Atmospheric Measurement Techniques Discussions www.atmos-meas-tech-discuss.net 1867-8610 3 1 2010 10.5194/amtd-3-637-2010 http://www.atmos-meas-tech-discuss.net/3/637/2010/ http://www.atmos-meas-tech-discuss.net/3/637/2010/amtd-3-637-2010.html http://www.atmos-meas-tech-discuss.net/3/637/2010/amtd-3-637-2010.pdf 637 674 2010-02-15 Results and recommendations from an intercomparison of six Hygroscopicity-TDMA systems A. Massling anma@dmu.dk N. Niedermaier T. Hennig E. Fors E. Swietlicki M. Ehn K. Hämeri P. Villani P. Laj N. Good G. McFiggans A. Wiedensohler Leibniz Institute for Tropospheric Research, Leipzig, Germany Aarhus University, National Environmental Research Institute, Department of Atmospheric Environment, Roskilde, Denmark Stockholm University, Department of Applied Environmental Science, Stockholm, Sweden Lund University, Department of Physics, Lund, Sweden University of Helsinki, Department of Physics, Helsinki, Finland Université Blaise Pascal, Laboratoire de Météorologie Physique, Clermont Ferrand, France University of Manchester, Department of Atmospheric and Environmental Sciences, Manchester, UK The performance of six custom-built Hygrocopicity-Tandem Differential Mobility Analyzers (H-TDMA) systems was investigated in the frame of an international calibration and intercomparison workshop held in Leipzig, February 2006. The goal of the workshop was to harmonize H-TDMA measurements and develop recommendations for atmospheric measurements and their data evaluation. The H-TDMA systems were compared in terms of the sizing of dry particles, relative humidity (RH) uncertainty and consistency in determination of number fractions of different hygroscopic particle groups. The experiments were performed in an air-conditioned laboratory using ammonium sulfate particles or an external mixture of ammonium sulfate and soot particles. The sizing of dry particles of the six H-TDMA systems was within 0.2 to 4.2% of the selected particle diameter depending on investigated size and individual system. With regard to RH uncertainties, the H-TDMA systems showed deviations up to 4.5% RH from the set point at RH=90% investigating the hygroscopic growth of ammonium sulfate particles and comparing the results with theory. The evaluation of number fractions investigating an externally mixed aerosol delivered differences up to +/−8% in calculated number fraction for one and the same aerosol type. 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