The Environmental Protection Agency (EPA) is proposing to approve revisions to the California State Implementation Plan (SIP) concerning the provisions for clean fuels or advanced control technology for boilers for the 2015 ozone national ambient air quality standards (``2015 ozone NAAQS'') in the San Joaquin Valley and Los Angeles--South Coast Air Basin, California (``South Coast'') ozone nonattainment areas. The SIP revisions include the ``Certification that the San Joaquin Valley Unified Air Pollution Control District's Current Rules Address the Clean Air Act's Clean Fuels for Boilers Requirements for the 2015 8-hour Ozone Standard'' for San Joaquin Valley (``2021 San Joaquin Valley Certification'') and the ``Clean Fuels for Boilers Compliance Demonstration for the South Coast Air Basin'' for South Coast (``2021 South Coast Certification''), both submitted on August 3, 2021. We are proposing to approve these revisions under the Clean Air Act (CAA or ``the Act''), which establishes clean fuels or advanced control technology for boilers requirements for ``Extreme'' ozone nonattainment areas.