The Mercury and Air Toxics Standards (MATS) are EPA regulations first established in 2012 under Section 112 of the Clean Air Act. They set the first-ever federal limits on mercury, arsenic, lead, acid gases, and other hazardous air pollutants from coal- and oil-fired power plants. Before MATS, power plants were the largest unregulated source of mercury emissions in the United States. The standards led to a 90% reduction in mercury emissions and were estimated to prevent up to 11,000 premature deaths annually. In 2024, EPA strengthened MATS with tighter limits and continuous monitoring requirements, but the Trump administration repealed those updates in February 2026.