Understanding the Photochemical Production of Complex Organosulfur Compounds in Archean-Analog Aerosols: Implications for Early Earth and Exoplanets

CADE CHRISTENSEN, Nathan Reed, Margaret Tolbert, Eleanor Browne, Jason Surratt, University of North Carolina at Chapel Hill

     Abstract Number: 247
     Working Group: Planetary Aerosols: From Earth to Exoplanets

Abstract
The Archean atmosphere on Earth was anoxic and mostly composed of nitrogen, with trace gases such as methane (CH4), carbon dioxide (CO2), and sulfur gases (e.g., hydrogen sulfide (H2S) and sulfur dioxide (SO2)). These trace gaseous precursors can undergo photochemical reactions that produce organic and inorganic sulfate aerosols. Understanding the molecular-level chemical composition of these photochemically-generated aerosols is central to the atmospheres of the Archean Earth and potentially Archean-like atmospheres elsewhere. Recent work has challenged the assumption that inorganic sulfur is the only reservoir for sulfur in these atmospheres by showing large portions of total aerosol formation being linked to organosulfur compounds. The structures and formation of these organosulfur compounds are currently lacking and could hold implications for the early beginnings of life. We will describe results obtained from laboratory analog experiments using an irradiated mixture of 0.5% CO2, 0.1% CH4 and 5 ppm H2S in a nitrogen background to investigate the formation of organosulfur aerosols. A hydrophilic interaction liquid chromatography (HILIC) method coupled to electrospray ionization and a high-resolution quadrupole time-of-flight mass spectrometer (ESI-HR-QTOFMS) was used for the offline molecular-level characterization of resultant organosulfur-containing aerosols. Tandem mass spectrometry (MS/MS) results obtained from HILIC/ESI-HR-QTOFMS analyses provided details about various functional groups and overall molecular structures for particulate sulfur species. A complex mixture containing a rich array of molecules was found, including C1-C4 species with sulfur found in multiple oxidation states. Ionizable sulfur functional groups such as sulfates, sulfonates, sulfites and sulfinic acids were detected. Compounds with more than one sulfur functional group provided tentative structures containing thiols, sulfite esters, thiocarboxylic acids, sulfides, sulfoxides, and sulfones. These results show that atmospheric chemistry produces complex organosulfur molecules that may be important as nutrients and for early metabolism as well as for our interpretation of sulfur in the geological record.