Mercury and Air Toxics Standards

Mercury and Air Toxics Standards
Name	Mercury and Air Toxics Standards
Acronym	MATS
Jurisdiction	United States
Administered by	Environmental Protection Agency
Statute	Clean Air Act
Effective	2012
Type	Regulation

Mercury and Air Toxics Standards are federal Environmental Protection Agency regulations promulgated under the Clean Air Act to limit emissions of hazardous air pollutants from coal- and oil-fired power plants, aiming to reduce releases of mercury, arsenic, lead, cadmium, and acid gases. The rule was finalized during the Administration of Barack Obama and has been subject to multiple judicial reviews by the United States Court of Appeals for the D.C. Circuit and the Supreme Court of the United States, influencing national environmental policy and energy sector practices.

Background and Rationale

The rule's development responded to scientific assessments by the National Academy of Sciences, findings from the Centers for Disease Control and Prevention, and air quality studies conducted by the National Oceanic and Atmospheric Administration and the United States Geological Survey that linked atmospheric mercury deposition to bioaccumulation in fish and risks to vulnerable populations such as fetuses and children. Congressional action under the Clean Air Act Amendments of 1990 and policy guidance from the Office of Management and Budget and the Council on Environmental Quality framed regulatory authority, while advocacy from organizations like the Natural Resources Defense Council and the Sierra Club pressed for stringent limits against opposition from groups including the American Petroleum Institute and the National Mining Association.

Regulatory History

Initial rulemaking traces to Environmental Protection Agency risk assessments and a 2000 Supreme Court of the United States decision interpreting hazardous pollutant regulation under the Clean Air Act. The 2011 and 2012 rulemakings were informed by technical analyses from the Electric Power Research Institute, compliance cost studies by the Energy Information Administration, and commentary from state agencies such as the California Air Resources Board and the Texas Commission on Environmental Quality. Judicial milestones include rulings by the United States Court of Appeals for the D.C. Circuit and a 2015 opinion by the Supreme Court of the United States clarifying cost consideration in regulation, followed by subsequent rule reconsiderations during the Trump administration and reinstatements during the Biden administration.

Standards and Requirements

The standards set numeric emission limits and performance requirements for hazardous air pollutants from existing and new large fossil fuel combustion units, specifying technology-based controls such as activated carbon injection, fabric filters, wet scrubbers, and selective catalytic reduction systems. Compliance benchmarks reference continuous emissions monitoring systems approved by the Environmental Protection Agency and testing protocols established by the American Society for Testing and Materials and the United States Environmental Protection Agency Reference Methods. The rule delineates requirements for major source classification, operating permits under New Source Review and Title V of the Clean Air Act, and timeline milestones coordinated with state environmental protection agencies and regional grid operators.

Implementation and Compliance

Utilities and independent power producers responded with retrofits, retirements, and fuel switching strategies guided by planners at the North American Electric Reliability Corporation and analyses from the Institute of Electric and Electronics Engineers. Compliance strategies were subject to oversight by state permitting authorities, enforcement actions by the Environmental Protection Agency, and reporting to the Energy Information Administration and the Department of Energy. Financing of control installations involved investment banks, the World Bank-linked private sector, and tax equity structures influenced by guidance from the Internal Revenue Service. Training and workforce adjustments engaged unions such as the United Mine Workers of America and trade groups like the Edison Electric Institute.

Environmental and Health Impacts

Modeling and monitoring by the Environmental Protection Agency, National Oceanic and Atmospheric Administration, and the United States Fish and Wildlife Service documented reductions in atmospheric mercury deposition and co-benefits in decreased emissions of sulfur dioxide and nitrogen oxides. Public health assessments by the Centers for Disease Control and Prevention and the National Institutes of Health associated the rule with lowered exposure risks for pregnant women and children and projected declines in neurodevelopmental impairments and cardiovascular events. Ecosystem studies from institutions like the Smithsonian Institution and the Woods Hole Oceanographic Institution recorded improvements in aquatic food webs and piscivorous bird populations.

Legal Challenges and Litigation

Litigation involved coal producers, utility companies, states, and environmental groups in courts including the United States Court of Appeals for the D.C. Circuit and the Supreme Court of the United States, raising issues under administrative law doctrines such as Chevron deference and major questions doctrine. Key litigants included the American Lung Association, the Utility Air Regulatory Group, the State of West Virginia, and industry plaintiffs represented by firms linked to the American Coal Council. Decisions addressed statutory interpretation of the Clean Air Act, the role of cost considerations in determining appropriate and necessary regulation, and procedural obligations under the Administrative Procedure Act.

Economic and Industry Effects

Economic analyses by the Congressional Budget Office, the Office of Management and Budget, and the Energy Information Administration estimated compliance costs, public health benefits, and net job impacts, while research from academic centers at Harvard University, Massachusetts Institute of Technology, and Resources for the Future examined market responses including plant retirements, shifts toward natural gas and renewable energy sources, and effects on electricity prices. Industry adaptation involved capital expenditures by utilities like Duke Energy, American Electric Power, and Southern Company, procurement practices with equipment manufacturers, and influence on international negotiations at forums such as the United Nations Environment Programme and trade discussions involving the World Trade Organization.

Category:United States environmental law