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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 4, issue 3
Atmos. Meas. Tech., 4, 485–497, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 4, 485–497, 2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

  08 Mar 2011

08 Mar 2011

Results and recommendations from an intercomparison of six Hygroscopicity-TDMA systems

A. Massling1,*, N. Niedermeier1, T. Hennig1,2, E. O. Fors3, E. Swietlicki3, M. Ehn4, K. Hämeri4, P. Villani5, P. Laj5, N. Good6, G. McFiggans6, and A. Wiedensohler1 A. Massling et al.
  • 1Leibniz Institute for Tropospheric Research, Leipzig, Germany
  • 2Stockholm University, Department of Applied Environmental Science, Stockholm, Sweden
  • 3Lund University, Department of Physics, Lund, Sweden
  • 4University of Helsinki, Department of Physics, Helsinki, Finland
  • 5Université Blaise Pascal, Laboratoire de Météorologie Physique, Clermont Ferrand, France
  • 6University of Manchester, Department of Atmospheric and Environmental Sciences, Manchester, UK
  • *now at: Aarhus University, National Environmental Research Institute, Department of Atmospheric Environment, Roskilde, Denmark

Abstract. The performance of six custom-built Hygrocopicity-Tandem Differential Mobility Analyser (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 harmonise 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 sulphate particles or an external mixture of ammonium sulphate 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. Measurements of ammonium sulphate aerosol found deviations equivalent to 4.5% RH from the set point of 90% RH compared to results from previous experiments in the literature. Evaluation of the number fraction of particles within the clearly separated growth factor modes of a laboratory generated externally mixed aerosol was done. The data from the H-TDMAs was analysed with a single fitting routine to investigate differences caused by the different data evaluation procedures used for each H-TDMA. The differences between the H-TDMAs were reduced from +12/−13% to +8/−6% when the same analysis routine was applied. We conclude that a common data evaluation procedure to determine number fractions of externally mixed aerosols will improve the comparability of H-TDMA measurements.

It is recommended to ensure proper calibration of all flow, temperature and RH sensors in the systems. It is most important to thermally insulate the aerosol humidification unit and the second DMA and to monitor these temperatures to an accuracy of 0.2 °C. For the correct determination of external mixtures, it is necessary to take into account size-dependent losses due to diffusion in the plumbing between the DMAs and in the aerosol humidification unit.

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