Charged Aerosol Particles Research Articles

Efficiency of filtration through fibrous materials with nonuniform charge distribution on fibers

Formulas have been derived for electric fields generated by charges arbitrarily distributed over the surface of cylindrical fibers with circular cross sections. The Monte Carlo method has been used to determine the efficiency of aerosol filtration for a cell model implying a three-dimensional character of the motion of particles being captured. The collection efficiency for weakly charged particles has been studied as depending on particle diameter and charge density distribution on fibers for several modes. It has been shown that there is a range of sizes of charged aerosol particles for which a nonuniform distribution of charges over fibers increases the filtration efficiency as compared with the uniform distribution in a filter, which is, on average, neutral. A model has been proposed for Hansen filters, and the dependences of penetration of particles on their diameters and charges generated on resin particles deposited onto wool fibers have been plotted.

Mechanism of the formation of tropospheric nanoaerosols

The atmospheric aerosol is among the most significant environmental and climate formation factors. Therefore, studies of the physicochemical properties of aerosols and the dynamics of aerosol formation are of paramount importance for forecasting climatic changes on the Earth. The spread of aerosols from the source of pollution dramatically affects human health. A special role is played by secondary nanoaerosols, which easily penetrate the human body. In this brief overview, we present updated information on the physical chemistry of atmospheric nanoaerosols. Special attention is focused on recent advances in the theories of aerosol particle formation, charging, and growth.

High-efficiency electrical charger for nanoparticles

An electrical charger, based on a point-to-plate DC corona discharge, for the high-efficiency charging of aerosol particles with diameter of a few nanometers, has been designed, constructed, and evaluated. The discharge takes place between a needle and a perforated plate, and the results presented here have shown that this specific design allows reduction of electrostatic losses of charged particles within the charger in comparison with other typical designs. Besides, the small effective volume of the charger leads to a relatively small diffusion loss of particles. As a consequence of the reduced electrostatic and diffusion losses, the extrinsic charging efficiency attainable is higher than in similar devices.

Numerical model of the electro-gas-dynamics of a gas–particle system based on the equations of motion of a two-velocity two-temperature gas–particle mixture

A mathematical model of the electro-gas-dynamics of a gas–particle system is described. A numerical method for solving the system of equations is proposed, and an analysis is made of the motion of charged solid aerosol particles in gas–particle flow in the electric field produced by the corona electrode of the atomizer, the grounded surface on which deposition is performed, and the charge of the aerosol particles in the interelectrode space. The solution is based on the two-velocity two-temperature model of a monodisperse medium without phase transitions and coagulation assuming that only the carrier medium, described by the Navier–Stokes equations for a compressible gas, has viscosity. The dispersed phase is defined by the equation of conservation of mass, the equations of conservation of momentum components taking into account the Coulomb force and aerodynamic friction, and the equation of conservation of internal energy. The system is written in generalized coordinates in dimensionless form and solved using the explicit McCormack method with splitting over the spatial coordinates and a conservative correction scheme. The velocity and density fields of the gas–particle mixture were investigated in the interelectrode space and near the surface on which solid aerosol particles in the gas–particle flow are deposited.

Focused Deposition of Nanoparticles on Polymer Film with an Improved TSI-Nanoparticle Sampler (Model 3089)

A two-dimensional array of spots of deposited nanoparticles as small as 7 × 7 μm was fabricated on a polymer film using a modified commercial nanometer aerosol sampler (NAS; TSI-model 3089) coupled with a surface-discharge microplasma aerosol charger (SMAC). The charged aerosol particles were electrostatically focused by a metal mesh (electrically grounded) on the polymer film (insulator) and electrode (3 kV). The effect of mesh geometry on the concentration ratio (focusing ratio × collection efficiency) was evaluated using monodisperse polystyrene latex particles with diameters of 48, 100, and 300 nm. The electrostatic focusing effect was also analyzed by a numerical simulation of the electrostatic field. The two-dimensional patterning of nanoparticles is an effective method in concentrating particles for the subsequent observation and chemical analysis of aerosol particles. In our experiments, the SMAC-NAS system achieved a net concentration ratio of more than 20 times for 48- and 100-nm particles, whic...

Theory of unipolar charging of particles in dust-ion plasmas.

The theoretical model for description of the unipolar charging of aerosol particles in the dust-ion plasma is proposed. The dependencies of particle charging on the charging time, ion number density, particle sizes and number density are analyzed.

Passage of Charged Particles Through Segmented Axial-Field Tubes

We propose a mathematical theory explaining the passage of charged aerosol particles through segmented tube mobility filters recently suggested by Bezantakos et al. A segmented tube is composed of conductive segments and semiinsulating segments, which are made of electrostatic dissipative material. Electric potential applied to a semi-insulating segment generates a uniform electric field and holds back penetration of charged particles. Analytic equations of penetration efficiency of nondiffusing particles are derived for problems, where the length of the decelerating semi-insulating section exceeds the tube diameter at least twice and the air flow profile is uniform or follows the Hagen–Poiseuille law. The equations well explain the experimental results obtained by Bezantakos et al. The requirements for the tube parameters necessary for the application of analytic equations are derived by means of a numerical model. The motion of particles in segmented tube mobility filters is illustrated with diagrams co...

Development and performance test of a ZnO nanowire charger for measurements of nano-aerosol particles

The most efficient and widely used technique for monitoring aerosol particles is essentially an electrical method. For the development of any miniaturized aerosol classifier based on electrical techniques the miniaturized aerosol charger must provide a sufficient and stable charging efficiency. We designed and fabricated a ZnO nanowire charger (4cm length×2cm width×1cm height) and then carried out an aerosol particle charging performance test. To test the electrical characteristics of this charger, corona currents were measured according to various applied voltages to determine the maximum stable ion number concentration. The average particle charge and wall loss of the charger were evaluated with monodispersed NaCl aerosol particles with diameters of 15–80nm. The particle charge and wall loss were also obtained utilizing FLUENT (version 6.3), a commercial computational fluid dynamics (CFD) software, with an external user-defined function (UDF) code, by solving equations for the electric field, flow field, and particle trajectories. The measured data for particle loss and particle charge were in good agreement with the results calculated by FLUENT.

Area-selective deposition of charged particles derived from colloidal aerosol droplets on a surface with different hydrophilic levels

The effect of chemical treatment of a metallic substrate on the deposition behavior of charged aerosol particles derived from spraying droplets was investigated. A single substrate with areas having different hydrophilic levels was prepared as target surface. The treated (i.e., higher hydrophilic level) area, measured using a surface potential meter, showed a higher negative potential. A numerical simulation predicted that positively charged aerosol particles tended to approach and were subsequently immobilized on the high hydrophilic area. The area with higher hydrophilicity could collect particles with higher number concentration (density) than the other areas. The relationships were demonstrated in (i) the electrostatic surface potential, (ii) the hydrophilicity of surface, and (iii) the enhancement of adhesive force between the deposited particles and the surface.

Charge balance for the mesosphere with meteoric dust particles

An aerosol particle charging model initially developed for noctilucent cloud ice particles has been extended in several steps in order to better explain the data for charged meteoric smoke particles (MSPs) obtained by the nighttime and daytime CHAMPS rockets launched from Andøya, Norway, in October 2011. Addition of photodetachment to the model shows that this process reduces the number density of positively charged MSPs as well as the number density of negatively charged MSPs as a consequence of the photodetached electrons neutralizing the positively charged MSPs. In addition, the model shows that the ionization rate can be deduced from the electron number density and the electron–ion recombination rate only at the highest altitudes (those with ionization rates above 20cm−3s−1) as a consequence of recombination on the MSPs being dominant at lower altitudes. The differences between the daytime and the nighttime rocket data suggest a photodetachment rate between 0.1 and 0.01s−1. A further extension of the model to include the formation of negative ions and their destruction helps explain the ledge seen in the number density of the lightest negatively charged particles. The MSP number densities that are the inputs to the charging model are taken from the CARMA/CHEM2D model. The CHAMPS data are more consistent with number densities generated with an assumed input flux from ablation of 4td−1 than with 44td−1 assumed previously.

Comments on “Effect of Electric Charge on Collisions between Cloud Droplets”

AbstractFletcher’s simple model for the electric force between charged conducting spheres (with reference to cloud droplets) is compared with an exact model and also with another approximate model. His results for the charge ratio as a function of the distance at which the force of attraction changes to one of repulsion differs from that of the other treatments by a factor of 4 at large separations (where the effects of approximations should be negligible) and by a factor of 8 at small separations. The reasons for the discrepancy are explored, and the other treatments are found to be reliable. The attractive force is present for a much larger range of separations, and for more meteorologically plausible charge ratios, than in Fletcher’s results. The general results are discussed in the context of confounding effects of droplet inertia, which is the dominant factor in collisions unless there are very high droplet charges. Inertia is much less important for collisions of charged aerosol particles and cloud droplets, and an important application of models of electric-force calculations is in electrically enhanced scavenging in clouds that are weakly charged by current flow in the global atmospheric electric circuit.

Effect of Electrostatic Charge on Deposition of Uniformly Charged Monodisperse Particles in the Nasal Extrathoracic Airways of an Infant

The fraction of inhaled particles depositing in the nasal extrathoracic airways determines the amount of particles delivered to the lungs of infants. Electrostatic charge on particles can affect this deposition, and for this reason, deposition of charged aerosol particles in the Alberta Idealized Infant nasal geometry is examined. Charged aerosol particles were generated via Plateau-Rayleigh jet breakup atomization with induction charging. Nasal deposition was measured by collecting particles on a filter membrane at the inlet and outlet of the airway and measuring their mass with an ultramicrobalance. The experiments were carried out using monodisperse, uniformly charged particles with aerodynamic diameters of 3-6 μm at two flow rates of 7.5 and 15 L/min, for a charge range of 0-10,000 e per particle. Electrostatic charge effects are largest for the lowest flow rate, smallest particle size, and highest charge level, with deposition in this case being approximately three times that for neutral particles. Higher flow rates and larger particle size result in much weaker electrostatic effects, with even the highest charge levels giving only a few percent higher deposition for the largest particle size and flow rate considered in this study. A dimensionless empirical relation based on the experimental data was developed for predicting deposition of charged particles in the idealized infant airway. Electrostatic charge on inhaled aerosol particles has only a minor effect on deposition for large particles at higher flow rates, because in this case inertial impaction dominates deposition. However, for particles with low inertia, for example, small particles or low flow rates, large values of electrostatic charge strongly increase nasal deposition in the present infant extrathoracic airway.

Nanoaerosol formation in the troposphere under the action of cosmic radiation

The level of cosmic radiation has been shown to affect the rate of nanoparticle formation from gas emissions of natural and anthropogenic origins. The acceleration of particle formation processes is mainly caused by the increased concentration of atmospheric ions, which serve as condensation nuclei and thus strongly change the rate of aerosol charging processes. This paper provides a brief overview of the main processes leading to the formation of nanoparticles in the atmosphere. These processes include nucleation, condensational growth, charged particle growth, charging of aerosol particles, and recombination. Particular emphasis has been placed on the role of particle sizes in charging processes. Also, we discuss the influence of aerosol sinks on the rate of aerosol formation.

In-situ detection of noctilucent cloud particles by the Colorado Dust Detectors onboard the PHOCUS sounding rocket

The Particles, Hydrogen and Oxygen Chemistry in the Upper Summer mesosphere (PHOCUS) sounding rocket campaign is a payload that carried multiple in-situ instruments for the detection of charged icy particles of noctilucent clouds (NLCs). The PHOCUS payload was launched on July 21st, 2011 and carried 18 scientific instruments. Three of these instruments were dedicated to the detection of the charged aerosol particles. All three instruments detected a narrow ice layer at around 81.5km altitude. The Colorado Dust Detectors (CDDs) collected the net charge from the impact of aerosol particles on two graphite surfaces mounted flush with the payload skin. A combination of a small bias potential and permanent magnets were used to suppress the collection of plasma particles. The efficiency of the magnetic shielding improves with increasing altitude where there are fewer scattering collisions with neutrals. The data analysis shows that the net collected current can be decomposed into contributions from photoelectron emission, plasma electrons and ions, and the aerosol particles. The results show that the current corresponding to the collection of aerosol particles is positive, which is due to secondary charging effects.

An electrostatic sensor for the continuous monitoring of particulate air pollution

We developed and evaluated a particulate air pollution sensor for continuous monitoring of size resolved particle number, based on unipolar corona charging and electrostatic detection of charged aerosol particles. The sensor was evaluated experimentally using combustion aerosol with particle sizes in the range between approximately 50 nm and several microns, and particle number concentrations larger than 10 10 particles/m 3 . Test results were very promising. It was demonstrated that the sensor can be used in detecting particle number concentrations in the range of about 2.02× 10 11 and 1.03×10 12 particles/m 3 with a response of approximately 100 ms. Good agreement was found between the developed sensor and a commercially available laser particle counter in measuring ambient PM along a roadside with heavy traffic for about 2 h. The developed sensor proved particularly useful for measuring and detecting particulate air pollution, for number concentration of particles in the range of 10 8 to 10 12 particles/m 3 .

Electrostatic Evaluation of a Unipolar Diffusion and Field Charger of Aerosol Particles by a Corona Discharge

This article presents a unipolar diffusion and field charger by corona discharge is presented and electrostatically evaluated for charging aerosol particles. The electrostatic characteristics of the charger were investigated with an electrometer by measuring the ion number concentrations corresponding to the discharge and charging currents. The discharge and charging currents, and ion number concentration in the discharge and charging zones of the charger, increased with corona voltage. The magnitudes of the ion number concentration for positive and negative coronas in the discharge zone ranged from 1.34 × 1013 to 1.84 × 1015 ions/m3 and 7.34 × 1013 to 2.64 × 1015 ions/m3, respectively. For the charging zone, the ion number concentrations for positive and negative coronas ranged from 2.95 × 1013 to 1.52 × 1014 ions/m3 and 2.06 × 1013 to 1.47 × 1014 ions/m3, respectively. To predict the behavior of the electric field strength and lines in the discharge and charging zones of the charger, the electric field strength and distribution of the charger in the discharge and charging zones were calculated by a commercial computational fluid dynamics software package. Numerical calculation results of electric field distribution and lines through the inner electrode showed good agreement with experimental results. Also, the mean charge per particle for particle diameters were in the range of 0.01 to 50 µm for various operating conditions of the charger was theoretically evaluated. For both diffusion and field charging, lower aerosol flow rate and higher corona voltage resulted in an increase in the mean charge per particle within the charger. This simple charger proved to be particularly useful in diffusion and field charging of aerosol particles in particulate matter detector instruments for measuring PM10 and PM2.5 concentration.

Estimating neutral nanoparticle steady-state size distribution and growth according to measurements of intermediate air ions

Abstract. Continuous measurements of intermediate air ion size distributions were carried out in the small town Tartu, Estonia, from 1 April 2010 through 7 November 2011. The intermediate ions are charged aerosol particles of diameter 1.5–7.5 nm. In this paper we study what information about neutral nanoparticles of atmospheric aerosols can be drawn from the air ion measurements. Rough estimates of the growth rate and the size distribution of neutral nanoparticles were derived for the subset of measurements while the concentration of the intermediate ions was close to the median and remains in the range of 21 ± 2 cm−3. This criterion excludes the specific new particle formation events characterized with high concentration of intermediate ions and includes only most typical quiet periods between the events when the simultaneous growth, depletion and recharging of particles are described with steady-state equations. We estimated the growth rate of nanoparticles to be about 2 nm h−1 while the growth flux or apparent nucleation rate proved to be about 0.5 cm−3 s−1 at 3 nm and about 0.08 cm−3 s−1 at 7 nm. The results suggest that the process of new particle formation is not interrupted during the quiet periods between events of intensive nucleation of atmospheric aerosols.

Experimental quantification of contact freezing in an electrodynamic balance

Abstract. Heterogeneous nucleation of ice in a supercooled water droplet induced by external contact with a dry aerosol particle has long been known to be more effective than freezing induced by the same nucleus immersed in the droplet. However, the experimental quantification of contact freezing is challenging. Here we report an experimental method to determine the temperature-dependent ice nucleation probability of size-selected aerosol particles. The method is based on the suspension of supercooled charged water droplets in a laminar flow of air containing aerosol particles as contact freezing nuclei. The rate of droplet–particle collisions is calculated numerically with account for Coulomb attraction, drag force and induced dipole interaction between charged droplet and aerosol particles. The calculation is verified by direct counting of aerosol particles collected by a levitated droplet. By repeating the experiment on individual droplets for a sufficient number of times, we are able to reproduce the statistical freezing behavior of a large ensemble of supercooled droplets and measure the average rate of freezing events. The freezing rate is equal to the product of the droplet–particle collision rate and the probability of freezing on a single contact, the latter being a function of temperature, size and composition of the contact ice nuclei. Based on these observations, we show that for the types of particles investigated so far, contact freezing is the dominating freezing mechanism on the timescale of our experiment.

Note: A self-calibrating electrometer for atmospheric charge measurements from a balloon platform

Charged aerosol particles and water droplets are abundant throughout the lower atmosphere, and may influence interactions between small cloud droplets. This note describes a small, disposable sensor for the measurement of charge in non-thunderstorm cloud, which is an improvement of an earlier sensor [K. A. Nicoll and R. G. Harrison, Rev. Sci. Instrum. 80, 014501 (2009)]. The sensor utilizes a self-calibrating current measurement method. It is designed for use on a free balloon platform alongside a standard meteorological radiosonde, measuring currents from 2 fA to 15 pA and is stable to within 5 fA over a temperature range of 5 °C to -60 °C. During a balloon flight with the charge sensor through a stratocumulus cloud, charge layers up to 40 pC m(-3) were detected on the cloud edges.

Nucleation events for the formation of charged aerosol particles at a tropical station — Preliminary results

Simultaneous measurements of atmospheric ions in the mobility range of 3.16–0.00133cm2v−1s−1 (diameter range 0.46–50nm) made with a Neutral Cluster and Air Ion Spectrometer (NAIS) at a tropical station, Pune (18° 31′ N, 73° 55′ E) over a period of 47days, revealed that nucleation events for the formation of ions occurred on 17days. These events generally occurred between 0800 and 1000LT and enhanced concentrations of Aitken particles continued to be observed up to 1700–1800LT. During these events, particles grew at rates of 3.1±0.8 to 11.2±3.5nmh−1 for different particle size ranges. Three cases of nucleation events, two with large and one with small particle concentrations, are examined and differences in ion characteristics between the different cases are pointed out. Characteristics and contributions of opposite polarity of ions to the increase in total ion concentration have been examined. A unique type of nucleation event in which particles grew to a size of ~41nm at 0800LT diameter and then decreased to a size of 8.64nm diameter, is also reported. In this event, increase in total ion concentration occurred due to the increase of intermediate-, light large-, and heavy large-ions, but the decrease was mainly due to the decrease in only light and heavy large ions. Ratio of the positive to negative ions decreased during the period of this unique event as compared to before and after the event. Sulfur dioxide (SO2) concentration is positively correlated with the concentrations of intermediate, light large and heavy large ions but negatively correlated with the concentration of cluster ions.