Aqueous Reactivity of Reduced Sulfur Species under Anoxic Conditions: Implications for Planetary Habitability

REBECCA RAPF, Sukrit Ranjan, Jackson Witkow, Raider Horn, Marco Botello, Trinity University

     Abstract Number: 319
     Working Group: Planetary Aerosols: From Earth to Exoplanets

Abstract
Sulfur plays a key role in planetary habitability, through the generation of photochemical aerosol haze layers which interact with radiation and influence climate. Sulfur is primarily supplied to the atmosphere in the S[IV] oxidation state as sulfur dioxide and then partitions into the hydrosphere as sulfite. The aqueous loss efficiency of sulfite is a main control on the global fate of S[IV]. If aqueous loss of S[IV] is efficient, then sulfur dioxide is rapidly scrubbed from the atmosphere with minimal influence on planetary climate or chemistry. If, however, aqueous loss of S[IV] is inefficient, then S[IV] accumulates in the hydrosphere-atmosphere system, resulting in the formation of significant photochemical haze formation. To date, the kinetics of abiotic sulfur reactions in aqueous models under anoxic conditions are not well constrained. Here, we report on laboratory studies that examine the thermal disproportionation and wavelength-dependent photolysis of reduced sulfur species, using Raman and UV-vis spectroscopy. These experimentally-determined rate constants are then incorporated into atmospheric and aqueous models, giving bounds on the likelihood of formation of optically thick sulfate or S₈ hazes, which can significantly impact planetary climate and UV irradiation and ultimately habitability.