Abiotic Emission of Volatile Organic Compounds from the Ocean Surface: Relationship to Seawater Composition

An important goal in marine atmospheric chemistry is to determine the impact of the surface ocean on the overlying marine boundary layer in terms of the ocean’s potential to release volatile organic compounds (VOCs) that may impact atmospheric oxidizing capacity and aerosol growth. In addition to direct biogenic production of VOCs that are eventually emitted to the atmosphere, abiotic mechanisms that produce VOCs include direct or sensitized photochemistry and oxidation reactions initiated by gas phase oxidants. In this laboratory study, we use proton-transfer-reaction mass spectrometry to measure the emission fluxes resulting from both UV irradiation and ozone oxidation of Arctic surface microlayer water and the underlying bulk seawater. Under our experimental conditions, both mechanisms lead to comparable VOC emission fluxes, which scale closely with the total and dissolved organic carbon content of the sample. However, the composition of the seawater sample can strongly affect the emission fluxes of specific molecules. For example, nonanal fluxes from oxidation correlate closely with the phytoplankton abundance in the samples, indicating that unsaturated lipids may be the substrate. Conversely, the best predictor for the nitrogenated VOC flux under irradiation conditions is photosynthetic prokaryotes (i.e., cyanobacteria) abundance. Similar studies in a wider range of environments, ideally conducted in the field, will better constrain the importance of these abiotic processes to global ocean-to-atmosphere fluxes.