Nontarget Screening Exhibits a Seasonal Cycle of PM_2.5 Organic Aerosol Composition in Beijing

Abstract

The molecular composition of atmospheric particulate matter (PM) in the urban environment is complex, and it remains a challenge to identify its sources and formation pathways. Here, we report the seasonal variation of the molecular composition of organic aerosols (OA), based on 172 PM 2.5 filter samples collected in Beijing, China, from February 2018 to March 2019. We applied a hierarchical cluster analysis (HCA) on a large nontargetscreening data set and found a strong seasonal difference in the OA chemical composition. Molecular fingerprints of the major compound clusters exhibit a unique molecular pattern in the Van Krevelen-space. We found that summer OA in Beijing features a higher degree of oxidation and a higher proportion of organosulfates (OSs) in comparison to OA during wintertime, which exhibits a high contribution from (nitro-)aromatic compounds. OSs appeared with a high intensity in summer-haze conditions, indicating the importance of anthropogenic enhancement of secondary OA in summer Beijing. Furthermore, we quantified the contribution of the four main compound clusters to total OA using surrogate standards. With this approach, we are able to explain a small fraction of the OA (∼11−14%) monitored by the Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM). However, we observe a strong correlation between the sum of the quantified clusters and OA measured by the ToF-ACSM, indicating that the identified clusters represent the major variability of OA seasonal cycles. This study highlights the potential of using nontarget screening in combination with HCA for gaining a better understanding of the molecular composition and the origin of OA in the urban environment.

Exploring new molecular universes: How non-target screening analysis can open new perspectives in ice-core science

“…Methods have been successfully applied to freshwater, aerosol, soil and sediment samples (e.g. Ma et al 2022). Generally, two approaches are followed: non-target screening (NtS) and suspect screening (SUS).…”

Mass spectrometry-based aerosolomics: a new approach to resolve sources, composition, and partitioning of secondary organic aerosol

“…However, it need to be considered that signal intensities are not directly quantitative to its concentration. It is well known, that the ionization efficiency of HESI varies greatly for several compounds as well as compound classes (Kenseth et al, 2020;Ma et al, 2022). Nevertheless, variation in the intensity of a single compound or class of compounds can be qualitatively interpreted as variation of its concentration.…”

“…In recent years, non-target analysis (NTA) of UHPLC-HRMS measurements has become a powerful tool that builds peak lists of all detected compounds in complex samples, and determines the molecular formula based on the exact mass and isotopic pattern. Furthermore, MS 2 -spectra can be compared to fragmentation libraries and enable database-assisted identification of compounds (Ditto et al, 2018;Ma et al, 2022;Pereira et al, 2021;Pleil et al, 2018). However, there are currently no established databases of atmospheric SOA tracers, which can be applied on measurements of ambient PM 2 .5 filter samples.…”

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“…In the past decade, non-targeted analysis methods based on ultra-high resolution mass spectrometry (UHRMS), such as Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and Orbitrap mass spectrometry, have been widely used for molecular characterization of soluble components in atmospheric aerosols from different sources (Song et al, 2022(Song et al, , 2019Bianco et al, 2018a;Ma et al, 2022;Zeng et al, 2020;Yue et al, 2022). Based on non-targeted analysis, our understanding of the molecular composition and chemical diversity of atmospheric organic aerosols has greatly improved (Tang et al, 2022;Li et al, 2023a;Jiang et al, 2021).…”