The relationship between aerosol concentration and atmospheric potential gradient in urban environments

Urban aerosol is a growing concern for people living within cities; aerosol have been implicated in many ill health conditions, including that of the lung and of the heart. Atmospheric potential gradient is a consequence of charge carried to the ionosphere through thunderstorms, and its value depends on highly electrically mobile ion concentrations, hence local conductivity of the air. Ions attach to aerosol in the atmosphere, reducing their mobility and therefore increasing the potential gradient, and so potential gradient measurements have been suggested as a proxy for aerosol measurements. Particle number count, size distribution and potential gradient were measured for two campaigns in Manchester, U.K., and one campaign in Bristol, U.K. Using a factor based on size distribution to account for preferential attachment at larger sizes provided the best relationship with potential gradient, but particle count alone showed a weaker, but similar relationship. The increase in particle count caused by annual bonfire and fireworks celebrations (November) was evidenced in both potential gradient and particle numbers. Daily regression or correlation did not show a consistent relationship. In the larger Bristol data set, increasing humidity led to a reduction of potential gradient, while increasing particle number led to an increase.