Cross State Air Pollution Rule (CSAPR)


CSAPR addressed the interstate transport of nitrogen oxides (NOx) and sulfur dioxide (SO2), which are emitted by power plants. EPA found that such emissions impair the ability of numerous “downwind” states to comply with three National Ambient Air Quality Standards (NAAQS) established by EPA under the Clean Air Act – specifically, the 1997 8-hour ozone NAAQS, the 1997 Annual PM2.5 (fine particulate matter) NAAQS, and the 2006 24-hour PM2.5 NAAQS.

CSAPR replaced CAIR, a previous air transport rule. A 2008 D.C. Circuit decision invalidated CAIR but left it in effect until EPA could issue a replacement rule.

Section 110(a) of the Clean Air Act (CAA) imposes a “good neighbor” obligation on states, requiring them to ensure that their State Implementation Plans (SIPs) prohibit in-state sources from “significantly contributing” to nonattainment of NAAQS in downwind states. CSAPR used a two-step methodology to determine the extent to which upwind states were not meeting their “good neighbor” obligation. First, EPA used air quality measurements to find that certain states are contributors to downwind states’ nonattainment. Second, EPA established NOx and SO2 emission budgets for those states. These budgets were based on calculations of NOx and SO2 reductions achievable at a given cost per ton. Simultaneously with these determinations, the rule included Federal Implementation Plans (FIPs) for implementing these obligations.



Several states, companies, and trade associations petitioned for review of CSAPR. In December 2011, the D.C. Circuit stayed the rule pending resolution of the legal challenges, and directed EPA to continue to administer CAIR in the interim. On August 21st the US. District Court of Appeals rendered its decision to the CSAPR legal challenges, vacating the rule in a 2-1 decision. The Court's decision again directs EPA to continue administering the 2005 Clean Air Interstate Rule (CAIR) until the agency can finalize a replacement rule.

Subsequently, on October 5th EPA requested an en banc rehearing of the D.C. Circuit Court of Appeals’ Aug. 21 decision vacating CSAPR. The EPA says its request is “a petition for review of final agency action, not an appeal from the ruling of a district court.”

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