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UW scientists study effects of Asian dust

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After cruising along a river of air above the Pacific Ocean, dust originally from Asia arrives in North America daily. Ten years after first detecting dust and other pollutants from Asia in the western United States, UW scientists are adding a new perspective toward understanding long-term changes in the concentrations of dust.

Emily Fischer, a doctoral student in the UW department of atmospheric sciences, has identified a strong relationship between the strength of springtime dust storms in Asia and the quality of air in rural United States.

Fischer and her collaborators compared air quality data recorded at 10 sites in national parks around the western United States with dust concentrations over the Gobi and Taklamakan deserts in China and Mongolia.

"Lots of studies have characterized individual dust storm events," Fischer said. "What's neat about this is that it's looking at the larger picture."

Each spring, storms stir up dust over the deserts and dry cropland of eastern Asia. The particulates, about the size of human red blood cells, are then carried up into stronger winds and transported across the Pacific Ocean to the western United States.

Particulate matter (PM) is a byproduct of the burning of fuel from cars and other industries. Fischer chose sites away from urban areas in order to isolate the impact of dust.

"The study doesn't apply to urban areas," Fischer said. "Local sources of PM tend to dominate in cities, giving the dust a smaller relative impact on seasonal timescales. Big events are notable."

Nine years of data allowed Fischer to investigate year-to-year changes in the strength of dust storms in Asia and subsequent air quality in the western United States.

"My data shows that half of the springtime variability is likely due to changes in the intensity of dust storms," Fischer said. "Other factors impact year-to-year variations too, but were beyond the scope of our study. For example, forest fires and other biomass burning also vary between years."

Dan Jaffe, Fischer's doctoral advisor and professor of atmospheric and environmental chemistry at UW Bothell, said in addition to improving scientific understanding, the results bear on policy and human health as well.

"The better we can understand the processes that affect the variability, the better we'll know what to expect in the long term," Jaffe said.

Under mandate from the Clean Air Act, the Environmental Protection Agency (EPA) sets air quality standards for PM and five other pollutants considered potentially harmful to human health.

"Particulates can have acute effects immediately after exposure," said Keith Rose, an EPA air quality specialist. "Dust generated from farming or arid regions tends to be benign, with coughing and reduced visibility being the primary impacts. However, sensitive populations are susceptible to more adverse effects at the same concentrations."

Jaffe gave a hypothetical example demonstrating policy relevance.

"Say you're the mayor of Denver and the city violates the PM standard," Jaffe said. "That's not necessarily because of local factors. In some cases, variability in long range transport accounts for 20 to 30 percent of the standard."

Donald Wuebbles, a professor of atmospheric science and director of the School of Earth, Society and Environment at the University of Illinois, agreed.

"Studying variability in long range pollutants broadly would allow policy makers to take it into account when revising standards in the future," Wuebbles said. "It makes more complete analyses all the more relevant."

[Reach reporter Brian Smoliak at news@thedaily.washington.edu.]

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