Homegrown air pollution is bad enough, but for years scientists have tracked pollution rising out of Asia, crossing the Pacific Ocean, and descending over the western United States. Now they are able to sort out the imported air pollution from local varieties. In the Journal of Geophysical Research, a group of atmospheric scientists and modelers reports that a new, more finely detailed model can rather accurately simulate both atmospheric circulation and the airborne chemical reactions that produce pollutant ozone. By modeling two closely monitored Asian pollution episodes in the spring of 2010, they found that the Asian contribution over the southwestern United States could amount to 15 parts per billion of ozone (orange-red on three consecutive days in panels, left to right). The current U.S. air-quality standard for ozone is 75 parts per billion. The group found that about half of the times that that threshold was exceeded, the Asian contribution was responsible for the violation. That could become even more troublesome, the authors note, if Asian imports increase as expected in the coming decades.
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