Water activity as the determinant for homogeneous ice nucleation in aqueous solutions

Nature ◽  
2000 ◽  
Vol 406 (6796) ◽  
pp. 611-614 ◽  
Author(s):  
Thomas Koop ◽  
Beiping Luo ◽  
Athanasios Tsias ◽  
Thomas Peter
Keyword(s):  
Aqueous Solutions ◽  
Water Activity ◽  
Ice Nucleation

Heterogeneous Ice Nucleation in Aqueous Solutions:  the Role of Water Activity

2008 ◽  
Vol 112 (17) ◽  
pp. 3965-3975 ◽  
Author(s):  
B. Zobrist ◽  
C. Marcolli ◽  
T. Peter ◽  
T. Koop
Keyword(s):  
Aqueous Solutions ◽  
Water Activity ◽  
Ice Nucleation ◽  
Heterogeneous Ice Nucleation

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 3 – Aluminosilicates

2018 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Ion Exchange ◽  
Aqueous Solutions ◽  
Water Activity ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Dilute Solutions ◽  
Scanning Calorimetry ◽  
Immersion Freezing ◽  
Alkali Salts

Abstract. Aluminosilicates (such as feldspars, clay minerals and micas) and quartz (a crystalline form of silica), constitute the majority of airborne mineral dust. Despite similarities in structures and surfaces they differ greatly in terms of their ice nucleation (IN) efficiency. Here, we show that determining factors for their IN activity include surface ion exchange, NH3 or NH4+ adsorption, as well as surface degradation due to the slow dissolution of the minerals. We performed immersion freezing experiments with the (Na-Ca)-feldspar andesine, the K-feldspar sanidine, the clay mineral kaolinite, the micas muscovite and biotite, and gibbsite (Al(OH)3, a mineral form of aluminum hydroxide) and compare their IN efficiencies with those of the previously characterized K-feldspar microcline and quartz. Samples were suspended in pure water as well as in aqueous solutions of NH3, (NH4)2SO4, NH4Cl and Na2SO4, with solute concentrations corresponding to water activities aw = 0.88–1.0. Using differential scanning calorimetry (DSC) on emulsified micron-sized droplets, we derived onset temperatures of heterogeneous (Thet) and homogeneous (Thom) freezing as well as heterogeneously frozen water volume fractions (Fhet). Suspensions in pure water of andesine, sanidine and kaolinite yield Thet = 242.8 K, 241.2 K and 240.3 K, respectively, while no discernable heterogeneous freezing signal is present in case of the micas or gibbsite (i.e. Thet ≈ Thom ≈ 237.0 K). The presence of NH3 and/or NH4+-salts as solutes has distinct effects on the IN efficiency of most of the investigated minerals. When feldspars and kaolinite are suspended in very dilute solutions of NH3 or NH4+-salts ( ~ 0.99), Thet shifts to higher temperatures (by 2.6–7.0 K compared to the pure water suspension). Even micas and gibbsite develop weak heterogeneous freezing activities in ammonia solutions. Conversely, suspensions containing Na2SO4 cause Thet of feldspars to clearly fall below the water-activity-based immersion freezing description (Δaw = const) even in very dilute Na2SO4 solutions, while Thet of kaolinite follows the Δaw = const curve. The water activity determines how the freezing temperature is affected by solute concentration alone, i.e. if the surface properties of the ice nucleating particles are not affected by the solute. Therefore, the complex behavior of the IN activities can only be explained in terms of solute-surface-specific processes. We suggest that the immediate exchange of the native cations (K+/Na+/Ca2+) with protons, when feldspars are immersed in water, is a prerequisite for their high IN efficiency. On the other hand, excess cations from dissolved alkali salts prevent surface protonation, thus explaining the decreased IN activity in such solutions. In kaolinite, the lack of exchangeable cations in the crystal lattice explains why the IN activity is insensitive to the presence of alkali salts (Δaw = const). We hypothesize that adsorption of NH3 and NH4+ on the feldspar surface rather than ion exchange is the main reason for the anomalous increased Thet in dilute solutions of NH3 or NH4+-salts. This is supported by the response of kaolinite to NH3 or NH4+, despite lacking exchangeable ions. Finally, on longer timescales (hours to days) the dissolution of the feldspars in water or solutions becomes an important process leading to depletion of Al and formation of an amorphous layer enriched in Si within less than an hour. This hampers the IN activity of andesine the most, followed by sanidine, then eventually microcline, the least soluble feldspar.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline

2018 ◽  
Vol 18 (10) ◽  
pp. 7057-7079 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Beiping Luo ◽  
Thomas Peter
Keyword(s):  
Aqueous Solutions ◽  
Water Activity ◽  
Volume Fraction ◽  
Pure Water ◽  
Freezing Temperature ◽  
Solute Concentration ◽  
Ice Nucleation ◽  
Specific Chemical ◽  
Airborne Dust ◽  
Immersion Freezing

Abstract. Potassium-containing feldspars (K-feldspars) have been considered as key mineral dusts for ice nucleation (IN) in mixed-phase clouds. To investigate the effect of solutes on their IN efficiency, we performed immersion freezing experiments with the K-feldspar microcline, which is highly IN active. Freezing of emulsified droplets with microcline suspended in aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, NH4NO3, NH4Cl, Na2SO4, H2SO4, K2SO4 and KCl, with solute concentrations corresponding to water activities aw = 0.9–1.0, were investigated by means of a differential scanning calorimeter (DSC). The measured heterogeneous IN onset temperatures, Thet(aw), deviate strongly from ThetΔawhet(aw), the values calculated from the water-activity-based approach (where ThetΔawhet(aw)=Tmelt(aw+Δawhet) with a constant offset Δawhet with respect to the ice melting point curve). Surprisingly, for very dilute solutions of NH3 and NH4+ salts (molalities ≲1 mol kg−1 corresponding to aw ≳ 0.96), we find IN temperatures raised by up to 4.5 K above the onset freezing temperature of microcline in pure water (Thet(aw=1)) and 5.5 K above ThetΔawhet(aw), revealing NH3 and NH4+ to significantly enhance the IN of the microcline surface. Conversely, more concentrated NH3 and NH4+ solutions show a depression of the onset temperature below ThetΔawhet(aw) by as much as 13.5 K caused by a decline in IN ability accompanied with a reduction in the volume fraction of water frozen heterogeneously. All salt solutions not containing NH4+ as cation exhibit nucleation temperatures Thet(aw)<ThetΔawhet(aw) even at very small solute concentrations. In all these cases, the heterogeneous freezing peak displays a decrease as solute concentration increases. This deviation from Δawhet = const. indicates specific chemical interactions between particular solutes and the microcline surface not captured by the water-activity-based approach. One such interaction is the exchange of K+ available on the microcline surface with externally added cations (e.g., NH4+). However, the presence of a similar increase in IN efficiency in dilute ammonia solutions indicates that the cation exchange cannot explain the increase in IN temperatures. Instead, we hypothesize that NH3 molecules hydrogen bonded on the microcline surface form an ice-like overlayer, which provides hydrogen bonding favorable for ice to nucleate on, thus enhancing both the freezing temperatures and the heterogeneously frozen fraction in dilute NH3 and NH4+ solutions. Moreover, we show that aging of microcline in concentrated solutions over several days does not impair IN efficiency permanently in case of near-neutral solutions since most of it recovers when aged particles are resuspended in pure water. In contrast, exposure to severe acidity (pH ≲1.2) or alkalinity (pH ≳11.7) damages the microcline surface, hampering or even destroying the IN efficiency irreversibly. Implications for IN in airborne dust containing microcline might be multifold, ranging from a reduction of immersion freezing when exposed to dry, cold and acidic conditions to a 5 K enhancement during condensation freezing when microcline particles experience high humidity (aw≳0.96) at warm (252–257 K) and NH3/NH4+-rich conditions.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 3: Aluminosilicates

2019 ◽  
Vol 19 (9) ◽  
pp. 6059-6084 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Ion Exchange ◽  
Aqueous Solutions ◽  
Water Activity ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Dilute Solutions ◽  
Scanning Calorimetry ◽  
Immersion Freezing ◽  
Alkali Salts

Abstract. Aluminosilicates and quartz constitute the majority of airborne mineral dust. Despite similarities in structures and surfaces they differ greatly in terms of their ice nucleation (IN) efficiency. Here, we show that determining factors for their IN activity include surface ion exchange, NH3 or NH4+ adsorption, and surface degradation due to the slow dissolution of the minerals. We performed immersion freezing experiments with the (Na-Ca)-feldspar andesine, the K-feldspar sanidine, the clay mineral kaolinite, the micas muscovite and biotite, and gibbsite and compare their IN efficiencies with those of the previously characterized K-feldspar microcline and quartz. Samples were suspended in pure water as well as in aqueous solutions of NH3, (NH4)2SO4, NH4Cl and Na2SO4, with solute concentrations corresponding to water activities aw equal to 0.88–1.0. Using differential scanning calorimetry (DSC) on emulsified micron-sized droplets, we derived onset temperatures of heterogeneous (Thet) and homogeneous (Thom) freezing as well as heterogeneously frozen water volume fractions (Fhet). Suspensions in pure water of andesine, sanidine and kaolinite yield Thet equal to 242.8, 241.2 and 240.3 K, respectively, while no discernable heterogeneous freezing signal is present in the case of the micas or gibbsite (i.e., Thet≈Thom≈237.0 K). The presence of NH3 and/or NH4+ salts as solutes has distinct effects on the IN efficiency of most of the investigated minerals. When feldspars and kaolinite are suspended in very dilute solutions of NH3 or NH4+ salts, Thet shifts to higher temperatures (by 2.6–7.0 K compared to the pure water suspension). Even micas and gibbsite develop weak heterogeneous freezing activities in ammonia solutions. Conversely, suspensions containing Na2SO4 cause the Thet of feldspars to clearly fall below the water-activity-based immersion freezing description (Δaw= const.) even in very dilute Na2SO4 solutions, while Thet of kaolinite follows the Δaw= constant curve. The water activity determines how the freezing temperature is affected by solute concentration alone, i.e., if the surface properties of the ice nucleating particles are not affected by the solute. Therefore, the complex behavior of the IN activities can only be explained in terms of solute-surface-specific processes. We suggest that the immediate exchange of the native cations (K+, Na+, Ca2+) with protons, when feldspars are immersed in water, is a prerequisite for their high IN efficiency. On the other hand, excess cations from dissolved alkali salts prevent surface protonation, thus explaining the decreased IN activity in such solutions. In kaolinite, the lack of exchangeable cations in the crystal lattice explains why the IN activity is insensitive to the presence of alkali salts (Δaw= const.). We hypothesize that adsorption of NH3 and NH4+ on the feldspar surface rather than ion exchange is the main reason for the anomalous increased Thet in dilute solutions of NH3 or NH4+ salts. This is supported by the response of kaolinite to NH3 or NH4+, despite lacking exchangeable ions. Finally, the dissolution of feldspars in water or solutions leads to depletion of Al and formation of an amorphous layer enriched in Si. This hampers the IN activity of andesine the most, followed by sanidine, then eventually microcline, the least soluble feldspar.

scholarly journals Role of Salt, Pressure, and Water Activity on Homogeneous Ice Nucleation

2017 ◽  
Vol 8 (18) ◽  
pp. 4486-4491 ◽  
Author(s):  
Jorge R. Espinosa ◽  
Guiomar D. Soria ◽  
Jorge Ramirez ◽  
Chantal Valeriani ◽  
Carlos Vega ◽  
...  
Keyword(s):  
Water Activity ◽  
Ice Nucleation

scholarly journals The Impact of (bio-)organic substances on the ice nucleation activity of the K-feldspar microcline in aqueous solutions

2021 ◽  
Author(s):  
Kristian Klumpp ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Amino Acids ◽  
Citric Acid ◽  
Carboxylic Acids ◽  
Water Activity ◽  
Active Sites ◽  
Ice Nucleation ◽  
Organic Substances ◽  
Nucleation Activity ◽  
Ice Nucleation Activity ◽  
The Impact

Abstract. Potassium-feldspars (K-feldspars), such as microcline, are considered key dust minerals inciting ice nucleation in mixed phase clouds. Besides the high ice nucleation activity of microcline, recent studies also revealed a high sensi-tivity of microcline towards interaction with solutes on its surface. Here, we investigate the effect of organic and bio-organic substances on the ice nucleation activity of microcline, with the aim to better understand the underlying sur-face interactions. We performed immersion freezing experiments with microcline in solutions of three carboxylic acids, five amino acids and two polyols to represent these compound classes. By means of a differential scanning calorimeter we investigated the freezing of emulsified droplets of microcline suspended in various solutions. Depend-ing on the type of solute, different effects were observed. In the case of carboxylic acids (acetic, oxalic and citric acid), the measured heterogeneous onset temperatures, Thet, showed no significant deviation from the behavior pre-dicted by the water activity criterion, Thet(aw) = Tmelt(aw+Δaw), which relates Thet with the melting point temperature Tmelt via a constant water activity offset Δaw. While this behavior could be interpreted as a lack of interaction of the solute molecules with the surface, the carboxylic acids caused the fraction of heterogeneously frozen water, Fhet(aw), to decrease by up to 40 % with increasing solute concentrations. In combination, unaltered Thet(aw) and reduced Fhet(aw) suggest that active sites were largely deactivated by the acid molecules, but amongst those remaining active are also the best sites with the highest Thet. A deviation from this behavior is citric acid, which showed not only a de-crease in Fhet, but also a decrease in Thet of up to 4 K for water activities below 0.99, pointing to a depletion of the best active sites by interactions with the citrate ions. When neutralized solutions of the acids were used instead, the de-crease in Fhet became even more pronounced. The slope of Thet(aw) was different for each of the neutralized acid solu-tions. In the case of amino acid solutions, we found a decrease in Thet (up to 10 K), significantly below the Δaw-criterion, as well as a reduction in Fhet (up to 60 %). Finally, in case of the investigated polyols, no significant devia-tion of Thet from the Δaw-criterion was observed, and no significant deviation of Fhet in comparison to a pure water suspension was found. Furthermore, we measured the effects of aging on the ice nucleation activity in experiments with microcline suspended in solutions for up to seven days, and tested the reversibility of the interaction with the solutes after aging for 10 days. For citric acid, an ongoing irreversible degradation of the ice nucleation activity was observed, whereas the amino acids showed completely reversible effects. In summary, our experiments demonstrate a remarkable sensitivity of microcline ice nucleation activity to surface interactions with various solutes, underscoring the importance of the history of such particles from source to frozen cloud droplet in the atmosphere.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 2: Quartz and amorphous silica

2019 ◽  
Vol 19 (9) ◽  
pp. 6035-6058 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Aqueous Solutions ◽  
Amorphous Silica ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Special Focus ◽  
Quartz Surface ◽  
Mineral Surface ◽  
Glass Vial ◽  
Immersion Freezing

Abstract. Divergent ice nucleation (IN) efficiencies of quartz, an important component of atmospheric mineral dust, have been reported in previous studies. We show here that quartz particles obtain their IN activity from milling and that quartz aged in water loses most of its IN efficiency relative to freshly milled quartz. Since most studies so far reported IN activities of commercial quartz dusts that were milled already by the manufacturer, IN active samples prevailed. Also, the quartz surface – much in contrast to that of feldspars – is not prone to ammonia-induced IN enhancement. In detail we investigate the influence of solutes on the IN efficiency of various silica (SiO2) particles (crystalline and amorphous) with special focus on quartz. We performed immersion freezing experiments and relate the observed variability in IN activity to the influence of milling, the aging time and to the exposure conditions since milling. Immersion freezing with silica particles suspended in pure water or aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, Na2SO4 and NaOH, with solute concentrations corresponding to water activities aw=0.9–1.0, were investigated in emulsified droplets by means of differential scanning calorimetry (DSC) and analyzed in terms of the onset temperature of the heterogeneous freezing signal Thet and the heterogeneously frozen water volume fraction Fhet. Quartz particles, which originate from milling coarse samples, show a strong heterogeneous freezing peak in pure water with Thet equal to 247–251 K. This IN activity disappears almost completely after aging for 7 months in pure water in a glass vial. During this time quartz slowly grew by incorporating silicic acid leached from the glass vial. Conversely, the synthesized amorphous silica samples show no discernable heterogeneous freezing signal unless they were milled. This implies that defects provide IN activity to silica surfaces, whereas the IN activity of a natural quartz surface is negligible, when it grew under near-equilibrium conditions. For suspensions containing milled quartz and the solutes (NH4)2SO4, NH4HSO4 or Na2SO4, Thet approximately follows ThetΔawhet(aw), the heterogeneous freezing onset temperatures that obey Δawhet criterion, i.e., ThetΔawhet(aw)=Tmelt(aw+Δawhet) with Δawhet being a constant offset with respect to the ice melting point curve, similar to homogeneous IN. This water-activity-based description is expected to hold when the mineral surface is not altered by the presence of the solutes. On the other hand, we observe a slight enhancement in Fhet in the presence of these solutes, implying that the compliance with the Δawhet criterion does not necessarily imply constant Fhet. In contrast to the sulfates, dilute solutions of NH3 or NaOH (molality ≥5×10-4 mol kg−1) reveal Thet by 3–8 K lower than ThetΔawhet(aw), indicating a significant impact on the mineral surface. The lowering of Thet of quartz suspended in dilute NH3 solutions is opposite to the distinct increase in Thet that we found in emulsion freezing experiments with aluminosilicates, namely feldspars, kaolinite, gibbsite and micas. We ascribe this decrease in IN activity to the increased dissolution of quartz under alkaline conditions. The defects that constitute the active sites appear to be more susceptible to dissolution and therefore disappear first on a dissolving surface.

scholarly journals Analysis of the effect of water activity on ice formation using a new thermodynamic framework

2014 ◽  
Vol 14 (14) ◽  
pp. 7665-7680 ◽  
Author(s):  
D. Barahona
Keyword(s):  
Water Activity ◽  
Nucleation Rate ◽  
Ice Nucleation ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Classical Nucleation Theory ◽  
Solid Matrix ◽  
Effect Of Water ◽  
Thermodynamic Framework ◽  
New Framework

Abstract. In this work a new thermodynamic framework is developed and used to investigate the effect of water activity on the formation of ice within supercooled droplets. The new framework is based on a novel concept where the interface is assumed to be made of liquid molecules "trapped" by the solid matrix. It also accounts for the change in the composition of the liquid phase upon nucleation. Using this framework, new expressions are developed for the critical ice germ size and the nucleation work with explicit dependencies on temperature and water activity. However unlike previous approaches, the new model does not depend on the interfacial tension between liquid and ice. The thermodynamic framework is introduced within classical nucleation theory to study the effect of water activity on the ice nucleation rate. Comparison against experimental results shows that the new approach is able to reproduce the observed effect of water activity on the nucleation rate and the freezing temperature. It allows for the first time a phenomenological derivation of the constant shift in water activity between melting and nucleation. The new framework offers a consistent thermodynamic view of ice nucleation, simple enough to be applied in atmospheric models of cloud formation.

scholarly journals Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions. Part 2 – Quartz and amorphous silica

2018 ◽  
Author(s):  
Anand Kumar ◽  
Claudia Marcolli ◽  
Thomas Peter
Keyword(s):  
Aqueous Solutions ◽  
Amorphous Silica ◽  
Pure Water ◽  
Ice Nucleation ◽  
Water Volume ◽  
Special Focus ◽  
Quartz Surface ◽  
Mineral Surface ◽  
Glass Vial ◽  
Immersion Freezing

Abstract. Divergent ice nucleation (IN) efficiencies of quartz, an important component of atmospheric mineral dust, have been reported in previous studies. We show here that quartz particles obtain their IN activity from milling and that quartz aged in water loses most of its IN efficiency relative to freshly milled quartz. Also, the quartz surface – much in contrast to that of feldspars – is not prone to ammonia-induced IN enhancement. In detail we investigate the influence of solutes on the IN efficiency of various silica (SiO2) particles (crystalline and amorphous) with special focus on quartz. We performed immersion freezing experiments and relate the reported contradictory behavior to the influence of milling, and to the aging time and conditions since milling. Immersion freezing with silica particles suspended in pure water or aqueous solutions of NH3, (NH4)2SO4, NH4HSO4, Na2SO4 and NaOH, with solute concentrations corresponding to water activities aw = 0.9–1.0, were investigated in emulsified droplets by means of differential scanning calorimetry (DSC) and analyzed in terms of the onset temperature of the heterogeneous freezing signal Thet and the heterogeneously frozen water volume fraction Fhet. Quartz particles, which originate from milling coarse samples, show a strong heterogeneous freezing peak in pure water with Thet = 247–251 K. This IN activity disappears almost completely after aging for 7 months in pure water in a glass vial. During this time quartz slowly grew by incorporating silicic acid leached from the glass vial. Conversely, the synthesized amorphous silica samples show no discernable heterogeneous freezing signal unless they were milled. This implies that defects provide IN activity to silica surfaces, whereas the IN activity of a natural quartz surface is negligible, when it grew under near-equilibrium conditions. For suspensions containing milled quartz and the solutes (NH4)2SO4, NH4HSO4 or Na2SO4, Thet approximately follows Thet(Δawhet) (aw), the heterogeneous freezing onset temperatures that obey Δawhet-criterion, i.e. Thet(Δawhet) (aw) = Tmelt (aw + Δawhet) with Δawhet being a constant offset with respect to the ice melting point curve, similar to homogeneous IN. This water-activity-based description is expected to hold when the mineral surface is not altered by the presence of the solutes. On the other hand, we observe a slight enhancement in Fhet in the presence of these solutes, implying that the compliance with the Δawhet-criterion does not necessarily imply constant Fhet. In contrast to the sulfates, dilute solutions of NH3 or NaOH (molality &amp;geq; 5 × 10−4 mol kg−1) reveal Thet by 3–8 K lower than Thet(Δawhet) (aw), indicating a significant impact on the mineral surface. The lowering of Thet of quartz suspended in dilute NH3 solutions is opposite to the distinct increase in Thet that we found in emulsion freezing experiments with aluminosilicates, namely feldspars, kaolinite, gibbsite and micas. We ascribe this decrease of IN activity to the increased dissolution of quartz under alkaline conditions. The defects that constitute the active sites appear to be more susceptible to dissolution and therefore disappear first on a dissolving surface.

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