Chemical Characterization of Organosulfur Compounds in Aerosols from Archean-Analog Photochemistry: Insights from Liquid Chromatography and High-Resolution Tandem Mass Spectrometry

Abstract

Fine aerosols are critical in influencing planetary climate and surface conditions, and thus, understanding the sources and chemical composition of aerosols is vital for constraining the habitability potential of a planet. Molecular nitrogen (N₂), methane (CH₄), carbon dioxide (CO₂), and sulfur gases (e.g., hydrogen sulfide (H₂S) and sulfur dioxide (SO₂)) are common components of planetary atmospheres that can undergo atmospheric photochemical reactions to produce both inorganic and organic aerosols. Recent studies have shown that organic aerosol production is closely tied to the presence of H₂S, potentially through the formation of organosulfur compounds. However, molecular-level speciation of organosulfur compounds is lacking, thus limiting our understanding of what, if any, implications these compounds hold for the early beginnings of life or the planetary climate. Here, we chemically characterized 60 organosulfur compounds in aerosols produced during laboratory analog experiments using an irradiated mixture of 0.5% CO₂ with 0.1% CH₄ and 5 ppm of H₂S in a N₂ background by hydrophilic interaction liquid chromatography coupled to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (HILIC/ESI-HR-QTOFMS). Accurate mass and tandem mass spectrometry measurements provided information regarding sulfur functionality and the overall chemical structure. Sulfur was found in multiple oxidation states within functional groups such as sulfates, sulfonic acids, sulfites, sulfinic acids, and thiols. We found that five simple organosulfur species, including methyl sulfate, ethyl sulfate, methanesulfonic acid, ethanesulfonic acid, and isethionic acid, contributed 6.2–7.9% of the total aerosol mass. These results suggest that organosulfur could have played a significant role in the Archean sulfur cycle.