Unambiguous identification of N-containing oxygenated organic molecules using a chemical-ionization Orbitrap (CI-Orbitrap) in an eastern Chinese megacity

Abstract

Abstract. Oxygenated organic molecules (OOMs) are dominated by the N-containing species in polluted urban environments. As N-containing OOMs, especially those with more than one nitrogen atom, prevail in the high m/z (mass-to-charge) range (m/z> 350 Th), unambiguous identification of N-containing OOMs is highly desirable for understanding of their formation processes, precursors and influencing factors. To achieve this, we applied an ultra-high-resolution chemical-ionization Orbitrap (CI-Orbitrap) in a field campaign and found that OOMs contain one (1N-OOMs), two (2N-OOMs) and three (3N-OOMs) nitrogen atoms comprised 50 %, 26 % and 4 %, respectively, of total OOMs. More interestingly, the fraction of 2N-OOMs increased with the increase in carbon number (nC) and was dominated by the ones derived from aliphatic precursors (2N-OOMAli, 64.2 %), indicating the importance of multistep oxidation. Plausible precursors of 2N-OOMs were aliphatics (2N-OOMAli, 64.2 %), aromatics (2N-OOMAro, 16 %) and monoterpenes (2N-OOMMT, 15.4 %). The absolute concentrations of 2N-OOMs were greatly affected by the pollution level for most cases. The 2N-OOMAli was the most abundant 2N-OOM, and its fraction even increased on the polluted day with an enhanced proportion of the ones with nC >10. While 2N-OOMAli and 2N-OOMAro were dominated by daytime photochemical production, nighttime NO3-initiated oxidation played a comparable role to the daytime photochemistry in the formation of 2N-OOMMT. The 2N-OOMAro species were of the highest oxygenation level, followed by 2N-OOMMT and 2N-OOMAli, which were affected by photochemistry and NOx concentrations. These results highlight the significant formation of 2N-OOMs and the influencing factors on their formation in polluted urban environments, where various volatile organic compound (VOC) precursors and atmospheric oxidants are present.

Aqueous-Phase Reactions of Anthropogenic Emissions Lead to the High Chemodiversity of Atmospheric Nitrogen-Containing Compounds during the Haze Event

“…The workflow, based on current knowledge of VOC oxidation using the measured molecular composition, enabled us to assign these O x N compounds to their likely VOC precursor classes, corresponding to aliphatic-O x N, aromatic-O x N, isoprene-O x N, and monoterpene-O x N (Figure a). Overall, the main categories are remarkably similar throughout the haze event, with the O x N compounds predominantly originating from anthropogenic sources (89–96%), which is in agreement with several recent works conducted in other Chinese places, such as Beijing, Shanghai. ,, …”

“…Overall, the main categories are remarkably similar throughout the haze event, with the OxN compounds predominantly originating from anthropogenic sources (89−96%), which is in agreement with several recent works conducted in other Chinese places, such as Beijing, Shanghai. 15,27,68 As shown in Figure 2a, the aromatic-OxN accounted for 88 ± 2.5% of the total oxidized-N abundance, which was a comparable previous observation result obtained in the urban atmosphere of Northern China. 25,69 Although the oxidation pathways and molecular composition of some aromatic VOCderived products have been reported in previous studies, 70,71 the known aromatic-CHON species were relatively scarce and could only account for 0.2−0.6‰ of total OM mass reported by a recent field observation.…”

First Online Observation of Aerosol Total Organic Nitrogen at an Urban Site: Insights Into the Emission Sources and Formation Pathways of Nitrogenous Organic Aerosols

“…For instance, organic nitrates, formed as a product of reactions between organic peroxy radicals and nitric oxide, as well as alkenes with the nitrate radical, represent a notable fraction of OA mass at multiple sites, according to aerosol mass spectrometer (AMS) measurements (Kiendler‐Scharr et al., 2016; Xu et al., 2021). Recent studies have suggested that nitrogenous molecules dominate the condensing anthropogenic organic vapors over China's megacities, indicating the potentially abundant contribution of OA N to SOA mass in the urban atmosphere (Lu et al., 2023; Nie et al., 2022). Third, nitroaromatic compounds, derived from primary emissions such as biomass burning and secondary formation between phenols and NO x , are critical light‐absorbing aerosols (Lin et al., 2017; Palm et al., 2020).…”