The Environmental Protection Agency (EPA) is taking final action to approve revisions to the California State Implementation Plan (SIP) concerning the base year emissions inventories for 18 areas designated as nonattainment areas (NAAs) for the 2015 ozone national ambient air quality standards (``2015 ozone NAAQS'') submitted on July 24, 2020. The areas include Amador County, Butte County, Calaveras County, Imperial County, Kern County (Eastern Kern), Los Angeles--San Bernardino Counties (West Mojave Desert), Los Angeles--South Coast Air Basin, Mariposa County, Nevada County (Western part), Riverside County (Coachella Valley), Sacramento Metro, San Francisco Bay Area, San Joaquin Valley, San Luis Obispo (Eastern part), Sutter Buttes, Tuolumne County, Tuscan Buttes, and Ventura County. We are approving these revisions under the Clean Air Act (CAA), which establishes emissions inventory requirements for all ozone nonattainment areas.