16 Jan 2023
16 Jan 2023
Status: this preprint is currently under review for the journal ACP.

The Important Contribution of Secondary Formation and Biomass Burning to Oxidized Organic Nitrogen (OON) in a Polluted Urban Area: Insights from In Situ FIGAERO-CIMS Measurements

Yiyu Cai1,2,3,4,5,, Chenshuo Ye6,, Wei Chen1,2,3,4,5, Weiwei Hu1,2,3,4, Wei Song1,2,3,4, Yuwen Peng7,8, Shan Huang7,8, Jipeng Qi7,8, Sihang Wang7,8, Chaomin Wang7,8, Caihong Wu7,8, Zelong Wang7,8, Baolin Wang9, Xiaofeng Huang10, Lingyan He10, Sasho Gligorovski1,2,3,4, Bin Yuan7,8, Min Shao7,8, and Xinming Wang1,2,3,4 Yiyu Cai et al.
  • 1State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640. China
  • 2CAS Center for Excellence in Deep Earth Science, Guangzhou, 510640, China
  • 3Guangdong-Hong Kong-Macao, Joint Laboratory for Environmental Pollution and Control, Guangzhou Institute of Geochemistry, Chinese Academy of Science, Guangzhou 510640, China
  • 4Guangdong Provincial Key Laboratory of Environmental Protection and Resources Utilization, Chinese Academy of Science, Guangzhou 510640, China
  • 5University of Chinese Academy of Sciences, Beijing 100049, China
  • 6Guangdong Provincial Academy of Environmental Science, Guangzhou, 510640, China
  • 7Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China
  • 8Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Guangzhou 511443, China
  • 9School of Environmental Science and Engineering, Qilu University of Technology, Jinan 250353, China
  • 10Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen, 518055, China
  • These authors contributed equally to this work.

Abstract. To investigate the sources and formation mechanism of oxidized organic nitrogen (OON), field measurements of OON were conducted using an iodide-adduct chemical ionization mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-CIMS) during fall of 2018 in the megacity of Guangzhou, China. Using levoglucosan as tracer of biomass burning emissions, the results show that biomass burning (49 %) and secondary formation (51 %) accounted for comparable fractions to the total particle-phase OON (pOON), while 24 % and 76 % to the gas-phase OON (gOON), respectively, signifying the important contribution of biomass burning to pOON and secondary formation to gOON in this urban area. Calculations of production rates of gas-phase organic nitrates (gON) indicated that hydroxyl radical (42 %) and nitrate radical (NO3) (49 %) oxidation pathways potentially dominated the secondary formation of gON. High concentration of NO3 radical during the afternoon daytime was observed, demonstrating that the daytime NO3 oxidation might be more important than the previous recognition. Monoterpenes, found to be major precursor of secondary gON, were mainly from anthropogenic emissions in this urban area. The ratio of secondary pOON to Ox ([Ox] = [O3] + [NO2]) increased as a function of relative humidity and aerosol surface area, indicating that heterogeneous reaction might be an important formation pathway for secondary pOON. Finally, the highly oxidized gOON and pOON with 6 to 11 oxygen atoms were observed, highlighting the complex secondary reaction processes of OON in the ambient air. Overall, our results can improve the understanding of the sources and dynamic variation of OON in urban atmosphere.

Yiyu Cai et al.

Status: open (until 27 Feb 2023)

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Yiyu Cai et al.


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Short summary
We studied the variability and molecular composition of ambient oxidized organic nitrogen (OON) in both gas and particle phases using a state-of-the-art online mass spectrometer in urban air. Biomass burning and secondary formation were found to be the two major sources for OONs. Daytime nitrate radical chemistry for OON formation was important than previous thought. Our results improved the understanding of the sources and molecular composition of OON in the polluted urban atmosphere.