ON THE STEADY-STATE ASSUMPTION FOR THE ENERGY-DISTRIBUTION FUNCTION OF THE NONTHERMAL N(S-4) ATOMS AND THE EFFICIENCY OF NO PRODUCTION BY THESE ATOMS IN THE TERRESTRIAL THERMOSPHERE

The time dependent energy distribution functions (EDF) of N(S-4) atoms for altitudes greater than 100 km at 1400 hr local time are calculate d by solving the time dependent Boltzmann equation. At time t=0 the ti me dependent sources and sinks are switched on into a Maxwell-Boltzman n distribution of N(S-4) atoms and the time dependence of the EDF is f ollowed by solving the Boltzmann equation. It is found that the non-Ma xwellian tail of the EDF reaches a steady-state in 0.01 a giving the f raction of nascent N(S-4) atoms that react with O-2 before the establi shment of steady-state to be less than 1%. The number of NO molecules produced per second, after the establishment of steady-state, by the n on-Maxwellian tail of the EDF is at most about 3% of the number of N(S -4) atoms in the sources. The last fraction, often referred to as ''NO reaction efficiency'' is about an order of magnitude smaller than tha t given in recent literature. An important consequence of this study i s that the models still calculate less NO in the mesosphere and lower thermosphere than is measured.