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 NO_x fate, nitrate production, and particulate chloride activation. Accurate measurement of its uptake coefficient (γN₂O₅) and representation in air quality model 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/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 in a regional air quality model (WRF-CMAQ) has improved the simulation of nitrogen oxides and secondary nitrate in the polluted regions of China. [ABSTRACT FROM AUTHOR]