EPA Approves Indiana's Decade-Long Ozone Air Plan
Published Date: 11/21/2025
Proposed Rule
Summary
The EPA wants to approve Indiana’s updated plan to keep the air clean from ozone pollution in the Cincinnati area for 10 more years. This plan affects local residents and drivers by making sure pollution limits stick and are enforceable. You’ve got until December 22, 2025, to share your thoughts, but no extra costs or big changes are expected.
Analyzed Economic Effects
3 provisions identified: 2 benefits, 0 costs, 1 mixed.
Indiana SIP Makes Ozone Limits Enforceable
If you live or drive in the Indiana portion of the Cincinnati, Ohio-Kentucky-Indiana area (including Dearborn County), EPA is proposing to approve Indiana’s second maintenance plan to keep the area in attainment of the 2008 ozone standard through 2037 and to make certain commitments federally enforceable as part of the Indiana State Implementation Plan (SIP). You can submit comments on this proposal by December 22, 2025.
Contingency Triggers and Possible Controls
Indiana’s maintenance plan includes contingency responses if ozone rises: a warning-level study is triggered when a 1-year fourth-highest 8-hour ozone is 0.079 ppm or higher or a 2-year fourth-highest is 0.076 ppm or higher; an action-level response is triggered when the 3-year average fourth-highest 8-hour ozone is equal to 0.076 ppm or higher. If triggered, IDEM must study and, if needed, adopt measures (examples include tighter VOC RACT, fuel vapor controls, offsets for new/modified sources, transportation measures, and diesel retrofit programs) with implementation timelines of within 12 months for warning responses and within 18 months for action responses after the relevant ozone season.
2037 Mobile Emissions Budgets Proposed
If you are involved in federally funded transportation planning or projects in the Indiana portion of the Cincinnati area, EPA is proposing to find adequate and approve motor vehicle emissions Budgets for the 2037 maintenance year: VOC 11.01 tons/day and NOX 9.32 tons/day. These Budgets will be used to determine whether new federally funded transportation plans, programs, or projects 'conform' to the SIP; comments are due December 22, 2025.
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