EPA is taking direct final action to approve a revision to the Knox County portion of the Tennessee State Implementation Plan (SIP) submitted by the State of Tennessee on April 21, 2008. The revision pertains to the Knox County Department of Air Quality Management (KCDAQM) Regulation, Section 25.0 "Permits," specifically subsection 25.6--Exemptions. This revision removes "mobile sources" from the list of exempted air contaminant sources, with respect to operating permits and reserves subsection 25.6.A. This revision is part of KCDAQM strategy to attain and maintain the National Ambient Air Quality Standards for 8-hour ozone, particulate matter (PM)<INF>2.5</INF> and PM<INF>10</INF>. This revision was certified by the Tennessee Department of Environment and Conservation to be at least as stringent as the State of Tennessee's existing requirements in Chapter 1200-3- 9-.04 "Exemptions," and is being approved pursuant to section 110 of the Clean Air Act (CAA).