Based on its reconsideration of the primary and secondary national ambient air quality standards (NAAQS) for ozone (O3) set in March 2008, EPA proposes to set different primary and secondary standards than those set in 2008 to provide requisite protection of public health and welfare, respectively.[2938 Federal Register / Vol. 75, No. 11 / Tuesday, January 19, 2010 / Proposed Rules]
With regard to the primary standard for O3, EPA proposes that the level of the 8-hour primary standard, which was set at 0.075 ppm in the 2008 final rule, should instead be set at a lower level within the range of 0.060 to 0.070 parts per million (ppm), to provide increased protection for children and other ‘‘at risk’’ populations against an array of O3-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.
With regard to the secondary standard for O3, EPA proposes that the secondary O3 standard, which was set identical to the revised primary standard in the 2008 final rule, should instead be a new cumulative, seasonal standard expressed as an annual index of the sum of weighted hourly concentrations, cumulated over 12 hours per day (8 am to 8 pm) during the consecutive 3-month period within the O3 season with the maximum index value, set at a level within the range of 7 to 15 ppm-hours, to provide increased protection against O3-related adverse impacts on vegetation and forested ecosystems.