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Researchers Shed Light On Long-Distance Dust Clouds

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By DOUG STRUCK, The Washington Post

Published: February 9, 2008

Seventy-five years ago, aviator Charles Lindbergh turned the controls of his pontoon plane over to his co-pilot, wife Anne Morrow Lindbergh, while flying above Iceland. He thrust a makeshift metal arm holding a sticky glass plate from the cockpit. He wanted to see if the winds high aloft the Earth were as clean as they seemed.

They were not.

Now, with NASA satellites and sampling by researchers around the world, scientists know that great billowing clouds of dust waft over the oceans in the upper atmosphere, arriving in North America from deserts in Africa and Asia.

Researchers also have found that the dust clouds contain not only harmful minerals and industrial pollutants, but also living organisms: bacteria, fungus and viruses that may transmit diseases to humans. Some say an alarming increase in asthma in children in the Caribbean is the consequence of dust blown from Africa, and predict they will find similar connections in the Southeast and Northwest United States.

Scientists are beginning to look at these dust clouds as possible suspects in transcontinental movement of diseases such as influenza and SARS in humans, or foot-and-mouth disease in livestock. Until recently, epidemiologists had looked at people, animals and products as carriers of the diseases.

"We are just beginning to accumulate the evidence of airborne dust implications on human health," said William Sprigg, a climate expert at the University of Arizona. "Until now, it's been like the tree falling in the forest. Nobody heard, so nobody knew it was there."

The World Meteorological Organization, a science arm of the United Nations, is alarmed enough to set up a global warning system to track the moving clouds of dust and to alert those in the path. Sprigg is heading the project.

He foresees a system soon in which forecasters can predict "down to the ZIP code" the arrival of dust clouds. That forecast could prompt schools and nursing homes to keep their wards inside, and help public health doctors predict a surge of respiratory complaints.

Analysis of soil samples has long shown that minerals picked up from barren deserts reach distant shores, for good or bad. The Amazon rain forest in South America, for example, gets phosphate nutrients from dust blown in from northern Africa's Sahara Desert.

Traveling for a week over the Pacific from the Gobi and Taklimakan deserts in Asia, clouds carrying hundreds of millions of tons of dust regularly reach the northwestern United States. From the Sahara and Sahel deserts in Africa and the East, they roll across the Atlantic to the Caribbean and reach the southeastern United States in three to five days.

Authorities in Los Angeles estimate that on some days, one-quarter of the city's smog comes from China.

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