The Environmental Protection Agency (EPA) is approving a State Implementation Plan (SIP) revision submitted by the State of Tennessee on April 9, 2021. Specifically, EPA is approving updates to the incorporation by reference of Federal guidelines on air quality modeling in the Tennessee SIP. EPA is also converting the previous conditional approval regarding infrastructure SIP prevention of significant deterioration (PSD) elements for the 2015 ozone national ambient air quality standards (NAAQS) for Tennessee to a full approval. EPA is approving this revision pursuant to the Clean Air Act (CAA or Act).