Air Plan Approval; Mississippi; PSD and Air Quality Modeling Infrastructure Requirements for the 2015 8-Hour Ozone National Ambient Air Quality Standards

The Environmental Protection Agency (EPA) is conditionally approving portions of a State Implementation Plan (SIP) submission provided by the State of Mississippi, through the Mississippi Department of Environmental Quality (MDEQ), via a letter dated January 25, 2021, and supplemented through a letter dated November 18, 2022. This approval pertains to certain infrastructure requirements of the Clean Air Act (CAA or Act) for the 2015 8-hour ozone national ambient air quality standards (NAAQS or standards). Whenever EPA promulgates a new or revised NAAQS, the CAA requires that each state adopt and submit a SIP for the implementation, maintenance, and enforcement of that NAAQS. The January 25, 2021, SIP submission addresses all infrastructure elements except for those pertaining to the contribution to nonattainment or interference with maintenance of the NAAQS in other states. EPA is conditionally approving the portions of the submittal related to the prevention of significant deterioration (PSD) infrastructure elements and the air quality modeling element.