Chemical characterisation of marine aerosol at Amsterdam Island during the austral summer of 2006–2007

International audienceAtmospheric aerosols were collected in separate fine (2.5$\mu$m) sizefractions in the period December 2006–March 2007 at Amsterdam Island in the southern In-dian Ocean. A major objective of the study was to assess biogenic impact on the marine aerosol.The samples were analysed for organic carbon, water-soluble organic carbon, major inorganicionic species, and organic species, including methanesulphonate (MSA), dicarboxylic acids,and organosulphates. The concentrations of sea salt, non-sea-salt sulphate, and water-solubleand water-insoluble organic matter (WSOM and WIOM) were estimated. Sea salt dominated the composition of the aerosol and accounted for 83% and 91% of the sum of the mass ofthe four aerosol types in the fine and coarse size fractions, respectively. WSOM, which canserve as a proxy for biogenic secondary organic aerosol (SOA), accounted for only 2.8% of thesum of the mass of the four aerosol types in the fine size fraction. MSA was the dominatingorganic compound with a median concentration of 47ngm−3. The organosulphates were char-acterised as sulphate esters of hydroxyl acids and a dihydroxylaldehyde, which may originatefrom the oxidation of algal/bacterial unsaturated fatty acid residues. No evidence was found forisoprene SO