BOULDER--From 50% to 60% of sulfate-aerosol pollution over the PacificNorthwest is coming from industrialized Asia, according to a modeldeveloped by a team of researchers at the National Center forAtmospheric Research (NCAR). While the total column of air contains"imported" sulfate aerosols, near the surface most of the aerosols comefrom North American sources. In contrast, sulfates in Europe are comingprimarily from European sources, both at the surface and higher in theatmosphere. Jeffrey Kiehl, head of NCAR's Climate Modeling Section, willpresent the group's findings December 7 at the American GeophysicalUnion conference in San Francisco. Research funds came from the NationalAeronautics and Space Administration and the National ScienceFoundation. NSF is NCAR's primary sponsor.
"It's widely recognized that sulfate aerosols are playing a major rolein the climate system," says Kiehl. The ability of these aerosols (tinyparticles of liquids and solids) to reflect the sun's radiation may beone reason that increasing greenhouse gases have not warmed the earth asmuch as some climate models have predicted. Sulfates also contribute tolocal pollution and acid rain.
"One important way that sulfur moves in the atmosphere is throughtransport by the earth's winds," Kiehl explains. But winds are not thewhole story. For the past three years, Kiehl and colleagues Mary Barth,Philip Rasch, and Timothy Schneider have been developing an integratedmodel of climate and sulfur chemistry. The model includes the emissionof natural and industrial sulfur into the earth's atmosphere. To modelhow the sulfur gas changes into sulfate aerosol particles, they includedchemical processes and the chemical and physical effects of clouds,including clouds' ability to remove sulfates from the atmosphere. Theyalso included the effect of the sulfate aerosols on the reflection ofsunlight to address the key question of sulfates' role in the climatesystem. The researchers compared their model simulations of sulfur andsulfate aerosols with real-world observations near the surface. Morecomparisons with observations yet to be made far above the surface areneeded to confirm the model findings.
Fully integrating sulfur chemistry into the climate model allowed theteam to account for the effects of interacting winds, precipitation, andclouds on that chemistry. This integrated modeling allowed them tocalculate the amount of sulfate aerosols formed or removed in any givenregion. By tagging the sulfates in the climate simulations by sourceregion, the team could calculate the percent of sulfates transportedfrom one region to another. The source regions considered are NorthAmerica, Asia, and Europe, with the rest of the world grouped as thefourth region.
NCAR is managed by the University Corporation for Atmospheric Research,a consortium of more than 60 universities offering Ph.D.s in atmosphericand related sciences.
Writer: Zhenya Gallon
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