A discharge flow tube experiment has been conducted to determine the rate coefficient, k2, for reaction (2): NO3+ NO2+ N2→ N2O5+ N2 from 236 to 358 K and 0.5 to 8 Torr. This represents the first study of the temperature dependence of k2 at low pressures, i.e. under conditions relevant to the middle and upper stratosphere. The date obtained here have been combined with other measurements of k2 and the following fall-off parameters are recommended: k0=(2.8 ± 0.4)× 10–30(T/300)(–3.5 ± 0.5) cm6 s–1, k∞=(1.66 ± 0.25)× 10–12(T/300)(–0.2 ± 0.2) cm3 s–1, for Fc= 2.5 exp(–1950/T)+ 0.9 exp(–T/430).