Abstract
Abstract. Heterogeneous reactivity of N2O5 on aerosols is a critical parameter in assessing NOx fate, nitrate production, and particulate chloride activation. Accurate measurement of its uptake coefficient (γN2O5) and representation in air quality models are challenging, especially in the polluted environment. With an in situ aerosol flow-tube system, the γN2O5 was directly measured on ambient aerosols at two rural sites in northern and southern China. The results were analyzed together with the γN2O5 derived from previous field studies in China to obtain a holistic picture of N2O5 uptake and the influencing factors under various climatic and chemical conditions. The field-derived or measured γN2O5 was generally promoted by the aerosol water content and suppressed by particle nitrate. Significant discrepancies were found between the measured γN2O5 and that estimated from laboratory-determined parameterizations. An observation-based empirical parameterization was derived in the present work, which better reproduced the mean value and variability of the observed γN2O5. Incorporating this new parameterization into a regional air quality model (WRF-CMAQ) has improved the simulation of N2O5, nitrogen oxides, and secondary nitrate in the polluted regions of China.
Highlights
Heterogeneous reaction of dinitrogen pentoxide (N2O5) on aerosol surfaces plays an important role in the nocturnal removal of nitrogen oxides (NOx), secondary nitrate formation, and chlorine activation through nitryl chloride (ClNO2) production on chloride-containing aerosols (Brown et al, 2006; Osthoff et al, 2008; Thornton et al, 2010; Wang et al, 2016)
The currently accepted mechanism of the heterogeneous reaction of N2O5 on aqueous aerosols starts with the mass accommodation of N2O5 on aerosol surface (Reaction R1), followed by reversible N2O5 hydrolysis to form nitrate and intermediate H2ONO+2 in the aqueous phase (Reaction R2)
Based on the measurements from five field campaigns at four sites across China with different atmospheric conditions, our study examined the factors influencing N2O5 uptake processes and derived an observation-based empirical parameterization of N2O5 uptake
Summary
Heterogeneous reaction of dinitrogen pentoxide (N2O5) on aerosol surfaces plays an important role in the nocturnal removal of nitrogen oxides (NOx), secondary nitrate formation, and chlorine activation through nitryl chloride (ClNO2) production on chloride-containing aerosols (Brown et al, 2006; Osthoff et al, 2008; Thornton et al, 2010; Wang et al, 2016). Representing this process in air quality models is necessary for the prediction and mitigation of ground-level ozone and particulate pollution. Yu et al.: Heterogeneous N2O5 reactions on atmospheric aerosols at four Chinese sites
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