertilized farmlands.
    Response 4: We disagree with CCEJN's assertion that the EPA must 
review the State's control measures analysis under the MSM standard. As 
outlined in the PM2.5 SIP Requirements Rule, the CAA 
requirement for MSM is tied to a specific trigger in the act--an 
extension of the Serious area deadline under CAA section 188(e).\134\ 
The EPA addressed the relevance of MSM to a 189(d) plan as part of our 
discussion of the control strategy for such plan in the technical 
support document accompanying the final rule: \135\
---------------------------------------------------------------------------

    \134\ 81 FR 58010, 58094.
    \135\ EPA, ``Response to Comments on the Fine Particulate Matter 
National Ambient Air Quality Standards: State Implementation Plan 
Requirements,'' July 29, 2016.

    In addition to meeting the 5 percent emission reduction 
requirement for PM2.5 or any PM2.5 plan 
precursor, for any Serious nonattainment area that fails to attain 
by the Serious area attainment date, the state is required to update 
its control measures analysis in the section 189(d) plan. In the 
event the area previously had received an extension of the Serious 
area attainment date pursuant to section 188(e), the reevaluation of 
control measures referenced in section 51.1010(c)(2) should include 
a reevaluation of MSM. (For this reason, section 51.1010(c)(2)(i) 
refers to the reevaluation of MSM ``as applicable.'') If, however, 
the area did not previously request and receive an extension of the 
Serious area attainment date under section 188(e), the MSM 
---------------------------------------------------------------------------
requirement does not apply.

    Thus, we noted in the summary of the requirements for Serious 
PM2.5 areas that fail to attain in our proposed action that 
MSM is applicable only if the EPA granted an extension of the 
attainment date under CAA section 188(e) for the area for the NAAQS at 
issue.\136\
---------------------------------------------------------------------------

    \136\ 88 FR 45276, 45280, fn. 57.
---------------------------------------------------------------------------

    As discussed in our proposal, California's Serious area plan for 
the 1997 PM2.5 NAAQS submitted in 2015 included a request 
under CAA section 188(e) to extend the attainment date for the 1997 
annual PM2.5 NAAQS by five years to December 31, 2020.\137\ 
However, after considering public comments, the EPA denied California's 
request for an extension of the attainment date and subsequently 
determined that the area failed to attain by the December 31, 2015 
Serious area

[[Page 86600]]

attainment date, triggering the requirement for the 189(d) plan. 
Consequently, because the San Joaquin Valley area did not receive an 
extension of the Serious area attainment date under CAA section 188(e), 
the MSM requirement does not apply for purposes of the 1997 annual 
PM2.5 NAAQS.
---------------------------------------------------------------------------

    \137\ Id. at 45277.
---------------------------------------------------------------------------

    Regarding the commenter's claim that the State appears to 
acknowledge in its submission that MSM applies, we note that the 
State's controls analysis in the 2018 PM2.5 Plan was 
developed to address multiple PM2.5 NAAQS, including the 
2006 PM2.5 NAAQS for which the State requested an attainment 
date extension under CAA section 188(e), triggering the MSM requirement 
for those NAAQS. Any assertion by the State in the SJV PM2.5 
Plan that a particular measure meets the MSM standard may not 
necessarily indicate that the State believes that the requirement 
applies for the 1997 annual PM2.5 NAAQS. Regardless, 
regarding CCEJN's comment that the State's control measures do not meet 
the BACM or MSM standards, given that the MSM standard does not apply 
to the 1997 annual PM2.5 NAAQS, as discussed earlier in this 
response, we are responding only to the commenter's assertion regarding 
BACM.
    We also disagree with the commenter's assertion that the control 
measures in the Plan do not meet the requirement for BACM for the 1997 
annual PM2.5 NAAQS. As discussed in our proposed rule, in 
our review of the State's and District's BACM demonstration, we 
considered our evaluation of the State's and District's rules, 
supporting information provided in the SJV PM2.5 Plan, and 
our prior evaluations of the BACM and MSM demonstrations in the 2018 
PM2.5 Plan for other PM2.5 NAAQS.\138\ These 
prior evaluations include those to support our approval of the 
demonstration for BACM (including BACT) for the 1997 24-hour 
PM2.5 NAAQS,\139\ our approval of the demonstrations for 
BACM and MSM for the 2006 24-hour PM2.5 NAAQS,\140\ and our 
proposed disapproval of the demonstration for BACM for the 2012 annual 
PM2.5 NAAQS.\141\ The EPA's prior actions for the 1997 24-
hour, 2006 24-hour, and 2012 annual PM2.5 NAAQS are relevant 
to our evaluation for this final rulemaking because the State relied on 
a common analysis for each of the PM2.5 standards. The EPA 
conducted a thorough analysis of the State's BACM demonstration for 
purposes of these prior actions, and updated the analysis for certain 
source categories, as appropriate, for purposes of our proposed 
approval of the BACM demonstration in the SJV PM2.5 Plan for 
the 1997 annual PM2.5 NAAQS.
---------------------------------------------------------------------------

    \138\ Id. at 45305-45306.
    \139\ 87 FR 4503 (January 28, 2022).
    \140\ 85 FR 44192 (July 22, 2020).
    \141\ 86 FR 74310 (December 29, 2021).
---------------------------------------------------------------------------

    Regarding the EPA's prior approval of the BACM demonstration in the 
2018 PM2.5 Plan as meeting the CAA requirements for the 2006 
24-hour PM2.5 NAAQS, we note that on September 17, 2020, a 
group of five environmental, public health, and community groups 
petitioned the Ninth Circuit Court of Appeals (``Ninth Circuit'') for 
review of the EPA's final rulemaking approving the 2018 
PM2.5 Plan's demonstration of BACM, BACT, and MSM for 
emissions sources of direct PM2.5 and NOX for 
purposes of the 2006 PM2.5 NAAQS.\142\ On April 13, 2022, 
the Ninth Circuit denied the petitioners' challenge with respect to the 
EPA's approval of the Plan's BACM/MSM demonstration, upholding such 
approval for those NAAQS.
---------------------------------------------------------------------------

    \142\ See Medical Advocates for Healthy Air v. EPA, Case No. 20-
72780, Dkt. #58-1 (9th Cir., April 13, 2022). The five 
environmental, public health, and community organizations, in order 
of appearance in the petition, are Medical Advocates for Healthy 
Air, National Parks Conservation Association, Association of 
Irritated Residents, and Sierra Club.
---------------------------------------------------------------------------

    Following approval of the State's BACM and MSM demonstrations for 
the 2006 24-hour PM2.5 NAAQS, on December 29, 2021, the EPA 
proposed to approve portions of the 2018 PM2.5 Plan as 
meeting the Serious area requirements for the San Joaquin Valley for 
the 2012 annual PM2.5 NAAQS, including the requirement that 
the plan include BACM. However, after considering public comments, on 
October 5, 2022, the EPA proposed to disapprove portions of the 
District's BACM demonstration, including the evaluations of ammonia 
emissions sources and building heating sources.\143\ We proposed to 
disapprove the BACM demonstration for ammonia sources based in part on 
our on proposed disapproval of the State's ammonia precursor analysis 
for the 2012 annual PM2.5 NAAQS,\144\ as well as the State's 
control measure analysis for ammonia.\145\ We proposed to disapprove 
the BACM demonstration for building heating sources based on recent 
control measure developments and the time horizon of the 2012 annual 
PM2.5 NAAQS portion of the SJV PM2.5 Plan, which 
raised questions about the feasibility of implementing additional 
controls for such sources for BACM purposes in the San Joaquin 
Valley.\146\ Notably, we did not re-propose action on any other 
portions of the State's and District's BACM demonstration that we had 
previously proposed to approve.
---------------------------------------------------------------------------

    \143\ 87 FR 60494.
    \144\ Based on our proposed disapproval of the precursor 
demonstration for the 2012 annual PM2.5 NAAQS, we 
proposed to determine that ammonia remained a regulated precursor 
for that NAAQS in the San Joaquin Valley.
    \145\ 87 FR 60494, 60509.
    \146\ Id. at 60511-60512.
---------------------------------------------------------------------------

    In response to the EPA's proposed disapproval of portions of the 
BACM demonstration for the 2012 annual PM2.5 NAAQS, CARB and 
the District developed and submitted additional information to support 
the ammonia precursor demonstration and building heating BACM 
demonstration for purposes of meeting the Serious area and CAA section 
189(d) requirements for the 1997 annual PM2.5 NAAQS. Our 
proposal and accompanying ``Technical Support Document, San Joaquin 
Valley PM2.5 Plan Revision for the 1997 Annual 
PM2.5 NAAQS,'' April 2023 (``EPA's 1997 Annual 
PM2.5 TSD'') summarize the additional information provided 
by the State and District and the EPA's evaluation. Based on our 
review, we determined that the additional information provided by the 
State and District addressed the deficiencies identified in the 
proposed disapproval of the 2018 PM2.5 Plan for the 2012 
annual PM2.5 NAAQS as they pertained to the 1997 annual 
PM2.5 NAAQS. Thus, considering our prior approvals of the 
State's and District's BACM analysis for the 1997 24-hour 
PM2.5 NAAQS, BACM and MSM analysis for the 2006 
PM2.5 NAAQS (which was upheld by the Ninth Circuit), and the 
supplemental information provided to update the SJV PM2.5 
Plan based on the latest information available, we proposed to approve 
the BACM demonstration for the 1997 annual PM2.5 NAAQS.
    Regarding the measures in Exhibit B to CCEJN's comment letter, the 
EPA has reviewed and considered the recommendations for improvements to 
the District's PM2.5 control strategy as outlined in the two 
letters in Exhibit B sent by environmental groups to the EPA in 2021 
\147\ and 2022.\148\ A detailed summary of our evaluation of the 
feasibility of these measures, as well as numerous others, is provided 
in Sections III and IV of the ``EPA Source Category and Control Measure 
Assessment and Reasoned Justification

[[Page 86601]]

Technical Support Document'' (``Control Measure Assessment TSD'') \149\ 
accompanying our proposed action to promulgate a federal implementation 
plan for contingency measures for the 1997 annual PM2.5 
NAAQS, the 2006 24-hour PM2.5 NAAQS, and the 2012 annual 
PM2.5 NAAQS.\150\ The EPA determined that the recommended 
measures are either not technologically feasible or not economically 
feasible within the two year timeframe for implementation as 
contingency measures discussed in the EPA's draft guidance.\151\ Given 
that by statute, contingency measures are additional requirements that 
go beyond attainment planning requirements, and the shorter timeframe 
of the attainment plan for the 1997 annual PM2.5 NAAQS 
(i.e., by December 31, 2023), we similarly conclude that these measures 
are not feasible for purposes of the BACM requirement for the SJV 
PM2.5 Plan for the 1997 annual PM2.5 NAAQS.
---------------------------------------------------------------------------

    \147\ Letter dated October 22, 2021, from environmental 
organizations to Michael S. Regan, Administrator, EPA, Subject: 
``Meeting Request to Discuss PM-2.5 Crisis in the San Joaquin 
Valley.''
    \148\ Letter dated May 18, 2022, from environmental 
organizations to Michael S. Regan, Administrator, Environmental 
Protection Agency, Subject: ``Meeting Request to Discuss PM-2.5 
Crisis in the San Joaquin Valley.''
    \149\ EPA Region IX, ``EPA Source Category and Control Measure 
Assessment and Reasoned Justification Technical Support Document, 
Proposed Contingency Measures Federal Implementation Plan for the 
Fine Particulate Matter Standards for San Joaquin Valley, 
California,'' July 2023.
    \150\ 88 FR 53431 (August 8, 2023).
    \151\ EPA, Office of Air Quality Planning and Standards, Air 
Quality Policy Division, ``DRAFT: Guidance on the Preparation of 
State Implementation Plan Provisions that Address the Nonattainment 
Area Contingency Measure Requirements for Ozone and Particulate 
Matter'' (``Draft Guidance''), March 16, 2023, p. 41.
---------------------------------------------------------------------------

    Lastly, we disagree with CCEJN's assertion that the EPA must 
require the State to analyze the control measures for soil 
NOX emissions outlined in Exhibit A in order to approve the 
BACM demonstration for the 1997 annual PM2.5 NAAQS. The EPA 
previously addressed the issues of soil NOX emissions and of 
analyzing potential controls for such emissions in the context of the 
2018 PM2.5 Plan in the EPA's ``Response to Comments Document 
for the EPA's Final Action on the San Joaquin Valley Serious Area Plan 
for the 2006 PM2.5 NAAQS,'' June 2020 (``EPA's 2020 Response 
to Comments'').\152\ More recently, the EPA also addressed the issue of 
soil NOX emissions from the use of fertilizers and 
pesticides in the context of our final rulemaking approving CARB's 
submission of emissions inventories for VOC and NOX for the 
2015 ozone NAAQS for areas in California (``2015 Ozone Inventory Final 
Rule'').\153\
---------------------------------------------------------------------------

    \152\ EPA's 2020 Response to Comments, pp. 148-156, Comments and 
responses 6.P-1 and 6.P-2.
    \153\ 87 FR 59015 (September 29, 2022).
---------------------------------------------------------------------------

    In both the EPA's 2020 Response to Comments and the 2015 Ozone 
Inventory Final Rule, the EPA acknowledged the studies cited by 
commenters finding that soil NOX emissions from fertilizer 
and pesticide use contribute to atmospheric NOX levels in 
California.\154\ Particularly, the EPA acknowledged the growing body of 
research surrounding the identification and quantification of soil 
NOX emissions from fertilizer application in agricultural 
soils. However, in light of the uncertainties and disagreements among 
the studies regarding the contribution of fertilized cropland soils to 
NOX emissions in California, the EPA found that CARB's 
emissions inventories met the applicable requirements of the CAA 
notwithstanding the absence of soil NOX emissions from 
fertilizer or pesticide use.\155\ Furthermore, for purposes of our 
final action on the San Joaquin Valley Serious Area Plan for the 2006 
PM2.5 NAAQS, we determined that there was not sufficient 
information available to require a controls evaluation for soil 
NOX emissions for purposes of the BACM analysis for those 
NAAQS.\156\
---------------------------------------------------------------------------

    \154\ Id. at 59018.
    \155\ Id. at 59018-59020.
    \156\ EPA's 2020 Response to Comments, p. 156.
---------------------------------------------------------------------------

    Upon reviewing the studies cited by CCEJN in its comment letter, we 
similarly find that the information provided is not sufficient to 
compel a revision to the emissions inventories in the SJV 
PM2.5 Plan for the 1997 annual PM2.5 NAAQS, given 
the large uncertainties in the emissions estimates. As discussed in 
Response 2.A, the magnitude of soil NOX emissions varies 
based on temperature; agricultural practices, such as the timing and 
amount of fertilizer application and irrigation; crop type; and other 
factors. Additionally, soil NOX is not directly emitted and 
involves numerous natural emissions sources and processes. Thus, soil 
NOX emissions are inherently difficult to estimate and 
model. Likewise, given that the production of NOX in the 
soil is complex, it may also be challenging to estimate the effects of 
potential controls. Due to the complexity of estimating soil 
NOX emissions, the partially natural source of the 
emissions, and the uncertainties in the effectiveness of potential 
control measures, the EPA concludes that there is not sufficient 
information available at this time to warrant an evaluation of 
potential controls for soil NOX emissions in the San Joaquin 
Valley for purposes of the BACM analysis for the 1997 annual 
PM2.5 NAAQS. We encourage CARB and the District to continue 
their ongoing efforts to resolve the uncertainties in soil 
NOX emissions and examine any implications for air quality 
modeling and planning.
5. Public Process
    Comment 5: CCEJN asserts that the EPA must disapprove portions of 
the attainment plan for the 1997 annual PM2.5 NAAQS because 
the State did not provide public notice and the opportunity to comment 
on portions of the Plan.
    The commenter identifies two submissions made by CARB in March 2023 
and June 2023 to provide additional information relevant to the 
original SIP submissions comprising the Plan: the March 2023 Ammonia 
Supplement and the March 2023 Building Heating Supplement, discussing 
the ammonia precursor demonstration and the BACM requirement for 
building electrification, and the Title VI Supplement, addressing 
necessary assurances under CAA section 110(a)(2)(E). CCEJN notes that 
CAA section 110(a)(2) requires ``[e]ach implementation plan submitted 
by a State under this chapter shall be adopted by the State after 
reasonable notice and public hearing.'' The commenter states that the 
supplements are ``required contents of such plans'' and notes that the 
EPA's supplemental proposal for the 2012 annual PM2.5 NAAQS 
indicated the EPA's expectation that any Title VI necessary assurances 
would go through state-level notice and comment along with the 
remainder of the Plan.
    Because CARB submitted these supplements directly to the EPA 
without first going through additional public process and after CARB 
had formally submitted the Plan, the commenter asserts that the EPA 
cannot rely upon these supplements to approve the State's precursor 
demonstration, BACM demonstration, or necessary assurances under CAA 
section 110(a)(2)(E)(i).
    Response 5: Generally, the EPA agrees with CCEJN that SIP 
submissions must meet the reasonable notice and public hearing 
requirements of CAA section 110(a)(2). This is a basic requirement for 
SIP submissions that appears in section 110(a)(1), section 110(a)(2), 
and section 110(l), as well as EPA regulations pertaining to the 
completeness of SIP submissions in 40 CFR part 51, Appendix V. However, 
the EPA does not agree that this requirement necessarily applies to all 
information of any type that a state may provide to the EPA. This 
includes such instances as when the state is providing additional 
information to supplement a SIP submission that did previously meet 
notice and public hearing process

[[Page 86602]]

requirements, particularly when the EPA has requested that the state 
provide such additional information to clarify an ambiguity in the 
original SIP submission or to aid the EPA in evaluating adverse 
comments raising an issue related to the original SIP submission.\157\ 
The EPA considers it appropriate to rely on such supplemental 
information, even if it is not in the form of a formal SIP submission 
that underwent full notice and public hearing process, when it expands 
on and confirms information presented in the state's original SIP 
submission or addresses potential deficiencies in the pre-existing 
data.\158\ In such situations, the EPA considers the relevant question 
to be whether the state provided reasonable notice and public hearing 
with respect to the issue as part of the original SIP submission. It 
would be illogical to require a state to restart the entire SIP 
development process and would delay the EPA's action on a SIP 
submission, thereby potentially delaying needed emissions reductions, 
were the Agency to interpret CAA section 110(a)(2) notice and public 
hearing requirements to apply to any and all supplemental information 
provided by state. Thus, the EPA disagrees with CCEJN's assertion that 
it is inappropriate for the Agency to rely on the additional 
information provided by CARB in the two supplements in its analysis of 
the SJV PM2.5 Plan because it would violate the requirement 
under section 110(a)(2) that plans submitted to the EPA for inclusion 
in the SIP must go through ``reasonable notice and public hearing.''
---------------------------------------------------------------------------

    \157\ The EPA has previously explained that it may be 
appropriate to rely on a supplemental letter from a state to resolve 
ambiguities in a SIP submission. See 80 FR 33840, 33888 (June 12, 
2015).
    \158\ See 80 FR 33840, 33888 (``It is the EPA's practice to 
neither require a state to resubmit a SIP submission nor repropose 
action on the submission, so long as the clarification provided in 
the interpretive letter is a logical outgrowth of the proposed SIP 
provision.'').
---------------------------------------------------------------------------

    With respect to the 2023 Ammonia Supplement and the 2023 Building 
Heating Supplement, the EPA believes the information contained therein 
falls within the EPA's discretion to accept as a supplement, as it 
expands upon and confirms information provided in the State's 
previously submitted SIP submissions that did undergo the full notice 
and public hearing process. CARB submitted the supplement to ``support 
action on the attainment plan'' and the supplement was intended as 
``clarifying information'' rather than a formal SIP revision.\159\ 
Also, CARB submitted this information in reaction to prior comments 
related to the EPA's proposed action on the SIP submissions with 
respect to the 2012 annual PM2.5 NAAQS, and in anticipation 
of receiving those same comments in this action. In this respect, CARB 
provided additional information that it anticipated the EPA would 
request to help evaluate the issues raised in such comments.
---------------------------------------------------------------------------

    \159\ Letter dated March 29, 2023, from Steven S. Cliff, 
Executive Officer, CARB, to Martha Guzman, Regional Administrator, 
EPA Region 9, with enclosures.
---------------------------------------------------------------------------

    In the ammonia context, the 2018 PM2.5 Plan and 15 
[micro]g/m\3\ SIP Revision present the fundamental elements of the 
State's demonstration that ammonia does not contribute significantly to 
exceedances of the 1997 annual PM2.5 NAAQS, including 
research that supports its conclusion that ammonium nitrate 
PM2.5 formation in the San Joaquin Valley is NOX-
limited rather than ammonia-limited; \160\ evidence that the area's 
measures targeting VOC reductions are already reducing ammonia; \161\ 
and an analysis of how the District's control measures compare with 
other state's rules and regulations.\162\ Upon initial review of the 
State's submission, and in light of related comments received on 
attainment plans for other PM2.5 NAAQS for the San Joaquin 
Valley, the EPA requested clarifying information and additional 
analysis to support the State's conclusions in the SJV PM2.5 
Plan for the 1997 annual PM2.5 NAAQS.\163\ The information 
and analysis the State provided in the March 2023 Ammonia Supplement 
does not deviate from or fundamentally alter the analysis in the SJV 
PM2.5 Plan; rather, it provides a wide array of potential 
controls and analyses to support the fundamental conclusions in the 
submitted SIP. The EPA believes that CARB provided reasonable notice 
and public hearing on its position with respect to the ammonia 
precursor issue in the initial SIP submission, and the additional 
information in the March 2023 Ammonia Supplement merely expands upon 
that position. Moreover, by taking into account the information that 
CARB provided in that supplement during this rulemaking action, the EPA 
itself has provided the commenters with the opportunity to address that 
supplemental information now.
---------------------------------------------------------------------------

    \160\ 2018 PM2.5 Plan, Appendix G, pp. 9-10; CARB 
December 2018 Staff Report, Appendix C, pp. 12-15; Attachment A to 
CARB's May 9, 2019, submittal letter.
    \161\ 2018 PM2.5 Plan, Appendix C, Section C-25.
    \162\ Id.
    \163\ 40 CFR 51.1010 authorizes the EPA to require supplemental 
information on potential controls when the EPA deems it necessary to 
evaluate the comprehensive precursor demonstration. The regulations 
and EPA guidance do not instruct on what state-level processes this 
supplemental information should go through in being submitted to the 
EPA. See PM2.5 Precursor Demonstration Guidance, p. 31.
---------------------------------------------------------------------------

    Similarly, the building heating BACM demonstration in the 2018 
PM2.5 Plan provides the foundations and analysis for CARB's 
conclusions that the State is implementing BACM with respect to 
building heating appliances. As discussed in Section II.A.4, in 2020, 
the EPA approved this demonstration as meeting BACM for the 2006 24-
hour PM2.5 NAAQS.\164\ However, given comments concerning 
this same issue on an EPA proposal related to the 2018 PM2.5 
Plan with respect to 2012 annual PM2.5 NAAQS, the EPA 
requested that the State support its conclusion with more up-to-date, 
additional analysis.\165\ Like the supplemental information for the 
ammonia precursor demonstration, the March 2023 Building Heating 
Supplement merely provides additional support for the State's original 
analysis and determination that it is implementing BACM for this source 
category in the San Joaquin Valley area. The EPA believes that CARB 
provided reasonable notice and public hearing on its position with 
respect to the building heating and electrification issue during the 
development of initial SIP submission, and the additional information 
in the March 2023 Building Heating Supplement merely expands upon that 
position.
---------------------------------------------------------------------------

    \164\ 85 FR 44192 (July 22, 2020).
    \165\ 87 FR 60494 (October 5, 2022); Comment letter dated and 
received January 28, 2022, from Brent Newell, Public Justice, et 
al., to Rory Mays, EPA Region IX, including Exhibits 1 through 47. 
We note, however, that there is no Exhibit 23; so, there are 46 
exhibits in total. Email dated February 1, 2022, from Brent Newell, 
Public Justice, to Rory Mays, EPA Region IX. The 13 environmental, 
public health, and community organizations are Public Justice, 
Central Valley Environmental Justice Network, Association of 
Irritated Residents, Central Valley Air Quality Coalition, 
Leadership Counsel for Justice and Accountability, Valley 
Improvement Projects, The LEAP Institute, Little Manila Rising, 
Center for Race, Poverty, and the Environment, Central California 
Asthma Collaborative, Animal Legal Defense Fund, National Parks 
Conservation Association, and Food and Water Watch.
---------------------------------------------------------------------------

    Thus, the EPA believes the State provided reasonable notice and 
opportunity for public engagement with respect to its conclusions in 
the ammonia precursor demonstration and building heating BACM elements 
of the SIP and satisfied the reasonable notice and public hearing 
requirements of the CAA.\166\
---------------------------------------------------------------------------

    \166\ The EPA notes that a review of the State's records 
submitted with the SIP indicates that the public did identify these 
two elements prior to and during the public hearing held on the 
State's approval of the SIP in 2021.
---------------------------------------------------------------------------

    With respect to the Title VI Supplement, the EPA acknowledges that

[[Page 86603]]

it provides additional information related to an issue that the State 
did not expressly address during the development of the SJV 
PM2.5 Plan, i.e., the State did not previously engage in 
public process specifically with respect to CAA section 110(a)(2)(E) 
necessary assurances that implementation of the Plan would not be 
prohibited by Title VI. However, in this instance, the issue of 
necessary assurances arose in adverse comments on a related EPA 
proposed action on the same 2018 PM2.5 Plan with respect to 
the 2012 PM2.5 NAAQS.\167\ In order to address the concerns 
raised by the commenter, the EPA sought additional information from the 
State to supplement the SJV PM2.5 Plan by providing 
necessary assurances and CARB provided that information in the Title VI 
Supplement to do so.
---------------------------------------------------------------------------

    \167\ 86 FR 74310 (December 29, 2021). Some of the environmental 
and community organizations that contributed to the adverse comments 
related to necessary assurances on the EPA's proposed SIP action for 
the 2012 annual PM2.5 NAAQS are among the organizations 
that provided the adverse comments on the EPA's proposal for the 
1997 annual PM2.5 NAAQS discussed herein.
---------------------------------------------------------------------------

    In light of prior comments, and the responsiveness of the Title VI 
Supplement to the prior comments, the EPA considers it appropriate to 
rely on the additional information provided by CARB in this way. Going 
forward, as part of developing new SIP submissions, the EPA requests 
that CARB and the District include consideration of issues related to 
compliance with Title VI as part of that process, in order to ensure 
public awareness and engagement. The public notice and comment process 
required for development of SIP submissions provides an opportunity for 
an air agency to share its position on necessary assurances publicly, 
and to develop the record supporting their analysis of CAA section 
110(a)(2)(E)(i) as it pertains to a particular SIP submission. Through 
this process, the EPA expects states to develop adequate necessary 
assurances so that they can be reviewed during the air agency-level 
public comment process and subsequently by the EPA.\168\
---------------------------------------------------------------------------

    \168\ The EPA notes that the content of the Title VI Supplement 
is substantially similar to recent submissions of necessary 
assurances from the State on the attainment plan for the 2015 ozone 
NAAQS (see ``Staff Report, CARB Review of the San Joaquin Valley 
2022 Plan for the 70 ppb 8-Hour Ozone Standard'' (release date: 
December 16, 2022), pp. 21-23). The plan for the 2015 ozone NAAQS, 
which was submitted after the EPA's supplemental proposal on the 
plan for the 2012 annual PM2.5 NAAQS, was made available 
for public review during the State's public comment processes (see 
CARB's ``Notice of Public Meeting to Consider Proposed San Joaquin 
Valley 70 parts per billion Ozone State Implementation Plan,'' dated 
December 16, 2022).
---------------------------------------------------------------------------

B. Comments From Central Valley Air Quality Coalition (CVAQ)

    Comment 6: CVAQ's comments cover many of the same issues as the 
comments from CCEJN. In summary, they assert that the State's plan 
``improperly relies upon faulty emission inventories and modeling data, 
fails to regulate key PM2.5 precursors like ammonia and soil 
NOX, does not analyze the most stringent measures needed for 
attainment, and does nothing to prove State compliance with Title VI of 
the Civil Rights [Act] (Title VI).'' The commenter also notes that the 
two CARB-submitted supplements did not go through the State's public 
process, and that the EPA had an obligation to issue a federal 
implementation plan in January 2021 and has failed to do so.
    Response 6: The EPA has addressed CVAQ's concerns about the 
emissions inventory and modeling data in Response 2.B; ammonia in 
Responses 3.A through 3.D; soil NOX in Responses 2.A and 4; 
MSM in Response 4; Title VI in Responses 1.A and 1.B, Response 5, and 
in Response 7 that follows; and the State's public process in Response 
5 of this document.
    Regarding the EPA's federal implementation plan (FIP) obligation, 
we do not dispute that the EPA has had an obligation to implement a FIP 
for the San Joaquin Valley for the 1997 annual PM2.5 NAAQS 
due to a prior finding of failure to submit the required attainment 
plan. As we explained in the proposed rule, as a result of the EPA's 
December 6, 2018 determination effective January 7, 2019, that 
California had failed to submit the required attainment plan for the 
1997 annual PM2.5 NAAQS, among other required SIP 
submissions for the San Joaquin Valley, the EPA became subject to a 
statutory deadline to promulgate a FIP for this purpose no later than 
two years after the effective date of that determination--i.e., by 
January 7, 2021.\169\ However, as a result of this final rulemaking 
approving all but the contingency measure requirement of the submitted 
Serious area and section 189(d) plan for the 1997 annual 
PM2.5 NAAQS, the only outstanding deficiency for these NAAQS 
relates to contingency measures. We note that CARB has submitted three 
SIP submissions to address the CAA contingency measure requirements for 
the 1997 annual PM2.5 NAAQS (as well as other 
PM2.5 NAAQS) in the San Joaquin Valley, including (1) the 
``PM2.5 Contingency Measure State Implementation Plan 
Revision,'' submitted to the EPA on June 8, 2023; \170\ (2) amendments 
to District Rule 8051 (``Open Areas''), submitted to the EPA on October 
16, 2023; \171\ and (3) the state-wide ``California Smog Check 
Contingency Measure for the State Implementation Plan,'' submitted to 
the EPA on November 13, 2023.\172\ The EPA will act on the contingency 
measure SIP revisions, and/or promulgate a FIP for the contingency 
measure requirement for the 1997 annual PM2.5 NAAQS and 
other NAAQS, in a separate rulemaking.
---------------------------------------------------------------------------

    \169\ 88 FR 45276, 45278.
    \170\ Letter dated June 7, 2023, from Steven S. Cliff, Executive 
Officer, CARB, to Martha Guzman, Regional Administrator, EPA Region 
IX.
    \171\ Letter dated October 13, 2023, from Steven S. Cliff, 
Executive Officer, CARB, to Martha Guzman, Regional Administrator, 
EPA Region IX.
    \172\ Letter dated November 13, 2023, from Steven S. Cliff, 
Executive Officer, CARB, to Martha Guzman, Regional Administrator, 
EPA Region IX.
---------------------------------------------------------------------------

C. Comments From a Private Individual

    Comment 7: The private citizen commenter believes that the State's 
plan contains ``aspirational and misleading `assurances' of compliance 
with the Civil Rights Act'' and that the ``EPA has missed an 
opportunity to live up to the commitments of the Biden administration 
and EPA Administrator Regan to prioritize environmental justice and 
civil rights.''
    In addition, the commenter notes the length of time that has passed 
since the EPA committed to put out guidance on what would constitute 
``necessary assurances'' under the Act and its failure to do so prior 
to accepting the necessary assurances demonstration in the SJV 
PM2.5 Plan for the 1997 annual PM2.5 NAAQS. The 
commenter recommends that a simple interim guidance could include: (1) 
``some sort of equity or environmental justice assessment,'' and (2) 
``consideration of alternative measures to lessen or eliminate any 
potentially discriminatory burdens revealed by that assessment.''
    The commenter provides a short summary of the interaction between 
CAA section 110(a)(2)(E) and Title VI at the EPA, including identifying 
a SIP rulemaking in 1997 where the connection between section 
110(a)(2)(E) and Title VI was raised and a 2012 rulemaking pertaining 
to the San Joaquin Valley on which the EPA received comments about the 
same issue.
    The commenter generally recommends that the EPA exercise its 
discretion in determining what constitutes necessary assurances to 
require more from the State in favor of a more rigorous posture as to 
what constitutes necessary assurances. In doing so, the commenter 
disputes the

[[Page 86604]]

EPA's distinction in its proposal between necessary assurances under 
CAA section 110(a)(2)(E) and a formal finding of compliance with Title 
VI.
    Next, the commenter outlines the contents of CARB's Title VI 
supplement. In particular, the commenter alleges that CARB's Civil 
Rights and Discrimination Process does not have processes or procedures 
for handling a complaint originating from outside of CARB, that the 
policy has been rarely used, and was adopted prior to complaints filed 
at the EPA against CARB for procedural deficiencies in the State's 
policy. Additionally, the commenter believes that neither the EPA nor 
CARB has demonstrated that the State's policy will be implemented in a 
systemic manner to avoid disproportionate effects.
    The commenter asserts that the EPA's approval of the necessary 
assurances conflates the concrete statutory requirements of Title VI 
with policy-based programs and policies of environmental justice. The 
commenter believes that relying on the policy-based environmental 
justice initiatives does not rise to the level of the systematic and 
defined methods of Title VI compliant laws.
    The commenter then describes many of the environmental justice 
resources available to CARB and the EPA in developing and determining 
the adequacy of necessary assurances. The commenter acknowledges that 
the EPA identified many of these resources in its proposal but believes 
the necessary assurances discussion should demonstrate that these 
resources were considered and used in determining whether there is a 
disproportionate effect in a particular SIP-based action.
    Ultimately, based on 2013 EPA guidance on compliance with CAA 
section 110(a)(2)(E) and the terms of conditions under Title VI for 
CARB receiving funding from the EPA, the commenter does not believe 
that CARB submitted a sufficient demonstration that the required Title 
VI compliance programs exist under CARB's purview. In their conclusion, 
the commenter notes that the EPA could conditionally approve the Plan, 
accompanied by an enforceable condition requiring CARB and the District 
to bring their programs into demonstrated compliance with Title VI.
    Response 7: To the extent the comment letter is providing input to 
the EPA on content for a forthcoming guidance document for CAA section 
110(a)(2)(E)(i) with respect to Title VI, such considerations are 
outside the scope of this action.
    As we noted in our proposal, the EPA has discretion with regard to 
what may constitute necessary assurances under CAA section 
110(a)(2)(E)(i). For this action, we believe the State has provided 
adequate necessary assurances to support approval, under these specific 
facts and circumstances. The EPA notes that what constitutes necessary 
assurances for purposes of Title VI for a given SIP submission depends 
upon the facts and circumstances of the Plan, and the Agency may 
require more or different information as needed in other SIP actions. 
This finding does not limit the Agency to review for different factors 
in the future.
    Importantly, as explained in the proposal action, the EPA's 
evaluation of necessary assurances pertains to CAA section 
110(a)(2)(E)(i) compliance with respect to a specific SIP submission, 
and not to Title VI compliance more broadly.\173\ Formal findings of 
compliance with Title VI follow procedures outlined in the CFR after 
administrative complaints are filed with the EPA alleging 
discrimination prohibited by Title VI and the other civil rights 
laws,\174\ or if the EPA initiates an affirmative compliance 
review.\175\ Section 110(a)(2)(E)(i), in contrast, requires a state to 
provide necessary assurances that the state's implementation of the SIP 
submission at issue is not prohibited by federal law, including Title 
VI. As an additional point of clarification, this necessary assurances 
analysis concerning Title VI is distinct from considerations of 
environmental justice more broadly. Title VI involves specific 
considerations of federal law as it pertains to individuals on the 
basis of race, color, or national origin. The language at issue in CAA 
section 110(a)(2)(E)(i) is specific to implementation of the SIP 
submissions and prohibitions under Title VI.
---------------------------------------------------------------------------

    \173\ 88 FR 45276, 45320.
    \174\ 40 CFR 7.120.
    \175\ 40 CFR 7.115.
---------------------------------------------------------------------------

    The EPA separately reviewed information related to environmental 
justice considerations and those considerations are addressed in 
Section IV of this document. The EPA reiterates that in our proposed 
approval of the Plan, the EPA completed a Demographic Index analysis of 
the area subject to the Plan, identifying environmental burdens and 
susceptible populations in disadvantaged communities in the San Joaquin 
Valley nonattainment area. As explained in more detail in Section 
II.A.1 of this document, we believe the State has provided the 
necessary assurances, including information that through its initial 
implementation that the State has meaningfully considered input from 
the public through public outreach that is beyond the minimum legal 
requirements for public comment during SIP development, and that the 
Plan submission complies with CAA section 110(a)(2)(E)(i).
    With respect to the ``EPA's processing prior (to this 2023 action 
but subsequent to the 2016 policy) complaints against CARB and in which 
it had noted several procedural deficiencies,'' the EPA is not aware of 
any complaints filed against CARB within that time period regarding 
CARB's Civil Rights and Discrimination Complaint Process, and no 
complaint was specifically cited to by the commenter.\176\ The EPA 
notes that it publishes all external civil rights complaints and 
compliance reviews online.\177\
---------------------------------------------------------------------------

    \176\ On June 6, 2016, the EPA resolved a civil rights complaint 
filed against CARB and the Bay Area Air Quality Management District. 
After an investigation by the EPA's Office of Civil Rights (OCR), 
the Agency found ``insufficient evidence of current non-compliance 
with Title VI or EPA' s Title VI regulation'' and closed the 
complaint. In the letter closing the complaint, the EPA notes that 
``OCR has provided technical assistance to CARB to improve the 
elements of its non-discrimination program,'' including improvements 
to CARB's Civil Rights and Discrimination Complaint Process. The 
closure letter specifically found ``CARB has also adopted a 
grievance procedure that is contained in the Civil Rights Policy and 
Discrimination Complaint Process that provides complainants a prompt 
and impartial investigation of and response to complaints filed with 
CARB alleging discrimination in CARB's programs or activities 
prohibited by the federal non-discrimination statutes.'' The EPA 
does not believe this complaint resolution and the conclusions 
therein conflicts with the determinations in this final action. 
https://www.epa.gov/sites/default/files/2016-06/documents/2r-00-r9_carb_resolution_letter.pdf.
    \177\ EPA, External Civil Rights Docket, https://www.epa.gov/external-civil-rights/external-civil-rights-docket-2014-present.
---------------------------------------------------------------------------

III. Motor Vehicle Emissions Budgets and Transportation Conformity

    The EPA previously determined that the 2020 and 2023 motor vehicle 
emissions budgets in the 15 [micro]g/m\3\ SIP Revision were adequate 
for use in transportation conformity findings. In a letter dated 
February 1, 2022, the EPA notified CARB and other agencies involved in 
the interagency consultation process in the San Joaquin Valley that we 
had reviewed the 2020 RFP and 2023 attainment year budgets in the 15 
[micro]g/m\3\ SIP Revision and found that they are adequate for 
transportation conformity purposes.\178\ The EPA announced the 
availability of the budgets and notified the public of the adequacy 
finding via a Federal Register

[[Page 86605]]

notice on February 10, 2022.\179\ This adequacy finding became 
effective on February 25, 2022 and the budgets have been used in 
transportation conformity determinations in the San Joaquin Valley area 
since that date.
---------------------------------------------------------------------------

    \178\ Letter dated February 1, 2022, from Matthew Lakin, Acting 
Director, Air and Radiation Division, EPA Region IX, to Richard 
Corey, Executive Officer, CARB.
    \179\ 87 FR 7834 (February 10, 2022).
---------------------------------------------------------------------------

    The EPA proposed approval of these same budgets, shown in Table 1 
of this document, on July 14, 2023.180 181 The Plan 
establishes separate direct PM2.5 and NOX subarea 
budgets, based on EMFAC2014, for each county, and partial county (for 
Kern County), in the San Joaquin Valley.\182\ The EPA discussed the 
State's evaluation of the significance/insignificance factors for 
ammonia, SO2, and VOC, and re-entrained road dust emissions 
in the proposed rule.\183\ In this action, the EPA is finalizing 
approval of the State's demonstration that emissions of ammonia, 
SO2, and VOCs do not contribute significantly to 
PM2.5 levels that exceed the 1997 annual PM2.5 
NAAQS in the San Joaquin Valley. Therefore, consistent with the 
transportation conformity regulation,\184\ motor vehicle emissions 
budgets are not required for transportation-related emissions of 
ammonia, SO2, and VOC for purposes of the 1997 annual 
PM2.5 NAAQS in the San Joaquin Valley. In addition, since 
neither the State nor the EPA has made a finding that re-entrained road 
dust emissions are significant, under 40 CFR 93.103(b)(3) and 
93.122(f), re-entrained road dust emissions are not required to be 
included in the budgets for 1997 annual PM2.5 NAAQS in the 
San Joaquin Valley.
---------------------------------------------------------------------------

    \180\ 88 FR 45276, 45322.
    \181\ The EPA did not receive any comments related to our 
proposed approval of the motor vehicle emissions budgets during the 
30-day comment period.
    \182\ 40 CFR 93.124(c) and (d).
    \183\ 88 FR 45276, 45316-45317.
    \184\ 40 CFR 93.102(b)(2)(v).

       Table 1--Motor Vehicle Emissions Budgets for the San Joaquin Valley for the 1997 Annual PM2.5 NAAQS
                                         [Annual average, tons per day]
----------------------------------------------------------------------------------------------------------------
                                                 2020 (RFP year)                   2023 (attainment year)
               County                ---------------------------------------------------------------------------
                                            PM2.5               NOX               PM2.5               NOX
----------------------------------------------------------------------------------------------------------------
Fresno..............................                0.9               25.3                0.8               15.1
Kern................................                0.8               23.3                0.7               13.3
Kings...............................                0.2                4.8                0.2                2.8
Madera..............................                0.2                4.2                0.2                2.5
Merced..............................                0.3                8.9                0.3                5.3
San Joaquin.........................                0.6               11.9                0.6                7.6
Stanislaus..........................                0.4                9.6                0.4                6.1
Tulare..............................                0.4                8.5                0.4                5.2
----------------------------------------------------------------------------------------------------------------
Source: 15 [micro]g/m\3\ SIP Revision, Appendix D, Table 18. Budgets are rounded up to the nearest tenth of a
  ton.

    For the reasons discussed in Sections IV.D and IV.E of the proposed 
rule, the EPA is approving the attainment, RFP, and 5 percent 
demonstrations, respectively, in the SJV PM2.5 Plan. The 
2020 RFP and 2023 attainment year budgets are consistent with these 
demonstrations, are clearly identified and precisely quantified, and 
meet all other applicable statutory and regulatory requirements 
including the adequacy criteria in 40 CFR 93.118(e)(4) and (5). For 
these reasons, the EPA is finalizing approval of the 2020 and 2023 
budgets listed in Table 1 of this document.
    The Plan also included budgets for direct PM2.5 and 
NOX emissions for 2017 (RFP milestone year) and 2026 (post-
attainment quantitative milestone year). We are not approving the 2017 
budgets \185\ or the post-attainment year 2026 budgets at this time. 
Although the post-attainment year quantitative milestone is a required 
element of the Serious area plan, it is not necessary to demonstrate 
transportation conformity for 2026 or to use the 2026 budgets in 
transportation conformity determinations until such time as the area 
fails to attain the 1997 annual PM2.5 NAAQS. Therefore, the 
EPA is not taking action on the submitted budgets for 2026 in the SJV 
PM2.5 Plan at this time. However, if the EPA determines that 
the San Joaquin Valley has failed to attain the 1997 annual 
PM2.5 NAAQS by the applicable attainment date, the EPA would 
begin the budget adequacy and approval processes under 40 CFR 93.118 
for the 2026 post-attainment year budgets concurrent with such 
determination that the area failed to attain.
---------------------------------------------------------------------------

    \185\ We are not approving the 2017 budgets because such budgets 
would not be used in any future transportation conformity 
determination because the Plan includes budgets for 2020.
---------------------------------------------------------------------------

Conformity Trading Mechanism
    Also on July 14, 2023, the EPA proposed to approve a trading 
mechanism for transportation conformity analyses that would allow the 
MPOs in the area to use future decreases in NOX emissions 
from on-road mobile sources to offset any on-road increases in direct 
PM2.5 emissions as allowed for under 40 CFR 
93.124(b).186 187 As described in the proposed rule, the EPA 
reviewed the trading mechanism and found it is appropriate for 
transportation conformity purposes in the San Joaquin Valley for the 
1997 annual PM2.5 NAAQS.\188\ The methodology for estimating 
the trading ratio for conformity purposes is essentially an update 
(based on newer modeling) to the State's approach, approved in the 
previous plan, to model the effect of areawide direct PM2.5 
and NOX emissions reductions on ambient PM2.5, 
and to express the ratio of these modeled sensitivities as an inter-
pollutant trading ratio.
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    \186\ 88 FR 45276, 45322.
    \187\ The EPA did not receive any comments related to our 
proposed approval of the trading mechanism for transportation 
conformity during the 30-day comment period.
    \188\ 88 FR 45276, 45318-45319.
---------------------------------------------------------------------------

    In a previous action on the 2018 PM2.5 Plan for the 2012 
annual PM2.5 NAAQS, we found that the State's approach is a 
reasonable method to use to develop ratios for transportation 
conformity purposes and approved the 6.5 to 1 NOX to 
PM2.5 trading mechanism as an enforceable component of the 
transportation conformity program for the San Joaquin Valley for the 
2012 PM2.5 NAAQS.\189\ Here, we similarly find that the 
State's approach is reasonable and are approving the 6.5 to 1 
NOX for PM2.5 trading mechanism as enforceable 
components of the

[[Page 86606]]

transportation conformity program for the San Joaquin Valley for the 
1997 annual PM2.5 NAAQS. This trading ratio replaces the 9 
to 1 NOX to PM2.5 trading ratio approved for the 
San Joaquin Valley for analysis years after 2014 for the 1997 annual 
PM2.5 NAAQS.\190\
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    \189\ See 86 FR 49100, 49128 (September 1, 2021) (proposed rule) 
and 86 FR 67343, 67346 (November 26, 2021) (final rule).
    \190\ 76 FR 69896.
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IV. Environmental Justice Considerations

    As described in detail in our proposal, the EPA reviewed 
environmental and demographic data for the San Joaquin Valley using the 
EPA's environmental justice (EJ) screening and mapping tool 
(``EJSCREEN''),191 192 and compared the data to the 
corresponding data for the United States as a whole. The results of the 
analysis are provided for informational and transparency purposes.
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    \191\ EJSCREEN provides a nationally consistent dataset and 
approach for combining environmental and demographic indicators. 
EJSCREEN is available at https://www.epa.gov/ejscreen/what-ejscreen. 
The EPA used EJSCREEN to obtain environmental and demographic 
indicators representing each of the eight counties in the San 
Joaquin Valley. These indicators are included in EJSCREEN reports 
that are available in the rulemaking docket for this action.
    \192\ EPA Region IX, ``EJSCREEN Analysis for the Eight Counties 
of the San Joaquin Valley Nonattainment Area,'' August 2022.
---------------------------------------------------------------------------

    This final action approves the State's plan for attaining the 1997 
annual PM2.5 NAAQS. Information on the 1997 annual 
PM2.5 NAAQS and its relationship to health impacts can be 
found at 62 FR 38652 (July 18, 1997). We expect that this action and 
resulting emissions reductions will generally be neutral or contribute 
to reduced environmental and health impacts on all populations in the 
San Joaquin Valley, including people of color and low-income 
populations. At a minimum, this action would not worsen existing air 
quality and is expected to ensure the area is meeting requirements to 
attain and/or maintain air quality standards. Further, there is no 
information in the record indicating that this action is expected to 
have disproportionately high or adverse human health or environmental 
effects on a particular group of people.

V. Final Action

    For the reasons discussed in this final rule, the proposed rule, 
and the related technical support documents, under CAA section 
110(k)(3), the EPA is approving the portions of the SJV 
PM2.5 Plan as meeting CAA requirements for implementation of 
the 1997 annual PM2.5 NAAQS as follows:
    (1) We are finding that the 2013 base year emissions inventories 
continue to satisfy the requirements of CAA section 172(c)(3) and 40 
CFR 51.1008 for purposes of both the Serious area and the CAA section 
189(d) attainment plans, and to find that the forecasted inventories 
for the years 2017, 2018, 2019, 2020, 2023, and 2026 provide an 
adequate basis for the BACM, RFP, five percent, and modeled attainment 
demonstration analyses;
    (2) We are approving the following elements as meeting the Serious 
nonattainment area planning requirements:
    (a) the BACM/BACT demonstration as meeting the requirements of CAA 
section 189(b)(1)(B) and 40 CFR 51.1010(a);
    (b) the demonstration (including air quality modeling) that the 
Plan provides for attainment as expeditiously as practicable as meeting 
the requirements of CAA sections 179(d) and 189(b) and 40 CFR 
51.1011(b);
    (c) the RFP demonstration as meeting the requirements of CAA 
sections 172(c)(2) and 171(1) and 40 CFR 51.1012; and
    (d) the quantitative milestone demonstration as meeting the 
requirements of CAA section 189(c) and 40 CFR 51.1013;
    (3) We are approving the following elements as meeting the CAA 
section 189(d) planning requirements:
    (a) the BACM/BACT demonstration as meeting the requirements of CAA 
sections 189(a)(1)(C) \193\ and 189(b)(1)(B) and 40 CFR 51.1010(c);
---------------------------------------------------------------------------

    \193\ As discussed in Section III.B of the proposal, a section 
189(d) plan must address any outstanding Moderate or Serious area 
requirements that have not previously been approved. Because we have 
not previously approved a subpart 4 RACM demonstration for the San 
Joaquin Valley nonattainment area, we also proposed to approve the 
BACM/BACT demonstration in the SJV PM2.5 Plan as meeting 
the subpart 4 RACM/RACT requirement for the area (88 FR 45276, 
45322).
---------------------------------------------------------------------------

    (b) the demonstration that the Plan will, at a minimum, achieve an 
annual five percent reduction in emissions of NOX as meeting 
the requirements of CAA section 189(d) and 40 CFR 51.1010(c);
    (c) the demonstration (including air quality modeling) that the 
Plan provides for attainment as expeditiously as practicable as meeting 
the requirements of CAA sections 179(d) and 189(d) and 40 CFR 
51.1011(b);
    (d) the RFP demonstration as meeting the requirements of CAA 
sections 172(c)(2) and 171(1) and 40 CFR 51.1012; and
    (e) the quantitative milestone demonstration as meeting the 
requirements of CAA section 189(c) and 40 CFR 51.1013;
    (4) We are approving the motor vehicle emissions budgets for 2020 
and 2023 as shown in Table 1 of this final rulemaking because they are 
derived from approvable RFP and attainment demonstrations and meet the 
requirements of CAA section 176(c) and 40 CFR part 93, subpart A; and
    (5) We are approving the trading mechanism provided for use in 
transportation conformity analyses for the 1997 annual PM2.5 
NAAQS, in accordance with 40 CFR 93.124(b).
    As discussed in Section I.B of the proposal, on November 26, 2021, 
the EPA partially approved and partially disapproved portions of the 
2018 PM2.5 Plan that addressed attainment of the 1997 annual 
PM2.5 NAAQS in the San Joaquin Valley nonattainment area. 
The elements that the EPA disapproved include the attainment 
demonstration, comprehensive precursor demonstration, five percent 
annual emissions reductions demonstration, BACM demonstration, RFP 
demonstration, quantitative milestones, motor vehicle emissions 
budgets, and contingency measures. This disapproval was effective on 
December 27, 2021. In a separate final partial approval and partial 
disapproval action, also effective December 27, 2021, the EPA 
disapproved the contingency measure element of the 2018 
PM2.5 Plan as it relates to the requirements for the Serious 
area plan 2006 24-hour PM2.5 NAAQS and the Moderate area 
plan for the 2012 annual PM2.5 NAAQS.\194\
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    \194\ 86 FR 67343.
---------------------------------------------------------------------------

    In our November 26, 2021 final disapprovals, we noted that offset 
and highway sanctions under CAA sections 179(b)(2) and 179(b)(1), 
respectively, would not apply if California submits, and the EPA 
approves, a SIP submission that corrects all of the deficiencies 
identified in our final actions prior to the imposition of 
sanctions.\195\ Through this final approval action, we find that 
California has corrected the deficiencies associated with the Serious 
area and CAA section 189(d) SIP elements for the 1997 annual 
PM2.5 NAAQS for the San Joaquin Valley (except for the 
contingency measures element). Thus, upon the effective date of this 
final rule, all sanctions and any sanctions clocks associated with the 
Serious area and CAA section 189(d) SIP elements for the 1997 annual 
PM2.5 NAAQS for the San Joaquin Valley (except the 
contingency measures element) will be permanently terminated.
---------------------------------------------------------------------------

    \195\ 86 FR 67329.
---------------------------------------------------------------------------

    This final action does not address the prior disapprovals of the 
contingency measure elements for the 1997 annual

[[Page 86607]]

PM2.5 NAAQS, the 2006 24-hour PM2.5 NAAQS, and 
the 2012 annual PM2.5 NAAQS. Therefore, all sanctions and 
any sanctions clocks associated with the disapprovals of the 
contingency measure elements for those standards will continue to apply 
in the San Joaquin Valley as outlined in the November 26, 2021 final 
disapprovals unless or until the EPA approves a SIP submission or 
submissions meeting the outstanding contingency measure requirements 
for these NAAQS. As discussed in Response 6, CARB has submitted three 
SIP submissions to address the CAA contingency measure requirements for 
the 1997 annual PM2.5 NAAQS, the 2006 24-hour 
PM2.5 NAAQS, and the 2012 annual PM2.5 NAAQS in 
the San Joaquin Valley. The EPA will act on these submissions and 
determine the effects on the sanctions, if any, in accordance with 40 
CFR 52.31 through one or more separate rulemaking actions.

VI. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a 
SIP submission that complies with the provisions of the Act and 
applicable federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). 
Thus, in reviewing SIP submissions, the EPA's role is to review state 
choices, and approve those choices if they meet the minimum criteria of 
the Act. Accordingly, this final action merely approves State law as 
meeting federal requirements and does not impose additional 
requirements beyond those imposed by State law. For that reason, this 
action:
     Is not a significant regulatory action subject to review 
by the Office of Management and Budget under Executive Orders 12866 (58 
FR 51735, October 4, 1993) and 14094 (88 FR 21879, April 11, 2023);
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not subject to Executive Order 13045 (62 FR 19885, 
April 23, 1997) because it approves a State program;
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001); and
     Is not subject to requirements of Section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the Clean Air Act.
    In addition, the SIP is not approved to apply on any Indian 
reservation land or in any other area where the EPA or an Indian tribe 
has demonstrated that a tribe has jurisdiction. In those areas of 
Indian country, the rule does not have tribal implications and will not 
impose substantial direct costs on tribal governments or preempt tribal 
law as specified by Executive Order 13175 (65 FR 67249, November 9, 
2000).
    Executive Order 12898 (Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations, 59 FR 7629, 
Feb. 16, 1994) directs federal agencies to identify and address 
``disproportionately high and adverse human health or environmental 
effects'' of their actions on minority populations and low-income 
populations to the greatest extent practicable and permitted by law. 
The EPA defines environmental justice (EJ) as ``the fair treatment and 
meaningful involvement of all people regardless of race, color, 
national origin, or income with respect to the development, 
implementation, and enforcement of environmental laws, regulations, and 
policies.'' The EPA further defines the term fair treatment to mean 
that ``no group of people should bear a disproportionate burden of 
environmental harms and risks, including those resulting from the 
negative environmental consequences of industrial, governmental, and 
commercial operations or programs and policies.''
    The State did not evaluate environmental justice considerations as 
part of its SIP submittal; the CAA and applicable implementing 
regulations neither prohibit nor require such an evaluation. The EPA's 
evaluation of environmental justice is described in the section of this 
document titled, ``Environmental Justice Considerations.'' The analysis 
was done for the purpose of providing additional context and 
information about this rulemaking to the public, not as a basis of the 
action. Due to the nature of the action being taken here, this action 
is expected to have a neutral to positive impact on the air quality of 
the affected area. In addition, there is no information in the record 
upon which this decision is based that is inconsistent with the stated 
goal of E.O. 12898 of achieving environmental justice for people of 
color, low-income populations, and Indigenous peoples.
    This action is subject to the Congressional Review Act, and the EPA 
will submit a rule report to each House of the Congress and to the 
Comptroller General of the United States. This action is not a ``major 
rule'' as defined by 5 U.S.C. 804(2).
    Under section 307(b)(1) of the Clean Air Act, petitions for 
judicial review of this action must be filed in the United States Court 
of Appeals for the appropriate circuit by February 12, 2024. Filing a 
petition for reconsideration by the Administrator of this final rule 
does not affect the finality of this action for the purposes of 
judicial review nor does it extend the time within which a petition for 
judicial review may be filed, and shall not postpone the effectiveness 
of such rule or action. This action may not be challenged later in 
proceedings to enforce its requirements. (See section 307(b)(2).)

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Particulate matter, Reporting and recordkeeping 
requirements.

    Authority: 42 U.S.C. 7401 et seq.

    Dated: December 5, 2023.
Martha Guzman Aceves,
Regional Administrator, Region IX.

    Part 52, chapter I, title 40 of the Code of Federal Regulations is 
amended as follows:

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for Part 52 continues to read as follows:

    Authority: 42 U.S.C. 7401 et seq.

Subpart F--California

0
2. Section 52.220 is amended by adding paragraphs (c)(537)(ii)(A)(9) 
and (10) and (c)(537)(ii)(B)(7), (8), and (9) to read as follows:


Sec.  52.220  Identification of plan--in part.

* * * * *
    (c) * * *
    (537) * * *
    (ii) * * *
    (A) * * *
    (9) CARB Resolution No. 21-21, September 23, 2021, submitted as a 
revision to the 2018 PM2.5 Plan on

[[Page 86608]]

November 8, 2021, by the Governor's designee.
    (10) ``Staff Report, Proposed SIP Revision for the 15 [mu]g/m\3\ 
Annual PM2.5 Standard for the San Joaquin Valley,'' August 
13, 2021, submitted as a revision to the 2018 PM2.5 Plan on 
November 8, 2021, by the Governor's designee.
    (B) * * *
    (7) 2018 Plan for the 1997, 2006, and 2012 PM2.5 
Standards (``2018 PM2.5 Plan''), adopted November 15, 2018 
(portions pertaining to the 1997 annual PM2.5 NAAQS only, 
and excluding Chapter 4 (``Attainment Strategy for PM2.5''), 
Chapter 5 (``Demonstration of Federal Requirements for 1997 
PM2.5 Standards''), Chapter 6 (``Demonstration of Federal 
Requirements for 2006 PM2.5 Standards''), Chapter 7 
(``Demonstration of Federal Requirements for 2012 PM2.5 
Standards''), Appendix D (``Mobile Source Control Measure Analyses''), 
Appendix H (``RFP, Quantitative Milestones, and Contingency''), and 
Appendix K (``Modeling Attainment Demonstration'')).
    (8) ``Attainment Plan Revision for the 1997 Annual PM2.5 
Standard,'' August 19, 2021, excluding Appendix H, section H.3 
(``Contingency Measures''), submitted as a revision to the 2018 
PM2.5 Plan on November 8, 2021, by the Governor's designee.
    (9) SJVUAPCD Governing Board Resolution No. 21-08-13, August 19, 
2021, submitted as a revision to the 2018 PM2.5 Plan on 
November 8, 2021, by the Governor's designee.
* * * * *

0
3. Section 52.237 is amended by revising paragraph (a)(11) to read as 
follows:


Sec.  52.237  Part D disapproval.

    (a) * * *
    (11) The contingency measures portion of the 2018 Plan for the 
1997, 2006, and 2012 PM2.5 Standards (``2018 
PM2.5 Plan''), adopted November 15, 2018, are disapproved 
for San Joaquin Valley with respect to the 1997 annual PM2.5 
NAAQS because they do not meet the requirements of Part D of the Clean 
Air Act.
* * * * *

0
4. Section 52.244 is amended by adding paragraph (f)(4) to read as 
follows:


Sec.  52.244  Motor vehicle emissions budgets.

* * * * *
    (f) * * *
    (4) San Joaquin Valley, for the 1997 annual PM2.5 NAAQS 
only (years 2020 and 2023 budgets only), approved January 16, 2024.

[FR Doc. 2023-27088 Filed 12-13-23; 8:45 am]
BILLING CODE 6560-50-P