A discussion of the recovery time of ionization in the low ionosphere (60- to 100-km altitude). It is known that both the local air chemistry and the level of ambient ionization affect the lifetime of free electrons in the ionosphere. The model for the air chemistry used assumes a standard air mixture for which the superoxide ion is the dominant negative ion. Day and night environments are considered. To illustrate, the recovery time of ionization produced by x-rays from a nuclear explosion is examined. The suggestion is made that an experiment using x-rays from a small-yield nuclear explosion in space could provide important knowledge of the characteristics of the ionosphere.