Air Plan Approval; Indiana; Second Maintenance Plan for 2008 Ozone NAAQS

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.