The U.S. receives plenty of exports from China — including electronics, toys, clothing — and even toxic air pollution stemming from Chinese factories miles away. Researchers from University of California, Irvine today published results from their study in the Proceedings of the National Academy of Sciences, which found that air pollution from Chinese production of televisions, cell phones, and other manufactured items actually blows across the ocean into the U.S. West Coast, filling the states with contaminated air.

“We’ve outsourced our manufacturing and much of our pollution, but some of it is blowing back across the Pacific to haunt us,” earth system scientist and co-author Steve Davis of UC Irvine said in a press release. “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 U.S. is certainly already producing much of its own pollution — whether from cars, factories, trucks, or refineries. But global winds called “westerlies” can push chemicals and toxins from China across the ocean in only days, especially in the spring, when these winds are strongest. As a result, dust, ozone, and carbon flow into California, gathering in valleys and basins.

The study found that Los Angeles experiences about one extra day per year of smog exceeding federal ozone limits, due to exposure to nitrogen oxides and carbon monoxide originating in Chinese factories. On top of that, up to a quarter of the sulfate pollution on the West Coast of the U.S. is linked to Chinese exports, the authors claim; all of the toxins and contaminants identified in the study are typical ingredients found in hazardous smog and soot. “When you buy a product at Wal-Mart,” Davis said in the press release, “it has to be manufactured somewhere. The product doesn’t contain the pollution, but creating it caused the pollution.”

Air pollution reaching the U.S. West Coast from China has been a concern for a while now, as China’s pollution problem continues to worsen, with big cities like Shanghai or Hong Kong often draped in thick, polluted hazes. At the same time, China’s neighboring countries — such as Japan and Korea — are at an even higher risk of being hit with drifts of pollution. “The countries most directly affected by air pollution from China are its nearest neighbors,” Paul Harris, chair professor of global and environmental studies at the Hong Kong Institute of Education, told The Star Online. “As with every other aspect of relations with China, there is a limit to what they can do about it.”

Dan Jaffe, professor of atmospheric and environmental chemistry at the University of Washington-Bothell, notes that on the West Coast, places at higher elevations are more likely to be exposed to “pollutants coming from Asia,” he told The Star Online. Jaffe works at a station located 3,000m high on a mountain in Oregon; it’s much easier to measure air pollutants high up than it is at sea level. The Pacific Ocean is also at risk. Once a clean and relatively untouched environment, the Pacific will now see an uptick in pollution as Chinese air drifts over the water.

However, some scientists think that the pollution coming from China and other Asian countries is small compared to U.S. domestic sources of pollution and other neighboring countries, throughout North America and South America.

Though China has attempted to cut down on its pollution recently, Asian countries don’t have as strong of a tendency to cooperate on cross-border anti-pollution action. Loren Cass, an associate professor of political science at the College of the Holy Cross in Massachusetts, told The Star Online that while European countries have successfully cooperated to reduce cross-border air pollution, “there’s really been no history of that regional cooperation in Asia.”

The authors of the study urge the U.S. to be more aware that many of the products they demand and import from China actually contribute to a worldwide effect on the environment: “International cooperation to reduce transboundary 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.”