Direct observation of the complex S(IV) equilibria at the liquid-vapor interface
Year: 2024
Type: article
Abstract: The multi-phase oxidation of S(IV) plays a crucial role in the atmosphere, leading to the formation of haze and severe pollution episodes. We here contribute to its understanding on a molecular level by reporting experimentally determined pKa values of the various S(IV) tautomers and reaction barriers for SO2 formation pathways. Complementary state-of-the-art molecular-dynamics simulations reveal a depletion of bisulfite at low pH at the liquid-vapor interface, resulting in a different tautomer ratio at the interface compared to the bulk. On a molecular-scale level, we explain this with the formation of a stable contact ion pair between sulfonate and hydronium ions, and with the higher energetic barrier for the dehydration of sulfonic acid at the liquid-vapor interface. Our findings highlight the contrasting physicochemical behavior of interfacial versus bulk environments, where the pH dependence of the tautomer ratio reported here has a significant impact on both SO2 uptake kinetics and reactions involving NOx and H2O2 at aqueous aerosol interfaces.
Authors: Buttersack, Tillmann, Gladich, Ivan, Gholami, Shirin, Richter, Clemens, Dupuy, Rémi, Nicolas, Christophe, Trinter, Florian, Trunschke, Annette, Delgado, Daniel, Corral Arroyo, Pablo, Parmentier, Evelyne A., Winter, Bernd, Iezzi, Lucia, Roose, Antoine, Boucly, Anthony, Artiglia, Luca, Ammann, Markus, Signorell, Ruth, Bluhm, Hendrik
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6928707146
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