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
Received: 21 Mar 2014 – Discussion started: 20 May 2014
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.
Revised: 22 May 2015 – Accepted: 14 Jun 2015 – Published: 13 Jul 2015
Wimmer, D., Lehtipalo, K., Nieminen, T., Duplissy, J., Ehrhart, S., Almeida, J., Rondo, L., Franchin, A., Kreissl, F., Bianchi, F., Manninen, H. E., Kulmala, M., Curtius, J., and Petäjä, T.: Technical Note: Using DEG-CPCs at upper tropospheric temperatures, Atmos. Chem. Phys., 15, 7547-7555, doi:10.5194/acp-15-7547-2015, 2015.