Ground based in situ observations of smps at TMNT09 Vielsalm (BE0007R). These measurements are gathered as a part of the following projects ACTRIS, EMEP, GAW-WDCA and they are stored in the EBAS database (http://ebas.nilu.no/). Parameters measured are: particle_number_size_distribution in pm10, particle_number_size_distribution in pm10, particle_number_size_distribution in pm10