Long-term study of cloud condensation nuclei (CCN) activation of the atmospheric aerosol in Vienna

► CCN concentrations (at 0.5% super-saturation) are highly variable. ► No seasonal differences were found. ► CN show typical diurnal trends, while CCN do not. ► Activation ratios were found to be low (0.02-0.47, average: 0.13) but equally highly variable.