SAN FRANCISCO - The United States is importing more than automobiles and VCRs from the Pacific Rim. Smog is crossing the ocean, too.
Scientists said yesterday they have documented for the first time that industrial pollution and dust from Asia travels thousand of miles across the Pacific and degrades air quality over the United States.
In some cases during the past two years, levels of airborne particles that originated in China and central Asia spread as far as Texas and briefly spiked some U.S. pollution levels as high as two-thirds of federal health standards.
However, the pollution is diluted as it hitches a ride on midlevel winds circulating around the globe and poses no real public health threat in most instances, scientists said at the annual meeting of the American Geophysical Union.
"In most cases, the concentrations are going to be low, and we could expect very low health impacts," said Dan Jaffe, an atmospheric chemist at the University of Washington's Bothell campus. "But everybody's garbage goes someplace."
The Asian pollution transfer occurs mostly in the spring and fall.
The international contribution to a metropolitan area's total volume of air pollution remains very small but could increase as industrialization, rain-forest burning and other polluting sources grow, scientists said.
"I think we're being bombarded on a regular basis," said Douglas Westphal, a marine meteorologist with the Naval Research Laboratory in Monterey, Calif. "It's much more often than I expected."
Scientists presented preliminary data on a pair of instances when satellites spotted signs that large amounts of dust and industrial pollution were rapidly moving across the Pacific toward the United States. The pollution clouds were confirmed by ground-based stations in the western United States.
On March 29, 1997, researchers at the Cheeka Peak Observatory in Washington state measured carbon-monoxide levels that were 10 percent higher than average and fine-particulate levels that were 50 percent higher than average. The station is on the remote Olympic Peninsula and the pollution levels could not have come from a local source, Jaffe said.
And from April 25 to May 2 of this year, huge volumes of dust from the Gobi Desert in Mongolia and other Asian deserts traveled in a cloud across the Pacific, reaching as far east as Texas.
In Seattle, Portland and other western U.S. cities, the sky turned milky white from the dust. Mineralogical tests showed the grit originated in Asia.
Scientists said dust transport probably always has occurred. It leaps across the ocean on winds in the troposphere to about 20,000 feet, or below the jet stream. The winds travel about 60 mph.
Of greater concern to scientists and public-health researchers are fine particles of industrial pollution and soot from Asian factories, where pollution controls are not as stringent as in the United States. Burning rain forests are another source of far-ranging soot and combustion chemicals.
Similar movements of dust and pollution occur between the United States and Europe and between other continents, but those atmospheric patterns have not been as closely studied.