The Environmental Protection Agency (EPA) is approving state implementation plan (SIP) revisions submitted by the Commonwealth of Kentucky, through the Energy and Environment Cabinet (Cabinet), on March 29, 2021. The SIP revisions include the 1997 8-hour ozone National Ambient Air Quality Standards (NAAQS or standards) Limited Maintenance Plans (LMPs) for the Kentucky portion (hereinafter referred to as the Boyd County Area) of the Huntington-Ashland, WV-KY 1997 8- hour ozone maintenance area (hereinafter referred to as the Huntington- Ashland, WV-KY Area) and the Kentucky portion (hereinafter referred to as the Christian County Area) of the Clarksville-Hopkinsville, TN-KY 1997 8-hour ozone maintenance area (hereinafter referred to as the Clarksville-Hopkinsville, TN-KY Area). EPA is approving Kentucky's LMPs for the Boyd County and Christian County Areas because they provide for the maintenance of the 1997 8-hour ozone NAAQS within these Areas through the end of the second 10-year portion of the maintenance period. The effect of this action would be to make certain commitments related to maintenance of the 1997 8-hour ozone NAAQS in the Boyd County and Christian County Areas federally enforceable as part of the Kentucky SIP.