16 Jan 2023
 | 16 Jan 2023
Status: a revised version of 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 Cai, Chenshuo Ye, Wei Chen, Weiwei Hu, Wei Song, Yuwen Peng, Shan Huang, Jipeng Qi, Sihang Wang, Chaomin Wang, Caihong Wu, Zelong Wang, Baolin Wang, Xiaofeng Huang, Lingyan He, Sasho Gligorovski, Bin Yuan, Min Shao, and Xinming Wang

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: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2023-8', Anonymous Referee #1, 26 Feb 2023
    • AC1: 'Reply on RC1', Weiwei Hu, 30 May 2023
  • RC2: 'Comment on acp-2023-8', Anonymous Referee #2, 07 Mar 2023
    • AC2: 'Reply on RC2', Weiwei Hu, 30 May 2023

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.