High voltage (HV) power transmission lines often undergo corona discharge, creating clouds of space charge consisting of corona ions and, later, charged aerosols. These generally unipolar clouds, under the influence of a crosswind can be transported away from the line, dispersing to ground level over time. Previous survey measurements have shown elevated electric (E)-field levels, with large fluctuations downwind of AC powerlines in the U.K. (Fews et al., 2002).

It has been proposed that corona ions from HV powerlines could cause adverse health effects due to additional aerosol charging (Henshaw, 2002). To assess the plausibility of this hypothesis, the influence of corona ions at ground level needs to be investigated. DC field mill meters have been used to measure the vertical E-field, while ion concentration measurements were made simultaneously to assess the contribution at ground level.