Articles | Volume 17, issue 1
Research article
13 Jan 2017
Research article |  | 13 Jan 2017

OH reactivity at a rural site (Wangdu) in the North China Plain: contributions from OH reactants and experimental OH budget

Hendrik Fuchs, Zhaofeng Tan, Keding Lu, Birger Bohn, Sebastian Broch, Steven S. Brown, Huabin Dong, Sebastian Gomm, Rolf Häseler, Lingyan He, Andreas Hofzumahaus, Frank Holland, Xin Li, Ying Liu, Sihua Lu, Kyung-Eun Min, Franz Rohrer, Min Shao, Baolin Wang, Ming Wang, Yusheng Wu, Limin Zeng, Yinson Zhang, Andreas Wahner, and Yuanhang Zhang

Abstract. In 2014, a large, comprehensive field campaign was conducted in the densely populated North China Plain. The measurement site was located in a botanic garden close to the small town Wangdu, without major industry but influenced by regional transportation of air pollution. The loss rate coefficient of atmospheric hydroxyl radicals (OH) was quantified by direct measurements of the OH reactivity. Values ranged between 10 and 20 s−1 for most of the daytime. Highest values were reached in the late night with maximum values of around 40 s−1. OH reactants mainly originated from anthropogenic activities as indicated (1) by a good correlation between measured OH reactivity and carbon monoxide (linear correlation coefficient R2 = 0.33) and (2) by a high contribution of nitrogen oxide species to the OH reactivity (up to 30 % in the morning). Total OH reactivity was measured by a laser flash photolysis–laser-induced fluorescence instrument (LP-LIF). Measured values can be explained well by measured trace gas concentrations including organic compounds, oxygenated organic compounds, CO and nitrogen oxides. Significant, unexplained OH reactivity was only observed during nights, when biomass burning of agricultural waste occurred on surrounding fields. OH reactivity measurements also allow investigating the chemical OH budget. During this campaign, the OH destruction rate calculated from measured OH reactivity and measured OH concentration was balanced by the sum of OH production from ozone and nitrous acid photolysis and OH regeneration from hydroperoxy radicals within the uncertainty of measurements. However, a tendency for higher OH destruction compared to OH production at lower concentrations of nitric oxide is also observed, consistent with previous findings in field campaigns in China.

Short summary
OH reactivity was measured during a 1-month long campaign at a rural site in the North China Plain in 2014. OH reactivity measurements are compared to calculations using OH reactant measurements. Good agreement is found indicating that all important OH reactants were measured. In addition, the chemical OH budget is analyzed. In contrast to previous campaigns in China in 2006, no significant imbalance between OH production and destruction is found.
Final-revised paper