Abstract: "Experimental investigation of aerosol particle capture by evaporating and condensing water drops has shown that capture is a function of the rate of water drop growth and aerosol particle diameter. Capture was found to be proportional to the rate of water vapor condensation and inversely proportional to aerosol particle diameter. The influence of water vapor gradient and particle size on aerosol particle capture during evaporation is insignificant. The experimental results are explained on the basis of particle penetration through the boundary layer of a water drop. An analysis of previous research on radioactivity of dry particulate matter in an urban atmosphere is included."