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The Microscopic Features of Heterogeneous Ice Nucleation May Affect the Macroscopic Morphology of Atmospheric Ice Crystals  [PDF]
Stephen J. Cox,Zamaan Raza,Shawn M. Kathmann,Ben Slater,Angelos Michaelides
Physics , 2014, DOI: 10.1039/C3FD00059A
Abstract: It is surprisingly difficult to freeze water. Almost all ice that forms under "mild" conditions (temperatures > -40 degrees Celsius) requires the presence of a nucleating agent - a solid particle that facilitates the freezing process - such as clay mineral dust, soot or bacteria. In a computer simulation, the presence of such ice nucleating agents does not necessarily alleviate the difficulties associated with forming ice on accessible timescales. Nevertheless, in this work we present results from molecular dynamics simulations in which we systematically compare homogeneous and heterogeneous ice nucleation, using the atmospherically important clay mineral kaolinite as our model ice nucleating agent. From our simulations, we do indeed find that kaolinite is an excellent ice nucleating agent but that contrary to conventional thought, non-basal faces of ice can nucleate at the basal face of kaolinite. We see that in the liquid phase, the kaolinite surface has a drastic effect on the density profile of water, with water forming a dense, tightly bound first contact layer. Monitoring the time evolution of the water density reveals that changes away from the interface may play an important role in the nucleation mechanism. The findings from this work suggest that heterogeneous ice nucleating agents may not only enhance the ice nucleation rate, but also alter the macroscopic structure of the ice crystals that form.
Mechanisms of Dendrites Occurrence during Crystallization: Features of the Ice Crystals Formation  [PDF]
Mark E. Perel'man,Galina M. Rubinstein,Vitali A. Tatartchenko
Physics , 2007, DOI: 10.1016/j.physleta.2008.03.009
Abstract: Dendrites formation in the course of crystallization presents very general phenomenon, which is analyzed in details via the example of ice crystals growth in deionized water. Neutral molecules of water on the surface are combined into the double electric layer (DEL) of oriented dipoles; its field reorients approaching dipoles with observable radio-emission in the range of 150 kHz. The predominant attraction of oriented dipoles to points of gradients of this field induces dendrites growth from them, e.g. formation of characteristic form of snowflakes at free movement of clusters through saturated vapor in atmosphere. The constant electric field strengthens DELs' field and the growth of dendrites. Described phenomena should appear at crystallization of various substances with dipole molecules, features of radio-emission can allow the monitoring of certain processes in atmosphere and in technological processes. Crystallization of particles without constant moments can be stimulated by DELs of another nature with attraction of virtual moments of particles to gradients of fields and corresponding dendrites formation.
Bacterial Ice Crystal Controlling Proteins  [PDF]
Janet S. H. Lorv,David R. Rose,Bernard R. Glick
Scientifica , 2014, DOI: 10.1155/2014/976895
Abstract: Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. 1. Introduction Throughout the planet, environmental temperatures can reach low to freezing levels. Organisms indigenous to these habitats are presented with potential desiccation, which can lead to potentially detrimental challenges such as decreased enzymatic rates, freezing, and aggregation of endogenous proteins [1, 2]. Besides hindering cellular processes, subzero temperatures induce ice formation, which can lead to cell death [3]. In some cases, intracellular ice crystals can rupture cells either physically or through osmotic pressure changes [4]. The temperature at which water freezes varies based on solution homogeneity [1]. Pure water was reported to freeze at ?40°C. On the other hand, a heterogeneous water solution can contain additional molecules, such as dust particles and ice active bacteria, that act as seeds for ice nucleation [1, 5]. In these situations, a solution can freeze at high subzero temperatures, up to ?2°C. Cellular cryodamage incurred from freezing is dependent on freezing rate and ice crystal location [1]. For intracellular ice, a flash freezing rate (e.g., ?100°C/min) minimizes potential damage while a slow rate is more detrimental [3]. Furthermore, with a slow rate of freezing, the internal ice acts as a solute drawing water into cells until they rupture. On the other hand, extracellular ice can cause membrane fracturing or shifting in osmotic pressures [6]. During external freezing, water solidification into ice removes available liquid water and concentrates extracellular solutes. This change simulates a high saline environment, drawing out internal water that is needed for cellular processes.
Heterogeneous ice nucleation controlled by the coupling of surface crystallinity and surface hydrophilicity  [PDF]
Yuanfei Bi,Raffaela Cabriolu,Tianshu Li
Physics , 2015,
Abstract: The microscopic mechanisms controlling heterogeneous ice nucleation are complex and remain poorly understood. Although good ice nucleators are generally believed to match ice lattice and to bind water, counter examples are often identified. Here we show, by advanced molecular simulations, that the heterogeneous nucleation of ice on graphitic surface is controlled by the coupling of surface crystallinity and surface hydrophilicity. Molecular level analysis reveals that the crystalline graphitic lattice with an appropriate hydrophilicity may indeed template ice basal plane by forming a strained ice layer, thus significantly enhancing its ice nucleation efficiency. Remarkably, the templating effect is found to transit from within the first contact layer of water to the second as the hydrophilicity increases, yielding an oscillating distinction between the crystalline and amorphous graphitic surfaces in their ice nucleation efficiencies. Our study sheds new light on the long-standing question of what constitutes a good ice nucleator.
On the ice nucleation spectrum
D. Barahona
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: This work presents a novel formulation of the ice nucleation spectrum, i.e. the function relating the ice crystal concentration to cloud formation conditions and aerosol properties. The new formulation is physically-based and explicitly accounts for the dependency of the ice crystal concentration on temperature, supersaturation, cooling rate, and particle size, surface area and composition. This is achieved by introducing the concepts of ice nucleation coefficient (the number of ice germs present in a particle) and nucleation probability dispersion function (the distribution of ice nucleation coefficients within the aerosol population). The new formulation is used to generate ice nucleation parameterizations for the homogeneous freezing of cloud droplets and the heterogeneous deposition ice nucleation on dust and soot ice nuclei. For homogeneous freezing, it was found that by increasing the dispersion in the droplet volume distribution the fraction of supercooled droplets in the population increases. For heterogeneous ice nucleation the new formulation consistently describes singular and stochastic behavior within a single framework. Using a fundamentally stochastic approach, both cooling rate independence and constancy of the ice nucleation fraction over time, features typically associated with singular behavior, were reproduced. Analysis of the temporal dependency of the ice nucleation spectrum suggested that experimental methods that measure the ice nucleation fraction over few seconds would tend to underestimate the ice nuclei concentration. It is shown that inferring the aerosol heterogeneous ice nucleation properties from measurements of the onset supersaturation and temperature may carry significant error as the variability in ice nucleation properties within the aerosol population is not accounted for. This work provides a simple and rigorous ice nucleation framework where theoretical predictions, laboratory measurements and field campaign data can be reconciled, and that is suitable for application in atmospheric modeling studies.
Factors influencing ice formation and growth in simulations of a mixed-phase wave cloud
C. Dearden,T. Choularton,P. R. Field,A. J. Heymsfield
Journal of Advances in Modeling Earth Systems , 2012,
Abstract: In this paper, numerical simulations of an orographically induced wave cloud sampled in-situ during the ICE-L (Ice in Clouds Experiment - Layer clouds) field campaign are performed and compared directly against the available observations along various straight and level flight paths. The simulations are based on a detailed mixed-phase bin microphysics model embedded within a 1-D column framework with the latest parameterizations for heterogeneous ice nucleation and an adaptive treatment of ice crystal growth based on the evolution of crystal habit. The study focuses on the second of two clouds sampled on 16th November 2007, the in-situ data from which exhibits some interesting and more complex microphysics than other flights from the campaign. The model is used to demonstrate the importance of both heterogeneous and homogeneous nucleation in explaining the in-situ observations of ice crystal concentration and habit, and how the ability to isolate the influence of both nucleation mechanisms helps when quantifying active IN concentrations. The aspect ratio and density of the simulated ice crystals is shown to evolve in a manner consistent with the in-situ observations along the flight track, particularly during the transition from the mixed-phase region of the cloud to the ice tail dominated by homogeneous nucleation. Some additional model runs are also performed to explore how changes in IN concentration and the value of the deposition coefficient for ice affect the competition between heterogeneous and homogeneous ice formation in the wave cloud, where the Factorial Method is used to isolate and quantify the effect of such non-linear interactions. The findings from this analysis show that the effect on homogeneous freezing rates is small, suggesting that any competition between the microphysical variables is largely overshadowed by the strong dynamical forcing of the cloud in the early stages of ice formation.
Some ice nucleation characteristics of Asian and Saharan desert dust  [PDF]
P. R. Field,O. M?hler,P. Connolly,M. Kr?mer
Atmospheric Chemistry and Physics Discussions , 2006,
Abstract: The large (7 m×4 m cylinder) AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber facility at Forschungszentrum, Karlsruhe, Germany was used to test the ice nucleating ability of two desert dust samples from the Sahara and Asia. At temperatures warmer than 40°C droplets were formed before ice crystals formed, there was no deposition nucleation observed. At temperatures colder than 40°C both dust samples exhibited dual nucleation events that were observed during the same expansion experiment. The primary nucleation event occurred at ice saturation ratios of 1.1 to 1.3 and is likely to be a deposition nucleation mode. The secondary nucleation event occurred at ice saturation ratios between 1.35 and 1.5. It is unclear whether this ice nucleation event is via a further deposition mode or a condensation mode. The activated fractions of desert dust ranged from ~5–10% at 20°C to 20–40% at temperatures colder than 40°C. There was no obvious difference between the nucleation behaviour of the two dust samples.
Parameterization of homogeneous ice nucleation for cloud and climate models based on classical nucleation theory  [PDF]
V. I. Khvorostyanov,J. A. Curry
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012, DOI: 10.5194/acp-12-9275-2012
Abstract: A new analytical parameterization of homogeneous ice nucleation is developed based on extended classical nucleation theory including new equations for the critical radii of the ice germs, free energies and nucleation rates as simultaneous functions of temperature and water saturation ratio. By representing these quantities as separable products of the analytical functions of temperature and supersaturation, analytical solutions are found for the integral-differential supersaturation equation and concentration of nucleated crystals. Parcel model simulations are used to illustrate the general behavior of various nucleation properties under various conditions, for justifications of the further key analytical simplifications, and for verification of the resulting parameterization. The final parameterization is based upon the values of the supersaturation that determines the current or maximum concentrations of the nucleated ice crystals. The crystal concentration is analytically expressed as a function of time and can be used for parameterization of homogeneous ice nucleation both in the models with small time steps and for substep parameterization in the models with large time steps. The crystal concentration is expressed analytically via the error functions or elementary functions and depends only on the fundamental atmospheric parameters and parameters of classical nucleation theory. The diffusion and kinetic limits of the new parameterization agree with previous semi-empirical parameterizations.
Single ice crystal measurements during nucleation experiments with the depolarization detector IODE
M. Nicolet, O. Stetzer, F. Lü nd, O. M hler,U. Lohmann
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2010,
Abstract: In order to determine the efficiency of different aerosol particles to nucleate ice, an Ice Optical DEpolarization detector (IODE) was developed to distinguish between water droplets and ice crystals in ice nucleation chambers. A laser beam polarized linearly (power: 50 mW, wavelength: 407 nm) is directed through the chamber. The scattered light intensity from particles is measured at a scattering angle of Θ=175° in both polarization components (parallel and perpendicular). The ratio between the perpendicular intensity over the total one yields the depolarization ratio δ. Single particle detection is possible, using a peak detection algorithm. For high particle concentrations, a real-time signal averaging method can also be run simultaneously. The IODE detector was used in connection with the Zurich ice nucleation chamber during the ICIS 2007 workshop where ice nucleation experiments were performed with several aerosol types. In presence of ice crystals, a depolarization ratio could be measured on a particle-by-particle basis. Mean values of δ ranged from 0.24 to 0.37 and agree well with theoretical calculations.
Single ice crystal measurements during nucleation experiments with the depolarization detector IODE  [PDF]
M. Nicolet,O. Stetzer,U. Lohmann,O. M?hler
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: In order to determine the efficiency of aerosol particles of several types to nucleate ice, an Ice Optical DEpolarization detector (IODE) was developed to distinguish between water droplets and ice crystals in ice nucleation chambers. A laser beam polarized linearly (power: 50 mW, wavelength: 407 nm) is directed through the chamber. The scattered light intensity from particles is measured at a scattering angle of Θ=175° in both polarization components (parallel and perpendicular). The ratio between the perpendicular intensity over the total one gives the depolarization ratio δ. Single particle detection is possible, using a peak detection algorithm. For high particle concentrations, a real-time signal averaging method can also be run simultaneously. The IODE detector was used in connection with the Zurich ice nucleation chamber during the ICIS 2007 workshop where ice nucleation experiments were performed with several aerosol types. In presence of ice crystals, peaks were detected in both channels, generating depolarization signals. Mean values of δ ranged from 0.24 to 0.37.
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