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Airborne Mineral Dust Adds Sulfate To Aerosols

Results point to altered climate-cooling effects of atmospheric particles

by Jyllian Kemsley
May 13, 2013 | A version of this story appeared in Volume 91, Issue 19

Aerosol particles in the air undergo chemical reactions that change their size and hygroscopicity. Those properties in turn influence how airborne aerosols affect climate by scattering radiation and modifying the brightness and lifetime of clouds. Adding sulfate to those particles is a particularly important process. A research group led by Peter Hoppe, Eliza Harris, and Bärbel Sinha of the Max Planck Institute for Chemistry, in Germany, now pinpoints transition-metal ions as key oxidants that turn SO2 into SO42– on airborne mineral dust within clouds (Science 2013, DOI: 10.1126/science.1230911). The team studied so-called orographic clouds at Mount Schmücke, in Germany, where clouds form as air rises to go over the mountain. The researchers compared sulfur isotope ratios upwind and downwind of the clouds to determine whether SO2 was oxidized by H2O2, O3, or transition metals. They estimate that transition metals may account for about 1% of SO42– production in urban locations but as much as 58% in rural areas. If incorporated into climate models, the results would decrease the amount and change the geographic distribution of aerosol-driven climate cooling.


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