U.S. Congressman Xavier Becerra (D-CA), Attorney General nominee for the state of California. December 8, 2016. Photo: Diego M. Radzinschi/ALM

California and seven other states on Thursday moved to defend Obama-era ozone pollution standards that Attorney General Xavier Becerra said may be left to die under Scott Pruitt’s leadership of the U.S. Environmental Protection Agency.

The states, led by Becerra’s office, urged the U.S. Court of Appeals for the D.C. Circuit to let them intervene as defendants in a challenge of EPA rules that limit ozone levels, a prime component of smog. Coal mining giant Murray Energy Corp. and several states, including Oklahoma, led by then-Attorney General Pruitt, filed the challenge in 2016.

The EPA defended the ozone rules under President Barack Obama. But under the Trump administration and Pruitt, the EPA reversed course, indicating in a June 6 letter and a June 28 notice in the Federal Register that “it will no longer vigorously defend” the pollution standard.

“EPA’s statements signaling concerns about the 2015 ozone [rules] show that the agency no longer supports state movants’ interests in defending and implementing the strengthened ozone standard,” Becerra’s office wrote in Thursday’s court filing. Massachusetts and New York were among the states that joined the motion.

It’s unclear what role Pruitt will play in handling the states’ request to intervene in the case. Pruitt said in May he will step away from cases in which Oklahoma is a party, a petitioner or intervenor to avoid the appearance of a possible conflict of interest.

“The origins of EPA’s newfound uncertainty about the justifications for the standards it finalized in October 2015 can be found in the papers current administrator Pruitt filed in this very case while he was suing EPA as Oklahoma’s attorney general,” Becerra’s office wrote in the D.C. Circuit filing.

An EPA spokesperson did not immediately respond to a message seeking comment Thursday.

In April, lawyers for the EPA asked the D.C. Circuit to postpone oral arguments in the case, noting that the agency “intends to closely review the 2015 rule, and the prior positions taken by the agency … may not necessarily reflect its ultimate conclusions after that review is complete.”

The effort to defend the ozone levels is just the latest action taken by California and Becerra to block the Trump administration’s proposed rollback of environmental regulations. In March, the state moved to intervene in another D.C. Circuit case challenging vehicle pollution rules crafted by the EPA. Becerra has also sued to end federal delays in setting product efficiency standards and to stop a coal leasing program on public lands.

Lawyers for California say the state could incur more than $1 billion in costs, mostly from paying for medical treatment of its residents, if the ozone standards are dropped. Opponents of the rule argue that the standards fail to adequately consider ozone that’s generated by foreign countries or distant domestic areas.