It isn't just global warming emissions that the EPA plans to deregulate. 

At a meeting last Thursday, a key air quality standards board at the agency cast doubt on longstanding findings that particulate matterthe microscopic particles spewing from diesel tailpipescan cause health problems leading to premature deaths.

In the absence of several key science panels eliminated by EPA administrator Andrew Wheeler last year, decisions regarding air pollution have been left up to the Agency's much smaller, seven-member Clean Air Scientific Advisory Committee.

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Members of that committee met Thursday to review draft recommendations that would dramatically limit what studies are used to determine safe limits on air pollution, and several members cast doubt on the conclusion that particulate pollution leads to ill-health effects that can reduce life expectancy, according to an NPR report.

Just as with those who would sow doubt about global warming, the question hinges on what constitutes scientific certainty.

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Most scientists would prefer to rely on binary, double-blind studies to determine cause and effect. In many cases, however, scientists who study environmental health effects don't have that luxury. It's not possible to have the same person live their life once in a polluted environment and once in a clean oneat least not that's ever been demonstrated. So these scientists have to look at more generalized trends toward health outcomes in different population groups that could have multiple causes. They follow correlation, rather than strict causality.

Still, the correlation of high amounts of particulate matter from vehicle exhaust (and powerplant and factory smoke) and diseases such as asthma, is well established by a wide range of studies over many decades. These are the studies that the new EPA policy, decided by a single member board, would eliminate from consideration.

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Chairman Tony Cox of the Clean Air Scientific Advisory Committee said, "If we don't know that X causes Y, then we should say we don't know." He said he was "actually appalled" at how little of what he considered evidence backs EPA air quality standards. "Members [of the Committee] have varying opinions on the adequacy of the evidence supporting the EPA's conclusion that there is a causal relationship between PM exposure and mortality," he said.

In the past, such decisions would be vetted by larger committees with more focused expertise on certain environmental problems. Particulates had their own 20-member committee, the Particulate Matter Review Panel. It is one of several more focused committees that Wheeler eliminated in October.