Real-Time Detection of Gas-Phase Organohalogens from Aqueous Photochemistry Using Orbitrap Mass Spectrometry

Marine short-lived halogenated compounds, emitted from algae, phytoplankton, and other marine biota, significantly affect both the troposphere and the stratosphere. Here, we show that such compounds might also be photochemically produced through photosensitized reactions in surface water. Gas-phase products were detected and identified by high-resolution mass spectrometry, more particularly by means of an atmospheric pressure chemical ionization source coupled to an Orbitrap mass spectrometer. Under simulated solar irradiation, halogenated organic compounds were produced and detected in the gas phase when a proxy of dissolved organic matter, i.e., 4-benzoylbenzoic acid, was excited into its triplet state. We present a mechanism explaining the formation of a variety of such halogenated compounds. These photochemical reactions take place at the air/sea interface and are, therefore, a potential source of short-lived halogenated compounds in the atmosphere, participating in the tropospheric halogen cycle.