Observational constraints on abiotic marine VOC sources

Gordon Novak, Cooperative Institute for Research in Environmental Sciences (CIRES), Boulder, United States, Michael P Vermeuel, University of Wisconsin Madison, Chemistry, Madison, United States, Delaney B. Kilgour, University of Wisconsin Madison, Department of Chemistry, Madison, WI, United States and Timothy Bertram, University of Wisconsin Madison, Chemistry, Madison, WI, United States
The ocean surface acts as both a source and sink for a variety of reactive trace gases, including volatile organic compounds (VOCs) and oxidized volatile organic compounds (oVOCs). Considerable attention has been focused on emission of species with direct biogenic sources, such as dimethyl sulfide. Recent field studies have suggested the presence of significant abiotic sources of VOCs, including glyoxal and formic acid, in the remote marine atmosphere [1-2]. Laboratory studies have shown production at high yield of a wide variety of VOC and oVOC species from the photolysis or ozonolysis of surfactant coated water surfaces [3-4]. However, to date, direct field observations of ocean-atmosphere VOC transfer have only targeted a select set of molecules. Despite suggestions that abiotic marine VOC emission sources could be comparable to biogenic emissions, there remains significant uncertainty in abiotic VOC production mechanisms, product speciation, and the applicability of laboratory observations of model system studies to the marine atmosphere.

Here we present preliminary field measurements of VOC ocean-atmosphere exchange from a coastal ocean site at Scripps Pier, La Jolla CA via the eddy covariance technique using a latest generation ultrahigh sensitivity, high resolution, time-of-flight proton-transfer reaction mass spectrometer (HR-ToF-PTRMS). This data allows for a broad survey of the bi-directional exchange of VOCs across the ocean interface. Additional observations of dissolved VOC concentrations, bacteria and phytoplankton speciation, and other ocean properties allow for potential determination of biotic and abiotic marine VOC sources. We also present direct measurements of O3 deposition flux to the same coastal site, which are used to constrain the magnitude of possible VOC emissions driven by interfacial reactions with O3.

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[2]. Mungall et al. PNAS. (2017)

[3]. Zhou et al. Atmos. Chem. Phys. (2014)

[4]. Rossignol et al. Science (2016)