Influence of particle size on the ice nucleating ability of mineral dusts

Abstract

The recently developed Zurich Ice Nucleation Chamber (ZINC) was used to explore ice nucleation of size-selected mineral dust particles at temperatures between −20 • C and −55 • C. Four different mineral dust species have been tested: montmorillonite, kaolinite, illite and Arizona test dust (ATD). The selected particle diameters are 100 nm, 200 nm, 400 nm and 800 nm. Relative humidities with respect to ice (RH i ) required to activate 1% of the dust particles as ice nuclei (IN) are reported as a function of temperature. An explicit size dependence of the ice formation efficiency has been observed for all dust types. 800 nm particles required the lowest RH i to activate. Deposition nucleation below water saturation was found only below −30 • C or −35 • C dependent on particle size. Minimum RH i for 1% activation were 105% for illite, kaolinite and montmorillonite at −40 • C, respectively 110% for ATD at −45 • C. In addition, a possible parameterisation for the measured activation spectra is proposed, which could be used in modeling studies.

A comprehensive laboratory study on the immersion freezing behavior of illite NX particles: a comparison of 17 ice nucleation measurement techniques

“…The role of IN modes upon the estimation of n s was also examined across various temperature ranges. The EDB-based method was used to measure the contact and immersion mode efficiencies of size segregated dry illite NX particles around −30 • C. Immersion freezing results from IMCA-ZINC were compared to previously reported ZINC data (Welti et al, 2009) at temperatures below −31 • C and to PINC data for temperatures below −26 • C. In the present study, we derived ZINC's n s values from the results reported in Welti et al (2009). Specifically, ice formation above 105 % RH w up to the water drop survival line was used to calculate n s based on given illite NX particle sizes.…”

“…In this figure, panels i, ii and iii show T -binned data averaged in the linear space of all 17 instruments, all suspension type measurements, and all measurements that involved dry particles, respectively, while panel iv shows a comparison between suspension and dryparticle measurements. We note that the data from "EDB (contact)" and "ZINC" (Welti et al, 2009) were not used for generating T -binned data since our focus was on immersion mode freezing. We also note that the n s results from nine IN measurement techniques provide n s data at −23 and −24 • C, where we find an abrupt increase in log(n s )/ T and n s deviations.…”

“…In this work, we distributed illite NX samples from the same batch [with the exceptions of the samples used for Leeds-NIPI, ZINC and IMCA-ZINC (acronyms are defined in the Supplement Sect. S4); Broadley et al, 2012;Welti et al, 2009] among the INUIT project and associated partners. With a total of 17 different IN measuring instruments, we intercompared IN data from each instrument in order to obtain a comprehensive data set for evaluating immersion freezing properties of illite NX particles.…”

A new temperature- and humidity-dependent surface site density approach for deposition ice nucleation

“…Mineral dust acts as an ice nucleus over a wide range of temperatures and supersaturations over ice, with the most active dusts nucleating ice at approximately 260 K (Welti et al, 2009;Eastwood et al, 2009;Hoose and Möhler, 2012;Murray et al, 2012;YakobiHancock et al, 2013). Using numerical modeling to estimate the climate impact of mineral dust through ice formation requires relations which connect aerosol properties, thermodynamic variables and resulting ice crystal concentrations.…”

“…INAS densities were also derived from ice fractions f ice observed in studies investigating the deposition nucleation mode properties of monodisperse ATD particles (Koehler et al, 2010;Sullivan et al, 2010;Welti et al, 2009) with…”