Accumulating SO2

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Science  13 May 2011:
Vol. 332, Issue 6031, pp. 768
DOI: 10.1126/science.332.6031.768-d
CREDIT (TOP TO BOTTOM): OTA AND RICHMOND, J. AM. CHEM SOC. 133, 10.1021/JA201027K (2011)

Once in the atmosphere, SO2 (a byproduct of coal combustion) can be oxidized further in the gas phase by radicals or undergo a more complex sequence of events within the aqueous phase of aerosol droplets, where (among other things) it may contribute to acid rain. The initial step in the latter process, the surface adsorption of SO2, probably depends on temperature and droplet composition. Ota and Richmond used vibrational sum-frequency generation—a technique highly sensitive to surface phenomena—to look at the adsorption of SO2 on water surfaces between the freezing point and room temperature. They found that at the coldest temperatures, almost all of the water molecules formed a surface complex with an adsorbed SO2 molecule, unlike the much lower surface coverage near room temperature. They also found that changing pH had little effect on adsorption, demarcating a clear division between the surface and internal chemistry of the droplets.

J. Am. Chem Soc. 133, 10.1021/ja201027k (2011).

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