On Feb. 24, 2009, in American Farm Bureau v. Environmental Protection Agency, No. 06-1410, the District of Columbia Circuit Court of Appeals ruled that the most recent version of the National Ambient Air Quality Standards (NAAQS) for fine particulate matter promulgated by the Environmental Protection Agency (EPA) in 2006 were contrary to law and unsupported by reasoned decisionmaking. The court upheld the coarse particulate NAAQS that were promulgated as part of the same rulemaking.

The 2006 NAAQS established a 24-hour primary standard for fine particulate matter based on short-term exposure studies, and an annual standard of 15 μg/m3 based exclusively on long-term exposure studies. However, the Clean Air Scientific Advisory Committee (CASAC), an independent scientific advisory committee established under the Clean Air Act, and the EPA’s own staff, had recommended a more stringent annual standard because of short-term health effects of fine particulate matter. By statute, the EPA was required to explain its rejection of CASAC’s recommendation, and the court found that it had failed to do so adequately.

The court also found that the EPA had failed to adequately consider whether a lower limit was necessary to protect children the from adverse health effects of fine particulates, and that the secondary standard for fine particulates, which also went against CASAC’s recommendations, was inadequately justified. The distinction between primary and secondary standards is that the former addresses the health effects of a particular pollutant, while the latter addresses “welfare” effects. For particulate matter, the “welfare” aspect in question was visibility. Finally, the court upheld a separate challenge by farm industry groups to the coarse particulate matter standards.

The immediate impact of the court’s decision will be negligible because the rule was remanded to the EPA and the 2006 standards were left in place pending either the formulation of a new rule or an adequate justification by the agency of the original one. However, given the change in administration, a new rule likely will eventually emerge, and it will be more stringent than the 2006 version.