In DepthAtmospheric Science

China blamed for U.S. ozone

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Science  12 Sep 2014:
Vol. 345, Issue 6202, pp. 1233
DOI: 10.1126/science.345.6202.1233

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Some U.S. states are starting to be caught between rising background levels of ozone pollution and legal standards that continue to be ratcheted down. Based on health studies, staff at the Environmental Protection Agency on 29 August recommended that the agency set an ozone limit somewhere between 60 to 70 parts per billion, down from the current 75 parts per billion limit. But background ozone pollution—some of it natural, some of it carried across the Pacific Ocean from Asia—continues to rise, especially in the high-altitude states of the mountain west. Scientists say that ozone pollution is no longer a problem that can be dealt with by local regulations alone.