The US Court of Appeals for the District of Columbia Circuit ruled Friday that the US Environmental Protection Agency (EPA) erred in finding that certain counties were meeting current federal ozone limits. The EPA was ordered to reconsider the designations of those counties under the Clean Air Act.
Under the Clean Air Act, the EPA is required to establish and periodically revise National Ambient Air Quality Standards (NAAQS) for pollutants that are considered harmful to public health and the environment. The NAAQS then determine the highest permissible outdoor air concentrations of those pollutants.
After the EPA creates or revises a NAAQS, it must label each area in the US as “attainment,” “nonattainment,” or “unclassifiable.” Areas that meet the relevant NAAQS are marked as attainment, those that exceed the NAAQS are designated as nonattainment, and areas that cannot be measured because of a lack of existing data are considered unclassifiable. An area’s designation also determines the strictness of the region’s emission controls.
In 2015, the EPA reduced the maximum allowable ozone value and designated new areas as either attainment, nonattainment, or unclassifiable. The plaintiffs, who are environmental groups, challenged a subset of those area designations. They argued that the EPA erred in determining that many counties were meeting the federal ozone limits.
The court found that the EPA engaged in “arbitrarily disparate treatment” by treating similar counties differently. The court also found that the EPA “inadequately explained” some of the area’s designations.
Because of this determination, the court decided to remand the designations because it believed that “there is at least a realistic possibility that EPA will be able to substantiate the relevant designations on remand.” The court remanded the EPA’s designations for several counties in Colorado, Michigan, Missouri, Illinois, and Wisconsin.