July 4, 2001. Copyright, 2001, Graphic News. All rights reserved

Ill wind blows no good
By Elisabeth Ribbans

LONDON, July 4, Graphic News:  AT this time of year, Òthe invisible windÓ becomes for many people a poetÕs myth, as swirling dust storms define all too clearly the shape and heading of the breeze. Picked up and whipped by the wind, dust may travel thousands of miles across land and sea in thick dense clouds that are capable at times of blocking out the sun. According to computer modelling conducted by the NASA Goddard Institute for Space Studies, the land beneath a dust cloud can cool by as much as 1 degree Celsius. But it is not the effect on the weather of these age-old phenomena that is troubling scientists.

Recent research carried out by the U.S. Geological Survey in the U.S. Virgin Islands found that dust storms blown in from Africa contained large amounts of fungi, bacteria and other unpleasant microbe migrants. Researchers who tested the dust samples warned that Òpathogenic microbes associated with dust clouds may pose a risk to the ecosystem and to human health.Ó The team, whose work is reported in the latest issue of the journal Aerobiologia, said the organisms could cause respiratory problems in people with weakened immune systems. Another scientist working in the Caribbean cited a 17-fold increase in asthma cases in Barbados between 1973 and 1996. Other studies suggest the dust may be to blame for damage to coral reefs.

Dust storms occur most frequently over regions of dry soil, where particles of dirt are loosely bound to the surface. Although sand falls back to earth within a few hours, smaller particles can remain suspended in the air for a week or more.
Between June and August, the deserts surrounding the Arabian Sea are the main source of dust clouds. These clouds are carried to the north-east by the Indian monsoons and to the west over North Africa. Along its westward journey, the plume is joined by dust from the Sahara, which regularly crosses the Atlantic causing bright red sunrises and sunsets in Florida. In the Southern Hemisphere, the Australian outback is the largest source of dust. NASA estimates that approximately half of the dust in todayÕs atmosphere may be the result of changes to the environment caused by human activity, including agriculture, overgrazing, and the cutting down of forests.

It is not only bugs that catch a ride on the wind: pollution likes to tag along, too. The huge dust cloud that blew out of north-west China, across the Pacific and into the U.S. earlier this year, will have picked up particles of industrial pollution as it crossed urban centres on its way to Beijing. As dust clouds increase in frequency and severity, the nasties they harbour causes growing concern. Russ Schnell, an official at the U.S. National Oceanic and Atmospheric Administration, told National Geographic News last month: ÒNature has sent us Ôa perfect stormÕ to reinforce the fact that we are all downwind of someone elseÕs pollution.Ó
/ENDS

Sources: AP, NASA, USGS, National Geographic