Possible new atmospheric sources and sinks of odd nitrogen: 2. A revisit with O-2(B) and discussions of other possibilities

Recently, modelers have expressed a concern that the currently known chemistry of atmospheric NOY is deficient. It is therefore necessary to explore possible sources and sinks of atmospheric NOX that may have been overlooked. In this context, it is noteworthy that the experimentally observed, four-center, Woodward-Hoffman forbidden, reaction O-2(B (3)Sigma) + N-2 --> NO(X) + NO (X) is atmospherically significant. In the 20 to 30 km region NOX production from this reaction may potentially exceed the production from the classical N2O + O(D-1) reaction, and may provide a new mechanism to couple the solar UV variability and stratospheric ozone. The avoidance of the non-conservation of the orbital symmetry via the production of one NO in the excited electronic state being endothermic, it appears that the interaction of O-2(B (3)Sigma) with the adjoining (1)Pi(u), (3)Pi(u) and (3)Sigma(u)(+) states might be responsible for the reaction. Experimental studies of the reaction as a function of the vibrational levels of the B-state, temperature and pressure are needed for reliable atmospheric applications of this reaction. At altitudes greater than about 50 km the production of NO from Oz(B) begins to decrease rapidly. The NO production from O-2 (A (3)Sigma(u)(+),) + N-2 --> NO + NO reaction may become important here, if the reaction is confirmed by experiments. These new sources of NOX call for new sinks of this species. In the upper stratosphere and mesosphere the chemical acceleration of NO dissociation via the reactions of electronically and vibrationally excited NO with O-2 may help. In the lower atmosphere there is a possibility of the annihilation of NO, NO2 pair leading to the recreation of a stable N=N bond. This might happen if N2O3, from NO and NO2 recombination may photodissociate as N2O + O-2. Unfortunately the requirements are stringent, and only experiments can tell whether or not this mechanism operates in the atmosphere. (C) 2000 Elsevier Science Ltd. All rights reserved.