Asian air pollution affects our weather

Carried on prevailing winds, the industrial outpouring of dust, sulfur, carbon grit and trace metals from booming Asian economies is having an intercontinental cloud-seeding effect, the researchers reported in the Proceedings of the National Academy of Sciences.

The study is the first large-scale analysis to draw a link between Asian air pollution and the changing Pacific weather patterns.

"The pollution transported from Asia makes storms stronger and deeper and more energetic," said lead author Renyi Zhang at Texas A&M University. "It is a direct link from large-scale storm systems to [human-produced] pollution."

Satellite measurements reveal that high-altitude storm clouds over the northern Pacific have increased up to 50% over the last 20 years as new factories, vehicles and power plants in China and India spew growing amounts of microscopic pollutant particles into the air.

The resulting changes have altered how rain droplets form and helped foster the creation of imposing formations over the northern Pacific known as deep convective clouds.

The clouds create powerful updrafts that spawn fiercer thunderstorms and more intense rainfall, particularly during the winter, the researchers said.

Only a decade ago did scientists in the University of California's Pacific Rim Aerosol Network help discover that the pollution crossing the Pacific from Asia was worse than suspected, with millions of tons of previously undetected contaminants carried on the wind.

In fact, on any spring or summer day, almost a third of the air high over Los Angeles, San Francisco and other California cities can be traced directly to Asia, researchers said.

"More stuff starting up over there means more stuff ending up over here," said UC Davis atmospheric scientist Steven Cliff.

Usually, dust and industrial pollutants take from five days to two weeks to cross the Pacific to California.

Zhang and his colleagues conducted their three-year study by comparing satellite imagery of the Pacific region taken from 1984 to 1994 with imagery of the same area from 1994 to 2005. The study, funded by NASA and the National Science Foundation, found that deep convective clouds had increased between 20% and 50%.