1Experimental Aerosol and Cloud Microphysics, Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
2Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland
3Faculty of Chemistry, Bielefeld University, Bielefeld, Germany
4Institute for Atmospheric and Environmental Sciences, Goethe University of Frankfurt, Frankfurt am Main, Germany
5Institute of Atmospheric Physics, University of Mainz, Mainz, Germany
6Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
7Institute for Environmental Physics, University of Heidelberg, Heidelberg, Germany
*now at: Institute Advanced Ceramics, Hamburg University of Technology (TUHH), Hamburg, Germany
**now at: Michigan Technological University, Houghton, MI, USA
***now at: Max Planck Institute for Chemistry, Multiphase Chemistry Department, Mainz, Germany
Received: 22 Aug 2014 – Discussion started: 01 Sep 2014
Abstract. Seven different instruments and measurement methods were used to examine the immersion freezing of bacterial ice nuclei from Snomax® (hereafter Snomax), a product containing ice-active protein complexes from non-viable Pseudomonas syringae bacteria. The experimental conditions were kept as similar as possible for the different measurements. Of the participating instruments, some examined droplets which had been made from suspensions directly, and the others examined droplets activated on previously generated Snomax particles, with particle diameters of mostly a few hundred nanometers and up to a few micrometers in some cases. Data were obtained in the temperature range from −2 to −38 °C, and it was found that all ice-active protein complexes were already activated above −12 °C. Droplets with different Snomax mass concentrations covering 10 orders of magnitude were examined. Some instruments had very short ice nucleation times down to below 1 s, while others had comparably slow cooling rates around 1 K min−1. Displaying data from the different instruments in terms of numbers of ice-active protein complexes per dry mass of Snomax, nm, showed that within their uncertainty, the data agree well with each other as well as to previously reported literature results. Two parameterizations were taken from literature for a direct comparison to our results, and these were a time-dependent approach based on a contact angle distribution (Niedermeier et al., 2014) and a modification of the parameterization presented in Hartmann et al. (2013) representing a time-independent approach. The agreement between these and the measured data were good; i.e., they agreed within a temperature range of 0.6 K or equivalently a range in nm of a factor of 2. From the results presented herein, we propose that Snomax, at least when carefully shared and prepared, is a suitable material to test and compare different instruments for their accuracy of measuring immersion freezing.
Revised: 17 Dec 2014 – Accepted: 20 Dec 2014 – Published: 10 Feb 2015
Wex, H., Augustin-Bauditz, S., Boose, Y., Budke, C., Curtius, J., Diehl, K., Dreyer, A., Frank, F., Hartmann, S., Hiranuma, N., Jantsch, E., Kanji, Z. A., Kiselev, A., Koop, T., Möhler, O., Niedermeier, D., Nillius, B., Rösch, M., Rose, D., Schmidt, C., Steinke, I., and Stratmann, F.: Intercomparing different devices for the investigation of ice nucleating particles using Snomax® as test substance, Atmos. Chem. Phys., 15, 1463-1485, doi:10.5194/acp-15-1463-2015, 2015.