Scavenging of electrified radioactive aerosol

Scavenging by water droplets is a mechanism for aerosol removal near clouds. Numerical methods are developed to quantify the removal of charged radioactive aerosols, including the electrical image force's contribution, attractive at small separations. Charging of radioactive aerosols is found to have significant effects on their collision efficiency and scavenging coefficient. The effect depends on the aerosol charge, and therefore, on the radioactive aerosol's decay rate and number concentration, but it does not depend significantly on the charge carried by the water drops. Scavenging coefficients are calculated for radioactive aerosols. For small particles at low aerosol concentrations (Z similar to 10-100 cm(-3)) charging can increase the scavenging coefficients by up to an order of magnitude. Electrification will, therefore, encourage the removal of small radioactive aerosols from the atmosphere, more rapidly than equivalent nonradioactive aerosols. The increase in removal at low radioactive-aerosol concentration may account for under-predictions of surface concentrations and will contribute to spatial variations in aerosol removal. (C) 2001 Elsevier Science Ltd, All rights reserved.