Evaluating the Impacts of N2O5 Heterogeneous Reaction and ClNO2 Production on Reactive Nitrogen and Tropospheric Ozone in Southern China
Thursday, 17 December 2015
Poster Hall (Moscone South)
Heterogeneous reaction of N2O5 on chloride-containing aerosols transforms N2O5 into nitrate and ClNO2. The production of nitrate is the loss pathway of NOx, while the formation and subsequent photolysis of ClNO2 acts as temporary reservoir of NOx and source of Cl atom, which reacts with VOCs like OH radical. The N2O5 uptake and ClNO2 production, therefore, influences the reactive nitrogen and ozone chemistry. Hong Kong and Pearl River Delta (the latter is known as the world factory), which are located in Southern China, has been experiencing severe photochemical and haze pollution in recent years. But the role of the N2O5 heterogeneous chemistry has not been studied. Yet elevated concentrations of N2O5 and ClNO2 have been observed at a high-altitude site in Hong Kong, suggesting the potential significance of the N2O5 and ClNO2 chemistry in this region. In this study, Weather Research and Forecasting coupled with Chemistry (WRF-Chem) model, which is a widely used coupled meteorology-chemistry model, was further developed to incorporate the parameterization of N2O5 heterogeneous reaction, ClNO2 production, and gas phase reactions of Cl with VOCs and then to evaluate the impacts on reactive nitrogen and tropospheric ozone in this region. The implementation of N2O5 and ClNO2 chemistry improved model performance of air pollutants. The updated model was able to reproduce the observed temporal patterns of N2O5 and ClNO2 at the mountain top site. We will present the simulations of effects of the N2O5 heterogeneous reactions and ClNO2 production on the concentrations of NOx, total nitrate, and ozone in the planetary boundary layer of Southern China. Overall, our study suggests significant impacts of the N2O5 and ClNO2 processes on reactive nitrogen budget and ozone chemistry and the necessity to consider them in future atmospheric chemistry modelling studies.