# Air Plan Approval; Indiana; Second Maintenance Plan for 2008 Ozone NAAQS
**AGENCY:**
Environmental Protection Agency (EPA).
**ACTION:**
Proposed rule.
**SUMMARY:**
The Environmental Protection Agency (EPA) is proposing to approve a revision to the Indiana State Implementation Plan (SIP). On April 1, 2025, the Indiana Department of Environmental Management (IDEM) submitted a revision to the State's plan for maintaining the 2008 ozone National Ambient Air Quality Standard (NAAQS or standard) in the Indiana portion of the Cincinnati, Ohio-Kentucky-Indiana area. EPA is proposing to approve this maintenance plan because it provides for the maintenance of the 2008 ozone NAAQS for the area for 10 additional years as required by the Clean Air Act (CAA). EPA is also initiating the adequacy review process for motor vehicle emission budgets (Budgets) for the area. This action, if finalized, would make certain commitments related to maintenance of the 2008 ozone NAAQS in this area federally enforceable as part of the Indiana SIP.
**DATES:**
Comments must be received on or before December 22, 2025.
**ADDRESSES:**
Submit your comments, identified by Docket ID No. EPA-R05-OAR-2025-0167 at *https://www.regulations.gov,* or via email to *[email protected].* For comments submitted at *Regulations.gov,* follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from the docket. EPA may publish any comment received to its public docket. Do not submit to EPA's docket at *https://www.regulations.gov* any information you consider to be Confidential Business Information (CBI), Proprietary Business Information (PBI), 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. 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, PBI, or multimedia submissions, and general guidance on making effective comments, please visit *https://www.epa.gov/dockets/commenting-epa-dockets.*
**FOR FURTHER INFORMATION CONTACT:**
Delaney Kilgour, Air and Radiation Division (AR18J), Environmental Protection Agency, Region 5, 77 West Jackson Boulevard, Chicago, Illinois 60604, (312) 886-1493, *[email protected].* The EPA Region 5 office is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding Federal holidays.
**SUPPLEMENTARY INFORMATION:**
Throughout this document whenever “we,” “us,” or “our” is used, we mean EPA. This *SUPPLEMENTARY INFORMATION* section is arranged as follows:
I. Summary of EPA's Proposed Action
II. Background
III. EPA's Evaluation of Indiana's SIP Submittal
A. Second Maintenance Plan
B. Transportation Conformity
IV. What action is EPA taking?
V. Statutory and Executive Order Reviews
**I. Summary of EPA's Proposed Action**
EPA is proposing to approve, as a revision to the Indiana SIP, the 2008 ozone NAAQS maintenance plan for the Indiana portion of the Cincinnati, Ohio-Kentucky-Indiana area. The Cincinnati area includes Lawrenceburg Township in Dearborn County in Indiana; Butler, Clermont, Clinton, Hamilton, and Warren Counties in Ohio; and parts of Boone, Campbell, and Kenton Counties in Kentucky. The maintenance plan is designed to keep the Cincinnati area in attainment of the 2008 ozone NAAQS through 2037.
**II. Background**
Ground-level ozone is formed when nitrogen oxides (NO <sub>X</sub> ) and volatile organic compounds (VOC) react in the presence of sunlight. These two pollutants are referred to as ozone precursors. Scientific evidence indicates that adverse public health effects occur following exposure to ozone.
On March 12, 2008, under section 109 of the CAA, EPA promulgated a revised primary and secondary 8-hour ozone NAAQS of 0.075 parts per million (ppm). *See* 73 FR 16436 (March 27, 2008). Under EPA's regulations at 40 CFR part 50, the 2008 ozone NAAQS is attained in an area when the 3-year average of the annual fourth highest daily maximum 8-hour average concentration is equal to or less than 0.075 ppm, when truncated after the thousandth decimal place, at all of the ozone monitoring sites in the area. *See* 40 CFR 50.15 and appendix P to 40 CFR part 50.
Following promulgation of a new or revised NAAQS, EPA is required by the CAA to designate areas throughout the nation as attaining or not attaining the NAAQS. On May 21, 2012 (77 FR 30088), EPA designated areas for the 2008 ozone NAAQS, including the Cincinnati, Ohio-Kentucky-Indiana area as nonattainment. These designations became effective on July 20, 2012. Under the CAA, States are also required to adopt and submit SIPs to implement, maintain, and enforce the NAAQS in designated nonattainment areas and throughout the State.
When a nonattainment area has three years of complete, certified air quality data that has been determined to attain the 2008 ozone NAAQS, and the area has met other required criteria described in section 107(d)(3)(E) of the CAA, the State can submit to EPA a request to be redesignated to attainment, referred to as a “maintenance area.” [^1] One of the criteria for redesignation is to have an approved maintenance plan under section 175A of the CAA. The maintenance plan must demonstrate that the area will continue to maintain the standard for the period extending 10 years after redesignation, and it must contain such additional measures as necessary to ensure maintenance and such contingency provisions as necessary to ensure that violations of the standard will be promptly corrected. At the end of the eighth year after the effective date of the redesignation, the State must also submit a second maintenance plan to ensure ongoing maintenance of the standard for an additional 10 years. *See* CAA section 175A.
[^1] Section 107(d)(3)(E) of the CAA sets out the requirements for redesignation. They include attainment of the NAAQS, full approval of the SIP under section 110(k) of the CAA, determination that improvement in air quality is a result of permanent and enforceable reductions in emissions, demonstration that the State has met all applicable section 110 and part D requirements, and a fully approved maintenance plan under CAA section 175A.
EPA has published long-standing guidance for States on developing maintenance plans. [^2] The Calcagni Memorandum provides that States may generally demonstrate maintenance by either performing air quality modeling to show that the future mix of sources and emission rates will not cause a violation of the NAAQS or by showing that future emissions of a pollutant and its precursors will not exceed the level of emissions during a year when the area was attaining the NAAQS ( *i.e.,* attainment year inventory). *See* Calcagni Memorandum at 9.
[^2] “Procedures for Processing Requests to Redesignate Areas to Attainment,” Memorandum from John Calcagni, Director, Air Quality Management Division, September 4, 1992 (the “Calcagni Memorandum”).
On February 23, 2016, IDEM submitted a request to EPA to redesignate the Indiana portion of the Cincinnati nonattainment area to attainment for the 2008 ozone NAAQS. This submittal included a plan to maintain the 2008 ozone NAAQS in the Cincinnati area through 2030 as a revision to the Indiana SIP. EPA approved the Cincinnati maintenance plan and the State's request to redesignate the Indiana portion of the area to attainment for the 2008 ozone NAAQS on April 7, 2017 (82 FR 16940).
Under section 175A(b) of the CAA, States must submit a revision to the first maintenance plan eight years after redesignation to provide for maintenance of the NAAQS for 10 additional years following the end of the first 10-year period. IDEM submitted a second maintenance plan on April 1, 2025, and supplemented the submission on October 8, 2025. The second maintenance plan shows attainment of the 2008 ozone NAAQS for Cincinnati through 2037, *i.e.,* through the end of the full 20-year maintenance period for the area.
**III. EPA's Evaluation of Indiana's SIP Submittal**
**A. Second Maintenance Plan**
Section 175A of the CAA sets forth the elements of a maintenance plan for areas seeking redesignation from nonattainment to attainment. Under section 175A, the maintenance plan must demonstrate continued attainment of the NAAQS for at least 10 years after the Administrator approves a redesignation to attainment. Eight years after the redesignation, the State must submit a revised maintenance plan which demonstrates that attainment of the NAAQS will continue for an additional 10 years beyond the initial 10-year maintenance period. To address the possibility of future NAAQS violations, the maintenance plan must contain contingency measures, as EPA determines necessary, to ensure prompt correction of the future NAAQS violation.
The Calcagni Memorandum provides further guidance on the content of a maintenance plan, explaining that a maintenance plan should address five elements: (1) an attainment emission inventory; (2) a maintenance demonstration; (3) a commitment for continued air quality monitoring; (4) a process for verification of continued attainment; and (5) a contingency plan.
On April 1, 2025, IDEM submitted, as a SIP revision, a plan to provide for maintenance of the 2008 ozone standard in the Indiana portion of the Cincinnati area through 2037, more than 20 years after the effective date of the redesignation to attainment. On October 8, 2025, IDEM submitted a supplement to the April 1 SIP revision submittal, revising the emission inventories. As discussed below, EPA proposes to find that IDEM's second maintenance plan includes the necessary components and to approve the maintenance plan as a revision to the Indiana SIP.
**1. Attainment Inventory**
The CAA section 175A maintenance plan approved by EPA for the first 10-year period included an attainment inventory for the Cincinnati area that reflected typical summer day VOC and NO <sub>X</sub> emissions in 2014. In addition, because the area continued to monitor attainment of the 2008 ozone NAAQS in 2016, 2016 is an appropriate year to use for an attainment year inventory. For the Cincinnati attainment inventory, Ohio and Indiana emissions of area, nonroad, and point sources, and Kentucky emissions of area and nonroad sources were based upon the 2016v2 Emissions Modeling Platform provided by EPA. [^3] Kentucky point source emissions (electric generating unit (EGU) and non-EGU) were derived from the Kentucky emissions reporting system, provided in tons per year (tpy), and based upon the actual locations of the sources within the partial areas of Kentucky counties in the maintenance area. Kentucky point source emissions were converted to tons per day (tpd) by multiplying by the ratio of average July day emissions to annual emissions for the point sector from the 2016v2 Emissions Modeling Platform. On-road mobile source emissions for the Cincinnati area were developed in conjunction with the Ohio-Kentucky-Indiana Regional Council of Governments and were calculated from emission factors produced by EPA's 2023 Motor Vehicle Emission Simulator (MOVES4) [^4] and data extracted from the region's travel demand model. All sectors of Kentucky emissions were multiplied by fractions representing the maintenance portions of the Kentucky counties. On-road mobile source emissions for Indiana were based on the partial maintenance area in Dearborn County, and remaining source sectors were based on the entire county. Attainment inventories for the Cincinnati area are in Tables 1 and 2.
[^3] The inventory documentation for this modeling platform can be found here: *https://gaftp.epa.gov/Air/emismod/2016/v2/.*
[^4] The documentation for MOVES4 can be found here: *https://www.epa.gov/moves/moves-versions-limited-current-use.*
| | Point | Area | Nonroad | On-road | Total |
| --- | --- | --- | --- | --- | --- |
| Indiana: | | | | | |
| Dearborn County | 6.21 | 1.37 | 0.37 | 0.20 | 8.15 |
| Entire Area | 13.38 | 65.80 | 17.39 | 27.30 | 123.87 |
| | Point | Area | Nonroad | On-road | Total |
| --- | --- | --- | --- | --- | --- |
| Indiana: | | | | | |
| Dearborn County | 1.75 | 0.26 | 0.38 | 0.57 | 2.96 |
| Entire Area | 58.92 | 11.90 | 15.60 | 64.90 | 151.32 |
**2. Maintenance Demonstration**
IDEM demonstrates maintenance through 2037 for the Cincinnati area by showing that future VOC and NO <sub>X</sub> emissions remain at or below attainment year emission levels. 2037 is an appropriate maintenance year for the Cincinnati area because this year is more than 10 years beyond the first 10-year maintenance period. The maintenance year emissions inventories of area, nonroad, and point sources are projected from the EPA 2016v2 Emissions Modeling Platform, which includes emissions for the modeling years of 2016, 2023, 2026, and 2032. The 2037 maintenance year emissions were projected from the platform by linear extrapolation. If the extrapolation resulted in a negative value, IDEM assumed that maintenance year emissions would remain at the levels from the 2032 modeling year included in the 2016v2 platform, which is a conservative assumption as emissions have been shown to be decreasing. On-road mobile source emissions for maintenance years were calculated from EPA's 2023 MOVES4. All sectors of Kentucky emissions were multiplied by fractions representing the maintenance portions of the Kentucky counties. On-road mobile source emissions for Indiana were based on the partial maintenance area in Dearborn County, and remaining source sectors were based on the entire county. The 2037 summer day emission inventories for the Cincinnati area are in Tables 3 and 4, and changes in VOC and NO <sub>X</sub> emissions in the Cincinnati area between 2016 and 2037 are summarized in Table 5.
In summary, the maintenance demonstration shows maintenance of the 2008 ozone standard by providing emissions information to support the demonstration that future emissions of NO <sub>X</sub> and VOC will remain at or below 2016 emission levels when considering both future source growth and implementation of future controls. In the Indiana portion of the Cincinnati area, Table 5 shows that VOC emissions are projected to increase by 0.01 tpd between 2016 and 2037, and NOx emissions are projected to decrease by 1.00 tpd between 2016 and 2037. In the entire Cincinnati area, Table 5 shows that VOC and NO <sub>X</sub> emissions are projected to decrease by 18.16 tpd and 102.23 tpd, respectively, between 2016 and 2037.
| | Point | Area | Nonroad | On-road | Total |
| --- | --- | --- | --- | --- | --- |
| Indiana: | | | | | |
| Dearborn County | 6.24 | 1.58 | 0.27 | 0.07 | 8.16 |
| Entire Area | 11.75 | 69.90 | 12.59 | 11.47 | 105.71 |
| | Point | Area | Nonroad | On-road | Total |
| --- | --- | --- | --- | --- | --- |
| Indiana: | | | | | |
| Dearborn County | 1.51 | 0.19 | 0.17 | 0.09 | 1.96 |
| Entire Area | 22.54 | 8.97 | 7.49 | 10.09 | 49.09 |
| | VOC | 2016 | 2037 | Net change | NO | 2016 | 2037 | Net change |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Indiana Portion of the Area: | | | | | | | | |
| Point | 6.21 | 6.24 | 0.03 | 1.75 | 1.51 | −0.24 | | |
| Area | 1.37 | 1.58 | 0.21 | 0.26 | 0.19 | −0.07 | | |
| Nonroad | 0.37 | 0.27 | −0.10 | 0.38 | 0.17 | −0.21 | | |
| On-road | 0.20 | 0.07 | −0.13 | 0.57 | 0.09 | −0.48 | | |
| Total | 8.15 | 8.16 | 0.01 | 2.96 | 1.96 | −1.00 | | |
| Entire Area: | | | | | | | | |
| Point | 13.38 | 11.75 | −1.63 | 58.92 | 22.54 | −36.38 | | |
| Area | 65.80 | 69.90 | 4.10 | 11.90 | 8.97 | −2.93 | | |
| Nonroad | 17.39 | 12.59 | −4.80 | 15.60 | 7.49 | −8.11 | | |
| On-road | 27.30 | 11.47 | −15.83 | 64.90 | 10.09 | −54.81 | | |
| Total | 123.87 | 105.71 | −18.16 | 151.32 | 49.09 | −102.23 | | |
**3. Continued Air Quality Monitoring**
IDEM has committed to continue to work with neighboring agencies to operate an approved ozone monitoring network in the Cincinnati area. IDEM has committed to consult with EPA prior to making changes to the existing monitoring network should changes become necessary in the future. Indiana remains obligated to meet monitoring requirements and to continue to quality assure monitoring data in accordance with 40 CFR part 58, and to enter all data into the Air Quality System in accordance with Federal guidelines.
**4. Verification of Continued Attainment**
Indiana has the legal authority to enforce and implement the requirements of the maintenance plan for the Indiana portion of the Cincinnati area. This includes the authority to adopt, implement, and enforce any subsequent emission control measures determined to be necessary to correct future ozone attainment problems.
Verification of continued attainment is accomplished through operation of the ambient ozone monitoring network and the periodic update of the area's emission inventories. IDEM will continue to work with neighboring agencies to operate an approved ozone monitoring network in the Cincinnati maintenance area. There are no plans to discontinue operation, relocate, or otherwise change the existing ozone monitoring network other than through revisions in the network approved by EPA.
In addition, to track future levels of emissions, IDEM will continue to develop and submit to EPA updated emission inventories for all source categories at least once every three years, consistent with the requirements of 40 CFR part 51, subpart A, and in 40 CFR 51.122.
**5. Contingency Plan**
Section 175A of the CAA requires that the State must adopt a maintenance plan, as a SIP revision, that includes such contingency measures as EPA deems necessary to ensure that the State will promptly correct a violation of the NAAQS that occurs after redesignation of the area to attainment of the NAAQS. The maintenance plan must identify: the contingency measures to be considered and, if needed for maintenance, adopted and implemented; a schedule and procedure for adoption and implementation; and a time limit for action by the State. The State should also identify specific indicators to be used to determine when the contingency measures need to be considered, adopted, and implemented. The maintenance plan must include a commitment that the State will implement all measures with respect to the control of the pollutant that were contained in the SIP before redesignation of the area to attainment in accordance with section 175A(d) of the CAA. *See* Calcagni Memorandum at 12-13.
As required by section 175A of the CAA, IDEM has adopted a contingency plan for the Cincinnati area to address possible future ozone air quality problems. The contingency plan adopted by IDEM has two levels of response: a warning level response and an action level response.
In IDEM's plan, a warning level response will be triggered when an annual (1-year) fourth highest 8-hour average ozone concentration of 0.079 ppm or higher or a 2-year fourth highest 8-hour average ozone concentration of 0.076 ppm or higher is monitored within the maintenance area. A warning level response will consist of IDEM conducting a study to determine whether the ozone value indicates a trend toward higher ozone values or whether emissions appear to be increasing. The study will evaluate whether the trend, if any, is likely to continue, and if so, the control measures necessary to reverse the trend. The study will consider ease and timing of implementation as well as economic and social impacts. Implementation of necessary controls in response to a warning level response trigger will take place within 12 months from the conclusion of the most recent ozone season.
In IDEM's plan, an action level response will be triggered whenever a violation of the standard (3-year average of the annual fourth highest 8-hour average ozone concentration equal to 0.076 ppm or higher) is monitored within the maintenance area. When an action level response is triggered, IDEM will determine what additional control measures are needed to ensure future attainment of the ozone standard and will adopt these measures through the necessary administrative and legal process, including the opportunity for a public hearing. Control measures selected will be adopted and implemented within 18 months from the close of the ozone season that prompted the action level. IDEM may also consider if significant new regulations not currently included as part of the maintenance provisions will be implemented in a timely manner and would thus constitute an adequate contingency measure response.
IDEM included the following list of potential contingency measures in its maintenance plan:
a. Lower-Reid vapor pressure gasoline program.
b. Broader geographic applicability of existing measures.
c. Tighten VOC Reasonably Available Control Technology (RACT) on existing sources covered by EPA Control Technique Guidelines issued after the 1990 CAA.
d. Apply VOC RACT to smaller existing sources.
e. One or more transportation control measures sufficient to achieve at least half a percent reduction in actual area wide VOC emissions. Transportation measures will be selected from the following, based upon the factors listed above, after consultation with affected local governments:
i. Trip reduction programs, including, but not limited to, employer-based transportation management plans, area-wide rideshare programs, work schedule changes, and telecommuting;
ii. Traffic flow and transit improvements; and
iii. Other new or innovative transportation measures, not yet in widespread use, that affected local governments deem appropriate.
f. Alternative fuel and diesel retrofit programs for fleet vehicle operations.
g. Apply controls on consumer products consistent with those adopted elsewhere in the U.S.
h. Require VOC or NO <sub>X</sub> emission offsets for new and modified major sources.
i. Require VOC or NO <sub>X</sub> emission offsets for new and modified minor (less than 100 tpy) sources.
j. Increase the ratio of emission offsets required for new sources.
k. Require VOC or NO <sub>X</sub> controls on new minor sources (less than 100 tons).
EPA concludes that the maintenance plan adequately addresses the five basic components of a maintenance plan required under section 175A of the CAA: an attainment emissions inventory, a maintenance demonstration, a commitment for continued air quality monitoring, a verification of continued attainment, and a contingency plan. As such, EPA proposes to find that the maintenance plan SIP revision submitted by IDEM for the Cincinnati area meets the requirements of section 175A of the CAA.
**B. Transportation Conformity**
Under section 176(c) of the CAA, new transportation plans, programs, or projects that receive Federal funding or support, such as the construction of new highways, must “conform” to ( *i.e.,* be consistent with) the SIP. Conformity to the SIP means that transportation activities will not cause or contribute to any new air quality violations, increase the frequency or severity of any existing air quality problems, or delay timely attainment or any required interim emissions reductions or any other milestones. Regulations at 40 CFR part 93 set forth EPA policy, criteria, and procedures for demonstrating and ensuring conformity of transportation activities to a SIP. Transportation conformity is a requirement for nonattainment and maintenance areas.
Under the CAA, States are required to submit, at various times, control strategy SIPs for nonattainment areas and maintenance plans for areas seeking redesignations to attainment of the ozone standard and for continuing maintenance of attainment. *See* the SIP requirements for the 2008 ozone standard in EPA's March 6, 2015, implementation rule (80 FR 12264). These control strategy SIPs and maintenance plans must include Budgets for criteria pollutants, including ozone, and their precursor pollutants (VOC and NO <sub>X</sub> ) to address pollution from on-road transportation sources. The Budgets are the portion of the total allowable emissions that are allocated to highway and transit vehicle use that, together with emissions from other sources in the area, will provide for attainment or maintenance. *See* 40 CFR 93.101.
Under 40 CFR part 93, Budgets for a maintenance area must be established for the last year of the maintenance period. The Budgets serve as a ceiling on emissions from an area's planned transportation system. The Budgets concept is further explained in the Preamble to the November 24, 1993 (58 FR 62188), Transportation Conformity Rule. The Preamble also describes how to establish the Budgets in the SIP and how to revise the Budgets, if needed, after initially establishing them in the SIP.
Indiana's maintenance plan includes NO <sub>X</sub> and VOC Budgets for the last year of the maintenance period (2037) for the Cincinnati area. Indiana's April 1, 2025, maintenance plan submission, including the Budgets for the maintenance area, is available for public comment via this proposed rulemaking. The submission was endorsed by the Governor's designee and IDEM provided opportunity for a public hearing. The Budgets were developed as part of an interagency consultation process which includes Federal, State, and local agencies. The Budgets were clearly identified and precisely quantified. These Budgets, when considered together with all other emission sources, are consistent with maintenance of the 2008 ozone NAAQS.
The Budgets for the Ohio and Indiana portions of the Cincinnati multi-state area are in Table 6. For ease of planning, the smaller Dearborn County, Indiana area is combined with the Ohio Budget. As shown, the 2037 Budgets exceed the estimated 2037 on-road sector emissions. To accommodate future variations in travel demand models and vehicle miles traveled forecast, IDEM allocated a portion of the safety margin, described further below, to the mobile source sector. IDEM has demonstrated that the Cincinnati area can maintain the 2008 ozone NAAQS in the 2037 maintenance year with mobile source emissions in the Ohio and Indiana portions of the area of 11.01 tpd of VOC and 9.32 tpd of NO <sub>X</sub> . Despite partial allocation of the safety margin for each area, emissions will remain under attainment year emission levels.
A “safety margin” is the amount by which the total projected emissions from all sources of a given pollutant are less than the total emissions that would satisfy the applicable requirement for maintenance. *See* 40 CFR 93.101. As noted in Table 5, the emissions in the Cincinnati area are projected to have safety margins of 102.23 tpd of NO <sub>X</sub> and 18.16 tpd of VOC in 2037. The safety margin is calculated as the difference between emissions in the 2016 attainment year and projected emissions in the 2037 maintenance year for all sources in the Cincinnati area. Even if emissions exceeded projected levels by the full amount of the safety margin, the area would still demonstrate maintenance since emission levels would equal those in the attainment year.
IDEM is allocating a portion of that safety margin to the mobile source sector. More specifically, in the Ohio and Indiana portions of the multi-state Cincinnati area, in 2037, IDEM is allocating 1.22 tpd and 1.44 tpd of the NO <sub>X</sub> and VOC safety margins, respectively, shown in Table 6. IDEM is not requesting allocation to the Budgets of the entire available safety margins reflected in the demonstration of maintenance. In fact, the amount allocated to the Budgets represents only a portion of the maintenance year safety margins. Therefore, even though the State is requesting Budgets that exceed the projected on-road mobile source emissions for the maintenance years contained in the demonstration of maintenance, the increase in on-road mobile source emissions that can be considered for transportation conformity purposes is within the safety margins of the ozone maintenance demonstration. Further, once allocated to mobile sources, these safety margins will not be available for use by other sources.
| | Attainment year | 2037 Estimated | 2037 Mobile | 2037 Budgets |
| --- | --- | --- | --- | --- |
| VOC | 23.56 | 9.57 | 1.44 | 11.01 |
| NO | 51.63 | 8.10 | 1.22 | 9.32 |
EPA is proposing to find adequate and approve the Budgets for use to determine transportation conformity in the Cincinnati area because EPA has determined that the area can maintain attainment of the 2008 ozone NAAQS for the maintenance year period with mobile source emissions at the levels of the Budgets. Also, EPA has reviewed the submitted Budgets and proposes to find that they meet the adequacy criteria in the transportation conformity regulations (40 CFR 93.118(e)(4)). As required by the transportation conformity rule (40 CFR 93.118(f)(2)), EPA is using this proposal to notify the public that EPA is beginning a 30-day comment period on the adequacy of the submitted motor vehicle emissions budgets. Comments on the adequacy of the Budgets should be submitted to the docket for this proposal. EPA will make a final determination on the adequacy of the submitted Budgets either in a final action on this proposal or by notifying the State in writing, notifying the public by publishing a *Federal Register* notice, and announcing the determination on EPA's adequacy web page. [^5]
[^5] EPA's adequacy web page can be found here: *https://www.epa.gov/state-and-local-transportation/conformity-adequacy-review-region-5.*
**IV. What action is EPA taking?**
EPA is proposing to approve the second maintenance plan for the 2008 ozone NAAQS submitted by IDEM on April 1, 2025, and supplemented on October 8, 2025, under sections 110(k) and 175A of the CAA for the reasons set forth above, for the Indiana portion of the Cincinnati area as a revision to the Indiana SIP. This second maintenance plan is designed to keep the Cincinnati area in attainment of the 2008 ozone NAAQS through 2037. EPA is also proposing to find adequate and approve the newly established Budgets for the Indiana portion of the Cincinnati maintenance area.
**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 CAA and applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in reviewing SIP submissions, EPA's role is to approve State choices, provided that they meet the criteria of the CAA. Accordingly, this action merely approves State law as meeting Federal requirements and does not impose additional requirements beyond those imposed by State law. For that reason, this action:
• Is not a significant regulatory action subject to review by the Office of Management and Budget under Executive Order 12866 (58 FR 51735, October 4, 1993);
• Is not subject to Executive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review 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 in Executive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject to Executive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;
• Is not a significant regulatory action subject to Executive Order 13211 (66 FR 28355, May 22, 2001); and
• Is not subject to requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) because application of those requirements would be inconsistent with the Clean Air Act.
In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where EPA or an Indian Tribe has demonstrated that a Tribe has jurisdiction. In those areas of Indian country, the rulemaking 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).
**List of Subjects in 40 CFR Part 52**
Environmental protection, Air pollution control, Incorporation by reference, Intergovernmental relations, Nitrogen oxides, Ozone, Reporting and recordkeeping requirements, Volatile organic compounds.
Dated: November 19, 2025.
Anne Vogel,
Regional Administrator, Region 5.