On October 1, 2020, the Environmental Protection Agency (“EPA”) issued its final rule allowing for a source classified as a “major source” of hazardous air pollutants (“HAP”) under section 112(a) of the Clean Air Act to reclassify as an “area source.”  A “major source” emits or has the “potential to emit” 10 tons per year or more of a single HAP or 25 tons per year or more of a combination of HAP.  The EPA had long-followed the “once-in-always-in” policy, under which a facility that qualified as a major source of HAPs as of the “first substantive compliance date” of the applicable Maximum Achievable Control Technology (“MACT”) standard was permanently subject to that standard, even if the source was later able to reduce its emissions below major source applicability thresholds.  With the final rule, branded as the “Major MACT to Area” (“MM2A”), EPA codified the withdrawal of the “once-in-always” policy and provided the requirements that apply to major sources choosing to reclassify, including reclassification that occurs after the first substantive compliance date of an applicable MACT standard.