On July 6, 2011, the US Environmental Protection Agency (EPA) finalized a rule designed to protect the health of Americans by reducing air pollution. The rule, which is known as the Cross-State Air Pollution Rule (CSAPR), requires states with significant generation capacity to improve air quality by reducing power plant emissions that contribute to ozone and/or fine particle pollution in other states. The rule required significant reductions in emissions from power plants in 28 Eastern and Midwestern states. This rule replaced EPA's 2005 Clean Air Interstate Rule (CAIR).
On Aug. 21, 2012, the United States Court of Appeals for the District of Columbia, in a 2-to-1 decision vacated the Cross-State Air Pollution Rule (CSAPR).
On April 29, 2014 the Supreme Court ruled 6 to 2 in favor of the Cross-State Air Pollution Rule (CSAPR) reversing the decision by the U.S. Court of Appeals for the D.C. Circuit.