The uptake of gases by aqueous aerosols is a primary step in many atmospheric interactions. Details about the machanism of surface adsorption compared to bulk accommodation are still unclear.

Stephanie Ota and Geraldine Richmond, University of Oregon, USA, provide the first direct examination of surface SO₂:H₂O complexation as a function of temperature and of solution acidity at conditions relevant to tropospheric surface reactions. Vibrational sum frequency spectroscopy (VSFS) showed that the SO₂ surface affinity is independent of aqueous solution acidity. It is enhanced at colder temperatures where the surface adsorption results in significant changes in water orientation at the surface.

At low atmospheric temperatures and the acidic conditions common in aqueous aerosols surface, accumulation of SO₂ is favored. The aqueous surfaces can act as a reservoir for SO₂ and other gases in the atmosphere by forming interfacial complexes even when the aqueous composition might otherwise impede uptake. This may be especially relevant to polluted environments rich of SO₂ and reactive organic species. The aqueous surface may lead to surface complexation, increasing the probability of reactions between otherwise noninteractive gases.

• Chilling Out: A Cool Aqueous Environment Promotes the Formation of Gas–Surface Complexes
  Stephanie T. Ota and Geraldine L. Richmond
  J. Am. Chem. Soc. 2011.
  DOI: 10.1021/ja201027k