Characterization of a modified expansion condensation particle counter for detection of nanometer-sized particles

Abstract

A newly developed condensation particle counter provides measurements of aerosol particle number densities for size diameters as low as 3 nm. This Expansion Condensation Particle Counter (ECPC) operates based on fast adiabatic expansion with specialized detection and evaluation of the temporal development of light scattered by the ensemble of growing droplets. In its new configuration the ECPC has been modified such that a previously needed calibration factor became obsolete. In this article the new design is described which now includes a fast pressure sensor for monitoring the pressure drop inside the measurement chamber. Extensive laboratory experiments for characterizing the ECPC are described where sulfuric acid droplets with diameters between 2.5 nm and 23 nm have been utilized. Water as well as butanol are demonstrated to be suitable working fluids. One experiment using tungsten oxide (WOx) particles shows that a 50% cut-off size diameter as low as 2.5 nm can be reached for this ECPC with a detection efficiency of several percent for particles as small as 1.4 nm. High and low supersaturations are experimentally examined and the corresponding different cut-off sizes are obtained. Measurements of ambient urban air in Mainz (Germany) obtained by this ECPC are juxtaposed to those from a TSI UCPC 3025A with satisfactory agreement. Similarly, in-situ data recorded with two ECPC units in the city of Isfahan (Iran) are shown to demonstrate the suitability of the technique for traffic related pollution measurements. Also, in future applications coarse information on the chemical nature of nucleated particles can be obtained by simultaneously using various condensing liquids in different channels of the ECPC setup.