Ground based in situ observations of denuder at Utö (FI0009R). These measurements are gathered as a part of the following projects EMEP, CAMPAIGN and they are stored in the EBAS database (http://ebas.nilu.no/). Parameters measured are: ammonia in air (mass_concentration_of_ammonia_expressed_as_nitrogen_in_air), ammonium in aerosol (mass_concentration_of_ammonium_expressed_as_nitrogen_in_dry_aerosol_particles_in _air), nitrate in aerosol (mass_concentration_of_nitrate_expressed_as_nitrogen_in_dry_aerosol_particles_in _air), nitric_acid in air (mass_concentration_of_nitric_acid_expressed_as_nitrogen_in_air)