Power plants in 28 US states, mostly east of the Mississippi River, received a reprieve on August 21 from a US appeals court.

The court struck down a federal cross-state air pollution rule also known as CSAPR that would have required certain power plants to reduce sulfur dioxide and nitrogen oxide emissions. The US Environmental Protection Agency estimated that CSAPR would have helped reduce SO2 emissions by 73% and NOx emissions by 54% percent by 2014 as compared to 2005 emissions.

The court ordered the government to continue administering a clean air interstate rule in the meantime that, according to government estimates, would reduce SO2 emissions by 57% and NOx emissions by 61% below 2003 emissions. The clean air interstate rule 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 the replacement.

EPA has 45 days to seek a rehearing in the US appeals court or appeal to the US Supreme Court; however, an appeal to the US appeals court would not be surprising given the scathing dissenting opinion written by one of the three US appeals court judges who heard the case. The court struck down CSAPR on a 2-1 vote.

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. CSAPR was originally scheduled to take effect January 1, 2012, but was delayed by the court pending resolution of the legal challenges. In the meantime, a predecessor rule, the clean air interstate rule, remained in effect.

Prior to the court ruling, EPA expressed confidence that CSAPR would be upheld; however, 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 EPA to continue administering the prior clean air interstate rule until EPA provides a replacement, which could take years.

In the meantime, there may be ramifications to already approved state implementation plans and other EPA rules that assumed they were building on pollutant reductions anticipated under CSAPR. This will take a while to sort out, but will need to be monitored.