Molecular evidence on potential contribution of marine emissions to aromatic and aliphatic organic sulfur and nitrogen aerosols in the South China Sea

Abstract. The origins of marine aromatic and aliphatic secondary organic aerosols (SOA) remain elusive. Here, organosulfates (OSs) and nitrogen-containing organic compounds (NOCs) were measured in PM_2.5 collected in Sansha (the South China Sea), a region with minimal anthropogenic pollution, to investigate the potential impact of marine emissions on their formation. The proportion of aliphatic and aromatic OSs in the total OSs was significantly higher in Sansha than in other Chinese cities investigated. Biogenic OSs correlated significantly with aliphatic and aromatic OSs and NOCs. Two typical SOA tracers (C₆H₅O₄S⁻ and C₇H₇O₄S⁻), which are formed via the atmospheric oxidation of marine benzene and toluene, were found to increase with rising chlorophyll-a and isoprene levels in seawater. Additionally, the impact of long-range transport and ship emissions on the abundance of OSs and NOCs was found to be insignificant. These results together with mantel test analysis suggest that marine-derived precursors may significantly contribute to the formation of aliphatic and aromatic OSs and NOCs in the Sansha region. Overall, this study provides the observation-based molecular evidence that marine biogenic emissions may play a significant role in the formation of aromatic and aliphatic SOA in the South China Sea.