The TROPOS-SMPS is designed for long-term measurement of aerosol particles and over there in highly burden regions. It is a mobility particle size spectrometer, which can measure continuously the particle number size distribution in a size range from 10 to 800 Nanometers. The temporal resolution to measure a complete particle number size distribution is approximately 5 minutes. Measured data are stored on a PC or notebook, which is part of the measuring system. The current particle number size distribution is displayed graphically as part of the data acquisition and control software. The instrument comprises a condensation particle counter and a radioactive source (Ni-63).