Dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) are volatile reduced sulfur compounds which are abundantly produced by anthropogenic sources. Previous studies on the photooxidation pathways of DMDS and DMS show that hydroxyl radical addition, hydrogen removal and photolytic decomposition are the main initial mechanisms by which the parent sulfur gases dissociate in the atmosphere during day time. This produces sulfates that ultimately lead to formation of secondary organic aerosols (SOA). In this study, we use kinetic modeling of the atmospheric oxidation of DMDS and DMS to simulate aerosol chamber experiments and to help interpret the ionic content of detected particles. The kinetic models were built as systems of differential equations for the atmospheric photooxidation mechanisms of both gases. Then, gas phase data from chamber experiments, where either DMDS or DMS in the presence of H2O2 or N2O5 as the oxidant source, was simulated to benchmark our models. Experimental data shows a large difference in the production of SO42- between DMS and DMDS, as well as a dramatic decrease on SO42- formation when different amines are present in the reaction mixture. This may indicate rapid aerosol formation or aqueous-phase reactions. Modeling the gas phase data allowed us to determine photon flux and initial radical concentrations. This allows for the accurate prediction of SO2 formation, which allows estimates of SO42- ion formation in a predictable manner. Observations from modeled data show prompt SO2 formation from DMDS, while SO2 production is slower for DMS. Also, due to its S-S bond and the relative stability of CH3S, photolytic dissociation of DMDS appears greatly favored, while DMS favors OH addition. Future research will include incorporation of amines commonly found in atmosphere, introducing other plausible oxidative species and atmospheric conditions affecting gas-phase reactions into our models to more accurately represent atmospheric conditions.

Kinetic modeling of the atmospheric oxidation pathways of dimethyl disulfide and dimethyl sulfide

253rd National Meeting (2017)

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