SAN FRANCISCO--It's a sign of spring in Asia: Winds pour off the Siberian plateau, kick up dust from Mongolian and Chinese deserts, and loft it over the Pacific Ocean. Such a storm howled in April, replete with industrial chemicals, and an armada of scientists caught it in full blow. Their results offer a startling view of how pollutants alter the contents of dust clouds, with near-global impacts.
This year's storm was the most severe in the Northern Hemisphere in at least 2 decades. It began to brew on 5 April in the Gobi and Taklamakan deserts, then it spread rapidly over China, Korea, and Japan. Within a week, milky dust clouds reached the west coast of North America, wafting as far east as the Canary Islands. The event coincided with Aerosol Characterization Experiment-Asia (ACE-Asia), a U.S.-led effort to study fine atmospheric particles, called aerosols, in regions such as China and Mongolia where many dust storms originate. A combination of satellites, airplane flights, shipboard measurements, and instruments on land produced the most detailed study yet of a dust storm and the aerosols it carries.
Early analysis, presented here on 11 December at a meeting of the American Geophysical Union, suggest that regional droughts and human impacts exacerbated the storm's effects. Sediments from a dried lake bed near Beijing, caused by overpumping of water, whipped into the wind and triggered another dense, unexpected dust cloud while the initial storm was still raging, says lead ACE-Asia scientist Barry Huebert of the University of Hawaii, Manoa.
Industrial soot from Asia polluted most of the dust to a surprising degree. Those heavy particles dropped out of the clouds before they crossed the ocean, but finer aerosols, including mercury from space heaters and arsenic from smelters, traveled in the clouds for more than a week. Harmful levels persisted for thousands of kilometers, says atmospheric physicist Thomas Cahill of the University of California, Davis, part of the ACE-Asia team. "The highest level of arsenic we ever saw in Nevada came from Manchuria," he notes.
"This was one of the most remarkable dust events in my memory," says atmospheric chemist Joseph Prospero of the University of Miami in Florida. The data on pollutants are crucial for climate models, Prospero says, because the dark particles absorb and redistribute far more heat in the atmosphere than typical aerosols from the Sahara Desert and elsewhere.