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

Organic aerosol (OA) over oceans is not well characterized, which hinders our understanding of OA sources, components, atmospheric transformation, and accurate model representations of OA to the global climate and marine ecosystem. In this study, the chemical composition of OA in 1-year-long samples collected over the South China Sea was characterized by gas chromatography-Orbitrap mass spectrometry (GC-Orbitrap MS) combined with nontarget analysis. Aromatic compounds contributed the most to the total number of identified compounds, with esters, polycyclic/monocyclic aromatic hydrocarbons, ketones, and phenols as the major components. Aliphatic compounds ranked second, followed by alicyclic and heterocyclic compounds. Specifically, the OA samples associated with continental or marine air masses exhibited large differences in their physicochemical properties. Continental-influenced OA was characterized by a high degree of oxidation and a broad range of volatilities, especially including low-volatile compounds. They were mainly from coal combustion, biomass burning, and secondary formation. In contrast, marine-influenced OA exhibited low oxidation levels and relatively high volatilities, primarily from oceanic biological activities. Interestingly, although some artificial organics such as phthalic acid esters were identified as key species in continental-influenced OA, they were also detected in marine-influenced OA, likely due to atmospheric long-range transport or air-sea exchange. This study provides insights into the chemical composition, oxidation status, and volatilities of OA over the South China Sea and highlights the differences between marine and continental OA.