The D.C. Circuit denied petitions challenging EPA's one-hour primary NAAQS for nitrogen dioxide (NOx). The new one-hour primary NAAQS requires that “the three-year average of the annual 98th percentile of the daily maximum one-hour average concentration be less than or equal to 100 parts per billi...

The D.C. Circuit dismissed petitions challenging EPA's primary NAAQS for sulfur dioxide (SO2). The petitioners—several states, state regulatory agencies, corporations, and industrial associations—argued that EPA failed to follow the APA's notice-and-comment rulemaking procedures because it did n...

The D.C. Circuit upheld four EPA rulemakings governing greenhouse gases. EPA issued the rules following the U.S. Supreme Court's decision in Massachusetts v. EPA, 549 U.S. 497 (2007), in which the Court clarified that greenhouse gases meet the definition of an air pollutant under the CAA. Petit...

The Fifth Circuit upheld EPA's decision to disapprove certain revisions to Texas' SIP. EPA disapproved the revisions concerning the state's "qualified facilities program" because it did not meet the minor new source review (NSR) SIP nor did it meet the NSR SIP requirement for a substitute major ...

The D.C. Circuit vacated an interim final rule issued by EPA that would allow manufacturers of heavy-duty diesel engines to pay nonconformance penalties in exchange for the right to sell engines that fail to satisfy nitrogen oxide requirements. In 2001, EPA issued a rule requiring a 95% reduction in...

The Sixth Circuit held that the CAA's citizen suit provision does not allow an environmental group to file suit to compel the state of Ohio to administer a particular federal CAA regulation it has chosen no longer to administer. In 2006, the Ohio General Assembly passed legislation that allows the s...