In November, EPA concluded that 2,646 counties, out of more than 3,100 counties in the United States, are in attainment with the 2015 ozone National Ambient Air Quality Standards (NAAQS). On October 1, 2015, the Obama administration revised both the primary and secondary NAAQS for ozone to a level of 0.070 parts per million (ppm) (annual fourth-highest daily maximum 8-hour average concentration, averaged over 3 years). The 2008 ozone NAAQS specified an ozone concentration level of 0.075 ppm. For all designations released, EPA classified the area as “Attainment/Unclassifiable” and did not include any areas classified as nonattainment. The approximately 10 percent of counties excluded from designation at this time includes many metropolitan areas such as Jefferson, Kenton and Campbell Counties in Kentucky and Hamilton, Franklin and Cuyahoga Counties in Ohio.

Over the summer, EPA announced that it was delaying the October 1, 2017, Clean Air Act due date to release the 2015 ozone NAAQS designations. After states sued EPA, it rescinded the announced delay. However, EPA missed the October 1 designation deadline. Statements of EPA Administrator Scott Pruitt suggest that EPA is working to reconsider the more stringent 2015 ozone NAAQS and, in August, EPA announced the agency would be moving forward with the 2015 ozone designations on a case-by-case basis. EPA also announced that it is considering withdrawal of its guidelines for states to use in reducing ozone precursors in the oil and gas industry.

EPA’s 2015 ozone NAAQS designations have already sparked litigation. On December 5, 2017, California, Connecticut, Illinois, Iowa, Maine, Maryland, Massachusetts, Minnesota, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Washington and the District of Columbia filed suit in the United States District Court for the Northern District of California challenging what these states characterize as EPA’s failure to designate the attainment status of certain areas. The states allege EPA has a duty to designate all areas in the country as opposed to the partial designation of counties released so far. A lawsuit with similar claims was filed in the same court on December 4, 2017 by non-governmental organizations including the Sierra Club, Environmental Defense Fund and National Parks Conservation Organization.

On December 19, 2017, the D.C. Circuit issued an order requiring EPA to file a report describing when it plans to issue a final rule establishing air quality designations for the 2015 ozone NAAQS.