The role of activated salts in ice nucleation

When an ice crystal is born from liquid water, two key changes occur: (i) The molecules order and (ii) the mobility of the molecules drops as they adopt their lattice positions. Most research on ice nucleation (and crystallization in general) has focused on understanding the former with less attention paid to the latter. However, supercooled water exhibits fascinating and complex dynamical behavior, most notably dynamical heterogeneity (DH), a phenomenon where spatially separated domains of relatively mobile and immobile particles coexist. Strikingly, the microscopic connection between the DH of water and the nucleation of ice has yet to be unraveled directly at the molecular level. Here we tackle this issue via computer simulations which reveal that (i) ice nucleation occurs in low-mobility regions of the liquid, (ii) there is a dynamical incubation period in which the mobility of the molecules drops before any ice-like ordering, and (iii) ice-like clusters cause arrested dynamics in surrounding water molecules. With this we establish a clear connection between dynamics and nucleation. We anticipate that our findings will pave the way for the examination of the role of dynamical heterogeneities in heterogeneous and solution-based nucleation.

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Mechanism of Phase Inversion in Arctic Stratiform Clouds

10.5194/egusphere-egu2020-4541 ◽

2020 ◽

Author(s):

Pei-Hsin Liu ◽

Jen-Ping Chen ◽

Xiquan Dong ◽

Yi-Chiu Lin

Keyword(s):

Phase Inversion ◽

Model Simulation ◽

Wrf Model ◽

Vertical Gradient ◽

Temperature Inversion ◽

Ice Nucleation ◽

Number Concentration ◽

Strong Inversion ◽

Stratiform Clouds

<p>Arctic stratiform clouds (ASC) often exhibit phase inversion structure (i.e., liquid top and mixed- or ice-phase below) and can persist for a very long time. According to past studies, the phase inversion structure is the result of persistent liquid cloud generation aloft and gravitational ice precipitation; however, observation reveals that the largest cloud reflectivity appears in the middle of the cloud, implying that the gravitational ice precipitation cannot fully explain the mechanism of phase inversion structure. Also, the role of ice nucleation in ASC is not fully addressed before. Ice nucleation processes are affected by temperature, ice nuclei (IN) species and number concentration. As the result, strong inversion or strong vertical gradient of IN number concentration may favor ice nucleation to occur in the lower levels and result in phase inversion.</p><p>This study aims to find out the mechanism of phase inversion and the dominant ice nucleation processes in ASC. Weather Research and Forecasting (WRF) model with detailed ice nucleation mechanisms is applied. The ice nucleation scheme used in the model takes different ice nucleation processes and IN species into account. Dust and soot, taken from MERRA-2, are the two main IN considered in this study and are fitted into lognormal distributions for providing the initial and boundary conditions. The 2008 Mar 04-05 case, chosen from the Atmospheric Radiation Measurement (ARM) program, is simulated. From observation, ASC and the phase inversion structure persisted for half a day. Temperature decreases with height in cloud, indicating that temperature inversion is not the mechanism of phase inversion in this case. More dust in the lower levels is seen from the model simulation results. In this case, strong vertical gradient of IN number concentration serves as the main mechanism of phase inversion, suggesting that ice nucleation process plays an important role in ASC. The role of soot particles will also be addressed.</p>

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Role of the electric double layer in the ice nucleation of water droplets under an electric field

Atmospheric Research ◽

10.1016/j.atmosres.2016.04.001 ◽

2016 ◽

Vol 178-179 ◽

pp. 150-154 ◽

Cited By ~ 11

Author(s):

Xiang-Xiong Zhang ◽

Xin-Hao Li ◽

Min Chen

Keyword(s):

Electric Field ◽

Double Layer ◽

Electric Double Layer ◽

Ice Nucleation ◽

Water Droplets

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The Role of Ice Nucleation-active Bacteria on Frost Damage of Tea Plants.

Japanese Journal of Phytopathology ◽

10.3186/jjphytopath.59.535 ◽

1993 ◽

Vol 59 (5) ◽

pp. 535-543 ◽

Cited By ~ 3

Author(s):

Masao GOTO ◽

Masahiko KOMABA ◽

Tomohiro HORIKAWA ◽

Noriyuki NAKAMURA

Keyword(s):

Frost Damage ◽

Ice Nucleation ◽

Active Bacteria ◽

Tea Plants

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The Role of Contact Angle and Pore Width on Pore Condensation and Freezing

10.5194/acp-2019-1019 ◽

2019 ◽

Cited By ~ 2

Author(s):

Robert O. David ◽

Jonas Fahrni ◽

Claudia Marcolli ◽

Fabian Mahrt ◽

Dominik Brühwiler ◽

...

Keyword(s):

Contact Angle ◽

Active Sites ◽

Water Saturation ◽

Capillary Condensation ◽

Contact Angles ◽

Ice Nucleation ◽

Pore Width ◽

Kelvin Effect ◽

Pore Condensation

Abstract. It has recently been shown that pore condensation and freezing (PCF) is a mechanism responsible for ice formation under cirrus cloud conditions. PCF is defined as the condensation of liquid water in narrow capillaries below water saturation due to the Kelvin effect, followed by either heterogeneous or homogeneous nucleation depending on the temperature regime and presence of an ice nucleating active site. By using sol-gel synthesized silica with well-defined pore diameters, morphology and distinct chemical surface-functionalization, the role of the water-silica contact angle and pore width on PCF is investigated. We find that contact angle and pore width play an important role in determining the relative humidity required for capillary condensation as predicted by the Kelvin effect and subsequent ice nucleation at cirrus temperatures. For the pore diameters and contact angles covered in this study, 2.2–9.2 nm and 15–78°, respectively, our results reveal that the contact angle plays an important role in predicting the humidity required for pore filling while the pore diameter determines the ability of pore water to freeze. For T > 235 K and below water saturation, pore diameters and contact angles were not able to predict the freezing ability of the particles suggesting an absence of active sites, thus ice nucleation did not proceed via a PCF mechanism. Rather, the ice nucleating ability of the particles depended solely on chemical functionalization. Therefore, parameterizations for the ice nucleating abilities of particles at cirrus conditions should differ from parameterizations at mixed-phase clouds conditions. Our results support PCF as the atmospherically relevant ice nucleation mechanism below water saturation when porous surfaces are encountered in the troposphere.

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Exploratory experiments on pre-activated freezing nucleation on mercuric iodide

10.5194/acp-2020-969 ◽

2020 ◽

Author(s):

Gabor Vali

Keyword(s):

Liquid Water ◽

Laboratory Experiments ◽

Ice Nucleation ◽

Mercuric Iodide ◽

Multiple Sample ◽

Pore Condensation ◽

Basic Level ◽

Activation Cycle

Abstract. Pre-activation of freezing nucleation was examined in laboratory experiments with mercuric iodide suspensions in water. The experiments followed the procedure designed by Edwards, Evans and Zipper (1970) but employed multiple sample drops and many repetitions of the pre-activation cycle. The results obtained confirm the basic findings of the earlier work and refine it. By also drawing on the results of Seeley and Seidler (2001), pre-activated freezing nucleation (PFN in this work) is analyzed in search of constraints that help define the process responsible for it. No firm conclusions are reached, but evidence is accumulated pointing to the role of definite structures being involved in PFN, similar to the role of sites in heterogeneous freezing nucleation in general. PFN differs from pore condensation and freezing described by Marcolli (2020) and David et al. (2020) in that it takes place in liquid water. Further exploration of this process can help understading ice nucleation at the basic level and in its practical manifestations. The results call attention to an ice nucleation pathway hitherto barely explored and which can be expected to have consequences in how ice nucleation occurs in atmospheric clouds and in other systems.

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