Freezing Mode Research Articles

Changes in the thermophysical and mechanical properties of blocked soils during compaction and the promotion

Introduction. It is known that flooded, blocked soils prevail in the North of Russia and in the territory of its Arctic zone. Such soils have a low bearing capacity, which reduces the possibility of their use in the construction of winter roads. Compaction (crimping) of blocked soils changes their thermophysical and physico-mechanical properties by changing the modes of freezing and thawing of weak bases, as well as the bearing capacity of overland winter trucks in wetlands. The article reflects the results of experimental studies of changes in the thermophysical and physico-mechanical parameters of the blocked soil at different degrees of its compaction.Methods and materials. Low-moisture soil with a high content of organic matter (peat) of more than 50% was used for research. It was compacted with loads, the magnitude of which is typical for sealing (crimping) operations of weak blocked bases on autosomes (0.01, 0.03 and 0.06 MPa), and frozen in a chamber to a temperature of -15 °C. Temperature control was carried out at different depths at predetermined intervals. To do this, we put together a device, the main elements of which are DS18B20 brand thermal sensors and an Arduino Nano microcontroller. The thermal conductivity of thawed and frozen soil was determined using the MIT-1 probe device. A dynamic density meter D-51 was used to determine the strength (hardness) of the samplesand the universal penetrometer PUS-3M.Results. The properties of the studied organic soil have been clarified. The heat capacity of this soil is determined depending on its humidity, temperature and density. The influence of the degree of soil compaction on the kinetics of its freezing is estimated. The results of the study of the dependence of the conditional strength (hardness) of the soil at different temperatures and densities, as well as the results of the interpretation of the results of dynamic zonation and the modulus of elasticity for the studied blocked soil are presented.Conclusion. Compaction (crimping) of the blocked soil increases its thermal conductivity and the rate of freezing of the upper layer of the swamp, which helps to accelerate the commissioning of the winter truck. Compaction (crimping) of the blocked soil significantly increases its strength during freezing, which determines an increase in the bearing capacity of autozymers in swamps. The most promising use for operational control of the density and strength of a frozen peat slab on autozymers is dynamic sensing methods with penetrometers of various designs. The results of determining the conditional strength index (hardness) of peat soil using probing with a dynamic density meter and a universal penetrometer are obtained.

Ice nucleating ability of mineral particles from subtropical South American deserts

Mineral aerosols are one of the most important ice nucleating particles (INPs) because their efficiency in nucleating ice, wide transport and largest mass contribution to particulate matter in the atmosphere. They are sourced from the arid regions of the world. In this context, this work evaluates the INP potential of fourteen topsoil samples collected from subtropical South American deserts, the major source of mineral aerosols in South America, in the immersion freezing mode. Samples were obtained from three distinct regions located in the South American Arid Diagonal and recognized as potential dust source areas: the Puna-Altiplano Plateau in the north, the central-west of Argentina, and Patagonia in the south. In general, results reveal that samples from the Puna-Altiplano and Patagonia regions, and the central-west of Argentina region exhibit the highest and lowest INP abilities, respectively. The active sites per unit surface area for a given temperature were calculated and compared with previously reported values. The results demonstrate that soil mineral particles from the region of study exhibit ice nucleating abilities comparable to the inorganic fraction of agricultural soils of central Argentina. No direct relationship was identified between INP ability and the major minerals observed in the samples. This study is the first to analyze the ice nucleation properties of soil samples collected along the South American Arid Diagonal and one of the few in South America. Since the analyzed topsoil particles were collected from potential dust source regions, this work contributes to understanding the role of aerosols in initiating atmospheric ice formation, providing valuable data for empirical parameterizations. This could contribute to the improvement in the performance of climate models, as the obtained results suggest that the underestimation of coarse and super-coarse aerosols at altitudes relevant for cloud formation may lead to underestimations in INP concentrations, particularly in regions near to the emission sources.

A temporally insensitive spatio-temporal fusion method for remote sensing imagery via semantic prior regularization

Spatio-temporal fusion has become a popular technology for generating remote sensing images with high spatial and high temporal resolutions, thus providing valuable data support for remote sensing monitoring applications, such as environmental monitoring and city planning. Currently, deep learning-based methods have garnered a significant amount of attention, and they mostly employ the fine image at the neighboring date as an auxiliary image. However, capturing usable neighboring fine images may be challenging due to the adverse effects of weather conditions on optical images. Moreover, the fusion performance drops sharply when the temporal interval is long (i.e., there are significant differences in images). In this paper, we proposed a bidirectional pyramid fusion network with semantic prior regularization (BPFN-SPR), which exhibits remarkable flexibility and robustness to temporal intervals.Specifically, the proposed BPFN-SPR contains dual-path operations (i.e., Semantic Extraction path and Image Reconstruction path). The semantic extraction path has two modes: parameter learning mode and parameter freezing mode. The parameter learning mode aims to learn the information representation of the auxiliary fine image, while the parameter freezing mode aims to perceive the accurate semantic information of the target fine image. The image reconstruction path progressively reconstructs spatial details of fine images from coarse images, which jointly optimizes the target fine image and the auxiliary fine image, reducing the temporal sensitivity of the reconstruction branch, and thereby improving its generalization ability. Experimental results show that the proposed method has competitive performance, especially for areas with land cover changes. In addition, extensive experiments using images at multi-temporal intervals as auxiliary images have also demonstrated the significant advantages of the proposed method. The mean PSNR value attains 31.0713, while the average spectral index SAM measures 0.1640 on the LGC test set. Meanwhile, for the CIA test set, the average PSNR is recorded at 29.5332, accompanied by an average spectral index SAM of 0.1865. Therefore, the proposed BPFN-SPR has considerable potential in monitoring Earth's surface dynamics.

Impact and freezing characteristics of deionized water droplets on cold curved surfaces

Processes involving droplet impact and subsequent freezing occur widely in practical engineering applications. In the present study, a visualization experimental setup is utilized to investigate the effects of the impact of single millimeter-scale droplets on curved surfaces at room and low temperatures. The influences of the Weber number We, wall temperature, and wall wettability on the dynamics of droplet impact and the characteristics of ice formation are examined. The morphological evolution of droplet impact and the variations of the dimensionless spreading coefficient are analyzed. The results indicate that at high We (We = 277), droplets reach their maximum spread on cold walls in a shorter time than on room-temperature walls, and their peak spreading coefficient is smaller. Upon impact with a cold wall, droplets exhibit a spread–splatter behavior. Low temperatures suppress the oscillatory behavior of droplets on a curved wall. In the case of a hydrophilic wall surface, as the impact We increases from 42 to 277, the impact mode gradually transitions from spread–retract–freeze to spread–splatter–freeze. The maximum spreading coefficient first increases and then decreases with increasing impact We. At high We (We = 277), the wall wettability has a minimal effect on the dynamics of droplet impact and freezing, with a spread–splatter–freeze mode being exhibited for both hydrophobic and hydrophilic walls, and the final freezing morphology is similar.

Microplastic Particles Contain Ice Nucleation Sites That Can Be Inhibited by Atmospheric Aging.

Recent research has shown that microplastics are widespread in the atmosphere. However, we know little about their ability to nucleate ice and their impact on ice formation in clouds. Ice nucleation by microplastics could also limit their long-range transport and global distribution. The present study explores the heterogeneous ice-nucleating ability of seven microplastic samples in immersion freezing mode. Two polypropylene samples and one polyethylene terephthalate sample froze heterogeneously with median freezing temperatures of -20.9, -23.2, and -21.9 °C, respectively. The number of ice nucleation sites per surface area, ns(T), ranged from 10-1 to 104 cm-2 in a temperature interval of -15 to -25 °C, which is comparable to that of volcanic ash and fungal spores. After exposure to ozone or a combination of UV light and ozone, simulating atmospheric aging, the ice nucleation activity decreased in some cases and remained unchanged in others. Our freezing data suggest that microplastics may promote ice formation in cloud droplets. In addition, based on a comparison of our freezing results and previous simulations using a global transport model, ice nucleation by microplastics will impact their long-range transport to faraway locations and global distribution.

On the Role of Starchy Grains in Ice Nucleation Processes.

Little is known about the role of starchy food on climate change processes like ice nucleation. Here, we investigate the ice nucleation efficiency (INE) of eight different starchy food materials, namely, corn (CO), potato (PO), barley (BA), brown rice (BR), white rice (WR), oats (OA), wheat (WH), and sweet potato (SP), in immersion freezing mode under mixed-phase cloud conditions. Notably, among all these food materials, PO and BA exhibit the highest ice nucleation efficiency with ice nucleation temperatures as high as -4.3 °C (T50 ∼ -7.0 ± 0.5 °C) and -6.5 °C (T50 ∼ -7.2 ± 0.2 °C), respectively. We also explore the effect of environmentally relevant physicochemical conditions on ice nucleation efficiency, including different pH, temperature, UV/O3/NOx exposure, and various cocontaminants. The change in shape, size, surface properties, hydrophobicity, and crystallinity of materials accounted for the altered INE. The increase in shape, size, and hydrophobicity of the sample generally reduces the INE, whereas an increase in crystallinity enhances the INE of the sample under our experimental conditions. The results suggest that environmentally relevant concentrations slightly alter INE, indicating their role as catalysts in environmental matrices. The outcome of studies on the ice nucleation properties of these food-containing aerosols might help in the physicochemical understanding of other biomolecule-induced ice nucleation, which is still an underdeveloped research area.

Measurement report: Atmospheric ice nuclei in the Changbai Mountains (2623 m a.s.l.) in northeastern Asia

Abstract. Atmospheric ice nucleation plays an important role in modulating the global hydrological cycle and atmospheric radiation balance. To date, few comprehensive field observations of ice nuclei have been carried out at high-altitude sites, which are close to the height of mixed-phase cloud formation. In this study, we measured the concentration of ice-nucleating particles (INPs) in the immersion freezing mode at the summit of the Changbai Mountains (2623 m above sea level), northeast Asia, in summer 2021. The cumulative number concentration of INPs varied from 1.6 × 10−3 to 78.3 L−1 over the temperature range of −5.5 to −29.0 °C. Proteinaceous-based biological materials accounted for the majority of INPs, with the proportion of biological INPs (bio-INPs) exceeding 67 % across the entire freezing-temperature range, with this proportion even exceeding 90 % above −13.0 °C. At freezing temperatures ranging from −11.0 to −8.0 °C, bio-INPs were found to significantly correlate with wind speed (r = 0.5–0.8, p < 0.05) and Ca2+ (r = 0.6–0.9), and good but not significant correlation was found with isoprene (r = 0.6–0.7) and its oxidation products (isoprene × O3) (r = 0.7), suggesting that biological aerosols may attach to or mix with soil dust and contribute to INPs. During the daytime, bio-INPs showed a positive correlation with the planetary boundary layer (PBL) height at freezing temperatures ranging from −22.0 to −19.5 °C (r > 0.7, p < 0.05), with the valley breezes from southern mountainous regions also influencing the concentration of INPs. Moreover, the long-distance transport of air mass from the Japan Sea and South Korea significantly contributed to the high concentrations of bio-INPs. Our study emphasizes the important role of biological sources of INPs in the high-altitude atmosphere of northeastern Asia and the significant contribution of long-range transport to the INP concentrations in this region.

Changes in freezing temperature, energy consumption, exergy loss and efficiency, and cooling coefficient of R22 and R404a refrigerants over experimental time

This article is to study the working efficiency of air freezing systems using R22 and R404a refrigerants. The main objective is to determine the loss, exergy efficiency and cooling coefficient (COP) of the freezing refrigeration system using R22 and R404a refrigerants. Theoretically, find the law of change in freezing time, energy consumption for the freezing refrigeration system using R22 and R404a refrigerants, machine running at without load (do not leave ingredients in the freezer when the air temperature in the freezer reaches -45oC), with load (when the product core temperature reaches -18oC) by direct and indirect fluid supply methods and find appropriate fluid supply methods for the system's R22 and R404a of refrigerants two-level compression freezer, at the same time analyze exergy and find the suitable freezing mode for the refrigeration system in freezing conditions at temperatures from -30oC to -45oC, wind speed of 6 m/s.

Cyclic freeze–thaw induced stiffness anisotropy of sandy silt under all-round and unidirectional freezing modes

The stiffness anisotropy of soil is a critical factor that influences the deformation characteristics of soil in landform evolution, geological disaster mitigation and engineering applications. However, the effects of freeze–thaw cycles on the stiffness anisotropy of soil have not been clearly understood. In this study, a new thermal boundary-controlled triaxial testing system equipped with bender elements is developed to investigate the effects of cyclic freeze–thaw on the stiffness of a sandy silt under both unidirectional and all-round freezing modes. It is revealed that under all-round freeze–thaw cycles, the shear wave velocity in the horizontal and vertical planes undergoes a continuous increase of 14% and 8%, respectively. In contrast, unidirectional freeze–thaw leads to a non-monotonic evolution of shear wave velocity, eventually resulting in a 3% reduction in the horizontal plane and a 16% reduction in the vertical plane after 10 freeze–thaw cycles. The increase in shear stiffness anisotropy of the sandy silt after freeze–thaw cycles is more significant in the unidirectional freeze–thaw condition (from 1.11 to 1.49) compared with the all-round freeze–thaw condition (from 1.13 to 1.19). This study illustrates the significance of unidirectional freeze–thaw in the evolution of mechanical anisotropy of soils in cold regions.

The Effects of Aminium and Ammonium Cations on the Ice Nucleation Activity of K‐Feldspar

AbstractMineral dust is one of the most abundant types of ice nucleating particles in the atmosphere. During atmospheric transport, mineral dust particles can become coated with inorganic and organic solutes, which can impact their ice nucleation activity. Aminium cations formed from amines are one type of organic solute that can coat mineral dust particles in the atmosphere, but their effects on the ice nucleation activity of mineral dust have not been studied. We investigated the effects of primary, secondary, and tertiary aminium cations with methyl and ethyl groups, as well as ammonium cations, on the ice nucleation activity of K‐feldspar, an important type of mineral dust, in the immersion freezing mode at low cation concentrations (0.2–20 mM) using a droplet‐freezing apparatus. Ammonium cations substantially increased the ice nucleation activity of K‐feldspar, consistent with previous studies. In contrast, primary aminium cations significantly reduced K‐feldspar ice nucleation activity, and secondary and tertiary aminium cations had no significant effect (the effect was less than the uncertainty of our measurements). Our combined results are consistent with the following mechanisms: ammonium cations undergo ion exchange with K‐feldspar, providing exposed N–H groups for hydrogen bonding with ice; primary aminium cations undergo ion exchange with K‐feldspar, exposing a hydrophobic tail that is not effective at nucleating ice; secondary and tertiary aminium cations do not undergo ion exchange with K‐feldspar due to steric effects caused by the multiple hydrophobic groups on the cation.

Integrating morphological, biochemical, behavioural, and molecular approaches to investigate developmental toxicity triggered by tebuthiuron in zebrafish (Danio rerio)

Tebuthiuron (TBU), a phenylurea herbicide, is widely applied in agricultural and non-agricultural soils. Because TBU resists degradation, it can contaminate water and reach the biota once it is released into the environment. However, the potential toxic effects of TBU on aquatic developing organisms have been poorly studied. By taking advantage of the early-life stages of zebrafish (Danio rerio), we have combined morphological, biochemical, behavioural, and molecular approaches to investigate the developmental toxicity triggered by environmentally relevant concentrations (from 0.1 to 1000 μg/L) of TBU. Exposure to TBU did not elicit morphological abnormalities but it significantly delayed hatching. In addition, TBU altered the frequency of tail coils in one-day post-fertilization (dpf) old embryos. Moreover, TBU exposure during four days significantly inhibited the whole body AChE activity of larvae. At the molecular level, TBU did not significantly affect the mRNA levels of four genes (elavl3, gfap, gap43, and shha) that play key roles during the neurodevelopment of zebrafish. By assessing the motor responses to repeated light-dark stimuli, 6 dpf larvae exposed to TBU displayed hyperactivity, showing greater travelling distance during the dark periods. Our categorization of swimming speed revealed an interesting finding – after the light was turned off, the exposed larvae abandoned the freezing mode (<2 mm/s) and travelled mainly at cruising speed (2–20 mm/s), showing that the larval hyperactivity did not translate into higher swimming velocity. Overall, our results offer new insights into the TBU toxicity to developing organisms, namely effects in AChE activity and hyperactivity, providing support data for future studies considering environmental risk assessment of this herbicide.

Laboratory Studies on the Influence of Freezing Methodology on the Shear Strength Behavior of Artificially Frozen Clays

It is essential and important for artificial ground freezing (AGF) engineering design and maintenance to systematically investigate the mechanical properties of artificially frozen soil. Based on a series of low-temperature triaxial shear tests, the mechanical properties of artificially frozen clays under different freezing methodologies (including freezing mode, freezing temperature, and confining pressure) were investigated and compared in this study. Importantly, the commonly used mechanical parameters of artificially frozen soil do not consider the effect of pressure during freezing, and the results presented that the stress–strain and shear strength behaviors of the artificially frozen clay freezing under pressure were better than those bearing freezing without pressure. In addition, both the lower freezing temperature and the higher confining pressure could lead to a notable improvement in the shear strength behavior of the artificially frozen clay. Furthermore, the significance of freezing factors was analyzed and revealed in this study, and the results demonstrated that the mechanical properties of the artificially frozen clay were more sensitive to the changes in freezing temperature, while the higher confining pressure would weaken the influence of the freezing temperature on mechanical properties. This could motivate, considering the effect of freezing conditions, especially the pressure during freezing, the development of a more practical design in AGF engineering.

Heterogeneous Ice Nucleation in Model Crystalline Porous Organic Polymers: Influence of Pore Size on Immersion Freezing.

Heterogeneous ice nucleation activity is affected by aerosol particle composition, crystallinity, pore size, and surface area. However, these surface properties are not well understood, regarding how they act to promote ice nucleation and growth to form ice clouds. Therefore, synthesized materials for which surface properties can be tuned were examined in immersion freezing mode in this study. To establish the relationship between particle surface properties and efficiency of ice nucleation, materials, here, covalent organic frameworks (COFs), with different pore diameters and degrees of crystallinity (ordering), were characterized. Results showed that out of all the highly crystalline COFs, the sample with a pore diameter between 2 and 3 nm exhibited the most efficient ice nucleation activity. We posit that the highly crystalline structures with ordered pores have an optimal pore diameter where the ice nucleation activity is maximized and that the not highly crystalline structures with nonordered pores have more sites for ice nucleation. The results were compared and discussed in the context of other synthesized porous particle systems. Such studies give insight into how material features impact ice nucleation activity.

P-256 Large for gestational age in singletons born following frozen embryo transfer: due to freezing technique or to endometrial preparation protocol? Lessons from the French registry

Abstract Study question Is large for gestational age (LGA) observed in singletons born following frozen embryo transfers (FET) either due to freezing technique or to endometrial preparation protocol? Summary answer Artificial cycles were associated with a higher rate of LGA when compared to ovulatory cycles, whereas no difference was observed between the freezing techniques. What is known already Several studies compared neonatal outcomes after fresh embryo transfer (fresh ET) and FET, and showed that FET was associated with improved neonatal outcomes, including reduced risks of preterm birth, low birth weight and small for gestational age (SGA) when compared to fresh ET. However, these studies also revealed an increased risk of LGA after FET. The underlying pathophysiology remains unclear; parental infertility, laboratory procedures including embryo culture conditions and freezing-thawing processes, as well as endometrial preparation treatments might be at play. Study design, size, duration A multicentric epidemiological data study was performed through a retrospective analysis of the standardized individual clinical records of the French national registry of in vitro fertilisation (IVF) from 2014 to 2018, including deliveries resulting from fresh ET and FET that were prospectively collected in fertility centres. Complementary data were collected from the participating fertility centres including the vitrification media and devices, as well as the endometrial preparation protocols. Participants/materials, setting, methods Data were collected from 35 French fertility centres, leading to the inclusion of a total of 72,789 fresh ET, 10,602 slow-freezing FET and 30,062 vitrification FET cycles. Fetal growth disorders were defined in liveborn singletons according to gestational age and sex-specific weight percentile distribution: SGA and LGA if &amp;lt; 10th and &amp;gt;90th percentile, respectively. Analyses were performed using linear mixed models with the centres as random effect. Main results and the role of chance Among a total of 26,585 liveborn singletons, 16,413 babies were born from fresh ET, 1,644 from slow-freezing FET and 8,528 from vitrification FET. Birthweight was significantly higher in the FET groups compared to the fresh ET group, with no difference between the two freezing techniques. Likewise, LGA rates were higher and SGA rates were lower in the FET groups compared to the fresh ET group (12.0% vs 6.4%, p &amp;lt; 0.001, and 7.8% vs 13.4%, p &amp;lt; 0.001 respectively). In a multivariable analysis, the risk of LGA following FET was not different between stimulated and natural cycles (adjusted odds ratio: 1.06, 95% confidence interval: 0.83-1.35, p = 0.64) but was significantly increased in artificial compared to natural cycles (aOR 1.36 [1.11-1.67], p = 0.003). On the contrary, the risk of LGA was not associated with either the freezing mode (slow-freezing vs vitrification) or the embryo stage (cleaved embryo vs blastocyst). When focusing on vitrification, the risk of LGA was not associated with either the freezing medium used or the embryo stage, and no difference was observed according to the vitrification device. Limitations, reasons for caution Most of the vitrification techniques were performed using the same device, and with two major vitrification media, limiting the interpretability of the comparison of the risk for LGA according to the device or the vitrification media. Wider implications of the findings Our results seem reassuring regarding potential fetal growth disorders following embryo vitrification in comparison to slow-freezing. Even if other factors may be involved, the impact of the endometrial preparation treatments seems to prevail for LGA risk following FET. FET during ovulatory cycles could minimize the risk for fetal growth disorders. Trial registration number N/A

Fruit and vegetable purees as cryoprotectants for vacuum freeze-dried fermented milk products

Fresh fermented milk products have a limited shelf life that can be extended by vacuum freeze-drying. Cryoprotectants are used to increase the survival of lactic acid microorganisms during freeze-drying. The most effective cryoprotectants are those of natural origin. Literature offers little information on the cryoprotective effects of fruit and vegetable purees. Therefore, we aimed to evaluate the effectiveness of fruit and vegetable purees in increasing the survival of lactic acid microorganisms during the freeze-drying and storage of fermented milk products. &#x0D; We studied bioyogurt samples containing pumpkin, fig, and banana purees. Rational modes of freezing and freeze-drying were established on the basis of thermal analysis. The cryoscopic temperature was determined by differential scanning calorimetry. The proportion of frozen moisture was calculated using the Nagaoka formula. Standard methods were employed to evaluate the sensory characteristics of bioyogurts and determine their protein, fat, and non-fat milk solids contents, as well as titratable acidity and microbiological indicators. &#x0D; The addition of pumpkin puree increased the cryoscopic temperature and reduced the freeze-drying stage and the total drying time by 13 h, depending on the amount of puree. However, the addition of sweet fig and banana purees decreased the cryoscopic temperature and increased the freeze-drying stage and the total drying time by 0.5–1.5 and 1.5–3 h, respectively. Based on the sensory evaluation of the freeze-dried bioyogurts, we selected the formulations with 15% of pumpkin and fig purees and 10% of banana puree. We found that the freeze-dried bioyogurts with puree had higher counts of lactic acid bacteria compared to the control. In the freeze-dried samples, the counts were higher at a storage temperature of 4 ± 2°C than at 20 ± 2°C. &#x0D; Pumpkin puree provided the best survival of lactic acid microorganisms during freeze-drying and storage.

Long-term variability in immersion-mode marine ice-nucleating particles from climate model simulations and observations

Abstract. Ice-nucleating particles (INPs) in the Southern Ocean (SO) atmosphere have significant impacts on cloud radiative and microphysical properties. Yet, INP prediction skill in climate models remains poorly understood, in part because of the lack of long-term measurements. Here we show, for the first time, how model-simulated INP concentrations compare with year-round INP measurements during the Macquarie Island Cloud Radiation Experiment (MICRE) campaign from 2017–2018. We simulate immersion-mode INP concentrations using the Energy Exascale Earth System Model version 1 (E3SMv1) by combining simulated aerosols with recently developed deterministic INP parameterizations and the native classical nucleation theory (CNT) for mineral dust in E3SMv1. Because MICRE did not collect aerosol measurements of super-micron particles, which are more effective ice nucleators, we evaluate the model's aerosol fields at other high-latitude sites using long-term in situ observations of dust and sea spray aerosol. We find that the model underestimates dust and overestimates sea spray aerosol concentrations by 1 to 2 orders of magnitude for most of the high-latitude sites in the Southern Hemisphere. We next compare predicted INP concentrations with concentrations of INPs collected on filter samples (typically for 2 or 3 d) and processed offline using the Colorado State University ice spectrometer (IS) in immersion freezing mode. We find that when deterministic parameterizations for both dust and sea spray INPs are used, simulated INPs are within a factor of 10 of observed INPs more than 60 % of the time during summer. Our results also indicate that the E3SM's current treatment of mineral dust immersion freezing in the SO is impacted by compensating biases – an underprediction of dust amount was compensated by an overprediction of its effectiveness as INPs. We also perform idealized droplet freezing experiments to quantify the implications of the time-dependent behavior assumed by the E3SM's CNT-parameterization and compare with the ice spectrometer observations. We find that the E3SM CNT 10 s diagnostic used in this study is a reasonable approximation of the exact formulation of CNT, when applied to ice spectrometer measurements in low-INP conditions similar to Macquarie Island. However, the linearized 10 s diagnostic underestimates the exact formula by an order of magnitude or more in places with high-INP conditions like the Sahara. Overall, our findings suggest that it is important to correct the biases in E3SM's simulated dust life cycle and update E3SM's INP parameterizations. INP prediction errors of 2 to 3 orders of magnitude can have considerable impacts on the simulated cloud and radiative properties in global climate models. On comparing INP concentrations during MICRE against ship-based campaigns, Measurements of Aerosols, Radiation, and Clouds over the Southern Ocean (MARCUS) and Antarctic Circumnavigation Expedition (ACE), we find that INPs from the latter are significantly higher only in regions closer to Macquarie Island. This alludes to the fact that physical, chemical and biological processes affecting INP concentrations as stimulated by the island could be partly responsible for the high INP concentrations observed at Macquarie Island during the MICRE campaign. Therefore, improvements to both aerosol simulation and INP parameterizations are required to adequately simulate INPs and their cloud impacts in E3SM. It will be helpful to include a parallel measurement of the size-resolved aerosol composition and explore opportunities for long-term measurement platforms in future field campaigns studying INP sources in remote marine regions.

Ice nucleation by smectites: the role of the edges

Abstract. Smectites, like other clay minerals, have been shown to promote ice nucleation in the immersion freezing mode and likely contribute to the population of ice-nucleating particles (INPs) in the atmosphere. Smectites are layered aluminosilicates, which form platelets that depending on composition might swell or even delaminate in water by intercalation of water molecules between their layers. They comprise among others montmorillonites, hectorites, beidellites, and nontronites. In this study, we investigate the ice nucleation (IN) activity of a variety of natural and synthetic smectite samples with different exchangeable cations. The montmorillonites STx-1b and SAz-1, the nontronite SWa-1, and the hectorite SHCa-1 are all rich in Ca2+ as the exchangeable cation; the bentonite MX-80 is rich in Na+ with a minor contribution of Ca2+, and the synthetic Laponite is a pure Na+ smectite. The bentonite SAu-1 is rich in Mg2+ with a minor contribution of Na+, and the synthetic interstratified mica-montmorillonite Barasym carries NH4+ as the exchangeable cation. In emulsion freezing experiments, all samples except Laponite exhibited one or two heterogeneous freezing peaks with onsets between 239 and 248 K and a quite large variation in IN activity yet without clear correlation with the exchangeable cation, with the type of smectite, or with mineralogical impurities in the samples. To further investigate the role of the exchangeable cation, we performed ion exchange experiments. Replacing NH4+ with Ca2+ in Barasym reduced its IN activity to that of other Ca-rich montmorillonites. In contrast, stepwise exchange of the native cations in STx-1b once with Y3+ and once with Cu2+ showed no influence on IN activity. However, aging of smectite suspensions in pure water up to several months revealed a decrease in IN activity with time, which we attribute to the delamination of smectites in aqueous suspensions, which may proceed over long timescales. The dependence of IN activity on platelet stacking and thickness can be explained if the hydroxylated chains forming at the edges are the location of ice nucleation in smectites, since the edges need to be thick enough to host a critical ice embryo. We hypothesize that at least three smectite layers need to be stacked together to host a critical ice embryo on clay mineral edges and that the larger the surface edge area is, the higher the freezing temperature. Comparison with reported platelet thicknesses of the investigated smectite samples suggests that the observed freezing temperatures are indeed limited by the surface area provided by the mostly very thin platelets. Specifically, Laponite, which did not show any IN activity, is known to delaminate into single layers of about 1 nm thickness, which would be too thin to host a critical ice embryo.

Metal Oxide Particles as Atmospheric Nuclei: Exploring the Role of Metal Speciation in Heterogeneous Efflorescence and Ice Nucleation

Mineral dust can indirectly impact climate by nucleation of atmospheric solids, for example, by heterogeneously nucleating ice in mixed-phase clouds or by impacting the phase of aerosols and clouds through contact nucleation. The effectiveness toward nucleation of individual components of mineral dust requires further study. Here, the nucleation behavior of metal oxide nanoparticle components of atmospheric mineral dust is investigated. A long-working-distance optical trap is used to study contact and immersion nucleation of ammonium sulfate by transition-metal oxides, and an environmental chamber is used to probe depositional ice nucleation on metal oxide particles. Previous theory dictates that ice nucleation and heterogeneous nucleation of atmospheric salts can be impacted by several factors including morphology, lattice match, and surface area. Here, we observe a correlation between the cationic oxidation states of the metal oxide heterogeneous nuclei and their effectiveness in causing nucleation in both contact efflorescence mode and depositional freezing mode. In contrast to the activity of contact efflorescence, the same metal oxide particles did not cause a significant increase in efflorescence relative humidity when immersed in the droplet. These experiments suggest that metal speciation, possibly as a result of cationic charge sites, may play a role in the effectiveness of nucleation that is initiated at particle surfaces.

Freezing modes of water droplet on cold plate surface under forced convection

The water droplet freezing modes on the cold plate surface under forced convection are experimentally studied. The formation mechanism of the peak freezing mode is analyzed. A new peakless freezing mode is found. The results indicate that the stronger convective heat transfer on the windward of the droplet causes the solid–liquid interface of the freezing droplet to incline windward. In the peakless mode, the droplet freezing is driven by frosting around the solid–liquid interface. A peakless solidification slope is formed by the liquid penetrating the frost layer. The increase of the airflow velocity can transform the freezing mode from the peak mode to the peakless mode, promoting ice nucleation on the droplet and postponing droplet solidification. The critical criterion for freezing mode transition is obtained.

Purification of heavy metal chromium in saturated sand by artificial freezing: Mechanism and method optimization

Heavy metal pollution of soil has become one of the most common hazards in human development. The artificial freezing method, especially the progressive freezing method, can reduce heavy metal pollutants in the soil and promises to be an effective in-situ treatment of contaminated sites. This study analyzes the freezing purification mechanism of heavy metal contaminants in saturated sand and identifies three main factors that impact the effects of purification: freezing rate, initial concentration, and diffusion coefficient. Moreover, one-dimensional freezing tests are carried out by different freezing modes. The experimental results show that the heavy metal chromium could only be removed effectively with a slow freezing rate. By optimizing the freezing mode and freezing rate, a long section of soil was frozen and purified, with the maximum purification rate reaching 65.8%. This study shows that it is feasible to treat contaminated saturated sand by a gradual-cooling freezing method.