Feldspar minerals as efficient deposition ice nuclei

Abstract

Mineral dusts are well known to be efficient ice nuclei, where the source of this efficiency has typically been attributed to the presence of clay minerals such as illite and kaolinite. However, the ice nucleating abilities of the more minor mineralogical components have not been as extensively examined. As a result, the deposition ice nucleation abilities of 24 atmospherically-relevant mineral samples have been studied, using a continuous flow diffusion chamber at −40.0 ± 0.3 °C. The same particle size (200 nm) and particle preparation procedure were used throughout. The ice nucleation behaviour of the pure minerals is compared to that of complex mixtures, such as Arizona Test Dust (ATD) and Mojave Desert Dust (MDD), and to lead iodide, which has been previously proposed for cloud seeding. Lead iodide was the most efficient ice nucleus (IN), requiring a critical relative humidity with respect to ice (RH_i) of 122.0 ± 2.0% to activate 0.1% of the particles. MDD (RH_i 126.3 ± 3.4%) and ATD (RH_i 129.5 ± 5.1%) have lower but comparable activity. From a set of clay minerals (kaolinite, illite, montmorillonite), non-clay minerals (e.g. hematite, magnetite, calcite, cerussite, quartz), and feldspar minerals (orthoclase, plagioclase) present in the atmospheric dusts it was found that the feldspar minerals (particularly orthoclase), and not the clays, were the most efficient ice nuclei. Orthoclase and plagioclase were found to have critical RH_i values of 127.1 ± 6.3% and 136.2 ± 1.3%, respectively. The presence of feldspars (specifically orthoclase) may play a significant role in the IN behaviour of mineral dusts despite their lower percentage in composition relative to clay minerals

Factors controlling the ice nucleating abilities of α‐pinene SOA particles

“…First, although cooled SOA‐WSOC particles were found to be IN in the deposition nucleation mode, their S 0.1% values are still somewhat higher than those of other materials recognized as efficient IN. For example, using exactly the same experimental approach, our group has recently studied several mineral dust particles such as Arizona test dust, Mojave Desert dust, and feldspar‐containing substrates and shown that they are able to nucleate ice via deposition nucleation at S 0.1% values between 1.30 and 1.40 at temperatures similar to this study [ Yakobi‐Hancock et al , ]. Similarly, the review of Hoose and Möhler [] has demonstrated that many other materials, including Snomax and solid AS, can nucleate ice via deposition nucleation at low ice supersaturations and low temperatures.…”

Identification of Ice Nucleation Active Sites on Feldspar Dust Particles

“…Recently Atkinson et al 24 performed the first comparative study on ice nucleation in the immersion mode looking not only at single minerals from the clay group but also at K-feldspar, Na/Ca-feldspar, quartz, and calcite as well. Almost simultaneously Yakobi-Hanock et al 25 conducted a similar study on ice nucleation of 24 mineral samples in the deposition mode. Both studies find the ice nucleating ability of K-feldspar exceptionally high compared to other minerals.…”

Ice nucleation of bare and sulfuric acid‐coated mineral dust particles and implication for cloud properties

“…In summary, our observations show that the acid treatment caused structural deformation or disorderliness in four dust test samples (ATD, illite, montmorillonite, and K‐feldspar) (Figure and Table ), but the acid treatment did not modify the structural properties of the quartz particles (Figure S1 and Table ). Acid treatment affected the K‐feldspar group minerals (albite, orthoclase, and anorthite; Figure ), which are suggested to be the important ice nucleating minerals for atmospheric ice nucleation [ Atkinson et al ., ; Yakobi‐Hancock et al ., ]. The peak intensities of the orthoclase and albite minerals were reduced in ATD, whereas the orthoclase from illite was completely lost.…”