Molecular Characterization of Water-Soluble Aerosol Particle Extracts by Ultrahigh-Resolution Mass Spectrometry: Observation of Industrial Emissions and an Atmospherically Aged Wildfire Plume at Lake Baikal

Abstract

Air pollution over Lake Baikal originating from anthropogenic emissions as well as wildfire events and secondary organic aerosol (SOA) formation poses a threat to this world heritage ecosystem. During a ship expedition in 2018, ambient aerosol particles were sampled on filters at different locations of Lake Baikal and extracted to obtain the fraction of water-soluble organic aerosol (WSOA). Subsequent analysis by Fourier transform ion cyclotron resonance (FTICR) mass spectrometry with direct-infusion electrospray ionization (ESI) in both ionization modes provides insights into the molecular composition of polar and high-molecular-weight species in WSOA. Light absorption spectral dependence determined by absorption Ångstrom exponent (AAE) is correlated to summed compound class abundancies to identify light-absorbing compounds. Most detected species are heavily oxidized, associated with intense atmospheric aging, and contain significant amounts of nitrogen or sulfur, with the most abundant compound classes being CHO, CHON, and CHOS. Nitrogen-containing species are more frequently found in positive ESI and correlate well with AAE. Oxygen-to-nitrogen ratios (O/N) larger than 3 indicate organic nitrates, and also less oxidized nitrogen species can be linked to brown carbon (BrC). ESI in both ionization modes provides complementary molecular information with, on the one hand, more sensitive detection of high average carbon oxidation state (OSC) and low-volatility oxidized organic aerosol species in negative mode, and on the other hand, lower OSC (OSC < 0) species as well as oligomers and potential biomass burning organic aerosol in positive mode. Additionally, a great overlap of sum formulae was found at all sampling sites along the expedition route, regardless of the potential primary emission sources, indicating strong atmospheric aging and mixing, leading to a similar oxidized organic aerosol (OOA) from different primary sources.

Detection of Polycyclic Aromatic Hydrocarbons in High Organic Carbon Ultrafine Particle Extracts by Electrospray Ionization Ultrahigh-Resolution Mass Spectrometry

“…1,4 Electrospray ionization (ESI) is a frequently applied ionization technique for the analysis of liquid aerosol extracts, due to its softness and sensitive ionization of polar compounds (e.g., oxygen-containing functionalities), which are frequently found in aerosol samples. 5,6 Nonpolar compounds like PAHs are usually not observed under standard ESI conditions, due to their poor ionization efficiency and ionization suppression from more readily ionized polar molecules. 7 For nonpolar compounds, atmospheric pressure photoionization (APPI) or laser desorption ionization (UV-LDI) have recently been established as comprehensive ionization techniques, but with the drawback of a lower sensitivity for highly oxygenated compounds.…”

Molecular Characterization of the Product Compounds Formed Upon Heterogeneous Chemistry of Ozone With Riverine Surface Microlayer

“…Figure 6c shows that the majority of the CHON product compounds are rich in oxygen atoms exhibiting O/N ratio higher than 3 and increasing up to O/N = 12. Namely 74.3% of the total common CHON product compounds emerged from the heterogeneous ozone reactions with HP‐SML and PZ‐SML, have O/N ≥ 3, suggesting the formation of highly oxygenated compounds (Schneider, Czech, et al., 2022). These compounds contain nitrogen (‐NO 2 ), nitrate (‐NO 3 ), and nitrooxy (‐ONO 2 ) functional groups implying that these product compounds are most likely nitrooxy (−ONO 2 ) amines and imines or organonitrates (Wang et al., 2017; Wang et al., 2021).…”

“…The CHON product compounds with O/N ≥ 4 contain oxygenated nitrooxy group which are most probably associated with nitrooxy‐aromatic compounds such as nitrophenols and nitric acid esters (Wang et al., 2018). A large fraction of common CHON compounds (59%) have O/N in the range between 5 and 12 indicating the formation of peroxyacetyl nitrates (PANs) compounds such as peroxypropionyl nitrate, peroxybenzoyl nitrate, peroxyacryloyl nitrate, peroxyisobutyryl nitrate, and peroxymethacryloyl nitrate among which peroxyacetic nitric anhydride is the most abundant in the atmosphere (Schneider, Czech, et al., 2022). The PANs compounds represent the main reservoir for nitrogen oxide radicals (NOx = NO + NO 2 ) enabling the transport and release of NOx to the remote atmosphere with major implications for the global distributions of the principal atmospheric oxidants, O 3 and OH (Fischer et al., 2014).…”

PyC2MC: an open-source software solution for visualization and treatment of high-resolution mass spectrometry data

“…The .csv files, if not exported from the already compatible vendor software, such as Bruker DataAnalysis or Thermo Fisher Scientific Xcalibur, should only be used for importing attributed data with the hereafter structure: m/z ratio, absolute intensity, attribution error (in ppm), molecular formula. Concerning Excel sheets, they are respectively the output format containing attributed peak lists of PetroOrg [14] and a MATLAB user-interface suite called CERES [42] (MATLAB R2022a) used in previous research 4,31,32 . All other variables and parameters are calculated further on.…”

“…Classical fingerprint visualization functions will be illustrated with the help of recently published data obtained from analyzing plastic pyrolysis oil by direct infusion ESI(+) and APCI(+) FTICR MS 33 . The representation of 7 parameters more common to environmental sciences will be performed using a dataset obtained with water-soluble ambient aerosol particles from emissions affected by anthropogenic industrial and wildfire sources analyzed by ESI(+/−) FTICR MS 31 . Specific use of the Kendrick mass defect plot will be shown using data gathered by the selective characterization of petroporphyrins in shipping fuels and their corresponding emission by electrontransfer MALDI FTICR MS 20 .…”