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WASHINGTON — One day after getting sued by 15 states, Environmental Protection Agency chief Scott Pruitt reversed his earlier decision to delay implementation of Obama-era rules reducing emissions of smog-causing air pollutants.

Pruitt presented the change as his agency being more responsive than past administrations to the needs of state environmental regulators. He made no mention of the legal challenge filed against his prior position in a federal appeals court.

At issue is an Oct. 1 deadline for states to begin meeting 2015 standards for ground-level ozone. Pruitt announced 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."

Pruitt, who was Oklahoma's state attorney general prior to his appointment by President Donald Trump, has long served as a reliable opponent of stricter environmental regulations. Since arriving in Washington, Pruitt has repeatedly moved to block or delay regulations opposed by the chemical and fossil-fuel industries.

Environmental Protection Agency Administrator Scott Pruitt speaks to the media during the daily briefing in the Brady Press Briefing Room of the White House in Washington. on June 2, 2017. Pablo Martinez Monsivais / AP

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Wednesday's sudden reversal is the latest legal setback for Pruitt's regulatory rollback agenda. Last month, 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.

Related: Federal Court Orders EPA to Move Ahead With Rule to Limit Methane

In a statement issued Wednesday evening, Pruitt suggested his about-face 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, who sued EPA more than a dozen times in his prior job. "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."

A view of the Los Angeles city skyline as heavy smog shrouds the city in California on May 31, 2015. MARK RALSTON / AFP/Getty Images

Still, the EPA's statement said Pruitt may at some point once again use his "delay authority and all other authority legally available" to ensure regulations "are founded on sound policy and the best available information."

Republicans in Congress are pushing for a broader rewrite of the ozone rules. A House bill approved last month seeks to delay implementation of the 2015 rules 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.

Related: EPA Accused of Interfering With Top Science Adviser’s Congressional Testimony

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."