A numerical study is presented of the chemistry of NOx (NO+NO2+NO3+2¿N2O5) in air parcels assumed to travel on constant pressure surfaces for a period in early February 1977. Airflow was observed to be stable and largely barotropic during this period. Strong coupling between photochemical and dynamical effects is found to play an important role in determining the distributions of these species. Comparison of model results to observations of the total column abundance of NO2 (Noxon, 1979) yields good agreement and implies that attention should be given to dynamical conditions when comparing model calculations and observations of odd nitrogen species in the stratosphere.