On the ability of chemical transport models to simulate the vertical structure of the N₂O, NO₂ and HNO₃ species in the mid-latitude stratosphere

Abstract. In this paper we study the impact of the modelling of N₂O on the simulation of NO₂ and HNO₃ by comparing in situ vertical profiles measured at mid-latitudes with the results of the Reprobus 3-D CTM (Three-dimensional Chemical Transport Model) computed with the kinetic parameters from the JPL recommendation in 2002. The analysis of the measured in situ profile of N₂O shows particular features indicating different air mass origins. The measured N₂O, NO₂ and HNO₃ profiles are not satisfyingly reproduced by the CTM when computed using the current 6-hourly ECMWF operational analysis. Improving the simulation of N₂O transport allows us to calculate quantities of NO₂ and HNO₃ in reasonable agreement with observations. This is achieved using 3-hourly winds obtained from ECMWF forecasts. The best agreement is obtained by constraining a one-dimensional version of the model with the observed N₂O. This study shows that the modelling of the NO_y partitioning with better accuracy relies at least on a correct simulation of N₂O and thus of total NO_y.