Air pollution from the industrial towns of Asia has affected cities in the US, according to a study published in the Nature journal.
The study has been conducted by the researchers from the Princeton University in New Jersey and the University of Washington Bothell.
From past few decades, researchers have been documenting the phenomenon of pollution crossing the Pacific Ocean.
Researchers discovered that emission from Asia directly contribute to ground-level pollution in the United States.
The study also found out that ground-level pollution in the US is higher than previously estimated.
Researchers have used chemical modeling that distinguished between locally generated pollution and that arriving from thousands of miles away.
They analysed air-quality data from satellites and ground measurements to track passage of ozone from Asia's churning factories to the western United States over the course of a few days in mid-2010.
Majority of US ground pollution came from local sources, but as much as 20 percent was attributable to Asian emissions, the study pointed out.
"We show that Asian emissions directly contribute to ground-level pollution in the United States," the Nature journal quoted Meiyun Lin, an atmospheric chemist at Princeton University, New Jersey, who is the lead author of the report as saying.