Ground based in situ observations of filter_3pack at Hurdal (NO0056R). These measurements are gathered as a part of the following projects NILU and they are stored in the EBAS database (http://ebas.nilu.no/). Parameters measured are: chloride in aerosol (mass_concentration_of_chloride_in_dry_aerosol_particles_in _air), magnesium in aerosol (mass_concentration_of_magnesium_in_dry_aerosol_particles_in _air), sodium in aerosol (mass_concentration_of_sodium_in_dry_aerosol_particles_in _air)