Unveiling the Molecular Diversity of Sulfur‐Containing Organic Compounds in Seasonal Snow From Northwestern China

Abstract A diverse array of sulfur‐containing organic compounds (SOCs) was identified in seasonal snow samples collected from northwestern China, using high‐performance liquid chromatography interfaced with an electrospray ionization high‐resolution mass spectrometer (HPLC–ESI–HRMS). Hierarchical cluster analysis (HCA) of the HPLC–HRMS data set classified SOCs into distinct clusters based on their molecular characteristics. Substantial differences in SOC composition were observed between urban (U) and rural/remote (R) clusters. In ESI− mode, the SOCs in the U cluster exhibited higher unsaturation degrees, oxidation levels, and larger molecular sizes than the R cluster. These compounds were likely derived from anthropogenic sources, such as transportation and industry, whereas those in the R cluster exhibited signatures of mixed sources, including biomass burning, cooking‐related emissions, and local biogenetic inputs. In ESI+ mode, SOCs were scarcely detected in the R cluster but were abundant in the U cluster. These compounds were predominantly reduced and unsaturated SOCs, with more than 85% (by intensity) containing one or no oxygen atoms in their elemental formulas. Tentative assignments for these species include sulfoxides, polycyclic aromatic S‐heterocycles, thiols, and sulfides, likely originating from the use and production of heavy oils. Additionally, volatility estimates suggest that the SOCs identified in this study are more volatile than those found in other environmental media. The findings highlight the unique SOCs composition in snowpack of northwestern China, particularly those detected via positive ESI mode, offering new insights into the environmental, climatic, and biogeochemical roles of SOCs.