Towards an Advanced DMS oxidation mechaNISm (ADOniS)

• Applicant: Professor Dr. Hartmut Herrmann
• Subject Area: Atmospheric Science
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 495046770

Interactions between the ocean and the troposphere are important for many processes in either system. A key process represents the exchange of trace gases between the atmosphere and the ocean. The emission of dimethyl sulfide (DMS) represents the largest natural reduced sulfur source into the atmosphere. There, DMS can be oxidized to sulfur dioxide, sulfuric acid or methane sulfonic acid. These compounds are important precursors for secondary aerosols that can impact the natural radiation budget and cloud formation. However, the chemical processing, i.e. secondary formation and aging of DMS oxidation products, remains still poorly understood. Hence, the implementation in current multiphase chemical mechanisms and climate models is limited and their current predictions are still very biased.To further close the existing gaps in our understanding of the DMS multiphase chemistry, the project ADOniS aims at (i) performing advanced laboratory investigations on gas and aqueous-phase chemistry of DMS oxidation products, (ii) developing an advanced multiphase DMS chemistry module and (iii) performing accompanied process and 3D model investigations. The proposed detailed laboratory investigations will focus on gas-phase OH oxidation of first-generation products, hydroperoxymethyl thioformate (HPMTF) and dimethyl sulfoxide (DMSO), and the formation of second-generation DMS oxidation products from both the addition and H-atom abstraction channel, respectively. The detailed mechanistic investigations will be conducted with a free-jet flow system. Further kinetic and mechanistic investigations will focus on the chemical fate of DMS oxidation products in the aqueous phase. OH-radical reactions of HPMTF surrogates will be studied by a laser flash photolysis – long path absorption (LFP-LPA) setup. Secondly, aqueous-phase studies will investigate the oxidation of MSA/MS- by OH(aq) and MSIA/MSI- by O3(aq) to reduce the large existing kinetic uncertainties. In addition, the uptake of key DMS oxidation products on different aerosol particles will be investigated by means of ACD-C chamber studies under different relative humidity conditions. The formation of gas-phase DMS oxidation products and their uptake on injected aerosol particles will be monitored by a CI-APi-TOF mass spectrometer. Based on the enhanced kinetic, mechanistic and uptake understanding of DMS oxidation products, an advanced DMS reaction module will be developed and subsequently applied in the multiphase model SPACCIM for detailed process studies. The gained knowledge on the key DMS oxidation pathways will provide the basis for an updated DMS mechanism treatment in global climate chemistry models (CCMs), here ECHAM-HAMMOZ. Finally, proposed simulations with ECHAM-HAMMOZ will investigate the impacts of the DMS chemistry mechanism improvements on the global atmospheric DMS chemistry and to assess the climate impact and future sensitivity.

• DFG Programme: Research Grants