Increased mortality from a two-year delay in Mercury and Air Toxics Standards (MATS) emission-reductions of filterable PM2.5 at specific coal-fired power plants in the United States.

Background: In 2024, the US Environmental Protection Agency tightened the Mercury and Air Toxics Standards (MATS) for emissions of filterable particulate matter (fPM) from coal-fired power plants to 0.010 lb/MMBtu. In April 2025, a presidential proclamation stated that 47 specific power plant companies received a 2-year exemption from the new requirements. The proclamation provided no estimates of the resulting health impacts. Methods: Our approach applies conventional risk-assessment calculations for mortality from inhalation of filterable PM2.5 (fPM2.5) emissions, for "with" versus "without" the exemption, across four steps: (1) calculate fPM2.5 emissions, based on government databases; (2) calculate the change in ambient PM2.5 concentrations, using the Intervention Model for Air Pollution (InMAP) source-receptor matrix (ISRM); (3) calculate mortality impacts from inhalation of PM2.5, using the Orellano et al., 2024 concentration-response function (CRF; relative risk (RR) per 10 μg/m3: 1.095, 95% confidence interval (CI) = 1.064, 1.127; in sensitivity analyses, we employ other CRFs); (4) aggregate results (e.g., by US state). Results: Most (83%) of the exempted power plant facilities already have sufficient control technology installed that they operate below the new MATS limit, indicating that much of that fleet already adopted cleaner technologies. For the remaining 17% of facilities, the proclamation will increase total fPM2.5 emissions to ~6,900 tons, from ~4,400 tons. We estimate that the additional ~2,500 tons emitted will lead to 32 (95% CI = 22, 43) deaths. The highest mortality is in St. Louis, Missouri, (population: 2.2 million) with an estimated 14 (95% CI = 10,19) deaths. The increased mortality is, for some states (e.g., Missouri, and Pennsylvania), caused by mostly in-state emissions; for other states (e.g., Illinois, Maryland, New Jersey, and Virginia), the cause is out-of-state emissions. Discussion: Results here quantify a portion of the health impacts but leave unquantified nonmortality impacts, impacts from hazardous air pollutant (HAP) exposures, and noninhalation pathways. The reduced computational demands of the air pollution model employed here allows for more timely investigation of government actions than would traditional air dispersion modeling. Sensitivity analyses yielded mortality results that ranged from 47% lower to 169% higher than the core findings. Conclusions: We estimate that a 2-year delay in MATS emission reductions of fPM2.5 at the exempted coal-fired power plants will lead to 32 (95% CI = 22, 43) additional deaths.