Condensation Of Supersaturated Vapor Research Articles

Direct and indirect photoinduced gas–liquid phase transitions

The condensation of supersaturated vapors of various substances in air under UV irradiation in a cloud chamber has been studied. The irradiation and subsequent photodissociation greatly facilitate the condensation of vapors in comparison with unirradiated mixtures, wherein both a vapor that directly absorbs radiation (direct photoinduced phase transition) and, for example, water vapor in the presence of photodissociating impurities (indirect photoinduced transition) can be condensed.

Removal of fine particles in WFGD system using the simultaneous acoustic agglomeration and supersaturated vapor condensation

The characteristics of fine particle removal from wet flue gas desulfurization (WFGD) using the simultaneous acoustic agglomeration and supersaturated vapor condensation were investigated experimentally. The impacts of supersaturation degree, residence time and acoustic intensity on the fine particle removal efficiency were demonstrated. High moisture and tiny droplets were contained in the flue gas after WFGD, which benefited the use of coupling external fields in WFGD system. The results showed that the removal of fine particles can be significantly improved in the simultaneous acoustic field and supersaturated vapor condensation. High value of sound pressure level (SPL>150dB) was needed to achieve a considerable removal efficiency using acoustic agglomeration only. While low SPL of 130–150dB can be used to remove fine particle efficiently in WFGD system using simultaneous external fields. Removal efficiency higher than 70% was obtained with S=1.15 and SPL=151dB. The residence time of the simultaneous acoustic agglomeration and condensational growth was determined by the time required by acoustic agglomeration. Particle removal efficiency increased with the residence time, but it tended to be constant as the residence time over 3s. Multiple horn numbers with low acoustic intensity benefited the improvement of fine particle removal efficiency and the reduction of energy consumption using the simultaneous external fields in WFGD system.

Synthesis of metal-carbon nanoparticles in pulsed UV-photolysis of Fe(CO)5-CCl4 mixtures at room temperature

Synthesis of iron-carbon nanoparticles in joint photolysis of iron pentacarbonyl (Fe(CO)5) and carbon tetrachloride (CCl4) has been studied. When mixtures containing iron pentacarbonyl and CCl4 are exposed to UV light, Fe(CO)5 molecules decompose to yield an atomic vapor of iron with well-known and easily controlled parameters, whereas CCl4 molecules decompose to give CCl3 radicals. A pulsed Nd:YAG laser (fourth harmonic, 266 nm) served as a source of light. The growth process of nanoparticles in condensation of supersaturated vapors was monitored by the laser extinction method; nanoparticle samples were examined with an atomic-force microscope. It was found that the concentration of the CCl4 additive affects the manner in which the optical properties of nanoparticles synthesized in a binary mixture change relative to the properties of nanoparticles synthesized in photolysis of pure Fe(CO)5, which indicates that a carbon shell grows on the surface of iron nanoparticles.

Composition of silicon fibrous nanostructures synthesized using ultrafast laser pulses under ambient conditions

In this study the composition of nanostructures generated owing to ablation of crystalline silicon using high repletion rate femtosecond laser under ambient condition is investigated. The web-like silicon fibrous nanostructures are formed in and around the laser irradiated area. Electron Microscopy investigation revealed that the nanostructures are made of nanoparticles of size about 40 nm. In addition Micro-Raman analysis shows that the nanofibrous structures comprises a mixture of amorphous and polycrystalline silicon. X-ray photoelectron spectroscopy analysis reveals the oxidized and un-oxidized elemental states of silicon in the nanostructures. Moreover web-like fibrous nanostructures are generated due to condensation of super saturated vapour and subsequent nucleus growth in the laser induced plasma plume.

Influence of Size Effects on the Formation of Aerosol Nanoparticles in Supersaturated Vapor Condensation

The influence of size effects on the formation of aerosol nanoparticles in supersaturated vapor condensation has been studied theoretically. Problems connected with the nucleation and nanoparticle growth rates are considered.

Direct observation of metal nanoparticles as heterogeneous nuclei for the condensation of supersaturated organic vapors: nucleation of size-selected aluminum nanoparticles in acetonitrile and n-hexane vapors.

This work reports the direct observation and separation of size-selected aluminum nanoparticles acting as heterogeneous nuclei for the condensation of supersaturated vapors of both polar and nonpolar molecules. In the experiment, we study the condensation of supersaturated acetonitrile and n-hexane vapors on charged and neutral Al nanoparticles by activation of the metal nanoparticles to act as heterogeneous nuclei for the condensation of the organic vapor. Aluminum seed nanoparticles with diameters of 1 and 2 nm are capable of acting as heterogeneous nuclei for the condensation of supersaturated acetonitrile and hexane vapors. The comparison between the Kelvin and Fletcher diameters indicates that for the heterogeneous nucleation of both acetonitrile and hexane vapors, particles are activated at significantly smaller sizes than predicted by the Kelvin equation. The activation of the Al nanoparticles occurs at nearly 40% and 65% of the onset of homogeneous nucleation of acetonitrile and hexane supersaturated vapors, respectively. The lower activation of the charged Al nanoparticles in acetonitrile vapor is due to the charge-dipole interaction which results in rapid condensation of the highly polar acetonitrile molecules on the charged Al nanoparticles. The charge-dipole interaction decreases with increasing the size of the Al nanoparticles and therefore at low supersaturations, most of the heterogeneous nucleation events are occurring on neutral nanoparticles. No sign effect has been observed for the condensation of the organic vapors on the positively and negatively charged Al nanoparticles. The present approach of generating metal nanoparticles by pulsed laser vaporization within a supersaturated organic vapor allows for efficient separation between nucleation and growth of the metal nanoparticles and, consequently controls the average particle size, particle density, and particle size distribution within the liquid droplets of the condensing vapor. Strong correlation is found between the seed nanoparticle's size and the degree of the supersaturation of the condensing vapor. This result and the agreement among the calculated Kelvin diameters and the size of the nucleating Al nanoparticles determined by transmission electron microscopy provide strong proof for the development of a new approach for the separation and characterization of heterogeneous nuclei formed in organic vapors. These processes can take place in the atmosphere by a combination of several organic species including polar compounds which could be very efficient in activating charged nanoparticles and cluster ions of atmospheric relevance.

Effect of ionizing radiation field on CsI aerosols formed by condensation of supersaturated vapor

The effect of the ionizing radiation field on the behavior of CsI aerosols formed by condensation of supersaturated vapor was examined. Supersaturated CsI vapor was formed by evaporation from a metal surface ohmically heated to high temperatures. A study of the size distribution function of CsI particles showed that, both in the field of 60Co γ-radiation and in a stationary electron beam, three modes of particle size are observed with the mean sizes of 0.13, 0.57, and 0.76 μm. The amount of particles of size 0.13 μm is larger by a factor of ∼10–20 than the amount of particles of sizes 0.57 and 0.76 μm. Comparison of the distribution functions of CsI aerosol particles formed by supersaturated vapor condensation in an ionizing radiation field and without it showed that the ionizing radiation affected not only the size but also the amount of particles.

MECCO: A method to estimate concentrations of condensing organics—Description and evaluation of a Markov chain Monte Carlo application

The development of a new method to estimate concentrations of condensing organics (MECCO) is described. A Markov chain Monte Carlo method is applied, and by using measured particle size distribution and random vapor concentrations as input, the predicted changes in particle population by an aerosol dynamics model are utilized. The method provides the ambient vapor concentrations required for the observed particle growth in particle number size distribution data, assuming all growth can be attributed to net condensation of super-saturated vapors. In this paper, MECCO was coupled with the UHMA box-model to provide aerosol dynamics. With few changes, MECCO could be applied to study other input parameters, and coupled with other dynamics models as well. Evaluation of the method was carried out with simulated output from the UHMA model using the assumption of three organic vapors, and MECCO-UHMA was able to estimate their concentrations with great accuracy. However, the condensation of vapors is currently considered irreversible, since the used particle size distribution data do not provide information on the composition of particles. The distinguishing between the vapors is based on few vapor parameters, which limits the possibilities of identifying actual vapors. An example of atmospheric application is also presented. This revealed the importance of quality control of the input particle concentrations: instrumental noise and changes in the observed air mass pose challenges for the presented method. Data need to be smoothed in a reasonable way so that the point-like measurements can be utilized, but also so that the important information on particle growth is conserved. MECCO is a useful tool to approximate vapor concentrations and may be applied to estimate vapor properties as well. However, a computationally efficient and physically accurate aerosol dynamics model is essential for MECCO's performance.

Molecular Dynamics Based Analysis of Nucleation and Surface Energy of Droplets in Supersaturated Vapors of Methane and Ethane

Homogeneous nucleation processes are characterized by the nucleation rate and the critical droplet size. Molecular dynamics simulation is applied for studying homogeneous nucleation during condensation of supersaturated vapors of methane and ethane. The results are compared with the classical nucleation theory (CNT) and the Laaksonen–Ford–Kulmala (LFK) model that introduces the size dependence of the specific surface energy. It is shown for the nucleation rate that the Yasuoka–Matsumoto method and the mean first passage time method lead to considerably differing results. Even more significant deviations are found between two other approaches to the critical droplet size, based on the maximum of the Gibbs free energy of droplet formation (Yasuoka–Matsumoto) and the supersaturation dependence of the nucleation rate (nucleation theorem). CNT is found to agree reasonably well with the simulation results, whereas LFK leads to large deviations at high temperatures.

Vapor phase nucleation on neutral and charged nanoparticles: Condensation of supersaturated trifluoroethanol on Mg nanoparticles

A new technique is described to study the condensation of supersaturated vapors on nanoparticles under well-defined conditions of vapor supersaturation, temperature, and carrier gas pressure. The method is applied to the condensation of supersaturated trifluoroethanol (TFE) vapor on Mg nanoparticles. The nanoparticles can be activated to act as condensation nuclei at supersaturations significantly lower than those required for homogeneous nucleation. The number of activated nanoparticles increases with increasing the vapor supersaturation. The small difference observed in the number of droplets formed on positively and negatively charged nanoparticles is attributed to the difference in the mobilities of these nanoparticles. Therefore, no significant charge preference is observed for the condensation of TFE vapor on the Mg nanoparticles.

A review of particle formation events and growth in the atmosphere in the various environments and discussion of mechanistic implications

This review highlights recent observations from a large number of studies investigating formation and growth within different environments and discusses the importance of various mechanisms of particle formation and growth between the different environments. Whilst, several mechanisms for new particle formation which proposed the importance of each mechanism are still the centre of much debate. Proposed nucleation mechanisms include condensation of a binary mixture of sulphuric acid and water; ternary nucleation of sulphuric acid, water and a third molecule, most likely ammonia; ion-induced nucleation; secondary organic aerosol formation involving condensation of low- or non-volatile organic compounds and homogeneous nucleation of iodine oxides. Laboratory and modelling studies have shown these mechanisms can occur in the atmosphere although the contribution depends on the concentrations of precursor compounds present. In addition, atmospheric particle formation events are significantly affected by environmental factors, such as temperature, humidity and the surface area of pre-existing particles, which is also discussed here. One major problem hampering our current understanding is that these new particles are smaller than the lower size detection limit of most instruments and are only observed after some particle growth has occurred. Particles growth occurs through condensation of supersaturated vapours on the surface of the nucleated particles. This requires a lower degree of supersaturation than nucleation and thus condensation of the nucleating species reduces the rate of particle formation. Therefore, it is believed that particle growth often occurs through the condensation of other gases, including organic and inorganic compounds, than those responsible for nucleation. This decoupling of nucleation and growth means that the individual gases responsible for nucleation and growth can be unclear. Since observations of particle formation only occur following growth to observable sizes it is possible that a pool of undetectable particles exist at all times but are only observed following significant condensational growth.

Condensation of Supersaturated Water Vapor on Charged/Neutral Nanoparticles of Glucose and Monosodium Glutamate

The effects of size, charge, dissolution, and dissociation on the condensation of supersaturated water vapor on monodisperse nanoparticles of glucose and monosodium glutamate (MSG) were investigated in a flow cloud chamber (FCC). The dependence of the critical supersaturation, S cr, on particle size in the range of 30 to 90 nm and on temperature in the range of 10 to 50°C were determined experimentally. The results show that the experimental S cr decreases with increasing particle size at a rate in reasonable agreement with the predictions of the Kohler and Volmer theories of nucleation for soluble particles, but decreases with increasing temperature at a rate higher than the prediction of the Volmer theory. The dissociation of MSG into ions lowers the experimental S cr to a value smaller than that for the more soluble glucose, agreeing with predictions. The experimental S cr is smaller than the predictions of both theories, and the discrepancy cannot be fully explained by the reductions in surface tension due to the dissolution of particles and curvature dependence. The condensation of supersaturated vapor on singly positively charged particles with diameters of 30, 60, and 90 nm was also examined, and no obvious charge effect on S cr was observed.

Condensation of Supersaturated n-Butanol Vapor on Charged/Neutral Nanoparticles of D-Mannose and L-Rhamnose

The effects of size, charge, and solubility on the condensation of supersaturated n-butanol vapor on monodisperse nanoparticles of D-mannose and L-rhamnose are investigated in a flow cloud chamber. The dependence of the critical supersaturation Scr on particle size in the range from 30 to 90 nm is determined experimentally. The results show that the experimental Scr decreases with increasing particle size and solubility, qualitatively in agreement with the prediction by the Volmer theory of nucleation on soluble particles and by the Kohler theory, but quantitatively smaller than both theoretical predictions. The condensation of supersaturated vapor on singly positive/negative charged particles with diameters of 30, 60, and 90 nm is examined, and no obvious charge effect and sign preference are observed.

Analysis of the Results of Numerical Simulation of the Supersaturated Vapor Condensation Relaxation

The process of bulk vapor condensation from the vapor-gas mixture after the fast creation of the supersaturated state as a result of vapor expansion is discussed. Scaling relations are derived for the time of condensation relaxation and droplet number density. The principal possibility of the experimental determination of nucleation rate is demonstrated based on the results obtained. The effect of initial phase, frequency, and pulsation amplitude on the condensation relaxation is analyzed for the case, when thermodynamic parameters of a mixture in the process of condensation are subjected to perturbations in the form of low-amplitude harmonic pulsations. The domain of applicability of results obtained on the scale of pulsation frequencies is determined.

Heterogeneous nucleation on aerosol particles

We have applied density functional theory in statistical mechanisms to study the heterogeneous nucleation of supersaturated vapors on spherical aerosol-like substrates. Our calculations reveal the inadequacy of the classical nucleation theory in describing the condensation of droplets on very small particles. The latter approach is particularly inaccurate both at high supersaturations and in the vicinity of the wetting transition. Comparisons are also made with recent experimental results for the condensation of supersaturated vapors on submicrometer particles.

The History of Condensation Nucleus Counters

Condensation of supersaturated vapors has been used for more than a century to grow small aerosol particles to sizes that can be detected optically. This paper discusses the history of instruments that use condensation to detect particles. I divide this history into two main sections. The first of these focuses on the development of expansion-type instruments including the ''dust counters'' in which John Aitken played the decisive role and ''photoelectric nucleus counters'' primarily by L. W. Pollak and coworkers. The second section deals with the development of steady-flow condensation nucleus counters (CNCs) in which Jean Bricard and coworkers played the decisive role. The importance of calibration methodologies is also pointed out. Refinements by instrumentation manufacturers and many aerosol scientists have led to the reliable, accurate instruments that are widely used today.

Condensation of supersaturated water vapor on submicrometer particles of SiO2 and TiO2

Condensation of supersaturated water vapor on monodisperse submicrometer SiO2 and TiO2 particles is investigated in a flow cloud chamber (FCC). The dependence of the critical supersaturation Scr on particle size in the range of 15 to 120 nm and on temperature in the range of 10 to 50 °C are determined experimentally. The results show that the experimental Scr decreases with increasing particle size, at a rate in reasonable agreement with that predicted by Fletcher’s version of Volmer’s theory of heterogeneous nucleation, but decreases with increasing temperature at a rate higher than that predicted by Fletcher’s theory. The experimental Scr is smaller than the theoretical prediction even with the line tension and surface diffusion taken into account; the particles induce heterogeneous nucleation better than theory predicts even for perfectly wetted particles. The discrepancy cannot be fully accounted for by the effects of line tension, surface diffusion, or the curvature dependence of the physical properties. The condensation of supersaturated vapor on singly-positively-charged particles with diameters of 30, 60, and 90 nm is also examined. No obvious effect of charge on Scr is observed, in agreement with the theoretical prediction. The law of corresponding states was extended to heterogeneous nucleation, and a simple correlation was obtained.

Automated particle collection and analysis. Near-real time measurement of aerosol cerium (III)

Growth of particles by supersaturated vapor condensation followed by impaction-based collection allows efficient collection of atmospheric particles in the micron and submicron range and results in a liquid output stream in which the collected particles are dissolved or suspended. The original apparatus ( Anal. Chem., 67, 1995, 71–78) has been substantially improved by obviating the need for a thermoelectrically cooled flow through the maze. The instrument is investigated for its potential to collect and measure metallic constituents in submicron size aerosols. Sodium sulfate aerosols containing traces of Ce (III) sulfate were used as the test aerosol. A fluorometric method was used to measure Ce (III). Excellent collection efficiencies and a limit of detection of 200 fmol m −3 air were observed.

Condensation of supersaturated vapors on monovalent and divalent ions of varying size

Vapor nucleation induced by seed ions of controlled size and charge is studied for several monovalent positive and negative ions as well as divalent cations. Ions from dissolved salts are transferred into a gas via electrospray, purified by differential mobility selection, and introduced into a condensation nucleus counter of the mixing type using supersaturated dibutyl phthalate vapors. The number of drops nucleated on the ions is then measured as a function of the vapor supersaturation S. None of the anions tested is activated. Singly charged cations with mobilities Z from 0.48 up to 0.93 cm2/V/s are activated at values of ln S 30% smaller than predicted by Thomson’s model. All doubly charged cations tested (Z from 0.46 to 1.08 cm2/V/s) fall very near the Thomson curve, independently of their size or of whether the double ionic charge is localized on one metal atom or on two separate monovalent sites.

Condensation of supersaturated vapors. X. Pressure and nonideal gas effects

Calculations of temperatures and supersaturations in nucleation experiments often include the assumption that all gases are ideal and they ignore the increase in vapor pressure due to the presence of noncondensible gases. Regardless of experimental technique, such assumptions can lead to substantial errors when comparing experiment to theory, especially when included in only one or the other. To demonstrate these effects, the procedures for calculating the temperatures and supersaturations in thermal diffusion cloud chambers are examined in detail. Nonideal gas effects do alter them; however, these effects also alter the rates calculated by nucleation theory and the effect is larger on nucleation theory than on the analysis of the experimental data. Due to the presence of noncondensible gases there also is a Poynting type effect, but it very nearly cancels in thermal diffusion cloud chambers when included consistently in both theory and experiment. An additional effect which arises only in nucleation theory is the nonzero compressibility of the critical nuclei. The net result (for n-nonane), when these effects are included consistently in both experiment and theory, is to reduce the temperature dependence of the multiplicative correction to theory necessary for agreement with experiment. None of these effects account for the previously observed apparent decrease in nucleation rate with increasing total pressure. Also critically examined are the uncertainties in the transport properties used to calculate the chamber profiles. Of particular interest is the uncertainty in the thermal diffusion factor which changes systematically with composition and thus with total pressure.