Organosulfur Speciation in Archean Analog Aerosols: Molecular Characterization and Formation Mechanisms
CADE CHRISTENSEN, Nathan Reed, Jason Surratt, Margaret Tolbert, Eleanor Browne,
University of North Carolina at Chapel Hill Abstract Number: 701
Working Group: Aerosol Chemistry
AbstractEarth’s Archean atmosphere is believed to be anoxic and nitrogen rich, containing trace gases such as methane (CH
4), carbon dioxide (CO
2), and sulfur gases. Photochemical gas-phase reactions between these constituents result in inorganic and organic sulfur aerosol formation. The chemical speciation of sulfur aerosols is central to our understanding of Archean atmospheric conditions. Traditional thought holds that only inorganic sulfur aerosols were important sulfur reservoirs. Recent experiments challenge that assumption by showing organosulfur may serve as a sulfur reservoir; however, in-depth molecular analysis had not yet been done to determine the molecular structure and functionality of the constituents. We describe results from laboratory analog experiments using an irradiated mixture of 0.5% CO
2, 0.1% CH
4 and 5 ppm H
2S in a nitrogen environment to investigate the formation of organosulfur aerosols. A hydrophilic interaction liquid chromatography (HILIC) method coupled to electrospray ionization high-resolution quadrupole time-of-flight tandem mass spectrometry (ESI-HR-QTOF-MS/MS) was developed for the molecular-level characterization of resultant particulate organosulfur species. Tandem mass spectrometry (MS/MS) experiments provided details about various functional groups and molecular structure. A complex mixture containing a rich array of molecules was found, ranging from C1-C4 species with sulfur being found in more than one oxidation state. Combining confirmed structures via authentic standards and tentative structural assignments from fragmentation analysis, a proposed gas-phase mechanism for the formation of these compounds is provided to understand the formation and nucleation of these molecules into particulates. These results will help improve our understanding of the atmospheric chemical processes currently found on other planetary bodies and likely during the Earth’s early atmospheric conditions.