ENVIRONMENTAL POLICY
ANALYSIS
AIR QUALITY The Difficult Challenge of Attaining EPA's New Ozone Standard A L L E N S. L E F O H N A.S.L. & Associates 111 North Last Chance Gulch Helena, MT 59601
DOUGLAS S. SHADWICK ManTech Environmental Technology, Inc. Research Triangle Park, NC 27709 S T E P H E N D. Z I M A N Chevron Research and Technology Richmond, CA 94804
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 concentrationbased 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 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 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.
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It has long been recognized that ozone and related pollutants affect public health (2). Replacement of the previous 1-hour primary ozone standard was based on public comment and EPA's review of air quality criteria and National Ambient Air Quality Standards for ozone. The agency also replaced the previous secondary standard that protects the environment with a standard identical to the new primary standard. For an interim period, the 1-hour standard will continue to apply to areas not currently in attainment to ensure an effective transition to the new standard. In concordance with provisions of the Clean Air Act (CAA), areas would be designated as nonattainment according to the 8-hour standard by the year 2000, and affected states must submit their nonattainment State Implementation Plans by 2003. EPA noted that a regional approach, coupled with implementation of existing state and federal CAA requirements, will allow the majority of areas that currently meet the 1-hour ozone standard, but would not omerwise meet the new 8-hour standard to achieve healthful air quality without additional local controls (3). The previous standard was attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm was equal to or less than 1, averaged over three years. This meant that no more than three exceedances in three years were allowed (4). Emissions control strategies, based on attaining the previous 1-hour ozone standard, were focused on reducing the high hourly average concentrations above 0.12 ppm. St. John and Chameides (5) questioned whether promulgation of the new standard would alter the choice of control strategies that would most effectively bring a nonattainment area into compliance. To address this problem, it is important to understand whether violations of the new standard are associated with high-level (>0.09 ppm) or midlevel (0.06-0.09 ppm) ozone concentrations. If midlevel hourly average concentrations at some sites are responsible for violations, control strategies need to focus on reducing these concentrations to attain the standard. Research indicates that midlevel ozone concentrations are reduced by control strategies at a different rate than the higher hourly average concentrations; the higher concentrations are reduced faster than the lower values (6-8). This observation implies that it may be more difficult to prevent violations of the new 8-hour standard. In 1985, EPA (6) reported that when the first-generation regional oxidant model was applied, emissions controls reduced peak concentrations by considerably larger 0013-936X/98/0932-276A$15.00/0 © 1998 American Chemical Society
percentages than the median or mean concentration values. The emissions controls had no significant effect on concentrations below approximately the 90th percentile value (0.080-0.090 ppm in the summer and approximately 0.070 ppm in the spring). Roselle and Schere (7) described similar observations. EPA (8) noted in its recent examination of air quality over the past 25 years that for sites that historically showed improvements, somewhat larger reductions occurred at the higher hourly average concentrations than at the middle or lower values. This observation of increased resistance in the midlevel hourly average concentrations, in comparison to the higher hourly values, is similar to the resistance of a gas when compressed by a piston. Although the resistance initially is low, it increases as the piston compresses the gas. The implication of the piston effect is that sites whose 8-hour daily maximum violation is influenced by midlevel hourly average concentrations will show slower improvements toward compliance than sites that are more influenced by the higher hourly average concentrations. Because of the potential importance of this effect on the efficacy of control strategies for reducing ozone levels, we investigated the number of sites that, during 1993-95, violated the new standard and whose midlevel hourly average concentrations played an important role in defining these violations. Data for these years were the most current at the time of the analysis, and violations of the new standard are based on a three-year averaging period. We evaluated the piston effect. Using data from EPA's air quality databases, we quantified, for ozone sites that experienced statistically significant declines, the rate of decline (at 0.01 ppm increments) of hourly average ozone concentrations at the highlevel (>0.09 ppm), midlevel (0.06-0.09 ppm), and lowlevel (
