Dust nothing to sneeze at, scientists say

WASHINGTON — Dust, dust, dust. It's everywhere, burrowing under beds, piling up on windowsills, clogging guns and machinery, irritating eyes, noses and lungs. It soars thousands of miles over continents and oceans, sometimes obliterating the sky.

Enormous masses of the stuff — fine grains of soil, sand, smoke, soot, sea salt and other tiny particles, both seen and unseen — pervade Earth's air, land and water.

Now scientists are beginning to have new respect for the way dust alters the environment and affects the health of people, animals and plants. As global warming raises temperatures and forests are cleared for agriculture and other development, the amount of dust swirling through the Earth's atmosphere is expected to grow. The likely impact is unknown.

"Environmental scientists are increasingly recognizing dust as both a major environmental driver and a source of uncertainty for climate models," said Jason Field, a soil researcher at the University of Arizona in Tucson, who cowrote a paper, "The Ecology of Dust," that was published in the latest edition of the journal Frontiers of Ecology and Environment.

By blackening snow and ice, dust even may have contributed to the end of the ice age 10,000 years ago, Karen Kohfeld, an environmental scientist at Queens College in Flushing, N.Y., wrote in Advances in Science, a publication of the Royal Society of London.

The amount of dust traveling through the atmosphere is huge, Kohfeld said.

"Although these individual particles are often invisible to the naked eye, billions of tons of material are transported every year" through the air, she said. "Some of these transport events are even visible from space."

Dust plays a complex role in the environment. Some of its effects are benign. Unlike CO2, a prime culprit in global warming, most airborne dust particles turn back the sun's rays and thus cool the planet. Dust also carries chemical nutrients that help agriculture.

"Dust can be an important and even, in some locations, essential parent material for soils," said Daniel Muhs, a researcher at the U.S. Geological Survey (USGS) in Denver. Windblown dust from Africa "may be critical in sustaining vegetation" in the Caribbean, Central America, Mexico and the southeastern United States, he said.

"Dust delivered to the oceans may also provide some essential nutrients, especially iron, for microscopic marine plants that draw down carbon dioxide from the atmosphere, another counterbalance to greenhouse gas warming," Muhs said.

On the other hand, like other airborne particles, dust can spread harmful pollutants around the world.

"The atmosphere connects all regions of the globe, and pollution emission within any country can affect populations and ecosystems well beyond national borders," Charles Kolb, chief executive officer of Aerodyne Research in Boston, wrote in a report published in October by the National Academies of Science.

Kolb called fine particles, particularly smoke and road dust, "the deadliest air pollutant," responsible for about 348,000 deaths in 25 European countries annually.

"The heavy loads of fine particles we find in many large urban areas exacerbate heart problems and also cause deaths from lung cancer and emphysema," he wrote.

Muhs said dust also cause silicosis, a serious lung disease, and asthma.

Natalie Mahowald, a climate scientist at Cornell University in Ithaca, N.Y., observed that dust particles "may carry microbes, or actually be microbes."

Besides the constant rain of dust, unusual events have greatly magnified the impact of dust.

More than 800 million tons of topsoil were blown away in the great southwestern Dust Bowl of the 1930s. The 1980 eruption of Mount St. Helens spewed an estimated half a billion tons of ash and dirt that drifted across the Northern Hemisphere.

More recently, the collapse of New York's World Trade Center on Sept. 11, 2001, produced huge clouds of toxic dust composed of particles of glass, wallboard, concrete, paper and other building materials, according to a report by USGS scientist Geoffrey Plumlee. Last year, dust clouds threatened the Beijing Olympics.

The champion of all recorded dust clouds was the 1815 eruption of the Tambora volcano on an island in what's now Indonesia. The volcano spewed so much dust around the globe that 1816 became known as "The Year without a Summer." Crops failed worldwide, and at least 70,000 people died.

Geologists say the major sources of dust are deserts in Africa, Asia and the Middle East, and dry lands, cleared by deforestation, livestock grazing or for agriculture.

"Human activity has increased dust deposition over the past 100 to 200 years," Field said. "Abandoned cotton fields in Texas and Arkansas and military-training grounds in Texas and California consistently produce large regional dust storms that can be seen on satellite imagery."

"Windblown dust that settles on the land surfaces can accumulate to great thickness," Kohfeld said, citing an over 650-foot-thick plateau of soft soil dumped by the wind in China.

In Hawaii, she said, "much of the soil has literally come from China and Central Asian deserts."

"High concentrations of African dust are measured in Florida and the southern and eastern United States every summer," Joseph Prospero, an atmospheric scientist at the University of Miami, wrote in the International Journal of Biometeorology.