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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 2019 confirm the effect. 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 as the standard is lowered. Our research indicates that the "piston effect" will be a problem across many sites in the United States. Our research results about the "piston effect" were summarized into a final report in May 1997 and a scientific paper was published in Environmental Science and Technology in June 1998 (Lefohn et al., 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.

Lefohn A. S., Shadwick D. S. and Ziman S. D. (1998). The Difficult Challenge of Attaining EPA's New Ozone Standard. Environmental Science & Technology. 32(11):276A-282A.

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