Ground based in situ observations of particle_number_size_distribution at Birkenes (NO0001R) using dmps. These measurements are gathered as a part of the following projects GAW-WDCA_NRT, NILU_NRT, EUSAAR_NRT and they are stored in the EBAS database (http://ebas.nilu.no/). Parameters measured are: particle_number_size_distribution in pm10