THE DIFFICULT CHALLENGE OF ATTAINING EPAS NEW OZONE STANDARD

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 a verages the annual fourth highest daily maximum 8-hour ozone concentra tions over three years (1). For control purposes, it is important to u nderstand whether high-level (>0.09 ppm) or instead midlevel (0.06-0.0 9 ppm) ozone concentrations are mainly responsible for violations. Usi ng information from EPAS air quality database, we found that, for 1993 -95, more than 50% of the areas that would violate the new standard we re influenced by midlevel hourly average concentrations. Our analysis shows that as control strategies are implemented, violating sites that experience high daily maximum 8-hour average concentrations will real ize faster declines than violating sites that experience daily maximum 8-hour average concentrations above, but near, the 8-hour 0.08-ppm st andard. For most sites that violate the new standard, attainment may b e difficult, and in some cases, impractical, to achieve.