Activation of “synthetic ambient” aerosols – Relation to chemical composition of particles <100 nm

Abstract

Abstract Cloud condensation nuclei (CCN) are an important fraction of atmospheric aerosols because of their role in cloud formation. Experimental studies focus either on direct field measurements of complex ambient aerosols or laboratory investigations on well defined aerosols produced from single substances or substance mixtures. In this study, we focussed on the ultrafine aerosol because in terms of number concentration, the majority of the CCN are expected to have sizes in this range. A field study was performed from July 2007 to October 2008 to investigate the activation behaviour of the atmospheric aerosol in Vienna ( Burkart et al., 2011 ). Filter samples of the aerosol Giebl et al., 2002; Dusek et al., 2006b ) at a nominal supersaturation (SS) of 0.5%. Activation diameters d act ranged from 54.5 nm to 66 nm, were larger than d act of typical single inorganic salts and showed no seasonal pattern in contrast to the fraction of water soluble organic carbon (WSOC), which ranged from 44% in spring to 15% in winter. The average hygroscopicity parameter κ ( Petters and Kreidenweis, 2007 ) obtained from the activation curves ranged from 0.20 to 0.30 (average 0.24), which was significantly lower than κ chem calculated from the chemical composition (0.43 ± 0.07).