Measurements of the aerosol concentrations of methanesulphonic acid, dimethyl sulphoxide and dimethyl sulphone in the marine atmosphere of the British Isles

Abstract

Aerosol concentrations of methanesulphonic acid (MSA), dimethyl sulphoxide (DMSO) and dimethyl sulphone (DMSO 2) have been measured from landbased stations at Plymouth (Devon, U.K.), Galway (EIRE), and from various shipboard stations in the North Sea and the North Atlantic Ocean. MSA, DMSO and DMSO 2 all show seasonal cycles with spring/summer maxima and winter minima. The summer concentrations of MSA are approximately an order of magnitude higher than in winter. The general levels of MSA (July 1985 mean = 9.27 × 10 −9 mol m −3, December 1986 mean = 1.14 × 10 −9 mol m −3) are comparable to those reported from Cape Grim, Tasmania. Modelling indicates that neither MSA nor DMSO 2 are present in sufficient quantity to represent major oxidation pathways for dimethyl sulphide (DMS). Rate constant ratios for both the reactions of DMS and DMSO with OH and IO have been estimated. Hydroxyl radical does not appear to be reactive enough for it to be the major sink of atmospheric DMS. It is also shown that the rate constants for the destruction of DMSO (the main reaction product of the DMS/IO system) with either IO or OH are likely to be slow. Thus low tropospheric concentrations of DMSO tend to indicate that it also is not a major product of DMS oxidation.