Westerly winds can carry air pollution from China across the Pacific Ocean in just a few days.
The study was published in the Proceedings of the National Academy of Sciences by researchers in the United Kingdom, China and the U.S.
And within China, roughly 5 percent of emissions of carbon monoxide, black carbon, Sulfur dioxide and nitrogen oxides came from making those exports, according to the report.
Coal-burning factories were the biggest sources of the air pollutants -– and greenhouse gases.
The amount of air pollution in the Western U.S. from China is still very small, compared to the amount we produce here already.
Almost a quarter of China’s economic output came from exports last year.