The Chemical Fate of Sulfur in Thiophene Against Nitrate Radical Oxidation
MICHAEL LUM, Kunpeng Chen, Bradley Ries, Linhui Tian, Raphael Mayorga, Yumeng Cui, Nilofar Raeofy, David Cocker, Haofei Zhang, Roya Bahreini, Ying-Hsuan Lin,
University of California, Riverside Abstract Number: 406
Working Group: Aerosol Chemistry
AbstractSulfur-containing volatile organic compounds (VOCs) emitted during wildfire events have been shown to form secondary organic aerosols (SOA) upon atmospheric oxidation. Particle phase sulfurous products resulting from dimethyl sulfide or SO
2 multiphase reactions have been well characterized due to their contribution to inorganic sulfate (SO
42-) and surfactant-like sulfurous product concentrations; however, little is known about the fate of sulfur in other reduced organosulfur species relevant to wildfire emissions. As a model organosulfur compound emitted from wildfires, this study aimed to determine the product distribution of sulfur in atmospheric oxidation of thiophene and the empirical identities of the major organosulfates and sulfonates formed. A unique combination of instrumentation, including a mini aerosol mass spectrometer (mAMS) was used to determine the fate of sulfur under a [NO
2]/[O
3] ratio of 0.1, representative of atmospheric conditions within wildfire plumes. Traditionally the mAMS cannot distinguish between inorganic and organic sulfate, so IC was first used to constrain the SO
42- concentrations. In addition, signals from mAMS measurements were deconvoluted using a linear combination of sulfur-containing standard fractionation to approximate the fractions of inorganic sulfate, organosulfates, and sulfonates. Empirical formulae of major organosulfate and sulfonate compounds were identified and confirmed through non-target search employing multiple MS techniques. With the constraint from IC measurements, our results indicated that sulfur-containing particle mass consisted of 27.7% inorganic sulfate and 72.3% organosulfate/sulfonates. The mAMS fractionation approach attributed 60.1% of sulfur product mass to sulfonates, 15.4% to organosulfates, and the remaining 24.5% to SO
42-. The organic fraction was determined to consist of C1-C8 organosulfates and sulfonates, with the majority being ≤C4 unsaturated compounds. Overall, this study highlights the nitrate radical oxidation of thiophene and its derivatives as a source of inorganic sulfate and organic sulfur compounds, which have important implications on the atmospheric S budget and aerosol/droplet physical and chemical properties.
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