This story has been updated with a response from the EPA.

For two years, the Trump administration has been planting seeds of change in the Environmental Protection Agency—installing allies of regulated industries onto its elite panels of science advisers. That effort now has borne fruit in dramatic fashion.

The EPA's new science advisers, sweeping aside decades of research on the grave health risks of fine particle air pollution, have launched a drive to force the agency to give greater weight to a handful of contrarian studies that dispute the harmful effects of soot.

Particulate matter is the pollution caused by combustion, a mixture of solid and liquid droplets that forms in the burning of fossil fuels or wood. The health risks of particulate matter have been an underpinning of the EPA's cost-benefit analysis of a number of air pollution regulations, including those meant to address climate change, like the Obama administration's Clean Air Act.

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The science is well-established—the World Health Organization estimates that there are 4.2 million premature deaths a year due to fine particle pollution, making it one of the leading environmental health risks globally. But allies of the fossil fuel industry have vigorously disputed the validity of fine particle pollution studies since they first emerged in the 1990s.

Significantly, the health damages from particle and other pollution coming from the combustion of fossil fuels have also been used by the EPA to justify controls on carbon dioxide, the main greenhouse gas. Controlling climate change has important co-benefits, the agency has reasoned. The Trump administration and its industry allies oppose this logic.

More Weight for 'Discordant' Claims?

The latest scientific dispute centers around the EPA's draft assessment of the science on particulate matter (PM), a comprehensive review that the agency is required by law to conduct every few years to update the state of the science on several key pollutants. EPA released its draft review last fall.

It affirmed the agency's previous findings that the science points consistently and overwhelmingly to a "causal relationship" between PM pollution and premature deaths. The assessment concludes the greatest risk is due to particles less than 2.5 microns in width, and that PM2.5 is associated with a range of cardiovascular and respiratory effects.

For the first time, the EPA concluded that the evidence was strong enough to show a "likely" causal relationship between long-term PM2.5 exposure and cancer, as well as nervous system effects. The EPA concluded, as it has in the past, that there is evidence of health risks even at extremely low levels of PM exposure.

Now, in a harshly worded draft review, the Trump administration's science advisors are blasting those findings as based on "unverifiable opinions" and lacking in scientific support.

The advisers are members of a seven-member panel called the Clean Air Science Advisory Committee. Although it is clear the members are not unified in their critique—individual members attached separate letters—the document calls for "substantial revisions" to EPA's assessment of PM, including giving more weight to what it called the "discordant" evidence among the 2,800 published studies cited in the EPA's 1,900-page science assessment.

"Substantial discordant and conflicting evidence remains ignored or unresolved," the Trump administration-appointed CASAC wrote, "leading to repeated assertions that the literature shows consistent and coherent positive associations when in fact it shows a mixture of positive and negative results."

When asked for comment on the critique, a spokesperson for the EPA said by email: "We appreciate the work of the CASAC and we will review the report."

Who Are New Committee Members Listening To?

The CASAC, now chaired by Louis Anthony "Tony" Cox, Jr., a Denver-based consultant, offers a few examples of the studies it wants to see the EPA give more weight to. Among them are studies that are authored, in fact, by Cox himself—whose clients have included the American Petroleum Institute, the tobacco industry and the chemical industry.

Other studies mentioned by the CASAC are by S. Stanley Young, a former pharmaceutical industry statistician based in Raleigh, N.C., who is an adviser to the Heartland Institute, a conservative think tank that has led a years-long campaign to discredit climate science. Young is now also an EPA science adviser.

The CASAC also pointed to the work of James Enstrom, a Los Angeles epidemiologist who for years has questioned the health risks of particulate matter. A former tobacco industry researcher, Enstrom was a plaintiff in a 2016 lawsuit brought by the fossil fuel industry-funded Energy and Environment Legal Institute that challenged the makeup of the previous CASAC.

Many of the environmental scientists who were appointed to EPA's advisory panels had received funding from EPA at some point in their careers, which the Enstrom suit said was a conflict of interest. In 2017, Trump's first EPA administrator, Scott Pruitt, made the same argument when he replaced scientific experts from the existing science advisory boards with new appointees—including a number of industry allies and consultants, like Cox and Young.

'CASAC Itself Lacks Necessary Expertise'

One scientist who was among those removed from the CASAC last year, H. Christopher Frey, an environmental engineer at the University of North Carolina, said the harsh science critique from the Trump administration-appointed committee comes amid "numerous major changes to the [air quality standards] review process that collectively undermine its quality, integrity and credibility."

"Most astonishing is the arrogant and insulting tone of this letter toward EPA scientific staff," Frey, a former chairman of the CASAC, said in an email to InsideClimate News. Frey dismissed as "patently absurd" the document's assertion that the EPA's approach on particulate matter was unscientific. "The statement is ironic given that the CASAC itself lacks necessary expertise," he said.

In fact, the CASAC recommended that it be given access to additional technical expertise in order to complete its review of EPA science on particulate matter. Two members of the CASAC called for the EPA to reconstitute a 20-member special review panel on particulate matter that EPA Administrator Andrew Wheeler disbanded in October, just prior to the start of the peer review. That panel included experts in the science of particulate matter and health effects—expertise that is now missing on the CASAC. Although much of the science on the health risks of particulate matter is from large human studies, there are no epidemiologists on the current CASAC.

In one striking passage of its draft peer review, the CASAC said it is unable to reach consensus on the link between particulate matter and mortality—the "causality determination of mortality from PM2.5 exposure." Some members "are of the opinion that, although uncertainties remain, the evidence supporting the causal relationship between PM2.5 exposure and mortality is robust, diverse, and convincing," the document said. But other committee members think EPA should provide a better justification for its determination that there is a causal relationship between PM exposure and premature death.

Daniel Greenbaum, president of the Boston-based Health Effects Institute (HEI), a research institute that has conducted major studies on air pollution, said that he was surprised at that passage.

"Given that there is more than a decade worth of work now looking at the epidemiology, the toxicology, and a number of other things to see whether or not PM can contribute to mortality, there's pretty robust literature that says that," said Greenbaum. HEI has offered its own critiques of some aspects of EPA's assessment—for example, it does not agree with EPA's conclusion on nervous system effects. But HEI does not dispute EPA's fundamental conclusion on mortality risk. "By most standards, people would say that the evidence has strengthened over the last 20 years," Greenbaum said.

But Greenbaum noted that the committee's review document is only a draft. The CASAC has set a conference call for March 28 to discuss the document and the next steps before submitting its final recommendations to Wheeler.