EC-23. The Influence of Hydrogen Sulfide on Archean Sulfur and Haze Aerosol

The current understanding of the Archean atmosphere hinges on sulfur gas and organic haze photochemistry. Sulfur dioxide (SO2) has received much of the focus on Archean sulfur chemistry, and there is only one known study on its role in the Archean organic haze chemistry (DeWitt et. al. 2010). However, there is a lack of attention on hydrogen sulfide (H2S) and its influence on Archean organic haze and sulfur chemistry. Here, we present laboratory results from UV photochemical experiments to investigate the influence of trace H2S on the composition of aerosol produced from Archean-like precursor mixtures (0.1-2% CO2, 0.1% CH4, 5 ppmv H2S) as a function of CO2 mixing ratio. We show that including trace H2S in the precursor mixture enhances organic aerosol production at all CO2 concentrations studied, including mixtures with a CO2:CH4 ratio greater than ~1, where organic aerosol production has been observed to decrease without H2S included. We also show that sulfur from H2S is present in the aerosol phase as both inorganic and organic sulfate aerosol. This is in contrast with predictions that Archean atmospheric sulfur enters the aerosol phase exclusively as either H2SO4 or S8 aerosol. These predictions are in line with results of haze experiments using SO2 by DeWitt et. al. 2010, though some oxidized organosulfur was observed in these experiments as well. Therefore, we show that H2S differs from SO2 in its photochemistry and influence on organic haze, and challenges past predictions of Archean sulfur reservoirs. These results could have a potential impact on the interpretation of the mass-independent fractionation of sulfur isotopes (S-MIF), our understanding of Archean organic haze chemistry, and potentially future observations of Archean-like haze of exoplanetary atmospheres.