The Environmental Protection Agency (EPA) is taking final action to approve revisions to the Butte County Air Quality Management District (BCAQMD), El Dorado County Air Quality Management District (EDCAQMD), Mojave Desert Air Quality Management District (MDAQMD), San Diego County Air Pollution Control District (SDCAPCD) and Ventura County Air Pollution Control District (VCAPCD) portions of the California State Implementation Plan (SIP). These revisions concern rules that include definitions for certain terms that are necessary for the implementation of local rules that regulate sources of air pollution. We are approving the definitions rules under the Clean Air Act (CAA or the Act).