Heterogeneous N₂O₅ reactions on atmospheric aerosols at four Chinese sites: improving model representation of uptake parameters

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 ( N₂O₅ ) and representation in air quality models are challenging, especially in the polluted environment. With an in situ aerosol flow-tube system, the N₂O₅ was directly measured on ambient aerosols at two rural sites in northern and southern China. The results were analyzed together with the N₂O₅ 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 N₂O₅ was generally promoted by the aerosol water content and suppressed by particle nitrate. Significant discrepancies were found between the measured N₂O₅ 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 N₂O₅ . Incorporating this new parameterization into a regional air quality model (WRFCMAQ) has improved the simulation of N₂O₅, nitrogen oxides, and secondary nitrate in the polluted regions of China.