The Environmental Protection Agency (EPA) is approving portions of a State Implementation Plan (SIP) submission provided by the State of Mississippi, through the Mississippi Department of Environmental Quality (MDEQ), through a letter dated January 25, 2021. 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. EPA is approving portions of Mississippi's January 25, 2021, submittal as the state has certified that its SIP contains provisions that ensure the 2015 8-hour ozone NAAQS is implemented, enforced, and maintained in Mississippi. EPA has determined that Mississippi's infrastructure SIP submission satisfies certain required infrastructure elements for the 2015 8-hour ozone NAAQS.