Dissipation of Planetary Atmospheres.
Escape-level density is approximately inversely proportional to gravity and with decreasing mass will tend toward that of interplanetary gas. When this value is reached, dissipation must cease. The minimum possible ground density of lunar air is calculated to be 10(-12) that of the air at normal temperature and pressure. Ionization creates a binding electrostatic charge at the escape level.
Firsoff
V A
VA