May 19, 2026

EPA Reverts MATS Rule to Pre-2024 Requirements

MATS, the mercury and air toxics standards, is a more common name for the coal- and oil-fired electric utility steam generating units (EGUs) NESHAP. Part 63, Subpart UUUUU contains emission standards for pollutants such as mercury (Hg), non-Hg HAPs, and hydrogen chloride (HCl), provides for alternative pollutant monitoring, such as filterable particulate matter (fPM), and requires numerous work practice standards. EPA estimates that since the standard’s promulgation in 2012, emissions from affected sources have decreased by 90% for Hg, 96% for acid gas HAPs, and 81% for non-Hg metals.

On May 7, 2024, EPA finalized amendments to MATS that would have cut mercury, particulate matter, and other pollutant emissions by tens of thousands of tons, yielding estimated health and climate benefits in the hundreds of millions of dollars. [89 FR 38508] However, on February 24, 2026, the agency repealed the 2024 rule, stating the revisions are unnecessary, impose unwarranted costs, and raise technical feasibility concerns. [91 FR 9088] Three key aspects of the 2024 rule have been reversed and took effect on April 27, 2026:

The non-Hg metal surrogate of fPM standard for existing coal-fired EGUs has reverted from 0.01 lb/MMBtu back to 0.03 lb/MMBtu. EPA claims “the cost-effectiveness of the [2024 standard] is not reasonable and compares unfavorably to prior decisions on cost-reasonableness across other” reviews. [91 FR 9095]
Continuous emission monitoring systems (CEMS) are no longer required, and coal-fired EGUs may rely on quarterly stack testing instead. The agency “concludes that mandating the use of PM CEMS and removing previously available compliance alternatives” is unnecessary. [91 FR 9102]
The lignite-fired EGU mercury standard is bumped back up to 4.0 lb Hg/TBtu, rather than remaining at the same 1.2 lb Hg/TBtu emission standard as bituminous- and subbituminous-fired EGUs or an alternative output-based standard of 0.013 lb/GWh. EPA states the 2024 “standard was based on insufficient data to demonstrate that lignite units can meet the lower limit over the range of boiler types and variable compositions of fuels.” [91 FR 9106]

Consequences of the 2026 MATS Repeal

Because the economic costs of harm to human health caused by fine particles are no longer considered in EPA rules (see our previous article, where the agency places this decision in a stationary turbine review), the true cost of repealing the 2024 MATS rule is understated. According to an agency fact sheet released when the 2024 rule was proposed, the estimated annualized compliance costs would have ranged from $33 million to $38 million. However, the health benefits would have ranged from $170 million to $220 million, and the climate benefits could have reached $170 million.

Taking EPA’s updated annualized compliance cost savings of between $69 million and $78 million into account, these savings are still far less than the price paid by the American populace. While coal is an undeniable part of a strong electric grid, supplying reliable baseload power 24/7, reduced operating costs for coal-fired power plants don’t change the fact that mercury is an undeniably persistent and bioaccumulative neurotoxin. Nor do those reduced costs have the luxury of ignoring the estimated 460,000 deaths attributed to coal power plants. Even disregarding the negative health impacts of the MATS reversal, should EPA rules meant to protect human health and the environment be based on the demands of data centers and artificial intelligence applications?

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