The immersion mode ice nucleation behavior of mineral dusts: A comparison of different pure and surface modified dusts

Abstract

In this study we present results from immersion freezing experiments with size‐segregated mineral dust particles. Besides two already existing data sets for Arizona Test Dust (ATD), and Fluka kaolinite, we show two new data sets for illite‐NX, which consists mainly of illite, a clay mineral, and feldspar, a common crustal material. The experiments were carried out with the Leipzig Aerosol Cloud Interaction Simulator. After comparing the different dust samples, it became obvious that the freezing ability was positively correlated with the K‐feldspar content. Furthermore, a comparison of the composition of the ATD, illite‐NX, and feldspar samples suggests that within the K‐feldspars, microcline is more ice nucleation active than orthoclase. A coating with sulfuric acid leads to a decrease in the ice nucleation ability of all mineral dusts, with the effect being more pronounced for the feldspar sample.

Classification of Arctic, midlatitude and tropical clouds in the mixed-phase temperature regime

“…As the estimated INP concentration based on aerosol measurements do not show clear conditions in the Arctic (see Fig. 13), a possible explanation for the large number of Type 1a/mostly liquid clouds could be a lack of biological INP at the time and location of our Arctic measurements as predicted in a model study by Wilson et al (2015), so those clouds might not freeze at low temperatures (Shupe et al, 2008;Augustin-Bauditz et al, 2014). This might explain the lack of ice crystals, even though -possibly due to the low altitude of those warm layers (see Fig.…”

“…The WBF process depends on the presence of INPs (or seed ice from higher cloud layers), which are likely available in higher quantities at midlatitudes than in the Arctic (compare Sect. 3.5.1 (Augustin-Bauditz et al, 2014;Kanji et al, 2017). In addition, the increasing fraction of Type 2/WBF clouds with decreasing temperature reflects the fact that the colder the environment, the higher the probability that the RH w falls below 100 %: with decreasing temperature, more and more droplets freeze and exploit the gas phase water when they grow.…”

“…Kanji et al (2017) and references therein. Biological particles are known to induce ice nucleation in the temperature range between about 0 and −20 • C (273 to 253 K), while mineral dust particles initiate ice at temperatures below about −20 • C Augustin-Bauditz et al, 2014).…”

Enhanced ice nucleation efficiency of microcline immersed in dilute NH<sub>3</sub> and NH<sub>4</sub><sup>+</sup>-containing solutions

“…In contrast to ∆ = const, several other studies conducted with clay minerals and ATD coated with sulfuric acid Chernoff and Bertram, 2010;Sullivan et al, 2010a;Augustin-Bauditz et al, 2014), reported a deterioration/inhibition of 100 IN efficiency of dust particles caused by an organic and/or inorganic coating/treatment. The reduction in the IN efficiency could possibly be attributable to surface deterioration from acid treatment resulting in destruction of the active sites.…”

“…The presence of additional external cations in a salt solution introduces competition in the cation exchange. The hydrated size of the externally introduced cations, the stability of surface complexes and the pH of the solution are factors that govern the cation-exchange selectivity of the aluminosilicate 240 surface (Garrels and Howard, 1959;Petrović et al, 1976;Auerbach et al, 2003;Ohlin et al, 2010;Belchinskaya et al, 2013). ] has reached a value of 1, with the exception of (NH4)2SO4 solutions.…”