— Weeks after state Department of Environmental Quality officials placed former agency chief Donald van der Vaart on "investigatory leave," he stepped down from the agency Monday, saying officials in Gov. Roy Cooper's administration were trying to "stifle" him.

Van der Vaart submitted his resignation letter to his successor, DEQ Secretary Michael Regan, shortly before the two were scheduled to meet for a "pre-disciplinary conference" to discuss Regan's intent to fire van der Vaart for "unacceptable personal conduct."

After Cooper defeated Republican Gov. Pat McCrory in the 2016 election, van der Vaart reclaimed his old job in the Division of Air Quality, a non-political position that made it harder for the new administration to fire him.

To support his recommendation for termination, Regan cited an opinion piece van der Vaart co-authored for the September issue of Environmental Law Reporter calling for the repeal of a permitting program that the Division of Air Quality oversees.

"Your use of a small print disclaimer stating that your views may not represent the views of the department is inadequate to separate the views you expressed as a matter of personal concern in the published commentary from the required compliance activities of this department," Regan wrote in a Nov. 22 letter to van der Vaart informing him of the pre-disciplinary conference. "This action creates confusion for the public and compromises the perception of fairness and impartiality that this department needs to effectively carry out its regulatory obligations."

Van der Vaart also signed on to an open letter shortly after last year's election, urging incoming President Donald Trump to rein in the U.S. Environmental Protection Agency, putting him out of step with the Cooper administration. In late October, the Trump administration appointed him to an advisory board for the U.S. Environmental Protection Agency in a shakeup that removed a number of university professors from the board.

DEQ leadership didn't support the EPA appointment and said van der Vaart wouldn't be speaking for the state on that board. Regan also placed him on paid "investigatory leave."

In his resignation letter, van der Vaart noted that DEQ officials never previously complained of his publications and called it "troubling" that "this administration is moving to stifle my contributions to scientific and legal discourse in professional journals."

He also said he was surprised by the agency's position on his appointment to the EPA advisory board.

"I do not think that any reasonable person would have expected that reaction, and I firmly believe that my involvement with the EPA's scientific advisory board, whose objective is to provide the EPA Administrator with independent scientific advice, is positive for North Carolina and DEQ," he wrote. "The State has traditionally found it difficult to recruit young people without the added specter of politicization of science and law. Sadly, that specter is now clearly visible."

DEQ officials declined to comment on van der Vaart's accusations.

Calls to van der Vaart requesting comment haven't been returned.