The residents of Beijing and Delhi are not the only ones feeling the effects of Asian air pollution — an unwanted byproduct of coal-fired economic development. The continent's tainted air is known to cross the Pacific Ocean, adding to homegrown air-quality problems on the U.S. West Coast.
Scientists call airborne particles of any sort — human-produced or natural — aerosols. The simplest effect of increasing aerosols is to increase clouds. To form clouds, airborne water vapor needs particles on which to condense. With more aerosols, there can be more or thicker clouds. In a warming world, that's good. Sunlight bounces off cloud tops into space without ever reaching Earth's surface, so we stay cooler under cloud cover.
But that simplest effect doesn't always happen. If there's no water vapor in the air — the air is dry — aerosols can't make clouds. Different types of aerosols have different effects, and the same aerosol can have different effects depending on how much is in the air and how high it is. Soot particles at certain altitudes can cause cloud droplets to evaporate, leaving nothing but haze. At other altitudes, soot can cause clouds to be deeper and taller, producing heavy thunderstorms or hailstorms. With so many possibilities, aerosols are one of the largest sources of uncertainty in predicting the extent of future climate change.
The experiments and result
During the last 30 years, clouds over the Pacific Ocean have grown deeper, and storms in the Northwest Pacific have become about 10 percent stronger. This is the same time frame as the economic boom in Asia. JPL researcher Jonathan Jiang and his postdoctoral fellow, Yuan Wang, designed a series of experiments to see if there was a connection between the two phenomena.
"We found that pollution from China affects cloud development in the North Pacific and strengthens extratropical cyclones," said Wang. These large storms punctuate U.S. winters and springs about once a week, often producing heavy snow and intense cold.