National Ambient Air Quality Standards for Ozone

Based on its review of the air quality criteria for ozone (O<INF>3</INF>) and related photochemical oxidants and national ambient air quality standards (NAAQS) for O<INF>3</INF>, EPA proposes to make revisions to the primary and secondary NAAQS for O<INF>3</INF> to provide requisite protection of public health and welfare, respectively, and to make corresponding revisions in data handling conventions for O<INF>3</INF>. With regard to the primary standard for O<INF>3</INF>, EPA proposes to revise the level of the 8-hour standard to a level within the range of 0.070 to 0.075 parts per million (ppm), to provide increased protection for children and other "at risk" populations against an array of O<INF>3</INF>-related adverse health effects that range from decreased lung function and increased respiratory symptoms to serious indicators of respiratory morbidity including emergency department visits and hospital admissions for respiratory causes, and possibly cardiovascular-related morbidity as well as total nonaccidental and cardiopulmonary mortality. The EPA also proposes to specify the level of the primary standard to the nearest thousandth ppm. The EPA solicits comment on alternative levels down to 0.060 ppm and up to and including retaining the current 8-hour standard of 0.08 ppm (effectively 0.084 ppm using current data rounding conventions). With regard to the secondary standard for O<INF>3</INF>, EPA proposes to revise the current 8-hour standard with one of two options to provide increased protection against O<INF>3</INF>-related adverse impacts on vegetation and forested ecosystems. One option is to replace the current standard with a cumulative, seasonal standard expressed as an index of the annual sum of weighted hourly concentrations, cumulated over 12 hours per day (8 a.m. to 8:00 p.m.) during the consecutive 3- month period within the O<INF>3</INF> season with the maximum index value, set at a level within the range of 7 to 21 ppm-hours. The other option is to make the secondary standard identical to the proposed primary 8-hour standard. The EPA solicits comment on specifying a cumulative, seasonal standard in terms of a 3-year average of the annual sums of weighted hourly concentrations; on the range of alternative 8-hour standard levels for which comment is being solicited for the primary standard, including retaining the current secondary standard, which is identical to the current primary standard; and on an alternative approach to setting a cumulative, seasonal secondary standard(s).