An Improved Filter Technique for Ice Nucleus Measurements

Abstract

No satisfactory standard field method has been established for the measurement of ice nucleus concentrations, although the filter technique is a promising candidate if the tendency for ice nucleus concentrations to decrease as the sample volume increases can be explained or eliminated. For this study, an improved ventilation (dynamic) chamber system for the development of exposed filter was developed and tested. The concentrations of natural ice nuclei obtained from the new dynamic chamber are compared with those simultaneously obtained from a static diffusion chamber system. The volume effect showed up in the results of the static chamber method, but disappeared in the results of the new dynamic system. To confirm the cited of ventilation flow, sample filters of two different artificial ice nuclei, silver iodide and metaldehyde, mixed either with or without sodium chloride particles (a hygroscopic material) were developed. The measured concentrations of artificial ice nuclei, whether mixed with or without hygroscopic material, were of the same order of magnitude. The consistency in measured concentrations of natural and artificial ice nuclei suggests that the volume effect can be eliminated with the new dynamic chamber technique.