The atmospheric importance of the reaction of ClO with NO3 has been tested in a one-dimensional photochemical model. This reaction has two product channels which are of atmospheric importance. The channel which forms Cl and NO2 can destroy ozone in a catalytic cycle. This cycle constitutes the main ozone loss mechanism during the night near 40 km. The other channel forms OClO and is a significant source of OClO in the upper stratosphere during the night. In the polar lower stratosphere this reaction does not significantly enhance OClO. ¿American Geophysical Union 1994