The stifling air pollution you keep reading about in China is actually a byproduct of American outsourcing and now that pollution is drifting across the globe to the Western U.S. At least, that's the claim made by a new study, that the paper's co-authors called a "boomerang" effect. 

In the paper, published on Monday in the Proceedings of the National Academy of Sciences, the authors find that China's export-related pollution contributes up to 12 to 24 percent of daily sulfate levels in the Western United States, making Los Angeles and other Western cities violate national ozone levels for an extra day each year. The study is the first to examine how China's pollution affects the U.S. and how global consumption impacts pollution, according to the New York Times

The movement of air pollutants associated with the production of goods in China for the American market has resulted in a decline in air quality in the Western United States, the scientists wrote, though less manufacturing in the United States does mean cleaner air in the American East.

The report's authors, nine scientists from the U.S., U.K., and China, write that about one-fifth of Chinese pollution results from manufacture for export. The researchers considered data from 2006 in making their conclusions, and found that though moving manufacturing production to China yielded a net gain in terms of U.S. air pollution, it decreased the quality of Western air — not to mention China's. The Los Angeles Times reports: 

Scientists followed the path of air pollutants, including sulfur dioxide, nitrogen oxides carbon monoxide and black carbon, through the atmosphere to gauge their effects on air quality in the United States. While the United States has reaped some of the benefits of outsourcing — cheaper cellphones, televisions and appliances and big declines in air pollution — rising emissions in China have paralyzed cities there with severe smog.

CNN notes that roughly 21 percent of export-related emissions from China come from goods sent to the U.S. The emissions include anthropogenic sulfur dioxide, nitrogen oxides, carbon monoxides and black carbon, which is linked to lung cancer, emphysema, and heart and lung disease. China saw a manufacturing boom from the early 2000s, but their production is generally less efficient than America's, and subject to less stringent safety standards. 

In China, air pollution has become a huge safety concern. Chinese residents have been instructed to stay indoors on heavy smog days, and major cities are trying to curb pollution by introducing reforms. U.S. smog levels, on the other hand, are so far changing only slightly. According to the researchers, most LA pollution is caused locally. 

The report authors hope that their findings will shine a light on shared responsibility for air quality. “We need to move beyond placing blame for who’s creating these emissions and realize that we all have a common interest in reducing the pollution,” UC Irvine's Steve Davis said