Abstract
Abstract. The oxidation of dimethyl sulfide (DMS) in the troposphere and subsequent chemical conversion into sulfur dioxide (SO2) and methane sulfonic acid (MSA) are key processes for the formation and growth of sulfur-containing aerosol and cloud condensation nuclei (CCN), but are highly simplified in large-scale models of the atmosphere. In this study, we implement a series of gas-phase and multiphase sulfur oxidation mechanisms into the Goddard Earth Observing System-Chemistry (GEOS-Chem) global chemical transport model – including two important intermediates, dimethyl sulfoxide (DMSO) and methane sulphinic acid (MSIA) – to investigate the sulfur cycle in the global marine troposphere. We found that DMS is mainly oxidized in the gas phase by OH (66 %), NO3 (16 %) and BrO (12 %) globally. DMS + BrO is important for the model's ability to reproduce the observed seasonality of surface DMS mixing ratio in the Southern Hemisphere. MSA is mainly produced from multiphase oxidation of MSIA by OH(aq) (66 %) and O3(aq) (30 %) in cloud droplets and aerosols. Aqueous-phase reaction with OH accounts for only 12 % of MSA removal globally, and a higher MSA removal rate is needed to reproduce observations of the MSA ∕ nssSO42- ratio. The modeled conversion yield of DMS into SO2 and MSA is 75 % and 15 %, respectively, compared to 91 % and 9 % in the standard model run that includes only gas-phase oxidation of DMS by OH and NO3. The remaining 10 % of DMS is lost via deposition of intermediates DMSO and MSIA. The largest uncertainties for modeling sulfur chemistry in the marine boundary layer (MBL) are unknown concentrations of reactive halogens (BrO and Cl) and OH(aq) concentrations in cloud droplets and aerosols. To reduce uncertainties in MBL sulfur chemistry, we should prioritize observations of reactive halogens and OH(aq).
Highlights
The biogenic emission of dimethyl sulfide (DMS: CH3SCH3) from the ocean is the largest natural sulfur source to the atmosphere (Andreae, 1990)
Rall; sea surface water DMS concentration obtained from Kettle et al (1999) Rall; without DMS + BrO reaction Rall; without multiphase oxidation of DMS, dimethyl sulfoxide (DMSO), methane sulphinic acid (MSIA) and methane sulfonic acid (MSA) Rall; without MSA + OH(aq) reaction Rall; kMSA+OH(aq) × 4.7 (Milne et al, 1989) Rall; OH(aq) concentrations in cloud droplets and aerosols reduced by a factor of 100 Rall; a unity yield of DMSO for the addition channel of DMS + OH reaction∗ Rall; Cl mixing ratios increased by a factor of 10 Rall; DMS emission from the ocean as the only sulfur source Rstd;DMS emission from the ocean as the only sulfur source
We investigate the impacts of reactive halogen and multiphase chemistry on tropospheric DMS chemistry by adding two new chemical tracers (DMSO and MSIA) and 12 new reactions for both the gas-phase and multiphase oxidation of DMS, DMSO, MSIA and MSA into a global chemical transport model, GEOS-Chem
Summary
The biogenic emission of dimethyl sulfide (DMS: CH3SCH3) from the ocean is the largest natural sulfur source to the atmosphere (Andreae, 1990). Some large-scale models have simulated the formation of the DMSO intermediate from DMS oxidation (Pham et al, 1995; Cosme et al, 2002; von Glasow et al, 2004; Castebrunet et al, 2009), which is important as DMSO is highly water soluble – Henry’s law constant (HDMSO) on the order of 107 M atm−1 – and can undergo dry and wet deposition in addition to gas- and aqueous-phase oxidation to MSA or SO2 (Lee and Zhou, 1994; Campolongo et al, 1999; Barnes et al, 2006; Zhu et al, 2006; Hoffmann et al, 2016). We conclude with recommendations for future laboratory experiments and field campaigns, and recommendations for sulfur chemistry that should be included in large-scale models of atmospheric chemistry and climate
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
