Six years of aerosol size distribution measurements between 20 and 600nm diameters and total aerosol concentration above 10nmfrom March 2008 to February 2014 at the high-alpine site Jungfraujoch are presented. The size distribution was found to be typically bimodal with mode diameters and widths relatively stable throughout the year and the observation period. New particle formation was observed on 14.5%of all days without a seasonal preference. Particles typically grew only into the Aitkenmode and did not reach cloud condensation nucleus (CCN) sizes on the time scale of several days. Growth of preexisting particles in the Aitkenmode, on average, contributed very few CCN. We concluded that the dominant fraction of CCN at Jungfraujoch originated in the boundary layer. A number of approaches were used to distinguish free tropospheric (FT) conditions and episodes with planetary boundary layer (PBL) influence. In the absence of PBL injections, the concentration of particles larger than 90nm (N90, roughly corresponding to the CCN concentration) reached a value ~40cm?3 while PBL influence caused N90 concentrations of several hundred or even 1000cm?3. Comparing three criteria for free tropospheric conditions, we found FT prevalence for 39% of the timewith over 60%during winter and below20%during summer. It is noteworthy that a simple criterion based on standard trace gas measurements appeared to outperform alternative approaches.
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