The U.S. Environmental Protection Agency reportedly will finalize a new approach to the way it measures the negative health effects of tiny airborne soot pollution as part of its replacement for the Obama-era Clean Power Plan.

The regulation, dubbed the Affordable Clean Energy, or ACE, rule, will include a cost-benefit analysis that assumes no additional health benefits can be gained by reducing fine particulate matter pollution below the current legal limit, according to The New York Times.

That novel approach could allow the EPA to rebut the legal argument that the ACE rule should be struck down because the agency's own analysis shows the proposal would cause up to 1,400 more deaths annually compared to the Clean Power Plan. But adopting the new approach would run contrary to virtually all of the latest peer-reviewed science on fine particulate matter, according to environmental attorneys.

Emissions from fossil fuel-fired power plants, industrial facilities and vehicles are the largest sources of fine particulate matter that measure 2.5 micrometers or less, also known as PM 2.5. The tiny particles can make their way from ambient air through the lungs and into the heart and brain, causing respiratory health problems and premature death.

Based on a lengthy review, the EPA in 2012 lowered the National Ambient Air Quality Standards for PM 2.5 to 12 micrograms per cubic meter from the previous standard of 15 micrograms per cubic meter. The agency based that decision on more than 1,000 pages of peer-reviewed scientific studies. However, in issuing the Clean Power Plan in 2015 the EPA estimated it would result in additional PM 2.5 pollution reductions due to the retirement of coal-fired power plants targeted by the regulation and between $14 billion to $34 billion in health benefits in 2030.

In proposing to repeal the Obama-era regulation, the Trump administration in October 2017 unveiled an alternative cost-benefit analysis that assumed human exposure to PM 2.5 is safe. In August 2018, the EPA included the same approach as part of the proposed ACE rule and is now planning to issue a final rule with a cost-benefit analysis that largely eliminates the 1,400 additional annual deaths compared to the Clean Power Plan, according to the Times.

The EPA did not respond to a request for comment on whether the agency is basing a more limited cost-benefit analysis for PM 2.5 on any peer-reviewed studies. But the now disbanded Utility Air Regulatory Group had asserted in comments on the EPA's October 2017 move to repeal the Clean Power Plan that the Obama-era regulation "improperly credits" the purported health benefits from reducing PM 2.5 below levels at which EPA has determined public health is protected.

"Because ... [National Ambient Air Quality Standards] are set at the level EPA has determined is protective of public health, it is improper to claim benefits below that level," said the utility-backed industry group.

Moreover, Bill Wehrum, the EPA's administrator of the Office of Air and Radiation, told the Times, "How in the world can you get $30 [billion] or $40 billion of benefit to public health when most of that is attributable to reductions in areas that already meet a health-based standard ... That doesn’t make any sense."

'Arbitrary and capricious'

But Andres Restrepo, a staff attorney with the Sierra Club, said doing so "makes perfect sense if you go by the science." Furthermore, he said relying on a cost-benefit analysis approach that is not supported by any peer-reviewed scientific studies could open the EPA to claims that the approach is arbitrary and capricious under the Administrative Procedure Act.

"Fundamental black-letter administrative law holds that agencies have to have some sort of justification for their decisions," Restrepo noted in an interview. "To me, this is a textbook case of an arbitrary and capricious agency action."

The Natural Resources Defense Council also argued that EPA's regulatory impact analysis ignores "the long-held conclusion of health experts that there are no levels of particulate matter that do not have dangerous impacts on human health."

John Walke, director of the Natural Resources Defense Council's clean air, climate and energy program, said in a May 20 interview that whether the difference in estimated deaths between the two regulations will factor into an inevitable legal challenge to the ACE rule is unclear. However, he said, "it's a very arresting fact tied to the agency's own record that should be a powerful argument for judges to consider in determining whether EPA has discharged its statutory responsibilities."

The EPA said in a recent court filing that it plans to finalize the ACE rule by the end of June. Parties will then have 60 days to ask the U.S. Court of Appeals for the District of Columbia Circuit to review the rule.