AN ANALYSIS OF THE FILTER DIFFUSION CHAMBER AND DROP FREEZING METHODS OF DETERMINING ICE NUCLEUS CONCENTRATIONS

The membrane filters used for sampling at a height of 60 m and at ground level were processed with a drop freezing technique and a static vapor-diffusion chamber. Comparisons of IN concentrations obtained by the two techniques are made. The blank filter counts and ice nucleus measurement reproducibility are analysed. The factors affecting IN concentration measurements are discussed and some favorable operation conditions are suggested. It has been found that: (a) the IN concentrations typically range from 0.2 L-1 to 2.0 L-1 at -20oC, (b) significant time variations in IN concentrations occurs, (c) the IN concentra-tions obtained by the drop freezing technique typically exceed the value given by the diffusion chamber, (d) their variation trends are generally in phase, (e) high IN concentrations are often associated with pre-cipitation events.