| Summary: | A recent hypothesis on the existence of neutral thermodynamically stable clusters is thoroughly investigated both experimentally and theoretically. Altogether, three different methods are utilized. First, the concentrations and size distributions of atmospheric ions, measured using ion spectrometers, are analyzed in parallel with aerosol size distribution data to find out the size dependencies of cluster and aerosol growth rates. The measurements are performed at SMEAR II station in Hyytiälä, Finland. Second, a condensation particle counter (CPC) is used as a nucleation chamber for homogeneous nucleation and ambient cluster activation studies. Both experimental methods support the existence of neutral clusters. Third, a large number of model simulations on aerosol and ion size distribution dynamics reveal that the existence of neutral clusters seems to be necessary to obtain consistency between modeling results and experimental measurements.
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