Insoluble Nuclei Research Articles

An adsorption theory of heterogeneous nucleation of water vapour on nanoparticles

Abstract. Heterogeneous nucleation of water vapour on insoluble nuclei is a phenomenon that can induce atmospheric water and ice cloud formation. However, modelling of the phenomenon is hampered by the fact that the predictive capability of the classical heterogeneous nucleation theory is rather poor. A reliable theoretical description of the influence of different types of water-insoluble nuclei in triggering the water condensation or ice deposition would help to decrease uncertainty in large-scale model simulations. In this paper we extend a recently formulated adsorption theory of heterogeneous nucleation to be applicable to highly curved surfaces, and test the theory against laboratory data for water vapour nucleation on silica, titanium dioxide and silver oxide nanoparticles. We show that unlike the classical heterogeneous nucleation theory, the new theory is able to quantitatively predict the experimental results.

Expansion of Insoluble Gas Nucleus in Delayed Expandable Foam

Delayed expandable foam (DEF) is a new material that can significantly extend the range of foam curtain in electromagnetic waves interference, fire extinguishing and pollution washdown, etc. This paper studied the expansion of insoluble gas nucleus (IGN) in supersaturated solution of DEF. The radius and volume of IGN as well as DEF was calculated using double membrane model of mass transfer. Results show that the size of IGN raises steadily over time meanwhile the bulk volume of DEF is nearly invariable when both initial radius r0 and number density ψ of IGN are small enough. This is called the volume sensitivity effect. At this stage, the time delay reduces linearly with r0 and the square root of ψ. Accordingly, the time delay of DEF expansion can be adjusted by setting initial radius and number density of IGN. This research can provide theoretical basis for DEF development.

Electrization of aerosol wetted in bipolarly ionized air

We studied the influence of the characteristics of the atmospheric ionization and physical-chemical state of condensation nuclei on the electric state of convective cells. Based on the results of experiments in an adiabatic chamber with a volume of 3200 m3, we found that, with increase in relative air humidity H from 40 to 95% with an equivalent ascent rate of 100–400 cm/s, excessive charges in amounts of about 103 or more elementary charges per cm3 may be accumulated on the nuclei. The sign of the charge depends on the chemical composition of the hygroscopic nuclei. For instance, media with insoluble nuclei (porous silica, etc.) typically have prevailing negative charges; those with soluble nuclei (sodium chloride, etc.) are dominated by positive charges. At H = 60−90%, the electrization of soluble nuclei can be interpreted in the diffusion-kinetic models of the ion charging of aerosols. Considerable negative volume charges, which appear on insoluble hygroscopic nuclei during a rise in humidity from 40 to 70%, are explained by the structuring of surface water films, which exhibit a resemblance to negative lightweight ions. At high values (H > 90%), it is necessary to take into account the resemblance of the wetted surfaces to positive lightweight ions. We showed for the first time that, at ion formation rates of 3 and 1010 ion pairs/(cm3 s), the differences in the volume charge and wetting rate of condensation nuclei are insignificant. It is concluded that, in many meteorological situations, the first stage of electrization of the convection-derived cloud media is the ion charging of the condensation nuclei.

Measurements of Depositional Ice Nucleation on Insoluble Substrates at Low Temperatures: Implications for Earth and Mars

Heterogeneous depositional nucleation of ice particles may dominate in atmospheric regions with very low temperatures, where low vapor pressures and insoluble nuclei would be expected. However, depositional ice nucleation has not been studied extensively at temperatures below 200 K and not at all below 170 K. Here, we show results of a study of heterogeneous depositional nucleation of ice on a solid silicon substrate at temperatures from 150 to 180 K. The results presented herein demonstrate an unexpected temperature dependence in which very high critical supersaturations are required to nucleate ice at T ≤ 180 K. The vapor pressures necessary for nucleation below 175 K are greater than the vapor saturation for supercooled liquid water. The temperature dependence observed is not predicted by classical heterogeneous nucleation theory, when assuming a temperature-independent contact parameter, m. Here, we use our new measurements in combination with previously published data to derive a temperature-dependen...

Water adsorption and cloud condensation nuclei activity of calcite and calcite coated with model humic and fulvic acids

Recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of insoluble nuclei, such as mineral dust aerosol. A large fraction of unidentified organic material in aerosol particles is composed of poly-acidic compounds resembling humic substances. The presence of these humic-like substances (HULIS) can alter the water adsorption and CCN activity of mineral dust aerosol. We have measured the CCN activity of model humic and fulvic acids and of mineral dust particles coated with these substances in the laboratory. We find that coatings of humic and fulvic acids on calcite particles significantly increases water adsorption compared to uncoated particles. CCN measurements indicate that humic- or fulvic acid-coated calcite particles are more CCN active than uncoated calcite particles. Additionally, thicker coatings of humic or fulvic acids appear to result in more efficient CCN activity. Thus, mineral dust particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the atmosphere than uncoated mineral dust particles, potentially altering the effect of mineral dust on the Earth's climate. In addition to the experimental results, we have explored a newly modified Köhler theory for predicting the CCN activity of insoluble, wettable particles based on multi layer water adsorption measurements of calcite.

Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation

Abstract. A counterflow virtual impactor was used to collect residual particles larger than about 0.1 μm diameter from anvil cirrus clouds generated over Florida in the southern United States. A wide variety of particle types were found. About one-third of the nuclei were salts, with varying amounts of crustal material, industrial metals, carbonaceous particles, and sulfates. Ambient aerosol particles near the anvils were found to have similar compositions, indicating that anvils act to redistribute particles over large regions of the atmosphere. Sampling occurred at a range of altitudes spanning temperatures from −21 to −56°C. More insoluble (crustal and metallic) particles typical of heterogeneous ice nuclei were found in ice crystals at warmer temperatures, while more soluble salts and sulfates were present at cold temperatures. At temperatures below about −35 to −40°C, soluble nuclei outnumbered insoluble nuclei, evidently reflecting the transition from primarily heterogeneous to primarily homogeneous freezing as a source of anvil ice.

Thermodynamics of heterogeneous binary condensation on insoluble nuclei

We consider heterogeneous binary condensation as the formation of wetting films of arbitrary thickness on insoluble nuclei. Using this approach, we show that the concurrence of the capillary and disjoining pressures in thin films plays a key role in the thermodynamics of the whole process. The limiting partial supersaturations necessary for barrierless condensation are obtained as functions of the droplet composition and an explicit expression for the formation free energy of a binary droplet on an insoluble nucleus is derived. The surface describing the formation free energy as a function of film thickness and composition has a minimum and a saddle point whose coordinates correspond to droplets in stable and unstable equilibria, respectively, with the vapor mixture. Equations for determining the coordinates of the well and saddle points are presented. The theoretical results are illustrated with numerical calculations for the butanol‐hexanol and butanol‐water droplets formation on quartz particles.

Condensation nuclei supersaturation spectrum: analysis of the relationship between the saturation droplet radius and the critical supersaturation in the Laktionov isothermal chamber

Computations testing the uniqueness of the relationship between the saturation droplet radius r 100 and the critical supersaturation S c have been performed for condensation nuclei ( CN) of different chemical composition: pure salts, mixtures of salts and partly insoluble nuclei; indeed, the reliability of this relationship is the key-point in determining the CN supersaturation spectrum by an isothermal chamber. The results show that in the case of typical natural inorganic aerosols the dependence of S c on r 100 is practically unique for all the CN considered, as the uncertainty in the CN electrolytic composition can lead to a maximum error of about 8% on the activated nuclei counts; by using Laktionov's relationship this error can reach about 12%. When surface-active organic materials are present, the relationship between r 100 and S c is significantly modified; the activated nuclei counts can differ, for continental aerosols, up to +100% from the corresponding counts of pure inorganic aerosols. Also a decrease in nuclei counts can be predicted; values up to −80% have been determined. In conclusion, when the Laktionov isothermal chamber is used, simultaneous measurements characterizing the organic materials are required for an accurate determination of the CN supersaturation spectrum.

Kinetic Model for Aerosol Formation in Rocket Contrails

A kinetic condensation model is presented for rocket contrail formation. The formulation treats condensation of water and acid species as a heterogeneous process occurring on soluble or insoluble nuclei particles in the rocket exhaust. The modeling objective is the prediction of condensate aerosol number densities and sizes in contrails. Numerical model results are presented for a HCI/H 2O exhausting rocket at several ambient conditions. It is found that plume condensate aerosol properties are affected by the loading and size distributions of the nuclei particles, especially at high altitudes. Nomenclature C = condensate mass concentration D = molecular diffusion coefficient e = saturated vapor pressure h = Harned coefficient A// = latent heat of vaporization or solution / = ionic strength of solution m = molality (moles solute/1000 g water) M2 - average acid molality of aerosol n = aerosol particle concentration P = pressure Pj, P2 = partial pressures R,z = radial and axial plume coordinates

Microphysical Implications of Precipitation Formation in an Adiabatic Vertical Current: Aerosol Scavenging by Enhanced Nucleation

The time-dependent effect of precipitation formation and development on the dynamics and microphysics of adiabatic vertical motion has been studied with the help of one-dimensional numerical models. Since the most important microphysical effect of precipitation formation is nucleation due to enhancement of supersaturation, efforts have been concentrated mainly on the elucidation of this effect. Essentially two time-dependent models have been considered: the first, having all its nucleation near the cloud base, and no additional nucleation as supersaturation develops; and the second, with nucleation proceeding in step with supersaturation development. The second model also examines the question of the activity of nuclei in that experiments have been performed separately with insoluble (but wettable) nuclei and soluble nuclei. The conclusions arrived at are the following: (i) in an updraft, with developing precipitation, a progressive development of supersaturation and the consequent activation of fresh nuclei is an essential requirement for maintaining the updraft in its approximately adiabatic state; (ii) a precipitating (adiabatic) cumulus can scavenge aerosol particles effectively by first activating them to form droplets and then removing the latter in the form of precipitation; (iii) the downdraft driven by precipitation is unsaturated; and (iv) within the restrictions of the model the downdraft is also warmer than the environment except very close to the ground where evaporative cooling causes a slight “temperature break.” The limitations of the model are discussed, the most important being that the model is adiabatic. Consequently the study reported should he considered as the results obtained in an idealized numerical laboratory, having implications for atmospheric processes.

A reexamination of the equilibrium conditions in the theory of water drop nucleation

The thermodynamic equations necessary to describe the conditions for equilibrium between a highly curved surface of a liquid and its vapour are re-examined. The complete equilibrium behaviour is reduced to one single differential equation for each component in an arbitrary c -component system. It is shown that this general formulation can be specialized to describe the conditions for equilibrium between water vapour and a pure water drop, the drop carrying an electric charge, containing a water soluble substance and/or containing a water insoluble nucleus. In the light of the present formulation, some incorrect physical statements of treatments by various authors reported in literature are pointed out. In an added note, the energy of homogeneous water drop formation is discussed and some erroneous conclusions which commonly are drawn in the literature from formulations on the energy of nucleus formation are mentioned. DOI: 10.1111/j.2153-3490.1975.tb01691.x

Numerical Solution for Condensation of Atmospheric Vapor on Soluble and Insoluble Nuclei

Abstract The growth of cloud droplets by condensation of vapor upon soluble and insoluble nuclei was computed for different nuclei distributions. The set of equations used takes into account the interdependence of vapor condensation and changes of temperature and pressure in the vertically moving air. The results show that the spectrum of cloud droplets is broader if the nuclei distribution includes hygroscopic and insoluble nuclei together, rather than different sizes of salt nuclei only. If different numbers of nuclei are assumed in neighboring air parcels, then the size spectrum in the cloud is even broader. The width of the spectrum obtained in this study seems to be broad enough to initiate the process of raindrop growth by coalescence. Results for different updraft velocities and a non-constant vertical velocity of the air parcel show that the final sizes of the drops are almost the same when measured at a certain altitude z, no matter what the vertical velocity was.

A LABORATORY INVESTIGATION OF DROPLET FREEZING

Abstract Laboratory experimentation was undertaken to investigate the effects of various soluble and insoluble nuclei on the freezing temperature of water droplets. The freezing temperature and size of over 15,000 droplets were obtained. Pure water was produced, and subsequently frozen in droplet form. The freezing temperatures of various sizes of pure water droplets were used as a reference standard for the other phases of the experiment. The experiment showed that soluble salts, commonly found in the atmosphere, caused the freezing temperatures of the droplets to become colder than would be anticipated by bulk freezing point lowering calculations in all cases. Insoluble nuclei increased the freezing temperatures of the droplets. The addition of soluble salts to water droplets containing insoluble nuclei caused a marked depression of the freezing point below that originally observed. The magnitude of the depression was found to be a function of the solute concentration. Certain aspects of the role of dro...

Sur la formation des germes de condensation et de solidification autour d'un noyau solide insoluble

Solid insoluble nuclei help the formation of water or ice inasmuch as the adhesion-coefficient of water or ice on the solid be positive. If this coefficient is greater than 1 and if the solid nucleus is great enough this effect may be sufficient to render null the free energy of formation of germs and to provoke the condensation or the solidification without germ. These effects can be calculated a priori , assuming a certain degree of saturation of the atmospheric water vapour provided the suitable adhesion-coefficient be known. DOI: 10.1111/j.2153-3490.1953.tb01057.x

Sur la formation des germes de condensation et de solidification autour d’un noyau solide insoluble

Solid insoluble nuclei help the formation of water or ice inasmuch as the adhesion-coefficient of water or ice on the solid be positive. If this coefficient is greater than 1 and if the solid nucleus is great enough this effect may be sufficient to render null the free energy of formation of germs and to provoke the condensation or the solidification without germ. These effects can be calculated a priori, assuming a certain degree of saturation of the atmospheric water vapour provided the suitable adhesion-coefficient be known.