The Environmental Protection Agency (EPA or Agency) is taking final action to approve a revision to the Chattanooga portion of the Tennessee State Implementation Plan (SIP), provided by the State of Tennessee, through the Tennessee Department of Environment and Conservation from Chattanooga/Hamilton County Air Pollution Control Bureau by a letter dated September 12, 2018. The revision updates the National Ambient Air Quality Standards (NAAQS) in the Chattanooga portion of the Tennessee SIP. The amendments in the Tennessee SIP reflect recent revisions made to the federal NAAQS. EPA is approving the changes because they are consistent with the Clean Air Act (CAA or Act).