Aerosol Coagulation Research Articles

Evaluation of the relative deviation for coagulation and gravitational sedimentation model from experimental results of submicron aerosol in water vapor environments

This paper evaluates the relative bias of submicron aerosol coagulation and gravity deposition experiments and model prediction results under water vapor conditions, and discusses the model prediction bias results at high steam fraction. When submicron aerosols are at room temperature and lower vapor molar ratios, the model predictions and experimental results are in good agreement. When the molar fraction of steam is high, the prediction results of the model are poor. Through analyzing thermal data and conducting gas superheating experiments, it was found that under saturated steam conditions in the experimental vessel, the number of suspended small droplets also increases with the increase of steam molar fraction. The presence of these droplets alters the coagulation and sedimentation results of submicron aerosols. Based on experimental data, this paper adds correction coefficients of coalescence and sedimentation to the original model, making it suitable for predicting submicron aerosol coagulation and sedimentation under high steam molar fraction.

Sedimentation of a Fine Aerosol in the Acoustic Fieldand with the Electrostatic Charge of Particles

Finding an efficient way to eliminate fine dust (particle diameter of 1–15 μm) from a room can be a challenging problem. Acoustic radiation emitters are widely used to accelerate particle coagulation and sedimentation. In this study, we propose one more method for depositing harmful particles – dispersion of electrostatically charged particles. These particles attract uncharged particles from the air and accelerate coagulation. The paper is devoted to a comparison of methods for the acoustic and electrostatic sedimentation of aerosols. The mathematical model for the coagulation of aerosols on the basis of Smoluchowski’s equation is proposed in the options corresponding to acoustic and electrostatic coagulation. A number of conclusions about the most effective conditions of sedimentation were made on the basis of the analysis of a kernel type of Smoluchowski’s integral equation. The results of the experiments on acoustic and electrostatic sedimentation of the model aerosol media (coal dust) are given. The results of the calculations according to the mathematical model of coagulation taking into account the proposed mechanisms for the sedimentation of aerosols in the acoustic field and electrostatic charging of particles are given.

Promoting the synergistic removal of SO3 aerosols and particles during the flue gas condensation by combining alkali spray and turbulent agglomeration

In the condensation process of desulfurized flue gas, not only the flue gas waste heat can be recovered, but also the SO3 aerosols and particles can be removed synergistically. However, the deep purification ability of a single heat exchanger for flue gas is quite poor. In this work, a novel removal technology is proposed for the synergistic removal of SO3 aerosols and particles in the process of flue gas condensation by combining alkali spray and turbulent agglomeration. The agglomeration and capture mechanisms were analyzed by simulating the motion trajectory and calculating the capture efficiency of single alkali droplets. The removal performance of this combined technology was evaluated through experiments. The vertexes generated in the turbulent agglomeration device can promote the agglomeration or coagulation of SO3 aerosols and particles, and finally achieve the enhanced capture effect of these particles by alkali droplets. Compared with the single alkali spray or turbulent agglomeration, the combined technology can achieve better removal performance. The number removal efficiency of the combined technology is up to 78.4% and the mass removal efficiency of SO3 and particles reaches 61.8% and 94.5% respectively under typical conditions. Moreover, the mass removal efficiencies of SO3 aerosols and particles all increase with the increase of initial particle concentration, spray amount of alkaline solution, and flue gas temperature drop.

On the Impact of Bell Sound on Ambient Particulates

Here the authors examine whether bell sounds can have an impact on ambient aerosol levels and size distribution under atmospheric conditions. The authors present calculation results for acoustic the coagulation by church bell sounds for a range of ambient aerosol types. The results show that for orthokinetic sonic agglomeration, while the frequency spectrum of church bells is ideal for causing coagulation of ambient aerosols, the sound pressure level (SPL) becomes too low for an effect. However, in very polluted conditions, at extremely short distances from the bell dust aerosols can readily undergo sonic coagulation.

High Free‐Tropospheric Aitken‐Mode Aerosol Concentrations Buffer Cloud Droplet Concentrations in Large‐Eddy Simulations of Precipitating Stratocumulus

AbstractA new Aitken mode aerosol microphysics scheme is developed for a large eddy simulation model in order to better investigate cloud‐aerosol interactions in the marine boundary layer and to study the Aitken buffering hypothesis of McCoy et al. (2021), https://doi.org/10.1029/2020jd033529. This scheme extends the single‐mode two‐moment prognostic aerosol scheme of Berner et al. (2013), https://doi.org/10.5194/acp-13-12549-2013. Seven prognostic variables represent accumulation and Aitken log‐normal aerosol modes in air and droplets as well as 3 gas species. Scavenging of interstitial and other unactivated aerosol by cloud and rain drops are treated using the scheme described in Berner et al. (2013), https://doi.org/10.5194/acp-13-12549-2013. The scheme includes coagulation of unactivated aerosol and a simple chemistry model with gas phase H2SO4, SO2, and DMS as prognostic variables to capture basic influences of sulfur chemistry on the model aerosols. Nucleation of H2SO4 aerosol particles from gas‐phase H2SO4 is neglected. A deep, precipitating stratocumulus case (VAMOS Ocean Cloud Atmosphere Land Study RF06) is used to test the new scheme. The presence of the Aitken mode aerosol increases the cloud droplet concentration through activation of the larger Aitken particles and delays the creation of an ultraclean, strongly precipitating cumulus state. Scavenging of unactivated accumulation and Aitken particles by cloud and precipitation droplets accelerates the collapse. Increasing either the above‐inversion Aitken concentration or the surface Aitken flux increases the Aitken population in the boundary layer and prevents the transition to an ultraclean state.

Experimental and Numerical Study on the Gravitational Deposition and Coagulation of Aerosols

The gravitational deposition and coagulation of aerosols were studied experimentally based on the COSTTHES (Containment Source-Term and Thermal Hydraulics Experiment System) facility and numerically investigated based on a continuous general dynamic equation; the experimental and the numerical results were in good agreement. In the present study, the applicability of the zero-dimensional model for deposition and coagulation of aerosols was verified. A considerable distortion can occur due to the coagulation of the aerosol, which significantly influenced the removal rate of the aerosol with a diameter greater than 0.76 µm, and the dynamic shape factor value of the aerosol used in the present experiment was obtained as 4. In the experimental and numerical studies, it was found that the combined effect of the gravitational deposition and coagulation of the aerosol can increase the number density of the aerosol with specific diameters, and the concentration-increment size would increase as settling continued.

Numerical Modeling of Droplet Aerosol Coagulation, Condensation/Evaporation and Deposition Processes

The differentially weighted operator-splitting Monte Carlo (DWOSMC) method is further developed to describe the droplet aerosol dynamic behaviors, including coagulation, deposition, condensation, and evaporation processes. It is first proposed that the droplet aerosols will experience firstly condensation and then evaporation, and this phenomenon is first implemented into the Monte Carlo method and sectional method with considering coagulation, deposition, and condensation/evaporation processes in both single-component and two-component aerosol particle systems. It is found that the calculated results of the DWOSMC method agree well with both the analytical solutions and the sectional method. The further developed DWOSMC method can predict the variation of particle number density, total particle volume, mean particle diameter, particle size distributions, and the component-related particle volume densities in both single component and two-component droplet aerosol systems considering coagulation, deposition, and condensation/evaporation processes.

Numerical study of the effect of droplet coagulation on the dynamics of a two-fraction aerosol in an acoustic resonator

The study is devoted to the study of the effect of coagulation of dispersed phase droplets on aerosol oscillations in an acoustic resonator. The mathematical model of aerosol dynamics implements a continuous mathematical model of the dynamics of a multiphase medium, taking into account the velocity and thermal inhomogeneity of the mixture components. To describe the dynamics of the carrier medium, a two-dimensional unsteady system of Navier – Stokes equations for a compressible gas is used, written taking into account the interphase force interaction and interphase heat transfer. To describe the dynamics of the dispersed phase, a system of equations is solved for each of its fractions, including the continuity equation for the «average density» of the fraction, the equations for the conservation of the spatial components of the momentum and the equation for the conservation of thermal energy of the fraction of the dispersed phase of the gas suspension. The interphase force interaction included the Archimedes force, the force of the added masses and the force of aerodynamic drag. The heat exchange between the carrier medium - gas and each of the dispersed phase fractions was also taken into account. The mathematical model of the dynamics of a polydisperse aerosol was supplemented by a mathematical model of collisional aerosol coagulation. For the velocity components of the mixture components, uniform Dirichlet boundary conditions were specified. For the remaining functions of the dynamics of the multiphase mixture, homogeneous Neumann boundary conditions were specified. The equations were solved by the explicit McCormack method with a nonlinear correction scheme that allows obtaining a monotonic solution. As a result of numerical calculations, it was determined that a region with an increased content of coarse particles is formed in the vicinity of the oscillating piston. The coagulation process leads to a monotonic increase in the volumetric content of the fraction of coarse particles and a monotonic decrease in the volumetric content of fine particles.

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.

Numerical study of the effect of droplet coagulation intensity on polydisperse aerosol fraction distribution

The paper is devoted to the study of the effect of the intensity of aerosol fluctuations on the distribution of fractions of the dispersed component of the coagulating aerosol. Oscillations of aerosol in closed channel are numerically modeled in operation. To describe the dynamics of the carrier medium, a two-dimensional non-stationary system of Navier-Stokes equations for compressed gas is used. They are written taking into account interfacial power interaction and interfacial heat exchange. To describe the dynamics of the dispersed phase, a system of equations is solved for each of its fractions. It includes an equation of continuity for the “average density” of the fraction, equations of preservation of spatial components of the pulse and an equation of preservation of thermal energy of the fraction of the dispersed phase of the gas suspension. Phase-to-phase power interaction included Archimedes force, attached mass force, and aerodynamic drag force. Heat exchange between the carrier medium-gas and each of the fractions of the dispersed phase was also taken into account. The mathematical model of dynamics of polydisperse aerosol was supplemented by the mathematical model of collision coagulation of aerosol. For the velocity components of the mixture, uniform Dirichlet boundary conditions were set. For the remaining functions of the dynamics of the multiphase mixture, uniform Neumann boundary conditions were set. The equations were solved by the explicit McCormack method with a nonlinear correction scheme that allows to obtain a monotone solution. As a result of numerical calculations, it was determined that in the vicinity of the oscillating piston, an area with an increased content of coarse particles is formed. The coagulation process results in a monotonous increase in volume content of the coarse particle fraction and a monotonous decrease in volume content of fine particles. Increasing the intensity of gas fluctuations leads to intensification of the process of coagulation of aerosol droplets.

On the concentration of SARS-CoV-2 in outdoor air and the interaction with pre-existing atmospheric particles

The spread of SARS-CoV-2 by contact (direct or indirect) is widely accepted, but the relative importance of airborne transmission is still controversial. Probability of outdoor airborne transmission depends on several parameters, still rather uncertain: virus-laden aerosol concentrations, viability and lifetime, minimum dose necessary to transmit the disease. In this work, an estimate of outdoor concentrations in northern Italy (region Lombardia) was performed using a simple box model approach, based on an estimate of respiratory emissions, with a specific focus for the cities of Milan and Bergamo (Italy). In addition, the probability of interaction of virus-laden aerosol with pre-existing particles of different sizes was investigated. Results indicate very low (<1 RNA copy/m3) average outdoor concentrations in public area, excluding crowded zones, even in the worst case scenario and assuming a number of infects up to 25% of population. On average, assuming a number of infects equal to 10% of the population, the time necessary to inspire a quantum (i.e. the dose of airborne droplet nuclei required to cause infection in 63% of susceptible persons) would be 31.5 days in Milan (range 2.7–91 days) and 51.2 days in Bergamo (range 4.4–149 days). Therefore, the probability of airborne transmission due to respiratory aerosol is very low in outdoor conditions, even if it could be more relevant for community indoor environments, in which further studies are necessary to investigate the potential risks. We theoretically examined if atmospheric particles can scavenge virus aerosol, through inertial impact, interception, and Brownian diffusion. The probability was very low. In addition, the probability of coagulation of virus-laden aerosol with pre-existing atmospheric particles resulted negligible for accumulation and coarse mode particles, but virus-laden aerosol could act as sink of ultrafine particles (around 0.01 μm in diameter). However, this will not change significantly the dynamics behaviour of the virus particle or its permanence time in atmosphere.

Study of coagulation efficiency of highly dispersed particles under the influence of high intensity ultrasonic vibrations

The article presents the results of experimental studies of the coagulation efficiency of fine-dispersed particles at the influence of high-intensity ultrasonic vibrations in various modes (including the standing wave mode). The study of the influence of various conditions of ultrasonic exposure on aerosol coagulation efficiency was conducted on the developed stand. The optimal distance from the ultrasonic emitter to the reflector has been established. This distance ensures maximum efficiency of aerosols coagulation at standing wave mode. Thus, it is possible to increase coagulation efficiency up to 2 times at optimal conditions.

The ION‐CAGE Code: A Numerical Model for the Growth of Charged and Neutral Aerosols

AbstractThe presence of small ions influences the growth dynamics of a size distribution of aerosols. Specifically, the often neglected mass of small ions influences the aerosol growth rate, which may be important for terrestrial cloud formation. To this end, we develop the Ion and Charged Aerosol Growth Enhancement (ION‐CAGE) code, a numerical model to calculate the growth of a species of aerosols in the presence of charge, which explicitly includes terms for ion condensation. It is shown that a positive contribution to aerosol growth rate is obtained by increasing the ion‐pair concentration through this ion condensation effect, consistent with recent experimental findings. The ion condensation effect is then compared to aerosol growth from charged aerosol coagulation, which is seen to be independent of ion‐pair concentration. Growth rate enhancements by ion condensation are largest for aerosol sizes less than ∼25 nm and increases proportional to the ion concentration. The effect of ion condensation is expected to be most important over pristine marine areas. The model source code is made available through a public repository.

Numerical Simulation of Aerosol Coagulation by LD Method

Numerical Simulation of Aerosol Coagulation by LD Method

Evaluation of thermophoretic effects on graphite dust coagulation in high-temperature gas-cooled reactors

In high-temperature gas-cooled reactors, graphite dust particles within the reactor core and the heat transfer equipment experience large temperature gradients. Under such conditions, thermophoresis may play an important role in determining aerosol evolution. This study presents a theoretical and numerical analysis of the thermophoretic effects on aerosol coagulation within these reactors. The coagulation rates for Brownian versus thermophoretic coagulation are calculated and compared for various temperature gradients. Our results show that thermophoretic coagulation dominates over Brownian coagulation for large temperature gradients. We defined an enhancement factor to evaluate the role of thermophoretic coagulation under various reactor conditions. The enhancement factor increased dramatically with increasing temperature gradient, decreasing pressure and increasing particle diameter, but was not very sensitive to temperature change. The time evolution of the particle size distribution related to combined Brownian and thermophoretic coagulation was simulated using a log-skew-normal method of moments. The simulation results indicate that aerosol evolution can be strongly accelerated by thermophoretic coagulation under large temperature gradients.

Use of nanodiamond for absorption of aerosol particles

Fine dust and fog which are formed on some productions are known to be a harmful factor of the environment. Particles of aerosol with a characteristic size less than 20 microns are especially hazardous to man health. Various ways, for example, electric precipitators and ultrasonic coagulation are applied to their catching. One of the new offered ways of neutralization of harmful aerosol structures is spraying in the air of nanostructural powder of a sorbent. Nanodiamond can be used as such sorbent, and electrostatic charging of particles can significantly increase the speed and efficiency of sorption. The purpose of work consists in the description of a method of neutralization of fine aerosol by means of the nanodiamond powder which is specially sprayed in the air with the electrostatic. Research methods: mathematical modeling, optical methods of measurement of dispersion and concentration of aerosol. The mathematical model of coagulation of aerosols based on an integrated type of the equation of Smolukhovsky with a type of the kernel considering a charge of particles allows calculating the speed of coagulation and sedimentation of aerosol. The electrostatic charge of sorbent particle is shown to lead to a significant acceleration of processes of coagulation and to interactions of a sorbent with sorptive. Results of a pilot and theoretical study of processes of electrostatic coagulation of fine aerosols are given in the article. Comparison of estimated and experimental results of the dynamics of coagulation and sedimentation of electrostatic charged and electroneutral particles of nanodiamond and sorbents with a larger initial size of particles is led. The characteristic time of interaction of particles of a sorbent with particles of harmful aerosol media is determined, the time of sedimentation of an aerosol cloud depending on the size of particles of a sorbent and a method of their dispersion. Results of work can be used in the systems of cleaning of the air environment off harmful aerosol emissions.

Ash aerosol partitioning and ash deposition during the combustion of petroleum coke/natural gas mixtures

This paper is concerned with the formation of ash aerosols and their subsequent deposition on a heat transfer surface during the combustion of petroleum coke. The subject is of interest for two reasons: first, petroleum coke is a good alternate fuel for power plants, and fouling has been identified as a challenging problem, especially under fuel rich conditions; second, this work sheds light on ash aerosol partitioning and subsequent deposition mechanisms as these relate to the fate of organically bound metals in solid fuels in general. In this work, which did not focus on ignition but on ash transformations and deposition, a 100 kW rated down-fired laboratory combustor was employed and natural gas was co-fired with the coke in order to facilitate ignition. Two conditions were considered: 1) air combustion (denoted as Air); 2) oxy combustion with 70% O2 in the inlet oxidant gas (denoted as OXY70). Experimental data presented here consist of particle size distributions (PSD’s), size segregated ash aerosol compositions and information on deposit compositions on a temperature controlled deposit probe. Experimental aerosol size distributions differ between air- and oxy-combustion conditions and are in good agreement with aerosol coagulation theory. The submicron mode in the ash aerosol PSD is proportionately several orders of magnitude greater (on a per kg total ash basis) for petroleum coke than it is for coal. Surprisingly, compositions of the ash deposits are dominated by Fe even though the Fe content in raw petroleum coke ash is low.

Coagulation of the Ionized Combustion Products in a Dust Flame of Aluminum Particles

The addition-agent effect of atoms of alkali metals (K, Na, Li, and Cs) and halogens (Cl and I) introduced into the combustion zone of a dust flame of aluminum particles on the average size of Al2O3 nanoparticles is studied. A physical model of coagulation of a monodisperse aerosol is proposed. The model takes into account the formation of a complex plasma consisting of positive and negative ions, electrons, neutral gas molecules, and suspended particles of the condensed phase in the combustion zone. The effect of the forces of Coulomb repulsion of unipolarly charged Al2O3 particles as well as their possible attraction by ion wind on the constant of the coagulation rate is also taken into account. It is shown that at low ion concentrations in the plasma, the coagulation rate is determined by the Coulomb repulsion of the particles, and at ion concentrations greater than 1020 m−3 the coagulation rate is determined by the attraction of the particles by the ion wind. The results of calculations of the dependence of the average Al2O3 particle size on the concentration of the additives are in a good quantitative agreement with the experimental data. The combined effect of the additives and the equilibrium products of aluminum oxide (AlO, Al, and Al2O) evaporation on the concentration of positive and negative gas ions, electrons, and Al2O3 particle size in the condensation zone is analyzed. The peculiarities of the influence of the additives of electronegative gases (Cl and I atoms) on the coagulation rate of a thermally ionized aerosol and on the particle size of Al2O3 are considered.

Experimental Investigation of Decontamination Factor Dependence on Aerosol Concentration in Pool Scrubbing

Because a pool scrubbing is important for reducing radioactive aerosols to the environment for a nuclear reactor in a severe accident situation, many researches have been performed. However, decontamination factor (DF) dependence on aerosol concentration was seldom considered in an aerosol number concentration with limited aerosol coagulation. To investigate an existence of DF dependence on the concentration, DF in a pool scrubbing with 2.4 m water submergence was derived from aerosol measurements by light scattering aerosol spectrometers. It was observed that DF increased monotonically with decreasing particle number concentration in a constant thermohydraulic condition: a gradual increase from 10 to 32 in the range of 1.3×1011 - 8.0×1011/m3 at the inlet and a significant increase from 32 to 77 in the range of 3.6×1010 - 1.3×1011/m3. Two validation experiments were conducted in the range with the gradual DF increase to confirm whether the DF dependence is a real pool scrubbing phenomenon. In addition, characteristics of the DF dependence in different water submergences were investigated experimentally. It was found that the DF dependence became more significant in higher water submergence. Significant DF dependence was observed in the condition of the water submergence higher than 1.6 m and the inlet particle number concentration less than around 1×1011 /m3. It is recommended to perform further analysis for the DF dependence mainly in such condition since it could make a difference to both experiment and model of the pool scrubbing.

Effects of near-source coagulation of biomass burning aerosols on global predictions of aerosol size distributions and implications for aerosol radiative effects

Abstract. Biomass burning is a significant global source of aerosol number and mass. In fresh biomass burning plumes, aerosol coagulation reduces aerosol number and increases the median size of aerosol size distributions, impacting aerosol radiative effects. Near-source biomass burning aerosol coagulation occurs at spatial scales much smaller than the grid boxes of global and many regional models. To date, these models have ignored sub-grid coagulation and instantly mixed fresh biomass burning emissions into coarse grid boxes. A previous study found that the rate of particle growth by coagulation within an individual smoke plume can be approximated using the aerosol mass emissions rate, initial size distribution median diameter and modal width, plume mixing depth, and wind speed. In this paper, we use this parameterization of sub-grid coagulation in the GEOS-Chem–TOMAS (TwO-Moment Aerosol Sectional) global aerosol microphysics model to quantify the impacts on global aerosol size distributions, the direct radiative effect, and the cloud-albedo aerosol indirect effect. We find that inclusion of biomass burning sub-grid coagulation reduces the biomass burning impact on the number concentration of particles larger than 80 nm (a proxy for CCN-sized particles) by 37 % globally. This cloud condensation nuclei (CCN) reduction causes our estimated global biomass burning cloud-albedo aerosol indirect effect to decrease from −76 to −43 mW m−2. Further, as sub-grid coagulation moves mass to sizes with more efficient scattering, including it increases our estimated biomass burning all-sky direct effect from −224 to −231 mW m−2, with assumed external mixing of black carbon and from −188 to −197 mW m−2 and with assumed internal mixing of black carbon with core-shell morphology. However, due to differences in fire and meteorological conditions across regions, the impact of sub-grid coagulation is not globally uniform. We also test the sensitivity of the impact of sub-grid coagulation to two different biomass burning emission inventories to various assumptions about the fresh biomass burning aerosol size distribution and to two different timescales of sub-grid coagulation. The impacts of sub-grid coagulation are qualitatively the same regardless of these assumptions.