Ground based in situ observations of filter_2pack at Birkenes (NO0001R). These measurements are gathered as a part of the following projects CAMP, EMEP, NILU, GAW-WDCA 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), potassium in aerosol (mass_concentration_of_potassium_in_dry_aerosol_particles_in _air)