Counting efficiency and detection limit of condensation nuclei counters for submicrometer aerosols: II. Measurements with monodisperse hydrophobic Ag and hygroscopic NaCl aerosols with particle diameters between 2 and 100 nm

Abstract

Submicrometer hydrophobic Ag and hygroscopic NaCl aerosols with particle diameters between 2 and 100 nm are generated by means of a condensation aerosol generator and a differential mobility analyzer. Particle size, size distribution, and shape are examined by means of the transmission electron microscopy and diffusion batteries. The aerosol concentration is absolutely determined by means of an aerosol filter electrometer. The counting efficiency of three condensation nuclei counters (GE-CNC1, GE-CNC2, and photographic CNC) are measured down to particle sizes of 2 nm and the influence of particle charge and concentration is tested. The results of counting efficiency and detection limit for hydrophobic Ag and hygroscopic NaCl aerosols of the photographic CNC are compared to theoretical considerations of Part I (H. G. Scheibel and J. Porstendörfer, J. Colloid Interface Sci. 109, 261–274, 1986). The counting efficiency depends on wall losses and on the particle material. The results for hydrophobic Ag aerosols show satisfactory agreement with Fletcher's theory, whereas the soluble NaCl particles show deviations from the theoretical evaluations. The Kelvin curve describes in no case the counting efficiency results.