The difficult challenge of attaining EPA's 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 averages the annual fourth highest daily 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. Using information from EPAS 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 are implemented, 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. For most sites that violate the new standard, attainment may be difficult, and in some cases, impractical, to achieve.