Research objectives and content: A main source of biogenic aerosols is the emission of dimethyl sulphide from the oceans. If the effects of atmospheric aerosols are to be included as interactive terms in models of climate and atmospheric chemistry, then a fundamental quantitative understanding of their source and sink mechanisms is required" (Andreae and Crutzen, 1997).Objectives1) Validation of techniques that are used for field measurements of air-sea gas fluxes.2) Quantification of the DMS flux.3) Investigation of the processes that determine the flux.4) Quantification of fluxes of other biogenic gases. Content Recent experiments have shown that the emission of dimethyl sulphide (DMS) can be measured by the relaxed eddy accumulation (REA) and gradient flux (GF) techniques (Zemmelink et al.). Moreover, these measurements have provided an accurate model for predicting the exchange of carbon dioxide. However, these techniques do not measure the absolute flux; the most direct method for the measurement of fluxes is the eddy correlation (EC) technique. New developments in gas analysis methodology, using Proton Reaction Mass Spectrometry (PTR-MS), makes EC for DMS feasible but this technique has never been applied yet. Moreover, the use of micrometeorological techniques for field measurements of the flux of any gas is still in its infancy and intercalibration of techniques is required. The proposed project aims at the intercalibration of the REA, Gp and EC techniques and the investigation of processes that determine fluxes, using DMS as a model gas. Moreover, the configuration of the REA and GF techniques allows field measurement of fluxes of a variety of other climatically and/or atmospherically reactive trace gases. The host group carries out research mainly in the area of air-sea exchange of trace gases. This involves studies of gases such as DMS, organo-halogens, non-methane hydrocarbons, carbon dioxide, carbon monoxide, ammonia and methylamines and some volatile trace metals. The group is interested in the processes of formation and destruction of these gases in seawater, how they cross the air-sea interface and how the rate of interfacial transfer can be parameterized and quantified, as well as their reactivity in the atmosphere. The development of systems that can be used for the measurement of fluxes in the field is important for the investigation of processes that determine fluxes. On the other side, the analysis of trace gases, both in the atmosphere and water, is not easily realized. The substantial experience (including the use of PTR-MS) of the host group will significantly facilitate the development of micrometeorological techniques for the measurement of fluxes of a variety of trace gases.