On Sept 16, 1997, the new 8-hour ozone standard replaced the previous 1-hour primary ozone standard. EPA set the new standard at 0.08 parts per million (ppm) and defined it as a concentration-based form that averages the annual fourth highestdaily maximum 8-hour ozone concentrations over three years (1). For control purposes, it is important to understand whether high-level (>0.09 ppm) or instead midlevel (0.06-0.09 ppm) ozone concentrations are mainly responsible for violations. Usinginformation from EPA's air quality database, we found that, for 1993-95, more than 50 of the areas that would violate the new standard were influenced by midlevel hourly average concentrations. Our analysis shows that as control strategies areimplemented, violating sites that experience high daily maximum 8-hour average concentrations will realize faster declines than violating sites that experience daily maximum 8-hour average concentrations above, but near; the 8-hour 0.08-ppm standard. Formost sites that violate the new standard, attainment may be difficult, and in some cases, impractical, to achieve.
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