AURORAL NO CONCENTRATIONS

Auroral NO chemistry is studied to determine the limits on left bracket NO right bracket and its production rate in steady auroral arcs. It is concluded conservatively that the NO concentration cannot exceed 0. 1 left bracket O//2 right bracket . The precise value of this upper limit depends very sensitively on the relative yields of N(**2D) and N(**4S) in the reactions that are the major auroral sources of N atoms, and on the basis of the requirements of mid-latitude models for odd nitrogen, a value of 0. 03 left bracket O//2 right bracket is estimated. Plausible auroral left bracket NO right bracket enhancements are of the order of (3 to 6) multiplied by 10**8 cm** minus **3 after 10**3 s and (1 to 4) multiplied by 10**9 cm** minus **3 after 10**4 for a steady IBC 2** plus arc.