EPA Office of Air and Radiation Administrator Bill Wehrum, an attorney who formerly represented power companies in their effort to roll back clean-air regulations, has resigned.

The biggest air-quality issues that the Office of Air and Radiation oversees are tailpipe emissions from cars, and emissions from power plants that increasingly provide power for electric cars.

EPA Administrator Andrew Wheeler made the announcement Wednesday. He didn't cite a reason for Wehrum's departure, but the air-office chief had expressed concern about the effects of a Congressional investigation into his former law firm, Hunton Andrews Kurth, according to a Washington Post report.

In his year and a half on the job, the office has drafted new regulations rolling back signature climate control programs from the Obama administration, including ratcheting up fuel-economy requirements from cars and the Clean Power Plan, which would have required coal-fired powerplants to capture carbon or convert to cleaner fuels. (The latter is mostly happening anyway for economic reasons.)

The long-anticipated final rule to freeze federal emissions and fuel economy standards at 2020 levels through 2026 is expected to be released at any time, though the EPA exchanged heated words with California officials in Congress last week.

Last Wednesday, the agency released the new Affordable Clean Energy rule, designed to replace the Clean Power Plan, which critics say will reduce global warming emissions from power plants by less than half the amount required to meet global climate-change reduction goals.

Under Wehrum, the agency also proposed a new rule that would change the way health benefits from proposed regulations are calculated to make it harder to pass new clean-air regulations.

Wehrum was confirmed under former EPA Administrator Scott Pruitt, who resigned last year under a cloud of ethical investigations over his relationships with lobbyists.

Automakers have been lobbying Congress and the Trump administration to work with California and come up with new vehicle emissions rules. Companies are okay with annual increases but want more flexibility in meeting them and more uniformity between the EPA, NHTSA, and California.

Environmental groups were quick to celebrate Wehrum's departure at the end of the month. No replacement has yet been named.