An in situ flow tube system for direct measurement of N 2O 5 heterogeneous uptake coefficients in polluted environments

Wang, Weihao; Wang, Zhe; Yu, Chuan; Xia, Men; Peng, Xiang; Zhou, Yan; Yue, Dingli; Ou, Yubo; Wang, Tao

The heterogeneous reactivity of dinitrogen pentoxide (inline-formulaN2O5) on ambient aerosols plays a key role in the atmospheric fate of inline-formulaNOx and formation of secondary pollutants. To better understand the reactive uptake of inline-formulaN2O5 on complex ambient aerosols, an in situ experimental approach to direct measurement of inline-formulaN2O5 uptake coefficient (inline-formulaγinline-formulaN2O5) was developed for application in environments with high, variable ambient precursors. The method utilizes an aerosol flow tube reactor coupled with an iterative chemical box model to derive inline-formulaγinline-formulaN2O5 from the depletion of synthetically generated inline-formulaN2O5 when mixed with ambient aerosols. Laboratory tests and model simulations were performed to characterize the system and the factors affecting inline-formulaγinline-formulaN2O5, including mean residence time, wall loss variability with relative humidity (RH), and inline-formulaN2O5 formation and titration with high levels of NO, inline-formulaNOx, and inline-formulaO3. The overall uncertainty was estimated to be 37 %–40 % at inline-formulaγinline-formulaN2O5 of 0.03 for RH varying from 20 % to 70 %. The results indicate that this flow tube coupled with the iterative model method could be buffered to NO concentrations below 8 ppbv and against air mass fluctuations switching between aerosol and non-aerosol modes. The system was then deployed in the field to test its applicability under conditions of high ambient inline-formulaNO2 and inline-formulaO3 and fresh NO emission. The results demonstrate that the iterative model improved the accuracy of inline-formulaγinline-formulaN2O5 calculations in polluted environments and thus support the further field deployment of the system to study the impacts of heterogeneous inline-formulaN2O5 reactivity on photochemistry and aerosol formation.

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Wang, Weihao / Wang, Zhe / Yu, Chuan / et al: An in situ flow tube system for direct measurement of N2O5 heterogeneous uptake coefficients in polluted environments. 2018. Copernicus Publications.

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