A new mobile wide range aerosol spectrometer (WRAS) was applied to measure atmospheric aerosol size distributions with high time and size resolution. This WRAS instrument package has been set up on the roof deck of the Meteorological Observatory Hohenpeissenberg (MOHp, 47°48’ N, 11°02’ E, 985m a.s.l.), which is located on a hill with about 300m elevation above a rural flat area in Bavaria, Germany. The measured aerosol size distributions have a high size resolution with more than 70 size channels ranging from 5.5 nm to 32 µm. It is shown that there occur large numbers of ultrafine airborne particles even at this altitude. A broad range of meteorological data, gases, and aerosol parameters were also continuously measured at the MOHp. These data are correlated with the aerosol size distribution measurement to accomplish particle source apportionment, and also to investigate aerosol transport and transformation.