Ground based in situ observations of aerosol_mass_spectrometer at Birkenes II (NO0002R). These measurements are gathered as a part of the following projects ACTRIS, COLOSSAL, EMEP, NILU and they are stored in the EBAS database (http://ebas.nilu.no/). Parameters measured are: ammonium in pm1_non_refractory (mass_concentration_of_ammonium_in_non_refractory_pm1_in_air), chloride in pm1_non_refractory (mass_concentration_of_chloride_in_non_refractory_pm1_in_air), nitrate in pm1_non_refractory (mass_concentration_of_nitrate_in_non_refractory_pm1_in_air), organic_mass in pm1_non_refractory (mass_concentration_of_organic_mass_in_non_refractory_pm1_in_air), sulphate_total in pm1_non_refractory (mass_concentration_of_sulphate_total_in_non_refractory_pm1_in_air)