Interfacial Ozone Oxidation Chemistry at a Riverine Surface Microlayer as a Source of Nitrogen Organic Compounds
Yiqun Wang, Huifan Deng, Pan Li, Jinli Xu, Gwendal Loisel, Hongwei Pang, Xin Xu, Xue Li, Sasho Gligorovski
Abstract
Nitrogen (N)-containing organic compounds, including “brown carbon” (BrC), represent an important fraction of organic aerosols. However, little is known about the processes of formation of the secondarily formed N-containing organics in the atmosphere. Here, we investigated the formation of gas-phase organic compounds, including N-containing organics, through interfacial oxidation chemistry of gaseous O3 with an authentic riverine surface microlayer (SML) by using a high-resolution quadrupole Orbitrap mass spectrometer coupled to a commercial secondary electrospray ionization source. The resulting hierarchical cluster diagram obtained for real-time observation for 60 min shows the occurrence of 677 ions in positive mode. The level of N-containing organics, including BrC compounds (e.g., imidazoles), formed during the heterogeneous processing of O3 on the SML in the dark and under ultraviolet–visible light irradiation, was on average 20.7% among all samples. Many of the detected N-containing compounds comprise a C═N bond, suggesting that they are potentially toxic compounds that also affect urban air quality. Overall, this study provides evidence that interfacial ozone oxidation chemistry at the riverine SML plays an important role as an additional source of air pollution in urban environments, which can affect both human health and the absorption properties of urban aerosols.