Abstract
Organosulfur compounds (OrgSs), especially organosulfates, have been widely reported at large quantities in particulate organic matter found in various atmospheric environments. Despite various kinds of organosulfates and their formation mechanisms being previously identified, a large fraction of OrgSs remain unexplained at the molecular level, impeding further knowledge on additional formation pathways and critical environmental parameters that help to explain their concentrations. In this work, the abundance and molecular composition of OrgSs in fine particulate samples collected in Guangzhou was reported. Our results revealed that organic sulfur can averagely contribute to 30 % of total particulate sulfur, and showed positively correlations with the SO2 (r = 0.37, p < 0.05) and oxidants (NOx+O3, r = 0.40, p < 0.01). Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) results presented that more than 80 % by number of the detected OrgSs in our samples have the elemental composition of O/(4S+3N) ≥ 1, indicating that they were largely in the form of oxidized organosulfates and/or nitrooxy organosulfates. Many OrgSs, which are tentatively attributed to previously identified biogenic and anthropogenic origins, were also present in aerosols derived from freshly-emitted combustion sources. Results show that the formation of OrgSs through an epoxide intermediate pathway could be as much as 46 %, and the oxidants levels could explain 20 % variation of organic sulfur mass. The analysis from our large FT-ICR MS dataset suggests that relative humidity, oxidation of biogenic volatile organic compounds via ozonolysis, and NOx-related nitrooxy organosulfate formations were the major reasons for the molecular variation of OrgSs, possibly highlighting the importance of heterogeneous reactions involving either the uptake of SO2 or the heterogeneous oxidations of particulate organosulfates into additional unrecognized OrgSs.
Highlights
Organosulfur compounds (OrgSs) have been widely identified in atmospheric media including fog, rainwater, and ambient 35 aerosols, and account for a substantial fraction of ambient OM mass, with ratios as large as 50% (Surratt et al, 2007; Altieri et al, 2009; Mazzoleni et al, 2010; LukAcs et al, 2009; Tolocka and Turpin, 2012; Surratt et al, 2008), with potentially adverse effects on the global climate system and toxicity to human health (Jimenez et al, 2009; Noziere et al, 2015; Nozière et al, 2010; Nguyen et al, 2012; Bates et al, 2019; Daellenbach et al, 2020)
The concentrations of organic sulfur (Org-S) over Guangzhou were higher than those observed in Hungary (0.02−0.33 140 μg/m3) (Surratt et al, 2008; LukAcs et al, 2009), and close to the upper-bound measured in the U.S (0.50 μg/m3), while the percentage of Org-S to fine particles (1.4%) was in the range of 0.75−2.0% estimated in U.S.A (Table S1)
These results suggest that Org-S plays a larger relative role in the atmosphere and is probably essential to the high particle pollution in Guangzhou compared to other sites
Summary
Organosulfur compounds (OrgSs) have been widely identified in atmospheric media including fog, rainwater, and ambient 35 aerosols, and account for a substantial fraction of ambient OM mass, with ratios as large as 50% (Surratt et al, 2007; Altieri et al, 2009; Mazzoleni et al, 2010; LukAcs et al, 2009; Tolocka and Turpin, 2012; Surratt et al, 2008), with potentially adverse effects on the global climate system and toxicity to human health (Jimenez et al, 2009; Noziere et al, 2015; Nozière et al, 2010; Nguyen et al, 2012; Bates et al, 2019; Daellenbach et al, 2020). Heterogeneous reactions between SO2 and unsaturated compounds or aerosol-phase organic peroxides were identified to generate OSs both by simulation experiments and field observations (Shang et al, 2016; Passananti et al, 2016; Ye et al, 2018; Zhu et al, 2019) Other mechanisms such as nucleophilic 50 substitution of organic nitrates by sulfate (Surratt et al, 2007; Iinuma et al, 2007b; Surratt et al, 2008), sulfate esterification of alcohols/epoxides (He et al, 2014), and sulfoxy radical-initiated oxidation of unsaturated compounds (Nozière et al, 2010; Huang et al, 2019; Wach et al, 2019; Huang et al, 2020) have been proposed in many studies. The above works suggest that there is insufficient understanding of the comprehensive sources, formation mechanisms and influencing factors of OrgSs overall for ambient 65 samples (Bruggemann et al, 2020), which makes it an urgent need to fully understand their molecular composition
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