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Pedestrians walk as haze partially obscures a view of downtown Harbin, Heilongjiang province, January 6, 2014. A new study shows that pollution from Chinese heavy industry is drifting across the Pacific and affecting air quality on the west coast of North America.Kim Kyung Hoon/Reuters

Canada and the United States may have outsourced a large amount of manufacturing to China over the years, but a new study shows that pollution from heavy industry concentrated on the east coast of Asia is drifting across the Pacific Ocean and helping foul the air on North America's west coast.

The emissions from that outsourced production – which have contributed to pushing heavily polluted areas such as Los Angeles over air quality limits – have even greater impact on sparsely populated areas with less industry, such as British Columbia.

The study was published in the Washington, D.C.-based Proceedings of the National Academy of Sciences, and was written by nine scientists on both sides of the Pacific, including scholars from the prestigious Peking and Tsinghua universities in China and the University of California, Irvine.

The paper's authors say it is the first to link Chinese emissions related to the export industry to pollution in North America. The study comes as China seeks to refocus its economy away from polluting, unsustainable exports and toward domestic consumption. It also adds to the debate about who should be held responsible for pollution that occurs in developing countries but is linked to western consumption.

Steven J. Davis, an assistant professor at the University of California's Department of Earth System Science and a co-author of the paper, said in an interview that the study's focus was on the United States, but he is confident up to 20 per cent of sulfate pollution – a product of burning coal and other fossil fuels – on Canada's west coast could come from China's export-geared industries.

"You guys have a pretty clean atmosphere up there," said Mr. Davis, who is based in the greater Los Angeles area. "In places like the west coast of Canada, there aren't as many sources of local pollution, so the Chinese pollution would be a larger source of the [overall] pollution."

China is the world's worst polluter, followed by the United States. As U.S. corporations moved manufacturing to Asia, China's emissions from that kind of production have increased between 3.6 per cent and 7.4 per cent, depending on the type of pollution, and U.S. emissions related to those industries has dropped off.

But China's less advanced technology to control emissions also means it "emits far more pollutants per unit of gross domestic product than countries with more advanced industrial and emission control technologies," the study said, in some cases, six to 17 times more than the United States.

The rapid expansion of heavy, industrial processes behind China's exports has been powered by the inefficient combustion of fossil fuels, particularly coal. This has led to a global increase in emissions of carbon dioxide and other air pollutants, such as sulfur dioxide, nitrogen oxides, black carbon and carbon monoxide.

"And as scientific evidence of transport of Chinese air pollution across the Pacific Ocean has grown since the late 1990s," the study notes, "the United States and Canada have a special interest in reducing Chinese air pollution."

China's leaders have said they want to reduce the country's reliance on coal for roughly three-quarters of its energy needs in part by growing the amount provided by cleaner-burning liquified natural gas, some of which could eventually come from British Columbia.

Although the study showed emissions related to production in China have fallen or flattened since the financial crisis crimped Western demand for Chinese-made goods, domestic growth in China has continued – and contributed to per capita increases in emissions related to Chinese consumption.

Mr. Davis stresses that Western consumers' role in rampant pollution in Asia – where some safeguards are less developed, and government-linked industries may lack transparency – is often understated. Between 2000 and 2007, as rural migrants flocked to factories on China's coast, Chinese exports grew by 390 per cent, according to official statistics.

During that period, China's coal use roughly doubled, according to Jennifer Turner, the long-time director of the China Environment Forum at the Woodrow Wilson Center in Washington, D.C. – and it is doubling again. And even though the majority of China's pollution can be traced to domestic uses, Ms. Turner said the new study offers a chance to have a broader debate about the responsibility for China's pollution problem.

That broader responsibility might also power new solutions, such as the Natural Resources Defense Council's efforts to help international clothing companies clean up the textile mills that are polluting China's waterways.

"I call it 'cash and carry karma,' " she said. "The pollution comes back. It kind of just shows us – it's one world."