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On February 16, 2012, EPA promulgated National Emission Standards for Hazardous Air Pollutants for Coal- and Oil-fired Electric Utility Steam Generating Units (77 FR 9304). The rule (40 CFR part 63, subpart UUUUU), commonly referred to as the Mercury and Air Toxics Standards (MATS), includes standards to control hazardous air pollutant (HAP) emissions from new and existing coal- and oil-fired electric utility steam generating units (EGUs) located at both major and area sources of HAP emissions. There have been several regulatory actions regarding MATS since February 2012, including a May 22, 2020, action that completed a reconsideration of the appropriate and necessary finding for MATS and finalized the residual risk and technology review (RTR) conducted for the Coal- and Oil-Fired EGU source category regulated under MATS (85 FR 31286). The Biden Administration's Executive Order 13990, Protecting Public Health and the Environment and Restoring Science To Tackle the Climate Crisis, "directs all executive departments and agencies (agencies) to immediately review and, as appropriate and consistent with applicable law, take action to address the promulgation of Federal regulations and other actions during the last 4 years that conflict with these important national objectives, and to immediately commence work to confront the climate crisis." Section 2(a)(iv) of the Executive Order specifically directs that the Administrator consider publishing, as appropriate and consistent with applicable law, a proposed rule suspending, revising, or rescinding the ‘‘National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units Reconsideration of Supplemental Finding and Residual Risk and Technology Review,’’ 85 FR 31286 (May 22, 2020). As directed by Executive Order 13990, EPA reviewed the RTR portion of the May 22, 2020 final action and, proposed to update and strengthen the MATS on April 24, 2023 (88 FR 24854). The final rule signed on April 25, 2024, finalized a lower filterable particulate matter (fPM), surrogate for non-Hg HAP metals, for existing coal-fired EGUs, reduced the Hg limit for lignite-fired EGUs, and required use of particulate matter continuous emission monitoring systems (PM CEMS) for demonstrating compliance with the revised fPM limit. EPA also finalized amendments revising the startup requirements in MATS to assure better emissions performance during startup. EPA finalized the Revocation of the 2020 Reconsideration and Affirmation of the Appropriate and Necessary Supplemental Finding on February 15, 2023 (88 FR 13956).