2009 was a dramatic year for the Clean Air Act (CAA). Under the Obama Administration, the U.S. Environmental Protection Agency (EPA) took significant steps on many fronts. As widely expected, it issued an endangerment finding with respect to greenhouse gases (GHGs) and granted California's waiver request. However, less expected, was the new national automobile GHG emissions standard that managed to garner the auto industry's support. EPA also finalized its Mandatory Reporting of Greenhouse Gases Rule, which provided an important foundation for regulating GHGs under both the CAA and any future climate change legislation. The Agency, in fact, delivered its draft rule on regulating stationary sources under the CAA late in 2009. In addition to addressing climate change, EPA has taken the bold step of promising to review all six of the national ambient air quality standards (NAAQS) by 2011. While the CAA requires that these standards be reviewed every five years, some of them have not been revised since they were first established in 1971. EPA is also working to rewrite several regulations that were struck down by the U.S. Court of Appeals for the District of Columbia (D.C.) Circuit. Shortly after President Obama took office, the Agency also withdrew or began reconsideration of a number of George W. Bush Administration rulemakings, particularly with respect to new source review (NSR).

The year 2009 did not see as many challenges to existing regulation under the CAA as in past years. However, there was a continued level of activity in regard to climate change lawsuits. 2010 will likely see an upward trend in such litigation. For example, the proposed rulemakings on GHG emissions and NAAQS will have significant impacts on a variety of interest groups. With the stakes raised and a wide variety of regulatory proposals on the table, 2010 should be another year of significant CAA developments.