Just before President Obama made waves on the climate change front, the U.S. Supreme Court decided to step into another contentious air pollution debate. On Monday, June 24, 2013, the Supreme Court agreed to review the D.C. Circuit decision to vacate EPA's Cross-State Air Pollution Rule (the "Transport Rule") in the case of EME Homer City Generation, LP v. Environmental Protection Agency, et al., Case No. 11-1302.

As previously discussed in this blog, EPA promulgated the Transport Rule to address sulfur dioxide ("SO2") and nitrogen oxide ("NOx") air pollution that crosses state lines. On August 21, 2012, the D.C. Circuit vacated the Transport Rule, holding that EPA had exceeded its authority.

A key issue in the appeal will be the level of deference the D.C. Circuit and the Supreme Court give the administrative agency to interpret and implement the complex requirements of the Clean Air Act. EPA will argue to the Supreme Court that the D.C. Circuit overstepped its authority when it vacated the Transport Rule. In its petition for Supreme Court review, EPA argued that the D.C. Circuit opinion "creates a substantial impediment to the EPA's authority to implement the [Clean Air Act]".

The Supreme Court's decision in this case will have a significant and direct impact on how EPA regulates cross-state air pollution. The decision may also impact the way EPA regulates greenhouse gases under the Clean Air Act. EPA's greenhouse gas regulations were upheld by the D.C. Circuit (previously discussed in this blog), a decision that was also appealed to the Supreme Court. The Supreme Court has not yet decided whether to accept the appeal regarding the greenhouse gas rules. In both the greenhouse gas and cross-state air pollution cases, EPA argues that it must have discretion to implement the Clean Air Act in a practical and effective manner. The Supreme Court is now poised to provide some guidance on the limits of that discretion in the coming term.