Considering its size and potential importance,the ocean is surprisingly poorly characterised in terms of organic gases that play important roles in global atmospheric chemistry.In this project we aim to characterise the nature of organic trace species,in particular organic oxygenates,and the rate of emissions from the marine biota.The oxidation of these compounds in air is directly linked to the global ozone budget while the oxidation pathways in seawater are largely unknown.We will conduct laboratory experiments on seawater samples and specific phytoplankton types to determine the effect of basic biophysical parameters (e.g.temperature,light,plankton growth rate and physiological state) on the emission of organic species.The photooxidation rates and products of these species will also be examined through measurements.Marine aerosols,with emphasis on the organic fraction,will also be investigated in terms of physical,chemical (mass closure),hygroscopic and optical properties.Two shipborne research cruises will be performed within the OOMPH project to assess both emission and uptake in the open ocean in the northern hemisphere Tropics and the Southern Atlantic Ocean.Based on the laboratory and field measurements an interactive atmosphere-ocean chemistry model will be developed,from box model to global Earth system simulations.