The Environmental Protection Agency (EPA) is taking final action to approve a revision to the San Diego County Air Pollution Control District (SDCAPCD) portion of the California State Implementation Plan (SIP). The California Air Resources Board (CARB) submitted the rule, on behalf of SDCAPCD, to the EPA as part of the requirement to implement major source reasonable available control technology (RACT) for emissions of oxides of nitrogen (NO<INF>X</INF>) for the San Diego County ozone nonattainment area. This revision concerns NO<INF>X</INF> emissions from boilers, process heaters, and steam generators. We are approving a local rule to regulate these emission sources under the Clean Air Act (CAA or the ``Act'').