Polluted air from China is blowing across the Pacific Ocean in large quantities and contributing to smog in the United States, according to new research by a team of Chinese and American scientists.
On some days, acid rain-inducing sulphate from burning of fossil fuels in China can account for as much as a quarter of sulphate pollution in the western United States - and ironically, much of that air pollution is being caused by the manufacture of goods in China for export to the United States and Europe, the researchers said.
They said that Cities like Los Angeles received at least an extra day of smog a year from nitrogen oxide and carbon monoxide from China's export-dependent factories.
Between 17 and 36 per cent of various air pollutants in China in 2006 were related to the production of goods for export, according to the report, and a fifth of that specifically tied to US-China trade.
The report shows that many pollutants, including black carbon - which contributes to climate change and is linked to cancer, emphysema and heart and lung diseases - travel huge distances on the global winds known through history as The Westerlies.
''We've outsourced our manufacturing and much of our pollution, but some of it is blowing back across the Pacific to haunt us,'' said co-author of the study Steve Davis, a scientist with the University of California at Irvine. ''Given the complaints about how Chinese pollution is corrupting other countries' air, this paper shows that there may be plenty of blame to go around.''
The paper was published in the Proceedings of the National Academy of Sciences on Monday. According to the researchers, it is the first to quantify how much of the pollution reaching the West Coast of the United States is caused by production in China.
A decrease in manufacturing in the United States amid growing local environment concerns has led to cleaner air in its Eastern regions. But pollutants wafting in from China have harmed the West, according to the study.
Los Angeles has at least one additional day each year that exceeds federal ozone standards because of nitrogen oxides and carbon monoxide emitted by Chinese factories. And as much as a quarter of the sulphate pollution on the West Coast can be tied to Chinese exports, the report says.
''When you buy a product at Wal-Mart,'' Davis said, ''it has to be manufactured somewhere. The product doesn't contain the pollution, but creating it caused the pollution.''
China's neighbours like Japan and South Korea have suffered from noxious clouds emanating from China over the last two decades.
The report said its findings showed that trade issues must play a role in global talks to cut pollution. "International cooperation to reduce trans-boundary transport of air pollution must confront the question of who is responsible for emissions in one country during production of goods to support consumption in another," it said.