Their study focuses on data for ozone in springtime above western North America at an altitude of between three and eight kilometers (two and five miles).
This height is between the stratosphere -- where a thin layer of ozone helps to filter out dangerous ultra-violet light from the Sun -- and ground level, where ozone can be a bad hazard for people with cardiac or respiratory problems.
The paper, published in the British journal Nature, said that ozone levels in the monitored area rose by 14 percent in springtime from 1995 and 2008.
When data were included for 1984, the year with the lowest average ozone level, the increase from that date up to 2008 was a whopping 29 percent.
The surge could only be explained by pollutants that are the precursors to ozone and were borne across the Pacific from East and South Asia by powerful winds, it says.
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