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The Piston Effect

Scientists and engineers around the world are becoming aware that the United States 8-hour ozone standard is presenting a problem that is called "unattainability." Over 20 years ago, the unattainability issue was discussed by Dr. Lefohn, President and Founder of A.S.L. & Associates. In November 1998, the topic was discussed at an international meeting in Beijing, China by Dr. Lefohn. Policymakers are now finding that the 8-hour ozone standard will be difficult to attain and control strategies will not work as planned as lower and lower standard levels are promulgated. Mid-range hourly average concentrations decline slower than the higher hourly average concentrations and make it difficult to attain the lower standards. Independent analyses have confirmed the "piston" effect. Two publications (Lefohn et al., 2017; Lefohn et al., 2018) identify how the "piston" effect influences ozone monitoring sites in the EU and the US. Watch a slide presentation of the "piston" effect.

Lefohn, A.S., Malley, C.S., Simon, H., Wells. B., Xu, X., Zhang, L., Wang, T., 2017. Responses of human health and vegetation exposure metrics to changes in ozone concentration distributions in the European Union, United States, and China. Atmospheric Environment 152: 123-145. doi:10.1016/j.atmosenv.2016.12.025.

Lefohn, A.S., Malley, C.S., Smith, L., Wells, B., Hazucha, M., Simon, H., Naik, V., Mills, G., Schultz, M.G., Paoletti, E., De Marco, A., Xu, X., Zhang, L., Wang, T., Neufeld, H.S., Musselman, R.C., Tarasick, T., Brauer, M., Feng, Z., Tang, T., Kobayashi, K., Sicard, P., Solberg, S., and Gerosa. G. 2018. Tropospheric ozone assessment report: global ozone metrics for climate change, human health, and crop/ecosystem research. Elem Sci Anth. 2018;6(1):28. DOI:

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