Aerosol modulation of the optical and electrical properties of urban air

Aerosol particles reduce the electrical conductivity of air, through removal of the small ions causing the conductivity. Visual range is also affected by aerosol. Early 20th century work linked increased smoke pollution concentrations with decreased air conductivity and visual range. By analysing newly-recovered monthly atmospheric electricity data from Kew Observatory, near London, for 1968–1979, averages of the visual range and air conductivity show a close empirical relationship: visual range is reduced when air conductivity is also reduced. The visibility–conductivity correlation is likely to be due to a common modulation of both atmospheric properties by the aerosol number concentration. For the urban air data from Kew, the visual range D and monodisperse aerosol number concentration Z were related by ZDx=A, with x and A found empirically: A is a function of the mean aerosol radius. Through this relationship, local meteorological observations of visual range can provide additional information on aerosol concentration or the electrical properties of air, when no direct measurements are available.