Correlation between airborne particle concentrations in seven industrial plants and estimated respiratory tract deposition by number,mass and elemental composition

The number and mass distribution of airborne particles were recorded in several industrial plants. From the data obtained, particle deposition was estimated in three regions of the respiratory tract using the ICRP grand average deposition model based on Hinds' (1999) parameterization. The median diameter was 30–70 nm (number distributions), and >4 μm (mass distributions) near most work activities, resulting in linear relationships between the deposited number/mass concentrations and the number/mass concentrations in the air. Welding and laser cutting produced particles in the 200–500-nm range; total deposition was small, not in accordance with the linear relationship observed for the other work activities. The elemental content varied between particle sizes in some workplaces, causing different elements to deposit in different respiratory regions. Iron was the most abundant element in the particles in many of the workplaces; in an iron foundry, however, Fe was most abundant only in the micron-sized particles whereas the nanoparticles mainly comprised Pb and Sb.     

DESIGN AND EXPERIMENTAL CHARACTERIZATION OF A PM1 AND A PM2.5 PERSONAL SAMPLER

This paper presents the development, laboratory and field evaluation of two personal particle samplers (PPS). Both samplers operate at a flow rate of 4 l min^-1, and collect particles smaller than 1.0 and 2.5 μm in aerodynamic diameter, respectively, on 3.7 cm Teflon filters. In each sampler, particles larger than 2.5 or 1.0 μm are retained by impaction onto a coated porous metal disk, which minimizes particle bounce. Using the substrates without any coating results in a substantial reduction of the collection efficiency for particles larger than the 50% cutpoint of the sampler. Particle losses in each sampler are quite low (e.g., on the order of 10% or less) and do not depend significantly on aerodynamic particle diameter. Both samplers display sharp particle cut characteristics, with the ratio of the aerodynamic particle diameter corresponding to 84% collection efficiency to the 50% cutpoint being approximately 1.18 and 1.27 for the PM₁ and the PM_2.5 samplers, respectively. Field tests showed that the mass, sulfate and nitrate concentrations measured by the PM_2.5 PPS and a collocated PM_2.5 Personal Exposure Monitor (PEM) agreed within 10% or less. Such agreement, however, was not observed between the PM_2.5 PPS and the Harvard/EPA Annular Denuder System (HEADS), with the HEADS nitrate concentrations being on the average higher by a factor of 2.1. The particle mass, sulfate and nitrate concentrations obtained with a modified MOUDI sampler collecting all particles smaller than 1 μm in aerodynamic diameter on a filter and the PM₁ PPS were also in very good agreement (e.g., within 7% or less). The two personal particle samplers will be used in field studies in different locations of the U.S. to provide better estimates of human exposures to exclusively particles of the accumulation mode. (e.g., without incorporating the contribution of the coarse mode).     

Micronization of ketoprofen by the rapid expansion of supercritical solution process

The particle size of the pharmaceutical substances is important for their bioavailability (the percentage of the drug absorbed compared to its initial dosage). The absorption rate can be increased by reducing particle size of the drug particles. This study was conducted to investigate the effects of the extraction pressure (140–220 bar), extraction temperature (308–338 K), nozzle length (2–15 mm), effective nozzle diameter (450–1700 μm), and collection distance (1–10 cm) on the size and morphology of the precipitated ketoprofen particles. The characterization (size and morphology) of the particles was investigated using scanning electron microscopy (SEM). The average particle size of the original material was 115.42 μm, while the average particle size of the micronized particles is between 0.35 and 7.03 μm near to quisi-spherical, needle and irregular shape depending upon the experimental conditions.     

Computational fluid dynamics simulations of submicrometer and micrometer particle deposition in the nasal passages of a Sprague-Dawley rat

Computational fluid dynamics (CFD) simulations were conducted in a model of the complete nasal passages of an adult male Sprague-Dawley rat to predict regional deposition patterns of inhaled particles in the size range of 1 nm to 10 μm. Steady-state inspiratory airflow rates of 185, 369, and 738 ml/min (equal to 50%, 100%, and 200% of the estimated minute volume during resting breathing) were simulated using Fluent?. The Lagrangian particle tracking method was used to calculate trajectories of individual particles that were passively released from the nostrils. Computational predictions of total nasal deposition compared well with experimental data from the literature when deposition fractions were plotted against the Stokes and Peclet numbers for micro- and nanoparticles, respectively. Regional deposition was assessed by computing deposition efficiency curves for major nasal epithelial cell types. For micrometer particles, maximum olfactory deposition was 27% and occurred at the lowest flow rate with a particle diameter of 7 μm. Maximum deposition on mucus-coated non-olfactory epithelium was 27% for 3.25 μm particles at the highest flow rate. For submicrometer particles, olfactory deposition reached a maximum of 20% with a particle size of 5 nm at the highest flow rate, whereas deposition on mucus-coated non-olfactory epithelium reached a peak of approximately 60% for 1–4 nm particles at all flow rates. These simulations show that regional particle deposition patterns are highly dependent on particle size and flow rate, indicating the importance of accurate quantification of deposition in the rat for extrapolation of results to humans.     

Computation of local enhancement factors for the quantification of particle deposition patterns in airway bifurcations

Spatial deposition patterns in two different geometric models of bronchial airway bifurcations were computed by solving numerically the 3D Navier–Stokes equations and simulating particle trajectories under the simultaneous action of impaction, sedimentation, diffusion, and interception by Monte Carlo techniques. To quantify the inhomogeneities of the predicted deposition patterns the whole surface of the bifurcation was scanned with a prespecified surface area element to determine the number of particles deposited per unit surface area. The local deposition density in a given surface element, relative to the average deposition density, was then defined as the local deposition enhancement factor.In the present study, the computation of local deposition enhancement factors focused on inspiratory particle deposition patterns. Our results revealed that the distributions of local deposition enhancement factors along the surface of a bifurcation exhibit strong inhomogeneities for all particle sizes and bifurcation geometries considered here. The maximum enhancement factor in a bifurcation was found to be about 100 in the upper bronchial airways for any particle size in the diameter range from 0.01 to 10 μm, obtained with a 100 μm×100 μm scanning element. These numerically computed local deposition enhancement factors can be directly applied to inhalation health effect protocols to consider the effects of highly localized doses.     

COAGULATION OF CIGARETTE SMOKE PARTICLES

Experimental measurements on the deposition of cigarette smoke particles (CSP) in the human airways have produced results that are inconsistent with typical deposition data based on particle size. Previous work relating to hygroscopic growth indicates that hygroscopicity alone can not account for this discrepancy. The present study investigates coagulation of CSP modeled as a polydisperse-charged aerosol as a possible explanation. The results of the model more accurately predict the experimental coagulation data for mainstream CSP than models that treat CSP as a monodisperse or polydisperse-uncharged aerosol. An aerosol with an initial charge distribution based on Boltzmann equilibrium yields slightly larger coagulation rates than the mainstream CSP polydisperse-charged model. The numerical results indicate that the size and charge distribution of sidestream CSP, with a concentration of 10⁶ particles cm^-3, remain stable. In 2 s, the size distribution of mainstream CSP, with a concentration of 10⁹ particles cm^-3, shifts to a larger size while becoming flatter and wider. The diameter of average mass increases from 0.29 to 0.5 μm. Numerical results confirm experimental reports for mainstream CSP, which indicate that the total number of charged particles increases with time and, in the early stages of coagulation, the amount of charge per particle cannot be estimated based on the particle size. This study shows that polydisperse-charged CSP, allowed to coagulate for 2 s in the mouth, will not produce size distributions that yield the observed deposition of CSP. However, additional coagulation will take place as the CSP travels through the respiratory tract, which will be investigated in future work.     

Size and shape characterization of polydisperse short-fiber systems

Two wollastonites, polydisperse with respect to size and shape, are characterized by image analysis. Aspect ratios are calculated for individual particles (1000–1500 objects) from the minimum and maximum Feret diameters measured. Although scatter is large (approximately 50%), average aspect ratios are well reproducible and approximately size-invariant, approximately 5 and 16 for wollastonite WM 45 and HSV 45, respectively. A transformation procedure is proposed and applied to transform the number-weighted size distributions obtained via image analysis into volume-weighted size distributions that can be compared with laser diffraction. The laser diffraction medians (21.6 μm and 29.1 μm for WM 45 and HSV 45, respectively) are close to the medians of the minimum Feret diameter distributions (20.6 μm and 29.9 μm for WM 45 and HSV 45, respectively). This is clear evidence of the fact that laser diffraction results need not at all correspond to projected area diameters determined by image analysis.     

Investigation of flow properties of metal powders from narrow particle size distribution to polydisperse mixtures through an improved Hall-flowmeter

Initially, we critically examined the results provided by the improved Hall-flowmeter, based on bulk volume flow rate, with narrow particle size distribution metal powders (iron, aluminium and copper) of different sizes (fine to coarse) and shapes (nearly spherical to non-spherical). Binary and ternary mixtures of various combinations of fine (< 100 μm) and coarse (> 100 μm) metal powders at different size ratios and weight fractions were allowed to discharge from a mass flow hopper. The results show that the mass flow rate of polydisperse mixtures of metal powders is affected by four factors: the size ratio, the volume fraction of the smallest sieved fraction, the initial mass flow rate and the shape of metal powders.     

Preparation of poly-lactic acid nano/microparticles using supercritical anti-solvent with enhanced mass transfer

Supercritical anti-solvent precipitation with enhanced mass transfer (SAS-EM) was applied for the production of micro and sub-microparticles of poly-lactic acid (PLA). SAS-EM technique uses an ultrasonic vibrating surface to enhance mass transfer rate between supercritical CO₂ and solvent. Without applying ultrasonic power, which is same as SAS process, PLA particles with average diameters ranging between 1 μm and 3 μm were obtained. Using SAS-EM with the power supply of 200 W, spherical PLA particles smaller than 1 μm were obtained. The particle size was able to be controlled in the range of 0.4 μm–1.0 μm, by adjusting the power supply of ultrasonic field, the system pressure and temperature.     

Particle deposition in juvenile rat lungs: A model study

Lung development disruption in childhood due to air pollution is gaining growing attention. Although rats are widely used for studies of pulmonary toxicology, little is known about the fate of inhaled particles in juvenile rat lungs. We investigated detailed particle deposition in rat lungs at 15, 28, 40, and 81 days of age using a single path mathematical model. For normal breathing conditions, particles smaller than 0.1 μm deposited in extrathoracic airways more in juvenile rats compared to adults whereas alveolar deposition fraction for juvenile rats was smaller compared to adults for most particle sizes. Alveolar deposition per minute per unit body mass was appreciably lower for juvenile rats compared to adults and deposition per minute per unit area was lower for juvenile rats over the entire lungs for most particle sizes.     

Abundance and size distribution of HULIS in ambient aerosols at a rural site in South China

HUmic-LIke Substances (HULIS) comprise a significant fraction of the water-soluble organic aerosol mass and influence the water uptake properties of aerosols in the atmosphere. In this work, the abundance and size distributions of HULIS in ambient aerosols were measured in a rural location in South China at a time with a visible presence of crop residue burning. PM_2.5 samples of fresh smoke from burning rice straw and sugar cane leaves were also collected and analyzed for HULIS and major aerosol constituents. HULIS were abundant in both ambient samples and in fresh biomass burning emissions, accounting for ～60% of the water-soluble organic carbon in the ambient aerosols and ～30% in the fresh biomass burning aerosols. In the particles in the range of 0.32–1.8 μm, the abundance of HULIS was 40–90% of the combined abundance of sulfate and ammonium, suggesting that HULIS should be considered when quantifying the role of sulfate aerosols serving as cloud condensation nuclei. The size distribution of HULIS was characterized by a dominant droplet mode with a mass median aerodynamic diameter (MMAD) in the range of 0.63–0.87 μm, accounting for 81% of the total HULIS mass, a minor condensation mode (12%, MMAD: 0.23–0.28 μm) and a coarse mode (7%, MMAD: 4.0–5.7 μm). The small amount of HULIS in the coarse mode indicated that soil-derived HULIS was a very minor source. On the basis of the size distribution characteristics, HULIS were postulated to have multiple sources, including secondary formation in cloud droplets, secondary formation through heterogeneous reactions or aerosol-phase reactions, and primary emissions from biomass burning.     

Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities

A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities.Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 μm at average concentrations up to 0.75 cm^?3. These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 μm was produced during all activities, but at lower concentrations of up to 0.14 cm^?3.Speech produced additional particles in modes near 3.5 and 5 μm. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm^?3, respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number.For the entire size range examined of 0.3–20 μm, average particle number concentrations produced during exhalation ranged from 0.1 cm^?3 for breathing to 1.1 cm^?3 for sustained vocalization.Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 μm, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.     

Micronization of fenofibrate by rapid expansion of supercritical solution

Micronization of fenofibrate was investigated using rapid expansion of supercritical solution (RESS) process. Effects of pressure, temperature and nozzle on particle size were optimized using Taguchi's orthogonal array and analyzed using XRD, DSC, FT-IR, SEM, laser diffractometer and dissolution testing. Processed fenofibrate retained crystalline structure and has a similar chemical structure with unprocessed fenofibrate. The average particle size of fenofibrate was reduced from its original 68.779 ± 0.146 μm to 3.044 ± 0.056 μm under the optimum condition (T at 35 °C, P at 200 bar and nozzle diameter at 200 μm). The processed fenofibrate showed an enhanced dissolution rate by 8.13 times.     

Polymethylmethacrylate (PMMA) sub-microparticles produced by Supercritical Assisted Injection in a Liquid Antisolvent

A recently developed supercritical assisted process, called Supercritical Assisted Injection in a Liquid Antisolvent (SAILA) is proposed to produce polymer micro and nanoparticles in water stabilized suspensions. Polymethylmethacrylate (PMMA) has been selected as the model polymer for a systematic study of the influence of the SAILA operating parameters on particle morphology and diameter. The effect of expanded liquid injection pressure on particle size and distribution was studied and different expanded liquid temperatures and compositions were also explored. Successful precipitation of the polymer in a water stabilized suspension was obtained and narrow particle size distributions were obtained using 70 and 90 bar injection pressures. PMMA particles controlled diameter were produced ranging between 0.2 ± 0.04 μm and 0.9 ± 0.2 μm. Particles are formed from the expanded liquid solution as a consequence of very fast supersaturation produced by spraying it the liquid antisolvent.     

EFFECT OF DEPOSITED PARTICLES AND PARTICLE CHARGE ON THE PENETRATION OF SMALL SAMPLING CYCLONES

Effects of particle mass deposited in the cyclone and particle electrostatic charge on the particle penetration of the commonly used 10 mm nylon cyclone have been experimentally investigated in this study. The solid particle penetration of the cyclone has been found to decrease with an increase in particle mass deposited in the cyclone. This effect is most significant for particles near the cutoff aerodynamic diameter and when the deposited particle mass is low. The penetration of the cyclone has also been found to be influenced by particle electrostatic charge. This effect is also significant for particles near the cutoff aerodynamic diameter and when the number of elementary units of charge is greater than several thousands. To overcome these problems, a new cyclone made of conductive aluminum and with inner diameter nearly twice that of the 10 mm nylon cyclone has been designed and tested. Experimental results indicate that effects of both deposited particle mass as well as electrostatic charge on the penetration are reduced substantially in this cyclone.     

Imaging extra-thoracic airways and deposited particles in laboratory animals

Laboratory animals are widely used as models for exploring adverse and beneficial health effects caused by inhalation of suspended particles. Mapping particle deposition throughout the airways of laboratory animals is crucial since the location of particle deposition often determines subsequent clearance, transport and the health effects elicited. Such mapping has yet to be performed systematically due to lack of available methods. In this paper, a new method is presented for imaging both the nasal airways of laboratory animals and particles deposited in them. After inhalation of particles, the rat airways are frozen to lock the particles in place and cast at this temperature to color and support the lumen. Once the cast is cured, an imaging cryomicrotome sections and images the airways as well as the deposited fluorescent particles. Computer software reconstructs the airways and particle maps from these serial images. The method was validated by manually placing boluses of fluorescent particles in nasal airways of a rat and then imaging them to ensure that they were displayed in the correct locations. To demonstrate the method, rats inhaled 2.5 μm particles in a nose-only exposure chamber. Images and reconstructions are presented of the nasal passage and deposited particles for one of these rats demonstrating the method’s usefulness for locating inhaled and deposited therapeutic and toxic particles in the extra-thoracic airways of laboratory animals.     

COUNTING EFFICIENCY OF THE API AEROSIZER

The Aerosizer (Amherst Process Instruments, Inc. Hadley MA) is a time-of-flight instrument frequently used to measure the size distribution of an aerosol. However, if the Aerosizer’s counting efficiency, defined as the number of particles counted divided by the total number entering the instrument, is not 100% or varies with particle size, the resulting size distribution will be inaccurate.Experiments were conducted to determine the effect of particle diameter, particle concentration, photomultiplier tube (PMT) voltage, and model type on the Aerosizer’s counting efficiency. To calculate counting efficiency, the number of particles between 0.3 and 10 μm recorded by the Aerosizer was divided by the number of particles of the same size collected on each stage of a cascade impactor.Particle diameter, aerosol concentration, Aerosizer model, PMT voltage, and the diameter interaction terms influenced counting efficiency. Counting efficiencies were less than 1% for particles smaller than 0.45 μm, and more than 100% for particles larger than 7 μm. Increasing the PMT voltage increased the counting efficiency for the smaller particles, but also created false, larger particles. Counting efficiency decreased as count rate increased for count rates greater than 20,000 particles per second. The Aerosizer LD counted particles more efficiently than the Aerosizer Mach 2 because of improved laser and optics systems. Four regression models that relate counting efficiency to the salient operating parameters were developed, one for each combination of Aerosizer model and photomultiplier tube voltage studied.     

Bimodal distribution of filler on viscosity and thermal expansion of glass composites

This paper investigates the bimodal oxide filler system to study the viscous behavior and thermal expansion properties of glass composites. Zinc oxide and cordierite, which are two types of filler, with different average diameters (10 μm and 1 μm, respectively), were considered in a Bi2O3 containing glass with various volume fractions (up to 40 vol%). The experimental results for the composites with the bimodal filler distribution show a reduced viscosity. The viscosity increased from fine particles to coarse particles with an increase in the volume fraction of the composite. Both viscosity and coefficient of thermal expansion (CTE) decreased significantly in the composite with the cordierite filler. The CTE is determined from the volume fraction with respect to particle size and distribution. On the other hand, viscosity is dependent on the particle distribution, particle size, and volume fraction of the composite.     

Characterizing the performance of two optical particle counters (Grimm OPC1.108 and OPC1.109) under urban aerosol conditions

The performance of Grimm optical particle counters (OPC, models 1.108 and 1.109) was characterized under urban aerosol conditions. Number concentrations were well correlated. The different lower cut-off diameters (0.25 and 0.3 μm) give an average difference of 23.5%. Both detect less than 10% of the total particle concentration (0.01–1 μm; Differential Mobility Analyzer), but in the respective size ranges, differences are <10%. OPC number size distributions were converted to mass concentrations using instrument-specific factors given by the manufacturer. Mass concentrations for OPC1.108 were 60% higher than for OPC1.109 and (in case of OPC1.109) much lower than those measured with an impactor in the relevant size range or a TSP filter. Using the C-factor correction suggested by the manufacturer, OPC1.109 underestimated mass concentrations by 21% (impactor) and by about 36% (TSP filter), which is in the range of comparability of co-located different mass concentration methods (Hitzenberger, Berner, Maenhaut, Cafmeyer, Schwarz, &; Mueller et al., 2004).     

AEROSOL CHARACTERISATION IN MEDIUM-SPEED DIESEL ENGINES OPERATING WITH HEAVY FUEL OILS

Aerosol measurements were carried out in medium-speed diesel engines to determine the aerosol characteristics and formation in four-stroke diesel engines equipped with turbocharger(s) burning heavy fuel and high ash-content heavy fuel oil. The mass size distributions are bimodal with a main mode at 60–90 nm and a second mode at 7–10 μm. The small mode particles are formed by nucleation of volatilized fuel oil ash species, which further grow by condensation and agglomeration. The large mode particles are mainly agglomerates of different sizes consisting of the small particles. The number size distributions peak at 40–60 nm, as also observed in the SEM micrographs. Agglomerates consisting of these primary spherical particles are also found. The TEM micrographs reveal that these particles consist of even smaller structures. Based on the mass and elemental size distributions evidence of high volatility of the fuel oil ash was found. The main effect on the aerosol size distributions was caused by the engine type and fuel oil properties.