Federal Register / Vol. 88, No. 239 / Thursday, December 14, 2023 / Rules and Regulations 86581 

1 88 FR 45276. 

2 81 FR 84481 (November 23, 2016). 

3The 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. 4The Valley State SIP Strategy was adopted by 

CARB on October 25, 2018. 5The ‘‘15 mg/m3 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. 

SUPPLEMENTARY INFORMATION: The Coast 

Guard will enforce a safety zone for the 

Crescent City Countdown Club/New 

Year’s Celebration fireworks display 

from 11:30 p.m. on December 31, 2023, 

through 12:30 a.m. on January 1, 2024, 

to provide for the safety of life on the 

navigable waterways during this event. 

Our regulation for annual fireworks 

displays and other events in the Eighth 

Coast Guard District, 33 CFR 165.801 

identifies this safety zone on the Lower 

Mississippi River MM 93.5–96.5, New 

Orleans, LA. During this enforcement 

period, as reflected in § 165.801(a) 

through (d), entry into this zone is 

prohibited unless authorized by the 

Captain of the Port or a designated 

representative. 

In addition to this notification of 

enforcement in the Federal Register, the 

Coast Guard plans to provide 

notification of this enforcement period 

via Marine Safety Information Bulletin 

and Broadcast Notice to Mariners. 

Dated: December 11, 2023. 

K.K. Denning, 

Captain, U.S. Coast Guard, Captain of the 

Port Sector New Orleans. 

[FR Doc. 2023–27507 Filed 12–13–23; 8:45 am] 

BILLING CODE 9110–04–P 

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. 

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 

graham.ashleyr@epa.gov. 

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

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 mg/m3 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 mg/ 

m3 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. 

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 

mg/m3 Annual PM2.5 Standard, March 


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6Letter 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 mg/m3 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 

mg/m3 Annual PM2.5 Standard’’ (‘‘District Title VI 

Supplement’’). 

7As 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). 

8On 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. 

9An adequacy finding for the 2020 and 2023 

motor vehicle emissions budgets was effective on 

February 25, 2022. (87 FR 7834, February 10, 2022). 

10Comment 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. 

11Comment 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. 

12Comment letter dated and received August 14, 

2023, from Richard Grow, to Docket ID No. EPA– 

R09–OAR–2023–0263. 

13 88 FR 45276, 45319–45321. 

14See El Comite ́ para el Bienestar de Earlimart et 

al. v. EPA, 786 F.3d 688 (9th Cir. 2015) (‘‘El Comite ́

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 Comite ́’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. 

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

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

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. 

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

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 


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17See El Comite ́ 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.’’) 18 88 FR 45276, 45320. 19See id. 20See, e.g., https://www.epa.gov/external-civilrights/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. 21Title VI Supplement, p. 8. 

final rulemaking is consistent with CAA 

section 110(a)(2)(E)(i).17

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). 

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 mg/m3

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. 

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 


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22 88 FR 45276, 45320. See also, El Comite ́ para 

el Bienestar de Earlimart et al. v. EPA, 786 F.3d 688 

(9th Cir. 2015). 

23Almaraz et al. (2018), Agriculture is a major 

source of NOX pollution in California, Science 

Advances, 4(1), 2018, doi:10.1126/sciadv.aao3477. 

24Sha 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. 

25Luo 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. 

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. 

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 mg/m3 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. 

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 


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Federal Register / Vol. 88, No. 239 / Thursday, December 14, 2023 / Rules and Regulations 86585 

26SJVUAPCD, 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). 

27Email 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. 

29Oikawa 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. 

30Parrish 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. 

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. 

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. 

For the SJV PM2.5 Plan, the State used 

the DeNitrification-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. 

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. 

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. 

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 


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32 Id. at 60 and 63. 

33 Id. at 77. 

34Chen 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. 

35Wang 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. 

37Luo 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. 

38Wang 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. 

39Almaraz 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. 

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. 

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 surfacebased 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 lowNO2 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. 

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. 

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. 

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. 

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 


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41Sha 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. 

42The EPA also compared these studies in 

approving California’s 2020 emissions inventory 

submittal. 87 FR 59015, 59017–59019 (February 9, 

2022). 

43Wang et al. (2021), op. cit. 

44Wang et al. (2023), op. cit. 

45The EPA reached a similar conclusion in 

approving California’s 2020 emissions inventory 

submittal. 87 FR 59015, 59017–59019 (February 9, 

2022). 

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 nitrogenand carbon-containing species, 

moisture, and temperature. 

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. 

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 


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46 88 FR 45276, 45279. 

47The 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. 

49 Id. at 67332–67334. 

50CARB, ‘‘Staff Report, Proposed SIP Revision for 

the 15 mg/m3 Annual PM2.5 Standard for the San 

Joaquin Valley,’’ release date August 13, 2021. 

51 88 FR 45276, 45284–45285. 52 Id. 53The EPA approved the use of EMFAC2021 for 

use in SIP development on November 15, 2022 (87 

FR 68483). 54EPA, ‘‘Technical Support Document, San 

Joaquin Valley PM2.5 Plan Revision for the 1997 

Annual PM2.5 NAAQS,’’ April 2023. 55 Id. at 53. 56Spreadsheet ‘‘EMFAC update effect on annual 

1997 p.m.2.5 NAAQS attainment 

demonstration.xlsx,’’ EPA Region IX, May 1, 2023. 57 Id. 

provided an accurate, up-to-date 

emissions inventory for NOX. 

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 alreadylax 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 EPAapproved’ 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

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 mg/m3 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. 

Given that the 15 mg/m3 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 EPAapproved 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. 

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 mg/m3 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 


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58Sierra 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)). 

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. 

62PM2.5 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. 

66 81 FR 58010 (August 24, 2016). 

67 40 CFR 51.1006; EPA’s PM2.5 Precursor 

Demonstration Guidance. 

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 EPAapproved 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. 

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

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 mg/m3 EPArecommended 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. 

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. 

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


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68Parrish, 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. 

70Memorandum 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.’’ 

Plan in accordance with these 

requirements. 

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. 

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. 

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 


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71Email 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. 

73CARB’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. 

74Lurmann 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. 

75Nitric 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. 

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. 

77CARB, ‘‘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). 

79Prabhakar 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. 

80Parworth 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). 

81CalNex, or California Research at the Nexus of 

Air Quality and Climate Change, was a NOAAsponsored 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). 

82The 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 

Continued 

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. 

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 ammonialimited. 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). 

Consistent with CRPAQS, aircraftborne 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 


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86592 Federal Register / Vol. 88, No. 239 / Thursday, December 14, 2023 / Rules and Regulations 

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. 

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). 

85 88 FR 45276, 45288–45290. 

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. 

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

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. 

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 


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Federal Register / Vol. 88, No. 239 / Thursday, December 14, 2023 / Rules and Regulations 86593 

86Pan, 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. 

87Ti 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. 

89March 2023 Ammonia Supplement, p. 94. 

90Association of Equipment Manufacturers, The 

Environmental Benefits of Precision Agriculture in 

the United States, https://newsroom.aem.org/ 

download/977839/environmentalbenefitsof

precisionagriculture-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. 

92E.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. 

94Eory, 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. 

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. 

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

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. 

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 


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86594 Federal Register / Vol. 88, No. 239 / Thursday, December 14, 2023 / Rules and Regulations 

95March 2023 Ammonia Supplement, p. 92. 

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. 

97Pan 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. 

99Pan et al. (2016) op. cit., p. 284. 

100 Id. at p. 286. 

101Ti 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=MitigationMethodsUser

GuideDecember2011FINAL.pdf, p. 52. 

103Association of Equipment Manufacturers, The 

Environmental Benefits of Precision Agriculture in 

the United States, https://newsroom.aem.org/

download/977839/environmentalbenefits

ofprecisionagriculture-2.pdf. 

104Whitmore J. (2019) Precision Farming Comes 

into Its Own, Mich. St. Univ., https://www.canr.

msu.edu/news/precision-farming-comes-into-itsown. 

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 predetermine 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. 

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. 

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.’’ 

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. 

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 


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105Lowenberg-DeBoer, J. and Erickson, B. (2019) 

Setting the Record Straight on Precision Agriculture 

Adoption, Agronomy J., p. 1565. 

106 Id. at 1552. 

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

op. cit. 

108 2018 PM2.5 Plan, Appendix C, pp. C–339 to C– 

341. 109March 2023 Ammonia Supplement, p. 92. 

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

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: 

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. 

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 


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110March 2023 Ammonia Supplement, Figure 5 

(showing that dairy cattle account for an estimated 

67.2 percent of ammonia emissions from CAFs). 

111 2018 PM2.5 Plan, Appendix C, pp. C–312 to C– 

323. 

112 Id.; March 2023 Ammonia Supplement, pp. 

25–26. 

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). 

114Whitmore (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, 

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. 

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

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. 

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 


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save time and money, and reduce environmental 

impacts. 116Lowenberg-DeBoer and Erickson (2019) op. 

cit., p. 1552. 117 Id. at 1564–1565. 118Whitmore (2019) op. cit. 

119 88 FR 45276, 45293, fn. 184. 

120 Kelly, J.T. et al. (2018), op. cit. 

121PM2.5 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. 

123Spreadsheet ‘‘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 mg/m3 SIP Revision, Appendix K, Table 33. 

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. 

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 

mg/m3 cannot accurately describe 2023 

conditions given that 2022 data show a 

design value well above 16 mg/m3. 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 mg/m3 for 2024 and 0.27 mg/ 

m3 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 mg/m3

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. 

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 mg/m3 down to 0.12 mg/m3. (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. 

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 mg/m3 by using a NOX emissionsbased interpolation between the Plan’s 

2018 and 2023 design values, 16.3 and 

14.7 mg/m3, 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 mg/m3, which is above the 

level of the 1997 annual PM2.5 NAAQS 


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125Spreadsheet ‘‘Estimated 2023 annual PM2.5

ammonia sensitivity and 2022 DV.xlsx,’’ ‘‘Whether 

30% ammonia reduction could attain early,’’ EPA 

Region IX, October 20, 2023. 

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. 

128EPA, ‘‘Technical Support Document, EPA 

Evaluation of Air Quality Modeling, San Joaquin 

Valley PM2.5 Plan for the 2006 PM2.5 NAAQS,’’ 

February 2020. 

129The issue of how model predictions may not 

match monitor observations despite a wellperforming 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). 

(i.e., 15.0 mg/m3). Thus, we conclude 

that ammonia emissions reductions 

would not have resulted in attainment 

before the Plan’s projected 2023 

attainment date. 

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 mg/m3 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. 

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 mg/m3 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 mg/m3

(reported as 0.27 mg/m3). Using baseline 

NOX emissions (153.6 tpd), the 

estimated 2023 response is 0.275 mg/m3, 

which is about 0.01 mg/m3 higher. Thus, 

the difference between using the 

baseline or controlled emissions for 

assessing the sensitivity to ammonia 

emissions reductions is negligible. 

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. 

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 mg/m3.’’ The commenter 

acknowledges that the State’s approach 

of using a 0.25 mg/m3 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 alreadyoutdated 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 mg/m3 is 

appropriate for the 2012 annual PM2.5

NAAQS of 12.0 mg/m3, and 0.25 mg/m3

is appropriate for the 1997 annual PM2.5

NAAQS of 15.0 mg/m3. 

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


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130PM2.5 Precursor Demonstration Guidance, p. 

17, fn. 20. 

131EPA, ‘‘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-ozoneand-fine-particles, https://www.epa.gov/sites/ 

default/files/2018-04/documents/ozone_pm2.5_

sils_technical_document_final_4-17-18.pdf. 

132Technical Basis Document, p. 26. 

133 Id. at 39. 

134 81 FR 58010, 58094. 

135EPA, ‘‘Response to Comments on the Fine 

Particulate Matter National Ambient Air Quality 

Standards: State Implementation Plan 

Requirements,’’ July 29, 2016. 

136 88 FR 45276, 45280, fn. 57. 

137 Id. at 45277. 

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

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 mg/m3) and the 2012 annual 

NAAQS (12 mg/m3). 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 mg/m3), 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 

(mg/m3 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 mg/m3 for 

the 2012 annual PM2.5 NAAQS makes it 

appropriate to scale that value according 

to the NAAQS level to arrive at 0.25 mg/ 

m3 for the 1997 annual PM2.5 NAAQS. 

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

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

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 


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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). 

142See 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. 

143 87 FR 60494. 

144Based 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. 

147Letter 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.’’ 

148Letter 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.’’ 

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. 

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. 

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. 

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. 

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 


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149EPA 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). 

151EPA, 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. 

152EPA’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). 

154 Id. at 59018. 

155 Id. at 59018–59020. 

156EPA’s 2020 Response to Comments, p. 156. 

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. 

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

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

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 


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157The 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). 

158See 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.’’). 

159Letter dated March 29, 2023, from Steven S. 

Cliff, Executive Officer, CARB, to Martha Guzman, 

Regional Administrator, EPA Region 9, with 

enclosures. 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. 

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. 

166The 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. 

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.’’ 

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. 

In the ammonia context, the 2018 

PM2.5 Plan and 15 mg/m3 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. 

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. 

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

With respect to the Title VI 

Supplement, the EPA acknowledges that 


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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. 

168The 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). 169 88 FR 45276, 45278. 

170Letter dated June 7, 2023, from Steven S. Cliff, 

Executive Officer, CARB, to Martha Guzman, 

Regional Administrator, EPA Region IX. 

171Letter dated October 13, 2023, from Steven S. 

Cliff, Executive Officer, CARB, to Martha Guzman, 

Regional Administrator, EPA Region IX. 

172Letter dated November 13, 2023, from Steven 

S. Cliff, Executive Officer, CARB, to Martha 

Guzman, Regional Administrator, EPA Region IX. 

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. 

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

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. 

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 


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173 88 FR 45276, 45320. 

174 40 CFR 7.120. 

175 40 CFR 7.115. 

176On 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. 

177EPA, External Civil Rights Docket, https://

www.epa.gov/external-civil-rights/external-civilrights-docket-2014-present. 

178Letter dated February 1, 2022, from Matthew 

Lakin, Acting Director, Air and Radiation Division, 

EPA Region IX, to Richard Corey, Executive Officer, 

CARB. 

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 policybased 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. 

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

III. Motor Vehicle Emissions Budgets 

and Transportation Conformity 

The EPA previously determined that 

the 2020 and 2023 motor vehicle 

emissions budgets in the 15 mg/m3 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 

mg/m3 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 


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179 87 FR 7834 (February 10, 2022). 

180 88 FR 45276, 45322. 

181The 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). 

185We 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. 

186 88 FR 45276, 45322. 

187The 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. 

189See 86 FR 49100, 49128 (September 1, 2021) 

(proposed rule) and 86 FR 67343, 67346 (November 

26, 2021) (final rule). 

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. 

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 reentrained 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 reentrained 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. 

TABLE 1—MOTOR VEHICLE EMISSIONS BUDGETS FOR THE SAN JOAQUIN VALLEY FOR THE 1997 ANNUAL PM2.5 NAAQS 

[Annual average, tons per day] 

County 

2020 (RFP year) 2023 (attainment year) 

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 μg/m3 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. 

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 onroad mobile sources to offset any onroad 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 interpollutant trading ratio. 

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 


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190 76 FR 69896. 

191EJSCREEN 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. 

192EPA Region IX, ‘‘EJSCREEN Analysis for the 

Eight Counties of the San Joaquin Valley 

Nonattainment Area,’’ August 2022. 

193As 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). 

194 86 FR 67343. 

195 86 FR 67329. 

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

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. 

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 lowincome 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); 

(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

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. 

This final action does not address the 

prior disapprovals of the contingency 

measure elements for the 1997 annual 


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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 

■ 1. The authority citation for Part 52 

continues to read as follows: 

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

Subpart F—California 

■ 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: 

§ 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 


lotter on DSK11XQN23PROD with RULES1
86608 Federal Register / Vol. 88, No. 239 / Thursday, December 14, 2023 / Rules and Regulations 

November 8, 2021, by the Governor’s 

designee. 

(10) ‘‘Staff Report, Proposed SIP 

Revision for the 15 mg/m3 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 

PM2.5üü), 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. 

* * * * * 

■ 3. Section 52.237 is amended by 

revising paragraph (a)(11) to read as 

follows: 

§ 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. 

* * * * * 

■ 4. Section 52.244 is amended by 

adding paragraph (f)(4) to read as 

follows: 

§ 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 

DEPARTMENT OF TRANSPORTATION 

Maritime Administration 

46 CFR Part 298 

[Docket Number MARAD–2023–0086] 

RIN 2133–AB98 

Amendment to the Federal Ship 

Financing Program Regulations; 

Financial Requirements 

AGENCY: Maritime Administration, 

Department of Transportation. 

ACTION: Final rule. 

SUMMARY: This document serves to 

inform interested parties and the public 

that the Maritime Administration 

(MARAD) is amending its regulations 

implementing the Federal Ship 

Financing Program’s (Title XI Program) 

financial requirements. This action is 

necessary to implement statutory 

changes and update the existing 

financial requirements imposed on Title 

XI Program obligors to align with more 

up-to-date vessel financing and federal 

credit best practices. 

DATES: This rule will be effective 

January 16, 2024. 

FOR FURTHER INFORMATION CONTACT: 

David M. Gilmore, Director, Office of 

Marine Financing, at (202) 366–5737, or 

via email at marinefinancing@dot.gov. 

You may send mail to Mr. Gilmore at 

Department of Transportation, Maritime 

Administration, Office of Marine 

Financing, 1200 New Jersey Avenue SE, 

Washington, DC 20590. If you have 

questions on viewing the Docket, call 

Docket Operations, telephone: (800) 

647–5527. 

SUPPLEMENTARY INFORMATION: 

Background 

The Secretary of Transportation, 

through MARAD, is authorized to 

provide guarantees of debt (obligation 

guarantees) to finance all types of vessel 

construction and shipyard 

modernization and improvement, 

except for fishing vessels. The Title XI 

Program is a loan guarantee program, 

administered by MARAD, which was 

established under Title XI of the 

Merchant Marine Act, 1936, Public Law 

74–835, codified at 46 U.S.C. Chapter 

537, as amended (the ‘‘Act’’). Title XI 

provides for the full faith and credit of 

the United States, acting by and through 

the Maritime Administrator, for the 

payment of debt obligations for: (1) U.S. 

shipowners for the purpose of financing 

or refinancing U.S. flag vessels 

constructed, reconstructed, or 

reconditioned in U.S. shipyards; and (2) 

U.S. shipyards for the purpose of 

financing advanced shipbuilding 

technology and modern shipbuilding 

technology of a privately-owned 

shipyard facility located in the U.S. As 

the Title XI Program guarantees full 

payment of the obligation’s unpaid 

principal and interest in the event of a 

default by the borrower, both the statute 

and regulations contain several criteria 

and requirements intended to reduce 

the risk of a loan default. Though the 

Title XI Program regulations have been 

amended over the years, the current 

financial requirements and limitations 

remain substantially the same as when 

MARAD introduced them in 1978. As 

lending practices have evolved, 

MARAD’s regulatory standards have not 

changed to reflect modern lending 

practices for vessel financing. For 

example, when the regulations where 

implemented, certain leases were not 

included as an expense under generally 

accepted accounting principles (GAAP), 

but today GAAP requires that all leases 

be included as an expense. Today, 

retained earnings are also expected to be 

included in any calculation of equity or 

net worth pursuant to GAAP. 

Accordingly, the modifications to the 

regulations will eliminate confusion and 

align the Title XI Program regulations 

with modern accounting standards. 

Prior to execution of a guarantee, 

MARAD is bound by statute to, among 

other things, make determinations of 

economic soundness of the project and 

the financial and operating capability of 

the applicant. To that end, the Title XI 

regulations currently require each 

borrower, and operator if applicable, to 

have and maintain: (1) working capital 

of at least $1; (2) at least 90 percent of 

its equity as shown on the last audited 

balance sheet; and (3) long-term debt 

not to exceed twice its equity. By this 

amendment, MARAD is modernizing its 

financial review process by removing 

static financial covenants and loan 

thresholds and replacing them with a 

review and evaluation of the 

creditworthiness of each borrower based 

on revenue metrics based on federal 

credit and maritime lending best 

practices. The use of these revenue 

metrics is intended to improve the 

quality of MARAD financial 

requirements applied to new borrowers. 

As part of its regular programmatic 

evaluation process, MARAD frequently 

seeks feedback from potential applicants 


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