The U.S. Court of Appeals for the District of Columbia denied EPA’s requests to rehear the case that struck down the federal cross-state air pollution rule, also known as CSAPR. Last August, a three-judge panel in EME Homer City Generation LP v. EPA struck the rule that would have required certain power plants to further reduce sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions. EPA’s appeal was not surprising given the scathing dissent issued by Circuit Judge Rogers, but the court denied EPA’s requests for both a panel rehearing and a hearing en banc on Thursday.

CSAPR was an attempt by the federal government to address complaints by eastern states that are downwind from large power plants in the coal belt in the Midwest. It set emissions caps that would have required reductions in SO2 and NOx emissions from existing power plants in 28 states, mostly east of the Mississippi River, but as far west as Texas. The EPA estimated that CSAPR would have helped reduce SO2 emissions by 73% and NOx emissions by 54% percent by 2014 as compared to 2005 emissions. CSAPR was originally scheduled to take effect January 1, 2012, but was delayed by the court pending resolution of the legal challenges.

The court found that the agency exceeded its statutory authority and held that the rule might have required some states to reduce emissions by more than their significant contribution to downwind states’ nonattainment with national ambient air quality standards and that the EPA impermissibly issued federal plans to implement the rule without allowing states the opportunity first to issue state plans to implement the rule. The court ordered the government to continue administering the clean air interstate rule (CAIR) in the meantime.

CAIR has been on the books since 2005, but in December 2008, a court found fault with it as well and sent it back to EPA with instructions for the agency to find a replacement. CSAPR was to be its replacement. In the aftermath of the August ruling, EPA issued a memo in November directing its regional directors to rely on reductions from CAIR as “permanent and enforceable” for certain actions. Environmentalists filed a petition for review of this direction in January because of their fears that EPA will continue to rely on the pollution reductions under CAIR instead of pushing for more significant reductions in air pollution. The EPA is weighing whether to appeal the court’s decision to the U.S. Supreme Court.