Effect of coagulation on the particle charge distribution and air conductivity

Abstract

The steady state charge distribution on submicron-size charged aerosols is calculated from the ion-aerosol balance equations including the effects of both the ion-particle charging mechanism as well as the coagulation of charged aerosols. The particle charge distribution is found to depend on the aerosol concentration and the ionization rate. The results show that for a given ionization rate the fraction of singly charged aerosols increases up to a critical value of aerosol concentration and then decreases with further increase in the aerosol concentration. However, the fractions of multiply charged aerosols show a steady increase with the aerosol concentration. The variation of the polar conductivity with aerosol concentration shows that the inverse relationship between them exists only up to a critical value of aerosol concentration which is decided by the prevailing ionization rate. Above this critical value the polar conductivity shows an increase with the aerosol concentration. Further, it is shown that though the polar conductivity is mainly due to small ions in a clean environment, the charged aerosols may dominantly contribute to the polar conductivity in a polluted atmosphere. For aerosols having larger mean radii the contribution of multiply charged aerosols becomes appreciable for higher values of aerosol concentration and is almost comparable to that of the small ions.