Chemical and Physical Transformations of Aluminosilicate Clay Minerals Due to Acid Treatment and Consequences for Heterogeneous Ice Nucleation

Abstract

Mineral dust aerosol is one of the largest contributors to global ice nuclei, but physical and chemical processing of dust during atmospheric transport can alter its ice nucleation activity. In particular, several recent studies have noted that sulfuric and nitric acids inhibit heterogeneous ice nucleation in the regime below liquid water saturation in aluminosilicate clay minerals. We have exposed kaolinite, KGa-1b and KGa-2, and montmorillonite, STx-1b and SWy-2, to aqueous sulfuric and nitric acid to determine the physical and chemical changes that are responsible for the observed deactivation. To characterize the changes to the samples upon acid treatment, we use X-ray diffraction, transmission electron microscopy, and inductively coupled plasma-atomic emission spectroscopy. We find that the reaction of kaolinite and montmorillonite with aqueous sulfuric acid results in the formation of hydrated aluminum sulfate. In addition, sulfuric and nitric acids induce large structural changes in montmorillonite. We additionally report the supersaturation with respect to ice required for the onset of ice nucleation for these acid-treated species. On the basis of lattice spacing arguments, we explain how the chemical and physical changes observed upon acid treatment could lead to the observed reduction in ice nucleation activity.

Deposition and immersion-mode nucleation of ice by three distinct samples of volcanic ash

“…The present experiment used to study depositional ice nucleation has been described previously; however, this paper represents our first measurements of immersion freezing. For the depositional nucleation experiments, the results are compared to previous results using the same system for the clay mineral kaolinite (KGa-1b, Sihvonen et al, 2014), which is generally thought to be an efficient depositional ice nucleus (Hoose and Möhler, 2012). For the immersion freezing experiments, the Raman microscope cold stage was validated using the same, standard kaolinite sample (Murray et al, 2011;Pinti et al, 2012).…”

“…It can be seen that all three ash samples exhibit minimal temperature dependence (Koop et al, 2000). Also included are onset results from depositional ice nucleation experiments on ash from the 2010 Eyjafjallajökull eruption (Hoyle et al, 2011;Steinke et al, 2011) and a parameterization for depositional ice nucleation on KGa-1b (Sihvonen et al, 2014).…”

“…Here, even the Icelandic ash has similar ice nucleation activity to the three types of ash used in this study. To further highlight their depositional ice nucleation efficiency, a parameterization of the critical ice saturation ratio of kaolinite from a previous study (Sihvonen et al, 2014) has also been added to Fig. 4.…”

Direct observation of ice nucleation events on individual atmospheric particles

“…[12][13][14][15][16][17][18] Hence, it represents a significant improvement over more commonly used optical microscopy (OM) approaches. [19][20][21][22][23][24][25] Complemented with X-rays microanalysis, ESEM has the potential to conduct microscopy studies of ice nucleation along with chemical characterization of the INPs. Currently, the limiting factor for ESEM ice nucleation experiments is the ability to accurately control temperature and relative humidity (RH) above the sample over a broad range of freezing temperatures.…”

On Modulating Interfacial Structure towards Improved Anti-Icing Performance

“…Additionally, the degree of substrate surface charge would control concentration and distribution of ions close to interfaces where ice accretion would occur, and hence influence the interfacial water structure. Traditionally, the role of ions in ice nucleation has been studied in atmospheric and geochemical contexts [181][182][183] and there is ambiguity in the exact mechanisms of ion-mediated ice nucleation [184][185][186][187]. Close to the interface, depending on local fields, the oxygens can point up or down (measured as a vector from hydrogen to oxygen), leading to variations in local structure and differentials in coordination geometry of ice formations (hexagonal vs. tetrahedral) [87,103,188].…”