Molecular characterization of water-soluble organic compounds in PM2.5 using ultrahigh resolution mass spectrometry
Graphical abstract
Introduction
Fine particulate matter with an aerodynamic diameter <2.5 μm (PM2.5) is an atmospheric pollutant of great concern in many cities across the world (Huang et al., 2014), and it contains a wide variety of components including metal oxides, inorganic salts, elemental carbon and organic compounds. Water-soluble organic compounds (WSOCs) are a critical component in particulate matter in significant proportions, which have impacts on the particle hygroscopicity and activity of cloud condensation nuclei (Asa-Awuku et al., 2010; Facchini et al., 1999; Jing et al., 2016; Sun et al., 2011). They may also have influence on human health, with potential biological effects from reactive oxygen and nitrogen species (Perring et al., 2013). WSOCs originate from a diversity of primary emission sources and secondary production. Anthropogenic and biogenic volatile organic compounds could be oxidized by ozone, the OH radical or the NO3 radical to form semivolatile secondary organic aerosols (Kondo et al., 2007; Putman et al., 2012; Zhang et al., 2012).
WSOC components are quite complex, making structural elucidation of individual compounds challenging (Altieri et al., 2009; Mazzoleni et al., 2010; Wang et al., 2010; Wozniak et al., 2008). Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has the inherent advantage of high resolving power (i.e., mass accuracy ≤1 part-per-million), which allows study of the molecular characteristics of chemicals in complex organic mixtures (Nozière et al., 2015). Recent studies have use FT-ICR MS for elemental composition characterization of dissolved organic matter (Herzsprung et al., 2017; Reemtsma et al., 2008; Zhang et al., 2019), disinfection byproducts (Kellerman et al., 2014; Lavonen et al., 2013; Zhang et al., 2012a, Zhang et al., 2012b), and aerosol phase humic-like substances (HULIS) (Hao et al., 2017; Lin et al., 2012b). Although a large quantity of WSOC molecular formulas have been observed, additional information on chemical structural features is scarce, being mainly based on bulk characterization approaches such as nuclear magnetic resonance and infrared spectroscopy analysis (Sun et al., 2011). Tandem mass spectrometry monitors the neutral loss of precursor ions by fragmentation methods such as collision-induced dissociation, in which information on specific functional groups and molecular structures can be obtained (Lin et al., 2012a). Carboxyl groups were observed as the abundant fragments of CHO species in a HULIS fraction isolated from aerosol samples, and precursor ions with high O/S ratios and sulfate fragments were found as organosulfate compounds (Lin et al., 2012b).
Polydimethylsiloxane (PDMS)-coated stir bar sorptive extraction (SBSE) is a solid phase microextraction sampling technique, which measures the partitioning of neutral polar and nonpolar chemicals between water and organic phases. PDMS-water distribution ratios (DPDMS) are the parameter for quantitative description of the distribution in equilibrium of all forms of WSOC in water and organic phases at certain pH conditions. It is known to correlate linearly with the octanol-water partition coefficient (Kow, a physical-chemical parameter determined by neutral or polar functional groups) (LeClair et al., 2012), and is thus an appropriate descriptor of molecular structure characteristics. It was also used as a biomimetic approach for prioritizing water-soluble substances with bioaccumulative potentials, which helped in understanding the source of acute toxicity in complex aquatic environments. For instance, polar neutral and basic (O+, NO+, and SO+) species were found to be more hydrophobic than naphthenic acids in oil sands process-affected water, and some of these compounds may contribute to the toxicity in the samples (Difilippo and Eganhouse, 2010; Surratt et al., 2007).
In this study, the characteristics of the molecular structure of water-soluble organic components in PM2.5 samples were investigated using FT-ICR ultrahigh resolution mass spectrometry, both in the negative and positive ion mode. Composition profiles of WSOCs were examined by accurate measurement of ion monoisotopic mass and elemental assignment. The hydrophobicity of WSOC analogues was estimated by a PDMS-water distribution test, with further structure information elucidated by MS/MS fragmentation analysis, in order to reveal the influence of crucial functional groups to the measured physical-chemical property.
Section snippets
Chemicals and materials
Glass-encapsulated magnetic stir bars (Twisters) were purchased from Gerstel (10 mm in length, surface-coated with a 1.0 mm film of PDMS, Mülheim a der Ruhr, Germany). Partitioning model compound standards (atrazine, propazine, prometryn, procaine, propranolol, warfarin, ibuprofen, and diclofenac) were obtained from Sigma-Aldrich (St. Louis, MO). Acetic acid was from Dikma (Richmond Hill, Canada) and Merck (Darmstadt, Germany), respectively. The purity of all chemicals was 95% or higher unless
Elemental composition profiles of WSOCs
Overall, 2508 species were detected with assigned elemental combinations in the negative ionization mode in PM2.5 water extracts, and 4881 species were found in the positive ionization mode. The identified elemental formulas could be classified into twelve major compound species, including CHO±, CHOS±, CHON±, CHONS±, CH+, CHS+, CHN+ and CHNS+. CHONS± compounds refer to compounds that were detected both in the ESI+ and ESI- modes containing carbon, hydrogen, oxygen nitrogen, and sulfur elements.
Conclusion
In this study, elemental compositions and molecular characteristics of >7300 WSOC compounds were investigated. Bioconcentration potentials of both positively and negatively charged compounds in the ESI source were found by estimating the distribution ratios between PM2.5 water extracts and stir-bar PDMS coating phases. The results from the MS/MS fragmentation analysis could be complementary for the assessment of contributions from diverse chemical structures to physical-chemical property such
Acknowledgements
We thank the National Natural Science Foundation of China (91843301, 21622705, 91743101, 21577151, and 21461142001) and the Youth Innovation Promotion Association CAS projects for joint financial support.
References (37)
- et al.
Differences in DOM of rewetted and natural peatlands – results from high-field FT-ICR-MS and bulk optical parameters
Sci. Total Environ.
(2017) - et al.
Transformation of dissolved organic matter during advanced coal liquefaction wastewater treatment and analysis of its molecular characteristics
Sci. Total Environ.
(2019) - et al.
O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-of-flight aerosol mass spectrometry
Environ. Sci. Technol.
(2008) - et al.
Oligomers, organosulfates, and nitrooxy organosulfates in rainwater identified by ultra-high resolution electrospray ionization FT-ICR mass spectrometry
Atmos. Chem. Phys.
(2009) - et al.
Water-soluble SOA from alkene ozonolysis: composition and droplet activation kinetics inferences from analysis of CCN activity
Atmos. Chem. Phys.
(2010) - et al.
Molecular characterization of cloud water samples collected at the Puy de Dôme (France) by Fourier transform ion cyclotron resonance mass spectrometry
Environ. Sci. Technol.
(2018) - et al.
Molecular characterization of organosulfur compounds in biodiesel and diesel fuel secondary organic aerosol
Environ. Sci. Technol.
(2017) - et al.
Assessment of PDMS-water partition coefficients: implications for passive environmental sampling of hydrophobic organic compounds
Environ. Sci. Technol.
(2010) - et al.
Cloud albedo enhancement by surface-active organic solutes in growing droplets
Nature.
(1999) - et al.
Probing and comparing the photobromination and photoiodination of dissolved organic matter by using ultra-high-resolution mass spectrometry
Environ. Sci. Technol.
(2017)
High secondary aerosol contribution to particulate pollution during haze events in China
Nature
Hygroscopic behavior of multicomponent organic aerosols and their internal mixtures with ammonium sulfate
Atmos. Chem. Phys.
Chemodiversity of dissolved organic matter in lakes driven by climate and hydrology
Nat. Commun.
Development of a liquid chromatographic method based on ultraviolet-visible and electrospray ionization mass spectrometric detection for the identification of nitrocatechols and related tracers in biomass burning atmospheric organic aerosol
Rapid Commun. Mass Spectrom.
Oxygenated and water-soluble organic aerosols in Tokyo
J. Geophys. Res. Atmos.
Molecular composition of boreal forest aerosol from Hyytiälä, Finland, using ultrahigh resolution mass spectrometry
Environ. Sci. Technol.
Selective chlorination of natural organic matter: identification of previously unknown disinfection byproducts
Environ. Sci. Technol.
Fragmentation analysis of water-soluble atmospheric organic matter using ultrahigh-resolution FT-ICR mass spectrometry
Environ. Sci. Technol.
Cited by (23)
Molecular characterization of humic-like substances (HULIS) in atmospheric particles (PM<inf>2.5</inf>) in offshore Eastern China Sea (OECS) using solid-phase extraction coupled with ESI FT-ICR MS
2023, Atmospheric EnvironmentCitation Excerpt :Fig. 4a and S8 present the Van Krevelen diagrams of the HULIS distributions in the three samples. The molecular formulas were classified into seven groups, including lignin-like species, protein/amino sugars, condensed aromatics, tannin-like species, carbohydrate-like species, unsaturated hydrocarbons, and lipid-like species according to a previous study (Ning et al., 2019; Feng et al., 2016; Wu et al., 2019). The classification rules for the formulas are shown in Table S8.
Dwindling aromatic compounds in fine aerosols from chunk coal to honeycomb briquette combustion
2022, Science of the Total EnvironmentCitation Excerpt :DBE and DBE/C ratios are usually used to characterize the unsaturation degree (Koch and Dittmar, 2006). It can be seen that a considerable higher DBE and DBE/C values are found in unique S-containing compounds of chunk coal, 89% of which are DBE ≥ 7, higher than ambient PM2.5 (DBE = 1–7) (Lin et al., 2012b; Tang et al., 2020; Tao et al., 2014; Wu et al., 2019). The unique molecules with distinguishing features of high unsaturation and high aromatic index indicated that the aromatic molecules are a major component in S-containing components of chunk coal derived PM2.5.