Influence on the conversion of DMS to MSA and SO42− in the Southern Ocean, Antarctica

Abstract

Abstract Dimethyl sulfide (DMS), methanesulphonic acid (MSA) and sulfate (SO42−) were measured simultaneously at high-time resolution in the Southern Ocean (SO) during February and March 2018, to characterize the conversion of DMS to MSA and SO42− in the marine atmosphere. DMS concentrations ranged up to ~10890.5 ng m−3 (with an average of 899.8 ± 957.9 ng m−3, representing the standard deviation), which were much higher than the MSA concentrations (with an average of 30.6 ± 16.8 ng m−3) and SO42− concentration (148.1 ± 32.5 ng m−3) in the aerosol phase. The spatial distribution of MSA was different from the distribution of DMS. The ratio of MSA to DMS (RM) ranged up to ~ 0.31, with an average of 0.044 ± 0.045. RM value decreased dramatically as DMS concentration increased, when DMS concentration was below 1000 ng m−3. The effects of temperature and relative humidity (RH) on RM were mostly negligible, indicating that neither DMS concentration, nor RH and temperature was the key parameter for the conversion of DMS to MSA in the SO. Ratios of nss-SO42- to DMS (RS) were used to estimate the conversion of DMS to SO42−. The calculated RS with mean Rp (the ratio of MSA to nss-SO42-) value correlated well with the observed RS, which provided an useful method to estimate the biogenic SO42− from the oxidation of DMS in the marine atmosphere, as biogenic SO42− levels can be calculated with Rs and DMS concentrations. The estimated biogenic SO42− levels ranged up to 163.8 ng m−3, with an average of 47.1 ± 30.2 ng m−3 in the SO during the cruise. The results extend the knowledge of the conversion of DMS to MSA and SO42− in the marine atmosphere.