Atmospheric aerosols become charged by ion-aerosol attachment, possibly leading to enhanced particle deposition in the lung on inhalation and an increased risk of related diseases. Ion mobility is an important parameter in determining the extent and timescale for aerosol charging, and is measured here in the vicinity of high-voltage power lines (HVPLs) using Gerdien-type mobility spectrometers. Ion mobility is higher downwind of HVPLs than upwind by ~14% (negative ions) to ~18% (positive ions), implying faster aerosol charging and possibly higher peak charge magnitudes than under lower mobility assumptions. Observed mobilities upwind are higher than previous studies report (1.47 and 1.90 × 10^-4 m² V^-1 s^-1 for positive and negative ions respectively). Results suggest ion growth may still be occurring > 20 s after production, but evidence is weak and more data are needed to determine this.