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Difficulty in Attaining the Ozone Standard
The "Piston Effect"

Scientists and engineers around the world are becoming aware that the United States 8-hour ozone standard may present a problem that is called "unattainability." In November 1998, the topic was discussed at an international meeting in Beijing, China. The unattainability issue has been raised by A.S.L. & Associates and others. In the coming years, policymakers will find that the 8-hour ozone standard as it is lowered will be difficult to attain and control strategies will not work as planned. Mid-range hourly average concentrations decline slower than the higher hourly average concentrations and make it difficult to attain the standard. Independent analyses have confirmed the "piston effect". EPA reports and papers published in 1985, 1995, 1996, 2014, and 2016 confirm the effect. A.S.L. & Associates has estimated that more than 50% of the areas originally identified by the EPA as violating the 8-hour ozone standard would have difficulty in attaining the standard. For many sites in the United States, there are simply too many concentrations in the mid range and these concentrations are responsible for the violation of the 8-hour standard. Our research indicates that the "piston effect" will be a widespread problem across sites in the United States. Our research results were summarized into a final report in May 1997 and a scientific paper was published in Environmental Science and Technology in June 1998. A slide presentation summarizing the "piston effect" is available. More detailed information about the effect and the possible reasons for its occurrences can be found by clicking here.

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