Roughly one quarter of the air pollution choking China comes from factories supplying the rest of the world with shoes, electronics, toys, and almost everything else, according to a new study.
But according to a team of U.S. and Chinese researchers, the smog made in China does not stay there. Findings of their work published in the Proceedings of the National Academy of Sciences indicate the pollution is drifting across the Pacific Ocean and clouding air in the United States.
Focusing on 2006, the study finds that export industries produce one-third of China's sulfur dioxide, one-fourth of its nitrogen oxides, one-fourth of its carbon monoxide, and one-sixth of its black carbon.
By first analyzing the amount of pollution generated by producing each good or service, the group then determined what proportion of those goods and services was exported.
Study co-author Steven Davis at the University of California, Irvine, says the research places images of the heavily polluted country in a different context. "Maybe a quarter of what you are seeing when you see pictures of that Chinese pollution and everyone wearing masks has to do with goods they are making for other parts of the world," he said.
Of the export-related pollution, 21 percent was due to trade with the United States, the researchers said, a significant portion of which boomeranged back to China.
Using atmospheric models, the researchers determined that as much as a quarter of the sulfur dioxide polluting the air over the western United States that year came from China.
California Air Resources Board officials say the Los Angeles area had 120 excessive-ozone days in 2006, of which, atmospheric models indicate, Chinese pollution contributed to two extra days. "We do have pollution still in this country," Davis said. "We are not completely blameless."
But the pollution did not stop at the West Coast. Chinese emissions also added two non-compliant days in Chicago and the surrounding areas, which had fewer than 10 in 2006, and regions on the East Coast were affected as well.
The authors note that while Chinese air has grown dirtier, it has grown cleaner in the northern and eastern United States as manufacturing has leave these regions -- often for China.
"What this paper is saying is that China is playing a role in terms of polluting U.S. air," said Texas A&M University atmospheric chemist Renyi Zhang, who was not involved in the research. "But the United States is actually playing a role as well because we are exporting the trading to the Chinese."
That, says Davis, puts some of the onus for China's polluted air on the United States and the other countries that rely on its export industries. "Insofar as you believe consumers somewhere down the road should bear some responsibility for the pollution that goes on to produce the goods and services they are consuming, the rest of the world has some responsibility to help China clean up that problem," he said.