AG 2007 10 15 - Laserfiche WebLink

Home Browse Search

Dr. Douglas Crawford-Brown Comments on Review of the National Ambient Air Quality Standards for Ozone: Policy Assessment of Scientific and Technical Information Doug Crawford-Brown (3-9-07) I begin by noting that I was not on the CASAC to review the previous drafts of this document, or to participate in the discussions surrounding that document. As a result, I cannot comment on whether the current draft is or is not a significant improvement over the earlier one. I also follow only the health effects side of this issue, and so comment only on that issue and its associated uncertainties. Having said that, I note that this draft was quite easy to follow. Whether I agree with the fmal conclusions or not (and I basically do), I found the arguments and analyses in the draft simple to follow, despite the authors confronting a wide array of complex information. They are to be congratulated for selecting appropriate studies, drawing appropriate conclusions from those individual studies, and then looking for coherent summary conclusions across the studies. It is clear from the data presented that the old standard is now problematic with respect to protection of health with an adequate margin of safety. My recommendation is that a standard in the vicinity of 0.70 ppm is consistent with the available data, and even this does not fully address the concerns over a margin of safety. There are, however, two ways to build in a margin of safety: through the exposure-response side of the assessment, or through the exposure assessment side. The staff maybe contending that the ways in which exposures will be determined has conservatism built in, and therefore the margin of safety is included in that way. But as currently written, the document is curiously silent on the issue of margin of safety. I recommend it be made more explicit, with reference to either exposure-response conservatism or exposure assessment conservatism. This leads me to my second consideration. The document contains some interesting discussions of how exposure assessment can be improved, presumably with the goal of better understanding exposure-response relationships. This includes a better ability to understand risks in subpopulations characterized by increased sensitivity or unusual activity patterns. One needs to think carefully through the ways in which highly detailed exposure information is used in health effects studies intended to establish acceptable exposure levels, and ensure that this use is not inconsistent with the ways in which compliance monitoring will eventually be done. Compliance monitoring does not reflect exposures at the levels of spatial and temporal resolution of the risk assessment studies, and so it quickly becomes possible for the exposure metric on an exposure- response function to fail to be equivalent to the exposure metric measured in compliance monitoring. I don't have an answer as to how this issue can be resolved, only to say that it is necessary to try to match as closely as possible the spatial and temporal scale of the exposure metric used in the health effects studies to the metric used in compliance monitoring. I don't believe this has yet been done in the draft document. ~,-"_ ~ `~ C-12