The six most significant production and seven most significant loss mechanisms are identified for NO+(a3&Sgr;) in the aurora. Rate constants are given for these reactions as well as for the 14 most important reactions competing with the production of NO+(a). Using available data and certain crucial deductions on chemical reaction rates to simulate a number of altitude profiles, we have concluded that the two predominant sources of NO+(a3&Sgr;) are probably N++O2→NO+(a) +O and N2++NO→NO+(a)+N2. Radiative decay is not the primary loss mechanism but can dominate above 150 km. Destruction via charge exchange with N2 and O are most important below 150 km. Total radiation in the a3&Sgr;--X1&Sgr; transition is estimated to be between 35 R and 350 R for a model aurora 0f 78 ergs cm-2 s-1 energy input, which is nearly IBC III in intensity.