Abstract
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.
Highlights
Condensation particle counters (CPCs) measure the total number concentration of aerosol particles by activating and growing them with a supersaturated vapour
Due to the huge scatter and large error bars a number of the red data points seem to indicate a small cut-off at 208.15 K, but the majority of the data points below 2 nm are at 0 and the fit shows that the cut-off relative to a particle size magnifier (PSM) is shifted
We investigated the performance of the diethylene glycol (DEG)-based CPC under temperatures typical for the upper troposphere by performing a set of calibration measurements at temperatures between 248.15 and 208.15 K
Summary
Condensation particle counters (CPCs) measure the total number concentration of aerosol particles by activating and growing them with a supersaturated vapour. CPCs provide information about the total particle concentration above a certain size. The parameter used to describe the performance of a CPC is the cut-off diameter, which is defined as the diameter at which the particles are counted with 50 % efficiency. By using several CPCs with different cut-off diameters, additional information such as the growth rates can be retrieved (Riipinen et al, 2007; Riccobono et al, 2012; Lehtipalo et al, 2014). CPCs capable of measuring reliably in the size range below 3 nm have been developed only recently (Kuang et al, 2012a, b; Vanhanen et al, 2011; Sipilä et al, 2009). The work presented here focuses on ultrafine CPCs using diethylene glycol (DEG) as condensing liquid, which has Published by Copernicus Publications on behalf of the European Geosciences Union
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