Analysis of Organic Anionic Surfactants in Fine and Coarse Fractions of Freshly Emitted Sea Spray Aerosol

The inclusion of organic compounds in freshly emitted sea spray aerosol (SSA) has been shown to be size-dependent, with an increasing organic fraction in smaller particles. Here we have used electrospray ionization-high resolution mass spectrometry in negative ion mode to identify organic compounds in nascent sea spray collected throughout a 25 day mesocosm experiment. Over 280 organic compounds from ten major homologous series were tentatively identified, including saturated (C-18-C-24) and unsaturated (C-12-C-22) fatty acids, fatty acid derivatives (including saturated oxo-fatty acids (C-5-C-18) and saturated hydroxy-fatty acids (C-5-C-18), organosulfates (C-2-C-7, C-12-C-17) and sulfonates (C-16-C-22). During the mesocosm, the distributions of molecules within some homologous series responded to variations among the levels of phytoplankton and bacteria in the seawater. The average molecular weight and carbon preference index of saturated fatty acids significantly decreased within fine SSA during the progression of the mesocosm, which was not observed in coarse SSA, sea-surface microlayer or in fresh seawater. This study helps to define the molecular composition of nascent SSA and biological processes in the ocean relate to SSA composition.