Progress Report

Affected Units

Affected Units Figures

Source: EPA, 2021
Last updated: 05/2021

Related Figures

Affected Units in CSAPR and ARP, 2020
Affected Units in CSAPR and ARP, 2020


Acid Rain Program (ARP)

  • In 2020, the ARP SO₂ requirements applied to 3,287 fossil fuel-fired combustion units at 1,159 facilities across the country; 536 units at 246 facilities were subject to the ARP NOₓ program.

Cross-State Air Pollution Rule (CSAPR)

  • In 2020, there were 2,181 affected EGUs at 678 facilities in the CSAPR SO₂ programs. Of those, 1,747 (80 percent) were also covered by the ARP.
  • In 2020, there were 2,181 affected EGUs at 678 facilities in the CSAPR NOₓ annual program and 2,527 affected EGUs at 809 facilities in the CSAPR NOₓ ozone season program. Of those, 1,747 (80 percent) and 2,063 (82 percent), respectively, were also covered by the ARP.

Mercury and Air Toxics (MATS)

  • The Mercury and Air Toxics Standards (MATS) set limits on the emissions of hazardous air pollutants from coal- and oil-fired electric utility steam generating units in all 50 states and U.S. territories. MATS was issued under section 112 of the Clean Air Act. EPA is including a summary of the mercury data submitted by affected sources in this report.
  • In 2020, 428 units at 197 facilities reported hourly mercury emissions to EPA under MATS.

Background Information

In general, the ARP and CSAPR programs apply to large EGUs – boilers, turbines, and combined cycle units – that burn fossil fuel, serve generators with nameplate capacity greater than 25 megawatts, and produce electricity for sale. MATS applies only to coal- and oil-fired steam generating EGUs (i.e., utility boilers). It does not apply to combustion turbines, combined cycle units, or to natural gas-fired utility boilers. The EGUs affected by these programs include a range of unit types, including units that operate year-round to provide baseload power to the electric grid, as well as units that provide power only on peak demand days. The ARP NOₓ program applies to a subset of these units that are older and historically coal-fired.