Properties of atmospheric small ions are studied in different environments including a valley in a semiarid region of the southwestern United States, a nearby mountain top, and a cave where the radon concentration and the absolute humidity are quite high and the condensation nuclei concentration is low. Owing to a high ion pair production rate from the radon and low condensation nuclei content, the electrical conductivity and the small ion densities in the cave air exceed those of the free atmosphere by 2 and 3 orders of magnitude, respectively. The relatively high water vapor and carbon dioxide levels coupled with a low aerosol concentration in the cave appear to favor the growth of ion complexes having lower mobilities than ordinary atmospheric small ions. Atmospheric electrical parameters on the mountain differ by small amounts in comparison with the valley. Atmospheric variables at the mountain site hinge largely on the summer thunderstorm season that set it off from the semiarid setting of the valley location.