Preprints
https://doi.org/10.5194/acp-2021-1021
https://doi.org/10.5194/acp-2021-1021

  04 Jan 2022

04 Jan 2022

Review status: this preprint is currently under review for the journal ACP.

OH and HO2 radicals chemistry at a suburban site during the EXPLORE-YRD campaign in 2018

Xuefei Ma1, Zhaofeng Tan2, Keding Lu1, Xinping Yang1, Xiaorui Chen1, Haichao Wang1,3, Shiyi Chen1, Xin Fang1, Shule Li1, Xin Li1, Jingwei Liu1, Ying Liu1, Shengrong Lou4, Wanyi Qiu1, Hongli Wang4, Limin Zeng1, and Yuanhang Zhang1,5,6 Xuefei Ma et al.
  • 1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing, China
  • 2Institute of Energy and Climate Research, IEK-8: Troposphere, Forschungszentrum Juelich GmbH, Juelich, Germany
  • 3School of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China
  • 4State Environmental Protection Key Laboratory of Formation and Prevention of the Urban Air Complex, Shanghai Academy of Environmental Sciences, Shanghai, China
  • 5Beijing Innovation Center for Engineering Sciences and Advanced Technology, Peking University, Beijing, China
  • 6CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Science, Xiamen, China

Abstract. The first OH and HO2 radical observation in Yangtze River Delta, one of the four major urban agglomerations in China, was carried out at a suburban site Taizhou in summer 2018 from May to June, aiming to elucidate the atmospheric oxidation capacity in this region. The maximum diurnal averaged OH and HO2 concentrations were 1.0 × 107 cm−3 and 1.1 × 109 cm−3, respectively, which were the second highest HOx (sum of OH and HO2) radical concentrations observed in China. HONO photolysis was the dominant radical primary source, accounting for 42 % of the total radical initiation rate. Other contributions were from carbonyl photolysis (including HCHO, 24 %), O3 photolysis (17 %), alkenes ozonolysis (14 %), and NO3 oxidation (3 %). A chemical box model based on RACM2-LIM1 mechanism could generally reproduce the observed HOx radicals, but systematic discrepancy remained in the afternoon for OH radical, when NO mixing ratio was less than 0.3 ppb. Additional recycling mechanism equivalent to 100 ppt NO was capable to fill the gap. The sum of monoterpenes was on average up to 0.4 ppb during daytime, which was allocated all to α-pinene in the base model. Sensitivity test without monoterpene input showed the modelled OH and HO2 concentrations would increase by 7 % and 4 %, respectively, but modelled RO2 concentration would significantly decrease by 23 %, indicating that monoterpene was an important precursor of RO2 radicals in this study. Consequently, the daily integrated net ozone production would reduce by 6.3 ppb if without monoterpene input, proving the significant role of monoterpene on the photochemical O3 production in this study. Besides, the generally good agreement between observed and modelled HOx concentrations suggested no significant HO2 heterogeneous uptake process during this campaign. Incorporation of HO2 heterogeneous uptake process would worsen the agreement between HOx radical observation and simulation, and the discrepancy would be beyond the measurement-model combined uncertainties using an effective uptake coefficient of 0.2. Finally, the ozone production efficiency (OPE) was only 1.7 in this study, a few folds lower than other studies in (sub)urban environments. The low OPE indicated slow radical propagation rate and short chain length. As a consequence, ozone formation was suppressed by the low NO concentration in this study.

Xuefei Ma et al.

Status: open (until 21 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on acp-2021-1021', Christa Fittschen, 10 Jan 2022 reply
    • AC1: 'Reply on CC1', Keding Lu, 15 Jan 2022 reply

Xuefei Ma et al.

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Short summary
This paper presents the first OH and HO2 radicals observation made in Yangtze River Delta in China and strong oxidation capacity is discovered based on direct measurements. The impacts of new OH regeneration mechanism, monoterpene oxidation and HO2 uptake process are examined and discussed. The sources and the factors to sustain such strong oxidation is the key to understand the ozone pollutions formed in this area.
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