Measurements of air pollutants over the North Pacific have documented one of Asia's biggest exports - air pollution. A NASA study has concluded that some 40 billion pounds of aerosols - smoke, ash, and acid droplets from forest fires, coal stoves, automotive and industrial exhaust  - drifted out across the Pacific between 2002 and 2005. About 10 billion pounds of that reached North America.

That incoming pollution is about 15 percent the volume of the pollution we generate ourselves. The study's lead author, Hongbin Yu, of the University of Maryland Baltimore County, said, “This is a significant percentage at a time when the U.S. is trying to decrease pollution emissions to boost overall air quality. This means that any reduction in our emissions may be offset by the pollution aerosols coming from East Asia and other regions.” Yu is an assistant research scientist at UMBC, currently working at the NASA Goddard Space Flight Center in Greenbelt.

Satellites have tracked the pollution during its journey from East Asia and Russia, and provided scientists with data for their estimates of the volume and contents of the brown clouds. Rapid industrial growth in China has made matters worse, the study found.

Here's how it looked to the satellite's instruments on one day in 2003. You can read all about it here.