Chemical Diversity of Organosulfur Species in Various Atmospheric Environments Over the Guanzhong Basin of Northwest China

Atmospheric organosulfur species (OrgS) were investigated at four different sites (urban, rural, forest, and remote mountain) in the Guanzhong basin of northwest China to probe their chemical diversity and distribution profiles. The organic molecular composition in ambient PM_2.5 samples was measured using an ultrahigh performance liquid chromatograph coupled with an electrospray ionization Orbitrap high-resolution mass spectrometer. We found that OrgS (including CHOS and CHONS herein) were ubiquitously present across these environments and predominated the number of organic species assigned in negative ionization mode. The fractions of OrgS (mean 41%–45%) in total number of organic species over the Guanzhong basin were at the upper range compared with those in worldwide areas (12%–37%), primarily attributing to the high levels of anthropogenic pollutants (SO₂, NO_x, sulfate, etc.) across this region. Organosulfates and nitrooxy-organosulfates in aliphatic-like structures from long-chain alkanes and biogenic precursors constituted a majority number of OrgS, yet with distinct molecular characteristics in each environment. The distribution of the number of carbon atoms in the molecules revealed that OrgS mainly originated from complex mixed sources at the urban site, whereas biogenic precursors were more prevalent at the non-urban sites. The production of OrgS resulted from synergistic interactions of multiple influencing factors in different conditions. Our results highlight the importance of anthropogenic pollution in modifying organic aerosol composition under various atmospheric environments.