Showing papers in "Aerosol Science and Technology in 1997"
TL;DR: The quadrature method of moments (QMOM) as mentioned in this paper was proposed to determine the evolution of the lower-order moments of an unknown aerosol distribution without requiring that the size distribution or growth law maintain any special mathematical form.
Abstract: The method of moments (MOM) may be used to determine the evolution of the lower-order moments of an unknown aerosol distribution. Previous applications of the method have been limited by the requirement that the equations governing the evolution of the lower-order moments be in closed form. Here a new approach, the quadrature method of moments (QMOM), is described. The dynamical equations for moment evolution are replaced by a quadrature-based approximate set that satisfies closure under a much broader range of conditions without requiring that the size distribution or growth law maintain any special mathematical form. The conventional MOM is recovered as a special case of the QMOM under those conditions, e.g., free-molecular growth, for which conventional closure is satisfied. The QMOM is illustrated for the growth of sulfuric acid-water aerosols and simulations of diffusion-controlled cloud droplet growth are presented.
1,062 citations
TL;DR: In this paper, the authors derived the governing equations for modal aerosol dynamics (MAD) models, where the size distribution of each population is approximated by an analytical modal distribution function; usually by a lognormal distribution function.
Abstract: The derivation of the governing equations for modal aerosol dynamics (MAD) models is presented. MAD models represent the aerosol size distribution as an assemblage of distinct populations of aerosol, where each population is distinguished by size or chemical composition. The size distribution of each population is approximated by an analytical modal distribution function; usually by a lognormal distribution function. By substituting the MAD representation of aerosol size distributions into the governing equation for aerosol processes, the governing differential equations for MAD models are derived. These differential equations express the time dependence of the moments of the aerosol size distribution and are called Moment Dynamics Equations (MDEs). The MDEs for Continuously-Stirred Tank Aerosol Reactors (CSTARs) are also derived.
300 citations
TL;DR: In this article, the authors examined the aerodynamic collection characteristics of the impactor inlet and the reproducibility of the sample mass collection of a PM10 sampler and compared them with one built from the same design in the US and comparable results were obtained.
Abstract: An integral part of several International Atomic Energy Agency sponsored coordinated research programmes involving the sampling and analysis of ambient airborne particules was the development of a PM10 sampler Each participant was provided with such a sampler so that comparable samples would be obtained by each of the participating groups Thus, in order to understand the characteristics of this sampler, we undertoke several characterization studies in which we examined the aerodynamic collection characteristics of the impactor inlet and the reproducibility of the sample mass collection One of the samplers machined in Belgium was compared with one built from the same design in the US and comparable results were obtained The sampler was operated side-by-side with a commercial PM10 beta gauge and an IMPROVE-design 25 μm cut-point cyclone Although the sampler was not wind tunnel tested as required for certification as a reference sampler, it does provide a collection efficiency that generally
286 citations
TL;DR: In this article, the effect of liquid dielectric constant on existing scaling laws for the electrospraying process was investigated, and the variations of the droplet size and the emitted current were measured as a function of the liquid Dielectric Constant (LDC) for the cone-jet mode.
Abstract: Experiments were performed to investigate the effect of liquid dielectric constant on existing scaling laws for the electrospraying process. The variations of the droplet size and the emitted current were measured as a function of the dielectric constant for the electrospray operating in the cone-jet mode. Eight different solvents with dielectric constants, κ, ranging from 12.5 to 182 were tested. The residue particle size distributions were measured using a TSI scanning mobility particle sizer, (SMPS). The produced liquid droplet sizes were then calculated from the known solution concentrations. The results show that: (1) For the produced droplet size, Dd , experimental data are in agreement with the scaling law (G(κ) = 1.66κ −1/6) proposed by Ganan-Calvo et al. (1994) for solvents with high dielectric constants. The derivation in low dielectric constant cases may be that the assumption of Ganan-Calvo (1994) on the characteristic length may not hold for the present system; (2) for the emitted cu...
220 citations
TL;DR: In this paper, the authors present a history of single particle particle lemmings in single-antenna aerosol physics, focusing on the first three decades of the 20th century.
Abstract: (1997). A History of Single Aerosol Particle Levitation. Aerosol Science and Technology: Vol. 26, No. 3, pp. 212-254.
188 citations
TL;DR: In this paper, the performance of different particle counters for different operating conditions was investigated at default temperature and flow settings as well as for other flow rates and temperature differences between the saturator and the condenser.
Abstract: Particle detection efficiency curves for 26 condensation particle counters were determined during a calibration workshop in preparation for the Aerosol Characterization Experiment 1 (ACE1). Three different types of commercially available particle counters, the ultrafine condensation particle counter (TSI-3025) and the condensation particle counters (TSI-3010 and TSI-3760 or TS1-7610) were investigated at default temperature and flow settings as well as for other flow rates and temperature differences between the saturator and the condenser. Furthermore, the pulse-height-analysis ultrafine condensation particle counter and a TSI-3010 modified to achieve a higher temperature difference were calibrated. In this study, the large number of particle counters investigated provided the opportunity to obtain a more statistically significant picture of the performance of different particle counters for different operating conditions.
154 citations
TL;DR: In this article, the influence of discharge polarity, current, relative humidity, air temperature, and wire diameter and material on ozone generation rate in two-stage, wire-plate indoor air cleaners was investigated.
Abstract: This experimental study extends prior studies to consider the influences of discharge polarity, current, relative humidity, air temperature, and wire diameter and material on ozone generation rate in two-stage, wire-plate indoor air cleaners. Promising methods of decreasing the quantity of ozone released into living and work spaces are identified. Use of positive corona discharge is imperative since ozone generation rates are nearly an order of magnitude higher with negative discharge. For a specific precipitator design, the most important parameter in predicting ozone generation rate is current level. Changes in temperature and relative humidity of the inlet air stream over the range of ambient conditions expected in typical homes have less impact. In the commercial air cleaner studied, a 40% reduction in current from 1.08 to 0.60 mA, reduces ozone generation rate by nearly 50% from 0.005 to 0.0025 mg s−1. This reduction in current reduces particle collection efficiency by 20%. An increase in re...
148 citations
TL;DR: In this paper, the collection efficiency of liquid impingers was studied experimentally as a function of the sampling flow rate with test particles in the bacterial size range, and three impingers were tested: two All-Glass Impingers (AGI-4 and AGI-30) and a newly developed slot impinger.
Abstract: The collection efficiency of liquid impingers was studied experimentally as a function of the sampling flow rate with test particles in the bacterial size range. Three impingers were tested: two All-Glass Impingers (AGI-4 and AGI-30), widely used for bioaerosol sampling, and a newly developed slot impinger. The aerosol particles were generated by a Collison nebulizer, and an Aerosizer was used to measure the particle concentrations and size distributions upstream and downstream of each impinger. The effect of the air pressure drop across the impinger on the Aerosizer performance was investigated, and the particle measurement system was modified and calibrated accordingly. While inertial impaction is the dominant particle removal mechanism in impingers, particle bounce and reaerosolization were also found to have significant effects on the impinger collection characteristics. At relatively high flow rates and low levels of collection fluid (corresponding to the collection fluid level after evapora...
127 citations
TL;DR: In this article, the transfer functions of five types of different mobility analyzers (Vienna-type DMA short, medium, and long, CIT radial, and TSI long; CIT = California Institute of Technology, Pasadena, CA; TST = TSI Inc., St Paul, MN) were experimentally characterized by height, width and area of their transfer functions.
Abstract: The differential mobility analyzer (DMA) is an important tool for determining particle size distributions. The physical performance of a DMA is quantified by the concept of the transfer function. Therefore, knowledge of the transfer function is important to interpret the mobility distributions recorded by a DMA.
During a calibration workshop in preparation for the Aerosol Characterization Experiment 1 (ACE1) field campaign, the transfer functions of five types of different mobility analyzers (Vienna-type DMA short, medium, and long, CIT radial, and TSI long; CIT = California Institute of Technology, Pasadena, CA; TST = TSI Inc., St. Paul, MN) were experimentally characterized by height, width, and area of their transfer functions. Different particles size ranges between 3 and 200 nm were investigated.
The transfer function was determined by scanning a DMA across the mobility distribution produced by another, identical DMA. Subsequently, the data were processed by a deconvolution algorithm assuming a triangular shape for the transfer function. For all DMA types, the area of the transfer function decreased with particle size, especially for ultrafine particles (d_p < 20 nm). The gradient with which this area decreases with particle size, however, is different for each of the DMA types investigated. The calibration provides an improved description of the performance of each DMA, particularly in the ultrafine size range.
116 citations
TL;DR: A method for writing the sectional aerosol equations in a form suitable for combination with a detailed kinetic model for gas-phase reactions has been developed in this paper, where the authors describe bin-bin coagulation, addition of C2H2; addition of polycyclic aromatic hydrocarbons (PAH) with 2 to 10 benzenoid rings; oxidation via OH attack.
Abstract: A method for writing the sectional aerosol equations in a form suitable for combination with a detailed kinetic model for gas-phase reactions has been developed. The sectional equations are given for arbitrary values of d, the ratio of molecular weights of adjacent bin boundaries, and are solved for d ≥ 2 for three different cases of the intra-bin distribution: (1) constant mass density w.r.t. ln(v), where v = molecular weight; (2) constant number density w.r.t. ln(v), or alternately, constant mass density w.r.t. v; (3) constant number density w.r.t. v. All the solutions given conserve mass; the extent of deviation from conservation of particle number is evaluated. An example of the approach is given for soot formation in combustion. The aerosol sections describe mass above 400 amu, with d = 2. Aerosol reactions are: bin-bin coagulation; addition of C2H2; addition of polycyclic aromatic hydrocarbons (PAH) with 2 to 10 benzenoid rings; oxidation via OH attack. The set of aerosol reactions is appen...
101 citations
TL;DR: In this article, a two-stage parallel-plate ESP experiment was carried out in the submicron particle size range and the experimental data were compared with the results of a numerical collection efficiency model which takes into consideration charging rate equations, particle equations of motion, and collection performance models.
Abstract: A well-defined two-stage ESP experiment was carried out in the submicron particle size range The experimental setup consisted of five components: a clean wind tunnel, a submicron particle generation system, an aerosol sampling and transport system, a submicron particle number concentration measurement system, and a pilot-scale two-stage parallel-plate ESP Experimental collection efficiency data were obtained with a GMD of 003–02 μm and a GSD of about 167 for air velocities between 19 and 41 m/s under the nominal operation condition of two-stage ESP The experimental data were then compared with the results of a numerical collection efficiency model which takes into consideration charging rate equations, particle equations of motion, and collection performance models The comparison showed good agreement It was confirmed from the comparison that the partial charging regime, where a portion of incoming particles is not charged, exists when the particle size range is below about 003 μm This
TL;DR: In this article, noniterative, unconditionally stable numerical techniques for solving condensational and dissolutional growth equations are given, compared to Gear-code solutions for three cases when growth is coupled to reversible equilibrium chemistry.
Abstract: Noniterative, unconditionally stable numerical techniques for solving condensational and dissolutional growth equations are given. Growth solutions are compared to Gear-code solutions for three cases when growth is coupled to reversible equilibrium chemistry. In all cases, results from the new growth schemes matched Gear-code solutions nearly exactly when growth and equilibrium calculations were operator-split with a 1 s time interval. Results also matched well for a 15 s interval. With a 15 s interval, the growth-equilibrium schemes can be used in a three-dimensional model. Longer operator splitting intervals, in some cases, induced oscillations in concentrations caused by delays in feedback between equilibrium and growth calculations. Simulation results indicated that gases and aerosols were closer to equilibrium when the relative humidity was 90% than when it was 40%.
TL;DR: In this article, the change in size distribution of agglomerates in a heated pipe is measured using a differential mobility analyzer and a condensation nucleus counter, and the population balance equation for sintering is solved numerically.
Abstract: In order to evaluate the sintering characteristics of polydisperse TiO2 and SiO2 fractal agglomerates consisting of nm-sized primary particles (nanoparticles), the change in size distribution of agglomerates in a heated pipe is measured using a differential mobility analyzer and a condensation nucleus counter. Change in the structure and the primary particle size of the agglomerates collected by a thermophoretic aerosol sampler is also measured by the transmission electron microscopy as a function of furnace temperature. Coalescence of the agglomerates and the growth of primary particles due to sintering are observed at temperatures corresponding to 50%–100% of the bulk melting points of the particle material. To model the changes in the size distribution of agglomerates and primary particles due to sintering, two-dimensional sectional representation of the size distribution is employed, and the population balance equation for sintering is solved numerically. The calculated results, considering a...
TL;DR: The minimum laser fluence required for the formation of ions from aerosol particles in a vacuum as a function of a number of parameters has been investigated in this paper, showing that the threshold energy density does depend on light absorption and lattice energy.
Abstract: The minimum laser fluence required for the formation of ions from aerosol particles in a vacuum as a function of a number of parameters has been investigated. Although the influences of various particle properties are complex, the threshold energy density does depend on light absorption and lattice energy. Ionization thresholds were lower at 193 and 157 nm than at 248 nm. The range in ion formation thresholds for different types of particles also decreased as the laser wavelength decreased, consistent with the fact that all the substances used are likely to absorb vacuum-ultraviolet radiation fairly strongly. The threshold for negative ion formation was generally greater than that for positive ion formation. Pure sulfuric acid aerosols were ionized well only at 157 nm.
TL;DR: Many commercially available devices initially developed for dispersion of biologically inert particles have been adopted for aerosolization of microoganisms in laboratory settings as mentioned in this paper, however, these devices are not suitable for use in outdoor environments.
Abstract: Many commercially available devices initially developed for dispersion of biologically inert particles have been adopted for aerosolization of microoganisms in laboratory settings. However, these d...
TL;DR: In this article, a mole fraction-based thermodynamic model is used to represent available activity data, salt solubilities, and electrodynamic balance measurements for aqueous NaCl, Na2SO4, NaNO3 and their mixtures at 298.15 K.
Abstract: A mole-fraction-based thermodynamic model is used to represent available activity data, salt solubilities, and electrodynamic balance measurements for aqueous NaCl, Na2SO4, NaNO3 and their mixtures at 298.15 K. The results are presented as fitted ion-interaction parameters and equilibrium constants. These enable ion and solvent activities, and saturation with respect to five possible solid phases (NaCl, NaNO3, Na2SO4·10H2O, Na2SO4, and NaNO3·Na2SO4·H2O) to be calculated for all mixture compositions to relative humidities of ≤60%, and to high degrees of supersaturation with respect to the dissolved salts. Extension of the model to other systems is discussed.
TL;DR: The transfer functions of the so-called Vienna type differential mobility analyzer (DMA) were studied experimentally at the size range of 1.2-20 nm following the procedure suggested by Stolzenburg (1988) Ph.D. as discussed by the authors.
Abstract: The transfer functions of the so called “Vienna type” differential mobility analyzer (DMA) were studied experimentally at the size range of 1.2–20 nm following the procedure suggested by Stolzenburg (1988) Ph.D. Thesis. For the study, two identical DMAs were used as a tandem DMA (TDMA) arrangement to measure nanoparticles from a hot wire WOx generator. The approximate analytical formulae by Stolzenburg describing diffusion broadening of the DMA transfer function were observed to be valid with high accuracy from 20 nm down to ∼ 2 nm. In the size range of 1.2–2 nm nominal mobility equivalent diameter small deviations of the shape of the TDMA output signal predicted by Stolzenburg were found.
TL;DR: In this article, the authors used a tandem differential mobility analyzer system to accurately determine the size of the particles and showed that penetration of particles down to 2 nm in particle diameter follows the predictions of the theories of Cheng and Yeh and Gormley and Kennedy.
Abstract: Penetration of nanometer-sized aerosol particles and ions through a single wire screen and a laminar flow tube has been measured using a tandem differential mobility analyzer system to accurately determine the size of the particles. The results obtained using a condensation nucleus counter as a particle detector showed that penetration of particles down to 2 nm in particle diameter follows the predictions of the theories of Cheng and Yeh and Gormley and Kennedy. This result suggests that thermal rebound of particles on wire or tube surfaces does not occur. The measured penetrations for negative ions smaller than 2 nm also agreed well with the theoretical predictions. In this case, however, concentration was measured with an electrometer, and there exists the possibility of electron transfer between the ions and the surfaces without the (neutralized) ions being attached to them.
TL;DR: In this paper, a review of the experimental results from the literature for single component metal and simple metal-oxide particles is presented and compared with the data available in the literature, i.e., whether the particles are solid or hollow, with process parameters and material properties during spray pyrolysis.
Abstract: This work is a review of the experimental results from the literature for single-component metal and simple metal-oxide particles. Criteria for correlating particle morphology, i.e., whether the particles are solid or hollow, with process parameters and material properties during spray pyrolysis are presented and compared with the data available in the literature. The materials were classified into two categories for which the precursor: (1) melts and (2) does not melt before chemical reaction takes place, and separate criteria were used for each category based on the work of Jayanthi et al. (1993) J. Aerosol Sci. 19:478. In systems where the precursor melts before chemical reaction occurs, e.g., decomposition of nitrates of Mg, Al, Fe, Zn, Pb, Ni, Co, Pd, Mn, Cu, Sr, and Ag, the particle morphology is determined primarily by the densities and formula weights of the reactant and product compounds unless high temperature densification or puffing up of the particles due to gases evolved during the ...
TL;DR: In this article, diffusion losses and charging efficiency were measured for three types of charge neutralizers commonly used in aerosol research: two with 85Kr and one with 210Po as radiation sources.
Abstract: Diffusion losses and charging efficiency were measured for three types of charge neutralizers commonly used in aerosol research: two with 85Kr and one with 210Po as radiation sources. The diffusion losses were characterized at flows of 0.5 -6 1 min−1 typically used in atmospheric aerosol physics measurements. All of the neutralizers tested exhibited high transmission efficiencies, with losses up to 25% at the smallest tested size of 3 nm, varying with size and flow in general agreement with diffusion loss theory. Charging efficiency was measured for a singly charged, monodisperse aerosol at the same flows and at concentrations of 103-104 particles cm−3. Neither of the 85Kr chargers brought the charge distribution close to equilibrium at 2 1 min−1, except at concentrations ≤ 103 cm−3. The 210Po charger produced the theoretically expected fraction of singly charged particles within the uncertainty of the experiment.
TL;DR: In this paper, the product aerosols are sampled directly into a mass spectrometer where the surface and total compositions are distinguished by laser desorption ionization, and the relative intensities of ions originating from the surface layer and core reflect the total composition.
Abstract: Laser desorption ionization is used to characterize the products of an aerosol reaction in real time. Sodium chloride aerosols are mixed with vapor phase ammonia and nitric acid to produce an ammonium nitrate surface layer. The product aerosols are sampled directly into a mass spectrometer where the surface and total compositions are distinguished by laser desorption ionization. With a low laser irradiance, only material near the particle surface is desorbed and ionized. In this case, the mass spectra are independent of the amount of ammonium nitrate deposited, and simply indicate a nitrate-enriched surface layer. With a higher laser irradiance, both the surface layer and core are ablated. The relative intensities of ions originating from the surface layer and core reflect the total composition. That is, the relative intensities of ions produced from the ammonium nitrate surface layer increase with increasing surface layer thickness. The laser irradiance dependences of the mass spectra allow the ...
TL;DR: In this paper, a model to describe the slowly scanning differential mobility analyzers (DMAs) is introduced and applied to investigate three different regimes of input mobility distributions: (i) a mobility distribution much narrower than the DMA transfer function, (ii) an intermediate mobility distribution of about the same width as the DMAs transfer function and (iii) a diffusion distribution much wider than the DL transfer function.
Abstract: The subject of this work is the theoretical investigation of slowly scanning differential mobility analyzers (DMAs) which are, e.g., utilized to determine DMA transfer functions and to measure particle mobility distributions. A model to describe such systems is introduced and applied to investigate three different regimes of input mobility distributions: 1) a mobility distribution much narrower than the DMA transfer function, 2) a mobility distribution of about the same width as the DMA transfer function, and 3) a mobility distribution much wider than the DMA transfer function. Cases 1) and 2) are relevant for DMA transfer function measurements utilizing tandem differential mobility analyzer (TDMA) systems. For either regime, it is not possible to determine DMA transfer functions directly from the concentration distributions measured at the outlet of a DMA. For these cases, a deconvolution procedure is needed. Therefore, an iterative deconvolution procedure was developed. Determining DMA transfer...
TL;DR: In this paper, plate-out measurements of radon progeny and aerosol particles in a spherical chamber under controlled laboratory conditions were monitored, and a laboratory mixer with variable speeds and speed control was used to increase turbulence in the chamber.
Abstract: In indoor and mining environments, deposition to “plate-out” of radon progeny onto walls occurs simultaneously with the attachment of progeny of airborne particles. Attachment and plate-out processes affect the atmosphere in which radon exposure takes place by reducing concentrations and shifting activity size distributions. Deposition of fine particles on paintings and other art objects is also a concern in museums. Here we describe plate-out measurements of radon progeny and aerosol particles in a spherical chamber under controlled laboratory conditions. The temperature and velocity profiles in still and turbulent air were monitored. A laboratory mixer with variable speeds and speed control was used to increase turbulence in the chamber. During mixing, air velocity was detected when rotational speeds were higher than 500 rpm. Monodisperse silver aerosols and polystyrene latex particles in the size range of 5 nm to 2 μm were used in the deposition study. Nanometer particles between 0.88 to 1.80 ...
TL;DR: Benes and Holub as discussed by the authors proposed a new expression for the eddy diffusion coefficient based on the rules of dimensional analysis, which can fit the measured deposition rates with the integer exponent needed for dimensional consistency.
Abstract: Particle deposition in indoor air is due primarily to turbulent diffusion to the boundary layer at macroscopic surfaces within the room. About 15 years ago, Crump and Seinfeld derived an equation for turbulent diffusion and deposition in an arbitrarily shaped vessel. They assumed that turbulent diffusivity near the wall is proportional to a power of the distance from the wall surface and an estimation of the turbulence intensity. Their values were found by fitting an equation with two parameters. Subsequently they showed that this theoretical result agreed with experimental data. However, other studies in which the turbulence intensity has been directly estimated, there have been problems fitting the measured deposition rates with the integer exponent needed for dimensional consistency. To eliminate this problem, Benes and Holub have recently proposed a new expression for the eddy diffusion coefficient based on the rules of dimensional analysis. However, their formulation did not include the grav...
TL;DR: In this article, the viscous flow fields around multifiber filters have been investigated and the fiber separation ratio was found to have significant effects on the pressure drop and the particle interception efficiency of a multifiber filter.
Abstract: The viscous flow fields around multifiber filters have been investigated in a previous paper. The results of the previous work show that the flow becomes periodic immediately after the first fiber array downstream from the entrance if the fibers are arranged uniformly along the flow direction. The characteristics of such flow fields enable the pressure drop and the particle interception efficiency of a multifiber filter to be represented by single-fiber models. The total filtration efficiency, however, cannot be so represented since fibers interact during filtration processes. In this study, the pressure drop and the interception efficiency were investigated by making use of the viscous flow fields modeled in the previous research. The fiber separation ratio was found to have significant effects on pressure drop and efficiency. At a given volume fraction, changes in the fiber separation ratio will result in changes to the patterns of fluid flow and aerosol particle motion. Therefore, the fiber se...
TL;DR: In this paper, water activity/concentration relationships of aqueous NaCl, NaNO3, Na2SO4 and their mixtures from dilute concentration to high supersaturation have been determined at room temperature in an electrodynamic balance.
Abstract: Water activity/concentration relationships of aqueous NaCl, NaNO3, Na2SO4 and their mixtures from dilute concentration to high supersaturation have been determined at room temperature in an electrodynamic balance. Using a dynamic measurement technique based on the evaporation of the droplets, a set of water activity measurements of a solution droplet can be obtained in less than an hour. The water activities of the mixtures are compared with theoretical predictions of the Pitzer-Simonson-Clegg (PSC) model, the Zdanovskii-Stokes-Robinson (ZSR) equation, and the Kusik and Meissner (KM) model. Comparisons of the data with model predictions indicate that the PSC, ZSR, and KM approaches agree well among themselves and with the experimental data. All three models give similar maximum (±0.02) and standard (0.01) deviations in mass fraction of the solute (mfs). These deviations are close to the experimental error of ±(0.01–0.02). The agreement of the models and the need for single-component water activit...
TL;DR: In this paper, particle deposition in symmetric bifurcating airways due to inertial impaction was studied numerically for inspiratory flows, and particle deposition efficiency was obtained using the limiting trajectory method.
Abstract: Particle deposition in symmetric bifurcating airways due to inertial impaction was studied numerically for inspiratory flows. Three-dimensional bifurcation models were constructed. The models had different parent and daughter diameters comparable to the airway generations 3–6 of the human lung. Bifurcation angles of the models were also varied (30®, 45®, and 60®). Airflow fields in the models were obtained by a finite–element method (FIDAP, Fluid Dynamics International, Evanston, IL) for different Reynolds numbers of 100, 265, 530, and 1060 under parabolic and uniform inlet velocity conditions. The calculated flow field data were used to simulate particle trajectory in the airways. Particle deposition efficiency was obtained using the limiting trajectory method. Inlet flow velocity profile, flow Reynolds number, and bifurcation angle were found to have substantial effects on particle deposition. Based on calculated deposition results, empirical equations were derived for particle deposition effic...
TL;DR: In this article, two test vegetative bacteria, Pseudomonas syringae and Erwinia herbicola, and a physical aerosol decay indicator, Bacillus subtilis var. niger spores, were sprayed into a particle size fractionating wind tunnel.
Abstract: Two test vegetative bacteria, Pseudomonas syringae and Erwinia herbicola, and a physical aerosol decay indicator, Bacillus subtilis var. niger spores, were sprayed into a particle size fractionating wind tunnel. Test bacterial survival significantly increased directly with droplet size for varying test cell to spore ratios and temperature. However, survival varied inversely with relative humidity.
TL;DR: The most powerful and elegant method for determining particle size distributions of aerosols by light scattering is to observe single particles suspended in a Millikan-Fenton electrostatic field as discussed by the authors.
Abstract: The most powerful and elegant method for determining particle size distributions of aerosols by light scattering is to observe single particles suspended in a Millikan–Fletcher electrostatic field The first such light scattering studies were carried out by Whytlaw-Gray and Patterson (1926), by Gucker and Egan (1961), and then by Wyatt and Phillips (1972) Optically levitated particles were studied by Grehan and Gousebet (1986) Optical particle counters were devised by Gucker and his associates (1947a,b) and Gucker and Rose (1954) for both forward and 90° viewing Gucker also built an instrument for on-line viewing of 360° scatter by particles flowing through a light beam in single file Individual particles were also analyzed in an ultramicroscope by Wells and Gerke (1919) The earliest angular scattering patterns from assemblies of particles were by Tolman and Vliet (1921) and by Sinclair and La Mer (1949) Other interesting systems have utilized acoustic detectors, power loss in a laser cavit
TL;DR: Particle analysis by laser mass spectrometry (PALMS) was used to examine sulfuric acid particles representative of stratospheric sulfate aerosols (SSAs) and ambient tropospheric aerosols as mentioned in this paper.
Abstract: Particle analysis by laser mass spectrometry (PALMS) was used to examine sulfuric acid particles representative of stratospheric sulfate aerosols (SSAs) and ambient tropospheric aerosols. Sulfuric acid particles were generated in the laboratory by condensing sulfuric acid vapors in a flow stream of particle-free dry air or nitrogen. The purest particles were produced using filtered, high-purity nitrogen in a clean glass and stainless steel system. In contrast, generation techniques using filtered compressed air, Tygon tubing, or Viton o-rings resulted in detectable organic impurities in the positive ion spectra of sulfuric acid droplets. With the PALMS instrument, the lower limit of our detection of organics is at most 0.02 wt% α-tocopherol in sulfuric acid, which in terms of surface coverage corresponds to less than one monolayer on a 0.2-μm-diameter particle. When we eventually deploy the PALMS instrument in the upper troposphere and lower stratosphere, we should be able to detect the presence ...