Key Issues Raised by EPA's Proposed Ozone Standards and Supporting Analysis. L. A. Beyer, B. D. Beck, J. T. Cohen, and P. A. Valberg, Gradient Corporation, 44Brattle Street, Cambridge, MA 02138
We evaluated the analysis that EPA conducted in support of their proposed ozone standards: 0.07 - 0.09 ppm ozone, 8-hour average, 1-5 exceedances per year. The primary basis of the proposed standards is concern for acute respiratory effects. EPA’s analysis consists of two main pieces: an evaluation of the human health effects as a result of exposure to ozone and a model to estimate the exposure of the U.S. population to ozone. We conclude that use of chamber studies to evaluate health effects from ozone exposure is sound, but that EPA’s choice of studies is inconsistent. EPA also used hospital admissions to evaluate health effects from ozone exposure; we found this analysis to be flawed. Further we considered the nine health endpoints evaluated by EPA and found that for virtually all of them, the exposure-response relationship reaches a population response rate of zero at 0.08 ppm at 8-hour exposures. Based on these results we conclude that EPA has not justified the regulation of ozone concentrations as low as 0.07 ppm. The exposure model used by EPA (pNEM/O3) is comprehensive and its overall conceptual framework is sound. However, it appears to overestimate exposures and we recommend some corrections based on recent field studies. When EPA’s health effects analysis and exposure analysis are combined, most of the exposure takes place at lower concentrations (often so low that there is no health data at these concentrations) and in addition the uncertainty is so great and overlaps to such a large degree from one proposed standard to another, that it is virtually impossible to differentiate between the proposed standards.