Monsoon-driven variations in the molecular composition of organosulfates in South China Sea marine aerosols

Abstract The South China Sea (SCS) is strongly influenced by monsoon-driven transport and mixing of continental and marine air masses, which shape the chemical composition of marine aerosols. Organosulfates (OSs) are important constituents of secondary organic aerosols (SOA), yet their molecular characteristics and formation pathways in marine atmospheres remain insufficiently understood. Here, we investigated OSs and nitrooxy-OSs (NOSs) in marine aerosols collected during the 2021 South China Sea Monsoon Integrated Cruise using ultra-high performance liquid chromatography coupled with Orbitrap mass spectrometry (UHPLC-Orbitrap MS). A total of 1925–3260 organic formulas were identified per sample, with organosulfur compounds (CHOS and CHONS) accounting for 38% by number and 25% by signal intensity. Targeted OS and NOS species together contributed ~26% of the total signal intensity assigned to OS-like compounds. Monsoon-associated transport patterns strongly influenced OS composition. Southwesterly marine air masses were enriched in aliphatic OSs exhibiting distinct CH 2 -homologous series, whereas easterly continental-influenced air masses showed enhanced aromatic OS and NOS fractions with higher double bond equivalence (DBE) and aromaticity (Xc), reflecting contrasting marine biogenic and terrestrial anthropogenic influences. Environmental factors, including sea surface temperature, chlorophyll-a, aerosol liquid water content, sulfate loading, aerosol surface area, and acidity, jointly modulated OS and NOS formation.