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EPA’s Clean Air Scientific Advisory Committee Comes to Agreement on Ozone Standard Recommendation

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Today the EPA’s chartered Clean Air Scientific Advisory Committee (CASAC) agreed on a recommendation to Administrator McCarthy regarding an update to the ambient air pollution standard for ozone (To get up to speed on the ozone standard update process, see my previous post on the topic). The deliberation of the committee and the Ozone Review Panel exemplified the challenges of translating science to policy and it was clear that the scientific experts on the panel had differing opinions on how this should be done.

The science-based ambient air pollution standard for ozone is updated every five years   with input from scientific experts, the public, and other other stakeholders.

The science-based ambient air pollution standard for ozone is updated every five years with input from scientific experts, the public, and other stakeholders.

What does the science tell us about ozone and health?

The Clean Air Act charges CASAC with recommending a value (or as they typically do, a range of values), to the EPA administrator based on what limit on pollution levels the science indicates will be protective of public health with an adequate margin of safety.

What should that value be for ozone? The panel agreed that 60 parts per billion (ppb) should be the lower limit of the range (note: this is the same lower limit that CASAC recommended in 2011). The committee concluded that 60 ppb continues to be the lowest level for which we have strong scientific evidence of health benefits. But what should the upper limit of the range be?

One way the committee thinks about this question is by focusing on susceptible populations, including children and the elderly. For these groups, we see marginal improvements in health outcomes at lower concentration of ozone, i.e. there are incremental improvements for lower and lower ozone levels. With this observation in the health studies, what then is the least restrictive standard that we consider to be “protective of public health with an adequate margin of safety”? The committee agreed that an upper limit of 72 ppb was inadequate to protect public health and that 70 ppb may be protective but only with a limited margin of safety.  Some members of CASAC pushed to go as low as 65 ppb based on scientific evidence, while others felt that there wasn’t sufficient evidence for this recommendation. “The question of what is an adequate margin of safety is a policy question, not a science one,” argued one CASAC member.

The making of a science policy decision

The conclusion? The committee ultimately agreed to recommend to Administrator McCarthy a range of 60-70 ppb for the primary ozone standard with the qualifier that the standard of 70 ppb ozone would have a limited margin of safety and thus would be less protective of public health than a lower standard would.  This qualifier provides additional scientific information for the administrator to consider in setting the standard, but the real question is how will the administrator interpret this scientific language in making her decision? Will she consider 70 ppb an adequate standard if it is included in the recommended range? Or will she consider this qualifying language to indicate that the science supports a lower standard to be protective of health? “We should recognize that this recommendation would mean that the administrator may set the standard at 70 ppb, recognizing it as our upper limit, and we [CASAC] would need to be comfortable with that outcome,” Christopher Fry, Chair of CASAC, noted in the meeting as the committee was deliberating this decision.

The ultimate question, of course, is how the administrator will interpret this. Next, CASAC will revise its draft letter to the administrator to reflect this morning’s discussion and we will wait and see how Administrator McCarthy decides to consider the scientific recommendations from its Clean Air Scientific Advisory Committee, when the final recommendation is on her desk.

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About the author: Gretchen Goldman is a lead analyst in the Center for Science and Democracy at UCS. She holds a PhD and MS in environmental engineering from the Georgia Institute of Technology and a BS in atmospheric science from Cornell University. Follow her on Twitter at @GretchenTG. See Gretchen's full bio.

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