DESIGN AND CALIBRATION OF A LOW VOLUME FOG SAMPLER

The modified low volume round jet impactor consists of a Teflon inlet and a Teflon cup as impaction surface, where the fog elements are collected, form bigger drops and then flow into a receiver vessel. The sampling apparatus has been designed in order to establish constant impaction conditions and a sharp cut-off at a droplet diameter of 10 mu mn, such conditions differentiating between fog droplets and non-activated aerosol particles. The apparatus has been calibrated with monodisperse DOP aerosol as a model for water droplets at a constant flow rate of 1. 6 m**3 h** minus **1. To verify if evaporation of the collected droplets or condensation of water vapour during sampling occurs, the impactor was tested with water droplets of well-defined sodium fluorescein concentration. A field test in a dense fog showed that it is possible to collect a volume of fog-water sufficient for ion chromatographic analysis within 1 h.