Hydroxy Fatty Acids in Remote Marine Aerosols over the Pacific Ocean: Impact of Biological Activity and Wind Speed

Current parametrization of cloud–aerosol interactions of nascent sea-spray aerosols (SSA) in the climate models is hampered by our limited understanding of the constituents of organic aerosols. We investigated here the mass concentrations, molecular distributions, and relative abundances of hydroxy fatty acids (FAs), ubiquitous lipid compounds in the SSA collected over the western Pacific Ocean (35°N–40°S). Detectable levels of methanesulfonic acid (an oxidation product of dimethyl sulfide) and high enrichment factors of Mg 2+ and Ca 2+ relative to Na + emphasize the impact of the marine biological activity on the organic fraction of SSA. The molecular distributions of β-hydroxy FAs with characteristic “ odd-C ” predominance (C 9 > C 10 and C 11 > C 12 ) among short-chain homologues (<C 14 ) reveal their formation from the photochemical oxidation of marine-derived organic matter. Molecular distributions and the carbon preference index of n -fatty acids and n -alkanes in the SSA also indicate their oceanic origin. A rapid decrease in the mass ratio of low molecular weight FAs to sea-salts with wind speed indicates the significant variability of organic compounds with production pathways of SSA (fine film-drops versus coarse jet-droplets). On the basis of the multitracer approach, this study underscores the background oceanic influence on the abundances of microbial lipids over the remote Pacific Ocean.