A new Monte Carlo type model of the lunar sodium atmosphere has been developed and applied to recent ground-based imaging observations. The model assumes a steady state atmosphere with production of sodium due to a spatially uniform source (e.g., meteor impact vaporization) or a solar zenith angle dependent source (e.g., solar wind sputtering or photodesorption). The loss processes included in the model are surface adsorption and photoionization. Solar radiation pressure is also accounted for. The model output is analyzed for overall spatial structure and compared with recent observations and theory. The results indicate that a sodium release mechanism that decreases in source rate with increasing solar zenith angle is best able to reproduce imaging data taken on September 30, 1991. ¿ American Geophysical Union 1995