Many researchers have presented measurements of atmospheric small ions or atmospheric potential gradient downwind of high voltage power lines. The relationship between these two measured properties, and the charge state of atmospheric aerosols, is not well understood. Simultaneous small ion concentration and potential gradient measurements were made at AC high voltage power lines using ion mobility spectrometers and electric field mills. A significant change in central tendency and variability of ion concentration and potential gradient can occur downwind of power lines. In some downwind measurements, there was a discrepancy of sign between the overall mean of these quantities, attributed to ion dispersion and ion-aerosol attachment.