SEASONAL AND SHORT-TERM VARIABILITY IN DIMETHYL SULFIDE, SULFUR-DIOXIDE AND BIOGENIC SULFUR AND SEA-SALT AEROSOL-PARTICLES IN THE ARCTIC MARINE BOUNDARY-LAYER DURING SUMMER AND AUTUMN

The International Arctic Ocean Expedition (IAOE), lasting from August to mid-October 1991, provided a unique opportunity to characterise and quantify relationships within the natural sulfur cycle in the marine boundary layer under conditions of limited anthropogenic influence. Co ncentrations of dimethyl sulfide, sulfur dioxide, and submicrometer ae rosol concentrations of methane sulfonate, non-sea-salt sulfate, ammon ium and elemental carbon ranged from 17 to 0.05 nmol m(-3) (380 to 1 p pt(v)), 1.7 to 0.04 nmol m(-3) (38 to 0.9 ppt(v)), 1.4 to 0.002 nmol m (-3) (31 to 0.05 ppt(v)), 6.9 to 0.03 nmol m(-3) (155 to 0.7 ppt(v)), 3.9 to 0.03 nmol m(-3) (90 to 0.7 ppt(v)) and 0.51 to 0.009 nmol m(-3) (11 to 0.2 ppt(v)), respectively. Observations showed a seasonal vari ation of concentrations with highest values for all the marine biogeni c sulfur gas-aerosol parametres along the ice edge zone in August and lowest values over the pack ice in late September. On average concentr ations fell with a decline rate of about 20-40% per week. A similar se asonal change was also reflected in particulate ammonium. This therefo re indicates links between the different sulfur compounds as well as b etween the biogenic sulfur and nitrogen cycles. Concentrations over th e pack ice region were generally lower than over the open waters at th e ice edge with an estimated net loss rate of roughly 35% per day of t ransport over the pack ice. Contrary to earlier marine sulfur studies performed outside the Arctic region, a constant methane sulfonate to n on-sea-salt sulfate molar ratio was found in the submicrometer size fr action for samples with a minimal influence from fog and anthropogenic sources. This ratio had a value of 0.22 in spite of large seasonal ch anges in temperature and concentrations of methane sulfonate and non-s ea-salt sulfate. Thus we conclude that the sum of the processes contro lling the measured particle properties do not exhibit a net temperatur e dependence. The one to one molar ratio of ammonium to non-sea-salt s ulfate indicated a partly neutralised ammoniated sulfate aerosol. This was further verified by single particle analysis. Measurements of non -sea-salt sulfate and ammonium revealed a bimodal size distribution wi th about 70% of their mass found in the submicrometer size fraction. M ethane sulfonate was mainly associated with submicrometer particles, w ith less than 8% of the mass observed in the largest particles. We hav e also shown that the interchange of air between the surface mixed lay er and clouds, caused by atmospheric wave motions, dominated the short time variations in atmospheric DMS and submicrometer aerosol concentr ations. This interchange will have a strong influence on the chemical and physical processes that control the properties of the aerosol, and deserves more attention in future work.