Size distribution measurements of ultrafine aerosols, dp > 1.8 nm, formed by radiolysis in a diameter measurement analyzer aerosol charger

Abstract

A University of Vienna differential mobility analyzer-electrometer arrangement was used to measure the size distribution of charged ultrafine aerosols (dp > 1.8 nm) generated from a N2-SO2-H2O mixture by radiolysis in a bipolar diffusion charger loaded with a 2.5 mCi Am-241 α-source. Despite the short residence time in the charger, tr < 1s, nucleation mode diameters near 2 nm were found for dry gas mixtures with water vapor concentrations > 32 ppm. At 20% relative humidity number concentrations increased and modal diameters shifted to larger sizes with increasing SO2 concentration. The addition of trace concentrations of nitric oxide or ethanol vapor to the gas mixtures resulted in a near complete suppression of particle formation. © 1990 Elsevier Science Publishing Co., Inc.