The U.S. may have sent jobs making cellphones and big-screen TVs to Chinese factories, but the pollution from those factories is coming back onshore.
China's famously foul urban air is blowing across the Pacific Ocean — much of it derived from factories that make popular consumer goods sold in the U.S. and Europe, according to a new paper by a group of researchers at the University of California at Irvine and other scientists published in the Proceedings of the National Academy of Sciences.
"When you buy a product at Walmart, it has to be manufactured somewhere," said co-author Steven Davis, an earth systems scientist at Irvine, in a press release. "The product doesn't contain the pollution, but creating it caused the pollution."
Air pollution is a major problem confronting China's leaders, who are coping with social, economic and environmental strains resulting from decades of rapid industrialization. A former Chinese health minister recently said that air pollution kills 500,000 people in China every year.
Most air pollution in the U.S. is produced locally by cars, trucks, refineries and other sources. But powerful global westerly winds can move airborne chemicals across the Pacific in days, according to the researchers.
The incoming dust, ozone and carbon is especially strong in the spring, causing dangerous spikes in contaminants that can accumulate in valleys and basins in California and other Western states, the study said. In Los Angeles, for example, the nitrogen oxide and carbon monoxide from Chinese factories pushes smog levels above U.S. federal ozone limits at least one extra day a year.
The researchers said their study is the first to quantify how much of the pollution is tied to the production in China of cellphones, televisions and other consumer items exported to the U.S. and the rest of the world.
The scientists note that while Chinese pollution exports have degraded air quality in Western states, the offshoring of U.S. manufacturing has improved air quality in the eastern half of the country.
Follow CNBC's John Schoen on Twitter @johnwschoen.