Air Ion Concentrations under Overhead High-Voltage Transmission Lines

Abstract

This paper reports air ion concentration monitored at 41 sites under overhead high voltage ac power lines in and around an urban environment. The net ionic polarity under power lines was of both signs but mostly positive, and concentrations varied widely from 0 to 3300 ions cm-3. Concomitant measurements of the vertical dc electric field at the ground confirmed the presence of a net positive charge above. Approximately 19% of the sites exhibited relatively high ion concentrations exceeding 1000 cm-3. The mean value of all the sites was 776 cm-3. Statistically, the mean for the transmission voltage (220-330 kV) line sites was significantly higher than that for the sub-transmission voltage (110-132 kV) line sites with means of 905 and 501 cm-3 respectively. These values were compared with the mean urban outdoor concentration well away from the lines which was about 400 cm-3 and of negative polarity. Overall, ion concentrations at approximately 76% of the power line sites exceeded the absolute mean urban outdoor value. The dc electric fields under the power lines showed a statistically significant relationship to the measured ion concentrations, although there was considerable scatter to indicate that electric field measurements do not necessarily reflect air ion concentrations at ground level.