The Environmental Protection Agency (EPA) is taking final action to approve a revision to the Maricopa County Air Quality Department's (MCAQD or ``County'') portion of the Arizona State Implementation Plan (SIP). This revision concerns emissions of oxides of nitrogen (NO<INF>X</INF>) and particulate matter (PM) from combustion equipment and internal combustion engines. We are approving local rules that regulate these emission sources under the Clean Air Act (CAA or ``Act'') and making the determination that the County's control measures implement Reasonably Available Control Technology (RACT) for major sources of NO<INF>X</INF> under the 2008 8-hour ozone National Ambient Air Quality Standard (NAAQS).