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Dr. Armistead (Ted) Russell Review of the January 2007 OAQPS Ozone Staff Paper and the "Analysis of Uncertainty in Ozone Population Exposure Modeling" Ted Russell This version of the ozone Staff Paper (SP), is a definite improvement over the prior version, and integrates public comments, as well as CASAC's, in to the context of their recommendations on a change of the ozone NAAQS. Of most interest are the additions in Chapters 6, 7 and 8. Given that these are, presumably, final documents, the comments are aimed at how what is presented should be considered in the choice of a revised ozone NAAQS. My main concern with Chapter 6 is that the analysis presented likely underestimates potential ozone exposure and risk reduction from tighter standards due to both biases in the current APEX application and the limited areas to which APEX was applied. I would not be surprised if such biases are relatively minor, but these biases should be stated quite explicitly and frequently so they are not forgotten. I would not suggest that they are calculated at this time as I think the analysis conducted so far provides ample evidence that the standazd should be tightened, though if they were, it may be that Staff would not consider the 0.074/4 level. Their current analysis shows a large number of exposures of concern at that level as it is. That said, I found the tables presenting exposures at various levels of the standard illuminating and a good foundation for assessing possible levels/form of a revised Ozone NAAQS. A second concern with Chapter 6 is that it takes quite a while to get through it, but that is life as I am sure EPA staff want to be thorough in providing support for the changes suggested. A third concern with Chapter 6, as well as Chapter 2, is that the "other photochemical oxidants" are given short shrift and more attention should be paid to them in future assessments, and for further consideration in the choice of a revised NAAQS at this time. In Chapter 7, they show, in Fig. 7-18, how W1261evels correlate with 8-hour levels and show the current and an alternative form of the primary standard with W 1261evels. It is important to recognize that the relationship implied here may not be true given future controls. Thus, a 0.070 ppm primary NAAQS would not necessarily provide as much in terms of lowering W 126 as might be taken away from this graph... though it actually may provide more. This provides increased support for a separate form for the secondary standard. In the future, they might look to provide an apportionment of uncertainty. I was pleased with the report "Analysis of Uncertainty in Ozone Population Exposure Modeling," not because it was an extensive uncertainty analysis, but because it was an appropriate analysis given the resource/time constraints, and it provides the needed information upon which one can conclude that the uncertainties should not play a major role in the choice of future standard. In future assessments, calculating the contributions to uncertainty would be insightful. ~.._~~'~ C-28