Challenges of a lowered U.S. ozone standard

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Science  05 Jun 2015:
Vol. 348, Issue 6239, pp. 1096-1097
DOI: 10.1126/science.aaa5748

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At Earth's surface, ozone is an air pollutant that causes respiratory health effects in humans and impairs plant growth and productivity (1). The Clean Air Act (CAA) of 1970 mandates that the U.S. Environmental Protection Agency (EPA) assess the ozone standard every 5 years and revise when necessary to protect human health. With a decision expected in October 2015 as to whether the standard will be toughened, we discuss limitations of ozone and precursor observations that hinder the ability of state and local air pollution–control agencies to accurately attribute sources of ozone within their jurisdictions. Attaining a lower standard may be particularly challenging in high elevations of the western United States, which are more likely to be affected by ozone that has been transported long distances or that originated in the stratosphere.