Articles | Volume 17, issue 1
Atmos. Chem. Phys., 17, 663–690, 2017

Special issue: Regional transport and transformation of air pollution in...

Atmos. Chem. Phys., 17, 663–690, 2017

Research article 13 Jan 2017

Research article | 13 Jan 2017

Radical chemistry at a rural site (Wangdu) in the North China Plain: observation and model calculations of OH, HO2 and RO2 radicals

Zhaofeng Tan1, Hendrik Fuchs2, Keding Lu1, Andreas Hofzumahaus2, Birger Bohn2, Sebastian Broch2, Huabin Dong1, Sebastian Gomm2,a, Rolf Häseler2, Lingyan He3, Frank Holland2, Xin Li1,2, Ying Liu1, Sihua Lu1, Franz Rohrer2, Min Shao1, Baolin Wang1, Ming Wang4, Yusheng Wu1, Limin Zeng1, Yinsong Zhang1, Andreas Wahner2, and Yuanhang Zhang1,5 Zhaofeng Tan 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 Jülich GmbH, Jülich, Germany
  • 3Key Laboratory for Urban Habitat Environmental Science and Technology, School of Environment and Energy, Peking University Shenzhen Graduate School, Shenzhen, China
  • 4School of Environmental Sciences and Engineering, Nanjing University of Information Science and Technology, Nanjing, China
  • 5CAS Center for Excellence in Regional Atmospheric Environment, Chinese Academy of Science, Xiamen, China
  • anow at: d-fine GmbH, Opernplatz 2, 60313 Frankfurt, Germany

Abstract. A comprehensive field campaign was carried out in summer 2014 in Wangdu, located in the North China Plain. A month of continuous OH, HO2 and RO2 measurements was achieved. Observations of radicals by the laser-induced fluorescence (LIF) technique revealed daily maximum concentrations between (5–15)  × 106 cm−3, (3–14)  × 108 cm−3 and (3–15)  × 108 cm−3 for OH, HO2 and RO2, respectively. Measured OH reactivities (inverse OH lifetime) were 10 to 20 s−1 during daytime. The chemical box model RACM 2, including the Leuven isoprene mechanism (LIM), was used to interpret the observed radical concentrations. As in previous field campaigns in China, modeled and measured OH concentrations agree for NO mixing ratios higher than 1 ppbv, but systematic discrepancies are observed in the afternoon for NO mixing ratios of less than 300 pptv (the model–measurement ratio is between 1.4 and 2 in this case). If additional OH recycling equivalent to 100 pptv NO is assumed, the model is capable of reproducing the observed OH, HO2 and RO2 concentrations for conditions of high volatile organic compound (VOC) and low NOx concentrations. For HO2, good agreement is found between modeled and observed concentrations during day and night. In the case of RO2, the agreement between model calculations and measurements is good in the late afternoon when NO concentrations are below 0.3 ppbv. A significant model underprediction of RO2 by a factor of 3 to 5 is found in the morning at NO concentrations higher than 1 ppbv, which can be explained by a missing RO2 source of 2 ppbv h−1. As a consequence, the model underpredicts the photochemical net ozone production by 20 ppbv per day, which is a significant portion of the daily integrated ozone production (110 ppbv) derived from the measured HO2 and RO2. The additional RO2 production from the photolysis of ClNO2 and missing reactivity can explain about 10 % and 20 % of the discrepancy, respectively. The underprediction of the photochemical ozone production at high NOx found in this study is consistent with the results from other field campaigns in urban environments, which underlines the need for better understanding of the peroxy radical chemistry for high NOx conditions.

Short summary
In this study, we performed accurate OH measurements as well as selective HO2 and RO2 measurements at a rural site in North China Plain with state-of-the-art instruments newly developed. We confirmed the previous discovery on the enhancement of the OH in low NOx with which little O3 production was associated, and we found a missing RO2 source in high NOx which promoted higher O3 production. Our results are of vital importance for ozone abatement strategies currently under discussion for China.
Final-revised paper