The rate constant for the combination reaction of CFCl2O2and NO2was measured as a function of pressure and temperature under stratospheric conditions. The results show that the reaction is fast and that significant amounts of the peroxynitrate CFCl2O2NO2can be formed. The data were introduced into a 2D photochemical model in order to evaluate an upper limit for the amount of chlorine stored in the form of the peroxynitrate. The calculation shows that this reservoir effect cannot exceed a few percent of the total chlorine contained in the stratosphere.