21 Feb 2022
21 Feb 2022
Status: a revised version of this preprint is currently under review for the journal ACP.

Radical chemistry in the Pearl River Delta: observations and modeling of OH and HO2 radicals in Shenzhen 2018

Xinping Yang1,2, Keding Lu1,2, Xuefei Ma1,2, Yue Gao1,2, Zhaofeng Tan3, Haichao Wang4, Xiaorui Chen1,2, Xin Li1,2, Xiaofeng Huang5, Lingyan He5, Mengxue Tang5, Bo Zhu5, Shiyi Chen1,2, Huabin Dong1,2, Limin Zeng1,2, and Yuanhang Zhang1,2 Xinping Yang et al.
  • 1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China
  • 2State Environmental Protection Key Laboratory of Atmospheric Ozone Pollution Control, Peking University, Beijing, China
  • 3Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Juelich GmbH, Juelich, Germany
  • 4School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai, China
  • 5Laboratory of Atmospheric Observation Supersite, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen, China

Abstract. The ambient OH and HO2 concentrations were measured continuously during the STORM (STudy of the Ozone foRmation Mechanism) campaign at the Shenzhen site, located in Pearl River Delta in China, in autumn 2018. The diurnal maximum OH and HO2 concentrations, measured by laser-induced fluorescence, were 4.5 × 106 cm−3 and 4.5 × 108 cm−3, respectively. The state-of-the-art radical chemical mechanism underestimated the observed OH concentration, similar to the other warm-season campaigns in China. The OH underestimation was attributed to the missing OH sources, which can be explained by the X mechanism. Good agreement between the observed and modeled OH concentrations was achieved when an additional numerical X equivalent to 0.1 ppb NO concentrations was added to the base model. The modeled HO2 could reproduce the observed HO2, indicating the HO2 heterogeneous uptake on HO2 chemistry was negligible. Photolysis reactions dominated the ROx primary production rate. The HONO, O3, HCHO, and carbonyls photolysis accounted for 29 %, 16 %, 16 %, and 11 % during the daytime, respectively. The ROx termination rate was dominated by the reaction of OH + NO2 in the morning, and thereafter the radical self-combination gradually became the major sink of ROx in the afternoon. The atmospheric oxidation capacity was evaluated, with a peak of 0.75 × 108 molecules cm−3 s−1 around noontime. A strong positive correlation between O3 formation rate and atmospheric oxidation capacity was achieved, illustrating the atmospheric oxidation capacity was the potential tracer to indicate the secondary pollution.

Xinping Yang 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-2022-113', Anonymous Referee #1, 14 Mar 2022
    • AC1: 'Reply on RC1', Keding Lu, 26 May 2022
  • RC2: 'Comment on acp-2022-113', Anonymous Referee #2, 02 Apr 2022
    • AC2: 'Reply on RC2', Keding Lu, 26 May 2022
  • RC3: 'Comment on acp-2022-113', Anonymous Referee #3, 02 Apr 2022
    • AC3: 'Reply on RC3', Keding Lu, 26 May 2022

Xinping Yang et al.

Xinping Yang et al.


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Short summary
The STORM campaign was carried out at Shenzhen site in autumn 2018. The maximum diurnal OH and HO2 concentrations were 4.5 × 106 cm−3 and 4.5 × 108 cm−3, respectively. The unclassical OH recycling was identified again. AOC exhibited well-defined diurnal patterns, and OH was the dominant oxidant as expected. The strong positive correlation between F(O3) and AOC makes the quantification of F(O3) achieved, indicating AOC is the core driving force for the generation of secondary pollutants.