Evaluating N₂O₅ heterogeneous hydrolysis parameterizations for CalNex 2010

Abstract

Abstract Nighttime chemistry in the troposphere is closely tied to the dinitrogen pentoxide (N 2 O 5 ) budget, but high uncertainties remain regarding the model representation of the heterogeneous hydrolysis of N 2 O 5 on aerosol particles. In this study we used the community model WRF‐Chem to simulate a 3‐day period during the California Nexus (CalNex) Campaign in 2010. We extended WRF‐Chem to include the heterogeneous hydrolysis of N 2 O 5 and contrasted the impact of different published parameterizations of N 2 O 5 heterogeneous hydrolysis on the spatial distribution of uptake coefficients and the resulting N 2 O 5 concentrations. For all the cases, modeled N 2 O 5 uptake coefficients showed strong spatial variability, with higher values in the nocturnal boundary layer compared to the residual layer, especially in environments with high relative humidities, such as over the ocean and along the coast. The best agreement of modeled and observed uptake coefficients was obtained using the parameterization by Davis et al. (2008) combined with the treatment of organic coating by Riemer et al. (2009). For this case the temporal evolution of lower boundary layer N 2 O 5 mixing ratios was reproduced well, and the predictions of surface mixing ratios of ozone and NO x were improved. However, the model still overpredicted the uptake coefficients in the residual layer and consequently underpredicted N 2 O 5 concentrations in the residual layer. This study also highlights that environments with low relative humidities pose a challenge for aerosol thermodynamic models in calculating aerosol water uptake, and this impacts N 2 O 5 heterogeneous hydrolysis parameterizations.