Urban and rural measurements of atmospheric potential gradient

Abstract Atmospheric potential gradient was measured at three sites within the Bristol area of the UK between 19th May and 24th June 2016. Two sites were on rooftops within the city of Bristol, 800 m apart from each other, while the third was in a rural location 17 km to the south. Potential gradient measurements at the two rooftop urban sites showed great temporal similarity, implying that a rooftop measurement may be assumed to represent the local urban area. Frequency domain analysis indicated a half-day cycle in the urban sites that was not observed in the rural site, consistent with other studies showing the effect of traffic aerosol on potential gradient measurements. The correlation between the two urban sites was not affected by an increase in aerosol concentration. Removal of data during rainfall, as well as one hour before and after rain, removed some of the larger changes in potential gradient typical of disturbed weather. However, large changes of potential gradient still existed, showing that rainfall alone should not be relied upon as an indicator of a non-fair weather potential gradient.