SUPPLEMENTARY INFORMATION:

Throughout this document, “we,” “us,” and “our” refer to the EPA.

Table of Contents

I. Background

A. Standard and Geographic Area Applicable to This Action

B. Motor Vehicle Emissions Budgets and Transportation Conformity

C. Existing Approved Budgets

D. Submission of Revised Budgets Based on EMFAC2021 and Off-Model Adjustment Factors

II. Clean Air Act Procedural and Administrative Requirements for SIP Submittals and Criteria for Approval of Revised Budgets

III. Revised Motor Vehicle Emissions Budgets for the 2008 8-Hour Ozone Standard

A. Review of Revised Budgets for the 2008 8-Hour Ozone Standard

B. Summary of Changes to Budgets and the EPA's Analysis of the State's Submittal

IV. Proposed Action and Request for Public Comment

V. Statutory and Executive Order Reviews

I. Background

A. Standard and Geographic Area Applicable to This Action

In 2008, the EPA revised the ozone NAAQS by setting the acceptable level of ozone in the ambient air at 0.075 ( printed page 42400) parts per million (ppm), averaged over an 8-hour period.^[1] Following promulgation of a new or revised NAAQS, the EPA is required under CAA section 107(d) to designate areas throughout the country as attaining or not attaining the NAAQS. In 2012, the EPA designated the San Joaquin Valley as nonattainment for the 2008 8-hour ozone standard and classified the area as “Extreme.” ^[2]

The SJV nonattainment area for the 2008 8-hour ozone standard consists of San Joaquin, Stanislaus, Merced, Madera, Fresno, Tulare, and Kings Counties, and the western portion of Kern County. The San Joaquin Valley nonattainment area stretches over 250 miles from north to south, averages a width of 80 miles, and encompasses over 23,000 square miles. It is partially enclosed by the Coast Mountain range to the west, the Tehachapi Mountains to the south, and the Sierra Nevada range to the east.^[3]

B. Motor Vehicle Emissions Budgets and Transportation Conformity

Under the CAA, States are required to submit, at various times, control strategy SIP revisions and maintenance plans for nonattainment and maintenance areas for a given NAAQS. These emission control strategy SIP revisions ( e.g., reasonable further progress (RFP) and attainment demonstration SIP revisions) and maintenance plans include motor vehicle emissions budgets for criteria pollutants and/or their precursors to address pollution from cars and trucks. The motor vehicle emissions budgets are the portions of the total allowable emissions that are allocated to on-road vehicle use that, together with emissions from other sources in the area, will provide for RFP, attainment or maintenance.^[4]

Under section 176(c) of the CAA, transportation plans, Transportation Improvement Programs (TIPs), and transportation projects must “conform” to ( i.e., be consistent with) the SIP before they can be adopted or approved. Conformity to the SIP means that transportation activities will not cause new air quality violations, worsen existing air quality violations, or delay timely attainment of the NAAQS or delay an 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 the transportation conformity rule, Metropolitan Planning Organizations (MPOs) 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 TIPs 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 budgets contained in all control strategy SIPs.

In California, budgets are derived using a computer model developed by the California Air Resources Board (CARB) and referred to as EMFAC (short for EMission FACtor). EMFAC is used to calculate current and future inventories of motor vehicle emissions at the State, air district, air basin, county, and project level. The EPA approved EMFAC2021 for use in SIP revisions and transportation conformity determinations in California in November 2022.^[5] The EPA approved off-model adjustment factors to EMFAC2021 in November 2025.^[6] With the approval of the adjustment factors, EMFAC2021 with these adjustment factors is the latest approved method for modeling emissions available in California, per 40 CFR 93.111.

C. Existing Approved Budgets

The EPA previously approved the NO_X and VOC budgets for SJV for the 2008 8-hour ozone standard. The EPA approved the budgets as part of the EPA's approval of three SIP revisions submitted by CARB to address the nonattainment planning requirements for the SJV for the 2008 ozone NAAQS, including the RFP and attainment demonstrations. These SIP revisions include the “San Joaquin Valley 2016 Plan for the 2008 8-Hour Ozone Standard” (“2016 Ozone Plan”) and the portions of the “Revised Proposed 2016 State Strategy for the State Implementation Plan” (“2016 State SIP Strategy”) and “2018 Updates to the California State Implementation Plan” (“2018 SIP Update”) that pertain to the San Joaquin Valley for the 2008 ozone NAAQS.^[7] Collectively, we refer to the approved SIP revisions for SJV for the 2008 ozone NAAQS as the “2016 SJV Ozone SIP.”

These approved ozone budgets were developed using EMFAC2014, but the 2020 and later budgets for certain SJV county-subareas reflected safety margins to accommodate the then-expected approval of EMFAC2017.^[8] In the SJV, the eight county-level MPOs, FHWA, and FTA are the relevant transportation agencies that must use applicable approved or adequate budgets in determining the conformity of transportation plans and TIPs within the SJV region.

D. Submission of Revised Budgets Based on EMFAC2021 and Off-Model Adjustment Factors

On March 26, 2026, CARB adopted revised budgets that were developed using EMFAC2021 and the November 21, 2025 adjustment factors.^[9] These revised budgets, which were adopted in a document titled 2026 Updates to Motor Vehicle Emissions Budgets for the San Joaquin Valley 75 Parts Per Billion Ozone State Implementation Plan (“2026 Valley Ozone Budget Update”), were submitted to the EPA on April 30, 2026.^[10] In addition, CARB requested that the EPA's approval allow the budgets in the 2026 Valley Ozone Budget Update to be superseded by the next budgets found to be adequate by the EPA ( e.g., that are based on the next version of EMFAC), per 40 CFR 93.118(e)(1).^[11]

( printed page 42401)

II. Clean Air Act Procedural and Administrative Requirements for SIP Submittals and Criteria for Approval of Revised Budgets

CAA sections 110(a)(1) and (2) and 110(l) require a State to provide reasonable public notice and opportunity for public hearing prior to the adoption and submittal 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 for a public hearing was provided, consistent with the EPA's implementing regulations in 40 CFR 51.102.

CARB satisfied applicable statutory and regulatory requirements for reasonable public notice and hearing prior to adoption and submittal of the revised budgets. In the documentation included as part of the April 30, 2026 SIP revision submittal, CARB provided evidence of the required public notice and opportunity for public comment prior to its March 26, 2026 public hearing and adoption of the revised budgets. We find, therefore, that the submittal of the revised budgets meets the procedural requirements for public notice and hearing in CAA sections 110(a) and 110(l).

Under section 110(l) of the CAA, SIP revisions must not interfere with any applicable requirements concerning attainment or RFP or any other applicable requirement of the Act. Generally, the EPA reviews budgets for approval in the context of the Agency's review of a control strategy implementation plan ( i.e., attainment or RFP plan) or maintenance plan. In addition, revisions to budgets can be approved without comprehensive updates to the related control strategy implementation or maintenance plan if the plan, including the revised budgets, continues to meet applicable requirements ( i.e., RFP, attainment, or maintenance).

A State may revise the motor vehicle emissions inventories and related budgets without revising its entire SIP, consistent with section 110(l), if: (1) the SIP continues to meet applicable requirements when the previous motor vehicle emissions inventories are replaced with new base year and milestone, attainment, or maintenance year inventories based on a more recent emissions model; and (2) the State can document that growth and control strategy assumptions for non-motor vehicle sources continue to be valid and any minor updates do not change the overall conclusions of the SIP.^[12]

In this proposed rulemaking, the EPA is not making a separate adequacy finding for the revised budgets that were submitted in the 2026 SJV Ozone Budget Update because the budgets they would replace are approved budgets from the 2016 SJV Ozone SIP (see 40 CFR 93.118(e)(1)).^[13] However, the budgets in the 2026 SJV Ozone Budget Update do meet the criteria in 40 CFR 93.118(e)(4),^[14] and therefore the EPA is proposing to approve them. If this proposal is finalized, these budgets would replace all the motor vehicle emissions budgets in the 2016 SJV Ozone SIP.

The EPA is also proposing that, once approved, these budgets could be superseded by future adequate budgets, as CARB requested and as allowed by the transportation conformity regulation at 40 CFR 93.118(e)(1). This would allow new information included in the next version of EMFAC, once approved, to be incorporated into the conformity process as soon as the EPA determines that updated budgets are adequate, instead of having to wait until updated budgets are approved.

III. Revised Motor Vehicle Emissions Budgets for the 2008 8-Hour Ozone Standard

A. Review of Revised Budgets for the 2008 8-Hour Ozone Standard

Table 1 of this document lists the revised budgets by subarea for the SJV for the 2008 8-hour ozone standard. CARB developed the revised budgets using EMFAC2021 with the November 2025 adjustment factors ^[15] and the travel activity projections provided by the San Joaquin Valley MPOs consistent with the 2025 Federal TIP.^[16] As such, we find that the revised budgets reflect the most recent planning forecasts and are based on the most recent emission factor data and approved calculation methods. A comparison of the existing approved budgets with the revised budgets and a discussion of the EPA's proposed action on the revised budgets is provided below in section III.B of this document.

B. Summary of Changes to Budgets and the EPA's Analysis of the State's Submittal

The 2026 Valley Ozone Budget Update includes updated budgets but does not revise any other element of the 2016 SJV Ozone SIP. As noted previously, we believe that a State may revise the motor vehicle emissions inventories and related budgets without revising their entire SIP, consistent with section 110(l), if: (1) the SIP continues to meet applicable requirements when the previous motor vehicle emissions inventories are replaced with new base year and milestone, attainment, or maintenance year inventories based on a more recent emissions model; and (2) the State can document that growth and control strategy assumptions for non-motor vehicle sources continue to be valid and any minor updates do not change the overall conclusions of the SIP. These considerations provide the framework for our evaluation of the revised budgets in the 2026 Valley Ozone Budget Update.

Tables 2 and 3 of this document compare the existing EPA-approved NO_X and VOC subarea budgets developed using EMFAC2014 with the revised subarea budgets developed using EMFAC2021 and the November 2025 adjustment factors. The budgets are provided by subarea and apply to the 2008 8-hour ozone standard.^[17]

The revised NO_X and VOC budgets for 2026, 2029, and 2031 are intended to replace the existing EPA-approved NO_X and VOC budgets in the 2016 SJV Ozone SIP developed for the 2008 8-hour ozone standard. A comparison of the ( printed page 42403) existing budgets with the revised budgets is shown in tables 2 and 3. The tables show that the NO_X and VOC regional totals for the revised budgets are less than the NO_X and VOC regional totals for the existing budgets for all years. On a subarea basis, there are certain VOC increases, e.g., Stanislaus County for years 2026, 2029, and 2031, respectively, and Tulare County for years 2026 and 2029, but RFP and attainment are demonstrated for the San Joaquin Valley on a regional, not a subarea, basis.

First, we note that the 2016 SJV Ozone SIP relied upon motor vehicle emissions inventories, from which the budgets were derived, to demonstrate compliance with RFP and attainment requirements. With respect to the RFP requirement, we found that the 2016 SJV Ozone SIP provided a significant surplus of NO_X emissions reductions beyond those necessary to meet the RFP requirement.^[18] As shown in tables 2 and 3, the regional totals for the revised budgets submitted by CARB for NO_X and VOC for 2026, 2029, and 2031 are lower than corresponding regional totals for the budgets approved in 2019. As such, the replacement of the existing budgets with the revised budgets would not change the conclusion that the 2016 SJV Ozone SIP meets the requirements for RFP.

Second, the 2026 Valley Ozone Budget Update does not document that growth and control strategy assumptions for non-motor vehicle sources in the 2016 SJV Ozone SIP continue to be valid. However, CARB and the San Joaquin Valley Unified Air Pollution Control District (SJVUAPCD or “District”) have submitted more recent emissions projections of NO_X and VOC emissions for San Joaquin Valley to address SIP requirements for the 2015 ozone NAAQS. Such updated emissions projections can be used to document that updates to the emissions estimates for non-motor vehicle sources do not change the overall conclusions of the SIP.

For that purpose, we have prepared updated NO_X and VOC emissions inventories from all sources ( i.e., stationary, area, on-road, and non-road sources) in the SJV for 2026, 2029, and 2031. For the most current emissions inventory data, the EPA used the latest available emissions inventory data for stationary, area, and non-road sources, which is from the District's 2022 Plan for the 2015 8-Hour Ozone Standard (adopted December 15, 2022).^[19] For on-road sources, the EPA used the revised budgets from the 2026 Valley Ozone Budget Update. These inventories provide a basis for comparison with the corresponding inventories from the 2016 SJV Ozone SIP.

We would expect that most current emissions estimates from all sources in SJV in 2026, 2029, and 2031 would be lower than those included in the 2016 SJV Ozone SIP because they reflect control measures adopted since that plan was approved, and as shown below in tables 4 and 5, the updated regional emissions for 2026, 2029, and 2031, including the revised budgets, are 10.5, 9.4, and 9.9 tons per summer day (tpsd) lower for NO_X and 3.0, 9.9, and 9.6 tpsd lower for VOC, respectively, than the corresponding figures in the 2016 SJV Ozone Plan. The current emissions estimates for 2031 (115.2 tpsd NO_X and 290.4 tpsd VOC) are consistent with the attainment target level for the 2008 ozone standard (131.9 tpsd NO_X and 296.7 tpsd VOC).^[20]

Therefore, we find that the 2016 SJV Ozone Plan will continue to meet applicable requirements for RFP and attainment when the existing approved, EMFAC2014-based budgets are replaced with the revised EMFAC2021 budgets with the November 2025 adjustment factors and that the changes in the growth and control strategy assumptions for non-motor vehicle sources do not change the overall conclusions of the 2016 SJV Ozone SIP. As such, we find that approval of the revised NO_X and VOC budgets from the 2026 Valley Ozone Budget Update for 2026, 2029, and 2031 as shown in table 1 would not interfere with attainment or RFP or any other requirement of the Act and would thereby comply with section 110(l), and we propose to approve them on that basis.

( printed page 42404)

Under our transportation conformity rule, as a general matter, once budgets are approved, they cannot be superseded by revised budgets submitted for the same CAA purpose and the same period of years addressed by the previously approved SIP until the EPA approves the revised budgets as a SIP revision. In other words, as a general matter, such approved budgets cannot be superseded by revised budgets found adequate, but rather only through approval of the revised budgets, unless the EPA specifies otherwise in its approval of a SIP by limiting the duration of the approval to last only until subsequently submitted budgets are found adequate.^[21]

In this instance, as noted above, CARB has requested that we limit the duration of our approval of the budgets in the 2026 Valley Ozone Budget Update only until the effective date of the EPA's adequacy finding for any subsequently submitted budgets. Generally, we will consider a State's request to limit an approval of a budget only if the request includes the following elements: ^[22]

• An acknowledgement and explanation as to why the budgets under consideration have become outdated or deficient;
• A commitment to update the budgets as part of a comprehensive SIP update; and
• A request that the EPA limit the duration of its approval to the time when new budgets have been found to be adequate for transportation conformity purposes.

CARB's request includes an explanation for why the budgets have become, or will become, outdated or deficient. In short, CARB has requested that we limit the duration of the approval of the budgets because CARB expects the next version of EMFAC to estimate higher emissions for certain on-road motor vehicle categories and certain areas of the State, necessitating updates to the budgets once the next version of EMFAC is submitted and approved by the EPA.

If the EPA approves the future EMFAC model, CARB explains that the budgets from the 2026 Valley Ozone Budget Update, for which we are proposing approval in this action, may become outdated and will need to be revised. In addition, CARB states that, without the ability to replace the budgets using the budget adequacy process, the benefits of using the updated data may not be realized for a year or more after the updated SIP (with the future budgets) is submitted, due to the length of the SIP approval process. For the reasons provided above, and in light of CARB's explanation for why the budgets will become outdated and should be replaced upon an adequacy finding for updated budgets, we propose to limit the duration of our approval of the budgets in the 2026 Valley Ozone Budget Update until new budgets have been found adequate. We find that CARB's explanation for limiting the duration of the approval of the budgets is appropriate and provides us with a reasonable basis on which to limit the duration of the approval of the budgets.

We note that, in relation to the request to limit the duration of approval of the budgets, CARB has not committed to update the budgets as part of a comprehensive SIP update, but as a practical matter, CARB must submit a SIP revision that includes updated demonstrations as well as the updated budgets to meet the adequacy criteria in 40 CFR 93.118(e)(4); ^[23] and thus, we do not need a specific commitment for such a plan at this time.

IV. Proposed Action and Request for Public Comment

For the reasons discussed above, the EPA is proposing to approve the revised ozone budgets in California's April 30, 2026 submittal for the SJV area. The revised budgets are shown in table 1 of this document and are based on estimates from California's EMFAC2021 model, with the EPA-approved November 2025 adjustment factors.

More specifically, under CAA section 110(k)(3), the EPA is proposing to approve the revised VOC and NO_X budgets for 2026, 2029, and 2031 for the 2008 8-hour ozone standard because replacement of the existing approved budgets with the revised budgets would not interfere with the approved RFP and attainment demonstrations for the 2008 8-hour ozone standard in the SJV and because emissions changes in non-motor vehicle emissions categories do not change the overall conclusions of the 2016 SJV Ozone SIP.

With respect to the motor vehicle emissions budgets, we are proposing to limit the duration of the approval of the budgets to last only until the effective date of an adequacy finding by the EPA for any subsequently submitted budgets for the same CAA purpose and years. We are doing so at CARB's request consistent with 40 CFR 93.118(e)(1).

Lastly, if the EPA takes final action to approve the revised budgets as proposed, the San Joaquin Valley MPOs, FHWA, and FTA would have to use the ( printed page 42405) revised budgets for future transportation conformity determinations.

The EPA is soliciting public comments on the issues discussed in this document. See the DATES and ADDRESSES sections of this Federal Register proposed action for further details. We will consider these comments before taking final action.

V. Statutory and Executive Order Reviews

Under the CAA, 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 CAA. Accordingly, this action merely proposes to approve a State plan 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 underExecutive Order 12866 (58 FR 51735, October 4, 1993);
• Is not anExecutive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this action is not significant under Executive Order 12866;
• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
• Is certified as not having a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.);
• Does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4);
• Does not have federalism implications as specified inExecutive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject toExecutive Order 13045 (62 FR 19885, April 23, 1997) because it proposes to approve a State program;
• Is not a significant regulatory action subject toExecutive 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 CAA.

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 rule does not have Tribal implications and will not impose substantial direct costs on Tribal governments or preempt Tribal law as specified by Executive Order 13175 (65 FR 67249, November 9, 2000).

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