The uptake of SO2 on synthetic sea salt facilitated by aqueous surface reaction

Atmospheric oxidation of sulfur compounds is central to acid deposition and global climate issues. The oxidation of SO₂ occurs largely within aerosol, fog and cloud droplets. A number of investigators have shown that sulfur oxidation can occur in sea salt aerosols. In the present studies, we have measured the uptake coefficient, g, for SO₂ on NaCl and sea salt powders, at 298 K, in a Knudsen cell interfaced to a quadruple mass spectrometer. Using approximately 0.1 mTorr SO₂ in the cell, uptake on dry NaCl is not measurable, while uptake on sea salt powders is significant. Initially, the measured g approaches that of the mass accommodation coefficient for SO₂ on water. Then it rapidly decreases by an order of magnitude but slow uptake continues for very long periods of time. The production of gas phase HCl is correlated with uptake. The uptake behavior can be modeled by a gas-liquid "resistance" model. The atmospheric implications will be discussed.