Comment to: Twentieth century secular decrease in the atmospheric potential gradient. Author's reply

Harrison [2002] has attributed the decline in surface potential gradient in the United Kingdom (UK) over the 20th century to the decline in cosmic radiation and the global electrical circuit. This paper addresses the supporting evidence for Harrison's explanation, and considers an alternative hypothesis for the observations based on local changes in aerosol concentration. This hypothesis is supported by the concurrent historical record of black carbon emission in the UK.