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Volume 18, issue 19 | Copyright

Special issue: Multiphase chemistry of secondary aerosol formation under...

Atmos. Chem. Phys., 18, 14465-14476, 2018
https://doi.org/10.5194/acp-18-14465-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Oct 2018

Research article | 10 Oct 2018

Atmospheric Δ17O(NO3) reveals nocturnal chemistry dominates nitrate production in Beijing haze

Pengzhen He1, Zhouqing Xie1,2,3, Xiyuan Chi1, Xiawei Yu1, Shidong Fan1, Hui Kang1, Cheng Liu1,2,3, and Haicong Zhan1 Pengzhen He et al.
  • 1Anhui Province Key Laboratory of Polar Environment and Global Change, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
  • 2Center for Excellence in Urban Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian 361021, China
  • 3Key Lab of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei, Anhui 230031, China

Abstract. The rapid mass increase of atmospheric nitrate is a critical driving force for the occurrence of fine-particle pollution (referred to as haze hereafter) in Beijing. However, the exact mechanisms for this rapid increase of nitrate mass have not been well constrained from field observations. Here we present the first observations of the oxygen-17 excess of atmospheric nitrate (Δ17O(NO3)) collected in Beijing haze to reveal the relative importance of different nitrate formation pathways, and we also present the simultaneously observed δ15N(NO3). During our sampling period, 12h averaged mass concentrations of PM2.5 varied from 16 to 323µgm−3 with a mean of (141±88(1SD))µgm−3, with nitrate ranging from 0.3 to 106.7µgm−3. The observed Δ17O(NO3) ranged from 27.5‰ to 33.9‰ with a mean of (30.6±1.8)‰, while δ15N(NO3) ranged from −2.5‰ to 19.2‰ with a mean of (7.4±6.8)‰. Δ17O(NO3)-constrained calculations suggest nocturnal pathways (N2O5 + H2O∕Cl and NO3 + HC) dominated nitrate production during polluted days (PM2.5 ≥ 75µgm−3), with a mean possible fraction of 56–97%. Our results illustrate the potentiality of Δ17O in tracing nitrate formation pathways; future modeling work with the constraint of isotope data reported here may further improve our understanding of the nitrogen cycle during haze.

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We present the first observations of the oxygen-17 excess of atmospheric nitrate (Δ17O(NO3)) collected in Beijing haze to reveal the relative importance of different nitrate formation pathways. We found that nocturnal pathways (N2O5 + H2O/Cl and NO3 + HC) dominated nitrate production during polluted days (PM2.5 ≥ 75 μg m–3), with a mean possible fraction of 56–97 %.
We present the first observations of the oxygen-17 excess of atmospheric nitrate (Δ17O(NO3))...
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