EVIDENCE FOR NEW SOURCES OF NOX IN THE LOWER ATMOSPHERE

Laboratory studies show that the reaction of short-lived O-2(B-3 Sigma (u)) molecules (lifetime similar to 10 picoseconds) with N-2 and the p hotodissociation of the N-2:O-2 dimer produce NOx in the stratosphere at a rate comparable to the oxidation of N2O by O(D-1). this finding i mplies the existence of unidentified NOX sinks in the stratosphere. Th e NO2 observed in this experiment is isotopically heavy with a large N -15/N-14 enhancement. However; photodissociation of this NO2 unexpecte dly produced NO molecules with a low N-15/N-14 ratio. The diurnal odd- nitrogen cycle in the stratosphere will be marked by a complex isotope signature that will be imprinted on the halogen and HOX catalytic cyc les.