One day after being sued by 15 states, Environmental Protection Agency chief Scott Pruitt on August 2 reversed an earlier decision to delay implementation of rules reducing smog-causing air emissions.

At issue is an Oct. 1 deadline for states to begin meeting 2015 standards for ground-level ozone. Pruitt said in June he would delay compliance by one year to give his agency more time to study the plan and avoid "interfering with local decisions or impeding economic growth."

The reversal is the second recent legal setback for Pruitt's regulatory rollback efforts. In July, a federal appeals court in Washington ruled the EPA administrator overstepped his authority in trying to delay implementation of an Obama administration rule requiring oil and gas companies to monitor and reduce methane leaks.

The National Ambient Air Quality Standard (NAAQS) for ground-level ozone is an outdoor air regulation under the Clean Air Act. As part of the process to determine what areas of the country are able to meet the current air quality standards, states are currently submitting their proposals for area designations under the 70 parts per billion (ppb) standard, which was cut from 75 ppb in 2015.

In a statement, Pruitt suggested his reversal on ozone standards simply reinforced the EPA's commitment to working with states through the complex process of meeting the new standards on time.

"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," said Pruitt. "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."

Republicans in Congress are pushing for a broader rewrite of the ozone rules. A House bill approved in July seeks to delay implementation of the 2015 rules by at least eight years. The measure has not yet been brought to a vote in the Senate.

New York Attorney General Eric Schneiderman, who led the coalition of states that sued the EPA this week, said the group intends to keep up the legal pressure.

"The EPA's reversal — following our lawsuits — is an important win for the health and safety of those 6.7 million New Yorkers, and the over 115 million Americans directly impacted by smog pouring into their communities," Schneiderman said.

New York was joined in the case by California, Connecticut, Delaware, Illinois, Iowa, Maine, Massachusetts, Minnesota, New Mexico, Oregon, Pennsylvania, Rhode Island, Vermont and Washington, and the District of Columbia.

Ground-level ozone is created when common pollutants emitted by cars, power plants, oil refineries, chemical plants and other sources react in the atmosphere to sunlight. The resulting smog can cause serious breathing problems among sensitive groups of people, contributing to thousands of premature deaths each year.

Public health advocates and environmentalists cheered Pruitt's surprising change of course.

"It's disturbing how much pressure it took to get this commonsense step from the guy in charge of protecting the air we breathe," said Lori Ann Burd of the Center for Biological Diversity. "We've got to keep fighting the Trump administration's ideological crusade to pander to polluters and special interests."