Abstract
Abstract. To improve the model prediction for the formation of H2SO4 and methanesulfonic acid (MSA), aerosol-phase reactions of gaseous dimethyl sulfide (DMS) oxidation products [e.g., dimethyl sulfoxide (DMSO)] in aerosol have been included in the DMS kinetic model with the recently reported gas-phase reactions and their rate constants. To determine the rate constants of aerosol-phase reactions of both DMSO and its major gaseous products [e.g., dimethyl sulfone (DMSO2) and methanesulfinic acid (MSIA)], DMSO was photooxidized in the presence of NOx using a 2 m3 Teflon film chamber. The rate constants tested in the DMSO kinetic mechanisms were then incorporated into the DMS photooxidation mechanism. The model simulation using the newly constructed DMS oxidation mechanims was compared to chamber data obtained from the phototoxiation of DMS in the presence of NOx. Within 120-min simulation, the predicted concentrations of MSA increase by 200–400% and those of H2SO4, by 50–200% due to aerosol-phase chemistry. This was well substantiated with experimental data. To study the effect of coexisting volatile organic compounds, the photooxidation of DMS in the presence of isoprene and NOx has been simulated using the newly constructed DMS kinetic model integrated with the Master Chemical Mechanism (MCM) for isoprene oxidation, and compared to chamber data. With the high concentrations of DMS (250 ppb) and isoprene (560–2248 ppb), both the model simulation and experimental data showed an increase in the yields of MSA and H2SO4 as the isoprene concentration increased.
Highlights
Dimethyl sulfide (DMS) is a major reduced sulfur compound of marine origin
Despite all the efforts exerted to understanding atmospheric DMS chemistry, a large discrepancy still exists between the ambient measurements of DMS products and the simulation results for compounds such as dimethyl sulfoxide (DMSO) (Chen et al, 2000), H2SO4 and methanesulfonic acid (MSA) (Lucas and Prinn, 2002)
The poor predictive capability of the kinetic model for the formation of DMS products was caused by uncertainties in the rate constants of DMS reactions in the gas phase, the lack of aerosol phase reactions of the DMS products, and missing information regarding the impact of volatile organic compounds (VOC) on the DMS photooxidation through both the gas and the particle phases
Summary
The major aerosol phase products of DMS are methanesulfonic acid (MSA) and sulfuric acid (H2SO4) (Bardouki et al, 2003; Barone et al, 1995; Gaston et al, 2010; Lukacs et al, 2009), both of which are postulated to have significant effects on the earth’s radiation budget (Charlson et al, 1987). The DMS photooxidation mechanism is an important factor for understanding the role DMS plays in the earth’s sulfur cycle and climate system, so it has been studied by many researchers (Yin et al, 1990a; Turnipseed and Ravishankara, 1993; Urbanski and Wine, 1999; Barnes et al, 2006). Some of reaction rate constants have been updated using recently reported values and new reaction mechanisms
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