Marine Modulation of the Formation Pathways and Sources of Organosulfates over the Coastal South China Sea

Abstract

Organosulfates (OSs) constitute a considerable part of airborne sulfur-containing organic aerosols, influencing aerosol physicochemical properties, biogeochemical cycles, and climate. This study investigated the compositions, formation pathways, and sources of OSs at a coastal site of the South China Sea in summer. Thirty-three OS species were quantified by using an UHPLC-Orbitrap MS and were assessed under marine and terrestrial air mass origins. iOSs (isoprene-derived OSs) ranked the highest, followed by C2/C3 OSs (OSs with two or three carbon atoms). The formation of iOSs was influenced by aerosol pH and their major precursor (isoprene), with photochemical processes playing a significant role in terrestrial transport. Different from urban conditions, sea breezes favored the formation of 2-MAS (C₄H₇O₇S^–) over 2-MTS (C₅H₁₁O₇S^–) even under low NO_x levels, mainly attributed to the high temperature and dominance of aqueous oxidation. Compared to terrestrial transport, the formation of C2/C3 OSs was more favored than that of iOSs under the influence of sea breezes. Marine biogenic emission was quantified as an important source of C2/C3 OSs. This study enhances our understanding of the influence of both terrestrial and marine factors on the formation pathways of atmospheric OSs and emphasizes the significant contribution of marine biogenic sources to OSs.