EC-20. The Role of Hydrogen Sulfide in Archean Organic Haze Chemistry

Abstract
Trace sulfur gases and planetary organic haze, produced by CH4 photochemistry, are ubiquitous in planetary atmospheres of the solar system and likely exoplanets. Their respective chemistries are also thought to be key in the understanding of the early Earth atmosphere. Investigations of atmospheric sulfur chemistry has largely focused on the production of S8 and H2SO4 and has neglected the formation of organosulfur compounds. However, evidence from present-day atmospheric studies shows that organosulfur contributes substantially to organic aerosol. Here, we describe laboratory studies to explore how the addition of trace amounts of H2S (0.5-5 ppmv) impacts organic haze produced from the ultraviolet photochemistry of CH4 and CO2/CH4 gas mixtures in N2. We analyze the aerosol product composition and size in real time using a quadrupole aerosol mass spectrometer (Q-AMS) and a scanning mobility particle sizer (SMPS). We find that the inclusion of trace amounts of H2S in the precursor mixture significantly enhances the formation of organic aerosol mass and the particle effective density, both of which increase as a function of initial H2S concentration and in the absence of an additional carbon source. We further find evidence that the addition of trace H2S to the precursor mixtures leads to the formation of organosulfur compounds. Thiyl-alkene chemistry is proposed as a possible organosulfur formation mechanism. In contrast to previous assumptions that sulfur and carbon chemistry occur largely independently of each other, these results suggest a coupling between the two chemistries. Ongoing studies explore how O from CO2 photochemistry alters these results in terms of organic aerosol produced and the aerosol composition. The altering of organic haze particle amount, size, and composition further suggests that trace amounts of H2S can impact how an organic haze affects climate, habitability, and prebiotic chemistry. These results may broadly influence the current understanding of organic haze and sulfur chemistry in planetary atmospheres and exoplanets.