Chinese Smog Clouding US Skies, Scientists Say
David Knowles
http://www.sphere.com/nation/article/chinese-smog-clouding-us-skies-scientists-say/19324469
Condensed by Native Village

Since the 1980s, surface ozone levels in the U.S. have decreased by 30%. That drop is due to stronger environmental regulations. But scientists puzzled over why ozone levels in the free troposphere -- two to five miles above sea level -- increased 14% from 1995 - 2008.

A new study points to air pollution from Asia as a major cause.  The study tracked smog from Asian nations like China as it drifted over the Pacific Ocean towards the U.S.

"We studied a broad range of ozone levels that we could track coming from Asia," said Owen R. Cooper from the University of Colorado. "And we know that, though the Chinese government has just started to measure ozone levels there, the gas has been increasing in China over the past 10 years."

Cooper studied the drifting ozone in springtime when the jet stream transports the most pollution across the Pacific. Spring ozone levels have risen 29% in the U.S. since 1984.

Cooper is not sure how much ozone comes from Asia but said the amount doubles when the jet stream passes over southern and eastern Asia.

"What we still don't know is how much of the ozone from Asia is coming down to the earth's surface and affecting health in the United States,"  Cooper said.

Along with other "greenhouse gases" like as carbon dioxide and methane, ozone contributes to global warming.