Mercury and Air Toxics Standards
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Rule Summary
In the National Emission Standards for Hazardous Air Pollutants for Coal- and Oil-Fired Electric Utility Steam Generating Units (EGUs), also known as the Mercury and Air Toxics Standards or MATS, EPA set technology-based emissions standards for mercury and other hazardous air pollutants (HAP) emitted by units with a capacity of more than 25 megawatts. These standards reflect levels achieved by the best-performing sources and apply to existing and new EGUs.
MATS, along with significant changes in the power sector, has achieved significant health and environmental benefits by reducing a broad range of hazardous air pollutants. By 2017 mercury emissions had dropped by 86 percent - down to approximately 4 tons. Acid gas HAP and non-mercury metals are down 96 percent and 81 percent respectively when compared to 2010 levels.
Information on Proposed Repeal
On June 11, 2025, EPA proposed to repeal certain amendments finalized in 2024 to the MATS Rule.
Rule Text Changes in Redline-Strikeout (RLSO) for the Proposed Repeal of Amendments to the NESHAP
Rule History
02/15/2023 - Final Revocation of the 2020 Reconsideration, and Affirmation of the Appropriate and Necessary Supplemental Finding
07/17/2020 - Final Electronic Reporting Provisions (85 FR 55744)
05/22/2020 - Final Supplemental Finding for MATS and Risk and Technology Review (85 FR 31286)
04/03/2020 - Proposed Electronic Reporting Revisions (85 FR 20342)
12/27/2018 - Proposed Revised Supplemental Finding for MATS and Risk and Technology Review (84 FR 2670)
08/08/2016 - Denials of Petitions for Reconsideration – Startup and Shutdown Provisions
- Notice of Final Action Denying Reconsideration on the MATS Startup and Shutdown Provisions (81 FR 52346)
- Denial Document for Reconsideration of Certain Startup and Shutdown Issues; MATS
04/14/2016 - Final Supplemental Finding about MATS and Costs (81 FR 24420)
03/17/2016 - Final Technical Corrections (81 FR 20172)
11/20/2015 - Proposed Supplemental Finding about MATS and Costs (80 FR 75025)
04/21/2015 - Denial of Petitions for Reconsideration of Certain Issues (80 FR 24218)
03/09/2015 - Interim Final Electronic Reporting Requirements (80 FR 15510)
12/19/2014 - Proposed Technical Corrections (80 FR 8442)
11/07/2014 - Final Updates to the Startup and Shutdown Provisions (79 FR 68777)
11/07/2014 - Direct Final Rule (79 FR 68795) with Parallel Proposal (79 FR 68840) on Electronic Reporting
03/28/2013 - Final Updates to the Standards for New Power Plants (78 FR 24073)
02/16/2012 - EPA Announces Final Mercury and Air Toxics Standards for Power Plants (77 FR 9304)
05/03/2011 - EPA Announces Proposed Mercury and Air Toxics Standards for Power Plants (76 FR 24976)
Additional Resources
Learn more about mercury, products that contain it, and actions to reduce it.