Field Detection of Highly Oxygenated Organic Molecules in Shanghai by Chemical Ionization–Orbitrap

Abstract

Secondary organic aerosol, formed through atmospheric oxidation processes, plays an important role in affecting climate and human health. In this study, we conducted a comprehensive campaign in the megacity of Shanghai during the 2019 International Import Expo (EXPO), with the first deployment of a chemical ionization Orbitrap mass spectrometer for ambient measurements. With the ultrahigh mass resolving power of the Orbitrap mass analyzer (up to 140,000 Th/Th) and capability in dealing with massive spectral data sets by positive matrix factorization, we were able to identify the major gas-phase oxidation processes leading to the formation of oxygenated organic molecules (OOM) in Shanghai. Nine main factors from three independent sub-range analysis were identified. More than 90% of OOM are of anthropogenic origin and >60% are nitrogen-containing molecules, mainly dominated by the RO 2 + NO and/or NO 3 chemistry. The emission control during the EXPO showed that even though the restriction was effectual in significantly lowering the primary pollutants (20−70% decrease), the secondary oxidation products responded less effectively (14% decrease), or even increased (50 to >200%) due to the enhancement of ozone and the lowered condensation sink, indicating the importance of a stricter multi-pollutant coordinated strategy in primary and secondary pollution mitigation.

Supplementary material to "Unambiguous identification of N-containing oxygenated organic molecules using CI-Orbitrap in an eastern Chinese megacity"

“…Since this method does not require a priori information about the factors, it is an ideal technique for extracting information from ambient measurements where the detailed chemistry, sources, and atmospheric processes are complex. PMF has already been used in source apportionment analysis of OOMs in previous studies (Yan et al, 2016;Zhang et al, 2019Zhang et al, , 2022. In this study, PMF was performed using the Igor-based interface Source Finder (SoFi, v6.3), run by the multilinear engine (ME-2) (Canonaco et al, 2013).…”

“…In this study, PMF was performed using the Igor-based interface Source Finder (SoFi, v6.3), run by the multilinear engine (ME-2) (Canonaco et al, 2013). The data for the PMF model inputs were prepared according to the method described in previous studies (Zhang et al, 2022). Note that the orbitrap analyzer does not measure signal below a certain threshold resulting in incomplete time series for species present at low concentration level.…”

“…Note that the orbitrap analyzer does not measure signal below a certain threshold resulting in incomplete time series for species present at low concentration level. Therefore, the species characterized by incomplete time series with more than 90% missing data and the spectra with more than 80% missing were removed (Zhang et al, 2022). PMF analysis in this work was performed in 2-10 factors as shown in Figure S3.…”

Unambiguous identification of N-containing oxygenated organic molecules using CI-Orbitrap in an eastern Chinese megacity

“…Secondary organic aerosol (SOA) accounts for a significant fraction of particulate matters (Donahue et al, 2009;Hallquist et al, 2009;Jimenez et al, 2009). Volatile organic compounds (VOCs) and their oxidation products, i.e., OVOCs, are important precursors of SOA in the atmosphere (Atkinson and Arey, 2003;Bianchi et al, 2019;Nie et al, 2022). The N-containing oxygenated organic molecules (OOMs) have been identified as the important products upon VOC oxidation.…”

“…The N-containing OOM molecules can be classified into 1N-OOMs, 2N-OOMs, and 3N-OOMs, according to the number of nitrate functional group in the molecule. The chemical composition of Ncontaining OOMs is determined by their precursors, formation pathways and NOx level in the atmosphere (Bianchi et al, 2019;Nie et al, 2022;Pye et al, 2019;Riva, 2016;Yan et al, 2016).…”