On February 24, EPA published the final rule repealing the 2024 amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Coal- and Oil-Fired Electric Utility Steam Generating Units (EGUs), commonly known as the Mercury and Air Toxics Standards (MATS). The rule affects coal- and oil-fired EGUs of more than 25 megawatts that serve generators producing electricity for sale, located at both major and area sources of HAP emissions. The repeal returns affected facilities to the standards established in the 2012 MATS Rule, which EPA maintains continue to protect public health with an ample margin of safety. The final rule becomes effective April 27, 2026.
Key Provisions and Legal Rationale
Provisions Repealed
The final rule repeals three specific amendments that were promulgated in the 2024 Final Rule:
- Tightened Filterable Particulate Matter (fPM) Emission Standard Repealed. EPA is repealing the revised fPM emission standard for existing coal-fired EGUs, which had been tightened from 0.030 lb/MMBtu to 0.010 lb/MMBtu. The fPM limit is a surrogate for non-mercury (non-Hg) HAP metal emissions. The standard reverts to the original 2012 limit. Corresponding reductions to total and individual non-Hg HAP metal emission standards are also repealed.
- PM CEMS Compliance Demonstration Requirement. EPA is repealing the mandate that all coal- and oil-fired EGUs demonstrate compliance with the fPM emission standard exclusively through PM Continuous Emissions Monitoring Systems (CEMS). Owners and operators may again choose among quarterly stack testing, continuous parametric monitoring systems (CPMS), or PM CEMS to demonstrate compliance. The Low Emitting EGU (LEE) program for fPM and non-Hg HAP metals is also reinstated; units that had previously qualified for LEE status do not need to re-demonstrate qualification.
- More Stringent Mercury Emission Standard for Lignite-Fired EGUs Repealed. EPA is repealing the revised mercury standard for lignite-fired EGUs, which had been lowered from 4.0 lb/TBtu to 1.2 lb/TBtu, reverting to the 2012 standard.
Legal Rationale
EPA's rationale for the repeal rests on several independent grounds under CAA section 112(d)(6), which requires the Agency to revise emission standards only as "necessary" in light of developments in practices, processes, and control technologies.
For the fPM standard, EPA advances two separate and severable bases. First, the Agency finds that the cost-effectiveness of the revised standard — approximately $11.1 million per ton of non-Hg HAP metals — is significantly higher than values previously accepted in other technology reviews under section 112. Second, EPA concludes that the low remaining risk from non-Hg HAP metals—— warrants greater emphasis on cost when determining whether revisions are "necessary." The 2020 Residual Risk Review found cancer risk below one-in-one million for every coal-fired EGU.
For the PM CEMS requirement, EPA finds that mandating CEMS was an unnecessary expense, particularly given that the fPM standard is reverting to the 2012 level. Up to two-thirds of EGU owners and operators would have faced higher compliance costs under the CEMS-only approach relative to using quarterly stack testing or CPMS. EPA estimates annual cost savings of approximately $2.9 million from repealing the PM CEMS mandate after the exemption period. The Agency also determined that there are multiple reliable performance indicators — such as ESP opacity, corona power, and voltage readings, as well as fabric filter bag leak detection systems and pressure differential monitoring — that adequately inform operators of control device malfunctions without requiring continuous PM emissions data.
For the lignite mercury standard, EPA concludes that the 2024 rule was based on insufficient data and failed to demonstrate that the 1.2 lb/TBtu standard is achievable across the broad range of boiler types and highly variable compositions of lignite fuels.
Severability and Additional Provisions
EPA emphasizes that the repeal of each of the three requirements is independently justified and severable from the others. If a court were to invalidate any one element of the final rule, EPA intends the remainder to remain effective. Additionally, the final rule makes minor clarifications to electronic reporting requirements.
Implications
The final rule provides immediate regulatory relief to coal- and oil-fired EGU owners and operators, particularly those that were facing substantial capital investments to comply with the now-repealed 2024 standards.
Importantly, compliance obligations under the 2012 MATS Rule remain in full force and effect, including emission standards for mercury, acid gases, non-Hg HAP metals, and organic HAPs. Facilities that had been planning compliance expenditures for the 2024 amendments — including PM control upgrades, PM CEMS installations, and enhanced mercury sorbent injection systems for lignite units — may now reassess those capital plans. The restoration of flexibility in compliance demonstration methods (quarterly stack testing, CPMS, or PM CEMS) and the reinstatement of the LEE program provide additional operational flexibility.
Of note is that the Regulatory Impact Analysis projects negligible impacts on retail electricity prices, natural gas prices, and natural gas consumption across all analysis years. Small increases in coal production for power sector use are projected (0.1% in 2030 and 0.3% in 2035), and the average price of coal delivered to the power sector may increase by 0.2% in 2030 and 2035. The RIA also declines to quantify health benefits, a change from the June 2025 RIA for the Proposed Rule in keeping with the Agency’s recently announced policy.
For EGUs receiving temporary compliance extensions under the Presidential Proclamation issued pursuant to CAA section 112(i)(4) — which exempted certain sources listed in Annex 1 from compliance with the 2024 rule for a two-year period beginning July 8, 2027 — this repeal provides long-term relief. Those units will remain subject to the 2012 MATS Rule but will no longer face the prospect of more stringent 2024 requirements at the conclusion of the exemption period.
Next Steps
Given the significance of this deregulatory action and the history of litigation surrounding the MATS rule, legal challenges to the repeal should be anticipated. The final rule specifies that challenges must be filed by April 27, 2026 in the D.C. Circuit.
For More Information
Van Ness Feldman closely monitors and counsels clients on energy transition and air quality law and policy, including the Clean Air Act. For further details or assistance with assessing the impacts of this final rule, please contact Britt Speyer Fleming or any member of VNF's Environmental Team.