Efficient N 2O 5 uptake and NO 3 oxidation in the outflow of urban Beijing

Wang, Haichao; Lu, Keding; Guo, Song; Wu, Zhijun; Shang, Dongjie; Tan, Zhaofeng; Wang, Yujue; Le Breton, Michael; Lou, Shengrong; Tang, Mingjin; Wu, Yusheng; Zhu, Wenfei; Zheng, Jing; Zeng, Limin; Hallquist, Mattias; Hu, Min; Zhang, Yuanhang

Nocturnal reactive nitrogen compounds play an important role in regional air pollution. Here we present the measurements of dinitrogen pentoxide (inline-formulaN2O5) associated with nitryl chloride (inline-formulaClNO2) and particulate nitrate (inline-formulapinline-formula M8inlinescrollmathml chem normal NO normal 3 - 25pt16ptsvg-formulamathimg8a872e45f44a0fc3c08e466e371cfb3a acp-18-9705-2018-ie00001.svg25pt16ptacp-18-9705-2018-ie00001.png ) at a suburban site of Beijing in the summer of 2016. High levels of inline-formulaN2O5 and inline-formulaClNO2 were observed in the outflow of the urban Beijing air masses, with 1 inline-formulamin average maxima of 937 and 2900 inline-formulapptv, respectively. The inline-formulaN2O5 uptake coefficients, inline-formulaγ, and inline-formulaClNO2 yield, inline-formulaf, were experimentally determined from the observed parameters. The inline-formulaN2O5 uptake coefficient ranged from 0.012 to 0.055, with an average of 0.034 inline-formula± 0.018, which is in the upper range of previous field studies reported in North America and Europe but is a moderate value in the North China Plain (NCP), which reflects efficient inline-formulaN2O5 heterogeneous processes in Beijing. The inline-formulaClNO2 yield exhibited high variability, with a range of 0.50 to unity and an average of 0.73 inline-formula± 0.25. The concentration of the nitrate radical (inline-formulaNO3) was calculated assuming that the thermal equilibrium between inline-formulaNO3 and inline-formulaN2O5 was maintained. In inline-formulaNOx-rich air masses, the oxidation of nocturnal biogenic volatile organic compounds (BVOCs) was dominated by inline-formulaNO3 rather than inline-formulaO3. The production rate of organic nitrate (ON) via inline-formulaNO3inline-formula+ BVOCs was significant, with an average of 0.10 inline-formula± 0.07 inline-formulappbv h−1. We highlight the importance of inline-formulaNO3 oxidation of VOCs in the formation of ON and subsequent secondary organic aerosols in summer in Beijing.

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Wang, Haichao / Lu, Keding / Guo, Song / et al: Efficient N2O5 uptake and NO3 oxidation in the outflow of urban Beijing. 2018. Copernicus Publications.

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