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Asian Pollution Drifts over North America


By R. Monastersky
Science News Online
December 12, 1998


Faster than mail traveling from Beijing to Seattle, air pollution and dust
from China can speed across the Pacific Ocean and blanket broad swaths of
North America, according to measurements made during the past 2 years.
"[This] is the first time that anyone has ever documented that pollution from
one continent can make it all the way to a downstream continent," says Dan
Jaffe of the University of Washington-Bothell. Jaffe and members of other
research teams presented the new data this week at a meeting of the American
Geophysical Union in San Francisco.

By the time Asian pollution crosses the Pacific—which takes from 4 to 10
days—it typically does not rival the strength of home-grown grime spewing out
of tailpipes and chimneys in North America. Nonetheless, these results provide
a vivid demonstration that environmental problems in one country can reach
nations on the other side of the globe. "We have to recognize that there is no
‘away.’ Everybody’s garbage goes somewhere," says Jaffe.

The Asian pollution rides over the ocean principally during springtime, when
strong winds cut a path to North America. Jaffe’s group first detected a clear
burst of pollution on March 29, 1997, at a research site located on Cheeka
Peak in Washington, near the westernmost tip of the contiguous United States.
Measurements of air coming from the Pacific showed a jump in the
concentrations of carbon monoxide, hydrocarbons, and other pollutants from
fossil-fuel combustion. A meteorological computer model that tracks winds
indicated that the polluted air had started in Asia 6 days earlier.

An even larger shipment of Asian pollution arrived in North America late last
April. A series of strong dust storms in China lifted 140 million tons of fine
soil particles into the atmosphere, where they were swept up by winds moving
east, says Douglas L. Westphal of the Naval Research Laboratory in Monterey,
Calif. The dust cloud appeared on satellite images, which showed the plume
crossing the Pacific toward North America, he says.

It took a week for the dust to reach western North America, where it turned
the sky milky white, says Thomas A. Cahill of the University of California,
Davis. In late April, the Asian dust was so thick that the concentrations of
fine particles in the air at the usually pristine site of Crater Lake, Ore.,
equaled 40 percent of the EPA daily allowable limit for the United States.
Along with the dust came measurable quantities of arsenic, copper, lead, and
zinc. Air concentrations of these metals rose across the western United States
on April 29. At Crater Lake, they reached more than 10 times their typical
values, says Cahill. The heavy metals came from smelters in Manchuria, he
concludes, because the Asian dust passed over that region before heading
toward North America. There are no sources of such pollutants near Crater
Lake, Cahill says.

Atmospheric scientists have previously recognized that dust from Asia or
Africa can reach North America, but the recent data provide the first firm
evidence that pollution travels that far. There are also hints that American
pollution sails across the Atlantic Ocean and lands in Europe, but clear-cut
proof of that connection has yet to emerge, says Cahill.

The pollutants crossing an ocean typically do not present a threat because
their concentrations are small in most cases, say the researchers. "We would
expect that there would be low health impacts, generally," says Jaffe. Yet in
certain instances, such as the April case, winds can carry substantial
quantities of unwanted foreign material across the seas, he says.

 

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