Primary and secondary marine organic aerosols over the North Atlantic Ocean during the MAP experiment

[1] The organic chemical composition of atmospheric submicron particles in the marine boundary layer was characterized over the northeast Atlantic Ocean in summer 2006, during the season of phytoplankton blooms, in the frame of the Marine Aerosol Production (MAP) experiment. First measurements of water-insoluble organic carbon (WIOC) in marine aerosol particles by nuclear magnetic resonance (NMR) spectroscopy showed that it is structurally similar to lipids, resembling the organic fraction of sea spray formed during bubble-bursting experiments. The composition of the water-soluble organic carbon (WSOC) fraction was investigated by liquid chromatography - mass spectrometry and by 1D- and 2D-NMR spectroscopy, and showed a less hydrophilic fraction containing traces of fatty acids and rich of alkanoic acids formed by lipid degradation, and a more hydrophilic fraction, containing more functionalized species encompassing short-chain aliphatic acids and sulfate esters of hydroxyl-carboxylic acids. The more oxidized fraction of WSOC accounts for the oxidized organic aerosol components, which can form by either gas-to-particle conversion or extensive chemical aging of lipid-containing primary particles, as also suggested by the parallel measurements using online mass spectrometric techniques (presented in a companion paper), showing oxidized organic substances internally mixed with sea salt particles. These measurements are also compared with online measurements using an Aerosol Time-Of-Flight Mass Spectrometer (ATOFMS) and Aerodyne Aerosol Mass Spectrometer (AMS). Given the large variability in the chemical composition of marine organic aerosol particles, a multitechnique approach is recommended to reduce method-dependent categorizations and oversimplifications and to improve the comparability with the results obtained in different oceanic areas.