Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act

Rule Summary

This rule implements the Clean Air Act language that allows a “major source” of hazardous air pollutants (HAP) to reclassify as an “area source” after acting to limit emissions. This rule is commonly referred to as Major MACT (Maximum Achievable Control Technology) to Area Source, also known as "MM2A."

Major sources that reclassify to area source status pursuant to the requirements in this final rule, will no longer be subject to major source National Emissions Standards for Hazardous Air Pollutant (NESHAP) requirements and may be exempt from Title V operating permit requirements, as long as the sources’ emissions remain below the applicable emissions thresholds.

Rule History

1/07/2025 - Final Rule Correction ; 9/10/2024 - Final Rule (89 FR 73293)

The 2024 MM2A Rule amended the 2020 MM2A Rule by requiring sources of persistent and bioaccumulative hazardous air pollutants (HAP) listed in Clean Air Act (CAA) section 112(c)(6) to continue to comply with major source emission standards under CAA section 112(d)(2) or standards under CAA section 112(d)(4) even if the sources reclassify as area sources.
On June 20, 2025, S.J. Res. 31, a joint Congressional resolution (under the Congressional Review Act, or “CRA”) disapproving the 2024 amendments to the 2020 MM2A Rule was signed into law by President Donald J. Trump. By the terms of the CRA, the signing into law of the joint resolution of disapproval means that the 2024 MM2A Rule is “treated as though [it] had never taken effect.” 5 U.S.C. 801(f).

9/21/2023 – Proposed Rule (88 FR 66336)

12/28/2020 – Technical Correction to Final Rule (85 FR 84261)

11/19/2020 – Final Rule (85 FR 73854)

07/31/2019 – Public Hearing Notice

06/26/2019 – Proposed Rule (84 FR 36304)

01/25/2018 – Guidance Memorandum