Agricultural waste, particularly from animal production, generates both sulfur- and nitrogen-containing organic compounds, both of which undergo photolysis and oxidative processes in the gas phase. As field studies have begun to show the anomalous gas-phase compositions at and near swine, poultry, and other animal facilities, aerosol emissions have also begun to come into focus. Aerosol chamber experiments on dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) produce modest amounts of SO<sub>2</sub> and, ultimately, sulfate-containing aerosols. However, addition of even very small amounts of amines increases aerosol production by an order of magnitude. Here, we present kinetic and computational models to help explain these surprising results. By modeling the production of SO<sub>2</sub> in the gas phase, and comparing to data from chamber experiments, we suggest that the increase in aerosol arises from the generation of organic radicals necessary to initiate the process of secondary organic aerosol (SOA) formation. The high levels of aerosol production in DMDS (compared to DMS) are dominated by disulfide bond cleavage rather than by oxidation, meaning that even a small amount of DMDS can produce large amounts of aerosol, especially in the presence of amines or ammonia. The models also allow prediction of the rates of pickup of different compounds into aerosols during the chamber experiments. Decreases in particle number and changes in composition with relative humidity suggest that formation of dry cores may actually favor SOA formation. All of this data together suggests that agricultural sites may be a disproportionately large source of atmospheric aerosols, at least in part because of the unique combination of sulfides and amines that they emit.

Formation of atmospheric aerosols in the presence of sulfide and amine compounds: implications for farm waste

255th National Meeting (2018)

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