As smog wafts westward from the booming industrial cities of Asia, the need for international emissions standards becomes crystal clear.

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The first high-resolution analysis of smog traveling across the Pacific reveals that the contribution of Asian smog to pollution in U.S cities is higher than previously thought. During the spring of 2010, for example, pollution from Asia contributed 20 percent of the ozone measured at key locations along the U.S. west coast.

What is more, on days when ozone levels in U.S. cities were higher than the maximum, Asian emissions pushed them over their safety limits more than half the time.

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Atmospheric scientists have tried in the past to quantify the role of imported pollution, but the latest analysis, published last month in the Journal of Geophysical Research, went a step further by showing that Asian emissions directly contribute to ground-level pollution in the U.S.

“The findings carry significant implications not only for regulating local emissions, but also for negotiating international standards,” science writer Katherine Rowland reported yesterday in Nature. “Although ozone emissions have been falling in the United States and Europe, they have been on the rise in Asia, and especially in China.”

This cloud’s silver lining is that satellites track pollution plumes over the Pacific nearly every day. If scientists put these satellites to work forecasting pollution spikes a day or two before they arrive, they could help safeguard the health of the people most susceptible.

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Photo: Natural color satellite image of a smog event in China on Oct. 8, 2010. The milky white and gray in the center of the image is a mixture of smog and fog; the brighter whites at the left and right edges are clouds. (Courtesy of NASA Earth Observatory)