Showing papers in "Aerosol Science and Technology in 1993"
TL;DR: In this paper, a simple model describing the evolution of particle morphology, size, and number concentration by coagulation and sintering is presented that neglects the spread of the polydispersity of aggregate and primary particles.
Abstract: A simple model describing the evolution of particle morphology, size, and number concentration by coagulation and sintering is presented that neglects the spread of the polydispersity of aggregate and primary particles. The influence of irregular/fractal structure on the collision kernel is accounted for, from the free molecular to the continuum regime. The model predictions compare well to those of a detailed two-dimensional sectional model of nonspherical particle dynamics. After a theoretical evaluation of the main sintering mechanism, the proposed model was applied to laser synthesis of silicon in an aerosol reactor.
342 citations
TL;DR: In this paper, a rigorous and computationally efficient thermodynamic model that estimates the state and composition of atmospheric inorganic species between the gas and aerosol phases is presented, and the estimation of important thermodynamic properties, equilibrium constants, ionic activity coefficients, water activity, and deliquescence points is described.
Abstract: A rigorous and computationally efficient thermodynamic model that estimates the state and composition of atmospheric inorganic species between the gas and aerosol phases is presented. The estimation of important thermodynamic properties, equilibrium constants, ionic activity coefficients, water activity, and deliquescence points is described. Various sources and estimation methods for inorganic gas-liquid-solid equilibrium properties are compared and optimal approaches for the new equilibrium routine are incorporated.
337 citations
TL;DR: In this paper, the relation between the aerosol agglomerate structure and transition regime mobility can be explained with a simple model incorporating fractal geometry and results from computer simulations.
Abstract: The relation between the aerosol agglomerate structure and transition regime mobility can be explained with a simple model incorporating fractal geometry and results from computer simulations. The model is consistent with previous measurements of the shape factors and allows some structural information to be inferred from these measurements, although the data are insufficient for a rigorous comparison between theory and experiment. Experiments conducted here with well-characterized TiO_2 and Si agglomerates support the model' assumption that the mobility diameter of a particle in the free-molecule regime is determined solely by the projected area of the particle. The correlation between the projected area and the mobility equivalent size remains remarkably good throughout the transition regime for the agglomerate particles studied here. The model predicts this result for particles with fractal dimensions of approximately D_f = 2
267 citations
TL;DR: In this article, the authors evaluated the sensitivity of thermodynamic calculations of aerosol composition to common approximations and the choice of activity coefficient estimation method, and provided recommendations for treating weak electrolytes and for selecting an activity coefficient estimator in atmospheric gas-aerosol equilibrium calculations.
Abstract: The gas-aerosol equilibrium model, SCAPE, presented in Part I is used to evaluate the sensitivity of thermodynamic calculations of aerosol composition to common approximations and the choice of activity coefficient estimation method. The treatment of weak electrolytes, associated ammonia, NH_3(aq), and bisulfate ion, HSO_4^−, is analyzed. Comparisons of the three multi-component activity coefficient estimation methods are carried out with a variety of data. On the basis of the sensitivity analysis results, recommendations are provided for treating these electrolytes and for selecting an activity coefficient estimation method in atmospheric gas-aerosol equilibrium calculations. The two gas-aerosol equilibrium models, SCAPE and AIM, are compared. Remaining questions in gas-aerosol equilibrium are highlighted.
205 citations
TL;DR: An aerosol sampling study was carried oat at six monitoring sites in California's San Joaquin Valley from June 14, 1988 through June 9, 1989 as discussed by the authors, where concentrations of PM10 and PM2.5 (particles < 2.5 μm in aerodynamic diameter) mass, elements, water-soluble nitrate, sulfate, ammonium, sodium, potassium and organic and elemental carbon were determined in 24-h aerosol samples collected during this period.
Abstract: An aerosol sampling study was carried oat at six monitoring sites in California's San Joaquin Valley from June 14, 1988 through June 9,1989. Concentrations of PM10 (particles < 10 μ m in aerodynamic diameter) and PM2.5 (particles < 2.5 μ m in aerodynamic diameter) mass, elements, water-soluble nitrate, sulfate, ammonium, sodium, potassium, and organic and elemental carbon were determined in 24-h aerosol samples collected during this period. Federal and state standards for PM10 were exceeded at both urban and nonurban sites. PM10 concentrations were generally highest during winter and were dominated by PM2.5 during this time. The coarse (PM10 minus PM2.5) aerosol fraction constituted more than half of PM10 mass during the summer and fall. PM10 concentrations of secondary ammonium nitrate were elevated during the winter at all sites. Conversely, concentrations of coarse particle iron, indicative of geologically related dust, were higher under less humid conditions during the summer and fall. Region-wide met...
172 citations
TL;DR: In this article, the evaporation state of solution aerosol thermolysis (SAT) was modeled to study the effect of various parameters on solid particle formation by solute precipitation.
Abstract: The evaporation state of solution aerosol thermolysis (SAT) was modeled to study the effect of various parameters on solid particle formation by solute precipitation. A comparison of the characteristic time constants for various processes demonstrated that droplet shrinkage and solute diffusion are the slowest processes, and that the fast processes, i.e., vapor diffusion and heat conduction in the gas phase and the liquid phase, can be assumed to have reached steady state. Differential equations for these faster processes were thus simplified and were solved numerically along with a modified solute diffusion equation, using an explicit first-order finite difference scheme. The computations were done until the solute concentration at the droplet surface reached the critical supersaturation. Then, if the solute concentration at the droplet center is higher than the equilibrium saturation, volume precipitation is proposed to occur. Solutes with a large difference between critical supersaturation and equilibr...
168 citations
TL;DR: In this paper, the authors measured the hygroscopic growth of aerosol particles from five sources (Cigarette smoke, incense smoke, natural gas flames, propane fuel flames, and candle flames) to provide a quantitative basis for the modeling of inhaled aerosol deposition pattern.
Abstract: Cigarette smoke, incense smoke, natural gas flames, propane fuel flames, and candle flames are contributors of indoor aerosol particles. To provide a quantitative basis for the modeling of inhaled aerosol deposition pattern, the hygroscopic growth of particles from these five sources as well as the source size distributions were measured. Because the experiments were performed on the bases of particles of single size, it provided not only the averaged particle's hygroscopic growth of each source, but also the detailed size change for particles of different sizes within the whole size spectrum. The source particle size distribution measurements found that cigarette smoke and incense smoke contained particles in the size range of 100–700 nm, while the natural gas, propane, and candle flames generated particles between 10 and 100 nm. The hygroscopic growth experiments showed that these combustion aerosol particles could grow 10% to 120%, depending on the particle sizes and origins
115 citations
TL;DR: In this article, the effect of humidity, particle hygroscopicity, and size on the mass loading capacity of glass fiber high efficiency particulate air filters was studied, and specific cake resistance K 2 was computed for different test conditions and used as a measure of the mass load capacity.
Abstract: The effect of humidity, particle hygroscopicity, and size on the mass loading capacity of glass fiber high efficiency particulate air filters was studied. Above the deliquescent point, the pressure drop across the filter increased nonlinearly with areal loading density (mass collected/filtration area) of a NaCl aerosol, thus significantly reducing the mass loading capacity of the filter compared to dry hygroscopic or nonhygroscopic particle mass loadings. The specific cake resistance K 2 was computed for different test conditions and used as a measure of the mass loading capacity. K 2 was found to decrease with increasing humidity for nonhygroscopic aluminum oxide particles and for hygroscopic NaCl particles (at humidities below the deliquescent point). It is postulated that an increase in humidity leads to the formation of a more open particulate cake which lowers the pressure drop for a given mass loading. A formula for predicting K 2 for lognormally distributed aerosols (parameters obtained from impact...
106 citations
TL;DR: In this paper, the diffusion coefficient of radon progeny is a critical parameter in determining its dynamics while airborne, depending on their diffusion coefficient and the breathing pattern of the subject, ultrafine particles have been shown to deposit in the nasal or oral airways.
Abstract: Radon and thoron progeny are ultrafine particles in the size range of 1–200 nm, depending on whether or not they are attached to other aerosol particles. The diffusion coefficient of radon progeny is a critical parameter in determining its dynamics while airborne. Depending on their diffusion coefficient and the breathing pattern of the subject, ultrafine particles have been shown to deposit in the nasal or oral airways. Substantial deposition in the head airways reduces the amount of radioactivity that deposits in the tracheobronchial tree. Thus, for accurate dosimetric calculations, it is important to know the deposition fraction of radon progeny in the head airways. Several adult head airway models were used to study the radon progeny deposition in human nasal and oral airways. Radon-220 progeny (212Pb) were used in the study. The particle size as measured by a graded screen diffusion battery was between 1.2 and 1.7 nm, indicating that the particles were molecular clusters. Deposition was measured by c...
85 citations
TL;DR: In this paper, the growth of primary particles in an aerosol generator that is cooling at a constant rate was studied theoretically, and the most important process parameter determining particle diameter is the maximum gas temperature, because the rate of sintering is a sensitive function of temperature.
Abstract: Solid particles in the 1 nm < dp < 100 nm size range form in gases as a result of gas phase condensation, particle collision processes, and solid-state processes. The relative rates of sintering and collision determine the size and morphology of the spheroidal primary particles. Rapid sintering is equivalent to the classical theory of coagulation with instantaneous coalescence. When the sintering rate is slow compared with the collision rate, fine primary particles form and aggregate into irregularly shaped agglomerates. The growth of primary particles in an aerosol generator that is cooling at a constant rate was studied theoretically. The most important process parameter determining particle diameter is the maximum gas temperature, because the rate of sintering is a sensitive function of temperature. Aerosol volume loading and cooling rate are important when the rate of particle growth is limited by collision processes. Experiments on the formation of alumina particles were made to study these effects. ...
68 citations
TL;DR: An original theory is presented for the simulation of laryngeal and tracheobronchial fluid dynamics, where conditions within the larynx are especially complex, encompassing localized eddies, and a jet formed at the vocal folds.
Abstract: The deposition sites of inhaled particles must be known to (1) promote therapeutic effects of airborne pharmacologic drugs via targeted delivery and (2) improve risk assessments of ambient contaminants. Because particle trajectories are affected by the motion of an entraining fluid, it is important to determine the character of an inhaled airstream. In this report, an original theory is presented for the simulation of laryngeal and tracheobronchial fluid dynamics. The mathematical model describes conditions in such respiratory tract airways of adult human subjects under various breathing conditions. The data describing fluid dynamics patterns are presented in two formats: graphical displays of mean streamlines and color illustrations of velocity distributions. In the defined airway system, fluid dynamics patterns are heterogeneous. Conditions within the larynx are especially complex, encompassing localized eddies, and a jet formed at the vocal folds. Moreover, the data indicate that the larynx exerts a pr...
TL;DR: In this article, the absorption coefficient σa was measured using an integrating plate photometer, and the mass size distribution of the aerosol between 0.06 and 16 μm in aerodynamic equivalent diameter, with a low-pressure Berner impactor, was conducted during a fairly stable period in April 1991.
Abstract: Simultaneous measurements of the aerosol absorption coefficient σa, using an integrating plate photometer, and of the mass size distribution of the aerosol between 0.06 and 16 μm in aerodynamic equivalent diameter, with a low-pressure Berner impactor, were conducted during a fairly stable period in April 1991. The size distributions were analyzed for total carbon (TC; i.e., the sum of organic and black carbon) by a combustion method; for SO4 2−, NO3 −, Cl−, NH4 +, Na+, and K+ by ion chromatography; and Ca and Mg by atomic absorption spectroscopy. This chemical analysis yielded nearly identical size distributions for SO4 2−, NO3 −, and NH+ 4, with mean aerodynamic equivalent diameters typically ∼ 0,7 μm. The ionic balance showed that the aerosol bad been chemically neutral all the time. More than 70% of the accumulation mode mass was due to TC, SO4 2−, NO3 −, and NH4 +. The relative amount of internally and externally mixed carbon (with respect to the other accumulation mode species) was estimated. The ext...
TL;DR: In this paper, an analytical solution that includes both transition regime corrections for mass and heat transfer and the Kelvin effect is derived for the condensational growth and evaporation of liquid droplets in the transition regime and in the continuum regime.
Abstract: The condensational growth and evaporation of liquid droplets in the transition regime and in the continuum regime are considered. An analytical solution that includes both transition regime corrections for mass and heat transfer and the Kelvin effect is derived. The solution represents an improvement over earlier analytical solutions, which are valid only in the continuum regime. The growth (evaporation) times predicted by the analytical solution are compared with the times obtained by a numerical solution. In the transition regime the new analytical expression estimates the growth time within 20%. The closer the saturation ratio is to unity, and the smaller the latent heat of vaporization of the substance in question, the better is the accuracy of the new expression
TL;DR: In this paper, a procedure for simulating the deposition of aerosol particles on a rough surface is developed, where the instantaneous turbulent flow field is generated as the sum of a mean and a randomly fluctuating Gaussian field.
Abstract: Dispersion and deposition of particles in a turbulent channel flow with rough walls are studied. A procedure for simulating the deposition of aerosol particles on a rough surface is developed. The instantaneous turbulent flow field is generated as the sum of a mean and a randomly fluctuating Gaussian field. Particle equation of motion including the effects of Brownian diffusion, Saffman lift force, and gravity is solved numerically. Starting with an initially uniform concentration near the wall, ensembles of particle trajectories are generated and statistically analyzed. Several simulations for deposition of aerosol particles of various sizes are performed and the corresponding deposition velocities are evaluated. The results are compared with those obtained by empirical equations and experimental data
TL;DR: This work has been using three-dimensional reconstruction techniques to examine various aspects of lung structure from the reconstruction of individual cells to reconstructing conducting airway and alveolar duct branching systems.
Abstract: Significant differences in lower respiratory tract structure exist both within species and among species at each level of anatomy. Irregular dichotomous and trichotomous branching patterns of airways are present in human and nonhuman primate lungs. In contrast, the dog and common laboratory rodents exhibit a predominantly monopodial branching system. The effects of these various branching patterns on airflow distribution, gas uptake, and the deposition of particles have not been sufficiently studied to determine the extent to which branching patterns impart regional inhomogeneities or local variations in the deposition of inhaled material. To date, detailed morphometric data have not been used to examine aerosol particle deposition. We have been using three-dimensional reconstruction techniques to examine various aspects of lung structure. Studies vary from the reconstruction of individual cells to reconstructing conducting airway and alveolar duct branching systems. When using physical models for dosimet...
TL;DR: In lung dosimetry of inhaled particulate compounds one has to consider both deposition and clearance kinetics throughout the respiratory tract as mentioned in this paper, where the main clearance mechanism for insoluble particles deposited in the conducting airways is via the mucociliary escalator.
Abstract: In lung dosimetry of inhaled particulate compounds one has to consider both deposition and clearance kinetics throughout the respiratory tract. The deposition is governed essentially by particle size, ventilatory parameters, as well as airway characteristics, whereas the clearance of particulate compounds, once deposited, is dependent on physicochemical characteristics of the compound. Predictive models of particle deposition for specific regions in the lung or specific airway generations can be applied to estimate regional and local doses of an inhaled compound. The main clearance mechanism for insoluble particles deposited in the conducting airways is via the mucociliary escalator. Soluble particles are cleared mainly by diffusional and pinocytotic processes from this region, depending on their lipo- or hydrophilicity. The main clearance mechanism for insoluble particles in the alveolar region is based on the function of the alveolar macrophages that effectively phagocytize deposited particles and trans...
TL;DR: In this article, data from a different mobility particle sizer (DMPS) or an electrical aerosol analyzer (EAA) has been combined with data from an aerodynamic particle Sizer (APS) and converted to obtain aerosol mass distribution parameters on a near real-time basis.
Abstract: Data from a different mobility particle sizer (DMPS) or an electrical aerosol analyzer (EAA) has been combined with data from an aerodynamic particle sizer (APS) and converted to obtain aerosol mass distribution parameters on a near real-time basis. A low pressure impactor (LPI), a direct and independent measure of this mass distribution, provided information for comparison. The number distribution of particles within the electrical measurement range was obtained with the DMPS and EAA. Data from the APS for particles greater than that size were used to complete the number distribution. Two methods of obtaining mass distribution parameters from this number data were attempted. The first was to convert the number data, channel by channel, to mass data and then fit a log-normal function to this new mass distribution. The second method was to fit a log-normal function to the combined number distribution and then use the Hatch-Choate equations to obtain mass parameters. Both the DMPS / APS and the EAA / APS sy...
TL;DR: In this paper, the surface distributions of particles that have impacted from a circular jet have been measured by optical microscopy and image analysis using 3-μm ammonium fluorescein particles were impacted onto greased surfaces at various velocities from the nozzle.
Abstract: The surface distributions of particles that have impacted from a circular jet have been measured by optical microscopy and image analysis Monodisperse, 3-μm ammonium fluorescein particles were impacted onto greased surfaces at various velocities from the nozzle The spot radius is approximately equal to the nozzle radius at √St = 08 At √St = 16, the spot radius is about half of the nozzle radius; convergence of the flow into the nozzle results in a focusing effect The surface density has a peak which moves out to larger radius with decreasing Stokes number, reaching the nozzle radius at about √St = 05 The radii enclosing 105% and 703% of the particles as a function of √St are in good agreement with the theoretical predictions of Marple (1970); however, the upturn of the experimental data for √St 05 is somewhat sharper Empirical formulas were fitted to the data
TL;DR: Using the anatomical data of the nasal passage, the deposition equations were rewritten as a function of the product of Stokes number and the total bend angle in nasopharynx and interspecies deposition differences were found to be greatly reduced in terms of the new variable.
Abstract: Based upon available experimental data, a set of empirical equations was derived for nasal deposition efficiency of inhaled particles in the inertial deposition range for four small laboratory animal species: the mouse, hamster, rat, and guinea pig. An equation for nasal deposition in humans was also derived in the same mathematical form to facilitate interspecies comparison. In these equations, deposition efficiency was expressed as a function of particle inertia d2 a Q where da is the particle aerodynamic diameter and Q is the flow rate. Results from the empirical equations showed that nasal deposition was species dependent, and that at the same d2 a Q, species with smaller body weight had higher deposition efficiency. By incorporating the anatomical data of the nasal passage, the deposition equations were rewritten as a function of the product of Stokes number and the total bend angle in nasopharynx. Interspecies deposition differences were found to be greatly reduced in terms of the new variable.
TL;DR: Systems used to provide unit doses of therapeutic aerosols are the metered dose inhaler (MDI), containing drug in a pressurized formulation, and the dry powder inhalers (DPI).
Abstract: The response to therapeutic aerosols is considered to be a function of the dose deposited at the target site in the lung. The dose, in turn, is dependent upon the system producing the aerosol, the particle size characteristics of the inhaled aerosol, the mode of inhalation, and the calibre of the airways. The influence of the pattern of deposition of the inhaled dose, i.e., selective delivery to the central vs. small, peripheral airways, on the response is not as well defined. Distribution of therapeutic aerosols in the lung has been measured using a variety of tracer methods; correlations with clinical response have been obtained in a limited number of these same studies. Systems used to provide unit doses of therapeutic aerosols are the metered dose inhaler (MDI), containing drug in a pressurized formulation, and the dry powder inhalers (DPI). Efficiency of delivery is on the order of 5–15% for these systems, even under optimal inhalation conditions. Continuous aerosol is provided by the jet or ultrason...
TL;DR: In this article, a new aerosol neutralizer, which makes use of a corona ionizer to produce bipolar ions, has been designed and evaluated, and the charge distribution of aerosol particles exiting the new corona neutralizer is found to depend on the ratio of electric current of positive ions and negative ions I − / I − and to attain the Boltzmann charge distribution at I + /I − = 1.
Abstract: A new aerosol neutralizer, which makes use of a corona ionizer to produce bipolar ions, has been designed and evaluated. The corona neutralizer consists of three components: a dual-needle ionizer for the generation of bipolar ions, an opposing-jet mixer for the uniform mixing of ions and particles, and a charging chamber for particle charge neutralization by ions. The bipolar ionizer consists of two unipolar ionizers for producing positive and negative ions, respectively. They are mixed to obtain the appropriate mixture of bipolar ions. Aerosol particals are then mixed with the bipolar ions in the mixer and are electrically discharged by collision with the bipolar ions in the charging chamber. The charge distribution of aerosol particles exiting the new corona neutralizer is found to depend on the ratio of electric current of positive ions and negative ions I − / I − and to attain the Boltzmann charge distribution at I + / I − = 1.0. The neutralizer has been shown to effectively reduce the particle charge...
TL;DR: In this article, a new formula is proposed to calculate the deposition efficiency of spherical particles from laminar flows in a horizontal circular duct by the combined mechanisms of sedimentation, diffusion and electrostatic precipitation based upon the efficiency derived for each individual mechanism.
Abstract: A new formula is proposed to calculate the deposition efficiency of spherical particles from laminar flows in a horizontal circular duct by the combined mechanisms of sedimentation, diffusion and electrostatic precipitation based upon the efficiency derived for each individual mechanism. The results from this formula compare well with the exact solutions previously obtained for several different cases of combined deposition as well as an empirical formula derived from experimental data for combined diffusion and sedimentation
TL;DR: In this paper, an aerosol dynamics model was used to predict indoor particle concentrations resulting from a specified combination of smoking frequency and building factors, and the rate of ETS mass accumulation in human lungs was determined as a function of particle size and lung airway generation.
Abstract: Inhalation exposure to environmental tobacco smoke (ETS) particles may increase health risks, but only to the extent that the particles deposit in the respiratory tract. We describe a technique to predict regional lung deposition of environmental tobacco smoke particles. Interpretation of particle size distribution measurements after cigarette combustion by a smoking machine in a test room yields an effective emissions profile. An aerosol dynamics model is used to predict indoor particle concentrations resulting from a specified combination of smoking frequency and building factors. By utilizing a lung deposition model, the rate of ETS mass accumulation in human lungs is then determined as a function of particle size and lung airway generation. Considering emissions of sidestream smoke only, residential exposures of nonsmokers to ETS are predicted to cause rates of total respiratory tract particle deposition in the range of 0.4–0.7 μg / day per kg of body weight for light smoking in a well-ventilated resi...
TL;DR: In this article, the integrating plate photometer (Lin et al., 1973) was calibrated with nonabsorbing and absorbing test aerosols to determine the systematical errors of the technique, which can be interpreted as apparent absorption coefficients σa a.
Abstract: In this study, the integrating plate photometer (Lin et al., 1973), used at the University of Vienna, was calibrated with nonabsorbing and absorbing test aerosols to determine the systematical errors of the technique, which can be interpreted as apparent absorption coefficients σa a. A nonlinear calibration curve was obtained from measurements with polystyrene latex particles of various sizes, which includes the scattering properties (expressed in terms of the scattering coefficient σs of the particles) and the area coverage ƒ of the filter. Application of this curve σa a/σs = 0.0398 f −0.441 to polydisperse paraffin aerosols gave satisfactory results. For the soot aerosol, σa a is < 10% of the calculated “true” absorption coefficient
TL;DR: The therapeutic activity of any drug or drug delivery system presented to the lung will depend on these physicochemical and biological characteristics that influence lung deposition and clearance.
Abstract: Studies of lung deposition and clearance show that a variety of mechanisms exist that protect the lung from the hazards of the environment. The behavior of inhaled toxicants and industrial airborne pollutants is of direct relevance to that of pharmaceutical aerosols. Particle characteristics of size, distribution, shape, hygroscopicity, and solubility influence lung deposition and clearance. The therapeutic activity of any drug or drug delivery system presented to the lung will depend on these physicochemical and biological characteristics. The results of inhalation toxicology and industrial hygiene studies are of great practical significance to pharmaceutics and drug delivery.
TL;DR: In this paper, the Stokes number based on the cut diameter was predicted to be a function of the Reynolds number and the geometry of the cyclone by using dimensionless data from various investigators.
Abstract: By using dimensional analysis, the Stokes number based on the cut diameter was predicted to be a function of the Reynolds number and the geometry of the cyclone. Data from various investigators were plotted versus the Reynolds number. At lower Reynolds numbers, the Stokes number decreased with increasing Reynolds number. At higher values of the Reynolds number, the data are inconclusive. For some data sets, the Stokes number approached a constant value, whereas, for other sets, the Stokes number decreased with increasing Reynolds number. The dimensionless data from this study can be used to estimate the cut diameter of geometrically similar cyclones and to make preliminary estimates for a cyclone of a different design.
TL;DR: In this article, a predictive model for the theoretical protection factor and leakage flow has been developed that uses the equation of particle conservation inside and outside the respirator, and the results are in good agreement with theory, but some discrepancy has been noted at lower flow rates and smaller leak hole sizes.
Abstract: The leak performance of half-mask, maintenance-free respirators was studied theoretically and experimentally. A predictive model for the theoretical protection factor and leakage flow has been developed that uses the equation of particle conservation inside and outside the respirator. An experimental study was conducted using NaCl particles of 10 nm in diameter and a condensation nucleus counter as the particle detector. A respirator fitted with controlled leak holes of 20–3000 μm in diameter was tested at steady flow rates of 10, 32, and 100 L/min. Results showed that the aerosol penetration into a respirator was strongly influenced by the filter efficiency, leak hole size, and flow rate through the respirator. The results are in good agreement with theory, but some discrepancy has been noted at lower flow rates and smaller leak hole sizes. For the dust/mist respirators, the experimental protection factor for ultrafine 0.01-μm NaCl particles ranged from 3145 to as low as 3. For the high efficiency dust/m...
TL;DR: In this article, the authors examined the nature and the causes of deviations between measured and estimated hydrogen ion concentrations and found that the measured hydrogen ion concentration were substantially higher than the estimated concentrations because dilution of the sample.
Abstract: The reference method currently being used in community health studies to characterize the acidity of atmospheric particles is based upon measuring the pH of aqueous extracts of atmospheric particles collected on filter media. These measurements represent total extractable acidity, i.e., hydrogen ion concentration at sufficient dilution of the sample, rather than the actual acidity of airborne particles. In contrast, models based upon chemical equilibrium theory can be used to estimate the hydrogen ion concentration and water content of atmospheric particles from the observed concentration of major solutes (sulfate, nitrate, chloride, ammonium, and sodium). Using about 100 data points from an intensive measurement study in Uniontown, Pennsylvania during 1990, we examined the nature and the causes of the deviations between measured and estimated hydrogen ion concentrations. We found that the measured hydrogen ion concentrations were substantially higher than the estimated concentrations because dilution of ...
TL;DR: In this article, the physical properties of an optical aerosol particle counter are simulated with a numerical algorithm showing the influence of monochromatic light scattering on the results of size distribution measurements.
Abstract: The physical properties of an optical aerosol particle counter are simulated with a numerical algorithm showing the influence of monochromatic light scattering on the results of size distribution measurements. By using model size distribution as an input to the simulation, the oscillations of the theoretical light-scattering curve are seen to cause unrealistic maxima and minima. This indicates that the structures in a number of published size distribution measurements might be artefacts and are possibly discussed incorrectly. The simulation shows that the counter under investigation is useful for measurements of cloud/fog droplet size distributions and for calculating the liquid water content. In addition, some published size distributions using the investigated optical laser particle counter are examined. By using model size distributions and published refractive indices, the resulting simulated size distributions are made to agree closely with those published. Artificial minima show up at nearly the sam...
TL;DR: In this paper, the authors present the design and calibration of a CVI intended for studying aerosol effects on cloud microphysics, which uses a polydispersion of glass beads, represents the first set of CVI collection efficiency results for diameters well below 10 μm.
Abstract: Unlike traditional virtual impactors, which suffer from a fixed level of small particle contamination in the large particle sample stream, the counterflow virtual impactor (CVI; Ogren et al., 1985) offers the potential for contamination-free sampling of large aerosol particles. Here we present the design and calibration of a CVI intended for studying aerosol effects on cloud microphysics. Such studies require that a large and well-characterized fraction of total cloud droplet number be sampled and that the interstitial aerosol be excluded. The new CVI provides cut sizes (i.e., 50% collection efficiency diameters) down to 7 μm, which is too small for calibration with previous methods (Noone et al., 1988a). Therefore, a new calibration method has been developed which is capable of measuring both cut size and cut sharpness at small diameters. This new method, which uses a polydispersion of glass beads, represents the first set of CVI collection efficiency results for diameters well below 10 μm. The new CVI i...