In this paper we study the impact of the modelling of N<sub>2</sub>O on the simulation of NO<sub>2</sub> and HNO<sub>3</sub> 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 N<sub>2</sub>O shows particular features indicating different air mass origins. The measured N<sub>2</sub>O, NO<sub>2</sub> and HNO<sub>3</sub> profiles are not satisfyingly reproduced by the CTM when computed using the current 6-hourly ECMWF operational analysis. Improving the simulation of N<sub>2</sub>O transport allows us to calculate quantities of NO<sub>2</sub> and HNO<sub>3</sub> 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 N<sub>2</sub>O. This study shows that the modelling of the NO<sub>y</sub> partitioning with better accuracy relies at least on a correct simulation of N<sub>2</sub>O and thus of total NO<sub>y</sub>.