Shipboard Measurements of DMS and SO2 in ASTEX

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A set of seven proposals and two supplement requests was submitted for participation in an international marine atmospheric chemistry experiment. The Atlantic Stratocumulus Transition in the eastern North Atlantic during June 1992, is a multinational effort designed to improve our capability for studying cloud-chemistry interactions and the air/sea fluxes that affect them. The specific goals of the MAGE atmospheric chemistry experiment in ASTEX include: 1) develop and test a Lagrangian strategy for studying chemical and meteorological evolution in a tagged airmass, using ships, balloons, and aircraft; 2) develop and test new techniques for estimating trace-gas and aerosol fluxes across the air/sea interface by comparison with traditional approaches; 3) evaluate the impact of marine and continental aerosols and the formation and dissipation of stratocumulus clouds; 4) compare the impacts of natural and anthropogenic sulfur, halogens, and hydrocarbons on marine aerosol chemistry; and 5) use a multinational, multi-agency field experiment as a means for addressing tropospheric chemistry issues. In this MAGE proposal, the PIs propose to conduct measurements of dimethyl sulfide (DMS) in ocean water and sulfur dioxide and DMS in air from shipboard in the study area of ASTEX. The primary objective is to determine the DMS content in the ocean along the track of the parcel sampled in a Lagrangian experiment. The PIs propose to compute the DMS flux along the parcel trajectory using a thin film model. Then, the DMS flux data would be used to reduce the number of variables in the Lagrangian budget analysis or to test the reliability of DMS flux data obtained directly from the budget analysis. Secondary objectives include the determination of DMS and sulfur dioxide in air before and after the air parcel passes over the ship. These data would provide information on the horizontal variation of DMS and sulfur dioxide upwind and downwind of the air parcel. These measurements would compliment those obtained from an aircraft platform because the aircraft will not sample exactly the same air parcel during the Lagrangian experiment. The PIs also propose to obtain sufficient data to characterize the diurnal variation of DMS and sulfur dioxide to aid in testing chemical models of the marine boundary layer.