Today, July 23, 2013, the Court of Appeals for the D.C. Circuit rendered a decision in Mississippi v. EPA, No. 08-1200, an appeal brought by several states, the District of Columbia, New York City, and several industry, and environmental groups against EPA regarding the National Ambient Air Quality Standards ("NAAQS") for ozone, set by EPA in 2008. The D.C. Circuit upheld the primary standard for ozone but remanded the identical numeric secondary standard for further explanation or reconsideration.
The secondary NAAQS "specify a level of air quality the attainment and maintenance of which… is requisite to protect the public welfare from any known or anticipated adverse effects associated with the presence of such air pollutant in the ambient air." 42 U.S.C. § 7409(b)(2). EPA set the 2008 secondary ozone NAAQS at .075 ppm 8 hour average to protect against harmful effects on vegetation and indirect effects on other ecosystem components.
The D.C. Circuit found that EPA's explanation for setting the secondary standard identical to the primary standard was insufficient. In particular, the D.C. Circuit found that "EPA failed to determine what level of protection was ‘requisite to protect the public welfare,'" and therefore "EPA's explanation for the secondary standard violates the Act."
The D.C. Circuit decided to leave the 2008 secondary ozone standard in place (as opposed to vacating) during the pendency of EPA's review for further explanation or reconsideration. Although the 2008 ozone standards remain in place, it is possible that after review or reconsideration, EPA will make the secondary standard more stringent.