Ice nucleation efficiency of clay minerals in the immersion mode

Abstract

Emulsion and bulk freezing experiments were performed to investigate immersion ice nucleation on clay minerals in pure water, using various kaolinites, montmorillonites, illites as well as natural dust from the Hoggar Mountains in the Saharan region. DSC (differential scanning calorimeter) measurements were performed on the kaolinites KGa-1b and KGa-2 from the Clay Mineral Society and kaolinite from Sigma-Aldrich; the montmorillonites SWy-2 and STx-1b from the Clay Mineral Society and the acid treated montmorillonites KSF and K-10 from Sigma Aldrich; the illites NX and SE from Arginotec. The emulsion experiments provide information on the average freezing behaviour characterized by the average nucleation sites. These experiments revealed one to two distinct heterogeneous freezing peaks, which suggest the presence of a low number of qualitatively distinct average nucleation site classes. We refer to the peak at the lowest temperature as "standard peak" and to the one at higher temperatures as "special peak". Conversely, freezing in bulk samples is not initiated by the average nucleation sites, but by a very low number of "best sites". The kaolinites showed quite narrow standard peaks with onset temperatures 239 K < <i>T</i><sub>on</sub><sup>std</sup> < 242 K and best sites with averaged median freezing temperature <i>T</i><sub>med</sub><sup>best</sup> = 257 K. Only the kaolinite from Sigma Aldrich featured a special peak with freezing onset at 248 K. The illites showed broad standard peaks with freezing onsets at 244 K < <i>T</i><sub>on</sub><sup>std</sup> < 246 K and best sites with averaged median freezing temperature <i>T</i><sub>med</sub><sup>best</sup> = 262 K. Montmorillonites had standard peaks with onsets 238 K < <i>T</i><sub>on</sub><sup>std</sup> < 240 K and best sites with <i>T</i><sub>med</sub><sup>best</sup>=257 K. SWy-2, M K10, and KSF featured special peaks with onsets at <i>T</i><sub>on</sub><sup>spcl</sup>=247, 240, and 242 K, respectively. M K10 and KSF both from Sigma Aldrich had less intense standard peaks compared to the ones from the Clay Mineral Society suggesting that a fraction of the standard sites are lost by the acid treatment. The acid treatment had however, no evident effect on best sites. Our investigations demonstrate that immersion freezing temperatures of clay minerals strongly depend on the amount of clay mineral present per droplet and on the exact type (location of collection and pre-treatment) of the clay mineral. We suggest that apparently contradictory results obtained by different groups with different setups can indeed be brought into good agreement when only clay minerals of the same type and amount per droplet are compared. The natural sample from the Hoggar Mountai...

On the representation of immersion and condensation freezing in cloud models using different nucleation schemes

“…Many laboratory studies and observations have shown that heterogeneous freezing occurs at higher temperatures (e.g., DeMott et al, 2003;McFarquhar et al, 2007;Chen et al, 2008;Niemand et al, 2012;Pinti et al, 2012). However, for IN freezing at these higher temperatures a consistent set of parameters for all five schemes as derived for kaolinite is not available.…”

Compositional and Mineralogical Effects on Ice Nucleation Activity of Volcanic Ash

“…Kaolinite is found to be efficient in the immersion mode using the cold stage method [55,56]. K-feldspars and quartz were found to be the two most efficient immersion INPs in mineral dust even though they were found in low weight percentages in samples [29].…”

Immersion Freezing of Kaolinite: Scaling with Particle Surface Area

“…In more recent experiments, improvements could be achieved as the particle surface area was determined and taken into account for the interpretation of the immersion freezing results (Connolly et al 2009;Niedermeier et al 2010;Sullivan et al 2010;Niedermeier et al 2011b;Augustin-Bauditz et al 2014;Zolles et al 2015). Other experiments examined the immersion freezing of droplets with varying particle sizes or particle loads: Archuleta et al (2005), Marcolli et al (2007), Welti et al (2009), Lüönd et al (2010), Welti et al (2012), and Pinti et al (2012) reported an increasing freezing probability with increased available particle surface area. In other words, the dependence of immersion freezing on the particle surface area was shown on a qualitative basis.…”