Secondary aerosol formation from dimethyl sulfide - Smog chamber experiments and detailed process modelling

Abstract: The aim of this thesis was to investigate the secondary aerosol formation from dimethylsulfide (DMS) using the aerosol dynamics, gas- and particle-phase chemistry kinetic multi-layer model, ADCHAM. The first simulations, concerning the butanol oxidation via hydroxyl radicals (OH), were performed to characterize the UV-light source of the AURA smog chamber (Aarhus university, Denmark), later used for the DMS experiments. The observed, strong impact of the relative humidity (RH) on the OH-concentration during the butanol-OH experiments may be related to the chamber walls, however, the modelled OH concentrations were not sensitive to the RH or the absolute water molecule concentration. The DMS oxidation via OH and subsequent secondary aerosol formation was simulated and compared to the measurements from the smog chamber experiments conducted at AURA. The results show that the recently observed DMS oxidation product hydroperoxymethyl thioformate (HPMTF) has most likely a negligible contribution to the new particle formation and further, the secondary particle formation from methanesul-fonic acid (MSA) condensation is highly sensitive to the ammonia (NH3) concentration and RH in the chamber. The final atmospheric DMS tests investigated the impact of the multi-phase (gas, particle, cloud) DMS chemistry involving halogens (Cl, Br, I) emitted from the ocean surface. Adding representative ocean halogen emissions as well as idealised aqueous-phase cloud passages led to increasing MSA and sulfuric acid (H2SO4)aerosol particle mass, but not increasing particle number concentrations. This could indicate that neglecting these processes may lead to inaccurate predictions of the indirect radiative climate effect of DMS-aerosols.