DIMETHYL SULFIDE, METHANE SULFONIC-ACID AND PHYSICOCHEMICAL AEROSOL PROPERTIES IN ATLANTIC AIR FROM THE UNITED-KINGDOM TO HALLEY BAY

The concentrations of dimethyl sulfide in air were obtained during a c ruise between the United Kingdom and the Antarctic in the period Octob er 1992 to January 1993 using a method of sampling and analysis optimi zed to avoid interferences from oxidants. In equatorial regions (30 de grees N to 30 degrees S) the atmospheric DMS concentration ranged from 3 to 46 ng (S) m(-3), with an average of 18 ng (S) m(-3). In the pola r waters and regions south of the Falkland Islands, concentrations fro m 3 to 714 ng (S) m(-3) were observed, with a mean concentration of 73 ng (S) m(-3). The concentrations of a range of DMS oxidation products were also obtained. No clear relationships between reactant and produ ct concentrations were seen. Information on particle number concentrat ion, Fuchs surface area and the thermal volatility characteristics of the ambient aerosol was obtained, but again no clear relationships wit h sulfur concentrations were observed. Accumulation mode particle conc entrations averaged 25 cm(-3) in the clean marine and polar air masses south of 58 degrees S while background condensation nuclei (CN) conce ntrations were of the order of 400-600 cm(-3). Simplistic calculations suggest that a particle source strength of about 20-60 particles cm(- 3) d(-1) is required to sustain this background CN concentration. It i s not clear whether boundary layer nucleation of new CN or entrainment from the free troposphere provided the source of CN. Periods of eleva ted CN concentrations (>4000 cm(-3)) were regularly observed in the bo undary layer over the Weddell Sea and were attributed to ''bursts'' of new particle formation. However, shortly after these nucleation event s the CN concentration rapidly decayed to the background level through coagulation losses, suggesting little impact on die background CN or cloud condensation nuclei (CCN) concentration.