Nontarget Analysis of Organic Aerosol over the South\nChina Sea by Gas Chromatography-Orbitrap Mass Spectrometry

Organic aerosol (OA) over oceans\nis not well characterized, which\nhinders our understanding of OA sources, components, atmospheric transformation,\nand accurate model representations of OA to the global climate and\nmarine ecosystem. In this study, the chemical composition of OA in\n1-year-long samples collected over the South China Sea was characterized\nby gas chromatography-Orbitrap mass spectrometry (GC-Orbitrap MS)\ncombined with nontarget analysis. Aromatic compounds contributed the\nmost to the total number of identified compounds, with esters, polycyclic/monocyclic\naromatic hydrocarbons, ketones, and phenols as the major components.\nAliphatic compounds ranked second, followed by alicyclic and heterocyclic\ncompounds. Specifically, the OA samples associated with continental\nor marine air masses exhibited large differences in their physicochemical\nproperties. Continental-influenced OA was characterized by a high\ndegree of oxidation and a broad range of volatilities, especially\nincluding low-volatile compounds. They were mainly from coal combustion,\nbiomass burning, and secondary formation. In contrast, marine-influenced\nOA exhibited low oxidation levels and relatively high volatilities,\nprimarily from oceanic biological activities. Interestingly, although\nsome artificial organics such as phthalic acid esters were identified\nas key species in continental-influenced OA, they were also detected\nin marine-influenced OA, likely due to atmospheric long-range transport\nor air-sea exchange. This study provides insights into the chemical\ncomposition, oxidation status, and volatilities of OA over the South\nChina Sea and highlights the differences between marine and continental\nOA.