The Environmental Protection Agency (EPA) is taking final action to approve state implementation plan (SIP) revisions to the Yolo-Solano Air Quality Management District (YSAQMD) portion of the California SIP. These revisions concern emissions of oxides of nitrogen (NO<INF>X</INF>) from biomass boilers, and address reasonably available control technology (RACT) requirements for major sources of NO<INF>X</INF> in the portion of the Sacramento Metro, CA, nonattainment area that is subject to YSAQMD jurisdiction.