Stochastic nucleation processes and substrate abundance explain time-dependent freezing in supercooled droplets

Abstract

Atmospheric immersion freezing (IF), a heterogeneous ice nucleation process where an ice nucleating particle (INP) is immersed in supercooled water, is a dominant ice formation pathway impacting the hydrological cycle and climate. Implementation of IF derived from field and laboratory data in cloud and climate models is difficult due to the high variability in spatio-temporal scales, INP composition, and morphological complexity. We demonstrate that IF can be consistently described by a stochastic nucleation process accounting for uncertainties in the INP surface area. This approach accounts for time-dependent freezing, a wide range of surface areas and challenges phenomenological descriptions typically used to interpret IF. The results have an immediate impact on the current description, interpretation, and experiments of IF and its implementation in models. The findings are in accord with nucleation theory, and thus should hold for any supercooled liquid material that nucleates in contact with a substrate.

On-chip analysis of atmospheric ice-nucleating particles in continuous flow

“…Further samples were collected independently during the field campaign using a micro-orifice uniform deposition impactor (MOUDI), and then analysed using the batch microfluidic "WeIzmann Supercooled Droplets Observation on a Microarray" (WISDOM) droplet freezing assay instrument. 71 WISDOM has previously been employed for the analysis of the ice-nucleating activity of size-resolved desert dust aerosol in the local region, 71,104 time-dependent freezing, 105 secondary ice processes in clouds, 106 the study of antifreeze proteins, 107 and the study of ice-binding proteins. 108 Briefly, samples were collected onto polycarbonate filters for ∼8 h and washed into suspension using water.…”

A pyroelectric thermal sensor for automated ice nucleation detection

“…There are also errors associated with the masses of K-feldspar and water when making suspensions, the volume of each droplet pipetted, and the amount of material which settled out of suspension during pipetting (Tarn et al, 2018). These are particularly important for small droplet volumes and low concentrations (Knopf et al, 2020;Beydoun et al, 2016); however, due to the relatively large droplet volumes used here they are insignificant compared to surface area per mass error.…”

“…At lower temperatures there are few liquid droplets remaining, leading to a breakdown in the approximation that Eqs. (1) and (3) is based on, that n/n remains small (Koop et al, 1997). Also, as the temperature falls the probability that there would be multiple nucleation events in a single droplet increases (Atkinson et al, 2016).…”

Mineral and biological ice-nucleating particles above the South East of the British Isles

“…Hence, large variability in the surface area of the aerosol per droplet can lead to signicant biases when calculating magnitudes such as the INP concentration using droplet-based assays. 66 In the Sect. S1, † we use Monte Carlo simulations to show the distribution of surface area through the droplet populations of our experiments for one of our samples.…”