Articles | Volume 15, issue 13
Atmos. Chem. Phys., 15, 7547–7555, 2015

Special issue: The CERN CLOUD experiment (ACP/AMT inter-journal SI)

Atmos. Chem. Phys., 15, 7547–7555, 2015

Technical note 13 Jul 2015

Technical note | 13 Jul 2015

Technical Note: Using DEG-CPCs at upper tropospheric temperatures

D. Wimmer1,2, K. Lehtipalo2,3, T. Nieminen2,4, J. Duplissy2,4, S. Ehrhart1,5, J. Almeida1,5, L. Rondo1, A. Franchin2, F. Kreissl1, F. Bianchi6,7, H. E. Manninen2, M. Kulmala2, J. Curtius1, and T. Petäjä2 D. Wimmer et al.
  • 1Institute for Atmospheric and Environmental Sciences, Goethe-University of Frankfurt, 60438 Frankfurt am Main, Germany
  • 2Department of Physics, University of Helsinki, 00014 Helsinki, Finland
  • 3Airmodus Ltd, Helsinki, Finland
  • 4Helsinki Institute of Physics, 00014, Helsinki, Finland
  • 5CERN, 1211 Geneva, Switzerland
  • 6Laboratory for Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen, Switzerland
  • 7Institute for Atmospheric and Climate Science, ETH Zürich, 8092 Zürich, Switzerland

Abstract. Over the last few years, several condensation particle counters (CPCs) capable of measuring in the sub-3 nm size range have been developed. Here we study the performance of CPCs based on diethylene glycol (DEG) at different temperatures during Cosmics Leaving OUtdoor Droplets (CLOUD) measurements at CERN. The data shown here are the first set of verification measurements for sub-3 nm CPCs under upper tropospheric temperatures using atmospherically relevant aerosol particles. To put the results in perspective we calibrated the DEG-CPC at room temperature, resulting in a cut-off diameter of 1.4 nm. All diameters refer to mobility equivalent diameters in this paper. At upper tropospheric temperatures ranging from 246.15 K to 207.15 K, we found cut-off sizes relative to a particle size magnifier in the range of 2.5 to 2.8 nm. Due to low number concentration after size classification, the cut-off diameters have a high uncertainty (±0.3 nm) associated with them. Operating two laminar flow DEG-CPCs with different cut-off sizes together with other aerosol instruments, we looked at the growth rates of aerosol population in the CLOUD chamber for particles smaller than 10 nm at different temperatures. A more consistent picture emerged when we normalized the growth rates to a fixed gas-phase sulfuric acid concentration. All of the instruments detected larger growth rates at lower temperatures, and the observed growth rates decreased as a function of temperature, showing a similar trend for all instruments. The theoretical calculations had a similar but much smaller temperature dependency.

Final-revised paper