BINARY: an optical freezing array for assessing temperature and time dependence of heterogeneous ice nucleation

Abstract

A new optical freezing array for the study of heterogeneous ice nucleation in microliter-sized droplets is introduced, tested and applied to the study of immersion freezing in aqueous Snomax ® suspensions. In the Bielefeld Ice Nucleation ARraY (BINARY) ice nucleation can be studied simultaneously in 36 droplets at temperatures down to −40 • C (233 K) and at cooling rates between 0.1 and 10 K min −1 . The droplets are separated from each other in individual compartments, thus preventing a Wegener-Bergeron-Findeisen type water vapor transfer between droplets as well as avoiding the seeding of neighboring droplets by formation and surface growth of frost halos. Analysis of freezing and melting occurs via an automated real-time image analysis of the optical brightness of each individual droplet. As an application ice nucleation in water droplets containing Snomax ® at concentrations from 1 ng mL −1 to 1 mg mL −1 was investigated. Using different cooling rates, a small time dependence of ice nucleation induced by two different classes of ice nucleators (INs) contained in Snomax ® was detected and the corresponding heterogeneous ice nucleation rate coefficient was quantified. The observed time dependence is smaller than those of other types of INs reported in the literature, suggesting that the BI-NARY setup is suitable for quantifying time dependence for most other INs of atmospheric interest, making it a useful tool for future investigations.

Intercomparing different devices for the investigation of ice nucleating particles using Snomax<sup>®</sup> as test substance

“…A slight time dependence of the ice nucleation process for Snomax can be observed (as discussed in detail in Budke and Koop, 2015). But as a change of the nucleation time of a factor of 10 shifts the freezing curve by roughly only 0.3 K (and a factor of 100 by 0.6 K etc.…”

“…This indicates that the group III protein complexes responsible for inducing the observed ice nucleation are all comparably similar in their ice nucleation ability. Furthermore, it was recently shown that ice nucleation by Snomax shows only a very small time dependence at cooling rates comparable to the current intercomparison (Budke and Koop, 2015), and hence a time-independent treatment of the freezing process seems justifiable. It was clearly shown in Hartmann et al (2013), that the number of ice nucleation active macromolecules (INM) (i.e., the protein complexes) scaled with the volume of the examined particles, and therefore also with the mass of Snomax present in a droplet.…”

“…The BINARY (Bielefeld Ice Nucleation ARraY) setup consists of an array of 36 microliter-sized droplets positioned on a thin hydrophobic glass surface placed on a Peltier cooling stage (Budke and Koop, 2015). With the Peltier stage connected to a sink bath at 5 • C, the droplets can be cooled to −40 • C at cooling rates between 0.1 and 10 • C min −1 .…”

Refreeze experiments with water droplets containing different types of ice nuclei interpreted by classical nucleation theory

“…Finally, A crit,het for the nonadecanol samples decrease from 16.1 to 27.2 nm 2 for the r = 1100 µm droplets with T fr = 260-265 K, to 13.2-21.6 nm 2 for the r = 370/320 µm droplets with T fr = 256-262 K, and finally to A crit,het = 10.4-16.1 nm 2 for the r = 48/31 µm droplets with T fr = 248-252 K. These critical site areas show a temperature dependence and are larger at higher temperatures. They are in the same size range as the ice nucleation active area of proteins expressed by the bacteria Pseudomonas syringae (P. syringae) and Erwinia herbicola, which are active at 263-265 K and have a mass of 150 kDa (Yankofsky et al, 1981;Govindarajan and Lindow, 1988;Budke and Koop, 2015;Pandey et al, 2016). Kajava and Lindow (1993) determined the area of the minimum ice-nucleating site of P. Syringae as 25 nm × 2.5 nm = 62.5 nm 2 , corresponding to the area on the protein that shows a lattice match with ice.…”

Ice nucleation efficiency of AgI: review and new insights

“…8916 C. Marcolli et al: Ice nucleation efficiency of AgI by a monolayer of long-chain alcohols forming 2-D crystals with close lattice matches to ice (Popovitz-Biro et al, 1994;Majewski et al, 1995;Cantrell and Robinson, 2006;Zobrist et al, 2007;Knopf and Forrester, 2011). Ice active proteins expressed by the bacteria Pseudomonas syringae (P. Syringae) and Erwinia herbicola, which are ice active up to 271 K, possess sites with a close fit to the ice lattice (Kajava and Lindow, 1993;Yankofsky et al, 1981;Govindarajan and Lindow, 1988;Budke and Koop, 2015). Therefore, a good ice lattice match with ice seems to be one of the properties that promotes ice nucleation, but it is certainly not the only one.…”