An explanation is given for time-variable and spatially discrete enhancements of neutral sodium (Na) and potassium (K) in Mercury's atmosphere. Some locations of increased intensity can be explained in terms of sodium and potassium ion implantation into the surface regolith grains during the long, 88 Earth day, Mercurian night with subsequent diffusion to the atmosphere when the enriched surface of Mercury rotates into the intense sunlight of day. Support for the suggested mechanism is shown by the K data which show a marked morning/afternoon assymmetry and can be explained by time and temperature dependent degassing. The magnetospheric mechanism necessary for ion implanation is discussed as is the diffusion mechanism. Alternative source, recycling, and distribution processes are also discussed. ¿American Geophysical Union 1992