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

• Published in: Atmospheric chemistry and physics 2018-07, Vol.18 (13), p.9705
• Main Authors: 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
• Format: Article
• Language: English
• Subjects: Air pollution; Analysis; Control; Environmental aspects; Nitrogen compounds; Urban ecology
• ISSN: 1680-7316; 1680-7324

Nocturnal reactive nitrogen compounds play an important role in regional air pollution. Here we present the measurements of dinitrogen pentoxide (N.sub.2 O.sub.5) associated with nitryl chloride (ClNO.sub.2) and particulate nitrate (pNO.sub.3 .sup.-) at a suburban site of Beijing in the summer of 2016. High levels of N.sub.2 O.sub.5 and ClNO.sub.2 were observed in the outflow of the urban Beijing air masses, with 1 min average maxima of 937 and 2900 pptv, respectively. The N.sub.2 O.sub.5 uptake coefficients, γ, and ClNO.sub.2 yield, f, were experimentally determined from the observed parameters. The N.sub.2 O.sub.5 uptake coefficient ranged from 0.012 to 0.055, with an average of 0.034 ± 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 N.sub.2 O.sub.5 heterogeneous processes in Beijing. The ClNO.sub.2 yield exhibited high variability, with a range of 0.50 to unity and an average of 0.73 ± 0.25. The concentration of the nitrate radical (NO.sub.3) was calculated assuming that the thermal equilibrium between NO.sub.3 and N.sub.2 O.sub.5 was maintained. In NO.sub.x -rich air masses, the oxidation of nocturnal biogenic volatile organic compounds (BVOCs) was dominated by NO.sub.3 rather than O.sub.3 . The production rate of organic nitrate (ON) via NO.sub.3 + BVOCs was significant, with an average of 0.10 ± 0.07 ppbv h.sup.-1 . We highlight the importance of NO.sub.3 oxidation of VOCs in the formation of ON and subsequent secondary organic aerosols in summer in Beijing.