The Trump administration has decided to keep and defend the Obama administration’s controversial 2015 smog regulation.

Justice Department attorneys representing the Environmental Protection Agency (EPA) told a federal court Wednesday that, after considering it for more than a year, the agency decided against pursuing revisions or a repeal to the 2015 rule that set a new standard for ground-level ozone, a component of smog.

In the brief, the attorneys said the Trump administration may have written the 2015 rule differently, considering factors like background levels of ozone that are outside of the control of states that are expected to comply with the standard.

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“While EPA officials in the current administration may have supported making different judgments about the significance of background concentrations of ozone and how to judge what standards are requisite to protect public health and welfare, the agency at this time does not intend to revisit the 2015 rule,” the attorneys wrote.

The smog rule was one of the most controversial regulations of the Obama administration’s EPA. It set the allowable ozone level in ambient air at 70 parts per billion, down from 75.

The agency estimated it would prevent thousands of premature deaths and save billions of dollars of healthcare costs. But opponents in fossil fuels and other industries said the benefits were doubtful, and estimated a cost of more than $3 trillion.

Scott Pruitt Edward (Scott) Scott PruittJuan Williams: Swamp creature at the White House Science protections must be enforceable Conspicuous by their absence from the Republican Convention MORE, the EPA’s administrator until last month, was a leading litigant trying to overturn the rule when he was Oklahoma’s attorney general. Under Pruitt, the EPA tried to delay implementing the ozone rule, but backtracked.

That lawsuit, joined by numerous conservative states and business groups, is ongoing. The Wednesday brief was filed in that case.

Andrew Wheeler, the EPA’s acting chief, rolled out a report Tuesday finding that key air pollutant levels continued to fall in 2017, including ozone. The EPA credited the 2015 rule with helping to bring down emissions levels.

The agency earlier this year started the process of evaluating whether to change the rule in 2020. The Clean Air Act requires that the EPA undertake such a consideration every five years.

Pruitt directed agency officials to consider background ozone levels in the evaluation. He also asked them to examine whether the compliance costs for ozone restrictions could hurt public health, though the Supreme Court has ruled previously that the EPA cannot consider costs when setting air quality standards.