A data base derived from Atmosphere Explorer C measurements of parameters important to the understanding of the diurnal variation of odd-nitrogen and ions in the thermosphere near equinox, at low latitudes, and for quiet geomagnetic conditions is presented. The data were taken during the period from August to September 1974, when perigee was near the equator and reached an altitude of about 135 km. The data base contains profiles of the odd-nitrogen species NO, and N(2D); the ions NO+, O+2, O+, N+2, and N+; the total ion density; O an N2; and the neutral, ion, and electron temperatures. The measured time-dependent variations of NO, N(2D), O+2, and NO+ compare favorably to the results of a time dependent, photochemical, diffusion model for odd-nitrogen and ion chemistry. In particular, the model reproduces the rapid increase in NO density in the morning hours, the mid-afternoon maximum, and the late afternoon decrease. The model also predicts the measured absolute densities for NO to within 20% over most of the diurnal cycle but falls below the measured density by as much as a factor of 2 in the late afternoon. The agreement between the data and the model indicates that the most important chemical processes for the production and loss of odd-nitrogen in the Earth's thermosphere are included in the model. ¿American Geophysical Union 1991