Ground based in situ observations of online_IC at Harwell (GB0036R). 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: ammonia in air (mass_concentration_of_ammonia_expressed_as_nitrogen_in_air), ammonium in pm10 (mass_concentration_of_ammonium_in_pm10_in_air), ammonium in pm25 (mass_concentration_of_ammonium_in_pm2p5_in_air), calcium in pm10 (mass_concentration_of_calcium_in_pm10_in_air), calcium in pm25 (mass_concentration_of_calcium_in_pm2p5_in_air), chloride in pm10 (mass_concentration_of_chloride_in_pm10_in_air), chloride in pm25 (mass_concentration_of_chloride_in_pm2p5_in_air), hydrochloric_acid in air (mass_concentration_of_hydrochloric_acid_expressed_as_chlorine_in_air), magnesium in pm10 (mass_concentration_of_magnesium_in_pm10_in_air), magnesium in pm25 (mass_concentration_of_magnesium_in_pm2p5_in_air), nitrate in pm10 (mass_concentration_of_nitrate_in_pm10_in_air), nitrate in pm25 (mass_concentration_of_nitrate_in_pm2p5_in_air), nitric_acid in air (mass_concentration_of_nitric_acid_expressed_as_nitrogen_in_air), nitrous_acid in air (mass_concentration_of_nitrous_acid_expressed_as_nitrogen_in_air), potassium in pm10 (mass_concentration_of_potassium_in_pm10_in_air), potassium in pm25 (mass_concentration_of_potassium_in_pm2p5_in_air), sodium in pm10 (mass_concentration_of_sodium_in_pm10_in_air), sodium in pm25 (mass_concentration_of_sodium_in_pm2p5_in_air), sulphate_corrected in pm10 (mass_concentration_of_sulphate_corrected_for_seaspray_expressed_as_sulphur_in_pm10_in_air), sulphate_corrected in pm25 (mass_concentration_of_sulphate_corrected_for_seaspray_expressed_as_sulphur_in_pm2p5_in_air), sulphate_total in pm10 (mass_concentration_of_sulphate_total_in_pm10_in_air), sulphate_total in pm25 (mass_concentration_of_sulphate_total_in_pm2p5_in_air), sulphur_dioxide in air (mass_concentration_of_sulphur_dioxide_expressed_as_sulphur_in_air)