A three-dimensional axisymmetric model is used to approximate the abundance of minor species in Io's atmosphere. This includes plasma and Joule heating, nonlocal thermodynamic equilibrium cooling, and photochemistry of SO2 with convective and diffusive transport, and extends our earlier work on a sublimation-driven atmosphere <Wong and Johnson, 1995> in which we studied the effect of plasma heating on the dynamics of the atmosphere near the exobase. In the present model a more advanced numerical technique is employed and spherical geometry is used. The new results confirm that plasma heating determines the atmospheric temperature near the exobase. This heating also causes the average column density on the dayside trailing hemisphere to exceed that of the dayside leading hemisphere by ~20%. We evaluated the suggestion that noncondensibles (O2 and, possibly, SO) would accumulate and dominate the atmospheric dynamics. We found that the buildup of a nightside atmosphere of noncondensible photochemical products does not overwhelm the dayside atmospheric flow, but it does raise the overall atmospheric pressure and reduce the wind speed. For a dayside hemispherically averaged column abundance of 5.5¿1016 SO2 cm-2 the column abundance of O2 is found to be ~1014 cm-2 on the dayside and ~1015 cm-2 on the nightside, while SO (if assumed noncondensible) is ~1015 cm-2 in most regions, ignoring plasma destruction processes. It is also found that the relative density of a photochemical product to that of SO2 and its spatial distribution depend strongly on the flow dynamics, a factor that cannot be accounted for in one dimensional models. The hemispherically averaged fraction of SO on the dayside is found to be 3% if SO is condensible and 6% if SO is noncondensible. ¿ American Geophysical Union 1996