The application of exposure-based criteria in developing alternative primary ambient ozone standards

The form of the primary National Ambient Air Quality Standard (NAAQS) for ozone has been a matter of some concern in recent years. The Environmental Protection Agency is reviewing the ozone NAAQS and has proposed a set of alternative standards that address some deficiencies. However, the proposed alternatives are all based upon the ozone concentrations occurring at the peak monitor, which may not be representative of the air quality and population exposure throughout a nonattainment area. Representativeness could be improved by converting the form of the standard from an exceedance-based metric (with x allowable exceedances per year, on average) to one based upon exposure. Three approaches to defining an exposure-based standard are developed here. Data from the San Francisco Bay area are used to illustrate the proposed standards.