Piotr Kupiszewski

Measurements of Ice Nucleating Particles and Ice Residuals

AbstractIt has been known that aerosol particles act as nuclei for ice formation for over a century and a half (see Dufour). Initial attempts to understand the nature of these ice nucleating particles were optical and electron microscope inspection of inclusions at the center of a crystal (see Isono; Kumai). Only within the last few decades has instrumentation to extract ice crystals from clouds and analyze the residual material after sublimation of condensed-phase water been available (see Cziczo and Froyd). Techniques to ascertain the ice nucleating potential of atmospheric aerosols have only been in place for a similar amount of time (see DeMott et al.). In this chapter the history of measurements of ice nucleating particles, both in the field and complementary studies in the laboratory, are reviewed. Remaining uncertainties and artifacts associated with measurements are described and suggestions for future areas of improvement are made.

Ice residual properties in mixed‐phase clouds at the high‐alpine Jungfraujoch site

Abstract Ice residual (IR) and total aerosol properties were measured in mixed‐phase clouds (MPCs) at the high‐alpine Jungfraujoch research station. Black carbon (BC) content and coating thickness of BC‐containing particles were determined using single‐particle soot photometers. The ice activated fraction (IAF), derived from a comparison of IR and total aerosol particle size distributions, showed an enrichment of large particles in the IR, with an increase in the IAF from values on the order of 10−4 to 10−3 for 100 nm (diameter) particles to 0.2 to 0.3 for 1 μm (diameter) particles. Nonetheless, due to the high number fraction of submicrometer particles with respect to total particle number, IR size distributions were still dominated by the submicrometer aerosol. A comparison of simultaneously measured number size distributions of BC‐free and BC‐containing IR and total aerosol particles showed depletion of BC by number in the IR, suggesting that BC does not play a significant role in ice nucleation in MPCs at the Jungfraujoch. The potential anthropogenic climate impact of BC via the glaciation effect in MPCs is therefore likely to be negligible at this site and in environments with similar meteorological conditions and a similar aerosol population. The IAF of the BC‐containing particles also increased with total particle size, in a similar manner as for the BC‐free particles, but on a level 1 order of magnitude lower. Furthermore, BC‐containing IR were found to have a thicker coating than the BC‐containing total aerosol, suggesting the importance of atmospheric aging for ice nucleation.