Molecular Characterization of the Product Compounds Formed Upon Heterogeneous Chemistry of Ozone With Riverine Surface Microlayer

Abstract

AbstractOzone (O3) is an important trace gas and oxidant in the atmosphere which sources and sinks are not well understood. In this study we measured the uptake coefficients of O3 (100 ppb) on authentic riverine surface microlayers (SML) collected on three different places on Pearl River in Guangzhou by a vertical wetted wall flow tube reactor which enables to estimate the deposition velocity of O3 on the fresh water surface. The product compounds formed upon interfacial reactions of O3 with the SML have been investigated by a Fourier transform ion cyclotron resonance mass spectrometry. About 10 times more product compounds were formed upon ozonolysis on the SML sample collected in a transportation hub close to the Estuary zone compared to the products formed upon ozonolysis on the SML sampled at the upper reach of the river at the periphery of Guangzhou. Moreover, 933 nitrogen (N)‐containing organic compounds which are associated with nitrooxy amines, organonitrates, nitroaromatics, and peroxyacetyl nitrates were formed upon heterogeneous reaction of ozone with the SML collected near the Estuary zone compared to 165 N‐containing compounds formed upon ozonolysis of the SML sample collected at the periphery of the city. Hence, the formed condensed phase product compounds through the reactions of ozone with the riverine SML can affect the freshwater biodiversity. An important fraction of brown carbon compounds was formed, which may be released to the air by wind‐wave interactions and influence the chemical composition of the atmosphere and thus, radiative forcing of the aerosols.