Atmospheric aerosols were collected in separate fine (< 2.5 mu m) and coarse (> 2.5 mu m) size fractions in the period December 2006-March 2007 at Amsterdam Island in the southern Indian 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 inorganic ionic species, and organic species, including methanesulphonate (MSA), dicarboxylic acids, and organosulphates. The concentrations of sea salt, non-sea-salt sulphate, and water-soluble and 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 of the four aerosol types in the fine and coarse size fractions, respectively. WSOM, which can serve as a proxy for biogenic secondary organic aerosol (SOA), accounted for only 2.8% of the sum of the mass of the four aerosol types in the fine size fraction. MSA was the dominating organic compound with a median concentration of 47 ng m(-3). The organosulphates were chatacterised as sulphate esters of hydroxyl acids and a dihydroxylaldehyde, which may originate from the oxidation of algal/bacterial unsaturated fatty acid residues. No evidence was found for isoprene SOA. (C) 2009 Elsevier Ltd. All rights reserved.