87850 Federal Register / Vol. 88, No. 242 / Tuesday, December 19, 2023 / Proposed Rules 

1The State of California refers to reactive organic 

gases (ROG) in some of its ozone-related SIP 

submissions. As a practical matter, ROG and VOC 

refer to the same set of chemical constituents, and 

for the sake of simplicity, we refer to this set of 

gases as VOC in this proposed rule. 2 ‘‘Fact Sheet—2008 Final Revisions to the 

National Ambient Air Quality Standards for 

Ozone,’’ dated March 2008. 

3 44 FR 8202 (February 8, 1979). When the CAA 

was amended in 1990, each area of the country that 

was designated nonattainment for the 1979 ozone 

NAAQS, including the San Diego area, was 

classified by operation of law as nonattainment and 

classified as Marginal, Moderate, Serious, Severe, or 

Extreme depending on the severity of the area’s air 

quality problem. The EPA redesignated the San 

Diego County area from Serious nonattainment to 

attainment for the 1979 ozone NAAQS, effective 

July 28, 2003. 68 FR 37976 (June 26, 2003). 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Part 52 

[EPA–R09–OAR–2021–0135; FRL–9538–02– 

R9] 

Air Quality Implementation Plans; 

California; San Diego County; 2008 

and 2015 8-Hour Ozone Nonattainment 

Area Requirements 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing to approve 

portions of two state implementation 

plan (SIP) revisions submitted by the 

State of California to meet Clean Air Act 

requirements for the 2008 8-hour ozone 

national ambient air quality standards 

(NAAQS or ‘‘standards’’) and the 2015 

8-hour ozone NAAQS in the San Diego 

County ozone nonattainment area (‘‘San 

Diego County area’’ or ‘‘area’’). The first 

SIP revision, ‘‘2020 Plan for Attaining 

the National Ambient Air Quality 

Standards for Ozone in San Diego 

County’’ (‘‘2020 San Diego County 

Ozone SIP’’ or ‘‘2020 Plan’’), addresses 

most of the SIP requirements for the 

area. The second SIP revision, referred 

to as the ‘‘Smog Check Certification,’’ 

supplements the motor vehicle 

inspection and maintenance program 

portion of the 2020 Plan. The EPA is 

proposing to approve the 2020 Plan, and 

the San Diego County portion of the 

Smog Check Certification, as meeting all 

the applicable ozone nonattainment area 

requirements for the 2008 and 2015 8- 

hour ozone NAAQS addressed by the 

plan except for the emissions statement 

requirement that the EPA previously 

found to have been met and the 

contingency measure requirements, for 

which the EPA is deferring action. 

DATES: Comments must be received on 

or before January 18, 2024. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–R09– 

OAR–2021–0135 at https://

www.regulations.gov. For comments 

submitted at Regulations.gov, follow the 

online instructions for submitting 

comments. Once submitted, comments 

cannot be edited or removed from 

Regulations.gov. The EPA may publish 

any comment received to its public 

docket. Do not submit electronically any 

information you consider to be 

Confidential Business Information (CBI) 

or other information whose disclosure is 

restricted by statute. Multimedia 

submissions (audio, video, etc.) must be 

accompanied by a written comment. 

The written comment is considered the 

official comment and should include 

discussion of all points you wish to 

make. The EPA will generally not 

consider comments or comment 

contents located outside of the primary 

submission (i.e., on the web, cloud, or 

other file sharing system). For 

additional submission methods, please 

contact the person identified in the FOR

FURTHER INFORMATION CONTACT section. 

For the full EPA public comment policy, 

information about CBI or multimedia 

submissions, and general guidance on 

making effective comments, please visit 

https://www.epa.gov/dockets/ 

commenting-epa-dockets. If you need 

assistance in a language other than 

English or if you are a person with 

disabilities who needs a reasonable 

accommodation at no cost to you, please 

contact the person identified in the FOR

FURTHER INFORMATION CONTACT section. 

FOR FURTHER INFORMATION CONTACT: John 

J. Kelly, Air Planning Office (AIR–2–1), 

EPA Region IX, 75 Hawthorne Street, 

San Francisco, CA 94105. By phone at 

(415) 947–4151, or by email at 

kelly.johnj@epa.gov. 

SUPPLEMENTARY INFORMATION: 

Throughout this document, ‘‘we,’’ ‘‘us,’’ 

and ‘‘our’’ refer to the EPA. 

Table of Contents 

I. Regulatory Context 

A. Ozone Standards, Area Designations, 

and SIPs 

B. The San Diego County Ozone 

Nonattainment Area 

C. Clean Air Act and Regulatory 

Requirements for 2008 and 2015 Ozone 

Nonattainment Area SIPs 

II. Submission From the State of California 

To Address Ozone Requirements in San 

Diego County 

A. Summary of State Submissions 

B. Clean Air Act Procedural Requirements 

for Adoption and Submission of SIP 

Revisions 

III. Evaluation of the 2020 San Diego County 

Ozone SIP 

A. Emissions Inventories 

B. Reasonably Available Control Measures 

Demonstration and Control Strategy 

C. Attainment Demonstration 

D. Rate of Progress Plan and Reasonable 

Further Progress Demonstration 

E. Transportation Control Strategies and 

Measures To Offset Emissions Increases 

From Vehicle Miles Traveled 

F. Contingency Measures 

G. Motor Vehicle Emissions Budgets for 

Transportation Conformity 

H. General Conformity Budgets 

I. Other Clean Air Act Requirements 

Applicable to Severe Ozone 

Nonattainment Areas 

IV. Environmental Justice Considerations 

V. Proposed Action 

VI. Statutory and Executive Order Reviews 

I. Regulatory Context 

A. Ozone Standards, Area Designations, 

and SIPs 

Ground-level ozone pollution is 

formed from the reaction of volatile 

organic compounds (VOC) and oxides of 

nitrogen (NOX) in the presence of 

sunlight.1 These two pollutants, referred 

to as ozone precursors, are emitted by 

many types of sources, including onand off-road motor vehicles and 

engines, power plants and industrial 

facilities, and smaller area sources such 

as lawn and garden equipment and 

paints. 

Scientific evidence indicates that 

adverse public health effects occur 

following exposure to ozone, 

particularly in children and adults with 

lung disease. Breathing air containing 

ozone can reduce lung function and 

inflame airways, which can increase 

respiratory symptoms and aggravate 

asthma or other lung diseases.2

Under section 109 of the Clean Air 

Act (CAA or ‘‘the Act’’), the EPA 

promulgates NAAQS for pervasive air 

pollutants, such as ozone, to protect 

public health and welfare. Under CAA 

section 110, following promulgation of 

a new or revised NAAQS, states are 

required to adopt and submit plans that 

provide for implementation, 

maintenance, and enforcement of the 

NAAQS (referred to as State 

Implementation Plans or SIPs). Under 

CAA section 107(d), the EPA is required 

to designate areas throughout the nation 

as either attaining or not attaining the 

NAAQS, and states with designated 

nonattainment areas are required to 

submit SIP revisions to, among other 

things, provide for attainment as 

expeditiously as practicable but not 

later than the applicable attainment 

dates. 

In 1979, the EPA established primary 

and secondary NAAQS for ozone at 0.12 

parts per million (ppm) averaged over a 

1-hour period (‘‘1979 ozone NAAQS’’).3

In 1997, the EPA revised the primary 


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4 62 FR 38856 (July 18, 1997). In 2004, the EPA 

designated areas of the country with respect to the 

1997 ozone NAAQS. See 69 FR 23858 (April 30, 

2004). The EPA redesignated the San Diego County 

area from Moderate nonattainment to attainment for 

the 1997 ozone NAAQS, effective July 5, 2013. 78 

FR 33230 (June 4, 2013). 

5 73 FR 16436 (March 27, 2008). 

6 80 FR 65292 (October 26, 2015). 

7 85 FR 87256. The SIP revision that is the subject 

of this proposed action relates to the requirements 

for the 2008 and 2015 ozone standards. 

8 40 CFR 50.9(b) and 40 CFR 50.10(c). 

9 77 FR 30087 (May 21, 2012), effective July 20, 

2012. 

10CAA section 181(a)(1); 40 CFR 51.1102 and 

51.1103(a). 

11 81 FR 26697 (May 4, 2016). 

12The State of California submitted the San Diego 

County area’s 2016 Moderate ozone attainment plan 

and the 2016 Moderate ozone RACT demonstration 

to the EPA as a SIP revision on April 12, 2017. The 

State withdrew the 2016 Moderate ozone 

attainment plan by letter dated December 16, 2021, 

following submittal of the 2020 plan and the EPA’s 

grant of the State’s request to reclassify San Diego 

County to Severe for the 2008 ozone NAAQS. The 

EPA approved the 2016 Moderate ozone RACT 

demonstration at 85 FR 77996 (December 3, 2020), 

87 FR 38665 (June 29, 2022) and 88 FR 2538 

(January 17, 2023). 

13 84 FR 44238 (August 23, 2019). 

14Letter dated January 8, 2021 from Richard 

Corey, Executive Officer, California Air Resources 

Board, to John Busterud, Regional Administrator, 

U.S. EPA Region IX; 86 FR 29522 (June 2, 2021), 

effective July 2, 2021. 

15 83 FR 25776 (June 4, 2018). Severe areas must 

attain the standard as expeditiously as practicable, 

but not later than 15 years after the effective date 

of designation. For the 2008 ozone NAAQS, the 

Severe attainment deadline is July 20, 2027. 

However, note that for attainment modeling 

purposes we refer to the attainment year as 2026. 

For the 2015 ozone NAAQS, the Severe attainment 

deadline is August 3, 2033, with a 2032 attainment 

year. 

16 86 FR 29522 (June 2, 2021), effective July 2, 

2021. 

17Three design value reports (EPA, Air Quality 

Design Value Report, July 12, 2011; San Diego 2008 

Ozone Trends Report, U.S. EPA Air Quality System, 

May 8, 2023; and San Diego 2015 Ozone Trends 

Report, U.S. EPA Air Quality System, May 8, 2023), 

are included in the docket for this action. For the 

2008 and 2015 ozone NAAQS, the design value at 

any given monitoring site is the 3-year average of 

the annual fourth highest daily maximum 8-hour 

average ambient air quality ozone concentration. 

The maximum design value among the various 

ozone monitoring sites is the design value for the 

area. 

18 2020 Plan, p. 13. 

and secondary standards for ozone in 

the ambient air to 0.08 ppm averaged 

over an 8-hour period (‘‘1997 ozone 

NAAQS’’).4

In 2008, the EPA lowered the 8-hour 

ozone NAAQS to 0.075 ppm (‘‘2008 

ozone NAAQS’’).5 Then in 2015, the 

EPA further lowered the 8-hour ozone 

NAAQS to 0.070 ppm (‘‘2015 ozone 

NAAQS’’).6 On December 31, 2020, the 

EPA finalized its most recent periodic 

review of the ozone NAAQS, retaining 

the form and level of the standards.7

The EPA has revoked both the 1979 

ozone NAAQS and the 1997 ozone 

NAAQS but not the 2008 ozone 

NAAQS.8

In 2012, the EPA designated San 

Diego County as nonattainment for the 

2008 ozone NAAQS and classified the 

area as ‘‘Marginal.’’ 9 Areas classified as 

Marginal must attain the NAAQS within 

three years of the effective date of the 

nonattainment designation.10 Following 

this initial classification as Marginal, 

the EPA found in 2016 that the area did 

not attain the 2008 ozone standards by 

the Marginal attainment deadline of July 

20, 2015.11 As a result of our finding, 

the area was reclassified by operation of 

law to Moderate nonattainment.12

Moderate nonattainment areas have six 

years to attain the standard. Following 

the Moderate attainment deadline of 

July 20, 2018, the EPA found that the 

area did not attain the 2008 ozone 

standards.13 As a result of our finding, 

the area was reclassified by operation of 

law to Serious nonattainment, with a 

Serious attainment deadline of July 20, 

2021, nine years after the effective date 

of designation as a nonattainment area 

for the 2008 ozone NAAQS. In response 

to a letter to the EPA dated January 8, 

2021 from the California Air Resources 

Board (CARB), the EPA reclassified the 

area to Severe for the 2008 ozone 

NAAQS.14 In the same letter, CARB 

requested that the EPA also reclassify 

the area as Severe for the 2015 ozone 

NAAQS. The EPA’s initial designation 

for the San Diego County area for the 

2015 ozone NAAQS was nonattainment, 

with a Moderate classification.15 The 

San Diego County area is now classified 

as Severe for both the 2008 and the 2015 

ozone NAAQS.16

Designations of nonattainment for a 

given NAAQS trigger requirements 

under the CAA to prepare and submit 

SIP revisions. The SIP revision that is 

the subject of this proposed action 

addresses the Severe nonattainment area 

requirements that apply to the San 

Diego County area for the 2008 and the 

2015 ozone NAAQS. 

Under California law, CARB is the 

state agency that is responsible for the 

adoption and submission to the EPA of 

California SIPs and SIP revisions, and it 

has broad authority to establish 

emissions standards and other 

requirements for mobile sources and 

certain area sources, such as consumer 

products. Local and regional air 

pollution control districts in California 

are responsible for the regulation of 

stationary sources and are generally 

responsible for the development of 

regional air quality management plans 

(‘‘plans’’). In the San Diego County area, 

the San Diego County Air Pollution 

Control District (SDCAPCD or 

‘‘District’’) develops and adopts plans to 

address CAA planning requirements 

applicable to that area. Such plans are 

then submitted to CARB for adoption 

and submittal to the EPA as revisions to 

the California SIP. 

B. The San Diego County Ozone 

Nonattainment Area 

The San Diego County area is located 

in the southwestern-most portion of the 

State of California, and its boundaries 

generally align with those of San Diego 

County. For a precise description of the 

geographic boundaries of the San Diego 

County area for both the 2008 and 2015 

ozone NAAQS, see 40 CFR 81.305. 

Prior plans and state control measures 

developed by the District and CARB 

have produced significant emissions 

reductions over the years and improved 

air quality in the area. For instance, the 

8-hour ozone design value for the San 

Diego County area decreased from 0.095 

ppm to 0.079 ppm from 2002 to 2022,17

despite increases in population and 

vehicular activity. 

Under certain weather conditions, the 

San Diego County area is downwind 

from the Los Angeles-South Coast Air 

Basin (‘‘South Coast’’) and, under 

certain other weather conditions, from 

Mexico, and is subject to transport of 

ozone from those areas. The South Coast 

is regulated by the South Coast Air 

Quality Management District 

(SCAQMD). The 2020 Plan describes 

ozone transport from these areas as 

follows: 

. . . air pollution from both regions 

significantly contribute to ozone levels in the 

San Diego region under certain weather 

conditions. This impact is acknowledged in 

State documentation and regulation. 

Importantly . . . SCAQMD has implemented 

effective emissions control programs, 

resulting in a trend of emission reductions 

and air quality improvements in the South 

Coast region. Though the region is designated 

as an Extreme Nonattainment Area for the 

2008 and 2015 ozone NAAQS, SCAQMD 

predicts continued ozone reductions through 

at least 2031 as shown in their SIP for the 

2008 ozone NAAQS. In turn, air pollution 

transported to San Diego County is expected 

to decrease as a result of their actions.18

Because of the transport from the 

South Coast into the San Diego County 

area, continued progress in the South 

Coast towards meeting the 2008 and 

2015 ozone NAAQS is expected to help 

the San Diego County area attain these 

ozone NAAQS. 

C. Clean Air Act and Regulatory 

Requirements for 2008 and 2015 Ozone 

Nonattainment Area SIPs 

States must implement the 2008 and 

2015 ozone NAAQS under title I, part D 


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19 80 FR 12264 (March 6, 2015). Anti-backsliding 

requirements are the provisions applicable to 

revoked NAAQS (including the 1979 1-hour ozone 

NAAQS and the 1997 ozone NAAQS). 

20 83 FR 62998 (December 6, 2018). 

21Letter (with enclosures) dated January 8, 2021, 

from Richard Corey, Executive Officer, CARB, to 

John Busterud, Regional Administrator, EPA Region 

IX (submitted electronically January 12, 2021). 

22SDCAPCD Board Resolution 20–166, October 

14, 2020; CARB Board Resolution 20–29, Proposed 

San Diego 8-Hour Ozone State Implementation Plan 

Submittal, November 19, 2020 (‘‘CARB Board 

Resolution 20–29’’). 

23 2020 Plan, at 58, 81–82. 

24CARB Board Resolution 20–29, at 6. 

25 87 FR 45657 (July 29, 2022). 

of the CAA, including sections 171– 

179B of subpart 1 (‘‘Nonattainment 

Areas in General’’) and sections 181– 

185 of subpart 2 (‘‘Additional Provisions 

for Ozone Nonattainment Areas’’). To 

assist states in developing effective 

plans to address ozone nonattainment 

problems, in 2015, the EPA issued a SIP 

Requirements Rule (SRR) that addresses 

implementation of various aspects of the 

2008 ozone NAAQS (‘‘2008 Ozone 

SRR’’), including attainment dates, 

requirements for emissions inventories, 

attainment demonstrations, and 

reasonable further progress (RFP) 

demonstrations, among other SIP 

elements. The 2008 Ozone SRR also 

addresses the transition from the 1997 

ozone NAAQS to the 2008 ozone 

NAAQS and associated anti-backsliding 

requirements.19 In 2018, the EPA also 

issued an SRR for the 2015 ozone 

NAAQS (‘‘2015 Ozone SRR’’) that 

addresses implementation of the 2015 

standards.20 The regulatory 

requirements of the 2008 Ozone SRR are 

codified at 40 CFR part 51, subpart AA; 

those for the 2015 Ozone SRR are 

codified in 40 CFR part 51, subpart CC. 

We discuss the CAA and regulatory 

planning requirements for the elements 

of 2008 and 2015 ozone plans relevant 

to this proposed action in more detail in 

Section III of this document. 

II. Submission From the State of 

California To Address Ozone 

Requirements in San Diego County 

A. Summary of State Submissions 

1. SDCAPCD’s 2020 Attainment Plan 

On January 12, 2021, CARB submitted 

the 2020 Plan to the EPA as a revision 

to the California SIP.21 The 2020 Plan 

addresses many of the nonattainment 

area requirements for the San Diego 

County area for both the 2008 and the 

2015 8-hour ozone NAAQS. In this 

document, we are proposing action on 

the 2020 Plan that addresses both the 

2008 and 2015 8-hour ozone NAAQS for 

the San Diego County area. 

The 2020 Plan SIP submittal includes 

the various sections and attachments of 

the plan, plus the District’s resolution of 

approval for the plan (District 

Resolution 20–166) and CARB’s 

resolution of adoption of the plan as a 

revision to the California SIP (CARB 

Resolution 20–29).22 The 2020 Plan 

includes a District commitment to 

achieve additional emissions reductions 

beyond those expected to occur from 

already-implemented control measures 

and relies on a similar commitment by 

CARB. More specifically, the 2020 Plan 

includes a commitment by the District 

to achieve an additional 1.7 tons per day 

(tpd) reduction in NOX by 2032 23 and 

relies on CARB’s commitment to 

achieve aggregate emissions reductions 

in San Diego County of 4 tpd of NOX by 

2032.24 Both commitments are part of 

the 2020 Plan’s attainment 

demonstration for the 2015 ozone 

NAAQS. With respect to both the 2008 

and the 2015 ozone NAAQS, the 2020 

Plan addresses the CAA requirements 

for emissions inventories, air quality 

modeling demonstrating attainment, 

reasonably available control measures 

(RACM), RFP, transportation control 

strategies and measures, new source 

review (NSR), contingency measures for 

failure to make RFP or to timely attain 

the relevant standards, and motor 

vehicle inspection and maintenance (I/ 

M) programs (also referred to as ‘‘smog 

check’’ programs), among other 

requirements. The 2020 Plan also 

addresses the emissions statement 

requirement, and in separate action, the 

EPA approved the emissions statement 

portion of the 2020 Plan as meeting the 

applicable requirements for emissions 

statements for the 2008 and 2015 ozone 

NAAQS.25

The 2020 Plan is organized into an 

executive summary, five sections, and 

attachments lettered A through Q. 

Section 1, ‘‘Introduction and 

Overview,’’ introduces the 2020 Plan, 

including its purpose, the two ozone 

NAAQS it addresses, current air quality 

in the area in comparison with those 

NAAQS, historical air quality progress 

in San Diego County, and the District’s 

approach to air quality planning. 

Section 2, ‘‘General Attainment Plan 

Requirements,’’ addresses CAA 

requirements that apply to the area as 

nonattainment for both the 2008 and the 

2015 ozone NAAQS. Section 3, ‘‘2008 

Eight Hour Ozone NAAQS Attainment 

Plan Requirements,’’ addresses CAA 

requirements that apply to the area as 

nonattainment specifically for the 2008 

ozone NAAQS, including antibacksliding requirements for the 

revoked 1979 and 1997 ozone standards. 

Section 4, ‘‘2015 Eight Hour Ozone 

NAAQS Attainment Plan 

Requirements,’’ addresses CAA 

requirements that apply to the area as 

nonattainment specifically for the 2015 

ozone NAAQS, including antibacksliding requirements for revoked 

standards. Section 5, ‘‘Conclusions,’’ 

presents the District’s conclusions 

regarding whether the 2020 Plan meets 

applicable Clean Air Act requirements. 

The 2020 Plan also includes technical 

attachments: 

• Attachment A (‘‘Emissions 

Inventories and Documentation for 

Baseline, RFP, and Attainment Years’’) 

presents tables, analysis, and 

documentation for the emissions 

inventories included in the plan. 

• Attachment B (‘‘Planned Military 

Projects Subject to General Conformity’’) 

contains annual data compiled by the 

United States Marine Corps (USMC) and 

Department of the Navy (DoN) for 

emissions changes resulting from USMC 

and DoN projects out to year 2037, for 

the purpose of demonstrating general 

conformity for USMC and DoN facilities 

in the area. 

• Attachment C (‘‘Planned San Diego 

International Airport Projects Subject to 

General Conformity’’) is a report that 

provides an emissions inventory for the 

San Diego International Airport, for the 

purpose of demonstrating general 

conformity for the airport. 

• Attachment D (‘‘CARB Control 

Measures, 1985 to 2019’’) is a listing of 

CARB control measures from 1985 to 

2019. 

• Attachment E (‘‘CARB Analyses of 

Key Mobile Source Regulations and 

Programs Providing Emission 

Reductions’’) describes CARB’s mobile 

source regulations and programs that 

provide emissions reductions in the San 

Diego County area. 

• Attachment F (‘‘Pre-Baseline 

Banked Emission Reduction Credits’’) 

describes emission reduction credits 

that were banked before the baseline 

year. 

• Attachment G (‘‘Analyses of 

Potential Additional Stationary Source 

Control Measures’’) provides the 

District’s analysis of the feasibility of 

additional stationary source control 

measures that could be pursued in the 

area. 

• Attachment H (‘‘Implementation 

Status of Transportation Control 

Measures’’) provides the 

implementation status of transportation 

control measures by the San Diego 

Association of Governments (SANDAG) 

and other transportation agencies. 

• Attachment I (‘‘CARB Analyses of 

Potential Additional Mobile Source and 

Consumer Products Control Measures’’) 


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26 84 FR 28132 (June 17, 2019), at 28134–28134, 

tables 10 and 11. The EPA finalized its approval of 

the 2016 South Coast Ozone SIP at 84 FR 52005 

(October 1, 2019). 

27 84 FR 28132, 28143–28157 (June 17, 2019), 

28 2016 State Strategy, 35. 

29CARB Review of the 2020 Plan for Attaining 

the National Ambient Air Quality Standards for 

Ozone in San Diego County, Release Date: October 

16, 2020, at 11; CARB Board Resolution 20–29, at 

6. 

30Letter (with enclosures) dated April 26, 2023, 

from Steven S. Cliff, Ph.D., Executive Officer, 

CARB, to Martha Guzman, Regional Administrator, 

EPA Region IX (submitted electronically April 26, 

2023). 

31CARB Board Resolution 23–9, March 23, 2023. 

32MOVES is the acronym for the EPA’s Motor 

Vehicle Emission Simulator model. 

33Letter dated October 20, 2020,from Robert 

Reider, Interim Director, SDCAPCD, to Richard 

Corey, CARB Executive Officer. See the letter’s 

response to comments document regarding the two 

webinars and its ‘‘Minute Order’’ document 

regarding the public hearing. 

34 Id. See the October 20, 2020 letter’s proof of 

publication document regarding public notice for 

the October 14, 2020 public hearing. 

35CARB Review of the 2020 Plan for Attaining 

the National Ambient Air Quality Standards for 

Ozone in San Diego County, Release Date: October 

16, 2020. 

analyzes the potential for further mobile 

source and consumer products controls 

in the area. 

• Attachment J (‘‘Calculation of 

Cumulative Potential Emission 

Reductions for Possible Reasonably 

Available Control Measures (RACM)’’) 

calculates the cumulative potential 

emissions reductions in the area in 

support of the plan’s RACM 

demonstration. 

• Attachment K (‘‘Modeling Protocol 

& Attainment Demonstration for the 

2020 San Diego Ozone SIP’’) provides 

the modeling protocol and attainment 

demonstration for the San Diego County 

area as Severe nonattainment for both 

the 2008 and the 2015 ozone NAAQS. 

• Attachment L (‘‘Modeling Emission 

Inventory for the Ozone State 

Implementation Plan in San Diego 

County’’) describes the modeled or 

‘‘gridded’’ emissions inventories for the 

area, in support of the area’s two 

modeled attainment demonstrations. 

• Attachment M (‘‘Weight of 

Evidence Demonstration for San Diego 

County’’) provides a weight-of-evidence 

demonstration for the area, in support of 

the area’s modeled attainment 

demonstrations. 

• Attachment N (‘‘VMT Offset 

Demonstration for San Diego County’’) 

provides the area’s VMT offset 

demonstration. 

• Attachment O (‘‘Contingency 

Measures for San Diego County’’) 

represents the District’s assessment of 

compliance with the contingency 

measure requirements for the area. 

• Attachment P (‘‘Federal Clean Air 

Act Requirements and References in 

Attainment Plan’’) provides a summary 

of CAA requirements that apply to the 

area with specific citations to locations 

in the plan that address those 

requirements. 

• Attachment Q (‘‘Endnotes’’) 

contains the text of all endnotes found 

in the plan. 

Attainment of the 2008 and the 2015 

ozone NAAQS in the San Diego County 

area is dependent on emissions 

reductions occurring in the adjacent 

South Coast nonattainment area. The 

2016 South Coast Ozone SIP documents 

baseline emissions reductions from 

already-adopted control measures and 

provides for new emissions reductions 

to be achieved through fulfillment of 

SCAQMD and CARB commitments for 

further reductions, and through new 

technology measures.26 More 

specifically, as discussed in Section 

III.D, ‘‘Attainment Demonstration,’’ of 

the EPA’s proposed approval of the 

2016 South Coast Ozone SIP,27 the 

ozone attainment demonstrations for 

South Coast for the 1997 and 2008 

ozone NAAQS include emissions 

reduction commitments made by the 

SCAQMD in the 2016 AQMP and by 

CARB in the ‘‘Revised Proposed 2016 

State Strategy for the State 

Implementation Plan’’ (‘‘2016 State 

Strategy’’). 

The 2016 State Strategy focuses on 

two areas: the South Coast and the San 

Joaquin Valley. Although it did not 

include specific emissions reduction 

commitments for San Diego County, 

CARB states that, ‘‘[s]hould additional 

areas require emission reductions to 

meet the current ozone and PM2.5

standards, ARB will quantify area and 

year specific reductions as part of 

individual attainment plans.’’ 28 The 

2020 Plan for the 2015 ozone NAAQS 

relies on CARB’s commitment to 

achieve 4 tpd of NOX emissions 

reductions in 2032 from mobile sources 

to demonstrate attainment of this 

standard in San Diego County.29

2. Smog Check Certification 

On April 26, 2023, CARB submitted 

the ‘‘California Smog Check 

Performance Standard Modeling and 

Program Certification for the 70 Parts 

Per Billion (ppb) 8-Hour Ozone 

Standard’’ (‘‘Smog Check Certification’’) 

to supplement the motor vehicle I/M 

portion of the 2020 Plan.30 The Smog 

Check Certification includes CARB’s 

evaluation of the California Smog Check 

program for compliance with the 

applicable I/M performance standard as 

defined in EPA’s regulations for certain 

nonattainment areas for the 2008 and 

2015 ozone NAAQS, including San 

Diego County. 

CARB’s SIP submittal package for the 

Smog Check Certification includes 

CARB Resolution 23–9, through which 

CARB adopted the Smog Check 

Certification as part of the California 

SIP,31 public notice of CARB’s hearing 

on the proposed SIP revision, public 

comments and responses, and 

MOVES 32 input and output data sheets. 

In this document, we are proposing 

action on the San Diego County portion 

of the Smog Check Certification as a 

supplement to the vehicle I/M portion 

of the 2020 Plan. 

B. Clean Air Act Procedural 

Requirements for Adoption and 

Submission of SIP Revisions 

CAA sections 110(a) and 110(l) 

require a state to provide reasonable 

public notice and opportunity for public 

hearing prior to the adoption and 

submission of a SIP or SIP revision. To 

meet this requirement, every SIP 

submittal should include evidence that 

adequate public notice was given and an 

opportunity to submit written 

comments and request a public hearing 

was provided consistent with the EPA’s 

implementing regulations in 40 CFR 

51.102. 

Both the District and CARB have 

satisfied the applicable statutory and 

regulatory requirements for reasonable 

public notice and hearing prior to the 

adoption and submittal of the 2020 

Plan. The District held two public 

webinars, one in July and another in 

August, 2020, and held a hearing on 

October 14, 2020, to discuss the plan 

and solicit public input.33 On 

September 14, 2020, the District 

published a notice in a local newspaper 

of the public hearing to be held on 

October 14, 2020, to consider approval 

of the 2020 Plan.34 On October 14, 2020, 

the District held the public hearing, and 

on that same date, through Resolution 

20–166, the District board approved the 

2020 Plan and directed the Air Pollution 

Control Officer to forward its resolution 

and the 2020 Plan to CARB for submittal 

to the EPA for inclusion in the 

California SIP. 

Upon receipt of the 2020 Plan from 

the District, CARB also provided public 

notice and opportunity for public 

comment on the plan. On October 16, 

2020, CARB released for public review 

its staff report for the 2020 Plan (‘‘CARB 

Staff Report’’) 35 and published a notice 

of public meeting to be held on 

November 19, 2020, to consider 


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36Notice of Public Meeting to Consider Approval 

of the Proposed San Diego 8-Hour Ozone State 

Implementation Plan Submittal, signed by Richard 

Corey, Executive Officer, CARB, October 16, 2020. 

37CARB Resolution 20–29, 6. 

38CAA section 110(k)(1)(B). 

39Notice of Public Meeting to Consider the 

Proposed California Smog Check Performance 

Standard Modeling and Program Certification for 

the 70 parts per billion 8-hour Ozone Standard, 

signed by Steven S. Cliff, Ph.D., Executive Officer, 

CARB, February 10, 2023. 

40CARB Resolution 23–9, 6. 

41 2008 Ozone SRR at 40 CFR 51.1115(a) and 40 

CFR 51.1110(b), 2015 Ozone SRR at 40 CFR 

51.1315(a) and 40 CFR 51.1310(b), and the Air 

Emissions Reporting Requirements at 40 CFR part 

51, subpart A. 

42 ‘‘Emissions Inventory Guidance for 

Implementation of Ozone and Particulate Matter 

National Ambient Air Quality Standards (NAAQS) 

and Regional Haze Regulations,’’ EPA–454/B–17– 

002, May 2017, available in the docket for this 

action and at https://www.epa.gov/air-emissionsinventories/air-emissions-inventory-guidanceimplementation-ozone-and-particulate. 

43For 2008 ozone, 40 CFR 51.1115(a) and (c), and 

40 CFR 51.1100(bb) and (cc). For 2015 ozone, 40 

CFR 51.1315(a) and (c), and 40 CFR 51.1300(p) and 

(q). 

44 80 FR 12264, 12290 (March 6, 2015); 83 FR 

62998, 63022 (December 6, 2018). 

45 2020 Plan, Attachment A. 

46EMFAC is short for EMission FACtor. The EPA 

announced the availability of the EMFAC2017 

model for use in state implementation plan 

development and transportation conformity in 

California on August 15, 2019. 84 FR 41717. The 

EPA’s approval of the EMFAC2017 emissions 

model for SIP and conformity purposes was 

effective on the date of publication of the notice in 

the Federal Register. 

47 2020 Plan, p. A–30. 

adoption of the 2020 Plan as a revision 

to the California SIP.36 On November 

19, 2020, CARB held the hearing and 

adopted the 2020 Plan as a revision to 

the California SIP and directed the 

Executive Officer to submit the 2020 

Plan to the EPA for approval into the 

California SIP.37 On January 12, 2021, 

the Executive Officer of CARB 

submitted the 2020 Plan to the EPA. Six 

months after submittal, on July 12, 2021, 

the 2020 Plan became complete by 

operation of law.38

CARB has also satisfied the applicable 

statutory and regulatory requirements 

for reasonable public notice and hearing 

prior to the adoption and submittal of 

the Smog Check Certification. On 

February 10, 2023, CARB released for 

public review the draft Smog Check 

Certification and published a notice of 

public meeting to be held on March 23, 

2023, to consider adoption of the Smog 

Check Certification as a revision to the 

California SIP.39 On March 23, 2023, 

CARB held the hearing and adopted the 

Smog Check Certification as a revision 

to the California SIP and directed the 

Executive Officer to submit the Smog 

Check Certification to the EPA for 

approval into the California SIP.40 On 

April 26, 2023, the Executive Officer of 

CARB submitted the Smog Check 

Certification to the EPA. 

Based on information provided in the 

SIP revisions submitted on January 12, 

2021 and April 26, 2023, and 

summarized in Section II.A this 

document, the EPA has determined that 

all hearings were properly noticed and 

that a reasonable opportunity to submit 

written comments was provided. 

Therefore, we find that the submittal of 

the 2020 Plan and the Smog Check 

Certification meets the procedural 

requirements for public notice and 

hearing in CAA sections 110(a) and 

110(l) and 40 CFR 51.102. 

III. Evaluation of the 2020 San Diego 

County Ozone SIP 

A. Emissions Inventories 

1. Statutory and Regulatory 

Requirements 

CAA sections 172(c)(3) and 182(a)(1) 

require states to submit for each ozone 

nonattainment area a ‘‘base year 

inventory’’ that is a comprehensive, 

accurate, current inventory of actual 

emissions from all sources of the 

relevant pollutant or pollutants in the 

area. In addition, the 2008 Ozone SRR 

and the 2015 Ozone SRR require that 

the inventory year be selected consistent 

with the baseline year for the RFP 

demonstration, which is the most recent 

calendar year for which a complete 

triennial inventory is required to be 

submitted to the EPA under the Air 

Emissions Reporting Requirements 

(AERR) at the time of designation for the 

ozone NAAQS.41 For the 2008 ozone 

NAAQS, the baseline year for the RFP 

demonstration is 2011, and for the 2015 

ozone NAAQS, the base year for the RFP 

demonstration is 2017. 

The EPA has issued guidance on the 

development of base year and future 

year emissions inventories for 8-hour 

ozone and other pollutants.42 Emissions 

inventories for ozone must include 

emissions of VOC and NOX and 

represent emissions for a typical ozone 

season weekday.43 States should 

include documentation explaining how 

the emissions data were calculated. In 

estimating mobile source emissions, 

states should use the latest emissions 

models and planning assumptions 

available at the time the SIP is 

developed.44

Future baseline emissions inventories 

must reflect the most recent population, 

employment, travel, and congestion 

estimates for the area. In this context, 

‘‘baseline’’ emissions inventories refer 

to emissions estimates for a given year 

and area that reflect rules and 

regulations and other measures that are 

already adopted. Future baseline 

emissions inventories are necessary to 

show the projected effectiveness of SIP 

control measures. Both the base year 

and future year inventories are 

necessary for photochemical modeling 

to demonstrate attainment. 

2. Summary of State’s Submission 

The 2020 Plan includes three sets of 

base year and future year average 

summer day baseline inventories for 

NOX and VOC for the San Diego County 

area, for both the 2008 and 2015 ozone 

NAAQS.45 One set of base year and 

future year baseline emissions 

inventories reflects emissions within the 

San Diego County area and includes 

marine emissions out to 100 nautical 

miles (NM) from the coast. A second set 

of emissions inventories adds emissions 

from the South Coast Air Basin to those 

generated within the San Diego County 

area (plus marine emissions out to 100 

NM from the coast) to produce 

combined inventories. A third set of 

emissions inventories reflects San Diego 

County area emissions including marine 

emissions but only out to three NM from 

the coast. All three sets of inventories 

include the years 2011, 2017, 2020, 

2023, 2026, 2029 and 2032. 

Documentation for the inventories is 

found in Sections 3 and 4 of the 2020 

Plan, addressing the 2008 and 2015 

ozone NAAQS, respectively, as well as 

in the Plan’s Attachment A. Because 

ozone levels in the area are typically 

highest during the summer months, the 

inventories provided in the 2020 Plan 

represent average summer day 

emissions from May through October. 

The inventories in the 2020 Plan reflect 

District rules adopted through the end 

of calendar year 2019 and CARB rules 

adopted through the end of calendar 

year 2017. For estimating on-road motor 

vehicle emissions, these inventories use 

EMFAC2017, the EPA-approved version 

of California’s mobile source emissions 

model available at the time the 2020 

Plan was developed.46

The VOC and NOX emissions 

estimates are grouped into two general 

categories, stationary sources and 

mobile sources. Stationary sources are 

further divided into ‘‘point’’ and ‘‘area’’ 

sources. Point sources typically refer to 

stationary sources that are permitted 

facilities and have one or more 

identified and fixed pieces of equipment 

and emissions points. Area sources 

consist of widespread and numerous 

smaller emissions sources, such as 

consumer products, fireplaces and 

agricultural burning.47 The mobile 


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48 Id. at A–35. SANDAG is the metropolitan 

planning organization (MPO) for San Diego County. 49 Id. at A–36. 50 Id., Attachment C, ‘‘Planned San Diego 

International Airport Projects Subject to General 

Conformity.’’ 

51 Id. at Q–2, footnote 29. 

52 Id. 

53Email dated March 21, 2023, from Nick 

Cormier, SDCAPCD to John J. Kelly, EPA, Subject: 

‘‘FW: 2011 emission inventory in SD’s 2020 ozone 

plan.’’ 

54 2020 Plan, Attachment A, Section A.8. 

55 Id. 

56 Id. 

57 2020 Plan, Section 2.1.3.1 and Attachment B. 

58 Id., Section 2.1.3.2 and Attachment C. 

59 ‘‘The Safer Affordable Fuel-Efficient (SAFE) 

Vehicles Rule Part One: One National Program’’ 

(SAFE 1), 84 FR 51310 (September 27, 2019). 

sources category is divided into two 

major subcategories, ‘‘on-road’’ and ‘‘offroad’’ mobile sources. On-road mobile 

sources include light-duty automobiles, 

light-, medium-, and heavy-duty trucks, 

and motorcycles. Off-road mobile 

sources include aircraft, locomotives, 

construction equipment, mobile 

equipment, and recreational vehicles. 

Point source (also referred to as 

‘‘stationary source’’) emissions for the 

2011 and 2017 base year emissions 

inventories are calculated using 

reported data from facilities using the 

District’s annual emissions reporting 

program, which applies under District 

Rule 19.3 to stationary sources in the 

San Diego County area that emit 25 tons 

per year (tpy) or more of VOC or NOX. 

Area sources include smaller emissions 

sources distributed across the 

nonattainment area. CARB and the 

District estimate emissions for 

numerous area source categories using 

established inventory methods, 

including publicly available emissions 

factors and activity information. 

Specific estimates are included in the 

2020 Plan for area source categories: 

consumer products, architectural 

coatings and related process solvent use, 

pesticides and fertilizers, asphalt paving 

and roofing, residential fuel 

combustion, farming operations, fires, 

managed burning and disposal, and 

cooking. 

On-road emissions inventories in the 

2020 Plan are calculated using CARB’s 

EMFAC2017 model and the travel 

activity data provided by SANDAG in 

SANDAG’s 2018 adopted Regional 

Transportation Improvement Program.48

CARB provided emissions inventories 

for off-road equipment, including 

construction and mining equipment, 

industrial and commercial equipment, 

lawn and garden equipment, 

agricultural equipment, ocean-going 

vessels, commercial harbor craft, 

locomotives, cargo handling equipment, 

pleasure craft, and recreational vehicles. 

CARB used several models to estimate 

emissions for off-road equipment 

categories.49 Aircraft emissions 

inventories are developed in 

conjunction with the airports in the 

region. In particular, an emissions 

analysis was included in the 2020 Plan 

for the San Diego International 

Airport.50

The 2020 Plan distinguishes between 

emissions sources within San Diego 

County, which includes coastal 

emissions (including marine vessel 

emissions) within three NM of the 

coastline, and emissions sources 

operating outside the county but within 

100 NM of the coastline. The base year 

emissions inventory reflects only those 

emissions sources that operate within 

the nonattainment area (i.e., within 

three NM of the coastline), but offshore 

emissions sources affect ozone 

concentrations in the nonattainment 

area and thus are included in the 

emissions inventories used for the 

attainment demonstrations in the 2020 

Plan. 

The calendar year 2017 is the base 

year in the 2020 Plan for both the 2008 

and 2015 ozone NAAQS because 2017 

the most recent calendar year for which 

a complete triennial inventory was 

required to be submitted to the EPA 

under the provisions of 40 CFR part 51, 

subpart A at the time of plan 

development. The 2020 Plan includes 

an emissions inventory for an earlier 

year, i.e., calendar year 2011, because 

that year is the RFP baseline year for the 

2008 ozone NAAQS. The 2017 base year 

inventory was used to forecast all future 

years for area and mobile sources and to 

‘‘backcast’’ such sources for 2011.51

To develop the 2011 inventory, CARB 

relied on actual emissions reported from 

industrial point sources for 2011 and 

backcast emissions from 2017 for 

smaller stationary and certain area 

sources.52 Area source emissions from 

pesticide were developed by CARB 

based on actual emissions reported for 

2011, while those from agricultural 

burning were developed by CARB based 

on actual emissions reported for 2008 

that were ‘‘grown’’ (that is, projected 

forward from 2008, based on estimated 

changes in agricultural burning) to 2011. 

CARB produced 2011 on-road emissions 

estimates using EMFAC2017. Non-road 

emissions were either backcast from 

2017 (commercial aircraft and military 

ocean-going vessels) or were estimated 

using CARB’s OFFROAD2007 model.53

For the 2020 Plan, CARB used the 

California Emission Projection Analysis 

Model (CEPAM), 2019 SIP Baseline 

Emission Projections, Version 1.00 to 

develop future year emissions forecasts 

(i.e., 2020, 2023, 2026, 2029 and 

2032).54 In doing so, CARB reviewed the 

growth and control factors for each 

category and relevant year along with 

the resulting emissions projections.55

CARB compared year-to-year trends to 

similar and past datasets to ensure 

general consistency, checked emissions 

for specific categories to confirm they 

reflect the anticipated effects of 

applicable control measures, and 

verified mobile source categories with 

CARB mobile source staff for 

consistency with the on-road and offroad emission models.56

In developing the 2020 Plan, the 

District worked with the Department of 

the Navy and the United States Marine 

Corps to identify specific growth 

increments from future anticipated 

actions to include in the baseline 

emissions forecasts for use by the 

military to comply with the applicable 

general conformity regulations. The 

District then coordinated with CARB to 

include the growth increments or 

‘‘budgets’’ in the applicable source 

categories in the CEPAM model used by 

CARB to develop the future year 

emissions inventories. More 

specifically, the CEPAM model runs 

used for the future year emissions 

estimates in the 2020 Plan reflect a 

military growth increment of 1.08 tpd of 

VOC and 8.34 tpd of NOX for all future 

years addressed in the plan.57 Similarly, 

the District worked with the San Diego 

County Regional Airport Authority to 

identify a growth increment for future 

anticipated actions at San Diego 

International Airport (SDIA) for use in 

connection with the general conformity 

regulations. The growth increment for 

SDIA for all future year emissions 

estimates in the 2020 Plan is 0.141 tpd 

of VOC and 1.756 tpd for NOX.58

Section III.H of this document provides 

further information on the military and 

SDIA growth increments reflected in the 

2020 Plan. 

The future year emissions estimates in 

the 2020 Plan include two additional 

specific adjustments—one to account for 

pre-base year emissions reduction 

credits (ERCs) and one to account for 

the EPA’s rescission, in a final action 

referred to as ‘‘SAFE 1,’’ of a waiver of 

preemption of CARB’s light-duty 

vehicle zero emission vehicle (ZEV) 

sales mandate and greenhouse gas 

(GHG) standards.59

Under the EPA’s SIP regulations for 

nonattainment new source review (NSR) 

programs, a state may allow new major 

stationary sources or major 

modifications to use as offsets ERCs that 

were generated through shutdown or 


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60 40 CFR part 51, Appendix S, section IV.C.5. 

61 2020 Plan, section 2.1.3.3 and Attachment F. 

62The EPA issued the ACC waiver on January 9, 

2013 (78 FR 2112). 

63Letter and enclosures dated March 5, 2020 from 

Steven S. Cliff, Ph.D., Deputy Executive Officer, 

CARB, to Elizabeth Adams, Director, Air and 

Radiation Division, EPA Region IX. 

64Letter dated March 12, 2020, from Elizabeth J. 

Adams, Director, Air and Radiation Division, EPA 

Region IX, to Steven S. Cliff, Ph.D., Deputy 

Executive Officer, CARB. 65Tables 1 and 2 summarize anthropogenic 

emissions sources only, which is consistent with 

the EPA’s ‘‘Emissions Inventory Guidance for 

Implementation of Ozone and Particulate Matter 

National Ambient Air Quality Standards (NAAQS) 

and Regional Haze Regulations’’ (May 2017). 

Anthropogenic emissions sources are 

distinguishable from natural sources, which include 

biogenic, geogenic and wildfire emissions sources. 

Both anthropogenic and natural sources of 

emissions are, however, included in emissions 

inventories used for attainment demonstration 

modeling purposes. 

curtailed emissions units occuring 

before the base year of an attainment 

plan. However, to use such ERCs, the 

projected emissions inventories used to 

develop the RFP and attainment 

demonstration must explicitly include 

the emissions from such previously 

shutdown or curtailed emissions 

units.60 The District has elected to 

provide for use of pre-base year ERCs as 

offsets by explicitly including such 

ERCs in the future year emissions 

estimates in the 2020 Plan. The ERC setaside in the 2020 Plan amounts to 0.71 

tpd of VOC and 0.56 tpd of NOX.61

The ‘‘EMFAC2017 Adjustment 

Factors’’ refers to adjustment factors that 

CARB developed for EMFAC2017 to 

account for the EPA’s SAFE 1 final 

action that, among other things, 

withdrew the EPA’s waiver of 

preemption for CARB’s Advanced Clean 

Car (ACC) regulation as it pertained to 

CARB’s ZEV sales mandate and GHG 

standards.62 EMFAC2017 reflected 

emissions reductions that were 

estimated to be achieved through 

implementation of the ACC regulation, 

including the ZEV sales mandate. In 

response to the EPA’s SAFE 1 action, 

CARB developed correction factors to be 

used to account for the foregone 

emissions reductions (EMFAC2017 

Adjustment Factors).63 In 2020, the EPA 

concurred on the use of CARB’s 

EMFAC2017 Adjustment Factors for the 

purposes of SIP development in 

California,64 and the 2020 Plan takes 

them into account as an adjustment to 

the EMFAC2017-derived motor vehicle 

emissions estimates included in the 

future year emissions inventories. For 

the 2020 Plan, the EMFAC2017 

Adjustment Factor is generally 0.1 tpd 

or less for VOC and NOX in all future 

years expected to be affected by the 

SAFE 1 action. 

Table 1 of this document provides a 

summary of the baseline emissions 

inventories for the base year and future 

years in tpd (average summer day) for 

VOC and NOX for the 2008 ozone 

NAAQS.65 The inventories summarized 

in Table 1 distinguish between 

emissions generated within the 

nonattainment area and emissions that 

are generated offshore between three 

NM and 100 NM from the coastline of 

San Diego County. Table 1 also shows 

the adjustments made to account for 

ERCs and the EMFAC2017 Adjustment 

Factors. Table 2 of this document 

provides the same type of summary 

information as Table 1, but presents the 

base year and future years that are 

relevant for the 2015 ozone NAAQS. 

Based on the emissions inventory for 

2017, stationary, area, and mobile 

sources (on-road and off-road) 

contribute roughly equally to countywide VOC emissions, whereas mobile 

sources (on-road and off-road) are the 

predominant sources of NOX emissions. 

The inventory for 2017 also shows the 

magnitude of marine offshore (3 NM to 

100 NM) emissions sources relative to 

those within the nonattainment area. A 

comparison of the base years with the 

future years shows the significant 

decrease that is expected to be achieved 

through CARB’s regulations for new onroad and off-road mobile sources 

together with vehicle turnover (i.e., the 

rate of replacement of older, more 

polluting models with new models 

manufactured to meet tighter emissions 

standards). For a more detailed 

discussion of the methodologies used to 

develop the inventories, see Attachment 

A of the 2020 Plan. 

TABLE 1—SAN DIEGO COUNTY BASE YEAR AND FUTURE YEAR BASELINE EMISSIONS INVENTORIES FOR THE 2008 OZONE

NAAQS 

[Summer planning inventory, tpd] 

2011 2017 2020 2023 2026 

NOX VOC NOX VOC NOX VOC NOX VOC NOX VOC 

Stationary Sources ... 4.4 27.4 4.1 27.6 4.0 26.9 3.9 26.3 4.0 26.3 

Area Sources ........... 1.9 36.8 1.7 33.6 1.5 34.3 1.4 34.8 1.2 35.2 

On-Road Mobile 

Sources ................. 71.2 34.4 37.7 20.5 28.5 16.5 19.7 13.8 17.5 12.3 

Off-Road Mobile 

Sources ................. 33.2 38.0 33.5 31.1 32.6 28.5 31.2 26.7 30.3 25.2 

Emission Reduction 

Credits adjustment ................ ................ ................ ................ 0.6 0.7 0.6 0.7 0.6 0.7 

EMFAC2017 Adjustment Factor .......... ................ ................ ................ ................ ................ ................ <0.1 0.1 <0.1 <0.1 

Total—San 

Diego County 

Nonattainment 

Area ............... 110.7 136.6 77.0 112.9 67.1 107.0 56.8 102.4 53.6 99.7 

Marine Emissions (3 

NM–100 NM) ........ 15.8 0.8 17.5 1.0 17.5 1.0 18.1 1.0 18.6 1.1 


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TABLE 1—SAN DIEGO COUNTY BASE YEAR AND FUTURE YEAR BASELINE EMISSIONS INVENTORIES FOR THE 2008 OZONE

NAAQS—Continued 

[Summer planning inventory, tpd] 

2011 2017 2020 2023 2026 

NOX VOC NOX VOC NOX VOC NOX VOC NOX VOC 

Total—Nonattainment 

Area plus Marine Emissions 

(3 NM–100 

NM) ................ 126.5 137.5 94.5 113.8 84.7 108.0 74.8 103.4 72.2 100.8 

Source: 2020 Plan, Attachment A, Tables A–1 and A–3. The sum of the emissions values may not equal the total due to rounding of the 

numbers. 

TABLE 2—SAN DIEGO COUNTY BASE YEAR AND FUTURE YEAR BASELINE EMISSIONS INVENTORIES FOR THE 2015 OZONE

NAAQS 

[summer planning inventory, (tpd)] 

2017 2023 2026 2029 2032 

NOX VOC NOX VOC NOX VOC NOX VOC NOX VOC 

Stationary Sources ... 4.1 27.6 3.9 26.3 4.0 26.3 4.0 26.6 4.1 27.2 

Area Sources ........... 1.7 33.6 1.4 34.8 1.2 35.2 1.0 35.6 1.0 36.1 

On-Road Mobile 

Sources ................. 37.7 20.5 19.7 13.8 17.5 12.3 16.0 11.1 15.1 10.0 

Off-Road Mobile 

Sources ................. 33.5 31.1 31.2 26.7 30.3 25.2 29.7 24.2 28.9 23.2 

Emission Reduction 

Credits adjustment ................ ................ 0.6 0.7 0.6 0.7 0.6 0.7 0.6 0.7 

EMFAC2017 Adjustment Factor .......... ................ ................ <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1 

Total—San 

Diego County 

Nonattainment 

Area ............... 77.0 112.9 56.8 102.4 53.6 99.7 51.3 98.2 49.7 97.2 

Marine Emissions (3 

NM–100 NM) ........ 17.5 1.0 18.1 1.0 18.6 1.1 19.0 1.0 19.3 1.1 

Total—Nonattainment 

Area plus Marine Emissions 

(3 NM–100 

NM) ................ 94.5 113.8 74.8 103.4 72.2 100.8 70.0 99.3 69.0 98.3 

Source: 2020 Plan, Attachment A, Tables A–1 and A–3. The sum of the emissions values may not equal the total due to rounding of the 

numbers. 

3. The EPA’s Review of the State’s 

Submission 

The 2020 Plan refers to year 2017 as 

the base year inventory for both the 

2008 and 2015 ozone NAAQS but also 

includes an inventory of actual 

emissions in calendar year 2011, which 

we have reviewed for the purpose of 

evaluating compliance with the base 

year emissions inventory SIP 

requirement for the 2008 ozone NAAQS. 

Year 2017 is the appropriate base year 

for the emissions inventory SIP 

requirement for the 2015 ozone NAAQS. 

We have reviewed the 2011 and 2017 

base year emissions inventories in the 

2020 Plan and the inventory 

methodologies used by the District and 

CARB for consistency with CAA 

requirements and EPA guidance. First, 

we find that the 2011 and 2017 

inventories include estimates for VOC 

and NOX for a typical ozone season 

weekday, and that CARB has provided 

adequate documentation explaining 

how the emissions are calculated. 

Second, we find that the 2011 and 2017 

base year emissions inventories in the 

2020 Plan reflect appropriate emissions 

models and methodologies, and, 

therefore, represent comprehensive, 

accurate, and current inventories of 

actual emissions during those years in 

the San Diego County area. Therefore, 

the EPA is proposing to approve the 

2011 and 2017 emissions inventories in 

the 2020 Plan as meeting the 

requirements for base year inventories 

for 2008 and 2015 ozone set forth in 

CAA sections 172(c)(3) and 182(a)(1), 

and 40 CFR 51.1115 and 40 CFR 

51.1315. In addition, although the 

requirement for a base year emissions 

inventory applies to the nonattainment 

area, we find that the District’s estimates 

of marine emissions out to 100 NM (i.e., 

beyond the nonattainment area 

boundary that extends three NM 

offshore) are reasonable and appropriate 

to include in the 2020 Plan given that 

such emissions must be accounted for in 


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66See Section III.H of this document for our full 

evaluation, and proposed approval, of the growth 

increments for the military and SDIA. 

67 87 FR 14332 (March 14, 2022). 

68See generally Committee for a Better Arvin v. 

EPA, 786 F.3d 1169, 1175–1177 (9th Cir. 2015). 

69The EPA’s review of District rules relied upon 

in developing the future baseline emissions 

inventories is presented in Memorandum to Docket 

EPA–R09–OAR–2021–0135 from Jeff Wehling, 

Office of Regional Counsel, EPA Region IX, August 

25, 2023. 

70 District Rule 61.4.1 should be submitted for 

approval as part of the SIP; however, the related 

emissions reductions are not of a magnitude as to 

implicate the RFP or attainment demonstrations. 

71See 81 FR 39424 (June 16, 2016), 82 FR 14446 

(March 21, 2017), and 83 FR 23232 (May 18, 2018). 

72 40 CFR 51.1112(c); 40 CFR 51.1312(c). The 

‘‘San Diego County area’’ is shorthand for two 

nonattainment areas, one for each of two ozone 

NAAQS: the 2008 and the 2015 ozone NAAQS. The 

boundary is the same for both areas. Accordingly, 

the District submitted two attainment 

demonstrations in the 2020 Plan, one for each of the 

two standards. 

73See General Preamble, 57 FR 13498, 13560 

(April 16, 1992) and memorandum dated November 

30, 1999, from John S. Seitz, Director, OAQPS, to 

Regional Air Directors, Subject: ‘‘Guidance on the 

Reasonably Available Control Measure Requirement 

and Attainment Demonstration Submissions for 

Ozone Nonattainment Areas.’’ 

74 Id. See also 44 FR 20372 (April 4, 1979), and 

memorandum dated December 14, 2000, from John 

S. Seitz, Director, OAQPS, to Regional Air 

Directors, Subject: ‘‘Additional Submission on 

RACM From States with Severe One-Hour Ozone 

Nonattainment Area SIPs.’’ 75California submitted the CAA section 182 

RACT SIP for the San Diego County area for both 

the 2008 and 2015 ozone NAAQS, as a Severe 

nonattainment area with a 25 tpy major source 

threshold, on December 29, 2020. To date, the EPA 

has taken several actions on the San Diego County 

RACT SIP. We are not taking action on the RACT 

SIP in this rulemaking but will be completing 

action on it in a separate rulemaking(s). 

the ozone attainment demonstrations for 

this nonattainment area. 

With respect to the future year 

emissions baseline projections, we have 

reviewed the growth and control factors 

and find them acceptable and conclude 

that the future baseline emissions 

projections in the 2020 Plan reflect 

appropriate calculation methods and the 

latest planning assumptions. We have 

also reviewed the documentation 

concerning the growth increments for 

the military and for SDIA and the 

documentation for the ERCs and find 

that they are appropriately accounted 

for in the future year baseline emissions 

inventories or, in the case of the ERCs, 

as an off-model adjustment to the 

inventories.66 With respect to the 

EMFAC2017 Adjustment Factors, we 

note that, since adoption of the 2020 

Plan, the EPA has rescinded SAFE 1 

(the withdrawal of the waiver of CARB’s 

ZEV sales mandate and GHG 

standards),67 which calls into question 

the use of the EMFAC2017 Adjustment 

Factor, as it may affect projections, 

particularly over the long term. 

However, as shown in Tables 1 and 2, 

the EMFAC2017 Adjustment Factor 

adjustment in the future year emissions 

inventories is insignificant (0.1 tpd or 

less for both VOC and NOX), and thus 

the change in circumstances regarding 

the status of CARB’s ZEV sales mandate 

does not affect the emissions projections 

used for the RFP and attainment 

demonstrations in the 2020 Plan. 

Also, as a general matter, the EPA will 

approve a SIP revision that takes 

emissions reduction credit for a control 

measure only where the EPA has 

approved the measure as part of the SIP. 

Thus, to take credit for the emissions 

reductions from District rules for 

stationary sources and CARB rules for 

mobile sources, the related rules must 

be approved by the EPA into the SIP.68

The EPA performed a review of District 

rules relied upon in developing the 

future baseline emissions inventories for 

the 2020 Plan.69 Based on our review, 

we find that, with only one exception 

that does not implicate the RFP or 

attainment demonstrations of the 2020 

Plan,70 District rules relied upon in 

developing the future baseline 

emissions inventories are approved as 

part of the SIP. With respect to mobile 

sources, the EPA has taken action in 

recent years to approve CARB mobile 

source regulations into the California 

SIP.71 We therefore find that the future 

year baseline projections in the 2020 

Plan are properly supported by SIPapproved stationary and mobile source 

measures. 

B. Reasonably Available Control 

Measures Demonstration and Control 

Strategy 

1. Statutory and Regulatory 

Requirements 

CAA section 172(c)(1) requires that 

each attainment plan provide for the 

implementation of all RACM as 

expeditiously as practicable (including 

such reductions in emissions from 

existing sources in the area as may be 

obtained through implementation of 

reasonably available control technology 

(RACT)), and to provide for attainment 

of the NAAQS. The 2008 Ozone SRR 

and the 2015 Ozone SRR require that, 

for each nonattainment area required to 

submit an attainment demonstration, 

the state concurrently submit a SIP 

revision demonstrating that it has 

adopted all RACM necessary to 

demonstrate attainment as expeditiously 

as practicable and to meet any RFP 

requirements.72

The EPA has previously provided 

guidance interpreting the RACM 

requirement, in the General Preamble 

for the Implementation of the Clean Air 

Act Amendments of 1990 (‘‘General 

Preamble’’) and in a memorandum 

entitled ‘‘Guidance on the Reasonably 

Available Control Measure Requirement 

and Attainment Demonstration 

Submissions for Ozone Nonattainment 

Areas.’’ 73 In short, to address the 

requirement to adopt all RACM, states 

should consider all potentially 

reasonable measures for source 

categories in the nonattainment area to 

determine whether they are reasonably 

available for implementation in that 

area and whether they would, if 

implemented individually or 

collectively, advance the area’s 

attainment date by one year or more.74

Any measures that are necessary to meet 

these requirements that are not already 

either federally promulgated, or part of 

the state’s SIP, must be submitted in 

enforceable form as part of the state’s 

attainment plan for the area. 

For ozone nonattainment areas 

classified as Moderate or above, CAA 

section 182(b)(2) also requires 

implementation of RACT for all major 

sources of VOC and for each VOC 

source category for which the EPA has 

issued a control techniques guideline. 

CAA section 182(f) requires that RACT 

under section 182(b)(2) also apply to 

major stationary sources of NOX. In 

Severe areas, a major source is a 

stationary source that emits or has the 

potential to emit at least 25 tpy of VOC 

or NOX (CAA sections 182(d) and (f)). 

Under the 2008 Ozone SRR and the 

2015 Ozone SRR, states were required to 

submit SIP revisions meeting the RACT 

requirements of CAA sections 182(b)(2) 

and 182(f) no later than 24 months after 

the effective date of designation for the 

2008 ozone NAAQS and the 2015 ozone 

NAAQS, respectively. Implementation 

of the required RACT measures is 

required as expeditiously as practicable 

but no later than January 1 of the 5th 

year after the effective date of 

designation for the 2008 ozone NAAQS 

(see 40 CFR 51.1112(a)) and for the 2015 

ozone NAAQS (see 40 CFR 

51.1312(a)).75

2. Summary of the State’s Submission 

The 2020 Plan presents two RACM 

demonstrations. The first is included in 

Section 3.2.1 and addresses the 2008 

ozone NAAQS. The second is presented 

in Section 4.2.1 for the 2015 ozone 

NAAQS. Within each Section, the 2020 

Plan presents a RACM analysis 

organized by several emissions source 

groups. The District and CARB each 

undertook a process to identify and 

evaluate potential RACM that could 

contribute to expeditious attainment of 

the 2008 ozone NAAQS and the 2015 


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76 2020 Plan, Sections 3.2.1 and 4.2.1. 

77 2020 Plan, p. 38. In this context, ‘‘transport 

couplet’’ refers to a ‘‘transport couple,’’ a term that 

refers to two air basins, one of which has an impact 

on ambient air pollutant concentrations in the other 

air basin due to transport of pollutants and 

precursors by prevailing wind patterns. See 

‘‘Assessment of the Impacts of Transported 

Pollutants on Ozone Concentrations in California,’’ 

CARB, March 2001. 

78 2020 Plan, Table A–2. 

ozone NAAQS in the San Diego County 

area. In addition, the District presented 

a ‘‘RACM Cumulative Analysis’’ for 

each standard as an overarching 

analysis of all source categories covered 

by CARB, the District and SANDAG.76

The 2020 Plan’s RACM section for the 

2008 ozone NAAQS begins by 

determining the magnitude of emissions 

reductions that would be needed to 

advance the area’s attainment date by 

one year. As noted in Section I.B of this 

document, air pollutants transported 

from the South Coast region contribute 

to higher ozone levels in San Diego 

County under certain weather 

conditions. Accordingly, the RACM 

analysis in the 2020 Plan for the 2008 

ozone NAAQS accounts for projected 

emissions from the San Diego CountySouth Coast transport couplet.77

Using emissions levels of the 

District’s chosen 2026 attainment 

demonstration year as a basis for 

comparison, the District compared 

emissions levels from 2026 to what the 

levels are projected to be one year 

earlier, that is, 2025. The lower levels in 

2026 were then subtracted from the 

higher levels of emissions in 2025, 

providing a difference in emissions 

levels that could then be compared 

against the 2020 Plan’s RACM, that is, 

emissions reductions from reasonably 

available control measures, to determine 

if enough RACM reductions would be 

available to advance the 2026 

attainment year to 2025. These levels 

are provided in Table 3 of this 

document. 

TABLE 3—EMISSIONS REDUCTIONS NEEDED TO ADVANCE ATTAINMENT BY ONE YEAR, 2008 OZONE NAAQS 

Emissions totals Emissions 

(tpd) 

2026 VOC Emissions Inventory .......................................................................................................................................................... 471.0 

2025 VOC Emissions Inventory .......................................................................................................................................................... 473.8 

VOC Emissions Reductions Needed in 2025 to Demonstrate Attainment ......................................................................................... 2.8 

2026 NOX Emissions Inventory ........................................................................................................................................................... 344.0 

2025 NOX Emissions Inventory ........................................................................................................................................................... 347.4 

NOX Emissions Reductions Needed in 2025 to Demonstrate Attainment .......................................................................................... 3.4 

Source: 2020 Plan, Table 3–2 and Table A–2. 

Because the District’s attainment 

demonstration relies on specific levels 

of emissions of both VOC and NOX, the 

reductions of emissions to advance that 

attainment date one year would require 

reductions in both VOC and NOX at the 

levels shown in Table 3, that is, 2.8 tpd 

of VOC and 3.4 tpd of NOX (‘‘2008 

ozone NAAQS RACM targets’’). These 

amounts of reductions are then viewed 

as targets to see if they can be met or 

exceeded, and if so, then the attainment 

year for the 2008 ozone NAAQS would 

be moved up one year, to 2025. The 

2020 Plan groups emissions sources into 

several large categories and assesses 

each one to identify potential RACM 

and to determine their potential 

collectively to provide emissions 

reductions equal to or greater than these 

targets. 

a. 2008 Ozone NAAQS, District’s RACM 

Analysis 

The District provides a 

comprehensive evaluation of its 2008 

ozone NAAQS RACM control strategy in 

Section 3.2.1 (‘‘Reasonably Available 

Control Measures (RACM) 

Demonstration’’) and Attachments A, D, 

G, H, I and J of the 2020 Plan. The 

evaluation includes: source 

descriptions; base year and projected 

baseline year emissions for the source 

category affected by the rule; discussion 

of the current requirements of the rule; 

and discussion of potential additional 

control measures, including, in many 

cases, a discussion of the technological 

and economic feasibility of the 

additional control measures. This 

includes a comparison of each District 

rule to analogous control measures 

adopted by other agencies. 

The District’s RACM demonstration 

for the 2008 ozone NAAQS begins with 

an analysis of stationary source controls, 

described in Section 3.2.1.2 

(‘‘Identifying Potential RACM for 

Stationary Sources’’) of the 2020 Plan. 

This section of the 2020 Plan identifies 

potential control measures and analyzes 

these measures for emissions reduction 

opportunities, as well as economic and 

technological feasibility. The District’s 

comprehensive demonstration considers 

potential control measures for stationary 

sources located throughout the area 

under its jurisdiction, that is, the 

entirety of San Diego County. 

As a first step in the RACM analysis, 

the District prepared a detailed 

inventory of emissions sources of VOC 

and NOX to identify source categories 

from which emissions reductions would 

effectively contribute to attainment. 

Details on the methodology and 

development of the emissions inventory 

are discussed in Section 3 and 

Attachment A of the 2020 Plan. Because 

the San Diego County area airshed is 

coupled with the South Coast Air Basin, 

which was used in the attainment 

demonstration modeling in the 2020 

Plan, the District prepared a ‘‘couplet’’ 

emissions inventory that includes the 

two areas’ combined emissions. A total 

of 75 source categories are included in 

the couplet emissions inventory: 45 for 

stationary and area sources and 30 for 

mobile sources.78 Although the couplet 

emissions inventory includes South 

Coast and is therefore used in 

calculating the 2008 ozone NAAQS 

RACM targets (2.8 tpd VOC, 3.4 tpd 

NOX), only sources of emissions within 

San Diego County were evaluated for 

their potential to either meet the 2008 

ozone NAAQS RACM targets or to 

contribute to a collective reduction to 

meet those targets. 

The District compared the 45 source 

categories to its rules for stationary and 

area sources. This analysis builds upon 

a foundation of District rules developed 

for earlier ozone plans and approved as 

part of the SIP. These rules establish 

emissions limits or other types of 

emissions controls for a wide range of 

sources, including VOC storage and 

handling, use of solvents, gasoline 

storage, gasoline transfer, dry cleaning 

with petroleum-based solvent, 

architectural coatings, surface coating 

operations, marine, wood products and 

aerospace coating operations, degreasing 

operations, cutback and emulsified 

asphalts, kelp processing and 


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79California Health & Safety Code sections 40918, 

40919, 40920 and 40920.5. 

80The State of California submitted the San Diego 

County area’s 2016 Moderate ozone attainment plan 

to the EPA as a SIP revision on April 12, 2017. At 

the time, the area was a Moderate nonattainment 

area for the 2008 ozone NAAQS. The State 

withdrew the 2016 Moderate ozone attainment plan 

by letter dated December 16, 2021 following 

submittal of the 2020 Plan and the EPA’s grant of 

the State’s request to reclassify San Diego County 

to Severe for the 2008 ozone NAAQS. 

81 2020 Plan, Table G–1, items G.1 to G.11. 

82Email dated August 31, 2023, from Nick 

Cormier, SDCAPCD, to John J. Kelly, EPA. 

83 2020 Plan, Table G–1, items G.12 to G.17. 

84EPA, MCM, April 12, 2012. 

85 2020 Plan, Attachment G, Table G–1. 

86The 2019 RTP was adopted by SANDAG’s 

Board on October 25, 2019. The 2019 RTP was 

approved by the Federal Highway Administration 

on November 15, 2019. 

87 2020 Plan, Attachment H, ‘‘Implementation 

Status of Transportation Control Measures,’’ Table 

H–1. 

biopolymer manufacturing operations, 

pharmaceutical and cosmetic 

manufacturing, and bakery ovens, 

among others. These rules have already 

provided significant reductions toward 

attainment of the 2008 ozone NAAQS 

by 2026. 

The District excluded RACT rules 

from their stationary source RACM 

analysis because those rules are already 

required by federal law to be included 

in the SIP and are therefore not 

‘‘potential’’ RACM control measures. 

Likewise, the District excluded 

stationary and area sources it regulates 

under the State’s requirement to adopt 

‘‘all feasible measures,’’ as these 

measures are also already implemented 

and incorporated into the area’s 

attainment demonstration, and are 

therefore also not potential RACM. In 

addition, California state law requires 

‘‘Best Available Retrofit Control 

Technology’’ or BARCT.79 Because 

BARCT is an ongoing requirement for 

the District, BARCT rules are already 

implemented, would provide no new 

emissions reductions, and are therefore 

not potential RACM. 

To demonstrate that the SDCAPCD 

considered all candidate measures that 

are available and technologically and 

economically feasible for stationary 

sources, the District conducted several 

steps in their analysis. 

Step 1. Stakeholder Outreach 

As part of a previous planning effort 

for the 2008 ozone NAAQS (the 2016 

Moderate Plan),80 and again as part of 

the SIP development effort for the 

(Severe) 2020 Plan, the District held 

multiple stakeholder outreach sessions. 

These sessions were intended to solicit 

stakeholder input on the full array of 

control measures that might be available 

for emissions sources in the area. Two 

public workshops were held in July 

2020, in addition to other individual 

stakeholder meetings that were held for 

feedback on the entire draft 2020 Plan 

before and after each public workshop. 

These meetings built upon similar 

outreach the District conducted for prior 

federal and state air quality plans, 

including the 2016 Moderate Plan. 

Step 2. Reasonably Available Control 

Technology Analysis 

The District then considered 

Reasonably Available Control 

Technology (RACT) stationary source 

categories and found 11 existing District 

control measures that could be further 

controlled when compared to existing 

rules in other California air districts.81

These 11 control measures apply to 

specific types of emissions sources: 

Receiving and Storing Volatile Organic 

Compounds at Bulk Plants and Bulk 

Terminals, Transfer of Organic 

Compounds into Mobile Transport 

Tanks, Metal Parts and Product Coating 

Operations, Paper, Film, and Fabric 

Coatings, Aerospace Coating Operations, 

Graphic Arts Operations, Marine 

Coating Operations, Adhesive Materials 

Application Operations, Industrial and 

Commercial Boilers, Process Heaters 

and Steam Generators, Natural GasFired Fan-Type Central Furnaces, and 

Stationary Gas Turbine Engines. The 

SDCAPCD compared its rules to the 

analogous rules for the same stationary 

source types in other California air 

districts, as candidate potential 

measures, and estimated the potential 

emissions reductions associated with 

each control measure if it were modified 

to reflect the other district’s rule. 

Step 3. EPA Technical Support 

Documents (TSDs) 

The District researched TSDs from 

recent EPA rulemakings but did not find 

any potential additional stationary 

source controls beyond what its RACT 

analysis found.82

Step 4. Control Measures in Other Areas 

The District reviewed stationary 

source control measures in other areas 

(i.e., San Francisco Bay Area, 

Sacramento, San Joaquin Valley, Santa 

Barbara, South Coast, and Ventura 

County) to evaluate whether control 

technologies available and cost-effective 

within other areas would be available 

and cost-effective for use in the San 

Diego County area.83 These include six 

control measures: Vacuum Truck 

Operations, Miscellaneous NOX

Sources, Equipment Leaks, Restaurant 

Cooking Operations, Food Products 

Manufacturing/Processing, and 

Metalworking Fluids and Direct-Contact 

Lubricants. 

Step 5. EPA Menu of Control Measures 

The Menu of Control Measures 

(MCM) 84 compiled by the EPA’s Office 

of Air Quality Planning and Standards 

was created to provide information 

useful in the development of emissions 

reduction strategies and to identify and 

evaluate potential control measures. 

District staff reviewed the EPA’s MCM 

for stationary source point and nonpoint 

sources of NOX and VOC. 

Based on its evaluation of all available 

stationary source control measures, the 

District concluded that its existing rules 

are generally as stringent as analogous 

rules in other districts, and where they 

were not, quantified the difference. In 

all, the District estimated that the total 

possible emissions reductions from 

further control of stationary sources 

subject to existing District rules and 

control of additional source categories 

would be approximately 0.4 tpd for 

VOC and 0.4 tpd for NOX.85

b. 2008 Ozone NAAQS, RACM Analysis 

for Transportation Control Measures 

Attachment H of the 2020 Plan 

contains the District’s transportation 

control measure (TCM) RACM 

evaluation. The implemented TCMs in 

Attachment H are applicable in San 

Diego County. The District conducted 

the TCM RACM analysis on behalf of 

SANDAG and local jurisdictions in San 

Diego County, based on SANDAG’s 

regional transportation plan (RTP), 

specifically, ‘‘San Diego Forward: The 

2019 Federal Regional Transportation 

Plan’’ (‘‘2019 RTP’’).86 The 2019 RTP 

was developed in consultation with 

federal, state and local transportation 

and air quality planning agencies and 

other stakeholders. 

As described in Attachment H of the 

2020 Plan, for the TCM RACM analysis, 

the District listed all TCMs that are 

included in CAA section 108(f) and 

their implementation status in San 

Diego County.87 Of the 16 TCMs listed 

in CAA section 108(f), 13 are 

implemented in San Diego County. Of 

these implemented TCMs, five were 

included in the area’s 1982 SIP. 

Of the three TCMs that are not 

implemented in San Diego County, one 

(‘‘Trip Reduction Ordinances’’) was 

adopted in 1994, but was then rescinded 

in 1995 when federal and State laws 

were amended eliminating the mandate 


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88As amended in 1990, CAA section 182(d)(1)(B) 

required states with Severe ozone nonattainment 

areas to adopt and submit SIP revisions requiring 

employers in such areas to implement programs to 

reduce work-related vehicle trips and miles traveled 

by employees, commonly referred to as ‘‘trip 

reduction ordinances.’’ Amendments to the CAA 

promulgated in 1995 revised CAA section 

182(d)(1)(B) such that trip reduction ordinances are 

no longer required but may be adopted and 

submitted as SIP revisions at the state’s discretion. 

89 ‘‘Transportation Control Measures for the Air 

Quality Plan,’’ SANDAG, 1992. 

90CARB’s 2016 State Strategy is available in the 

docket for this action and at https://ww3.arb.ca.gov/ 

planning/sip/2016sip/rev2016statesip.pdf. 91 2020 Plan, p. I–2. 92 2016 State Strategy, Chapter 4 (‘‘State SIP 

Measures’’). 

93CARB Resolution 17–7 (dated March 23, 2017), 

p. 7. CARB’s resolution is available in the docket 

for this action and at https://ww3.arb.ca.gov/ 

planning/sip/2016sip/res17-7.pdf. 

94See, e.g., the EPA’s approval of standards and 

other requirements to control emissions from in-use 

heavy-duty diesel-powered trucks, at 77 FR 20308 

(April 4, 2012), revisions to the California on-road 

reformulated gasoline and diesel fuel regulations at 

75 FR 26653 (May 12, 2010), and revisions to the 

California motor vehicle inspection and 

maintenance program at 75 FR 38023 (July 1, 2010). 

95 2020 Plan, p. I–6. 

96 Id., pp. I–6, I–7. CARB’s consumer product 

measures are found in the California Code of 

Regulations, Title 17 (‘‘Public Health’’), Division 3 

(‘‘Air Resources’’), Chapter 1 (‘‘Air Resources 

Board’’), Subchapter 8.5 (‘‘Consumer Products’’). 

for such measures.88 Another 

(‘‘Programs to limit or restrict vehicle 

use in downtown areas or other areas of 

emission concentration particularly 

during periods of peak use’’ or ‘‘Peak 

Use Restriction Programs’’) was found to 

be infeasible due to San Diego’s lowdensity land use pattern and 

accompanying longer transit travel 

times. However, the District notes that 

SANDAG’s Smart Growth Incentive 

Program provides funding to cities in 

San Diego County for infrastructure 

projects that enhance alternatives to 

driving in higher density areas. 

Finally, one TCM, (‘‘Programs to 

reduce motor vehicle emissions, 

consistent with Title II, which are 

caused by extreme cold start 

conditions’’ or ‘‘Cold Weather Start 

Programs’’) was found to be not 

applicable to San Diego County due to 

its mild climate. 

Based on its review of TCM projects 

implemented in San Diego County, the 

District determined that 13 of the 16 

TCMs listed in CAA section 108(f) are 

being implemented in the county and 

are therefore ineligible for consideration 

as potential RACM. To determine if the 

three unimplemented TCMs could be 

required as RACM, the District 

estimated the maximum emissions 

reductions to be attributed to those 

TCMs. 

The 2020 Plan estimates the 

maximum emissions reduction potential 

of the three unimplemented TCMs, 

citing a 1992 SANDAG study that 

estimated maximum emissions 

reductions for Trip Reduction 

Ordinances alone at less than 2 percent 

of on-road vehicle emissions.89 The 

1992 SANDAG study also found that 

potential reductions of all 15 of the 

other TCMs combined do not equal the 

Trip Reduction Ordinances TCM alone. 

Therefore, the 2020 Plan estimates the 

maximum potential emissions reduction 

potential of the three unimplemented 

TCMs as 2 percent of on-road vehicle 

emissions in a given year. For the 

modeled attainment year, 2026, 

projected on-road motor vehicle 

emissions in San Diego County are 12.2 

tpd VOC and 17.5 tpd NOX. Two 

percent of these projected emissions is 

0.2 tpd VOC and 0.4 tpd NOX. 

c. 2008 Ozone NAAQS, CARB’s RACM 

Analysis 

CARB’s RACM analysis is contained 

in Attachment I (‘‘CARB Analyses of 

Potential Additional Mobile Source and 

Consumer Products Control Measures’’) 

(‘‘CARB RACM assessment’’) of the 2020 

Plan. The CARB RACM analysis 

provides a general description of 

CARB’s existing mobile source 

programs. In its analysis, CARB 

includes mobile source control 

measures described in CARB’s ‘‘2016 

State Strategy for the State 

Implementation Plan’’ (2016 State 

Strategy).90 A more detailed description 

of CARB’s mobile source control 

program, including a comprehensive 

table listing on- and off-road mobile 

source regulatory actions taken by 

CARB from 1985 to 2019, is contained 

in Attachment D of the 2020 Plan 

(‘‘CARB Control Measures, 1985 to 2019 

(March 2020)’’). CARB’s RACM analysis 

and 2016 State Strategy collectively 

contain CARB’s evaluation of mobile 

source and other statewide control 

measures that reduce emissions of NOX

and VOC in California, including San 

Diego County. 

Source categories for which CARB has 

primary responsibility for reducing 

emissions in California include most 

new and existing on- and off-road 

engines and vehicles, motor vehicle 

fuels, and consumer products. CARB 

developed its 2016 State Strategy 

through a multi-step measure 

development process, including 

extensive public consultation, to 

develop and evaluate potential 

strategies for mobile source categories 

under CARB’s regulatory authority that 

could contribute to expeditious 

attainment of the standard.91 Through 

the process of developing the 2016 State 

Strategy, CARB identified certain 

defined measures as available to achieve 

additional VOC and NOX emissions 

reductions from sources under CARB 

jurisdiction, including tighter 

requirements for new light- and 

medium-duty vehicles (referred to as the 

‘‘Advanced Clean Cars 2’’ measure), a 

low-NOX engine standard for vehicles 

with new heavy-duty engines, tighter 

emissions standards for small off-road 

engines, and more stringent 

requirements for consumer products, 

among others.92 In adopting the 2016 

State Strategy, CARB committed to 

bringing the defined measures to the 

CARB Board for action according to the 

specific schedule included as part of the 

strategy.93

Given the need for substantial 

emissions reductions from mobile and 

area sources to meet the NAAQS in 

California nonattainment areas, CARB 

established stringent control measures 

for on-road and off-road mobile sources 

and the fuels that power them. 

California has unique authority under 

CAA section 209 (subject to a waiver by 

the EPA) to adopt and implement new 

emission standards for many categories 

of on-road vehicles and engines, and 

new and in-use off-road vehicles and 

engines. 

CARB’s mobile source program 

extends beyond regulations that are 

subject to the waiver or authorization 

process set forth in CAA section 209 to 

include standards and other 

requirements to control emissions from 

in-use heavy-duty trucks and buses, 

gasoline and diesel fuel specifications, 

and many other types of mobile sources. 

Generally, these regulations have been 

submitted and approved as revisions to 

the California SIP.94

In their RACM analysis, CARB 

concludes that, in light of the extensive 

public process culminating in the 2016 

State Strategy, with the current mobile 

source program and proposed measures 

included in the 2016 State Strategy, 

there are no additional mobile source 

RACM that would advance attainment 

of the 2008 ozone NAAQS in San Diego 

County. As a result, CARB concludes 

that California’s mobile source programs 

fully meet the RACM requirement.95

Attachment I of the 2020 Plan 

describes CARB’s current consumer 

products program and commitments in 

the 2016 State Strategy to achieve 

additional VOC reductions from 

consumer products.96 As described in 

Attachment I, CARB’s current consumer 

products program limits VOC emissions 

from 129 consumer product categories, 

including product categories such as 


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97 Id., p. D–34. 

98The compilation of such measures that have 

been approved into the California SIP, including 

Federal Register citations, is available at: https://

www.epa.gov/sips-ca/epa-approved-regulationscalifornia-sip. EPA’s most recent approval of 

amendments to California’s consumer products 

regulations was in 2020. 85 FR 57703 (September 

16, 2020). 

99 2020 Plan, Section 3.2.1.6, ‘‘RACM Cumulative 

Analysis,’’ pp. 41–42. 

100 Id., Table J–1. 

101Although the District based its RACM analysis 

for the 2008 ozone NAAQS on emissions reductions 

in the San Diego County-South Coast transport 

couplet, the District also analyzed emissions 

reductions from the District alone and also 

concluded that the attainment year could not be 

advanced one year with RACM emissions 

reductions. See email dated August 9, 2023, from 

Nick Cormier, SDCAPCD, to Jefferson Wehling, 

EPA. 

102 2020 Plan, Table 4–2, p. 58. 

103 2020 Plan, Attachment G, Table G–1, 

‘‘Stationary Source Categories for Which More 

Stringent Control Requirements Have Been Adopted 

by Another Air District,’’ p. G–1. 

antiperspirants and deodorants and 

aerosol coatings.97 The EPA has 

approved these measures into the 

California SIP as VOC emissions 

controls for a wide array of consumer 

products.98

d. 2008 Ozone NAAQS, the District’s 

RACM Conclusion 

In addition to evaluating a number of 

stationary, area, and mobile sources, as 

well as consumer products, in the 

separate groups as described in Section 

III.B.a. to Section III.B.c. in this 

document, the District presents a 

‘‘cumulative analysis’’ to assess whether 

all potential RACM combined could 

result in advancement of the modeled 

2026 attainment year to 2025.99

Attachment J (‘‘Calculation of 

Cumulative Potential Emission 

Reductions for Possible Reasonably 

Available Control Measures (RACM)’’) 

of the 2020 Plan presents the 

cumulative potential RACM.100 When 

taken together, all potential RACM 

reductions of VOC and NOX that the 

District and CARB evaluated amount to 

approximately 0.7 tpd VOC and 0.7 tpd 

NOX. These amounts fall far short of the 

2008 ozone RACM targets of 2.8 tpd 

VOC and 3.4 tpd NOX.101 The District 

therefore concludes that, collectively, 

there are not enough potential RACM 

reductions to advance the attainment 

date. 

e. 2015 Ozone NAAQS, RACM 

In addition to addressing RACM for 

the 2008 ozone NAAQS, the 2020 Plan 

addresses RACM for the 2015 NAAQS. 

Section 4.2.1, ‘‘Reasonably Available 

Control Measures (RACM) 

Demonstration,’’ of the 2020 Plan 

contains the plan’s RACM 

demonstration for the 2015 ozone 

NAAQS. The demonstration reflects 

much of what the 2020 Plan presents for 

demonstrating RACM for the 2008 

ozone NAAQS and relies on the same 

attachments described in Section 

III.B.2.a.–d. of this document, that is, 

Attachments A (‘‘Emissions Inventories 

and Documentation for Baseline, RFP, 

and Attainment Years’’), D (‘‘CARB 

Control Measures, 1985 to 2019’’), G 

(‘‘Analyses of Potential Additional 

Stationary Source Control Measures’’), 

H (‘‘Implementation Status of 

Transportation Control Measures’’), I 

(‘‘CARB Analyses of Potential 

Additional Mobile Source and 

Consumer Products Control Measures’’), 

and J (‘‘Calculation of Cumulative 

Potential Emission Reductions for 

Possible Reasonably Available Control 

Measures (RACM’’). 

In the 2020 Plan, the District 

compares 2032 projected emissions of 

the ozone precursors VOC and NOX to 

those of the year prior, 2031, to 

determine the amount of emissions 

reductions that would be necessary in 

order to advance attainment by one 

year, to 2031, providing a 2015 ozone 

NAAQS RACM target. These levels are 

provided in Table 4 of this document. 

Unlike the emissions projections used to 

determine the magnitude of emissions 

reductions that would be necessary to 

advance attainment by one year for the 

RACM demonstration for the 2008 

ozone NAAQS, the emissions 

projections used to determine the 

magnitude of emissions reductions 

necessary to advance attainment by one 

year for the RACM demonstration for 

the 2015 ozone NAAQS reflect 

emissions only for San Diego County 

(i.e., including marine emissions 3 to 

100 NM off the County coastline) rather 

than those for the South Coast-San 

Diego couplet. Using this more 

conservative approach, the District 

determined that VOC reductions of 0.1 

tpd and NOX reductions of 5.9 tpd 

would advance the attainment date for 

the 2015 ozone NAAQS by one year.102

TABLE 4—EMISSIONS REDUCTIONS NEEDED TO ADVANCE ATTAINMENT BY ONE YEAR, 2015 OZONE NAAQS 

Emissions totals Emissions 

(tpd) 

2032 VOC Emissions Inventory .......................................................................................................................................................... 98.3 

2031 VOC Emissions Inventory .......................................................................................................................................................... 98.4 

VOC Emissions Reductions Needed in 2031 to Demonstrate Attainment ......................................................................................... 0.1 

2032 NOX Emissions Inventory ........................................................................................................................................................... * 63.3 

2031 NOX Emissions Inventory ........................................................................................................................................................... 69.2 

NOX Emissions Reductions Needed in 2025 to Demonstrate Attainment .......................................................................................... 5.9 

Source: 2020 Plan, Table 4–2, ‘‘Emissions Reductions Required to Advance Attainment By One Year, 2015 Ozone NAAQS (tons per day).’’ 

* Adjusted for RACM. The unadjusted 2032 NOX emissions inventory for San Diego County is 69.0 tpd. However, for attainment purposes, 

CARB has committed to obtain additional emissions reductions, in the amount of 4 tpd NOX, as described in Section 4.3.5 of the 2020 Plan, and 

1.7 tpd NOX, as described in Section 4.3.4 of the 2020 Plan and in Attachment L, Section L.3.9. These commitments add up to 5.7 tpd NOX, 

leaving a total emissions inventory of NOX in 2032 of 63.3 tpd. 

Once the District identifies 2015 

ozone NAAQS RACM targets (0.1 tpd 

VOC, 5.9 tpd NOX) in the 2020 Plan, the 

District assesses all potential RACM 

reductions to determine if, collectively, 

they could equal or exceed the targets. 

The District analyzes these potential 

RACM reductions in essentially the 

same steps as those taken to assess 

potential RACM for the 2008 ozone 

NAAQS, starting with stationary 

sources. As described in Section 

III.B.2.a. of this document, for the 

stationary source portion of the RACM 

demonstration for the 2008 ozone 

NAAQS, if all potential stationary 

source RACM were adopted in the area, 

stationary source emissions would be 

reduced an additional 0.41 tpd for VOC 

and 0.40 tpd for NOX.103 With respect 

to TCMs, the District estimates that if all 

unimplemented TCMs were to be 

adopted, transportation-related 

emissions sources in San Diego County 

would be reduced by 2 percent of the 

on-road motor vehicle emissions 

inventory for year 2032, or 


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104 Id., Section 4.2.1.5, ‘‘Identifying Potential 

RACM for Mobile Sources and Consumer 

Products,’’ 61, and Attachment I, ‘‘CARB Analyses 

of Potential Additional Mobile Source and 

Consumer Products Control Measures.’’ 

105 Id., Attachment A–1, Table A–1. 

106 Id., Table 4–3, ‘‘Top Ten Categories of VOC 

Emissions in 2032 (Non-Mobile),’’ and Table 4–4, 

‘‘Top Ten Categories of NOX Emissions in 2032 

(Non-Mobile).’’ 

107Emissions inventory source categories are 

represented by a 14-digit emission inventory code 

(EIC) for area and mobile sources. 

108 2020 Plan, Section 4.2.1.7, ‘‘RACM 

Cumulative Analysis,’’ p. 74. 

approximately 0.2 tpd VOC and 0.3 tpd 

NOX. For mobile sources and consumer 

products, the District concludes in the 

2020 Plan that there are no potential 

RACM reductions available since all 

reasonable rules regulating both are 

currently being implemented.104 In the 

2020 Plan, the District bases this 

conclusion on analysis performed by 

CARB in Attachment I, which we 

describe in Section III.B.2.c. of this 

document regarding 2008 ozone 

NAAQS RACM. 

The District included an additional 

step in its RACM analysis for the 2015 

ozone NAAQS, which was not 

performed for the 2008 ozone NAAQS. 

The purpose was to determine whether 

further reductions would be possible, 

given that the area’s 2032 modeled 

attainment year was further in the future 

for the 2015 ozone NAAQS than for the 

2008 ozone NAAQS (2026). The District 

assessed the top ten non-mobile source 

categories of VOC and NOX in San Diego 

County’s emissions inventory.105

For each of these categories, the 

District estimates the percentage of the 

county’s 2032 emissions of VOC and 

NOX.106 In each of two tables in the 

2020 Plan (Table 4–3 and Table 4–4), 

the District provides, for each category: 

the numerical ranking from 1 to 10, with 

1 representing the category with the 

highest emissions of all ten categories; 

the source category name; the emission 

inventory code or EIC; 107 2017 base 

year and 2032 projected attainment year 

emissions of VOC or NOX; the 

percentage of the County’s projected 

2032 total emissions of VOC or NOX; a 

description of applicable regulations for 

the category; and whether there are 

potential RACM reductions, with an 

accompanying justification. The 

purpose of this last item, potential 

RACM and justification, is to determine 

first if there are RACM reductions 

available. A ‘‘yes’’ in this column 

indicates that the category has further 

reductions that are not being 

implemented. A ‘‘no’’ indicates that the 

category has no potential RACM 

reductions. Justifications for a ‘‘no’’ in 

this column vary. For example, the 

number 1 category of VOC non-mobile 

emissions is Consumer Products. These 

were discussed in both the 2008 and 

2015 ozone NAAQS RACM sections in 

the 2020 Plan. In both instances, the 

conclusions, based on the analyses 

provided, are that there are no further 

CARB Consumer Products regulations to 

put in place. 

In the 2020 Plan, text accompanying 

each of these two tables (that is, Tables 

4–3 and 4–4) provides further 

assessment of each category. To 

continue the example for Consumer 

Products, the text explains that CARB 

has been developing regulations for this 

category for thirty years, developing 

regulations for over 100 consumer 

product categories. These regulations 

have been amended frequently, with 

increasing levels of stringency for VOC 

limits and reactivity limits. 

In each of these two tables, the 

District demonstrates that the top ten 

categories of VOC and NOX are 

addressed in the 2020 Plan. Where a 

potential for RACM exists, each category 

is addressed in the 2020 Plan in 

Sections 3.2.1.1 and 4.2.1.1 regarding 

RACM for the 2008 and 2015 ozone 

NAAQS, respectively, and in 

Attachment G. 

f. 2015 Ozone NAAQS, the District’s 

RACM Conclusion 

After evaluating the emissions 

reduction potentials of stationary, area, 

and mobile sources, as well as consumer 

products, by themselves, the District 

presents a ‘‘cumulative analysis’’ to 

assess whether all potential RACM 

combined could result in advancement 

of the modeled 2032 attainment year to 

2031.108 Attachment J (‘‘Calculation of 

Cumulative Potential Emission 

Reductions for Possible Reasonably 

Available Control Measures (RACM)’’) 

of the 2020 Plan presents the 

cumulative potential RACM reductions 

in Table J–1, ‘‘Calculation of Cumulative 

Potential Emission Reductions for 

Possible Reasonably Available Control 

Measures (RACM).’’ When taken 

together, all potential RACM reductions 

of VOC and NOX that the District and 

CARB evaluated amount to 

approximately 0.6 tpd VOC and 0.7 tpd 

NOX. The potential RACM for combined 

VOC and NOX, 1.3 tpd potential RACM 

reduction falls far short of the 2015 

ozone RACM target (for combined VOC 

and NOX), 6.0 tpd. The District therefore 

concludes that collectively, there is not 

enough potential RACM reductions to 

advance the attainment date for the 

2015 ozone NAAQS. 

3. The EPA’s Review of the State’s 

Submission 

As described in Section III.B.2.a. of 

this document, the District already 

implements many rules to reduce VOC 

and NOX emissions from stationary and 

area sources in the San Diego County 

area. For the 2020 Plan, the District 

evaluated a range of potentially 

available measures. We find that the 

process followed by the District in the 

2020 Plan to identify additional 

stationary and area source RACM is 

generally consistent with the EPA’s 

recommendations in the General 

Preamble, that the District’s evaluation 

of potential measures is appropriate, 

and that the District has provided 

reasoned justifications for rejection of 

measures deemed not reasonably 

available. 

With respect to mobile sources, 

CARB’s current program addresses the 

full range of mobile sources in the San 

Diego County area through regulatory 

programs for both new and in-use 

vehicles. With respect to TCMs, we find 

that the District’s process for identifying 

additional TCM RACM and its 

conclusion that the TCMs being 

implemented in the San Diego County 

area (i.e., the TCMs listed in Attachment 

H of the 2020 Plan) represents all TCM 

RACM to be reasonably justified and 

supported. Further, we find that the 

District’s cumulative analyses 

appropriately sum the various sources 

of potential RACM, and we agree with 

the District’s conclusion that, taken 

together, all potential RACM would 

advance neither the 2026 modeled 

attainment year for the 2008 ozone 

NAAQS, nor the 2032 modeled 

attainment year for the 2015 ozone 

NAAQS. Based on our review of these 

RACM analyses and the District’s and 

CARB’s adopted rules, we propose to 

find that there are currently no 

additional RACM that would advance 

attainment of either the 2008 ozone 

NAAQS or the 2015 ozone NAAQS in 

the San Diego County area, and that the 

2020 Plan provides for the 

implementation of all RACM as required 

by CAA section 172(c)(1), 40 CFR 

51.1112(c) and 40 CFR 51.1312(c). 

C. Attainment Demonstration 

1. Statutory and Regulatory 

Requirements 

An attainment demonstration consists 

of: (1) technical analyses, such as base 

year and future year modeling, to locate 

and identify sources of emissions that 

are contributing to violations of the 

ozone NAAQS within the 

nonattainment area (i.e., analyses 

related to the emissions inventory for 


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109 78 FR 34178, 34184 (June 6, 2013) (proposed 

rule for implementing the 2008 ozone NAAQS), 

codified at 40 CFR 51.1108. For the 2015 ozone 

NAAQS, the EPA finalized modeling requirements 

at 40 CFR 51.1308. 

110 77 FR 30087 (May 21, 2012) and 83 FR 25776 

(June 4, 2018), respectively. 

111 80 FR 12264 and 83 FR 62998, respectively. 112Modeling Guidance, EPA 454/R–18–009, 

November 2018. Additional EPA modeling 

guidance can be found in 40 CFR 51 Appendix W, 

‘‘Guideline on Air Quality Models,’’ 82 FR 5182 

(January 17, 2017). These documents are available 

in the docket for this action and at https://

www.epa.gov/sites/default/files/2020-10/ 

documents/o3-pm-rh-modeling_guidance-2018.pdf 

and https://www.epa.gov/scram/clean-air-actpermit-modeling-guidance, respectively. 

113Modeling Guidance, Section 2.7.1, p. 35. 

114The National Emissions Inventory (NEI) is an 

electronic database of criteria pollutant and 

precursor emissions data for the United States. 

State, local and tribal agencies contribute to the NEI 

every three years (2011, 2014, 2017, 2020, etc.). For 

more information about the NEI, see: https://

www.epa.gov/air-emissions-inventories/nationalemissions-inventory-nei. 

115Modeling Guidance at Section 2.7.1, p 35. 

116See also CAA section 110(a)(2)(A). 

117 40 CFR 51.1108(d) and 40 CFR 51.1308(d), 

respectively. 

118 40 CFR 51.1100(h) for the 2008 ozone NAAQS 

and 40 CFR 51.1300(g), for the 2015 ozone NAAQS. 

the nonattainment area and the 

emissions reductions necessary to attain 

the standards); (2) a list of adopted 

measures (including RACT controls) 

with schedules for implementation and 

other means and techniques necessary 

and appropriate for demonstrating RFP 

and attainment as expeditiously as 

practicable but no later than the outside 

attainment date for the area’s 

classification; (3) a RACM analysis; and 

(4) contingency measures required 

under sections 172(c)(9) and 182(c)(9) of 

the CAA that can be implemented 

without further action by the state or the 

EPA to cover emissions shortfalls in 

RFP and failures to attain.109 In this 

section, we address the first two 

components of the attainment 

demonstration—the technical analyses 

and a list of adopted measures. We 

address the RACM component of the 

2020 Plan attainment demonstration in 

Section III.B (Reasonably Available 

Control Measures Demonstration and 

Control Strategy) of this document and 

the contingency measures component of 

the attainment demonstration in Section 

III.F (Contingency Measures) of this 

document. 

With respect to the technical analyses, 

section 182(c)(2)(A) of the CAA requires 

that a plan for an ozone nonattainment 

area classified Serious or above include 

a ‘‘demonstration that the plan . . . will 

provide for attainment of the ozone 

[NAAQS] by the applicable attainment 

date. This attainment demonstration 

must be based on photochemical grid 

modeling or any other analytical 

method determined . . . to be at least as 

effective.’’ The attainment 

demonstration predicts future ambient 

concentrations for comparison to the 

NAAQS, making use of available 

information on measured 

concentrations, meteorology, and 

current and projected emissions 

inventories of ozone precursors, 

including the effect of control measures 

in the plan. 

Areas classified Severe for the 2008 

and 2015 ozone NAAQS must 

demonstrate attainment as expeditiously 

as practicable, but no later than 15 years 

after the effective date of designation to 

nonattainment. San Diego County was 

designated nonattainment for the 2008 

ozone NAAQS effective July 20, 2012, 

and for the 2015 ozone NAAQS, the area 

was designated nonattainment effective 

August 3, 2018.110 Accordingly the area 

must demonstrate attainment of the 

2008 ozone NAAQS by July 20, 2027; 

for the 2015 ozone NAAQS, the area 

must demonstrate attainment by August 

3, 2033.111 An attainment 

demonstration must show attainment of 

the standards by the ozone season (for 

San Diego County, the ozone season is 

the entire calendar year) prior to the 

attainment date, so in practice, Severe 

nonattainment areas must demonstrate 

attainment in 2026 for the 2008 ozone 

NAAQS and in 2032 for the 2015 ozone 

NAAQS. 

The EPA’s recommended procedures 

for modeling ozone as part of an 

attainment demonstration are contained 

in ‘‘Modeling Guidance for 

Demonstrating Air Quality Goals for 

Ozone, PM2.5, and Regional Haze’’ 

(‘‘Modeling Guidance’’).112 The 

Modeling Guidance includes 

recommendations for a modeling 

protocol, model input preparation, 

model performance evaluation, use of 

model output for the numerical NAAQS 

attainment test, and modeling 

documentation. Air quality modeling is 

performed using meteorology and 

emissions from a base year, and the 

predicted concentrations from this base 

case modeling are compared to air 

quality monitoring data from that year 

to evaluate model performance. 

Once the model performance is 

determined to be acceptable, future year 

emissions are simulated with the model. 

The relative (or percent) change in 

modeled concentration due to future 

emissions reductions provides a relative 

response factor (RRF). Each monitoring 

site’s RRF is applied to its monitored 

base year design value to provide the 

future design value for comparison to 

the NAAQS. The Modeling Guidance 

also recommends supplemental air 

quality analyses, which may be used as 

part of a weight of evidence analysis. A 

weight of evidence analysis corroborates 

the attainment demonstration by 

considering evidence other than the 

main air quality modeling attainment 

test, such as trends and additional 

monitoring and modeling analyses. 

Lastly, an unmonitored area analysis is 

used to predict areas of high ozone 

concentrations where air quality 

monitoring data is not available. This 

analysis utilizes interpolated ambient 

data with modeled outputs to determine 

gradient-adjusted spatial fields. Section 

4.7 of the Modeling Guidance provides 

guidelines for estimating design values 

at unmonitored grid cells. 

The Modeling Guidance does not 

require a particular year to be used as 

the base year for 8-hour ozone plans.113

The Modeling Guidance states that the 

most recent year of the National 

Emissions Inventory 114 may be 

appropriate for use as the base year for 

modeling, but that other years may be 

more appropriate when considering 

meteorology, transport patterns, 

exceptional events, or other factors that 

may vary from year to year.115

Therefore, the base year used for the 

attainment demonstration need not be 

the same year used to meet the 

requirements for emissions inventories 

and RFP. 

With respect to the list of adopted 

measures, CAA section 172(c)(6) 

requires that nonattainment area plans 

include enforceable emissions 

limitations, and such other control 

measures, means or techniques 

(including economic incentives such as 

fees, marketable permits, and auctions 

of emission rights), as well as schedules 

and timetables for compliance, as may 

be necessary or appropriate to provide 

for timely attainment of the NAAQS.116

Under the 2008 Ozone SRR and the 

2015 Ozone SRR, all control measures 

needed for attainment must be 

implemented no later than the 

beginning of the attainment year ozone 

season.117 The attainment year ozone 

season is defined as the ozone season 

immediately preceding a nonattainment 

area’s maximum attainment date.118

2. Summary of the State’s Submission 

a. Photochemical Modeling 

The 2020 San Diego County Ozone 

SIP includes photochemical modeling 

for the 2008 and 2015 ozone NAAQS. 

CARB performed the air quality 

modeling for the 2020 Plan. The 

modeling relies on a 2017 base year and 

demonstrates attainment of the 2008 

ozone NAAQS in 2026 and attainment 

of the 2015 ozone NAAQS in 2032. 


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119 2020 Plan, Attachment K, ‘‘Modeling Protocol 

& Attainment Demonstration for the 2020 San Diego 

Ozone SIP’’ (March 2020). 

120Emissions reduction commitments are 

described in the 2020 Plan (Sections 4.3.4 and 4.3.5; 

Attachment L, Section 3.9; and Table 4–9), the 

CARB Staff Report, and the District’s and CARB’s 

Board resolutions. 

121Modeling TSD, p. 26. Section 4.0 of the 

Modeling Guidance focuses on establishing 

guidelines for analyzing simulated emissions 

reductions for a future year with the goal of meeting 

the NAAQS. The Modeling Guidance recommends 

examining relative changes in design values 

through Relative Response Factors instead of 

absolute values to reduce the effect of model biases. 

In short, the RRF is a relative change in 

concentration with respect to a change in emissions 

between a base and future year, i.e., the ratio of 

future year and base year modeled concentrations, 

and is multiplied by the base design value obtained 

from monitoring data at a particular site to obtain 

a future year design value at that site. 

122The terms base year and reference year can be 

used interchangeably. To use consistent EPA 

terminology, the terms ‘‘base year’’ and ‘‘base case’’ 

are used in this document and correspond to the 

District’s and CARB’s use of the terms ‘‘reference 

year’’ and ‘‘base year,’’ respectively. 

123See Modeling Guidance at section 4.2.1. 

124 2020 Plan, Attachment M, ‘‘Weight of 

Evidence Demonstration for San Diego County.’’ 

As a general matter, the modeling for 

the 2020 Plan represents the most up-todate photochemical modeling 

performed for the area, accounting for 

improved chemical gaseous and 

particulate mechanisms, improved 

computational resources and postprocessing utilities, enhanced spatial 

and temporal allocations of the 

emissions inventory, and CARB’s latest 

attainment demonstration methodology. 

Air quality modeling included in the 

2020 Plan is described briefly in the 

plan’s Sections 3.3 and 4.3 (for 2008 and 

2015 ozone NAAQS, respectively) and 

in detail in the plan’s Attachment K 

(‘‘Attachment K’’ or ‘‘Modeling 

Protocol’’).119 The 2020 Plan discusses 

its modeling emissions inventory in 

Attachment L, ‘‘Modeling Emissions 

Inventory,’’ while Attachment M, 

‘‘Weight of Evidence Demonstration for 

San Diego County,’’ supplements the 

plan’s modeling results with a weight of 

evidence analysis. 

Attachment K of the 2020 Plan 

provides a description of model input 

preparation procedures, various model 

configuration options, and model 

performance statistics. The Modeling 

Protocol contains all the elements 

recommended in the Modeling 

Guidance, including: selection of model, 

time period to model, modeling domain, 

and model boundary conditions and 

initialization procedures; a discussion 

of emissions inventory development 

and other model input preparation 

procedures; model performance 

evaluation procedures; selection of 

days; and other details for calculating 

Relative Response Factors (RRFs). 

Attachment K also provides the 

coordinates of the modeling domain. 

Attachment L of the 2020 Plan 

thoroughly describes the development 

of the modeling emissions inventory, 

including its chemical speciation, its 

spatial and temporal allocation, its 

temperature dependence, and quality 

assurance procedures. 

The CARB Staff Report for the 2020 

Plan provides additional information 

about CAA requirements that apply to 

the San Diego County area, including an 

attainment demonstration, emissions 

reductions commitments by CARB and 

the District and the source categories 

from which those reductions are 

expected to come.120

The modeling analysis uses version 

5.2.1 of the Community Multiscale Air 

Quality (CMAQ) photochemical model, 

developed by the EPA. To prepare 

meteorological input for CMAQ, the 

Weather Research and Forecasting 

model version 3.9.1.1 (WRF) from the 

National Center for Atmospheric 

Research was used. CMAQ and WRF are 

both recognized in the Modeling 

Guidance as technically sound, state-ofthe-art models. The areal extent and the 

horizontal and vertical resolution used 

in these models are adequate for 

modeling San Diego County ozone. 

The WRF meteorological model 

results and performance statistics are 

described in Section K.3.1 

(‘‘Meteorological Model Evaluation’’) of 

Attachment K. The District and CARB 

evaluated the performance of the WRF 

model through a series of simulations 

and concluded that the daily WRF 

simulation for 2017 performed 

comparably to recent WRF modeling 

studies of ozone formation in California. 

The District’s conclusions are supported 

by hourly time series, with performance 

statistics provided in Table K–7 for 

wind speed, temperature and relative 

humidity. 

Ozone model performance and related 

statistics are described in the 2020 Plan 

Attachment K, Section K.3.2 (‘‘Air 

Quality Model Evaluation’’), which 

includes tables of statistics 

recommended in the Modeling 

Guidance for ozone for San Diego 

County. Model performance metrics 

provided in the 2020 Plan include mean 

bias, mean error, mean fractional bias, 

mean fractional error, normalized mean 

bias, normalized mean error, root mean 

square error, and correlation coefficient. 

In addition, plots were provided in 

evaluating the modeling: time-series 

plots comparing the predictions and 

observations, scatter plots for comparing 

the magnitude of the simulated and 

observed mixing ratios, box plots to 

summarize the time series data across 

different regions and averaging times, as 

well as frequency distributions. 

After model performance for the 2017 

base case was accepted, the model was 

applied to develop RRFs for the 

attainment demonstration.121 This 

entailed running the model with the 

same meteorological inputs as before, 

but with adjusted emissions inventories 

to reflect the expected changes between 

2017 and the attainment years 2026 and 

2032. The base year, or ‘‘reference year’’ 

as referred to by the District and CARB, 

modeling inventory was the same as the 

inventory for the modeling base case, 

except for the exclusion of some 

emissions events that are random or 

cannot be projected to the future.122 The 

2026 and 2032 inventories project the 

base year into the future by including 

the effect of economic growth and 

emissions control measures. To develop 

the RRFs for the 8-hour ozone NAAQS, 

only the top 10 modeled days were 

used, consistent with the Modeling 

Guidance.123

The Modeling Guidance addresses 

attainment demonstrations with ozone 

NAAQS based on 8-hour averages, and 

for the 2008 and 2015 ozone NAAQS, 

the 2020 Plan carried out the attainment 

test procedure consistent with the 

Modeling Guidance. The RRFs were 

calculated as the ratio of future to base 

year concentrations. The resulting RRFs 

were then applied to two sets of 

reference design values. One set is for 

the period 2016–2018. Another set of 

design values was more current at the 

time of the state and District’s analysis, 

the period 2017–2019. However, 

because that set of design values 

included data for 2019 that was not 

finalized at the time of the analysis, the 

earlier 2016–2018 set was used as an 

additional reference. The RRFs were 

applied to five monitoring sites in the 

San Diego County area to obtain future 

year 2026 and 2032 design values, 

summarized in Table K–13 and Table 

K–14 of the 2020 Plan, respectively. The 

modeled 2026 and 2032 ozone design 

values at the Alpine monitoring site (the 

highest of the county’s monitors) are 

0.074 ppm and 0.070 ppm, respectively; 

these values demonstrate attainment of 

the 2008 and the 2015 ozone NAAQS. 

The 2020 Plan modeling 

demonstration includes a weight of 

evidence demonstration.124 The weight 

of evidence demonstration in 

Attachment M of the 2020 Plan includes 

ambient ozone data and trends, 

precursor emissions trends and 


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125CARB Staff Report, 10. 126CARB Board Resolution 20–29, 6; 2020 Plan, 

section 4.3.5. 

127 2020 Plan, section 4.3.4. 

reductions, to complement the regional 

photochemical modeling analyses. The 

CARB Staff Report for the 2020 Plan 

concludes that the weight of evidence 

analysis supports the conclusions of the 

photochemical modeling.125

b. Control Strategy for the 2008 Ozone 

NAAQS and for the 2015 Ozone 

NAAQS 

Continued air quality improvement in 

the San Diego County area is expected 

during the 2017 through 2032 timeframe 

because of the continued 

implementation of adopted District and 

CARB control measures and ongoing 

fleet turnover that replaces older more 

polluting mobile sources with newer, 

cleaner models and the downward 

emissions trends in the upwind South 

Coast Air Basin. 

The control strategy for the San Diego 

County area for the 2008 ozone NAAQS 

relies on emissions reductions from 

baseline (already-implemented) 

measures. The baseline control 

measures include the District’s 

stationary source rules and CARB’s 

mobile source and consumer products 

regulations adopted at the time of 

development of the 2020 Plan. 

The control strategy for the San Diego 

County area for the 2015 ozone NAAQS 

also relies on emissions reductions from 

baseline (already-implemented) 

measures. However, unlike the 2008 

ozone NAAQS attainment 

demonstration, the 2020 Plan concludes 

that baseline measures will not by 

themselves provide sufficient emissions 

reductions by 2032 to demonstrate 

attainment of the 2015 ozone NAAQS. 

Thus, the control strategy for the 

attainment demonstration for the 2015 

ozone NAAQS includes commitments 

by CARB and the District to adopt and 

submit new control measures to achieve 

additional emissions reductions that the 

modeling indicates are necessary to 

attain the 2015 ozone NAAQS in the 

San Diego County area by the 

attainment year (2032). 

To provide for attainment of the 2015 

ozone NAAQS by the attainment year 

(2032), CARB and the District commit in 

the 2020 Plan to reduce NOX emissions 

by 4.0 tpd 126 and by 1.7 tpd,127

respectively. CARB expects to adopt and 

submit certain mobile source control 

measures developed pursuant to CARB’s 

2016 State Strategy to fulfill the 4.0 tpd 

NOX aggregate emissions reduction 

commitment for San Diego County by 

2032. The specific control measures that 

CARB expects to adopt and submit are 

listed in Table 5 of this document. The 

District expects to adopt and submit 

certain stationary source control 

measures to fulfill the 1.7 tpd NOX

aggregate emissions reduction 

commitment by 2032, as listed in Table 

6 of this document. 

TABLE 5—SAN DIEGO COUNTY EXPECTED NOX EMISSIONS REDUCTIONS FROM CARB 2016 STATE SIP STRATEGY

MEASURES

2016 State strategy measure(s) Control measure/regulation 2032 

(tpd) 

On-Road Heavy-Duty Vehicles: Low-NOX Engine Standard—California Action and Lower In-Use Emission Performance Level.Heavy-Duty Engine and Vehicle Omnibus Regulation 

(‘‘Low NOX Omnibus Regulation’’).

1.9 

On-Road Heavy-Duty Vehicles: Last Mile Delivery ......................................... Advanced Clean Trucks Regulation ................................. 0.4 

On-Road Heavy-Duty Vehicles: Lower In-Use Emission Performance Level Heavy Duty Vehicle Inspection and Maintenance Regulation.1.7 

Total Aggregate CARB Commitment ....................................................... ........................................................................................... 4.0 

Sources: 2016 State Strategy, Chapters 3 and 4; 2020 Plan, Table 4–9. 

TABLE 6—SAN DIEGO COUNTY EXPECTED NOX EMISSIONS REDUCTIONS FROM SDCAPCD CONTROL MEASURES

Source type Control measure/rule 2032 

(tpd) 

Stationary Reciprocating Internal Combustion Engines .................................. Amended District Rule 69.4.1 ........................................... 0.8 

Small and Medium Boilers, Process Heaters, Steam Generators and Large 

Water Heaters.

New or Amended District Rules 69.2.1 and 69.2.2 .......... 0.9 

Total Aggregate SDCAPCD Commitment ................................................ ........................................................................................... 1.7 

Source: 2020 Plan, Section 4.3.4. 

c. Attainment Demonstration 

Table 7 of this document summarizes 

the attainment demonstration for the 

2008 ozone NAAQS by listing the 2011 

base year emissions level, the 

attainment year (2026) baseline 

emissions level, the modeled attainment 

(2026) emissions level, and the 

reductions that the District and CARB 

estimate will be achieved through 

implementation of baseline (i.e., 

adopted) measures taking into account 

area-wide growth, the growth 

increments for the military and SDIA, 

the District’s ERC set-aside and the 

EMFAC2017 Adjustment Factors 

adjustment. The District and CARB have 

not made any emissions reductions 

commitments as part of the control 

strategy for attainment of the 2008 

ozone NAAQS in San Diego County. 

The control strategy relies only on 

baseline measures. As shown in Table 7, 

baseline measures are expected to 

reduce base year (2011) emissions of 

NOX by 43 percent and VOC emissions 

by 27 percent by the 2026 attainment 

year, notwithstanding area-wide growth, 

the growth increments for the military 

and SDIA, the District’s ERC set-aside 

and the EMFAC2017 Adjustment 

Factors adjustment, and to attain the 

2008 ozone NAAQS in San Diego 

County by that year. 


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128 84 FR 28132. 

129Attachment K, ‘‘Modeling Protocol & 

Attainment Demonstration for the 2020 San Diego 

Ozone SIP,’’ 2020 Plan. 

TABLE 7—SUMMARY OF SAN DIEGO COUNTY 2008 OZONE NAAQS ATTAINMENT DEMONSTRATION

[Summer planning inventory, tpd] 

Row NOX VOC 

A ........ 2011 Base Year Emissions Level a .................................................................................................................. 126.5 137.5 

B ........ 2026 Attainment Year Baseline Emissions Level b .......................................................................................... 72.2 100.8 

C ........ 2026 Modeled Attainment Emissions Level c ................................................................................................... 72.2 100.8 

D ........ Total Reductions Needed from 2011 Levels to Demonstrate Attainment (A¥C) ........................................... 54.3 36.7 

E ........ Reductions from Baseline (i.e., adopted) Measures, net of growth, growth increment for military and SDIA, 

ERC set-aside and EMFAC2017 Adjustment Factors adjustment (A¥B).

54.3 36.7 

F ........ Reductions from District’s Aggregate Emissions Reduction Commitment from 2020 Plan ............................ 0 0 

G ....... Reductions from CARB’s Aggregate Emissions Reduction Commitment from 2016 State Strategy ............. 0 0 

H ........ Total Reductions from District’s and CARB’s Commitments ........................................................................... 0 0 

I ......... Total Reductions from Baseline Measures and the District’s and CARB’s Commitments (E + H) ................ 54.3 36.7 

J ........ 2026 Emissions with Reductions from Control Strategy (A¥I) ....................................................................... 72.2 100.8 

Attainment demonstrated? ............................................................................................................................... Yes Yes 

aSee Table 1 of this document. Includes emissions out to 100 NM from the coast. 

bSee Table 1 of this document. Includes emissions out to 100 NM from the coast. Year 2026 baseline emissions reflect area-wide growth, the 

growth increments for the military and SDIA, the District’s ERC set-aside and the EMFAC2017 Adjustment Factors adjustment. c 2020 Plan, Section 3.3.4. 

Table 8 of this document summarizes 

the attainment demonstration for the 

2015 ozone NAAQS by listing the 2017 

base year emissions level, the 

attainment year (2032) baseline 

emissions level, the modeled attainment 

(2032) emissions level, and the 

reductions that the District and CARB 

estimate will be achieved through 

implementation of baseline (i.e., 

adopted) measures taking into account 

area-wide growth, the growth 

increments for the military and SDIA, 

the District’s ERC set-aside and the 

EMFAC2017 Adjustment Factors 

adjustment. Table 8 also shows the 

aggregate emissions reductions 

commitments (for year 2032) made by 

the District and CARB as part of the 

control strategy for attainment of the 

2015 ozone NAAQS in San Diego 

County. As shown in Table 8, baseline 

measures are expected to reduce base 

year (2017) emissions of NOX by 27 

percent and VOC emissions by 14 

percent by the 2032 attainment year, 

notwithstanding area-wide growth, the 

growth increments for the military and 

SDIA, the District’s ERC set-aside and 

the EMFAC2017 Adjustment Factors 

adjustment. The District’s and CARB’s 

commitments would further reduce 

emissions of NOX by 2032 by an 

additional 5.7 tpd. Together, the 

baseline emissions reductions and the 

NOX emissions reduction commitments 

would provide for attainment of the 

2015 ozone NAAQS by the attainment 

year (2032). 

TABLE 8—SUMMARY OF SAN DIEGO COUNTY 2015 OZONE NAAQS ATTAINMENT DEMONSTRATION

[Summer planning inventory, tpd] 

Row NOX VOC 

A ........ 2017 Base Year Emissions Level a .................................................................................................................. 94.5 113.8 

B ........ 2032 Attainment Year Baseline Emissions Level b .......................................................................................... 69.0 98.3 

C ........ 2032 Modeled Attainment Emissions Level c ................................................................................................... 63.3 98.3 

D ........ Total Reductions Needed from 2017 Levels to Demonstrate Attainment (A¥C) ........................................... 31.0 15.5 

E ........ Reductions from Baseline (i.e., adopted) Measures, net of growth, growth increment for military and SDIA, 

ERC set-aside and EMFAC2017 Adjustment Factors adjustment (A¥B).

25.5 15.5 

F ........ Reductions from District’s Aggregate Emissions Reduction Commitment from 2020 Plan ............................ 1.7 0 

G ....... Reductions from CARB’s Aggregate Emissions Reduction Commitment from 2016 State Strategy ............. 4.0 0 

H ........ Total Reductions from District’s and CARB’s Commitments ........................................................................... 5.7 0 

I ......... Total Reductions from Baseline Measures and the District’s and CARB’s Commitments (E + H) ................ 31.2 15.5 

J ........ 2032 Emissions with Reductions from Control Strategy (A¥I) ....................................................................... 63.3 98.3 

Attainment demonstrated? ............................................................................................................................... Yes Yes 

aSee Table 1 of this document. Includes emissions out to 100 NM from the coast. 

bSee Table 1 of this document. Includes emissions out to 100 NM from the coast. Year 2032 baseline emissions reflect area-wide growth, the 

growth increments for the military and SDIA, the District’s ERC set-aside and the EMFAC2017 Adjustment Factors adjustment. c 2020 Plan, Section 4.3.4. 

3. The EPA’s Review of the State’s 

Submission 

a. Photochemical Modeling 

As discussed in Section III.A of this 

document, we are proposing to approve 

the base year emissions inventory and to 

find that the future year emissions 

projections in the 2020 San Diego 

County Ozone SIP reflect appropriate 

calculation methods and that the latest 

planning assumptions are properly 

supported by SIP-approved stationary 

and mobile source control measures. 

Here, we address our findings for the 

modeling submitted with the 2020 Plan. 

Because of the importance of ozone 

transport from the South Coast to 

attainment in San Diego County, and the 

close interactions of the modeling for 

each area, we have considered the 

influence of South Coast on the 

modeling for San Diego County. Similar 

and additional discussion for the South 

Coast can be found in our June 17, 2019 

proposed action on the 2016 South 

Coast Ozone SIP.128

Based on our review of Attachment 

K 129 of the 2020 Plan, the EPA finds 

that the photochemical modeling is 


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130The EPA’s review of the modeling and 

attainment demonstration is discussed in greater 

detail in the Modeling TSD for this action. 

131Modeling Guidance, 30. 

132Temperature, water vapor mixing ratio, and 

wind speed were evaluated in terms of normalized 

gross bias and normalized gross error. 

133These factors are discussed in greater detail in 

Section 3.1.2 of the EPA’s Modeling TSD, included 

in the docket to this action. 

adequate for purposes of supporting the 

attainment demonstration.130 First, we 

note the extensive discussion of 

modeling procedures, tests, and 

performance analyses in the 

Methodology section of Attachment K 

and the good model performance. 

Second, we find the WRF 

meteorological model results and 

performance statistics, including hourly 

time series graphs of wind speed, 

direction, and temperature for San 

Diego County to be satisfactory and 

consistent with our Modeling 

Guidance.131 Performance for wind 

speed, temperature, and relative 

humidity was evaluated from May to 

September 2017.132 Geographically, 

winds are predicted most accurately 

along the coast. Accurate wind 

predictions in this region are important 

in simulating chemical transport in the 

San Diego Air Basin. Overall, the WRF 

simulation provided reasonable 

meteorological fields comparable to 

other WRF modeling studies and is 

sufficient for the attainment 

demonstration. 

The model performance statistics for 

ozone are described in Attachment K 

Section K.3.2 and are based on the 

statistical evaluation recommended in 

the Modeling Guidance. Model 

performance was provided for 8-hour 

daily maximum ozone for San Diego 

County, separately for the Alpine site 

and the coastal sites. A geographical and 

temporal bias is shown in the time 

series, which sufficiently captures the 

variability in the maximum daily eighthour average ozone concentration at the 

Alpine site, but overpredicts this 

concentration from mid-June to midJuly at the coastal sites. Through a series 

of sensitivity tests and consideration of 

other meteorological phenomena, the 

observed ozone concentrations during 

the overprediction period are likely 

attributed to numerous meteorological 

factors affecting ozone transport (see, 

‘‘Technical Support Document, Review 

of Attainment Modeling in the 2020 San 

Diego Ozone Plan (July 2022)’’ 

(‘‘Modeling TSD’’)).133

The 2020 Plan presents scatter plots 

of monitored and modeled ozone 

concentrations that also suggest that the 

Alpine site has the best correspondence 

between modeled and observed 

concentrations. This correspondence 

reflects the model’s capability of 

reliably predicting the high 

concentrations that result in 

exceedances frequently observed at the 

Alpine site, which are important for the 

top ten days that form the basis for the 

RRF calculation. However, the 

overprediction of absolute ozone 

concentrations does not mean that 

future concentrations will be 

overestimated. In addition, the weight of 

evidence analysis presented in 

Attachment M of the 2020 Plan provides 

additional information with respect to 

the sensitivity to emissions changes and 

further supports the model performance. 

We are proposing to find the air quality 

modeling adequate to support the 

attainment demonstrations for the 2008 

and 2015 ozone NAAQS, based on 

reasonable meteorological and ozone 

modeling performance, and supported 

by the weight of evidence analyses. For 

additional information regarding the 

EPA’s analysis, please see the Modeling 

TSD for this action. 

b. Control Strategy 

As part of our evaluation of 

attainment demonstrations, we must 

find that the emissions reductions that 

are relied on for attainment are 

creditable and are sufficient to provide 

for attainment. As shown in Table 7 of 

this document, the 2020 Plan relies on 

baseline measures to achieve all the 

emissions reductions needed to attain 

the 2008 ozone NAAQS by 2026. The 

baseline measures are approved into the 

SIP (with only minor exceptions) and, 

as such, the emissions reductions are 

fully creditable. 

With respect to the attainment 

demonstration for the 2015 ozone 

NAAQS, we must also find that the 

emissions reductions that are relied on 

for attainment are creditable and are 

sufficient to provide for attainment. As 

shown in Table 8, the 2020 Plan relies 

on baseline measures to achieve a 

significant portion of the emissions 

reductions needed to attain the 2015 

ozone NAAQS by 2032. The balance of 

the reductions needed for attainment is 

in the form of enforceable commitments 

to achieve aggregate tonnage reductions 

of NOX through adoption and 

implementation of more stringent 

emissions limitations contained in 

certain new or amended rules and 

regulations. 

Table 9 of this document provides a 

summary of the status of the 

commitments made by the District and 

CARB in connection with the 2020 Plan. 

As shown in Table 9, the District and 

CARB have adopted all six of the rules 

or regulations that the agencies are 

relying on to meet their aggregate 

emissions reduction commitments. Four 

of the six rules or regulations have been 

submitted to the EPA for action as 

revisions to the California SIP. The rules 

or regulations are at various phases of 

implementation and at various stages of 

the process from adoption to approval 

by the EPA as part of the SIP. The 

commitments will be fulfilled once the 

EPA approves the rules or regulations as 

part of the SIP, assuming that the rules 

or regulations, as approved, provide 

NOX emissions reductions equal to or 

greater than the corresponding aggregate 

emissions reduction commitments by 

year 2032 in the San Diego County area. 

TABLE 9—STATUS OF DISTRICT AND CARB AGGREGATE EMISSIONS REDUCTION COMMITMENTS FOR 2020 PLAN

Rule Adoption date and district 

resolution of adoption 

Submission date to the 

EPA as SIP revision Most recent EPA SIP action 

District Commitment 

Amendments to Rule 69.2.1 (Small Boilers, Process 

Heaters, and Steam Generators and Large Water 

Heaters.

July 8, 2020 (Resolution 20– 

118).

September 21, 2020 ....... Proposed rule published at 88 FR 48150 

(July 26, 2023). 

New Rule 69.2.2 (Medium Boilers, Process Heaters, 

and Steam Generators).

September 9, 2021 (Resolution 21–005).March 9, 2022 ................ Final rule published at 88 FR 57361 (August 

23, 2023). 

Amendments to Rule 69.4.1 (Stationary Reciprocating 

Internal Combustion Engines).

July 8, 2020 (Resolution 20– 

120).

September 21, 2020 ....... No EPA action to date. 

Regulations 

Adoption date and 

CARB resolution of 

adoption 

CAA Section 209 

preemption waiver 

status 

Submission date to the 

EPA as SIP revision Most recent EPA SIP action 

CARB Commitment: 


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134See Committee for a Better Arvin v. EPA, 786 

F.3d 1169 (9th Cir. 2015) (approval of state 

commitments to propose and adopt emissions 

control measures and to achieve aggregate 

emissions reductions for San Joaquin Valley ozone 

and particulate matter plans upheld); Physicians for 

Social Responsibility—Los Angeles v. EPA, 9th Cir., 

memorandum opinion issued July 25, 2016 

(approval of air district commitments to propose 

and adopt measures and to achieve aggregate 

emissions reductions for South Coast 1-hour ozone 

plan upheld). 

135See our approval of these plans: San Joaquin 

Valley (SJV) PM10 Plan at 69 FR 30006 (May 26, 

2004); SJV 1-hour ozone plan at 75 FR 10420 

(March 8, 2010); Houston-Galveston 1-hour ozone 

plan at 66 FR 57160 (November 14, 2001); South 

Coast 1997 8-hour ozone plan at 77 FR 12674 

(March 1, 2012); and South Coast 1-hour ozone plan 

at 79 FR 52526 (September 3, 2014). 

Regulations 

Adoption date and 

CARB resolution of 

adoption 

CAA Section 209 

preemption waiver 

status 

Submission date to the 

EPA as SIP revision Most recent EPA SIP action 

Low-NOX Omnibus Regulation a ............... August 27, 2020 (Resolution 20–23).Notice of Opportunity for 

Public Hearing and 

Comment published at 

87 FR 35765 (June 13, 

2022).

Not yet submitted ...........

Advanced Clean Trucks Regulation ......... June 25, 2020 (Resolution 20–19).Notice of Decision published at 88 FR 20688 

(April 6, 2023).

Not yet submitted ...........

Heavy-Duty Vehicle Inspection and Maintenance Regulation.December 9, 2021 

(Resolution 21–29).

Not preempted ................ December 7, 2022 .......... No EPA action to date. 

a In July 2023, CARB proposed amendments to the Low-NOX Omnibus Regulation to provide additional flexibility for manufacturers of model year (MY) 2024–2026 

heavy-duty engines. 

The commitments made by the 

District and CARB through adoption of 

the 2020 Plan and 2016 State Strategy 

are similar to the enforceable 

commitments that the EPA has 

approved as part of attainment 

demonstrations in previous California 

air quality plans and that have 

withstood legal challenge.134 The EPA 

has previously accepted enforceable 

commitments in lieu of adopted control 

measures in attainment demonstrations 

when the circumstances warrant them 

and when the commitments meet 

specific criteria. We believe that, with 

respect to the 2015 ozone NAAQS, 

circumstances warrant the consideration 

of enforceable commitments as part of 

the attainment demonstration for San 

Diego County. First, as shown in Table 

8, a substantial portion of the emissions 

reductions needed to demonstrate 

attainment of the 2015 ozone NAAQS in 

the San Diego County area by 2032 will 

come from measures adopted prior to 

adoption and submittal of the 2020 

Plan. As a result of these State and 

District efforts, most emissions sources 

in the San Diego County area are 

currently subject to stringent emissions 

limitations and other requirements, 

leaving few opportunities to further 

reduce emissions. In the 2020 Plan and 

2016 State Strategy, the District and 

CARB identified potential control 

measures that could provide many of 

the additional emissions reductions 

needed for attainment. These are 

described in Section III.C.2.b of this 

document. However, the timeline 

needed to develop, adopt, and 

implement these measures went beyond 

the required submittal date for the 

attainment demonstration for the San 

Diego County area for the 2015 ozone 

NAAQS. These circumstances warrant 

the District’s and CARB’s reliance on 

enforceable commitments as part of the 

attainment demonstrations for the 2015 

ozone NAAQS. 

Given the State’s demonstrated need 

for reliance on enforceable 

commitments, we now consider the 

three factors the EPA uses to determine 

whether the use of enforceable 

commitments in lieu of adopted 

measures to meet CAA planning 

requirements is approvable: (i) does the 

commitment address a limited portion 

of the statutorily-required program?; (ii) 

is the state capable of fulfilling its 

commitment?; and (iii) is the 

commitment for a reasonable and 

appropriate period of time? 

i. Commitments Are a Limited Portion 

of Required Reductions 

For the first factor, we look to see if 

the commitment addresses a limited 

portion of a statutory requirement and 

review the magnitude of emissions 

reductions needed to demonstrate 

attainment in a nonattainment area. 

Table 8 of this document shows 

emissions reductions needed to 

demonstrate attainment of the 2015 

ozone NAAQS in San Diego County by 

2032 and the aggregate emissions 

reductions commitments by the District 

and CARB. Historically, the EPA has 

approved SIPs with enforceable 

commitments in the vicinity of 10 

percent of the total needed reductions 

for attainment.135 Based on the values in 

Table 8 of this document, we note that 

the sum of the aggregate emission 

reductions commitments (5.7 tpd NOX) 

represents approximately 18 percent of 

the total emissions reductions (31.0 tpd 

NOX) needed for attainment (relative to 

the 2017 base year). (The attainment 

demonstration for the 2015 ozone 

NAAQS for the San Diego County area 

does not rely on any commitments with 

respect to VOC emissions reductions.) 

While the value of 18 percent is higher 

than the EPA has generally found 

acceptable in the past, we note that all 

six of the rules or regulations that are 

relied upon to meet the aggregate 

emissions reduction commitments have 

already been adopted, and four of the 

six have been submitted to the EPA as 

revisions to the SIP. Taking into account 

the emissions reductions associated 

with rules or regulations already 

adopted and submitted (3.4 tpd NOX) 

reduces the remaining percentage 

associated with the commitments from 

18 percent to approximately 7 percent, 

which is well within historical norms 

for EPA approvals of enforceable 

commitments. Thus, we find that the 

District’s and CARB commitments in the 

2020 Plan for San Diego County for the 

2015 ozone NAAQS address a limited 

proportion of the required emissions 

reductions. 

ii. The State Is Capable of Fulfilling Its 

Commitment 

For the second factor, we consider 

whether the District and CARB are 

capable of fulfilling their commitments. 

All six rules or regulations that the 

District and CARB are relying on to 

meet the aggregate emissions reduction 

commitments have been adopted, and 

four have been submitted to the EPA as 

revisions to the California SIP. The 

emissions reductions associated with 

the four rules or regulations that have 

been adopted and submitted amount to 

approximately 3.4 tpd NOX, which 

represents approximately 60 percent of 

the overall aggregate commitment of 5.7 

tpd NOX. As such, the State and District 

are well on their way to meeting their 

commitments. Thus, we believe that the 

State and District are capable of meeting 

their enforceable commitments to adopt 

and submit control measures that will 

reduce emissions to the levels needed 

for the 2015 ozone NAAQS in the San 


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136 80 FR 12264, 12271 (March 6, 2015); 40 CFR 

51.1110(a)(2). 

137 Id. 

138 Id.; 40 CFR 51.1110(a)(2)(i)(C) and 40 CFR 

51.1110(a)(2)(ii)(B). 

139 83 FR 62998, 63004 (December 6, 2018); 

51.1310(a)(2). 

140 Id. 

141 Id.; 40 CFR 51.1310(a)(2)(i)(B) and 40 CFR 

51.1310(a)(2)(ii)(B). 

142 40 CFR 51.1110(a)(7) and 40 CFR 

51.1310(a)(7). 

143 40 CFR 51.1110(b). 

Diego County area by the 2032 

attainment year. 

iii. The Commitment Is for a Reasonable 

and Appropriate Timeframe 

For the third and final factor, we 

consider whether the commitment is for 

a reasonable and appropriate period of 

time. All six rules or regulations that the 

District and State are relying on to meet 

the commitments have been adopted, 

and four have been submitted to the 

EPA as revisions to the California SIP. 

The District and CARB have committed 

to take the necessary actions and to 

achieve the remaining reductions by 

2032. We believe that this period is 

appropriate given the technological and 

economic challenges associated with the 

rules and regulations adopted to achieve 

these reductions. In addition, these 

reductions are not needed to meet RFP 

targets for the 2015 ozone NAAQS. 

Thus, the commitments are for a 

reasonable and appropriate period of 

time. 

The reductions of NOX and VOC in 

the area, detailed in the control strategy 

in the 2020 Plan, allow for expeditious 

attainment of both the 2008 and 2015 

ozone NAAQS in the San Diego County 

area. The attainment years chosen by 

the District comport with those required 

by the Act for a Severe ozone 

nonattainment area for the 2008 and 

2015 ozone NAAQS. For the reasons 

described in this document and based 

on CARB’s and the District’s 

demonstration specific to the San Diego 

County area described in the 2020 Plan, 

we propose to find the District’s control 

strategy acceptable for purposes of 

attaining the 2008 ozone NAAQS and 

the 2015 ozone NAAQS in the San 

Diego County area. For additional 

information, please see the Modeling 

TSD for this action. 

c. Attainment Demonstration 

Based on our proposed 

determinations that the photochemical 

modeling and control strategy are 

acceptable, we propose to approve the 

attainment demonstrations for the 2008 

ozone NAAQS and for the 2015 ozone 

NAAQS in the 2020 San Diego County 

Ozone SIP as meeting the requirements 

of CAA section 182(c)(2)(A), 40 CFR 

51.1108 and 40 CFR 51.1308. 

D. Rate of Progress Plan and Reasonable 

Further Progress Demonstration 

1. Statutory and Regulatory 

Requirements 

Requirements for RFP for ozone 

nonattainment areas are specified in 

CAA sections 172(c)(2), 182(b)(1), and 

182(c)(2)(B). Under CAA section 171(1), 

RFP is defined as meaning such annual 

incremental reductions in emissions of 

the relevant air pollutant as are required 

under part D (‘‘Plan Requirements for 

Nonattainment Areas’’) of the CAA or as 

may reasonably be required by the EPA 

for the purpose of ensuring attainment 

of the applicable NAAQS by the 

applicable date. CAA section 182(b)(1) 

specifically requires that ozone 

nonattainment areas classified as 

Moderate or above demonstrate a 15 

percent reduction in VOC between the 

years of 1990 and 1996. The EPA has 

typically referred to section 182(b)(1) as 

the rate of progress (ROP) requirement. 

For ozone nonattainment areas 

classified as Serious or higher, section 

182(c)(2)(B) requires VOC reductions of 

at least 3 percent of baseline emissions 

per year, averaged over each 

consecutive three-year period, 

beginning six years after the baseline 

year until the attainment date. Under 

CAA section 182(c)(2)(C), a state may 

substitute NOX emissions reductions for 

VOC emissions reductions if such 

reductions would result in a reduction 

in ozone concentrations at least 

equivalent to that which would result 

from the amount of VOC emissions 

reductions otherwise required. 

Additionally, CAA section 

182(c)(2)(B)(ii) allows an amount less 

than 3 percent of such baseline 

emissions each year if a state 

demonstrates to the EPA that its plan 

includes all measures that can feasibly 

be implemented in the area in light of 

technological achievability. 

In the 2008 Ozone SRR, the EPA 

provides that areas classified Moderate 

or higher will have met the ROP 

requirements of CAA section 182(b)(1) if 

the area has a fully approved 15 percent 

ROP plan for the 1-hour or 1997 ozone 

NAAQS.136 For such areas, the EPA 

interprets the RFP requirements of CAA 

section 172(c)(2) to require areas 

classified as Moderate to provide a 15 

percent emissions reduction of ozone 

precursors within six years of the 

baseline year. Areas classified as 

Serious or higher must meet the RFP 

requirements of CAA section 

182(c)(2)(B) by providing an 18 percent 

reduction of ozone precursors in the 

first 6-year period, and an average ozone 

precursor emissions reduction of 3 

percent per year for all remaining 3-year 

periods thereafter.137 The 2008 Ozone 

SRR allows substitution of NOX

reductions for VOC reductions to meet 

the CAA section 172(c)(2) and 

182(c)(2)(B) RFP requirements.138

In the 2015 Ozone SRR, as with the 

2008 Ozone SRR, the EPA provides that 

areas classified Moderate or higher will 

have met the ROP requirements of CAA 

section 182(b)(1) if the area has a prior, 

fully approved 15 percent ROP plan.139

For such areas, the EPA interprets the 

RFP requirements of CAA section 

172(c)(2) to require areas classified as 

Moderate to provide a 15 percent 

emissions reduction of ozone precursors 

within six years of the baseline year. 

Areas classified as Serious or higher 

must meet the RFP requirements of CAA 

section 182(c)(2)(B) by providing an 18 

percent reduction of ozone precursors in 

the first 6-year period, and an average 

ozone precursor emissions reduction of 

3 percent per year for all remaining 3- 

year periods thereafter.140 The 2015 

Ozone SRR allows substitution of NOX

reductions for VOC reductions to meet 

the CAA section 172(c)(2) and 

182(c)(2)(B) RFP requirements.141

Except as specifically provided in 

CAA section 182(b)(1)(C), emissions 

reductions from all SIP-approved, 

federally promulgated, or otherwise SIPcreditable measures that occur after the 

baseline year are creditable for purposes 

of demonstrating that the RFP targets are 

met. Because the EPA has determined 

that the passage of time has caused the 

effect of certain exclusions to be de 

minimis, the RFP demonstration is no 

longer required to calculate and 

specifically exclude reductions from 

measures related to motor vehicle 

exhaust or evaporative emissions 

promulgated by January 1, 1990; 

regulations concerning Reid vapor 

pressure promulgated by November 15, 

1990; measures to correct previous 

RACT requirements; and measures 

required to correct previous inspection 

and maintenance (I/M) programs.142

The 2008 Ozone SRR requires the RFP 

baseline year to be the most recent 

calendar year for which a complete 

triennial inventory was required to be 

submitted to the EPA. For the purposes 

of developing RFP demonstrations for 

the 2008 ozone NAAQS, the applicable 

triennial inventory year is 2011.143 The 

2015 Ozone SRR similarly requires the 

RFP baseline year to be the most recent 

calendar year for which a complete 


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144 40 CFR 51.1310(b). 

145 2015 Ozone SRR, 63005. 

146 2020 Pan, Sections 3.2.2.1 and 4.2.2.1. 

147NOX substitution is permitted under EPA 

regulations for the 2008 ozone NAAQS. See 40 CFR 

51.1110(a)(2)(i)(C) and 40 CFR 51.1110(a)(2)(ii)(B); 

and 80 FR 12264, at 12271 (March 6, 2015). 

148NOX substitution is permitted under EPA 

regulations for the 2015 ozone NAAQS. See 40 CFR 

51.1310(a)(2)(i)(B) and 40 CFR 51.1310(a)(2)(ii)(B); 

and 83 FR 62998, at 63004 (December 6, 2018). 

triennial inventory was required to be 

submitted to the EPA.144 For the 

purpose of developing RFP 

demonstrations for the 2015 ozone 

NAAQS, the applicable triennial 

inventory year is 2017.145

2. Summary of the State’s Submission 

For both the 2008 and 2015 ozone 

NAAQS, the 2020 Plan cites the EPA’s 

1997 approval of the 15 percent VOConly ROP plan for the one-hour ozone 

NAAQS as the basis for concluding that 

the San Diego County area had met the 

15 percent VOC-only ROP plan SIP 

requirement.146

For the RFP demonstration for the 

2008 ozone NAAQS, the 2020 Plan 

includes updated inventories of ozone 

precursor emissions (VOC and NOX) for 

2017, the first RFP milestone year and 

the year from which future-year 

inventories are projected. As described 

further in Section III.A (‘‘Emissions 

Inventories’’) of this document, the RFP 

baseline year of 2011 was, for the most 

part, backcast from the 2017 emissions 

inventories except for point sources, 

which are based on actual reported 

emissions from the individual facilities. 

To develop the emissions inventories 

for remaining RFP milestone years (2020 

and 2023) and the attainment year 

(2026), the District and CARB relied 

upon the same growth and control 

factors used in the attainment 

demonstration, and included certain 

growth increments for the military and 

SDIA and certain adjustments (such as 

ERCs and EMFAC2017 Adjustment 

Factors impacts), as further described in 

Section III.A (‘‘Emissions Inventories’’) 

of this document. 

The RFP demonstration for the San 

Diego County area for the 2008 ozone 

NAAQS is provided in Section 3.2.2.3 of 

the 2020 Plan and is presented in Table 

10 of this document. The RFP 

demonstration calculates future year 

VOC targets from the 2011 baseline, 

consistent with CAA section 

182(c)(2)(B)(i), which requires 

reductions of ‘‘at least 3 percent of 

baseline emissions each year,’’ and it 

substitutes NOX reductions for VOC 

reductions beginning in milestone year 

2017 to meet VOC emissions targets.147

As shown in Table 10, the 2020 Plan 

provides a demonstration of RFP for 

each milestone year as well as the 

attainment year for the 2008 ozone 

NAAQS. 

TABLE 10—RFP DEMONSTRATION FOR SAN DIEGO COUNTY FOR THE 2008 OZONE NAAQS 

[Summer planning inventory, tpd or percent] 

VOC 

2011 2017 2020 2023 2026 

Baseline VOC Emissions (tpd) .................................................................................... 136.6 112.9 107.0 102.4 99.7 

Change in VOC since 2011 (tpd) ................................................................................ ................ 23.7 29.6 34.2 36.9 

Change in VOC since 2011 (percent) ......................................................................... ................ 17.4% 21.7% 25.1% 27.0% 

Required percentage change since 2011 .................................................................... ................ 18% 27% 36% 45% 

Shortfall (¥)/Surplus (+) in VOC (percent) ................................................................. ................ ¥0.6% ¥5.3% ¥10.9% ¥18.0% 

NOX

2011 2017 2020 2023 2026 

Baseline NOX Emissions (tpd) ..................................................................................... 110.7 77.0 67.1 56.8 53.6 

Change in NOX since 2011 (tpd) ................................................................................. ................ 33.7 43.6 53.9 57.1 

Change in NOX since 2011 (percent) .......................................................................... ................ 30.5% 39.3% 48.7% 51.6% 

NOX reductions since 2011 used for VOC substitution in this milestone year (percent) ......................................................................................................................... ................ 0.6% 5.3% 10.9% 18.0% 

NOX reductions since 2011 surplus after meeting VOC substitution needs in this 

milestone year (percent) .......................................................................................... ................ 29.8% 34.0% 37.8% 33.6% 

RFP shortfall (if any) (percent) .................................................................................... ................ 0% 0% 0% 0% 

RFP met? ..................................................................................................................... ................ Yes Yes Yes Yes 

Source: 2020 Plan, Table 3–3. 

For the RFP demonstration for the 

2015 ozone NAAQS, the 2020 Plan 

includes updated inventories of ozone 

precursor emissions for 2017, which is 

the baseline year and the year from 

which future-year inventories are 

projected. To develop the emissions 

inventories for RFP milestone years 

(2023, 2026 and 2029) and the 

attainment year (2032), the District and 

CARB relied upon the same growth and 

control factors as used in the attainment 

demonstration, and included certain 

growth increments for the military and 

SDIA and certain adjustments (such as 

ERCs and EMFAC2017 Adjustment 

Factors impacts), as further described in 

Section III.A (‘‘Emissions Inventories’’) 

of this document. 

The RFP demonstration for the San 

Diego County area for the 2015 ozone 

NAAQS is shown in Table 11 of this 

document. The RFP demonstration 

calculates future year VOC targets from 

the 2017 baseline, consistent with CAA 

section 182(c)(2)(B)(i), which requires 

reductions of ‘‘at least 3 percent of 

baseline emissions each year,’’ and it 

substitutes NOX reductions for VOC 

reductions beginning in milestone year 

2023 to meet VOC emission targets.148

For the San Diego County area, CARB 

concludes that the RFP demonstration 

meets the applicable requirements for 

each milestone year as well as the 

attainment year for the 2015 ozone 

NAAQS. 


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149 62 FR 1150, 1183 (January 8, 1997). 

150We note that the weight of evidence 

demonstration provided in Attachment M to the 

2020 Plan generally supports the substitution of 

NOX emissions reductions for VOC emissions 

reductions for the RFP demonstrations for the 2008 

and 2015 ozone NAAQS. See Modeling TSD, at 32 

and 33. 

151Email dated September 1, 2023, from Chenxia 

Cai, CARB, with attachment, to John J. Kelly, EPA. 

TABLE 11—RFP DEMONSTRATION FOR SAN DIEGO COUNTY FOR THE 2015 OZONE NAAQS 

[Summer planning inventory, tpd or percent] 

VOC 

2017 2023 2026 2029 2032 

Baseline VOC Emissions (tpd) .................................................................................... 112.9 102.4 99.7 98.2 97.2 

Change in VOC since 2017 (tpd) ................................................................................ ................ 10.5 13.2 14.6 15.7 

Change in VOC since 2017 (percent) ......................................................................... ................ 9.3% 11.7% 13.0% 13.9% 

Required percentage change since 2017 .................................................................... ................ 18% 27% 36% 45% 

Shortfall (¥)/Surplus (+) in VOC (percent) ................................................................. ................ ¥8.7% ¥15.3% ¥23.0% ¥31.1% 

NOX

2017 2023 2026 2029 2032 

Baseline NOX Emissions (tpd) ..................................................................................... 77.0 56.8 53.6 51.3 49.7 

Change in NOX since 2017 (tpd) ................................................................................. ................ 20.2 23.4 25.6 27.3 

Change in NOX since 2017 (percent) .......................................................................... ................ 26.3% 30.4% 33.3% 35.5% 

NOX reductions since 2017 used for VOC substitution in this milestone year (percent) ......................................................................................................................... ................ 8.7% 15.3% 23.0% 31.1% 

NOX reductions since 2017 surplus after meeting VOC substitution needs in this 

milestone year (percent) .......................................................................................... ................ 17.6% 15.1% 10.3% 4.3% 

RFP shortfall (if any) (percent) .................................................................................... ................ 0% 0% 0% 0% 

RFP met? ..................................................................................................................... ................ Yes Yes Yes Yes 

Source: 2020 Plan, Table 4–5. 

3. The EPA’s Review of the State’s 

Submission 

In 1997, the EPA approved a 15 

percent ROP plan for San Diego County 

for the 1-hour ozone NAAQS.149 The 

San Diego County nonattainment areas 

for the 2008 and 2015 ozone NAAQS are 

essentially the same geographic area as 

the nonattainment area for the 1-hour 

ozone NAAQS, and thus, we agree with 

the conclusion in the 2020 Plan that the 

ROP requirements of CAA section 

182(b)(1) for the San Diego County area 

have been met and that, as a result, 

there is no need to demonstrate another 

15 percent reduction in VOC for this 

area. 

The RFP demonstrations in the 2020 

Plan derive from the same emissions 

inventories as presented in Section III.A 

(‘‘Emissions Inventories’’) of this 

document. In Section III.A, we are 

proposing to approve the 2011 and 2017 

base year emissions inventories for the 

2008 and 2015 ozone NAAQS, 

respectively. With respect to the future 

year emissions baseline projections, as 

further explained in Section III.A of this 

document, we have reviewed the growth 

and control factors and find them 

acceptable and conclude that the future 

baseline emissions projections in the 

2020 Plan reflect appropriate 

calculation methods and the latest 

planning assumptions and appropriately 

account for the growth increments for 

the military and SDIA as well as the 

adjustments for ERCs and the 

EMFAC2017 Adjustment Factors. In 

addition, we have reviewed the 

calculations in Table 3–3 and Table 4– 

5 of the 2020 Plan and find that the 

District and CARB have used an 

appropriate calculation method to 

demonstrate RFP.150

CARB provided support for 

substituting NOX reductions for VOC 

reductions in the San Diego County area 

in Attachment K to the 2020 Plan and 

supplemented that information in an 

attachment to an email to the EPA dated 

September 1, 2023.151 Combining the 

information from Attachment K in the 

2020 Plan with additional explanation 

and analysis in the attachment, CARB 

presents two approaches to 

understanding the relationship between 

the two ozone precursors, NOX and 

VOC, in the area. First, CARB presents 

a table comparing emissions of the 

precursors over time and the modeled 

ozone design value. This table is shown 

here as Table 12 of this document 

(replacing the term ROG for VOC). 

TABLE 12—OZONE DESIGN VALUES IN SAN DIEGO COUNTY AND THE CORRESPONDING EMISSIONS OF NOX AND VOC IN

THE SAN DIEGO COUNTY AREA

Scenario Design value 

(ppb) 

Emissions (tpd) 

NOX VOC 

Base Year (2017) ........................................................................................................................................ 83.0 77.0 116.0 

Attainment Year (2032) ............................................................................................................................... 71.1 43.4 96.5 

Attainment Year (2032) with a 10 percent reduction in NOX ...................................................................... 69.9 39.1 96.5 

Sources: 2020 Plan, Attachment K, Section K.3.5 (‘‘NOX Sensitivity Analysis’’); Attachment to September 1, 2023 email from CARB to the 

EPA. 


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152For example, the 2017 baseline emissions in 

the 2020 Plan for the San Diego County 

nonattainment area are 77 tpd for NOX and 113 tpd 

for VOC (see Table 1 of this document—not 

including emissions beyond three NM from the 

coast), whereas the 2018 baseline emissions used 

for the simulations are 75 tpd for NOX and 112 tpd 

for VOC. 

153CAA section 182(d)(1)(A) includes three 

separate elements. In short, under section 

182(d)(1)(A), states are required to adopt 

transportation control strategies and measures to 

offset growth in emissions from growth in VMT, 

and, as necessary, in combination with other 

emission reduction requirements, to demonstrate 

RFP and attainment. For more information on the 

EPA’s interpretation of the three elements of section 

182(d)(1)(A), see 77 FR 58067 at 58068 (September 

19, 2012) (proposed withdrawal of approval of 

South Coast VMT emissions offset demonstrations). 

In Section III.E of this document, we address the 

first element of CAA section 182(d)(1)(A) (i.e., the 

VMT emissions offset requirement). In Sections 

III.C and III.D of this document, we propose to 

approve the attainment demonstrations and RFP 

demonstrations, respectively, for the 2008 ozone 

NAAQS and for the 2015 ozone NAAQS in the San 

Diego County area. Compliance with the second 

and third elements of section 182(d)(1)(A) is 

predicated on final approval of the attainment and 

RFP demonstrations. 

154See Association of Irritated Residents v. EPA, 

632 F.3d. 584, at 596–597 (9th Cir. 2011), reprinted 

as amended on January 27, 2012, 686 F.3d 668, 

further amended February 13, 2012 (‘‘Association of 

Irritated Residents’’). 

155EPA, ‘‘Implementing Clean Air Act Section 

182(d)(1)(A): Transportation Control Measures and 

Transportation Control Strategies to Offset Growth 

in Emissions Due to Growth in Vehicle Miles 

Travelled,’’ EPA–420–B–12–053, August 2012, 

https://nepis.epa.gov/Exe/ZyPDF.cgi/

P100EZ4X.PDF?Dockey=P100EZ4X.PDF. 

Table 12 of this document presents 

CARB’s summary data regarding NOX

sensitivity in the area, including the 

emissions of NOX and VOC for the 2015 

ozone NAAQS base year (2017) and the 

future attainment year (2032), as well as 

the measured 2017 ozone design value 

(83.0 ppb) and the predicted 2032 

design value (71.1 ppb) with emissions 

reflecting business-as-usual, that is, 

without further emissions reductions. 

The fourth row of the table shows the 

DV predicted for the 2032 attainment 

year if there were an additional NOX

reduction of ten percent from the 

business-as-usual scenario. When NOX

emissions in the area are modeled at 

39.1 tpd, the modeled design value for 

the area is 69.9 ppb, a design value that 

meets the 2015 ozone NAAQS. DVs are 

approximately linear with respect to the 

corresponding NOX emissions in Table 

12, indicating that the reduction of NOX

likely plays a dominant role in the 

attainment demonstration in the 2020 

Plan. 

Second, CARB presents information 

from a series of sensitivity tests for the 

area, in order to provide additional 

insight into the relative impact of 

reducing NOX and VOC on the modeled 

design value for the area. These 

simulations use different data than the 

2020 Plan, including a different model 

year, domain, and a 2018 emissions 

inventory base year. However, the 

(2018) baseline emissions used for the 

simulations are similar enough to the 

baseline emissions (2017) used for the 

2020 Plan that the results of the 

simulations provide useful information 

with which to evaluate the reliance on 

NOX substitution in the 2020 Plan for 

the RFP demonstrations for compliance 

with CAA section 182(c)(2)(C).152

The simulations were run from values 

of twenty percent to 100 percent of 

baseline emissions to produce ‘‘design 

value isopleths’’ at the Alpine 

monitoring site, the long-standing 

design value monitoring site in San 

Diego County. Such isopleths can be 

used to predict what the effect would be 

on the design value if either NOX or 

VOC emissions were held constant 

while the other ozone precursor were 

altered. Based on the isopleths 

produced by the simulations, a 

reduction of NOX of 40 percent (from 

2018 baseline emissions) results in a 

decrease in the design value (from 2018) 

at the Alpine monitoring site to the level 

of the 2008 ozone NAAQS whereas the 

same decrease in the design value 

requires a 60 percent decrease in VOC 

emissions (from 2018 baseline 

emissions). The isopleths that were 

produced by these simulations indicate 

that the design value in this area is more 

sensitive to decreases in NOX, and that 

the effect is more pronounced at lower 

NOX emissions. For example, if NOX

emissions were held constant at 20 

percent of the 2018 baseline, a change 

in VOC levels has almost no effect on 

the design value modeled for the area 

(in this case, around 60 ppb), whereas 

at a design value of 70.9 ppb, the design 

value is noticeably dependent on both 

pollutants, but still more sensitive to 

NOX. This isopleth indicates that NOX

control is more effective than VOC 

control in the area on both a percentage 

and a per ton basis. As such, we find 

that the reliance on NOX substitution for 

RFP demonstration purposes in the 

2020 Plan to be consistent with the 

requirements of CAA section 

182(c)(2)(C). 

For these reasons, we have 

determined that the 2020 Plan 

demonstrates RFP in each milestone 

year, as well as in each attainment year 

(2026 for the 2008 ozone NAAQS and 

2032 for the 2015 ozone NAAQS), 

consistent with applicable CAA 

requirements and EPA guidance and 

rulemakings. We therefore propose to 

approve the RFP demonstrations for the 

San Diego County area for the 2008 

ozone NAAQS and for the 2015 ozone 

NAAQS under sections 172(c)(2), 

182(b)(1) and 182(c)(2)(B) of the CAA, 

40 CFR 51.1110(a)(2), 40 CFR 

51.1110(a)(2)(i) and (ii), 40 CFR 

51.1310(a)(2) and 40 CFR 

51.1310(a)(2)(ii). 

E. Transportation Control Strategies and 

Measures To Offset Emissions Increases 

From Vehicle Miles Traveled 

1. Statutory and Regulatory 

Requirements 

Section 182(d)(1)(A) of the Act 

requires, in relevant part, a state to 

submit, for each area classified as 

Severe or above, a SIP revision that 

‘‘identifies and adopts specific 

enforceable transportation control 

strategies and transportation control 

measures to offset any growth in 

emissions from growth in vehicle miles 

traveled or number of vehicle trips in 

such area.’’ 153 Herein, we use ‘‘VMT’’ to 

refer to vehicle miles traveled and refer 

to the related SIP requirement as the 

‘‘VMT emissions offset requirement.’’ In 

addition, we refer to the SIP revision 

intended to demonstrate compliance 

with the VMT emissions offset 

requirement as the ‘‘VMT emissions 

offset demonstration.’’ The 2008 and 

2015 SRRs extend the VMT emissions 

offset requirement to Severe and above 

areas for the 2008 and 2015 ozone 

NAAQS at 40 CFR 51.1102 and 40 CFR 

51.1302, respectively. 

In Association of Irritated Residents v. 

EPA, the Ninth Circuit ruled that 

additional transportation control 

measures are required whenever vehicle 

emissions are projected to be higher 

than they would have been had VMT 

not increased, even when aggregate 

vehicle emissions are actually 

decreasing.154 In response to the court’s 

decision, in August 2012, the EPA 

issued guidance titled ‘‘Implementing 

Clean Air Act Section 182(d)(1)(A): 

Transportation Control Measures and 

Transportation Control Strategies to 

Offset Growth in Emissions Due to 

Growth in Vehicle Miles Travelled’’ 

(‘‘August 2012 Guidance’’).155

The August 2012 Guidance discusses 

the meaning of ‘‘transportation control 

strategies’’ (TCSs) and ‘‘transportation 

control measures’’ (TCMs) and 

recommends that both TCSs and TCMs 

be included in the calculations made for 

the purpose of determining the degree to 

which any hypothetical growth in 

emissions due to growth in VMT should 

be offset. Generally, TCS is a broad term 

that encompasses many types of 

controls (including, for example, motor 

vehicle emissions limitations, I/M 


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156See, e.g., 40 CFR 51.100(n). 

157See the August 2012 Guidance for specific 

details on how states might conduct the 

calculations. 

158 2020 Plan, pp. 37, 57 and N–1. 

159 2020 Plan, Attachment N, Appendix A–1, 

‘‘State of California Motor Vehicle Control Program 

(1990–Present); Appendix A–2, ‘‘Adopted 

Transportation Control Measures.’’ 

160 84 FR 41717 (August 15, 2019). 

programs, alternative fuel programs, 

other technology-based measures, and 

TCMs) that would fit within the 

regulatory definition of ‘‘control 

strategy.’’ 156 A TCM is defined at 40 

CFR 51.100(r) as ‘‘any measure that is 

directed toward reducing emissions of 

air pollutants from transportation 

sources,’’ including, but not limited to, 

those listed in section 108(f) of the 

Clean Air Act. TCMs generally refer to 

programs intended to reduce VMT, 

number of vehicle trips, or traffic 

congestion, such as programs for 

improved public transit, designation of 

certain lanes for passenger buses and 

high-occupancy vehicles, and trip 

reduction ordinances. 

The August 2012 Guidance explains 

how states may demonstrate that the 

VMT emissions offset requirement is 

satisfied in conformance with the 

Court’s ruling in Association of Irritated 

Residents. Under the August 2012 

Guidance, states would develop one 

emissions inventory for the base year 

and three different emissions inventory 

scenarios for the attainment year.157 The 

base year on-road VOC emissions 

should be calculated using VMT in that 

year, and they should reflect all 

enforceable TCSs and TCMs in place in 

the base year. This would include 

vehicle emissions standards, state and 

local control programs, such as I/M 

programs or fuel rules, and any 

additional implemented TCSs and 

TCMs that were already required by or 

credited in the SIP as of that base year. 

The first of the emissions calculations 

for the attainment year would be based 

on the projected VMT and trips for that 

year and assume that no new TCSs or 

TCMs beyond those already credited in 

the base year inventory have been put 

in place since the base year. This 

calculation demonstrates how emissions 

would hypothetically change if no new 

TCSs or TCMs were implemented, and 

VMT and trips were allowed to grow at 

the projected rate from the base year. 

This estimate would show the potential 

for an increase in emissions due solely 

to growth in VMT and trips. This 

represents a ‘‘no action’’ scenario. 

Emissions in the attainment year in this 

scenario may be lower than those in the 

base year due to the fleet that was on the 

road in the base year gradually being 

replaced through fleet turnover; 

however, provided VMT and/or 

numbers of vehicle trips in fact increase 

by the attainment year, they would still 

likely be higher than they would have 

been assuming VMT had held constant. 

The second of the attainment year’s 

emissions calculations would assume 

that no new TCSs or TCMs beyond 

those already credited have been put in 

place since the base year, but it would 

also assume that there was no growth in 

VMT and trips between the base year 

and attainment year. This estimate 

reflects the hypothetical emissions level 

that would have occurred if no further 

TCMs or TCSs had been put in place 

and if VMT and trip levels had held 

constant since the base year. Like the 

‘‘no action’’ attainment year estimate, 

emissions in the attainment year may be 

lower than those in the base year due to 

the fleet that was on the road in the base 

year gradually being replaced by cleaner 

vehicles through fleet turnover, but in 

this case they would not be influenced 

by any growth in VMT or trips. This 

emissions estimate would reflect a 

ceiling on the attainment emissions that 

should be allowed to occur under the 

statute as interpreted by the Court in 

Association of Irritated Residents 

because it shows what would happen 

under a scenario in which no offsetting 

TCSs or TCMs have yet been put in 

place and VMT and trips are held 

constant during the period from the 

area’s base year to its attainment year. 

This represents a ‘‘VMT offset ceiling’’ 

scenario. These two hypothetical status 

quo estimates are necessary steps in 

identifying the target level of emissions 

from which states would determine 

whether further TCMs or TCSs, beyond 

those that have been adopted and 

implemented, would need to be adopted 

and implemented in order to fully offset 

any increase in emissions due solely to 

VMT and trips identified in the ‘‘no 

action’’ scenario. 

Finally, the state would present the 

emissions that are expected to occur in 

the area’s attainment year after taking 

into account reductions from all 

enforceable TCSs and TCMs. This 

estimate would be based on the VMT 

and trip levels expected to occur in the 

attainment year (i.e., the VMT and trip 

levels from the first estimate) and all of 

the TCSs and TCMs expected to be in 

place and for which the SIP will take 

credit in the area’s attainment year, 

including any TCMs and TCSs put in 

place since the base year. This 

represents the ‘‘projected actual’’ 

attainment year scenario. If this 

emissions estimate is less than or equal 

to the emissions ceiling that was 

established in the second of the 

attainment year calculations, the TCSs 

and TCMs implemented by the 

attainment year would be sufficient to 

fully offset the identified hypothetical 

growth in emissions. 

If, instead, the estimated projected 

actual attainment year emissions are 

still greater than the ceiling that was 

established in the second of the 

attainment year emissions calculations, 

even after accounting for post-baseline 

year TCSs and TCMs, the state would 

need to adopt and implement additional 

TCSs or TCMs to further offset the 

growth in emissions. The additional 

TCSs or TCMs would need to bring the 

actual emissions down to at least the 

VMT offset ceiling estimated in the 

second of the attainment year 

calculations, in order to meet the VMT 

offset requirement of section 

182(d)(1)(A) as interpreted by the Court. 

2. Summary of State’s Submission 

CARB prepared the VMT emissions 

offset demonstration for San Diego 

County for the 2008 ozone NAAQS and 

for the 2015 ozone NAAQS. The District 

referenced the State’s demonstration in 

Sections 3.1.3 and 4.1.3 of the 2020 Plan 

and included the demonstration itself in 

Attachment N (‘‘VMT Offset 

Demonstration for San Diego 

County’’).158 In addition to the VMT 

emissions offset demonstration, 

Attachment N of the 2020 Plan includes 

two appendices—one listing the TCSs 

adopted by CARB since 1990 and 

another listing the TCMs adopted by 

SANDAG (as of 2018) in San Diego 

County.159 Based on the demonstration 

included as Attachment N of the 2020 

Plan, the District concludes that the 

TCSs and TCMs identified in 

Attachment N offset the growth in 

emissions due to growth in VMT, thus 

satisfying the VMT emissions offset 

requirement for both the 2008 and 2015 

ozone NAAQS. 

In Attachment N of the 2020 Plan, 

CARB presents the VMT offset 

demonstration for the area. For this 

demonstration, CARB used 

EMFAC2017, the latest EPA-approved 

motor vehicle emissions model for 

California available at the time the 2020 

Plan was developed.160 The 

EMFAC2017 model estimates the onroad emissions from two combustion 

processes (i.e., running exhaust and 

start exhaust) and four evaporative 

processes (i.e., hot soak, running losses, 

diurnal losses, and resting losses). The 

EMFAC2017 model combines trip-based 

VMT and speed distribution data from 

the regional transportation planning 


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161 2020 Plan, Attachment N, table N–5. 

162 2020 Plan, Attachment M, ‘‘Weight of 

Evidence Demonstration for San Diego County,’’ 

Table M–4. 

agency (i.e., SANDAG), starts data based 

on household travel surveys, and 

vehicle population data from the 

California Department of Motor 

Vehicles. These sets of data are 

combined with corresponding emissions 

rates to calculate emissions. 

Emissions from running exhaust, start 

exhaust, hot soak, and running losses 

are a function of how much a vehicle is 

driven. Emissions from these processes 

are thus directly related to VMT and 

vehicle trips, and CARB included these 

emissions in the calculations that 

provide the basis for the San Diego 

County VMT emissions offset 

demonstration. CARB did not include 

emissions from resting loss and diurnal 

loss processes in the analysis because 

such emissions are related to vehicle 

population, not to VMT or vehicle trips, 

and thus are not part of ‘‘any growth in 

emissions from growth in vehicle miles 

traveled or numbers of vehicle trips in 

such area’’ under CAA section 

182(d)(1)(A). 

The San Diego County VMT 

emissions offset demonstration for the 

2008 ozone NAAQS uses a 2011 base 

year. The base year for VMT emissions 

offset demonstration purposes should 

generally be the same base year used for 

nonattainment planning purposes. In 

Section III.A of this document, the EPA 

is proposing to approve the 2011 base 

year inventory for San Diego County for 

the purposes of the 2008 ozone NAAQS, 

and thus, CARB’s selection of 2011 as 

the base year for the area’s VMT 

emissions offset demonstration for the 

2008 ozone NAAQS is appropriate. 

The San Diego County VMT 

emissions offset demonstration for the 

2008 ozone NAAQS also includes the 

three different attainment year scenarios 

(i.e., no action, VMT offset ceiling, and 

projected actual) described in Section 

III.E.1 of this document. The 2020 Plan 

provides a demonstration of attainment 

of the 2008 ozone NAAQS in San Diego 

County by the applicable attainment 

date, based on the controlled 2026 

emissions inventory. As described in 

Section III.C of this document, the EPA 

is proposing to approve the attainment 

demonstration for the 2008 ozone 

NAAQS for San Diego County, and thus, 

we find CARB’s selection of year 2026 

as the attainment year for the VMT 

emissions offset demonstration for the 

2008 ozone NAAQS to be acceptable. 

Table 13 of this document 

summarizes the relevant distinguishing 

parameters for each of the emissions 

scenarios and shows CARB’s 

corresponding VOC emissions estimates 

for the demonstration for the 2008 

ozone NAAQS. 

TABLE 13—VMT EMISSIONS OFFSET INVENTORY SCENARIOS AND RESULTS FOR 2008 OZONE NAAQS 

Scenario VMT 

(1,000/day) 

Starts (trips) 

(1,000/day) 

VOC emissions 

(tpd) 

Base Year (2011) ................................................................................................................ 82,640 11,596 33 

No Action (2026) .................................................................................................................. 87,279 12,278 12 

VMT Offset Ceiling (2026) ................................................................................................... 82,640 11,625 11 

Projected Actual (2026) ....................................................................................................... 87,279 12,008 10 

Sources: 2020 Plan, Tables N–1 and N–2; supplemental email dated April 27, 2023, from Nesamani Kalandiyur, CARB, with attachment to 

John J. Kelly, EPA. 

For the base year scenario, CARB ran 

the EMFAC2017 model for the 2011 

base year using VMT and starts data 

corresponding to that year. As shown in 

Table 13, CARB estimates San Diego 

County VOC emissions at 33 tpd in 

2011. 

For the ‘‘no action’’ scenario, CARB 

first identified the on-road motor 

vehicle control programs (i.e., TCSs 161) 

put in place since the base year and 

incorporated into EMFAC2017, and 

then ran EMFAC2017 with the VMT and 

starts data corresponding to the 2026 

attainment year without the emissions 

reductions from the on-road motor 

vehicle control programs put in place 

after the base year. Thus, the no action 

scenario reflects the hypothetical VOC 

emissions in the attainment year if 

CARB had not put in place any 

additional TCSs after 2011. As shown in 

Table 13, CARB estimates the ‘‘no 

action’’ San Diego County VOC 

emissions at 12 tpd in 2026. 

For the ‘‘VMT offset ceiling’’ scenario, 

CARB ran the EMFAC2017 model for 

the attainment year but with VMT and 

starts data corresponding to base year 

values. Like the no action scenario, the 

EMFAC2017 model was adjusted to 

reflect the VOC emissions levels in the 

attainment years without the benefits of 

the post-base-year on-road motor 

vehicle control programs. Thus, the 

VMT offset ceiling scenario reflects 

hypothetical VOC emissions in San 

Diego County if CARB had not put in 

place any TCSs after the base year and 

if there had been no growth in VMT or 

vehicle trips between the base year and 

the attainment year. 

The hypothetical growth in emissions 

due to growth in VMT and trips can be 

determined from the difference between 

the VOC emissions estimates under the 

‘‘no action’’ scenario and the 

corresponding estimates under the 

‘‘VMT offset ceiling’’ scenario. Based on 

the values in Table 13, the hypothetical 

growth in emissions due to growth in 

VMT and trips in San Diego County 

would have been 1 tpd (i.e., 12 tpd 

minus 11 tpd). This hypothetical 

difference establishes the level of VMT 

growth-caused emissions that need to be 

offset by the combination of postbaseline year TCSs and any necessary 

additional TCSs. 

For the ‘‘projected actual’’ scenario 

calculation, CARB ran the EMFAC2017 

model for the attainment year with VMT 

and starts data at attainment year values 

and with the full benefits of the relevant 

post-baseline year motor vehicle control 

programs. For this scenario, CARB 

included the emissions benefits from 

TCSs put in place since the base year. 

Between 2000 and 2019, annual VOC 

emissions in San Diego County declined 

48 percent, approximately 65 percent of 

which was due to reductions from lightduty passenger vehicles.162 As shown in 

Table 13 of this document, on-road VOC 

emissions are projected to decline by 

more than two-thirds (from 33 tpd to 10 

tpd), from the 2011 base year to the 

2026 attainment year. The most 

significant measures reducing VOC 

emissions during this timeframe are the 

regulations included in the Advanced 

Clean Cars regulatory package, such as 

the Low Emission Vehicle (LEV) III 

regulations that establish increasingly 

stringent emission standards for both 

criteria pollutants and greenhouse gases 

for new passenger vehicles through the 

2025 model year and the Zero-Emission 


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163See also 2020 Plan, Attachment N, Table N– 

5. 

164 2020 Plan, Attachment N, Table N–5. 165 2020 Plan, Table M–4. 

Vehicle (ZEV) sales mandate 

regulations.163

As shown in Table 13, the projected 

actual attainment-year VOC emissions 

are 10 tpd. CARB compared this value 

against the corresponding VMT offset 

ceiling value to determine whether 

additional TCSs or TCMs would need to 

be adopted and implemented in order to 

offset any increase in emissions due 

solely to VMT and trips. Because the 

projected actual emissions are less than 

the corresponding VMT offset ceiling 

emissions, CARB concluded that the 

demonstration shows compliance with 

the VMT emissions offset requirement 

and that the adopted TCSs are sufficient 

to offset the growth in emissions from 

the growth in VMT and vehicle trips in 

the San Diego County area for the 2008 

ozone NAAQS. 

The San Diego County VMT 

emissions offset demonstration for the 

2015 ozone NAAQS uses a 2017 base 

year. The base year for VMT emissions 

offset demonstration purposes should 

generally be the same base year used for 

nonattainment planning purposes. In 

Section III.A of this document, the EPA 

is proposing to approve the 2017 base 

year inventory for the San Diego County 

area for the purposes of the 2015 ozone 

NAAQS, and thus, CARB’s selection of 

2017 as the base year for the area’s VMT 

emissions offset demonstration for the 

2015 ozone NAAQS is appropriate. 

The San Diego County area VMT 

emissions offset demonstration for the 

2015 ozone NAAQS also includes the 

three different attainment year scenarios 

(i.e., no action, VMT offset ceiling, and 

projected actual) described in Section 

III.E.1. The 2020 Plan provides a 

demonstration of attainment of the 2015 

ozone NAAQS in the San Diego County 

area by the applicable attainment date, 

based on the controlled 2032 emissions 

inventory. As described in Section III.C 

of this document, the EPA is proposing 

to approve the attainment 

demonstration for the 2015 ozone 

NAAQS for the San Diego County area, 

and thus, we find CARB’s selection of 

year 2032 as the attainment year for the 

VMT emissions offset demonstration for 

the 2015 ozone NAAQS to be 

acceptable. 

Table 14 of this document 

summarizes the relevant distinguishing 

parameters for each of the emissions 

scenarios and shows CARB’s 

corresponding VOC emissions estimates 

for the demonstration for the 2015 

ozone NAAQS. 

TABLE 14—VMT EMISSIONS OFFSET INVENTORY SCENARIOS AND RESULTS FOR 2015 OZONE NAAQS 

Scenario VMT 

(1,000/day) 

Starts (trips) 

(1,000/day) 

VOC emissions 

(tpd) 

Base Year (2017) ................................................................................................................ 83,217 10,783 18 

No Action (2032) .................................................................................................................. 91,751 13,411 10 

VMT Offset Ceiling (2032) ................................................................................................... 83,217 12,164 9 

Projected Actual (2032) ....................................................................................................... 91,751 13,130 8 

Sources: 2020 Plan, Tables N–1 and N–2; supplemental email dated April 27, 2023, from Nesamani Kalandiyur, CARB, with attachment, to 

John J. Kelly, EPA. 

For the base year scenario, CARB ran 

the EMFAC2017 model for the 2017 

base year using VMT and starts data 

corresponding to that year. As shown in 

Table 14, CARB estimates San Diego 

County VOC emissions at 18 tpd in 

2017. 

For the ‘‘no action’’ scenario, CARB 

first identified the on-road motor 

vehicle control programs (i.e., TCSs 164) 

put in place since the base year and 

incorporated into EMFAC2017, and 

then ran EMFAC2017 with the VMT and 

starts data corresponding to the 2032 

attainment year without the emissions 

reductions from the on-road motor 

vehicle control programs put in place 

after the base year. Thus, the no action 

scenario reflects the hypothetical VOC 

emissions in the attainment year if 

CARB had not put in place any 

additional TCSs after 2017. As shown in 

Table 14 of this document, CARB 

estimates the ‘‘no action’’ San Diego 

County VOC emissions at 10 tpd in 

2032. 

For the ‘‘VMT offset ceiling’’ scenario, 

CARB ran the EMFAC2017 model for 

the attainment year but with VMT and 

starts data corresponding to base year 

values. Like the no action scenario, the 

EMFAC2017 model was adjusted to 

reflect the VOC emissions levels in the 

attainment years without the benefits of 

the post-base-year on-road motor 

vehicle control programs. Thus, the 

VMT offset ceiling scenario reflects 

hypothetical VOC emissions in San 

Diego County if CARB had not put in 

place any TCSs after the base year and 

if there had been no growth in VMT or 

vehicle trips between the base year and 

the attainment year. 

The hypothetical growth in emissions 

due to growth in VMT and trips can be 

determined from the difference between 

the VOC emissions estimates under the 

‘‘no action’’ scenario and the 

corresponding estimates under the 

‘‘VMT offset ceiling’’ scenario. Based on 

the values in Table 14 of this document, 

the hypothetical growth in emissions 

due to growth in VMT and trips in San 

Diego County would have been 1 tpd 

(i.e., 10 tpd minus 9 tpd). This 

hypothetical difference establishes the 

level of VMT growth-caused emissions 

that need to be offset by the 

combination of post-baseline year TCSs 

and any necessary additional TCSs. 

For the ‘‘projected actual’’ scenario 

calculation, CARB ran the EMFAC2017 

model for the attainment year with VMT 

and starts data at attainment year values 

and with the full benefits of the relevant 

post-baseline year motor vehicle control 

programs. For this scenario, CARB 

included the emissions benefits from 

TCSs put in place since the base year. 

Between 2000 and 2019, annual VOC 

emissions in San Diego County declined 

48 percent, approximately 65 percent of 

which was due to reductions from lightduty passenger vehicles.165 Table 14 of 

this document shows that on-road VOC 

emissions are projected to decline by 

more than one half (from 18 tpd to 8 

tpd), from the 2017 base year to the 

2032 attainment year. Significant VOC 

emissions reductions during the 2017– 

2032 timeframe result from the ZEV 

provisions of the Advanced Clean Cars 

program. 

As shown in Table 14 of this 

document, the projected actual 

attainment-year VOC emissions are 8 

tpd. CARB compared this value against 

the corresponding VMT offset ceiling 

value to determine whether additional 

TCSs or TCMs would need to be 

adopted and implemented in order to 

offset any increase in emissions due 

solely to VMT and trips. Because the 


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166 70 FR 71612 (November 29, 2005); 2008 Ozone 

SRR, 80 FR 12264, 12285 (March 6, 2015); 2015 

Ozone SRR, 83 FR 62998, 63026 (December 6, 

2018). 

167See Bahr v. EPA, 836 F.3d 1218, 1235–1237 

(9th Cir. 2016) (‘‘Bahr’’) and Sierra Club v. EPA, 21 

F.4th 815, 827–828 (D.C. Cir. 2021). 

168 2008 Ozone SRR, 80 FR 12264, 12285 (March 

6, 2015); 2015 Ozone SRR, 83 FR 62998, 63026 

(December 6, 2018). 

169See Association of Irritated Residents v. EPA, 

10 F.4th 937 (9th Cir. 2021) (‘‘AIR’’). 

170 81 FR 58010, 58067 (August 24, 2016). 171 88 FR 17571 (March 23, 2023). 

projected actual emissions are less than 

the corresponding VMT offset ceiling 

emissions, CARB concluded that the 

demonstration shows compliance with 

the VMT emissions offset requirement 

and that the adopted TCSs are sufficient 

to offset the growth in emissions from 

the growth in VMT and vehicle trips in 

the San Diego County area for the 2015 

ozone NAAQS. 

3. The EPA’s Review of the State’s 

Submission 

Based on our review of the San Diego 

County VMT emissions offset 

demonstration in Attachment N of the 

2020 Plan, we find CARB’s analysis to 

be consistent with our August 2012 

Guidance and consistent with the 

emissions and vehicle activity estimates 

provided by CARB in support of the 

2020 Plan. We agree that CARB and 

SANDAG have adopted sufficient TCSs 

and TCMs to offset the growth in 

emissions from growth in VMT and 

vehicle trips in the San Diego County 

area for the purposes of both the 2008 

ozone NAAQS and the 2015 ozone 

NAAQS. Therefore, we propose to 

approve the San Diego County area 

VMT emissions offset demonstration 

element of the 2020 San Diego County 

Ozone SIP as meeting the requirements 

of CAA section 182(d)(1)(A), 40 CFR 

51.1102 and 40 CFR 51.1302. 

F. Contingency Measures 

1. Statutory and Regulatory 

Requirements 

Under the CAA, ozone nonattainment 

areas classified under subpart 2 as 

Serious or above must include in their 

SIPs contingency measures consistent 

with sections 172(c)(9) and 182(c)(9). 

CAA section 172(c)(9) requires states 

with nonattainment areas to provide for 

the implementation of specific measures 

to be undertaken if the area fails to make 

RFP or to attain the NAAQS by the 

applicable attainment date. Such 

measures must be included in the SIP as 

contingency measures to take effect in 

any such case without further action by 

the state or the EPA. CAA section 

182(c)(9) requires states to provide 

contingency measures in the event that 

an ozone nonattainment area fails to 

meet any applicable RFP milestone. The 

SIP should contain trigger mechanisms 

for the contingency measures, specify a 

schedule for implementation, and 

indicate that the measure will be 

implemented without significant further 

action by the state or the EPA.166

Contingency measures must be designed 

so as to be implemented prospectively; 

already-implemented control measures 

may not serve as contingency measures 

even if they provide emissions 

reductions beyond those needed for any 

other CAA purpose.167

The purpose of contingency measures 

is to continue progress in reducing 

emissions while a state revises its SIP to 

meet the missed RFP requirement or to 

correct ongoing nonattainment. Neither 

the CAA nor the EPA’s implementing 

regulations establish a specific level of 

emissions reductions that 

implementation of contingency 

measures must achieve, but the EPA’s 

2008 Ozone SRR and 2015 Ozone SRR 

reiterate the EPA’s policy that 

contingency measures should provide 

for emissions reductions approximately 

equivalent to one year’s worth of RFP, 

amounting to reductions of 3 percent of 

the baseline emissions inventory for the 

nonattainment area.168 A state cannot 

rely on already-implemented measures 

to serve as contingency measures, and 

in addition, a state cannot rely on 

already-implemented measures to 

justify the adoption of a contingency 

measure or contingency measures that 

would achieve less than one year’s 

worth of RFP to meet the contingency 

measures requirements of CAA sections 

172(c)(9) and 182(c)(9) for the 

nonattainment area.169 As part of the 

contingency measures SIP revision for a 

given area, the EPA expects states to 

explain the amount of anticipated 

emissions reductions that the 

contingency measures will achieve. In 

the event that a state is unable to 

identify and adopt contingency 

measures that will provide for 

approximately one year’s worth of RFP, 

then the EPA recommends that the state 

provide a reasoned justification why the 

smaller amount of emissions reductions 

is appropriate.170

In March 2023, the EPA published 

notice of availability announcing a new 

draft guidance addressing the 

contingency measures requirement of 

section 172(c)(9), entitled: ‘‘DRAFT: 

Guidance on the Preparation of State 

Implementation Plan Provisions that 

Address the Nonattainment Area 

Contingency Measure Requirements for 

Ozone and Particulate Matter (DRAFT— 

3/17/23—Public Review Version)’’ 

(herein referred to as the ‘‘Draft Revised 

Contingency Measure Guidance’’) and 

opportunity for public comment.171 The 

principal differences between the draft 

revised guidance and existing guidance 

on contingency measures relate to the 

EPA’s recommendations concerning the 

specific amount of emissions reductions 

that implementation of contingency 

measures should achieve, and the 

timing for when the emissions 

reductions from the contingency 

measures should occur. 

Under the draft revised guidance, the 

recommended level of emissions 

reductions that contingency measures 

should achieve would represent one 

year’s worth of ‘‘progress’’ as opposed to 

one year’s worth of RFP. One year’s 

worth of ‘‘progress’’ is calculated by 

determining the average annual 

reductions between the base year 

emissions inventory and the projected 

attainment year emissions inventory, 

determining what percentage of the base 

year emissions inventory this amount 

represents, then applying that 

percentage to the projected attainment 

year emissions inventory to determine 

the amount of reductions needed to 

ensure ongoing progress if contingency 

measures are triggered. 

With respect to the time period within 

which reductions from contingency 

measures should occur, the EPA 

previously recommended that 

contingency measures take effect within 

60 days of being triggered, and that the 

resulting emissions reductions generally 

occur within one year of the triggering 

event. Under the draft revised guidance, 

in instances where there are insufficient 

contingency measures available to 

achieve the recommended amount of 

emissions reductions within one year of 

the triggering event, the EPA believes 

that contingency measures that provide 

reductions within up to two years of the 

triggering event would be appropriate to 

consider towards achieving the 

recommended amount of emissions 

reductions. The draft revised guidance 

does not alter the 60-day 

recommendation for the contingency 

measures to take initial effect. 

2. Summary of the State’s Submission 

The 2020 Plan addresses the 

contingency measures requirement in 

Section 3.4 for the 2008 ozone NAAQS, 

Section 4.4 for the 2015 ozone NAAQS 

and Attachment O (‘‘Contingency 

Measures for San Diego County’’) to the 

plan. For both ozone NAAQS, the 2020 

Plan anticipates the District’s adoption 

of a revision to the District’s 

architectural coatings rule (Rule 67.0.1) 


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172 2020 Plan, Attachment O, p. O–1. 

173The percentages are based on one year’s worth 

of RFP, which is 3 percent of the 2011 VOC baseline 

emissions. 

174 2020 Plan, Attachment O, p. O–7. 

175 87 FR 78544 (December 22, 2022). 176 Id. 177 40 CFR 93.102(b)(2)(i). 

to include a specific contingency 

provision that would narrow the small 

container exemption in the rule in the 

event that the area misses an RFP 

milestone or fails to attain the ozone 

NAAQS by the applicable attainment 

date. The District estimates that the 

anticipated contingency provision in the 

architectural rule would achieve 0.72 

tpd of VOC reductions, i.e., if triggered 

by the EPA’s determination that the area 

failed to meet an RFP milestone or 

failed to attain the 2008 or 2015 ozone 

NAAQS by the applicable attainment 

date.172 The estimated emissions 

reductions from the amended 

architectural coatings rule (0.72 tpd of 

VOC) represent approximately 18 

percent of one year’s worth of RFP for 

the 2008 ozone NAAQS and 

approximately 21 percent of one year’s 

worth of RFP for the 2015 ozone 

NAAQS.173

For both ozone NAAQS, the 2020 

Plan demonstrates compliance with the 

contingency measures requirements in 

CAA sections 172(c)(9) and 182(c)(9) by 

coupling the anticipated emissions 

reductions from the contingency 

provision in the architectural coatings 

rule with projected surplus VOC and 

NOX emissions reductions that are 

expected to occur due to ongoing State 

mobile source control programs in San 

Diego County, providing for 

approximately one year’s worth of RFP 

in the years following RFP milestone 

and attainment years.174 In this context, 

‘‘surplus’’ emissions reductions refers to 

emissions reductions that are beyond 

those required to provide for RFP and 

attainment for the 2008 and 2015 ozone 

NAAQS. 

Since submission of the 2020 Plan, 

the District has adopted the contingency 

provision in the District’s architectural 

coatings rule (District Rule 67.0.1), and 

CARB has submitted the amended rule 

to the EPA as a revision to the California 

SIP. In late 2022, the EPA took final 

action to approve amended Rule 

67.0.1.175 In our final rule approving 

amended Rule 67.0.1, we concluded 

that the contingency provision in the 

amended rule (paragraph (b)(6) of the 

rule) meets the requirements for 

individual contingency measures under 

CAA sections 172(c)(9) and 182(c)(9). 

However, we also indicated that, while 

the amended rule meets the 

requirements for a stand-alone 

contingency measure, we were not 

making any determination at that time 

as to whether the individual 

contingency measure is sufficient in 

itself for San Diego County to fully 

comply with the contingency measures 

requirements under CAA sections 

172(c)(9) and 182(c)(9).176

3. The EPA’s Review of the State’s 

Submission 

Sections 172(c)(9) and 182(c)(9) 

require contingency measures to address 

potential failure to achieve RFP 

milestones or failure to attain the 

NAAQS by the applicable attainment 

date. The 2020 Plan was prepared and 

submitted following the Bahr decision 

and, thus, does not rely solely on 

surplus emissions reductions from 

already-implemented measures to 

demonstrate compliance with the 

contingency measures requirements, but 

rather, anticipated the revision of a 

District rule to include a specific 

contingency provision that would be 

designed to be both prospective and 

conditional. Since the 2020 Plan was 

submitted, the District has fulfilled the 

commitment in the 2020 Plan that the 

District amend the District’s 

architectural coatings rule to include 

contingency provisions, and the EPA 

has approved the amended rule as a 

stand-alone contingency measure. 

The 2020 Plan was, however, 

prepared and submitted prior to the AIR 

decision and relies on the surplus 

emissions reductions from alreadyimplemented measures, not as a 

contingency measure per se, but as 

justification for adopting a contingency 

measure that would provide far less 

than the EPA’s recommended amount of 

emissions reductions to meet the 

contingency measures requirements 

(i.e., one year’s worth of RFP). In doing 

so, the 2020 Plan takes an approach to 

meeting the contingency measures 

requirements that is essentially the same 

as the approach that was rejected in the 

AIR decision. Also, earlier this year, the 

EPA has published new draft guidance 

addressing the contingency measures 

requirements. The principal differences 

between the Draft Revised Contingency 

Measure Guidance and existing 

guidance on contingency measures 

relate to the EPA’s recommendations 

concerning the specific amount of 

emission reductions that 

implementation of contingency 

measures should achieve, and the 

timing for when the emissions 

reductions from the contingency 

measures should occur. 

In light of the change in 

circumstances arising from the AIR 

decision and the EPA’s Draft Revised 

Contingency Measure Guidance, we are 

deferring action on the contingency 

measures portion of the 2020 Plan at the 

present time to provide additional time 

for CARB and the District to supplement 

the contingency measures portion of the 

2020 Plan with additional contingency 

measures and a reasoned justification (if 

the contingency measures do not 

provide for the amount of reductions 

recommended by the EPA), as needed, 

to meet the contingency measure 

requirements of CAA sections 172(c)(9) 

and 182(c)(9). 

G. Motor Vehicle Emissions Budgets for 

Transportation Conformity 

1. Statutory and Regulatory 

Requirements 

Section 176(c) of the CAA requires 

federal actions in nonattainment and 

maintenance areas to conform to the 

SIP’s goals of eliminating or reducing 

the severity and number of violations of 

the NAAQS and achieving timely 

attainment of the standards. Conformity 

to the SIP’s goals means that such 

actions will not: (1) cause or contribute 

to violations of a NAAQS; (2) worsen 

the severity of an existing violation; or 

(3) delay timely attainment of any 

NAAQS or any interim milestone. 

Actions involving Federal Highway 

Administration (FHWA) or Federal 

Transit Administration (FTA) funding 

or approval are subject to the EPA’s 

transportation conformity rule, codified 

at 40 CFR part 93, subpart A. Under this 

rule, metropolitan planning 

organizations in nonattainment and 

maintenance areas coordinate with state 

and local air quality and transportation 

agencies, the EPA, the FHWA, and the 

FTA to demonstrate that an area’s 

regional transportation plans and 

transportation improvement programs 

conform to the applicable SIP. This 

demonstration is typically done by 

showing that estimated emissions from 

existing and planned highway and 

transit systems are less than or equal to 

the motor vehicle emissions budgets 

contained in all control strategy SIPs. 

Motor vehicle emissions budgets are 

generally established for specific years 

and specific pollutants or precursors. 

Ozone plans should identify motor 

vehicle emissions budgets for on-road 

emissions of ozone precursors (NOX and 

VOC) in the area for each RFP milestone 

year and, if the plan demonstrates 

attainment, the attainment year.177

For motor vehicle emissions budgets 

to be approvable, they must meet, at a 

minimum, the EPA’s adequacy criteria 


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178 40 CFR 93.118(e)(4)(iii), (iv) and (v). For more 

information on the transportation conformity 

requirements and applicable policies on motor 

vehicle emissions budgets, please visit our 

transportation conformity website at: https://

www.epa.gov/state-and-local-transportation. 179 40 CFR 93.118. 

180The EPA approved the use of EMFAC2017 for 

use in SIP development and transportation 

conformity at 84 FR 41717 (August 15, 2019). 

181 2020 Plan, endnote 130. SANDAG, San Diego 

Forward: The 2019 Federal Regional Transportation 

Plan (October 2019). 

182 84 FR 51310 (September 27, 2019). 

183The EPA Office of Transportation and Air 

Quality (OTAQ) maintains a website that lists motor 

vehicle emissions budgets we are reviewing or have 

reviewed for adequacy. See our OTAQ adequacy 

review web page: https://www.epa.gov/state-andlocal-transportation/adequacy-review-stateimplementation-plan-sip-submissions-conformity. 

184Letter from Elizabeth J. Adams, Air and 

Radiation Division Director, EPA Region IX to 

Richard Corey, Executive Officer, CARB, dated 

September 21, 2021. 

185 86 FR 54692, effective October 19, 2021. 

at 40 CFR 93.118(e)(4). To meet these 

requirements, the motor vehicle 

emissions budgets must be consistent 

with the attainment and RFP 

requirements and reflect all motor 

vehicle control measures contained in 

the attainment and RFP 

demonstrations.178

The EPA’s process for determining 

adequacy of a transportation budget 

consists of three basic steps: (1) 

providing public notification of a SIP 

submission; (2) providing the public the 

opportunity to comment on the motor 

vehicle emissions budgets during a 

public comment period; and, (3) making 

a finding of adequacy or inadequacy.179

2. Summary of the State’s Submission 

The 2020 Plan includes motor vehicle 

emissions budgets for both the 2008 and 

the 2015 ozone NAAQS. For the 2008 

ozone NAAQS, the 2020 Plan provides 

for motor vehicle emissions budgets for 

2020 and 2023 RFP milestone years, and 

a 2026 attainment year. For the 2015 

ozone NAAQS, the plan provides for 

motor vehicle emissions budgets for 

2023, 2026 and 2029 RFP milestone 

years and the 2032 attainment year. 

The motor vehicle emissions budgets 

in the 2020 Plan were calculated for an 

average summer day using EMFAC2017, 

the version of CARB’s EMFAC model 

approved by the EPA for estimating 

emissions from on-road vehicles 

operating in California at the time the 

2020 Plan was developed.180 The motor 

vehicle emissions budgets in the 2020 

Plan reflect the transportation activity 

data provided by SANDAG including 

updated VMT and speed distribution 

data developed for the 2019 Federal 

Regional Transportation Plan.181 The 

motor vehicle emissions budgets also 

reflect an upward adjustment to account 

for the EPA’s SAFE 1 action 182 and are 

rounded up to the nearest tenth of a ton 

per day. The 2008 and 2015 ozone 

NAAQS motor vehicle emissions 

budgets for NOX and VOC in the 2020 

Plan for the San Diego County area are 

shown in Table 15 and Table 16 of this 

document, respectively. 

TABLE 15—MOTOR VEHICLE EMISSIONS BUDGETS FOR THE 2008 OZONE NAAQS IN THE SAN DIEGO COUNTY AREA

[Summer planning inventory, tpd] 

Budget year VOC NOX

2020 ......................................................................................................................................................................... 16.3 28.1 

2023 ......................................................................................................................................................................... 13.6 19.3 

2026 ......................................................................................................................................................................... 12.1 17.3 

Source: 2020 Plan, Table 3–1. 

TABLE 16—MOTOR VEHICLE EMISSIONS BUDGETS FOR THE 2015 OZONE NAAQS IN THE SAN DIEGO COUNTY AREA

[Summer planning inventory, tpd] 

Budget year VOC NOX

2023 ......................................................................................................................................................................... 13.6 19.3 

2026 ......................................................................................................................................................................... 12.1 17.3 

2029 ......................................................................................................................................................................... 11.0 15.9 

2032 ......................................................................................................................................................................... 10.0 15.1 

Source: 2020 Plan, Table 4–1. 

3. The EPA’s Review of the State’s 

Submission 

The EPA previously found the motor 

vehicle emissions budgets in the 2020 

Plan to be adequate, using our adequacy 

criteria in 40 CFR 93.118(e)(4) and 

(5).183 On June 4, 2021, the EPA 

announced the availability of the 2020 

Plan and related motor vehicle 

emissions budgets on the EPA’s 

transportation conformity website, 

requesting comments by July 6, 2021. 

The EPA received no comments from 

the public. By letter dated September 

21, 2021, the EPA determined the 2020, 

2023, 2026 motor vehicle emissions 

budgets for the 2008 ozone NAAQS and 

the 2023, 2026, 2029 and 2032 motor 

vehicle emissions budgets for the 2015 

ozone NAAQS were adequate for 

transportation conformity purposes.184

On October 4, 2021, the notice of 

adequacy was published in the Federal 

Register.185 Since the effective date of 

our adequacy finding, October 19, 2021, 

the U.S. Department of Transportation 

and the applicable metropolitan 

transportation organization, SANDAG, 

have been using the adequate motor 

vehicle emissions budgets for 

transportation conformity 

determinations for the area. The EPA is 

not required under its transportation 

conformity rule to find motor vehicle 

emissions budgets adequate prior to 

proposing approval of them, but in this 

instance, we have completed the 

adequacy review of these motor vehicle 

emissions budgets prior to our proposed 

action on the 2020 Plan. 

The EPA is proposing to approve the 

motor vehicle emissions budgets the 

2020 Plan for transportation conformity 

purposes. The EPA has determined 

through its review of the 2020 Plan that 

the motor vehicle emissions budgets are 

consistent with emissions control 

measures in the SIP and the RFP and 

attainment demonstrations for the 2008 

ozone NAAQS and the 2015 ozone 

NAAQS. We note that the on-road motor 

vehicle emissions estimates used for the 

RFP and attainment demonstrations in 

the 2020 Plan are based on 


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186 40 CFR part 51, subpart W, and 40 CFR part 

93, subpart B. 

187 71 FR 40420 (July 17, 2006); 75 FR 17254 

(April 5, 2010); and 81 FR 58010, 58162 (August 24, 

2016). 

188SDCAPCD Rule 1501 (‘‘Conformity of General 

Federal Actions’’), approved at 64 FR 19916 (April 

23, 1999). 

189 40 CFR 93.151. 

transportation activity data developed 

for SANDAG’s 2018 Regional 

Transportation Improvement Program 

whereas the motor vehicle emissions 

budgets are based on updated VMT and 

speed distribution data from SANDAG’s 

2019 Regional Transportation Plan, and 

thus the on-road motor vehicle 

estimates are not exactly the same as the 

corresponding motor vehicle emissions 

budgets. However, we have compared 

the on-road motor vehicle emissions 

used for the RFP and attainment 

demonstrations with the motor vehicle 

emissions budgets and find that the 

latter are numerically the same or 

slightly lower (by 0.1 to 0.4 tpd) for both 

VOC and NOX than the corresponding 

estimates used for the RFP and 

attainment demonstrations. Thus, the 

motor vehicle emissions budgets are 

conservative in that they reflect slightly 

less vehicle activity than the level of 

such activity assumed for the RFP and 

attainment demonstrations that we are 

proposing to approve in this document. 

For the reasons discussed in Sections 

III.C and III.D of this document, we are 

proposing to approve the RFP and 

attainment demonstrations in the 2020 

Plan for the 2008 and 2015 ozone 

NAAQS. The motor vehicle emissions 

budgets, as listed in Tables 15 and 16 of 

this document, are consistent with the 

RFP and attainment 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). For these reasons, the 

EPA proposes to approve the motor 

vehicle emissions budgets in the 2020 

Plan for years 2020, 2023, and 2026 for 

the 2008 ozone NAAQS (and shown in 

Table 15 of this document), as well as 

the motor vehicle emissions budgets in 

the 2020 Plan for years 2023, 2026, 2029 

and 2032 (shown in Table 16 of this 

document), for the 2015 ozone NAAQS. 

H. General Conformity Budgets 

1. Statutory and Regulatory 

Requirements 

Section 176(c) of the CAA requires 

federal actions in nonattainment and 

maintenance areas to conform to the 

SIP’s goals of eliminating or reducing 

the severity and number of violations of 

the NAAQS and achieving timely 

attainment of the standards. Conformity 

to the SIP’s goals means that such 

actions will not: (1) cause or contribute 

to violations of a NAAQS; (2) worsen 

the severity of an existing violation; or 

(3) delay timely attainment of any 

NAAQS or any interim milestone. 

Section 176(c)(4) of the CAA 

establishes the framework for general 

conformity. The EPA first promulgated 

general conformity regulations in 

November 1993.186 In 2006, 2010, and 

again in 2016, the EPA revised the 

general conformity regulations.187 The 

general conformity regulations ensure 

that federal actions not covered by the 

transportation conformity rule will not 

interfere with the SIP and encourage 

consultation between the federal agency 

and the state or local air pollution 

control agencies before or during the 

environmental review process, as well 

as public participation (e.g., notification 

of and access to federal agency 

conformity determinations and review 

of individual federal actions). In San 

Diego County, federal actions not 

covered by the transportation 

conformity rule are subject to the 

general conformity requirements in 

District Rule 1501 (‘‘Conformity of 

General Federal Actions’’) 188 and in 40 

CFR part 93, subpart B, to the extent the 

requirements in 40 CFR part 93, subpart 

B are not contained in District Rule 

1501.189

The general conformity regulations in 

40 CFR part 93, subpart B provide 

criteria and procedures for federal 

agencies to follow in determining 

general conformity for federal actions. 

The applicability analysis under 40 CFR 

93.153 is used to find if a federal action 

requires a conformity determination for 

a specific pollutant. If a conformity 

determination is needed, federal 

agencies can use one of several methods 

to show that the federal action conforms 

to the SIP. In an area for which the EPA 

has not approved a revision to the 

relevant SIP since the area was 

designated or reclassified, a federal 

action may be shown to ‘‘conform’’ by 

demonstrating there will be no net 

increase in emissions in the 

nonattainment or maintenance area 

from the federal action. In an area with 

an approved SIP revision, conformity to 

the applicable SIP can be demonstrated 

in one of several ways. For actions 

where the direct and indirect emissions 

exceed the rates in 40 CFR 93.153(b), 

the federal action can include mitigation 

measures to offset the emissions 

increases from the federal action or can 

show that the action will conform by 

meeting any of the following 

requirements: 

• showing that the net emissions 

increases caused by an action are 

included in the SIP; 

• documenting that the state agrees to 

include the emissions increases in the 

SIP; 

• offsetting the action’s emissions in 

the same or nearby area of equal or 

greater classification; or 

• providing an air quality modeling 

demonstration in some circumstances. 

The general conformity regulations at 

40 CFR 93.161 allow state and local air 

quality agencies working with federal 

agencies with large facilities (e.g., 

commercial airports, ports, and large 

military bases) that are subject to the 

general conformity regulations to 

develop and adopt an emissions budget 

for those facilities in order to facilitate 

future conformity determinations. Such 

a budget, referred to as a facility-wide 

emissions budget, may be used by 

federal agencies to demonstrate 

conformity as long as the total facilitywide budget level identified in the SIP 

is not exceeded. 

A state or local agency responsible for 

implementing and enforcing the SIP can 

develop and adopt an emissions budget 

to be used for demonstrating conformity 

under 40 CFR 93.158(a)(1) so long as the 

budget meets certain criteria listed in 40 

CFR 93.161(a). The requirements 

include: (1) the facility-wide budget 

must be for a set time period; (2) the 

budget must cover the pollutants or 

precursors of the pollutants for which 

the area is designated nonattainment or 

maintenance; (3) the budgets must be 

specific about what can be emitted on 

an annual or seasonal basis; (4) the 

emissions from the facility along with 

all other emissions in the area must not 

exceed the total SIP emissions budget 

for the nonattainment or maintenance 

area; (5) specific measures must be 

included to ensure compliance with the 

facility-wide budget, such as periodic 

reporting requirements or compliance 

demonstrations when the federal agency 

is taking an action that would otherwise 

require a conformity determination; (6) 

the budget must be submitted to the 

EPA as a SIP revision; and (7) the SIP 

revision must be approved by the EPA. 

Having or using a facility-wide 

emissions budget does not preclude a 

federal agency from demonstrating 

conformity in any other manner allowed 

by the conformity rule. 

Once approved by the EPA, total 

direct and indirect emissions from 

federal actions in conjunction with all 

other emissions subject to general 

conformity from the facility that do not 

exceed the facility-wide budget are 

‘‘presumed to conform’’ to the SIP and 


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190 40 CFR 93.161(c). 

191 40 CFR 93.161(d). 

192 68 FR 13653 (March 20, 2003). 

193 68 FR 37976 (June 26, 2003), effective July 28, 

2003. 

194 68 FR 13653, 13654. 

195 78 FR 17902, at 17912 (March 25, 2013) 

(proposed approval of San Diego County RRMP for 

the 1997 ozone NAAQS); finalized at 78 FR 33230 

(June 4, 2013). 196 DoN and USMC report to SDCAPCD, 

‘‘Department of Navy 2017 Mobile Source Baseline 

and Emissions Growth Increment Request for 

Submittal to the San Diego Air Pollution Control 

District,’’ Naval Facilities Engineering Command 

Southwest, San Diego, California, December 2018. 

197 2020 Plan, Table B–2. 

198 2020 Plan, Table B–1. 

199 2020 Plan, p. 18. 

200 2020 Plan, p. 19. 

201 District Rule 1501, section 1551.853(b)(1). 

do not require a conformity analysis.190

However, if the total direct and indirect 

emissions from the federal actions in 

conjunction with the other emissions 

subject to general conformity from the 

facility exceed the budget, the action 

must be evaluated for conformity.191

2. Summary of the State’s Submission 

General conformity requirements are 

addressed in the 2020 Plan in Section 

2.1.3, ‘‘Emissions Budgets.’’ The 2020 

Plan includes facility-wide emissions 

budgets (facility-wide budgets) that 

allow for increments of growth for 

military and airport facilities in the area. 

Further information supporting the 

military facility-wide budgets is 

included in the 2020 Plan’s Attachment 

B, ‘‘Planned Military Projects Subject to 

General Conformity’’; further 

information supporting airport facilitywide budgets is included in Attachment 

C, ‘‘Planned San Diego International 

Airport Projects Subject to General 

Conformity.’’ 

The EPA has reviewed facility-wide 

budgets for military facilities in San 

Diego County in the past, prior to the 

2010 revisions to the EPA’s general 

conformity regulations that expressly 

authorized such budgets. In 2003, the 

EPA proposed to approve the San Diego 

County redesignation request and 

maintenance plan (RRMP) for the 1979 

1-hour ozone NAAQS.192 We approved 

the RRMP later that year, redesignating 

the area to attainment for the 1-hour 

ozone NAAQS and approving a ten-year 

maintenance plan for the area.193

Although our final action did not 

approve facility-wide budgets explicitly, 

expected growth of military facility 

emissions in the San Diego County area 

were included in the area’s RRMP. In 

our proposed approval of the RRMP, we 

indicated that the ‘‘military growth 

[general] conformity increment is 11.4 

tpd NOX in 2005, 2010, and 2014,’’ that 

is, over the ten-year period of the 

maintenance plan.194 Likewise, the EPA 

approved the San Diego County RRMP 

for the 1997 ozone NAAQS, which 

included a military growth increment 

for years 2015, 2020 and 2025.195

In 2018, for the 2020 Plan, the 

Department of the Navy (DoN) and 

United States Marine Corps (USMC) 

developed updated projections of future 

annual emissions increases and 

decreases from anticipated military 

actions in San Diego County from 2018 

through 2037.196 NOX was estimated to 

increase by 8.34 tpd and VOC was 

expected to increase by 0.86 tpd from 

2018 through 2037.197 Previously, the 

DoN and USMC had estimated 

emissions would increase by 5.91 tpd 

NOX and 1.08 tpd VOC between 2011 

and 2035.198 For the 2020 Plan, the 

District conservatively took the higher 

of both pairs of numbers and, again, 

conservatively assumed that the entire 

anticipated increase through 2037 

would occur in 2018. CARB 

incorporated that growth increment into 

the 2019 CARB CEPAM emissions 

inventories (Version 1.00) that are used 

to develop the RFP and attainment 

demonstrations in the 2020 Plan. 

Specifically, the District and CARB 

incorporated a total growth projection of 

8.34 tpd of NOX and 1.08 tpd of VOC 

emissions into the 2020 Plan and related 

RFP demonstrations and photochemical 

modeling for the attainment 

demonstrations. The modeling analysis 

CARB performed for the 2020 Plan 

indicates that the growth in military 

facility-related emissions is not 

expected to cause additional ozone 

violations.199

In Section 2.1.3.2 of the 2020 Plan, 

the District also accommodates facilitywide budgets (in the form of growth 

increments) for SDIA in San Diego 

County. The San Diego County Regional 

Airport Authority (Airport Authority) 

developed an emissions inventory for 

SDIA that the District includes in the 

2020 Plan as Attachment C. The SDIA 

emissions inventory includes emissions 

increases anticipated to occur at the 

airport from 2012 through 2040. As with 

the military growth increment, the 

District conservatively assumed that all 

emissions increases at SDIA would 

occur in 2018 and CARB included those 

emissions in their modeling. 

3. The EPA’s Review of the State’s 

Submission 

The 2020 Plan’s facility-wide budgets 

(i.e., increments of growth) are included 

in Table 17 of this document for both 

the military and for SDIA expected 

emissions increases (hereafter, the 

‘‘facilities’’). At these levels of growth, 

CARB air quality modeling predicts that 

there will not be an increase in ozone 

exceedances.200 These budgets represent 

emissions that are in addition to the 

baseline emissions projections in the 

2020 Plan and that are built into the 

2020 Plan as separate line items in the 

emissions inventories used for the RFP 

and attainment demonstrations. The 

purpose of the budgets is to 

accommodate anticipated federal 

actions by the military or by the federal 

agencies that permit, fund or approve 

actions at SDIA that would cause 

emissions increases greater than de 

minimis levels under the general 

conformity regulations. The de minimis 

level used to determine applicability of 

the general conformity requirements to 

federal actions in San Diego County is 

25 tons per year of VOC or NOX based 

on the area’s Severe classification for 

the 2008 and 2015 ozone NAAQS.201

TABLE 17—FACILITY-WIDE GENERAL CONFORMITY BUDGETS (INCREMENTS OF GROWTH) FOR THE DEPARTMENT OF THE

NAVY AND UNITED STATES MARINE CORPS, AND FOR THE SAN DIEGO INTERNATIONAL AIRPORT IN SAN DIEGO COUNTY

[Summer planning inventory, tpd] 

Facility VOC NOX

DoN and USMC ....................................................................................................................................................... 1.08 8.34 

SDIA ......................................................................................................................................................................... 0.141 1.756 

Source: 2020 Plan, pp. 18 and 19. 


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202A detailed description of how the facilitybased budgets were included in the future-year 

projections used for the RFP and attainment 

demonstrations is contained in an email dated May 

22, 2023, from Nick Cormier, SDCAPCD, to John J. 

Kelly, EPA Region IX. 

203Letter dated July 31, 2023, from Ted Anasis, 

Manager, Airport Planning, SDIA, to Nick Cormier, 

SDCAPCD, and letter dated August 16, 2023, from 

J.C. Golumbfskie-Jones, Fleet Environmental 

Director, Commander Navy Region Southwest, DoN, 

to Paula Forbis, Air Pollution Control Officer, 

SDCAPCD. 

204The CAA I/M SIP requirements apply to 

Moderate and above nonattainment areas for the 

2008 and 2015 ozone NAAQS pursuant to 40 CFR 

51.1102 (for the 2008 ozone NAAQS) and 40 CFR 

51.1302 (for the 2015 ozone NAAQS). 

205 40 CFR part 51, subpart S, sections 350–373. 

206 86 FR 1106 (January 7, 2021). 

The EPA reviewed the facility-wide 

budgets (i.e., increments of growth) for 

the facilities using the seven criteria 

listed for facility-wide budgets in 40 

CFR 93.161(a). Criterion 1 is that the 

facility-wide budgets must be for a set 

time period. This criterion is satisfied 

by the duration of the growth projected 

by the military (out to 2037) and by the 

Airport Authority (out to 2040). 

Criterion 2 is that the facility-wide 

budgets must cover the pollutants or 

precursors of the pollutants for which 

the area is designated nonattainment or 

maintenance. This criterion is satisfied 

because the area is designated 

nonattainment for the 2008 and the 

2015 ozone NAAQS and ozone’s 

precursors are VOC and NOX. Both 

precursors are addressed in the facilitywide budgets included in the 2020 Plan 

for the facilities, presented in Table 17 

of this document. Criterion 3 is likewise 

satisfied in that it requires that facilitywide budgets include specific quantities 

allowed to be emitted on an annual or 

seasonal basis. Table 17 of this 

document includes specific quantities 

allowed to be emitted by the facilities. 

Criterion 4 is that the emissions from 

the facilities along with all other 

emissions in the area will not exceed 

the emission budget for the area. This 

criterion will be satisfied if the EPA 

finalizes the proposed approval of the 

RFP and attainment demonstrations in 

the 2020 Plan for the 2008 and 2015 

ozone NAAQS because the 2020 Plan 

includes the facility-wide budgets and 

all other emissions in the area in the 

future-year emissions projections used 

for the RFP and attainment 

demonstrations.202

Criterion 5 is that there must be 

specific measures to ensure compliance 

with the budget, such as periodic 

reporting requirements or a compliance 

demonstration when the federal agency 

is taking an action that would otherwise 

require a general conformity 

determination. The District requested 

that the military and San Diego Regional 

Airport Authority each provide a 

written letter of commitment to track 

compliance with the facility-wide 

budgets and to make periodic reports to 

the District demonstrating compliance 

when they are taking actions that would 

otherwise require a general conformity 

determination. The requested letters of 

commitment have been provided to the 

District.203

Criterion 6 is that the facility-wide 

budgets must be submitted to the EPA 

as a SIP revision. The 2020 Plan 

includes the facility-wide budgets 

shown in Table 17 of this document. 

The seventh and last criterion is that the 

SIP revision must be approved by the 

EPA. For the reasons stated in this 

section of this document, we propose to 

approve the general conformity budgets 

included in the 2020 Plan. If the EPA 

finalizes this action as proposed, 

criterion 7 will be satisfied. 

I. Other Clean Air Act Requirements 

Applicable to Severe Ozone 

Nonattainment Areas 

In addition to the SIP requirements 

discussed in Sections III.A—III.H, of 

this document, the CAA includes 

certain other SIP requirements 

applicable to Severe ozone 

nonattainment areas, such as the San 

Diego County area. In Section III.I., we 

identify these other requirements and 

evaluate the compliance by the State 

and District with respect to them for the 

San Diego County area. 

1. Enhanced Vehicle Inspection and 

Maintenance Programs 

Section 182(b)(4) of the CAA requires 

states with ozone nonattainment areas 

classified under subpart 2 as Moderate 

to submit SIP revisions that provide for 

the implementation of a ‘‘Basic’’ vehicle 

inspection and maintenance (I/M) 

program in those areas. Section 

182(c)(3) of the CAA requires states with 

ozone nonattainment areas classified 

under subpart 2 as Serious or above to 

submit SIP revisions that provide for the 

implementation of an ‘‘Enhanced’’ I/M 

program in certain urbanized portions of 

those areas.204 As a Severe ozone 

nonattainment area for the 2008 and 

2015 ozone NAAQS, the State of 

California must implement an Enhanced 

I/M program in the urbanized portions 

of the San Diego County area. 

As a general matter, Basic and 

Enhanced I/M programs both achieve 

their objective by identifying vehicles 

that have high emissions as a result of 

one or more malfunctions and requiring 

them to be repaired. An Enhanced I/M 

program covers more of the vehicles in 

operation, employs inspection methods 

that are better at finding high emitting 

vehicles, and has additional features to 

better assure that all vehicles are tested 

properly and effectively repaired. The 

EPA has established specific 

requirements for Basic and Enhanced I/ 

M programs in 40 CFR part 51, subpart 

S (‘‘The EPA’s I/M regulation’’). The 

EPA’s I/M regulation establishes 

minimum performance standards for 

Basic and Enhanced I/M programs as 

well as requirements for certain 

elements of the programs, including, 

among other elements, test frequency, 

vehicle coverage, test procedures and 

standards, stations and inspectors, and 

data collection, analysis and 

reporting.205

Under 40 CFR 51.351(i), areas 

required to implement an Enhanced I/M 

program because of being designated 

and classified under the 8-hour ozone 

standard must meet or exceed the VOC 

and NOX emissions reductions (i.e., 

performance standard) achieved by the 

EPA’s model program for Enhanced I/M. 

An I/M performance standard is a 

collection of program design elements 

that defines a benchmark program to 

which a state’s proposed program is 

compared in terms of its potential to 

reduce emissions of the ozone 

precursors, VOC and NOX. The 

performance standard is expressed as 

emission levels in area-wide average 

grams per mile (grams/mile), achieved 

from on-road motor vehicles as a result 

of a specified model I/M program 

design. The emissions levels achieved 

by the state’s program design must be 

calculated using the most current 

version of the EPA mobile source 

emissions factor model and must meet 

or exceed the emissions reductions 

achieved by the performance standard 

program both in operation and for SIP 

approval. The current version of the 

EPA mobile source emissions factor 

model at the time of CARB’s evaluation 

of the California I/M program for 

compliance with 40 CFR 51.351(i) was 

the Motor Vehicle Emission Simulator 

model, version 3 (MOVES3).206

For subject ozone nonattainment 

areas, the performance standard must be 

met for both VOC and NOX unless a 

NOX waiver has been approved for the 

area. Enhanced I/M program areas must 

be shown to obtain the same or lower 

emissions levels as the model program 

described in section 51.351(i) to within 

+/¥0.02 grams/mile and must 

demonstrate through modeling the 

ability to maintain this level of 


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207 In 1995, the EPA corrected the design value 

for San Diego County used to establish San Diego 

County’s original nonattainment classification for 

the 1-hour ozone NAAQS and changed the 

classification from Severe to Serious. 60 FR 3771 

(January 19, 1995). 

208 62 FR 1150 (January 8, 1997); see also 74 FR 

41818, at 41820 (August 19, 2009). 

209California Bureau of Automotive Repair, Smog 

Check Reference Guide, revised August 2012, 

appendix A. 

210 75 FR 38023 (July 1, 2010). 

211The EPA did not classify San Diego County for 

the 1997 ozone NAAQS until 2012, and, in that 

rulemaking, classified San Diego County as 

‘‘Subpart 2/Moderate.’’ 77 FR 28424 (May 14, 2012). 

212 75 FR 38023, 38025–38026 (July 1, 2010). 

213 Id. 

214 2020 Plan, Section 3.1, pp. 33–34 (2008 ozone 

NAAQS) and Section 4.1, pp. 53–54 (2015 ozone 

NAAQS). 

215CH&SC section 44003(a)(1) provides: ‘‘An 

enhanced motor vehicle inspection and 

maintenance program is established in each 

urbanized area of the state, any part of which is 

classified by the Environmental Protection Agency 

as a serious, severe, or extreme nonattainment area 

for ozone or a moderate or serious nonattainment 

area for carbon monoxide with a design value 

greater than 12.7 ppm, and in other areas of the 

state as provided in this chapter.’’ In addition, we 

used BAR’s Smog Check Program Area Lookup tool 

and a list of zip codes for San Diego County to 

confirm the implementation of the Enhanced I/M 

program in the urbanized areas of San Diego 

County. 

216CARB, Progress Report on Implementation of 

PM2.5 State Implementation Plans (SIP) for the 

South Coast and San Joaquin Valley Air Basins and 

Proposed SIP Revisions (Release Date: March 29, 

2011), Table 1. 

217CARB, Revised Proposed 2016 State Strategy 

for the State Implementation Plan (March 7, 2017), 

pp. 52–53. 

218The most recent performance report is BAR’s 

Smog Check Performance Report 2023, July 1, 2023. 

219The most recent periodic report is BAR’s 

Sunset Review Report 2022: presented to the Senate 

Committee on Business, Professions and Economic 

Development and the Assembly Committee on 

Business and Professions. 

220See 87 FR 21842, at 21853 (April 13, 2022) 

(proposed determinations and reclassifications for 

Marginal areas for 2015 ozone NAAQS), finalized 

at 87 FR 60897 (October 7, 2022). 

221EPA, Performance Standard Modeling for New 

and Existing Vehicle Inspection and Maintenance 

(I/M) Programs Using the MOVES Mobile Source 

Emissions Model, EPA–420–B–22–034, October 

2022. 

222Smog Check Certification, Table 8, p. 20. 

emissions reduction (or better) through 

their attainment deadline for the 

applicable NAAQS. See 40 CFR 

51.351(i)(13). 

The California Bureau of Automotive 

Repair (BAR) implements the I/M 

program in California. BAR was 

required to implement an Enhanced I/M 

program in the urbanized portions of 

San Diego County due to the County’s 

classification as a Serious 

nonattainment area for the 1-hour ozone 

NAAQS.207 In 1997, the EPA issued an 

interim approval of the program as 

meeting the Enhanced I/M requirements 

for the 1-hour ozone NAAQS in 

California.208 Currently, BAR 

implements an Enhanced I/M program 

in the urbanized areas of the County, a 

Basic I/M program in certain parts of 

central San Diego County, and a change 

of ownership I/M program in the eastern 

half of the County.209

The EPA’s most recent approval of 

California’s I/M program occurred in 

2010, and in that action, the EPA 

approved the program as meeting the 

applicable I/M requirements for the 

various nonattainment areas in the 

State.210 However, at that time, because 

San Diego County had been 

redesignated to attainment for the 1- 

hour ozone NAAQS and had not yet 

been classified for the 1997 ozone 

NAAQS, San Diego County was no 

longer subject to the Enhanced I/M 

requirement, and the EPA did not 

review the program as it applies to San 

Diego County for compliance with 

Enhanced I/M program requirements.211

The statutory and regulatory 

foundation for the approved California 

I/M program is set forth in California 

Health & Safety Code (CH&SC), Division 

26, Part 5, Chapter 5 (Motor Vehicle 

Inspection Program), Articles 1 through 

9 and in Title 16 of the California Code 

of Regulations (16 CCR), Division 33, 

Chapter 1, Article 5.5 (Motor Vehicle 

Inspection Program).212 Additional I/Mrelated statutory and regulatory 

provisions in the California SIP include 

CH&SC section 39032.5; California 

Business and Professions Code sections 

9886 and 9886.1–9886.4; California 

Vehicle Code sections 4000.1, 4000.2, 

4000.3 and 4000.6; and 16 CCR sections 

3303.1, 3303.2, 3392.1–3392.6 and 

3394.1–3394.6.213

For the 2020 San Diego County Ozone 

SIP, the District reviewed the existing I/ 

M program as implemented in the San 

Diego County area and concluded, in 

light of the EPA’s approval of the 

program with respect to the 1-hour and 

1997 ozone NAAQS, that the area met 

all applicable I/M requirements for the 

2008 and 2015 ozone NAAQS.214 For 

this proposed action, we reviewed the 

existing I/M program and confirmed 

that the State implements and enforces 

an Enhanced I/M program in the 

urbanized areas of San Diego County as 

required in Severe ozone nonattainment 

areas.215 We also note that, since the 

EPA’s most recent approval of the 

California I/M program in 2010, the 

State has taken steps to improve the 

effectiveness of the Smog Check 

program by requiring the BAR to direct 

older vehicles to high-performing auto 

technicians and test stations for 

inspection and certification.216 Further 

changes to State law have required the 

BAR to implement an updated protocol 

for testing 2000 and newer model-year 

vehicles that collects more complete 

On-Board Diagnostic (OBD) information 

than had been collected under the 

existing protocol.217 The State publishes 

an annual report summarizing the 

performance of the California smog 

check program.218 The State also 

publishes periodic reports to the 

Legislature on the resources allocated to 

smog check program administration and 

enforcement.219

Additionally, in April 2023, in 

response to the EPA’s clarification of I/ 

M SIP requirements for areas designated 

nonattainment for the eight-hour ozone 

NAAQS,220 CARB supplemented the 

motor vehicle I/M portion of the 2020 

Plan with the submission of the Smog 

Check Certification as a revision to the 

California SIP. CARB’s Smog Check 

Certification includes Enhanced I/M 

performance standard evaluations for 

the urbanized areas within certain 

ozone nonattainment areas, including 

the San Diego County area, for the 2008 

and 2015 ozone NAAQS. For the Smog 

Check Certification, CARB relied upon 

the EPA’s MOVES3 emissions model 

and the EPA’s most recent guidance for 

I/M performance standard modeling 221

in preparing the Enhanced I/M 

performance standard evaluations for 

the various nonattainment areas 

addressed in the Smog Check 

Certification. 

For the San Diego County area, the 

Smog Check Certification presents a 

comparison of July weekday emissions 

rates (in grams/mile) for VOC and NOX

based on the existing California smog 

check program and the Enhanced I/M 

model program benchmark. The model 

program benchmark ultimately includes 

a 0.02 grams/mile buffer. The analysis 

was performed for the years 2017, 2026 

and 2032. Table 18 of this document 

summarizes the results of the 

performance standard modeling.222


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223See also CAA section 182(d). 

224 40 CFR 51.1114 and 80 FR 12264 (March 6, 

2015) (2008 ozone NAAQS); and 40 CFR 51.1314 

and 83 FR 62998 (December 6, 2018) (2015 ozone 

NAAQS). 

225 2020 Plan, section 2.3, pp. 25–26. 

226 85 FR 57727 (September 16, 2020). 

227 86 FR 29522 (June 2, 2021). 

228 87 FR 58729 (September 28, 2022). 

229 87 FR 29105, at 29107 (May 12, 2022) 

(proposed approval of amended District NSR rules); 

finalized at 87 FR 58729 (September 28, 2022). 

230See the definition of ‘‘covered areas’’ in CAA 

section 246(a)(2). The CFFP SIP requirement 

applies to the 2008 and 2015 ozone NAAQS 

pursuant to 40 CFR 51.1102 and 40 CFR 51.1302. 

TABLE 18—SUMMARY OF JULY WEEKDAY EMISSION RATES FOR SAN DIEGO COUNTY

Scenario NOX VOC 

Calendar Year 2017 July Weekday Emission Rates (grams/mile) 

CA Existing Program ............................................................................................................................................... 0.2604 0.2292 

Enhanced Performance Standard Benchmark ........................................................................................................ 0.2831 0.2357 

Enhanced Performance Standard Benchmark with 0.02 g/mile Buffer .................................................................. 0.3031 0.2557 

Calendar Year 2026 July Weekday Emission Rates (grams/mile) 

CA Existing Program ............................................................................................................................................... 0.0863 0.1284 

Enhanced Performance Standard Benchmark ........................................................................................................ 0.0902 0.1255 

Enhanced Performance Standard Benchmark with 0.02 g/mile Buffer .................................................................. 0.1102 0.1455 

Calendar Year 2032 July Weekday Emission Rates (grams/mile) 

CA Existing Program ............................................................................................................................................... 0.0374 0.0960 

Enhanced Performance Standard Benchmark ........................................................................................................ 0.0367 0.0921 

Enhanced Performance Standard Benchmark with 0.02 g/mile Buffer .................................................................. 0.0567 0.1121 

Source: CARB, Smog Check Certification, Table 8. 

For both VOC and NOX in all analysis 

years, CARB’s MOVES3 modeling 

results indicate that the California 

Enhanced I/M program meets or exceeds 

the federal Enhanced I/M performance 

standard benchmark program with the 

0.02 g/mile buffer in San Diego County. 

We find that CARB used appropriate 

methods and input data to perform the 

I/M performance standard evaluations 

for San Diego County, analyzed 

appropriate years consistent with 40 

CFR 351(i)(13), and included sufficient 

documentation to support the results. 

We also find that, based on our review 

of the District’s and CARB’s certification 

and the results presented in the Smog 

Check Certification, the California smog 

check program meets the Enhanced I/M 

program SIP requirements under CAA 

section 182(c)(3), 40 CFR 51.1102 and 

40 CFR 51.1302 for the 2008 and 2015 

ozone NAAQS in the San Diego County 

area. Therefore, the EPA proposes to 

approve the I/M portion of the 2020 

Plan, as supplemented by the San Diego 

County portion of the Smog Check 

Certification, as revisions to the 

California SIP. 

2. New Source Review Rules 

Section 182(a)(2)(C) of the CAA 

requires states to submit SIP revisions 

containing permit programs for each of 

their ozone nonattainment areas. The 

SIP revisions are to include 

requirements for permits in accordance 

with CAA sections 172(c)(5) and 173 for 

the construction and operation of each 

new or modified major stationary source 

for VOC or NOX anywhere in the 

nonattainment area.223 The 2008 Ozone 

SRR and 2015 Ozone SRR include 

provisions and guidance for 

nonattainment new source review (NSR) 

programs.224

In the 2020 San Diego County Ozone 

SIP, the District certifies compliance 

with NSR requirements for the 2008 and 

2015 ozone NAAQS through 

amendments to the District’s NSR rules 

(Rules 20.1–20.4) in June 2019.225 In 

2020, the EPA issued a final limited 

approval/limited disapproval of Rule 

20.1 and a full approval of Rules 20.2, 

20.3 and 20.4.226 In that rulemaking, we 

found that the rules, with one exception 

not directly related to the ozone 

NAAQS, met the applicable NSR 

requirements for San Diego County as a 

Serious nonattainment area for the 2008 

ozone NAAQS and as a Moderate 

nonattainment area for the 2015 ozone 

NAAQS. 

Since our NSR rulemaking in 2020, 

the San Diego County area has been 

reclassified to Severe for the 2008 and 

2015 ozone NAAQS. However, the 

approved NSR rules already include 

NOX and VOC applicability thresholds 

and offset ratios applicable to Severe 

ozone nonattainment areas that 

automatically applied upon the July 2, 

2021 effective date of the area’s 

reclassification to Severe.227 In addition, 

in 2022, the EPA issued a final full 

approval of four amended District rules, 

including Rule 20.1.228 In our 2022 

rulemaking, we found that the 

submitted NSR rules satisfy the 

applicable NSR requirements for both 

the 2008 and 2015 ozone NAAQS.229

Given the recent approval of the NSR 

program as meeting the applicable NSR 

requirements for the two relevant ozone 

NAAQS, including the applicability of 

the Severe area applicability threshold 

and offset ratio, we propose to approve 

the NSR certification in the 2020 Plan 

that the EPA-approved District NSR 

rules comply with the applicable NSR 

requirements under CAA sections 

172(c)(5), 173 and 182(a)(2)(C), and 40 

CFR 51.1114 and 51.1314 for the San 

Diego County area for the 2008 and 2015 

ozone NAAQS. 

3. Clean Fuels Fleet Program 

Sections 182(c)(4)(A) and 246 of the 

CAA require states to submit SIP 

revisions that establish a clean-fuel 

vehicle program for fleets (referred to 

herein as a Clean Fuels Fleets Program 

(CFFP)) in certain of their ozone 

nonattainment areas classified as 

Serious and above. The federal CFFP is 

specified in part C of title II of the CAA. 

Section 182(c)(4)(B) of the CAA allows 

states to opt out of the federal CFFP by 

submitting a SIP revision consisting of 

a program or programs that will result 

in at least equivalent long-term 

reductions in ozone precursors and 

toxic air emissions. The CFFP SIP 

requirement applies to the San Diego 

County area as an ozone nonattainment 

area with a 1980 population of 200,000 

or more and classified as Severe for the 

2008 and 2015 ozone NAAQS.230


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231 64 FR 46849 (August 27, 1999). 

232 81 FR 39424 (June 16, 2016). 

233 2020 San Diego County Ozone SIP, Section 

3.1, pp. 33–34 and endnote 78 (2008 ozone 

NAAQS) and Section 4.1, pp. 53–54 and endnote 

126 (2015 ozone NAAQS). 

234 General Preamble, 57 FR 13498, 13514 (April 

16, 1992). 

235 77 FR 28772, at 28774 (May 16, 2012). 

236 40 CFR 51.126(b). 

237 78 FR 897. 

238 58 FR 8452 (February 12, 1993). 239 82 FR 45191 (September 28, 2017). 240 71 FR 61236 (October 17, 2006). 241 40 CFR 58.2(b) now provides that ‘‘[t]he 

requirements pertaining to provisions for an air 

quality surveillance system in the SIP are contained 

in this part.’’ 

242The 2008 and 2015 ozone SRRs address 

PAMS-related requirements. For the 2008 ozone 

NAAQS, see 80 FR 12264, at 12291 (March 6, 2015); 

for the 2015 ozone NAAQS, see 83 FR 62998, at 

63008 (December 6, 2018). 

243SDCAPCD, Annual Air Quality Monitoring 

Report 2021, submitted for EPA review on June 29, 

2022. 

244 2021 ANP, chapter 11 (‘‘Photochemical 

Assessment Monitoring Stations (PAMS)’’). Starting 

Continued 

In 1994, CARB submitted a SIP 

revision to the EPA to opt out of the 

federal CFFP. The submittal included a 

demonstration that California’s lowemissions vehicle program (now 

referred to as the low-emissions vehicle 

(LEV I) regulation) achieved emissions 

reductions at least as large as would be 

achieved by the federal program. The 

EPA approved the SIP revision to opt 

out of the federal program on August 27, 

1999.231 There have been no changes to 

the federal CFFP since the EPA 

approved the California SIP revision to 

opt out of the federal program, and thus, 

no corresponding changes to the SIP are 

required. In addition, California 

continues to implement its lowemissions vehicle program and has 

tightened the low-emissions vehicle 

emissions standards through adoption 

of the LEV II and LEV III regulations. 

The EPA approved the LEV II and LEV 

III regulations as part of the California 

SIP in 2016.232

In the 2020 San Diego County Ozone 

SIP, the District certified that, in light of 

the EPA’s approval of the SIP revision 

to opt out of the federal program, the 

San Diego County area continues to 

meet the requirements of CAA sections 

182(c)(4) and 246 for the 2008 and 2015 

ozone NAAQS.233 We agree with the 

District’s conclusion and find that the 

California SIP revision to opt out of the 

federal program, as approved in 1999, 

continues to meet the requirements of 

CAA sections 182(c)(4) and 246, and 40 

CFR 51.1102 and 51.1302, for the San 

Diego County area for the 2008 and 2015 

ozone NAAQS. For that reason, we 

propose to approve the certification in 

the 2020 San Diego County Ozone SIP 

that the San Diego County area 

continues to meet the CFFP SIP 

requirements for the 2008 and 2015 

ozone NAAQS. 

4. Gasoline Vapor Recovery 

Section 182(b)(3) of the CAA requires 

states to submit SIP revisions by 

November 15, 1992, that require owners 

or operators of gasoline dispensing 

systems to install and operate gasoline 

vehicle refueling vapor recovery (‘‘Stage 

II’’) systems in ozone nonattainment 

areas classified as Moderate and above. 

California’s ozone nonattainment areas 

implemented Stage II vapor recovery 

well before the passage of the CAA 

Amendments of 1990.234

Section 202(a)(6) of the CAA requires 

the EPA to promulgate standards 

requiring motor vehicles to be equipped 

with onboard refueling vapor recovery 

(ORVR) systems. The EPA promulgated 

the first set of ORVR system regulations 

in 1994 for phased implementation by 

vehicle manufacturers, and since the 

end of 2006, essentially all new 

gasoline-powered light and mediumduty vehicles are ORVR-equipped.235

Section 202(a)(6) also authorizes the 

EPA to waive the SIP requirement under 

CAA section 182(b)(3) for installation of 

Stage II vapor recovery systems after 

such time as the EPA determines that 

ORVR systems are in widespread use 

throughout the motor vehicle fleet. 

Effective May 16, 2012, the EPA waived 

the requirement of CAA section 

182(b)(3) for Stage II vapor recovery 

systems in ozone nonattainment areas 

regardless of classification.236 Thus, a 

SIP submittal meeting CAA section 

182(b)(3) is not required for the 2008 

ozone NAAQS or the 2015 ozone 

NAAQS. 

While a SIP submittal meeting CAA 

section 182(b)(3) is not required for the 

2008 or 2015 ozone NAAQS, under 

California state law (i.e., Health and 

Safety Code section 41954), CARB is 

required to adopt procedures and 

performance standards for controlling 

gasoline emissions from gasoline 

marketing operations, including transfer 

and storage operations. State law also 

authorizes CARB, in cooperation with 

local air districts, to certify vapor 

recovery systems, to identify defective 

equipment and to develop test methods. 

CARB has adopted numerous revisions 

to its vapor recovery program 

regulations and continues to rely on its 

vapor recovery program to achieve 

emissions reductions in ozone 

nonattainment areas in California. 

In the San Diego County area, the 

installation and operation of CARBcertified vapor recovery equipment is 

required and enforced by SDCAPCD 

Rule 61.4 (‘‘Transfer of Volatile Organic 

Compounds into Vehicle Fuel Tanks’’). 

This rule was most recently approved 

into the SIP on January 7, 2013.237

5. Enhanced Ambient Air Monitoring 

Section 182(c)(1) of the CAA requires 

states to submit SIP revisions for all 

ozone nonattainment areas classified as 

Serious or above that contain measures 

to enhance and improve monitoring for 

ambient concentrations of ozone, NOX, 

and VOC, and to improve monitoring of 

emissions of NOX and VOC in those 

areas. The enhanced monitoring 

network for ozone is referred to as the 

photochemical assessment monitoring 

station (PAMS) network. The EPA 

promulgated final PAMS regulations on 

February 12, 1993.238 San Diego County 

is subject to the CAA PAMS network 

SIP requirement as a Severe 

nonattainment area for the 2008 and 

2015 ozone NAAQS pursuant to 40 CFR 

51.1102 and 51.1302. 

On November 10, 1993, CARB 

submitted to the EPA a SIP revision 

addressing the PAMS network for six 

ozone nonattainment areas, including 

San Diego County, to meet the enhanced 

monitoring requirements of CAA section 

182(c)(1) and the PAMS regulations for 

the 1-hour ozone NAAQS. At the time, 

San Diego County was classified as a 

‘‘Severe-15’’ ozone nonattainment area 

for the 1-hour ozone NAAQS but that 

classification was later corrected to be 

‘‘Serious.’’ The EPA determined that the 

PAMS SIP revision met all applicable 

requirements for enhanced monitoring 

and approved the PAMS submittal into 

the California SIP.239

Prior to 2006, the EPA’s ambient air 

monitoring regulations in 40 CFR part 

58 (‘‘Ambient Air Quality 

Surveillance’’) set forth specific SIP 

requirements (see former 40 CFR 52.20). 

In 2006, the EPA significantly revised 

and reorganized 40 CFR part 58.240

Under revised 40 CFR part 58, SIP 

revisions are no longer required; rather, 

compliance with EPA monitoring 

regulations is established through 

review of required annual monitoring 

network plans.241 The 2008 Ozone SRR 

and 2015 Ozone SRR made no changes 

to these requirements.242

The most recent annual monitoring 

plan for San Diego County that the EPA 

has reviewed is the District’s ‘‘Annual 

Air Quality Monitoring Network Report 

2021’’ (2021 ANP).243 The District’s 

2021 ANP describes the steps taken to 

address the requirements of section 

182(c)(1), includes descriptions of the 

PAMS program and provides additional 

details about the PAMS network.244 The 


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in 2007, the EPA’s monitoring rules at 71 FR 61236 

(October 17, 2006) required the submittal and EPA 

action on ANPs. SDCAPCD’s 2021 ANP can be 

found in the docket for this action. 

245Letter dated October 31, 2022, from Gwen 

Yoshimura, EPA Region IX to David Sodeman, 

Chief, Monitoring and Technical Services, 

SDCAPCD, approving the 2021 San Diego ANP with 

certain exceptions unrelated to the PAMS 

requirements. 

246 2020 Plan, pp. 33–34 and endnote 80 (2008 

ozone NAAQS) and pp. 53–54 and endnote 128 

(2015 ozone NAAQS). 

247See 40 CFR 51.1117 (2008 ozone NAAQS) and 

51.1317 (2015 ozone NAAQS). The deadline for 

submittal to the EPA for the area’s CAA section 185 

SIP revision for the 2015 ozone NAAQS is August 

3, 2028. 

248See 80 FR 12264, at 12291 (March 6, 2015). 

249See 83 FR 62998, at 63023 (December 6, 2018). 

250 2020 Plan, at 23–25. 

251 65 FR 12472 (March 9, 2000). 

252 87 FR 45657 (July 29, 2022). 

253Ozone National Ambient Air Quality 

Standards (NAAQS): https://www.epa.gov/groundlevel-ozone-pollution/ozone-national-ambient-airquality-standards-naaqs; Health Effects of Ozone 

Pollution: https://www.epa.gov/ground-level-ozonepollution/health-effects-ozone-pollution. 

EPA approved the District’s current 

PAMS network as part of our approval 

of the District’s ANP.245

The 2020 Plan certifies compliance 

with the CAA section 182(c)(1) 

enhanced ambient monitoring 

requirement for the 2008 ozone NAAQS 

and 2015 ozone NAAQS by reference to 

the area’s approved PAMS SIP revision 

for the 1-hour ozone NAAQS.246 We 

agree that the San Diego County area 

meets the CAA section 182(c)(1) 

enhanced ambient monitoring 

requirement for the 2008 and 2015 

ozone NAAQS based on the District’s 

compliance with the EPA’s monitoring 

regulations in 40 CFR part 58 for PAMS 

networks. On that basis, we propose to 

approve the 2020 Plan’s certification of 

compliance with the enhanced 

monitoring requirements for the 2008 

and 2015 ozone NAAQS for the San 

Diego County area under CAA section 

182(c)(1) and 40 CFR 51.1102 and 

51.1302. 

6. CAA Section 185 Fee Program 

Sections 182(d)(3) and 185 of the CAA 

require that the SIP for each Severe and 

Extreme ozone nonattainment area 

provide that, if the area fails to attain by 

its applicable attainment date, each 

major stationary source of VOC and 

NOX located in the area shall pay a fee 

to the state as a penalty for such failure 

for each calendar year beginning after 

the attainment date, until the area is 

redesignated as an attainment area for 

ozone. These requirements apply to the 

San Diego County area as a Severe 

nonattainment area for both the 2008 

and the 2015 ozone NAAQS. States 

were required to submit to the EPA by 

July 20, 2022, a SIP revision that meets 

the requirements of CAA section 185 for 

the 2008 ozone NAAQS. The District 

adopted Rule 45 to meet those 

requirements and the state submitted it 

to the EPA on July 20, 2022. The EPA 

plans to take action on that submittal 

separately from this action. States are 

not yet required to submit a SIP revision 

that meets the requirements of CAA 

section 185 for the 2015 ozone 

NAAQS.247

7. Emissions Statement 

Section 182(a)(3)(B)(i) of the Act 

requires states to submit a SIP revision 

requiring owners or operators of 

stationary sources of VOC or NOX to 

provide the state with statements of 

actual emissions from such sources. 

Statements must be submitted at least 

every year and must contain a 

certification that the information 

contained in the statement is accurate to 

the best knowledge of the individual 

certifying the statement. Section 

182(a)(3)(B)(ii) of the Act allows states 

to waive the emissions statement 

requirement for any class or category of 

stationary sources that emit less than 25 

tpy of VOC or NOX, if the state provides 

an inventory of emissions from such 

class or category of sources as part of the 

base year or periodic inventories 

required under CAA sections 182(a)(1) 

and 182(a)(3)(A), based on the use of 

emissions factors established by the 

EPA or other methods acceptable to the 

EPA. 

The preamble of the 2008 Ozone SRR 

states that if an area has a previously 

approved emissions statement rule for 

the 1997 ozone NAAQS or the 1-hour 

ozone NAAQS that covers all portions 

of the nonattainment area for the 2008 

ozone NAAQS, such rule should be 

sufficient for purposes of the emissions 

statement requirement for the 2008 

ozone NAAQS. The state should review 

the existing rule to ensure it is adequate 

and, if so, may rely on it to meet the 

emissions statement requirement for the 

2008 ozone NAAQS.248 The same 

approach was included in the 2015 

Ozone SRR.249 Where an existing 

emissions statement requirement is still 

adequate to meet the requirements of 

these rules, states can provide the 

rationale for that determination to the 

EPA in a written statement in the SIP to 

meet this requirement. States should 

identify the various requirements and 

how each is met by the existing 

emissions statement program. Where an 

emissions statement requirement is 

modified for any reason, states must 

provide the revision to the emissions 

statement as part of its SIP. 

The 2020 Plan addresses compliance 

with the emissions statement 

requirement in CAA section 182(a)(3)(B) 

for the San Diego County area for the 

2008 and 2015 ozone NAAQS in Section 

2.2 (‘‘Emissions Statement Rule 

Certification’’) of the plan.250 In Section 

2.2 of the 2020 Plan, the District 

evaluates compliance with CAA section 

182(a)(3)(B) by reference to District Rule 

19.3 that, among other things, requires 

emissions reporting from stationary 

sources of NOX and VOC greater than or 

equal to 5 tpy, as deemed appropriate by 

the District’s Air Pollution Control 

Officer (APCO). In addition, the District 

reports emissions of VOC and NOX from 

sources that emit less than 25 tpy via 

CARB’s California Emission Inventory 

Development and Reporting System 

(CEIDARS). All sources with emissions 

of VOC or NOX greater than or equal to 

25 tpy must provide an emissions 

statement to the District. District Rule 

19.3 applies throughout the San Diego 

County area. On April 6, 1993, the 

District adopted District Rule 19.3 to 

meet the requirements in CAA section 

182(a)(3)(B). The District amended 

District Rule 19.3 on May 15, 1996, and 

the EPA approved the rule into the 

California SIP, effective May 8, 2000.251

In a separate action, the EPA 

approved the ‘‘Emissions Statement 

Rule Certification’’ portion of the 2020 

Plan that certifies District Rule 19.3 as 

meeting the emissions statement 

requirement under CAA section 

182(a)(3)(B) for the San Diego County 

area for the 2008 and 2015 ozone 

NAAQS.252

IV. Environmental Justice 

Considerations 

This document proposes to approve 

certain SIP elements included in the 

2020 Plan and the San Diego County 

area portion of the Smog Check 

Certification. Information on ozone and 

its relationship to negative health 

impacts can be found on the EPA’s 

website.253 We expect that this 

proposed action, once approved, will 

generally be neutral or contribute to 

reduced environmental and health 

impacts on all populations in the San 

Diego County area, including people of 

color and low-income populations in 

the area. At a minimum, the approved 

action would not worsen any existing 

air quality and is expected to ensure the 

area is meeting requirements to attain 

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. Lastly, 


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254See email dated March 2, 2023, from Nick 

Cormier, SDCAPCD, to John J. Kelly, EPA, regarding 

environmental justice information on San Diego 

County communities. The State’s Community Air 

Protection Program was created by passage of the 

State’s Assembly Bill (AB) 617. At the time of the 

email, the District had developed a plan to address 

emissions of air pollutants in one community 

(Portside) that was identified by the program and 

another community (the ‘‘International Border 

Community,’’ that is, the San Ysidro-Otay Mesa 

area) had also been identified. 

255Regarding other applicable requirements for 

the 2008 and 2015 ozone NAAQS in San Diego 

County, the EPA has previously approved the 

portion of the 2020 Plan that addresses the 

emissions statement requirement and will be taking 

action on the San Diego RACT submittal in separate 

rulemakings. See 87 FR 45657 (July 29, 2022) 

(approval of emissions statement certification); and 

88 FR 57361(August 23, 2023) (final approval of 

District Rule 69.2.2), and 88 FR 48150 (July 26, 

2023) (proposed approval of District Rule 69.2.1). A 

SIP revision for San Diego County addressing the 

penalty fee requirements under CAA sections 

182(d)(3) and 185 for the 2008 ozone NAAQS was 

submitted by CARB to the EPA on July 20, 2022, 

and EPA will take action on the July 20, 2022 SIP 

revision in a separate rulemaking. The area’s 

penalty fee SIP revision is not due for the 2015 

ozone NAAQS until August 3, 2028. 

although the District did not perform an 

environmental justice review 

specifically for the 2020 Plan, the 

District does implement the State’s 

‘‘Community Air Protection Program’’ in 

San Diego County.254 This program 

identifies specific communities based 

on environmental, health and 

socioeconomic information in order to 

reduce their pollution exposure. 

V. Proposed Action 

For the reasons discussed in this 

document, under CAA section 110(k)(3), 

the EPA is proposing to approve all of 

the ‘‘2020 Plan for Attaining the 

National Ambient Air Quality Standards 

for Ozone in San Diego County,’’ 

submitted on January 12, 2021, with two 

exceptions, and the San Diego County 

area I/M SIP revision for the 2008 and 

2015 ozone NAAQS, i.e., the San Diego 

County portion of the ‘‘Smog Check 

Performance Standing Modeling and 

Certification,’’ submitted on April 26, 

2023. The portions of the 2020 Plan on 

that we are not proposing action are the 

portion addressing the emissions 

statement requirement, which we 

already approved in a separate 

rulemaking, and the portion addressing 

the contingency measures requirement, 

for which we are deferring action.255

More specifically, we are proposing 

approval of the following portions of the 

2020 Plan, as supplemented by the 

Smog Check Certification, as meeting 

the following requirements: 

• Base year emissions inventory 

element as meeting the requirements of 

CAA sections 172(c)(3) and 182(a)(1) for 

the 2008 and 2015 ozone NAAQS, 40 

CFR 51.1115 for the 2008 ozone 

NAAQS, and 40 CFR 51.1315 for the 

2015 ozone NAAQS; 

• RACM demonstration element as 

meeting the requirements of CAA 

section 172(c)(1) for the 2008 and 2015 

ozone NAAQS, 40 CFR 51.1112(c) for 

the 2008 ozone NAAQS, and 40 CFR 

51.1312(c) for the 2015 ozone NAAQS; 

• Attainment demonstration element 

for the 2008 ozone NAAQS as meeting 

the requirements of CAA section 

182(c)(2)(A) and 40 CFR 51.1108; 

• Attainment demonstration element 

for the 2015 ozone NAAQS as meeting 

the requirements of CAA section 

182(c)(2)(A) and 40 CFR 51.1308, and 

the related commitments by CARB 

(through CARB Resolution 20–29) to 

achieve an aggregate emissions 

reduction of 4 tpd of NOX by 2032 in 

the San Diego County area and by the 

District (through District Resolution 20– 

166) to achieve emissions reductions of 

1.7 tpd by 2032; 

• ROP demonstration element as 

meeting the requirements of CAA 

section 182(b)(1) for the 2008 and 2015 

ozone NAAQS, 40 CFR 51.1110(a)(2) for 

the 2008 ozone NAAQS, and 40 CFR 

51.1310(a)(2) for the 2015 ozone 

NAAQS; 

• RFP demonstration element as 

meeting the requirements of CAA 

sections 172(c)(2), 182(b)(1), and 

182(c)(2)(B) for the 2008 and 2015 ozone 

NAAQS, 40 CFR 51.1110(a)(2)(i) and (ii) 

for the 2008 ozone NAAQS, and 40 CFR 

51.1310(a)(2)(ii) for the 2015 ozone 

NAAQS; 

• VMT emissions offset 

demonstration element as meeting the 

requirements of CAA section 

182(d)(1)(A) for the 2008 and 2015 

ozone NAAQS, 40 CFR 51.1102 for the 

2008 ozone NAAQS, and 40 CFR 

51.1302 for the 2015 ozone NAAQS; 

• Motor vehicle emissions budgets for 

the 2020 and 2023 RFP milestone years 

and the 2026 attainment year (see Table 

15) because they are consistent with the 

RFP and attainment demonstrations for 

the 2008 ozone NAAQS proposed for 

approval herein and meet the other 

criteria in 40 CFR 93.118(e)(4); 

• Motor vehicle emissions budgets for 

the 2023, 2026 and 2029 RFP milestone 

years and the 2032 attainment year (see 

Table 16) because they are consistent 

with the RFP and attainment 

demonstrations for the 2015 ozone 

NAAQS proposed for approval herein 

and meet the other criteria in 40 CFR 

93.118(e)(4); 

• General conformity budgets (or 

growth increments, in this case) for the 

Department of the Navy and United 

States Marine Corps, and for the San 

Diego International Airport (see Table 

17) as meeting the requirements of CAA 

section 176(c) and 40 CFR 93.161; 

• Enhanced vehicle inspection and 

maintenance program element in the 

2020 Plan, as supplemented by the San 

Diego County area portion of the Smog 

Check Certification, as meeting the 

requirements of CAA section 182(c)(3) 

for the 2008 and 2015 ozone NAAQS, 40 

CFR 51.1102 for the 2008 ozone 

NAAQS, and 40 CFR 51.1302 for the 

2015 ozone NAAQS; 

• Clean fuels fleet program element as 

meeting the requirements of CAA 

sections 182(c)(4)(A) and 246 for the 

2008 and 2015 ozone NAAQS, 40 CFR 

51.1102 for the 2008 ozone NAAQS, and 

40 CFR 51.1302 for the 2015 ozone 

NAAQS; 

• New Source Review program 

element as meeting the requirements of 

CAA sections 172(c)(5), 173 and 

182(a)(2)(C) for the 2008 and 2015 ozone 

NAAQS, 40 CFR 51.1114 for the 2008 

ozone NAAQS, and 40 CFR 51.1314 for 

the 2015 ozone NAAQS; and 

• Enhanced monitoring element as 

meeting the requirements of CAA 

section 182(c)(1) for the 2008 and 2015 

ozone NAAQS, 40 CFR 51.1102 for the 

2008 ozone NAAQS, and 40 CFR 

51.1302 for the 2015 ozone NAAQS. 

The EPA is soliciting public 

comments on the issues discussed in 

this document. We will accept 

comments from the public on this 

proposal for the next 30 days and will 

consider comments before taking final 

action. 

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 

approve state choices, provided that 

they meet the criteria of the Clean Air 

Act. Accordingly, this proposed action 

merely proposes to approve state law as 

meeting federal requirements and does 

not impose additional requirements 

beyond those imposed by state law. For 

that reason, this proposed 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), 13563 (76 FR 3821, 

January 21, 2011) 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.); 


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• 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 an economically significant 

regulatory action based on health or 

safety risks subject to Executive Order 

13045 (62 FR 19885, April 23, 1997); 

• 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 proposed action 

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). 

Furthermore, Executive Order 12898, 

‘‘Federal Actions To Address 

Environmental Justice in Minority 

Populations and Low-Income 

Populations,’’ (59 FR 7629, February 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. However, as described in 

Section IV (Environmental Justice 

Considerations) of this document, the 

District does participate in the State’s 

environmental justice program. The 

EPA did not perform an EJ analysis and 

did not consider EJ in this proposed 

action. Due to the nature of this 

proposed action, if finalized, this action 

is expected to have a neutral to positive 

impact on the air quality of San Diego 

County. Consideration of EJ is not 

required as part of this action, and there 

is no information in the record 

inconsistent with the stated goal of 

Executive Order 12898, to achieve 

environmental justice for people of 

color, low-income populations, and 

Indigenous peoples. 

List of Subjects in 40 CFR Part 52 

Environmental protection, Air 

pollution control, Incorporation by 

reference, Intergovernmental relations, 

Nitrogen dioxide, Ozone, Reporting and 

recordkeeping requirements, Volatile 

organic compounds. 

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

Dated: December 8, 2023. 

Martha Guzman Aceves, 

Regional Administrator, Region IX. 

[FR Doc. 2023–27513 Filed 12–18–23; 8:45 am] 

BILLING CODE 6560–50–P 


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