10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Fast Heterogeneous N2O5 Uptake and ClNO2 Production in Summer in Urban Beijing, China
WEI ZHOU, Jian Zhao, Bin Ouyang, Asan Bacak, Conghui Xie, Qingqing Wang, Junfeng Wang, Yuying Wang, Wei Du, Weiqi Xu, Archit Mehra, Stephen Worrall, Xinlei Ge, Penglin Ye, James Lee, Hugh Coe, Roderic Jones, Pingqing Fu, Zifa Wang, Douglas Worsnop, Yele Sun, Institute of Atmospheric Physics
Abstract Number: 652 Working Group: Aerosol Chemistry
Abstract The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) has a significant impact on nocturnal particulate nitrate formation and photochemistry on the secondary day through the photolysis of nitryl chloride (ClNO2), yet their roles and processes in the highly polluted areas remain less understood. Here we present the measurements of gas-phase N2O5 and ClNO2 by a high-resolution time-of-flight chemical ionization mass spectrometer during the Air Pollution and Human Health (APHH) campaign to investigate the nocturnal chemistry in summer in urban Beijing, China. N2O5 and ClNO2 show large day-to-day variations that are closely related to their precursors (i.e., O3 and NOx). High reactivity of N2O5 with τ(N2O5)-1 ranging from 0.20×10-2 to 1.46×10-2 s-1 suggests active nocturnal chemistry and a large nocturnal nitrate formation potential via N2O5 heterogeneous uptake. We also observed high ClNO2/N2O5 ratios, likely due to the correspondingly high ClNO2 production rate under sufficient chloride in Beijing. The N2O5 uptake coefficients estimated from the product formation rates of ClNO2 and particulate nitrate are in the range of 0.017-0.190, corresponding to the direct N2O5 loss rates of 0.00044-0.0034 s-1. Further analysis indicate that the fast N2O5 loss in the nocturnal boundary layer in urban Beijing is mainly attributed to the indirect NO3 loss pathway, for example, through the reactions with volatile organic compounds and NO, while the contribution of heterogeneous uptake of N2O5 is small (7-33%). We also observed high ClNO2 yields ranging from 0.10 to 0.35 which might have important implications for air quality by affecting the nitrate and ozone formation.