Molecular characteristics, sources, and formation pathways of organosulfur compounds in ambient aerosol in Guangzhou, South China

Abstract

Abstract. Organosulfur compounds (OrgSs), especially organosulfates, have been widely reported to be present in large quantities in particulate organic matter found in various atmospheric environments. Despite hundreds of organosulfates and their formation mechanisms being previously identified, a large fraction of OrgSs remain unexplained at the molecular level, and a better understanding of their formation pathways and critical environmental parameters is required to explain the variations in their concentrations. In this study, the abundance and molecular composition of OrgSs in fine particulate samples collected in Guangzhou were reported. The results revealed that the ratio of the annual average mass of organic sulfur to total particulate sulfur was 33 ± 12 %, and organic sulfur had positive correlations with SO2 (r=0.37, p<0.05) and oxidant (NOx + O3, r=0.40, p<0.01). A Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis revealed that more than 80 % of the sulfur-containing formulas detected in the samples had the elemental composition of o/(4s+3n)≥1, indicating that they were largely in the form of oxidized organosulfates or nitrooxy organosulfates. Many OrgSs that were previously tentatively identified as having biogenic or anthropogenic origins were also present in freshly emitted aerosols derived from combustion sources. The results indicated that the formation of OrgSs through an epoxide intermediate pathway could account for up to 46 % of OrgSs from an upper bound estimation, and the oxidant levels could explain 20 % of the variation in the mass of organic sulfur. The analysis of our large dataset of FT-ICR MS results suggested that relative humidity, oxidation of biogenic volatile organic compounds via ozonolysis, and NOx-related nitrooxy organosulfate formation were the major reasons for the molecular variation of OrgSs, possibly highlighting the importance of the acid-catalyzed ring-opening of epoxides, oxidation processes, and heterogeneous reactions involving either the uptake of SO2 or the heterogeneous oxidation of particulate organosulfates into additional unrecognized OrgSs.

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

“…Figure a–c presents the distributions of carbon atom numbers in the molecular formula assignments. The majority of the CHOS and CHONS species have carbon atom numbers of C 4 –C 11 , which can be derived from a variety of biogenic precursors and anthropogenic aromatic hydrocarbons and long-chain alkanes. ,− The species with C 8 –C 10 were particularly predominant, which might be associated with the oxidation products of benzene, polycyclic aromatic hydrocarbons, long-chain alkanes, and monoterpenes . The number of the CHOS species with C 12 –C 19 was apparently increased during the haze episode, suggesting that the precursors such as long-chain alkanes and/or sesquiterpenes have made some contributions.…”

“…The maximum number of molecular formula candidates for each peak was set to 40. The molecular formula assignments in the two modes were performed using the elements of 12 C, 1 H, 16 O, 14 N, and 32 S, with the atom number constrained to the ranges of 1−50, 0−200, 0−50, 0−5, and 0− 2, respectively. 26−28 An additional 23 Na (atom number 0−1) was also used in positive mode for possible sodium adducts.…”

“…Organosulfur species (OrgS) are ubiquitous in the atmosphere and have been found worldwide from remote to highly polluted urban areas. , They are demonstrated to be a very important component in ambient PM 2.5 , which could have crucial impacts on the aerosol properties of acidity, volatility, reactivity, hygroscopicity, and light absorption. − The OrgS are mostly produced by the heterogeneous/multiphase reactions of sulfur dioxide (SO 2 ) and sulfate particles with anthropogenic and biogenic organic precursors, although they can also be directly emitted from the combustion of fossil fuels and biomass. − The chemical composition and concentrations of OrgS vary considerably among different ambient environments. Many sulfonates and organosulfates are found to be highly abundant particulate sulfur compounds during haze episodes. , However, the OrgS in the atmosphere remain poorly understood with regard to their properties, composition, sources, and formation pathways. , …”

Molecular characteristics of ambient organic aerosols in Shanghai winter before and after the COVID-19 outbreak

“…The double-bond equivalence (DBE) indicates the number of rings and double bonds in the molecules. DBE is calculated by the following equation ( Jiang et al, 2022 ). The aromaticity equivalent (X C ) is a more sensitive way to identify the aromatic and condensed aromatic rings possessing long alkyl chains, which was obtained using the equation: X C = [3(DBE − (p × o + q × s)) − 2] / [DBE − (p × o + q × s)], where p and q, respectively, denote the fraction of oxygen and sulfur atoms involved in the π-bond structure of a compound ( Yassine et al, 2014 ).…”

Significant Conversion of Organic Sulfur from Hydroxymethanesulfonate to Inorganic Sulfate and Peroxydisulfate Ions upon Heterogeneous OH Oxidation

“…Organosulfur compounds have been found to be ubiquitous in atmospheric aerosols and can potentially play a role in determining aerosol physicochemical properties such as water uptake, viscosity, acidity, morphology and phase state. − Sulfonate is an important class of organosulfur compounds in atmospheric aerosols. For instance, methanesulfonic acid (CH 3 SO 3 H, MSA) is known to be abundant in marine aerosols, which can be formed through aqueous-phase or gas-phase oxidation of dimethyl sulfide (DMS). − Hydroxymethanesulfonate (CH 2 (OH)­SO 3 – , HMS) was also found to be present in atmospheric aerosols (Table S1) with concentrations ranging from 0.002 μg/m 3 in clean regions to 7 μg/m 3 in polluted environments. − Atmospheric model simulations have also suggested that HMS can account for 10% of global aerosol sulfur in continental surface air and over 25% in most of urban polluted areas during winter. , …”