Growth Of Aerosol Particles Research Articles

Aggregation and growth of submicron oxide particles in flames

Growth of aerosol particles in concentrated silica synthesis flames was measured by laser light scattering. Nitrogen adsorption was employed to characterize surface area. Throughout their detectible existence, the particles consist of flocs or aggregates which contain multitudes of smaller primary or protoparticles. Growth of these primary particles, controlled by fusion rate, is consistent with a classical coalescence model. The rate of aggregate growth is precisely described by a model based on Brownian collision frequencies. Experimental data corresponding to mean Knudsen numbers ranging from 0.3 to 6.0 reveal a shift from free-molecule to continuum behavior that is surprisingly sharp. Excellent agreement between theory and observations is, in fact, observed when the transition occurs at a point.

Nucleation and Growth of Stratospheric Aerosols

Formation mechanisms and nucleation processes are examined, and nucleation in the stratosphere is considered, taking into account binary nucleation, ternary nucleation, binary heterogeneous nucleation, and heteromolecular nucleation. Attention is also given to the growth of aerosol particles, nucleation and growth in models, and the role of aerosols in the upper atmosphere. It is pointed out that various sampling studies and numerical models have provided evidence that the in situ oxidation of sulfur-bearing gases is responsible for the sulfate mass of the stratospheric aerosol. Data obtained by Castleman et al. (1974) suggest that there is a common source of sulfur compounds for the stratosphere of both the northern and southern hemispheres.

A Numerical Determination of the Evolution of Cloud Drop Spectra due to Condensation on Natural Aerosol Particles

The time variation in size of aerosol particles growing by condensation is studied numerically by means of an air parcel model which allows entrainment of air and aerosol particles. Particles of four types of aerosols typically occurring in atmospheric air masses were considered. The present model circumvents any assumption about the size distribution and chemical composition of the aerosol particles by basing the aerosol particle growth on actually observed size distributions and on observed amounts of water taken up under equilibrium by a deposit of the aerosol particles. Characteristic differences in the drop size distribution, liquid water content and supersaturation were found for the clouds which evolved from the four aerosol types considered.

Growth of aerosol particles by adiabatic expansion at the throat of a venturi scrubber

The condensational growth of aerosol particles in the throat section of a venturi scrubber and the contribution of it to the dust collection efficiency were discussed. The condensable water vapor produced in the throat of venturi was quantitatively obtained for various conditions assuming the change in pressure and temperature to be adiabatic process. In terms of this condensable water vapor and the particle number concentration, the diameter of grown particles was determined, and the degree of contribution due to particle growth to the particle collection by venturi scrubber was evaluated as the change in particle collection efficiency involved in the particle growth. Experimental verification of the above results was qualitatively made by changing the humidity of the inlet gas, which is the most important property dominating the particle growth, in the particle collection by venturi scrubber.

Dynamic of the growth of watersoluble aerosol particles in water saturated air

Dynamic of the growth of watersoluble aerosol particles in water saturated air

Some approximations for the wet and dry removal of particles and gases from the atmosphere

Semi-empirical formulae are presented which can be used to estimate precipitation scavenging and dry deposition of particles and gases. The precipitation scavenging formulae are appropriate both for in- and below-cloud scavenging and comparisons with data indicate the importance of accounting for aerosol particle growth by water vapor condensation and attachment of the pollutant to plume or cloud particles. It is suggested that both wet and dry removal of gases is usually dictated by other than atmospheric processes. Dry deposition of particles to a canopy is shown to depend on canopy height, biomass, vegetative type and mean wind. Two large-scale practical problems are addressed dealing with the relative importance of wet and dry deposition and with the sources which contribute to deposition in a specific location.

Phase transformation and growth of aerosol particles composed of mixed salts

Thermodynamical considerations are given to the phase transformation and growth of a mixed-salt particle suspended in moist air. A mathematical expression is derived to relate the equilibrium droplet size to the solution properties of a multicomponent system. It is shown that, at a given relative humidity, the partition between the liquid and solid phases, the chemical form of the solid phase, and the composition of the aqueous solution may be deduced directly from the solubility diagram, provided that water activities are known over the entire concentration range. A graphical method is developed for making incremental extrapolations of wateractivity data from dilute solutions up to the two-phase region. Growth curves for the systems H 2O-NaCl-MgCl 2 and H 2O-H 2SO 4-(NH 4) 2SO 4 have been calculated as a function of r.h. and chemical composition. Depending on humidity and composition, ambient sulfate aerosols may contain (NH 4) 2SO 4, 3(NH 4) 2SO 4, H 2SO 4, or NH 4HSO 4 as the solid phase.

Growth of Aerosol Particles by Condensation

Growth of Aerosol Particles by Condensation

The growth of sulphuric acid aerosol particles when contacted with water vapour

When aerosols of 100% sulphuric acid were contacted with humidified nitrogen it was observed that droplet-vapour equilibrium was reached in less than a few seconds. Calculations of diffusion rates to and into sub-micron sized droplets have predicted this equilibration to be complete in 10 −510 −2 s, depending on original size and surface accommodation. It is inferred that a dropletvapour chemical interaction such as occurs in the atmosphere will be controlled by reaction kinetics, and will be independent of droplet size in the sub-micron range. The dependences of liquid-phase conversion rate on volume fraction and on concentration of a dissolved reactant are in some common circumstances mutually cancelling. It can be concluded that in the event of acid droplets being inhaled there is no risk of their reaching lung tissue before substantial dilution has occurred.

Experimental studies on aerosol particle formation by sulfur dioxide

The formation and growth of aerosol particles of dilute sulfuric acid produced by photochemical oxidation of SO 2 (0.05–10 ppm. by volume) in purified air has been studied qualitatively in laboratory apparatus. The number of particles formed is strongly dependent on SO 2 concentration, relative humidity (< 10–80%) and u.v. light intensity. The number concentration increases rapidly to a maximum within a few minutes after the start of irradiation and then decreases slowly during the next 10 min. Particle size increases with irradiation time and is dependent on SO 2 concentration, and on relative humidity when the SO 2 concentration is less than 0.1 ppm. In the conditions employed the volumetric rate of formation of particles ranged from 0.15 to 18.7μm 3 cm −3. The overall quantum yield of photochemical reaction was 8 × 10 −3. The oxidation rate was 0.04% h −1: extrapolation of this rate to noonday sunlight in summer at latitude 35°N gives 0.7% h −1.

Effect of relative humidity on the size of atmospheric aerosol particles

In situ measurements of the growth of atmospheric aerosol particles with increasing humidity, from 0 to 98 per cent r.h., were made with the use of miniature diffusion batteries and a continuous flow condensation nuclei counter. Particle size distributions computed from the battery measurements were log normal. The number median diameter (NMD) increased two-fold from 0.018 to 0.036 μm over the range of humidity. The range of geometric S.D. ( σ g ) for the particle size distributions was 1.53–2.06 with the larger NMD having the smaller σ g . This indicates that the smaller particles grew proportionately more than the larger.

The growth of atmospheric aerosol particles as a function of the relative humidity—II. An improved concept of mixed nuclei

This paper deals with processes influencing the growth of continental atmospheric aerosol particles ( r > 0·1 μm) with relative humidity. The results presented are valid for average conditions, individual cases may of course yield deviations. The main results are: 1. (1) Atmospheric aerosol particles each consist of a mixture of different substances. 2. (2) Atmospheric aerosol particles show continuous smooth growth, without suddenly increased or reduced absorption of water, unlike pure salt particles whose growth is characterized by a sharp increase at the critical humidity. This feature is controlled by three properties of the atmospheric aerosol particles: The steady and smooth growth character is caused by 2.1. (a) gradual deliquescence of soluble matter with increasing humidity, the reverse being observed for decreasing humidity. Reduced absorption of water is caused by 2.2. (b) insoluble matter which amounts to about 40 per cent of the aerosol mass and 2.3. (c) increase of the solubility of the various ions due to their mutual interaction in the special salt mixture forming the water soluble fraction of the aerosol particles. 2.4. (3) Variations in content of insoluble matter and in chemical composition contribute almost equally to the effect on the growth curve. 2.5. (4) Growth curves can be described by the following equation r/r o=(1+ C ∗F(ƒ)/(1−ƒ)) 1 3 r being the radius at the relative vapour pressure ƒ, r o the particle radius at ƒ = 0, F the dissolving characteristic describing the gradual deliquescence of the water soluble matter with relative humidity, and C = sav, a constant where s is the fraction of water soluble matter within the sample, v the ratio of the density of the aerosol particles to the density of water, and a a dimensionless constant ( a ≈ 0·14 on the average) which is a measure of the solubility of the soluble matter.