Coagulation Of Aerosol Particles Research Articles

Symmetries and Invariant Solutions for the Coagulation of Aerosols

The coagulation of aerosol particles plays an important role in the structural morphological changes of suspended particles at any time and in any space. In this study, based on the Smoluchowski equation of population balance, a kinetic model of aerosol coalescence considering Brownian motion collision is established. By applying the developed Lie group method, we derive the allowed infinitesimal symmetries and group-invariant solutions of the integro-differential equation, as well as the exact solution under some special conditions. We also provide detailed steps and a discussion of the properties. The content and results provide an effective analytic solution for the progressive evolution of aerosol particle size considering boundary and initial conditions. This solution reveals the self-conservative phenomena in the process of aerosol coalescence and also provides validation for the numerical algorithms of general dynamics equations.

Modeling particle nucleation and growth over northern California during the 2010 CARES campaign

Abstract. Accurate representation of the aerosol lifecycle requires adequate modeling of the particle number concentration and size distribution in addition to their mass, which is often the focus of aerosol modeling studies. This paper compares particle number concentrations and size distributions as predicted by three empirical nucleation parameterizations in the Weather Research and Forecast coupled with chemistry (WRF-Chem) regional model using 20 discrete size bins ranging from 1 nm to 10 μm. Two of the parameterizations are based on H2SO4, while one is based on both H2SO4 and organic vapors. Budget diagnostic terms for transport, dry deposition, emissions, condensational growth, nucleation, and coagulation of aerosol particles have been added to the model and are used to analyze the differences in how the new particle formation parameterizations influence the evolving aerosol size distribution. The simulations are evaluated using measurements collected at surface sites and from a research aircraft during the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted in the vicinity of Sacramento, California. While all three parameterizations captured the temporal variation of the size distribution during observed nucleation events as well as the spatial variability in aerosol number, all overestimated by up to a factor of 2.5 the total particle number concentration for particle diameters greater than 10 nm. Using the budget diagnostic terms, we demonstrate that the combined H2SO4 and low-volatility organic vapor parameterization leads to a different diurnal variability of new particle formation and growth to larger sizes compared to the parameterizations based on only H2SO4. At the CARES urban ground site, peak nucleation rates are predicted to occur around 12:00 Pacific (local) standard time (PST) for the H2SO4 parameterizations, whereas the highest rates were predicted at 08:00 and 16:00 PST when low-volatility organic gases are included in the parameterization. This can be explained by higher anthropogenic emissions of organic vapors at these times as well as lower boundary-layer heights that reduce vertical mixing. The higher nucleation rates in the H2SO4-organic parameterization at these times were largely offset by losses due to coagulation. Despite the different budget terms for ultrafine particles, the 10–40 nm diameter particle number concentrations from all three parameterizations increased from 10:00 to 14:00 PST and then decreased later in the afternoon, consistent with changes in the observed size and number distribution. We found that newly formed particles could explain up to 20–30 % of predicted cloud condensation nuclei at 0.5 % supersaturation, depending on location and the specific nucleation parameterization. A sensitivity simulation using 12 discrete size bins ranging from 1 nm to 10 μm diameter gave a reasonable estimate of particle number and size distribution compared to the 20 size bin simulation, while reducing the associated computational cost by ~ 36 %.

Study of the Coagulation of Aerosol Particles and Disaggregation of Powder of Nanoglobular Disperse Carbon during Movement in An Air Flow

Study of the Coagulation of Aerosol Particles and Disaggregation of Powder of Nanoglobular Disperse Carbon during Movement in An Air Flow

The coagulation of aerosol particles in turbulent flow

A statistical model is given for determining the kernel of coagulation in the presence of turbulent, Brownian, gradient, and gravitational mechanisms of collisions in view of accumulation effect.

Numerical modeling of the formation of aerosol particles in jet engine plumes

The formation of liquid sulfate aerosols in the isobaric axisymmetric plume of a subsonic aircraft is modeled numerically. The specific features of the appearance and evolution of sulfate aerosols attributable to 2D effects, such as the parameter nonuniformity in the initial section (at the nozzle outlet), mixing of the hot engine jet with the cold air stream, and the transverse turbulent diffusion of aerosol particles and gas mixture components. The equations of gas dynamics for a turbulent axisymmetric jet, the equations of chemical kinetics, the equations for the liquid fractions (water and sulfuric acid), and the relations for the binary nucleation, condensation growth and coagulation of aerosol particles are used. The distributions of the parameters determining the formation of the aerosol phase in the exhaust plume of a B-747 aircraft are obtained and the geometry of the nucleation zone in this plume is determined.

Influence of Condensation on Coagulation of Aerosol Particles during Their Brownian and Turbulent Motion

Influence of Condensation on Coagulation of Aerosol Particles during Their Brownian and Turbulent Motion

Coagulation of aerosol particles in intermittent turbulent flows

Coagulation of aerosol particles in intermittent turbulent flows

The effect of weak Shear-induced motion on brownian coagulation of aerosol particles

The coagulation rate of a dilute polydisperse aerosol dispersion of particles is considered for small Peclet number, which provides a measure of the ratio of the relative shear-induced motion to Brownian motion between two rigid spherical aerosol particles. The asymptotic form of the relative velocity of two unequal particles immersed in a simple shear flow when they are far apart is obtained. Using a singular perturbation method, a two term expansion for the dimensionless coagulation rate (Nusselt number) as function of the Peclet number is developed. In the limit of the radius of one of the two spheres becoming small, the result agrees with the dimensionless mass transfer rate to an aerosol particle at small Peclet number.

Simulation of Brownian Coagulation in the Presence of van der Waals Forces and Viscous Interactions

Coagulation of aerosol particles in the size range of 0.001–10 μm in particle aerodynamic diameter is simulated by using a model based on a sectional representation of the aerosol size distribution. The influence of van der Waals forces and viscous interactions are both incorporated, and this interaction enhanced coagulation is compared with coagulation resulting from pure Brownian movement. The interparticle van der Waals potential applied in calculations is based partially on Hamaker's theory and partially on the limiting approximations to the equations of Langbein. Viscous interactions are incorporated by using a corrected form of the particle binary diffusion coefficient. As expected, coagulation between ultrafine particles was clearly enhanced due to the interactions. No essential differences between Brownian and interaction influenced coagulation was to be seen above 0.05 μm of particle diameter or between particles located in separate size modes.

Log-Normally Preserving Size Distribution for Brownian Coagulation in the Free-Molecule Regime

Coagulation of aerosol particles in the free-molecule regime has been studied theoretically by converting the governing partial integrodifferential equation into a set of two ordinary differential equations. The approach assumes that the size distribution of an aerosol attains or can at least be represented by a time-dependent log-normal distribution function during the coagulation process. The calculations have been performed and the results found to be in good agreement with results for previous theories. In addition, the following asymptotic size distribution function is found as an alternative solution for the self-preserving particle size distribution function for Brownian coagulation of an aerosol in the free-molecule regime: , where n is the particle size distribution function, N ∞ is the total number of particles, r is the particle radius, and rg∞ is the geometric mean particle radius. In terms of the parameters used by the self-preserving size distribution theory, the proposed distribution is wri...

火山噴火後に見られる成層圏エアロゾル層のdecay過程におけるエアロゾルの凝集及び凝縮の役割

火山噴火後に見られる成層圏エアロゾル層のdecay過程におけるエアロゾルの凝集及び凝縮の役割

ChemInform Abstract: EFFECT OF BROWNIAN DIFFUSION ON CHEMICAL KINETICS

A new method of theoretical prediction of the kinetic rate constants of fast chemical reactions in solutions is presented. It takes into account the effect of finite diffusive displacements of the reacting molecules. The approach is based on the solution of the steady-state Fokker–Planck equation by the moments method of Grad developed in the theory of coagulation of aerosol particles. A comparison of the predicted rate constants with the experimental data provided by Schuh and Fischer for the self-reaction of tert-butyl radicals in n-alkanes shows a good correspondence.

Some remarks about the coagulation of aerosol particles by Brownian motion

The development of the theory for collision and coagulation of aerosols in Brownian motion is reviewed. Theoretical conclusions resulting from the application of continuum theory are compared with calculations based on the kinetic theory of gases. These two approaches lead to different results which are applicable only to charged dilute aerosol clouds, in a limited range of the ratio of the mean free path of the suspending medium λ to the particle radius R. The present theories suggest that ( a) the rate of coagulation of aerosols reaches a maximum between the ratio λ/ R = 5 and 10, ( b) charging of particles should have an increasing effect on coagulation rates as the ratio of the average charge per particle to the particle radius increases. There is a substantial region of aerosol behavior for which the present theory and experimental work are incomplete, particularly in accounting for the effects of charged particles. It is likely that a completion of the theory for coagulation of aerosols must await new developments in the physics of ionized dense gases.