Enhanced Production of Organosulfur Species during a Severe Winter Haze Episode in the Guanzhong Basin of Northwest China

Abstract

The molecular composition of organic aerosols in ambient PM 2.5 was investigated in an urban area in the Guanzhong basin of northwest China during a severe regional haze episode in the winter of 2018/2019. Organic matter, accounting for 20−35% of PM 2.5 mass concentration, was characterized using direct infusion and electrospray ionization coupled with high-resolution Orbitrap mass spectrometry. The number of organic molecular formula assignments was primarily dominated by organosulfur species (OrgS, including CHOS and CHONS) in negative ion mode. The number and peak signal intensity of OrgS distinctly increased during the severe haze episode. Organosulfates and nitrooxyorganosulfates constituted the majority number (72−94%) of OrgS over the entire period. Although the OrgS were mostly present in aliphatic molecular structures, an increase in the number of polycyclic aromatic OrgS on haze days revealed the enhanced contribution from anthropogenic sources. The number of OrgS strongly correlated with ambient relative humidity and the oxidation ratios of sulfur and nitrogen, suggesting the important roles of aqueous phase chemistry and atmospheric oxidation in the formation of OrgS. A thorough understanding of the significance of OrgS will be essential to assess and mitigate the adverse impacts of haze pollution.

Measurement report: Characteristics of nitrogen-containing organics in PM2.5 in Urumqi, northwest China: differential impacts of combustion of fresh and old-age biomass materials

“…In contrast, the species with the strong signal intensity fell between 100 Da and 300 Da in ESI−. This mass range detected in Urumqi organic aerosols was comparable to previous observations in urban aerosols (Han et al, 2023) but significantly lower than that in firework-related urban aerosols (300-400 Da) (Xie et al, 2020). On average, the molecular number and relative abundance of CHON compounds (150-500 Da) were dominant in ESI+, accounting for 45.99% of the total molecular number and 62.70 ± 6.83% of the total signal intensity (Figures 1a and Table S2).…”

“…CC BY 4.0 License. including NO3 -, SO4 2-, Cl -, Ca 2+ , Mg 2+ , Na + , and NH4 + in the samples were determined using an ion chromatograph system (Dionex Aquion, Thermo Scientific, USA) (Xu et al, 2022a;Lin et al, 2023).…”

“…However, the abundance of CHN compounds tended to increase from the warm period to the cold period. Since the ESI+ mode is highly sensitive to protonatable species, organic amines were expected to predominate the CHN compounds (Han et al, 2023;Wang et al, 2021a). It is well documented that the formation of amine salt in the particle phase is tightly associated with aerosol acidity and water (Liu et al, 2023).…”