The U.S. Environmental Protection Agency made a surprise announcement Aug. 2 that it will stick with designating attainment and nonattainment areas for its 2015 ozone standard in October, reversing its decision in June to delay that deadline by a year.

The EPA gave little indication why it changed its position but noted that past delays on designations had spurred citizen lawsuits. A coalition of public health and environmental groups moved quickly to sue EPA after it postponed the designations deadline.

"Under previous administrations, EPA would often fail to meet designation deadlines, and then wait to be sued by activist groups and others, agreeing in a settlement to set schedules for designation," EPA Administrator Scott Pruitt said. "We do not believe in regulation through litigation, and we take deadlines seriously. We also take the statute and the authority it gives us seriously."

To meet the reinstated deadline, the EPA said it will "[work] with states to help areas with underlying technical issues, disputed designations, and/or insufficient information."

In June, the EPA issued a notice in the Federal Register delaying its deadline for designations by one year, to Oct. 1, 2018. At the time, Pruitt said he lacked the information to make determinations this year. In 2015, the EPA strengthened the National Ambient Air Quality Standards, or NAAQS, for ground-level ozone to 70 parts per billion from a prior limit of 75 ppb. Ozone is formed from both natural and man-made emissions, including nitrogen oxide pollution from coal-fired power plants.

Many industry groups attacked the new standard, but the rule was expected to require little extra action on the part of the existing electricity generating fleet. The EPA projected only five power plant units would need to make changes to help nonattaining counties lower ozone pollution.

Despite expectations for easy compliance, many states, business groups and lawmakers opposed the new standard and have pushed for broader reforms to the NAAQS program. Republicans in the U.S. House of Representatives have sponsored legislation to postpone implementation of the 2015 standard and double the amount of time between mandatory reviews of NAAQS for all criteria pollutants. Critics of the NAAQS program say states and industries are burdened by having to comply with multiple standards at one time and must wait too long for implementation guidance from EPA after the agency has finalized new rules.