Ground based in situ observations of pm25_mass at Donon (FR0008R) using optical_particle_size_spectrometer. These measurements are gathered as a part of the following projects EMEP and they are stored in the EBAS database (http://ebas.nilu.no/). Parameters measured are: pm25_mass in pm25 (mass_concentration_of_pm2p5_ambient_aerosol_particles_in_air)