Aerosol Science And Technology[JOURNAL]
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138 papers
Particle Count Statistics Applied to the Penetration of a Filter Challenged with Nanoparticles.
O'Shaughnessy PT, Schmoll LH
Aerosol Sci Technol · 2013 Jan · PMID 24678138 · Full text
Statistical confidence in a single measure of filter penetration (P) is dependent on the low number of particle counts made downstream of the filter. This paper discusses methods for determining an upper confidence limit...
Statistical confidence in a single measure of filter penetration (P) is dependent on the low number of particle counts made downstream of the filter. This paper discusses methods for determining an upper confidence limit (UCL) for a single measure of penetration. The magnitude of the UCL was then compared to the P value, UCL ≤ 2P, as a penetration acceptance criterion (PAC). This statistical method was applied to penetration trials involving an N95 filtering facepiece respirator challenged with sodium chloride and four engineered nanoparticles: titanium dioxide, iron oxide, silicon dioxide and single-walled carbon nanotubes. Ten trials were performed for each particle type with the aim of determining the most penetrating particle size (MPPS) and the maximum penetration, P. The PAC was applied to the size channel containing the MPPS. With those P values that met the PAC for a given set of trials, an average P and MPPS was computed together with corresponding standard deviations. Because the size distribution of the silicon dioxide aerosol was shifted towards larger particles relative to the MPPS, none of the ten trials satisfied the PAC for that aerosol. The remaining four particle types resulted in at least 4 trials meeting the criterion. MPPS values ranged from 35 - 53 nm with average P values varying from 4.0% for titanium dioxide to 7.0% for iron oxide. The use of the penetration acceptance criterion is suggested for determining the reliability of penetration measurements obtained to determine filter P and MPPS.
Toward Developing a New Occupational Exposure Metric Approach for Characterization of Diesel Aerosols.
Cauda EG, Ku BK, Miller AL … +1 more , Barone TL
Aerosol Sci Technol · 2012 Dec · PMID 26361400 · Full text
The extensive use of diesel-powered equipment in mines makes the exposure to diesel aerosols a serious occupational issue. The exposure metric currently used in U.S. underground noncoal mines is based on the measurement...
The extensive use of diesel-powered equipment in mines makes the exposure to diesel aerosols a serious occupational issue. The exposure metric currently used in U.S. underground noncoal mines is based on the measurement of total carbon (TC) and elemental carbon (EC) mass concentration in the air. Recent toxicological evidence suggests that the measurement of mass concentration is not sufficient to correlate ultrafine aerosol exposure with health effects. This urges the evaluation of alternative measurements. In this study, the current exposure metric and two additional metrics, the surface area and the total number concentration, were evaluated by conducting simultaneous measurements of diesel ultrafine aerosols in a laboratory setting. The results showed that the surface area and total number concentration of the particles per unit of mass varied substantially with the engine operating condition. The specific surface area (SSA) and specific number concentration (SNC) normalized with TC varied two and five times, respectively. This implies that miners, whose exposure is measured only as TC, might be exposed to an unknown variable number concentration of diesel particles and commensurate particle surface area. Taken separately, mass, surface area, and number concentration did not completely characterize the aerosols. A comprehensive assessment of diesel aerosol exposure should include all of these elements, but the use of laboratory instruments in underground mines is generally impracticable. The article proposes a new approach to solve this problem. Using SSA and SNC calculated from field-type measurements, the evaluation of additional physical properties can be obtained by using the proposed approach.
Investigation of Aerosol Surface Area Estimation from Number and Mass Concentration Measurements: Particle Density Effect.
Ku BK, Evans DE
Aerosol Sci Technol · 2012 Apr · PMID 26526560 · Full text
For nanoparticles with nonspherical morphologies, e.g., open agglomerates or fibrous particles, it is expected that the actual density of agglomerates may be significantly different from the bulk material density. It is...
For nanoparticles with nonspherical morphologies, e.g., open agglomerates or fibrous particles, it is expected that the actual density of agglomerates may be significantly different from the bulk material density. It is further expected that using the material density may upset the relationship between surface area and mass when a method for estimating aerosol surface area from number and mass concentrations (referred to as "Maynard's estimation method") is used. Therefore, it is necessary to quantitatively investigate how much the Maynard's estimation method depends on particle morphology and density. In this study, aerosol surface area estimated from number and mass concentration measurements was evaluated and compared with values from two reference methods: a method proposed by Lall and Friedlander for agglomerates and a mobility based method for compact nonspherical particles using well-defined polydisperse aerosols with known particle densities. Polydisperse silver aerosol particles were generated by an aerosol generation facility. Generated aerosols had a range of morphologies, count median diameters (CMD) between 25 and 50 nm, and geometric standard deviations (GSD) between 1.5 and 1.8. The surface area estimates from number and mass concentration measurements correlated well with the two reference values when gravimetric mass was used. The aerosol surface area estimates from the Maynard's estimation method were comparable to the reference method for all particle morphologies within the surface area ratios of 3.31 and 0.19 for assumed GSDs 1.5 and 1.8, respectively, when the bulk material density of silver was used. The difference between the Maynard's estimation method and surface area measured by the reference method for fractal-like agglomerates decreased from 79% to 23% when the measured effective particle density was used, while the difference for nearly spherical particles decreased from 30% to 24%. The results indicate that the use of particle density of agglomerates improves the accuracy of the Maynard's estimation method and that an effective density should be taken into account, when known, when estimating aerosol surface area of nonspherical aerosol such as open agglomerates and fibrous particles.
The Structure of Agglomerates consisting of Polydisperse Particles.
Eggersdorfer ML, Pratsinis SE
Aerosol Sci Technol · 2012 Mar · PMID 23729953 · Full text
Agglomeration is encountered in many natural or industrial processes, like growth of aerosol particles in the atmosphere and during material synthesis or even flocculation of suspensions, granulation, crystallization and...
Agglomeration is encountered in many natural or industrial processes, like growth of aerosol particles in the atmosphere and during material synthesis or even flocculation of suspensions, granulation, crystallization and with colloidal particle processing. These particles collide by different mechanisms and stick together forming irregular or fractal-like agglomerates. Typically, the structure of these agglomerates is characterized with the fractal dimension, , and pre-exponential factor, , of simulated agglomerates of monodisperse primary particles (PP) for ballistic or diffusion-limited particle-cluster and cluster-cluster collision mechanisms. Here, the effect of PP polydispersity on and is investigated with agglomerates consisting of 16 - 1024 PP with closely controlled size distribution (geometric standard deviation, σ = 1-3). These simulations are in excellent agreement with the classic structure ( and ) of agglomerates consisting of monodisperse PPs made by four different collision mechanisms as well as with agglomerates of bi-, tri-disperse and normally distributed PPs. Broadening the PP size distribution of agglomerates decreases monotonically their and for sufficiently broad PP distributions (σ > 2.5) the reaches about 1.5 and about 1 regardless of collision mechanism. Furthermore with increasing PP polydispersity, the corresponding projected area exponent, , and pre-exponential factor, , decrease monotonically from their standard values for agglomerates with monodisperse PPs. So as well as and can be an indication for PP polydispersity in mass-mobility and light scattering measurements, if the dominant agglomeration mechanism is known, like diffusion-limited and/or ballistic cluster-cluster coagulation in aerosols.
Satellite Remote Sensing for Developing Time and Space Resolved Estimates of Ambient Particulate in Cleveland, OH.
Kumar N, Chu AD, Foster AD … +2 more , Peters T, Willis R
Aerosol Sci Technol · 2011 Sep · PMID 22238503 · Full text
This article empirically demonstrates the use of fine resolution satellite-based aerosol optical depth (AOD) to develop time and space resolved estimates of ambient particulate matter (PM) ≤2.5 µm and ≤10 µm in aerodynam...
This article empirically demonstrates the use of fine resolution satellite-based aerosol optical depth (AOD) to develop time and space resolved estimates of ambient particulate matter (PM) ≤2.5 µm and ≤10 µm in aerodynamic diameters (PM(2.5) and PM(10), respectively). AOD was computed at three different spatial resolutions, i.e., 2 km (means 2 km × 2 km area at nadir), 5 km, and 10 km, by using the data from MODerate Resolution Imaging Spectroradiometer (MODIS), aboard the Terra and Aqua satellites. Multiresolution AOD from MODIS (AOD(MODIS)) was compared with the in situ measurements of AOD by NASA's AErosol RObotic NETwork (AERONET) sunphotometer (AOD(AERONET)) at Bondville, IL, to demonstrate the advantages of the fine resolution AOD(MODIS) over the 10-km AOD(MODIS), especially for air quality prediction. An instrumental regression that corrects AOD(MODIS) for meteorological conditions was used for developing a PM predictive model.The 2-km AOD(MODIS) aggregated within 0.025° and 15-min intervals shows the best association with the in situ measurements of AOD(AERONET). The 2-km AOD(MODIS) seems more promising to estimate time and space resolved estimates of ambient PM than the 10-km AOD(MODIS), because of better location precision and a significantly greater number of data points across geographic space and time. Utilizing the collocated AOD(MODIS) and PM data in Cleveland, OH, a regression model was developed for predicting PM for all AOD(MODIS) data points. Our analysis suggests that the slope of the 2-km AOD(MODIS) (instrumented on meteorological conditions) is close to unity with the PM monitored on the ground. These results should be interpreted with caution, because the slope of AOD(MODIS) ranges from 0.52 to 1.72 in the site-specific models. In the cross validation of the overall model, the root mean square error (RMSE) of PM(10) was smaller (2.04 µg/m(3) in overall model) than that of PM(2.5) (2.5 µg/m(3)). The predicted PM in the AOD(MODIS) data (∼2.34 million data points) was utilized to develop a systematic grid of daily PM at 5-km spatial resolution with the aid of spatiotemporal Kriging.
Design Optimization of a Portable Thermophoretic Precipitator Nanoparticle Sampler.
Miller A, Marinos A, Wendel C … +2 more , King G, Bugarski A
Aerosol Sci Technol · 2012 · PMID 26702194 · Full text
Researchers at the National Institute for Occupational Safety and Health (NIOSH) are developing methods for characterizing diesel particulate matter in mines. Introduction of novel engine and exhaust after treatment tech...
Researchers at the National Institute for Occupational Safety and Health (NIOSH) are developing methods for characterizing diesel particulate matter in mines. Introduction of novel engine and exhaust after treatment technologies in underground mines is changing the nature of diesel emissions, and metrics alternative to the traditional mass-based measurements are being investigated with respect to their ability to capture changes in the properties of diesel aerosols. The emphasis is given to metrics based on measurement of number and surface area concentrations, but analysis of collected particles using electron microscopy (EM) is also employed for detailed particle characterization. To collect samples for EM analysis at remote workplaces, including mining and manufacturing facilities, NIOSH is developing portable particle samplers capable of collecting airborne nano-scale particles. This paper describes the design, construction, and testing of a prototype thermophoretic precipitator (TP) particle sampler optimized for collection of particles in the size range of 1-300 nm. The device comprises heated and cooled metal plates separated by a 0.8 mm channel through which aerosol is drawn by a pump. It weighs about 2 kg, has a total footprint of 27 × 22 cm, and the collection plate size is approximately 4 × 8 cm. Low power consumption and enhanced portability were achieved by using moderate flow rates (50-150 cm/min) and temperature gradients (10-50 K/mm with Δ between 8 K and 40 K). The collection efficiency of the prototype, measured with a condensation particle counter using laboratory-generated polydisperse submicrometer NaCl aerosols, ranged from 14-99%, depending on temperature gradient and flow rate. Analysis of transmission electron microscopy images of samples collected with the TP confirmed that the size distributions of collected particles determined using EM are in good agreement with those determined using a Fast Mobility Particle Sizer.
New Approach for Near-Real-Time Measurement of Elemental Composition of Aerosol Using Laser-Induced Breakdown Spectroscopy.
Diwakar P, Kulkarni P, Birch ME
Aerosol Sci Technol · 2012 · PMID 26692632 · Full text
A new approach has been developed for making near-real-time measurement of elemental composition of aerosols using plasma spectroscopy. The method allows preconcentration of miniscule particle mass (pg to ng) directly fr...
A new approach has been developed for making near-real-time measurement of elemental composition of aerosols using plasma spectroscopy. The method allows preconcentration of miniscule particle mass (pg to ng) directly from the sampled aerosol stream through electrostatic deposition of charged particles (30-900 nm) onto a flat-tip microneedle electrode. The collected material is subsequently ablated from the electrode and monitored by laser-induced breakdown spectroscopy. Atomic emission spectra were collected using a broadband spectrometer with a wavelength range of 200-980 nm. A single-sensor delay time of 1.3 s was used in the spectrometer for all elements to allow simultaneous measurement of multiple elements. The system was calibrated for various elements including Cd, Cr, Cu, Mn, Na, and Ti. The absolute mass detection limits for these elements were experimentally determined and found to be in the range of 0.018-5 ng. The electrostatic collection technique has many advantages over other substrate-based methods involving aerosol collection on a filter or its focused deposition using an aerodynamic lens. Because the particle mass is collected over a very small area that is smaller than the spatial extent of the laser-induced plasma, the entire mass is available for analysis. This considerably improves reliability of the calibration and enhances measurement accuracy and precision. Further, the aerosol collection technique involves very low pressure drop, thereby allowing higher sample flow rates with much smaller pumps-a desirable feature for portable instrumentation. Higher flow rates also make it feasible to measure trace element concentrations at part per trillion levels. Detection limits in the range of 18-670 ng m can be achieved for most of the elements studied at a flow rate of 1.5 L min with sampling times of 5 min.
Particle Collection Efficiency for Nylon Mesh Screens.
Cena LG, Ku BK, Peters TM
Aerosol Sci Technol · 2012 · PMID 26692631 · Full text
Mesh screens composed of nylon fibers leave minimal residual ash and produce no significant spectral interference when ashed for spectrometric examination. These characteristics make nylon mesh screens attractive as a co...
Mesh screens composed of nylon fibers leave minimal residual ash and produce no significant spectral interference when ashed for spectrometric examination. These characteristics make nylon mesh screens attractive as a collection substrate for nanoparticles. A theoretical single-fiber efficiency expression developed for wire-mesh screens was evaluated for estimating the collection efficiency of submicrometer particles for nylon mesh screens. Pressure drop across the screens, the effect of particle morphology (spherical and highly fractal) on collection efficiency and single-fiber efficiency were evaluated experimentally for three pore sizes (60, 100 and 180 μm) at three flow rates (2.5, 4 and 6 Lpm). The pressure drop across the screens was found to increase linearly with superficial velocity. The collection efficiency of the screens was found to vary by less than 4% regardless of particle morphology. Single-fiber efficiency calculated from experimental data was in good agreement with that estimated from theory for particles between 40 and 150 nm but deviated from theory for particles outside this size range. New coefficients for the single-fiber efficiency model were identified that minimized the sum of square error (SSE) between the values estimated with the model and those determined experimentally. Compared to the original theory, the SSE calculated using the modified theory was at least one order of magnitude lower for all screens and flow rates with the exception of the 60-μm pore screens at 2.5 Lpm, where the decrease was threefold.
Numerical Model to Characterize the Size Increase of Combination Drug and Hygroscopic Excipient Nanoparticle Aerosols.
Longest PW, Hindle M
Aerosol Sci Technol · 2011 Jan · PMID 21804683 · Full text
Enhanced excipient growth is a newly proposed respiratory delivery strategy in which submicrometer or nanometer particles composed of a drug and hygroscopic excipient are delivered to the airways in order to minimize ext...
Enhanced excipient growth is a newly proposed respiratory delivery strategy in which submicrometer or nanometer particles composed of a drug and hygroscopic excipient are delivered to the airways in order to minimize extrathoracic depositional losses and maximize lung retention. The objective of this study was to develop a validated mathematical model of aerosol size increase for hygroscopic excipients and combination excipient-drug particles and to apply this model to characterize growth under typical respiratory conditions. Compared with in vitro experiments, the droplet growth model accurately predicted the size increase of single component and combination drug and excipient particles. For typical respiratory drug delivery conditions, the model showed that droplet size increase could be effectively correlated with the product of a newly defined hygroscopic parameter and initial volume fractions of the drug and excipient in the particle. A series of growth correlations was then developed that successively included the effects of initial drug and excipient mass loadings, initial aerosol size, and aerosol number concentration. Considering EEG delivery, large diameter growth ratios (2.1-4.6) were observed for a range of hygroscopic excipients combined with both hygroscopic and non-hygroscopic drugs. These diameter growth ratios were achieved at excipient mass loadings of 50% and below and at realistic aerosol number concentrations. The developed correlations were then used for specifying the appropriate initial mass loadings of engineered insulin nanoparticles in order to achieve a predetermined size increase while maximizing drug payload and minimizing the amount of hygroscopic excipient.
Regional deposition of particles in an image-based airway model: large-eddy simulation and left-right lung ventilation asymmetry.
Lambert AR, O'Shaughnessy P, Tawhai MH … +2 more , Hoffman EA, Lin CL
Aerosol Sci Technol · 2011 Jan · PMID 21307962 · Full text
Regional deposition and ventilation of particles by generation, lobe and lung during steady inhalation in a computed tomography (CT) based human airway model are investigated numerically. The airway model consists of a s...
Regional deposition and ventilation of particles by generation, lobe and lung during steady inhalation in a computed tomography (CT) based human airway model are investigated numerically. The airway model consists of a seven-generation human airway tree, with oral cavity, pharynx and larynx. The turbulent flow in the upper respiratory tract is simulated by large-eddy simulation. The flow boundary conditions at the peripheral airways are derived from CT images at two lung volumes to produce physiologically-realistic regional ventilation. Particles with diameter equal to or greater than 2.5 microns are selected for study because smaller particles tend to penetrate to the more distal parts of the lung. The current generational particle deposition efficiencies agree well with existing measurement data. Generational deposition efficiencies exhibit similar dependence on particle Stokes number regardless of generation, whereas deposition and ventilation efficiencies vary by lobe and lung, depending on airway morphology and airflow ventilation. In particular, regardless of particle size, the left lung receives a greater proportion of the particle bolus as compared to the right lung in spite of greater flow ventilation to the right lung. This observation is supported by the left-right lung asymmetry of particle ventilation observed in medical imaging. It is found that the particle-laden turbulent laryngeal jet flow, coupled with the unique geometrical features of the airway, causes a disproportionate amount of particles to enter the left lung.
Association between increased DNA mutational frequency and thermal inactivation of aerosolized spores exposed to dry heat.
Johansson E, Adhikari A, Reponen T … +2 more , Yermakov M, Grinshpun SA
Aerosol Sci Technol · 2011 · PMID 31660000 · Full text
Inactivation of viable bioaerosol particles, especially stress-resistant microorganisms, has important implications for biodefense and air quality control. It has earlier been shown that the loss of viability of bacteria...
Inactivation of viable bioaerosol particles, especially stress-resistant microorganisms, has important implications for biodefense and air quality control. It has earlier been shown that the loss of viability of bacterial endospores due to exposure to dry heat is associated with mutational damage. Previous studies, however, used non-aerosolized spores, long exposure times, and moderately elevated temperatures. This study was designed to investigate the mechanism of inactivation of aerosolized endospores exposed to high temperatures for sub-second time periods. Bioaerosol was tested in a continuous air flow chamber under two flow rates, 18 L/min and 36 L/min. The chamber had a cylindrical electric heating element installed along its axis. The estimated characteristic exposure temperature ( ) ranged from 164°C to 277°C (with an uncertainty of 21-26°C). To quantify mutational frequency, spores were cultivated after dry heat exposure on tryptic-soy agar and on antibiotic nalidixic acid media. Increases in the exposure temperature caused viability loss and increase in mutational frequency of the spore DNA. Significant association was found between the inactivation factor and the mutational frequency ratio (heat exposed versus non-exposed) with R of 0.985 for both flow rates combined. The results suggest that mutational damage is involved in the causal chain of events leading to inactivation of aerosolized endospores exposed to heat for sub-second time periods.
A New Electrospray Aerosol Generator with High Particle Transmission Efficiency.
Fu H, Patel AC, Holtzman MJ … +1 more , Chen DR
Aerosol Sci Technol · 2011 · PMID 22829715 · Full text
A new single-capillary electrospray (ES) aerosol generator has been developed for monodisperse particle production with maximal transmission efficiency. The new generator consists of both a spray chamber in a point-to-or...
A new single-capillary electrospray (ES) aerosol generator has been developed for monodisperse particle production with maximal transmission efficiency. The new generator consists of both a spray chamber in a point-to-orifice-plate configuration and a charge reduction chamber that can hold up to 4 Nuclespot ionizers (Model P-2042, NRD Inc.). The 2 chambers are partitioned by an orifice plate. To optimize the particle transmission efficiency of the prototype, a systematic study was performed on the generator by varying the system setup and operation. Two key dimensions of the generator setup, the orifice diameter and the distance from the capillary tip to the orifice plate, were varied. Fluorescence analysis was applied to characterize the loss of ES-generated particles at different locations of the prototype. It was found that particle loss in the generator could be reduced by either increasing the orifice diameter or decreasing the distance between the capillary tip and the orifice plate. Increasing either the total radioactivity of the ionizers or the flowrate of the particle carrier gas also further decreased the particle loss in the system. The maximum particle transmission efficiency of 88.0% was obtained with the spray chamber fully opened to the charge reduction chamber, the capillary tip at the same level as the orifice plate, and 4 bipolar ionizers installed.
Characterization of Nanoaerosol Size Change During Enhanced Condensational Growth.
Longest PW, McLeskey JT, Hindle M
Aerosol Sci Technol · 2010 Jun · PMID 20640054 · Full text
Increasing the size of nanoaerosols may be beneficial in a number of applications including filtration, particle size selection, and targeted respiratory drug delivery. A potential method to increase particle or droplet...
Increasing the size of nanoaerosols may be beneficial in a number of applications including filtration, particle size selection, and targeted respiratory drug delivery. A potential method to increase particle or droplet size is enhanced condensational growth (ECG), which involves combining the aerosol with saturated or supersaturated air. In this study, we characterize the ECG process in a model tubular geometry as a function of initial aerosol size (mean diameters - 150, 560 and 900 nm) and relative humidity conditions using both in vitro experiments and numerical modeling. Relative humidities (99.8 - 104%) and temperatures (25 - 39 °C) were evaluated that can safely be applied to either targeted respiratory drug delivery or personal aerosol filtration systems. For inlet saturated air temperatures above ambient conditions (30 and 39 °C), the initial nanoaerosols grew to a size range of 1000 - 3000 nm (1 - 3 μm) over a time period of 0.2 seconds. The numerical model results were generally consistent with the experimental findings and predicted final to initial diameter ratios of up to 8 after 0.2 s of humidity exposure and 14 at 1 s. Based on these observations, a respiratory drug delivery approach is suggested in which nanoaerosols in the size range of 500 nm are delivered in conjunction with a saturated or supersaturated air stream. The initial nanoaerosol size will ensure minimal deposition and loss in the mouth-throat region while condensational growth in the respiratory tract can be used to ensure maximal lung retention and to potentially target the site of deposition.
Redox Dynamics of Mixed Metal (Mn, Cr, and Fe) Ultrafine Particles.
Nico PS, Kumfer BM, Kennedy IM … +1 more , Anastasio C
Aerosol Sci Technol · 2009 Jan · PMID 20046215 · Full text
The impact of particle composition on metal oxidation state, and on changes in oxidation state with simulated atmospheric aging, are investigated experimentally in flame-generated nanoparticles containing Mn, Cr, and Fe....
The impact of particle composition on metal oxidation state, and on changes in oxidation state with simulated atmospheric aging, are investigated experimentally in flame-generated nanoparticles containing Mn, Cr, and Fe. The results demonstrate that the initial fraction of Cr(VI) within the particles decreases with increasing total metal concentration in the flame. In contrast, the initial Mn oxidation state was only partly controlled by metal loading, suggesting the importance of other factors. Two reaction pathways, one reductive and one oxidative, were found to be operating simultaneously during simulated atmospheric aging. The oxidative pathway depended upon the presence of simulated sunlight and O(3), whereas the reductive pathway occurred in the presence of simulated sunlight alone. The reductive pathway appears to be rapid but transient, allowing the oxidative pathway to dominate with longer aging times, i.e. greater than ∼8 hours. The presence of Mn within the particles enhanced the importance of the oxidative pathway, leading to more net Cr oxidation during aging implying that Mn can mediate oxidation by removal of electrons from other particulate metals.
Aerosol Deposition in the Extrathoracic Region.
Cheng YS
Aerosol Sci Technol · 2003 · PMID 19011693 · Full text
The extrathoracic region, including the nasal and oral passages, pharynx, and larynx, is the entrance to the human respiratory tract and the first line of defense against inhaled air pollutants. Estimates of regional dep...
The extrathoracic region, including the nasal and oral passages, pharynx, and larynx, is the entrance to the human respiratory tract and the first line of defense against inhaled air pollutants. Estimates of regional deposition in the thoracic region are based on data obtained with human volunteers, and that data showed great variability in the magnitude of deposition under similar experimental conditions. In the past decade, studies with physical casts and computational fluid dynamic simulation have improved upon the understanding of deposition mechanisms and have shown some association of aerosol deposition with airway geometry. This information has been analyzed to improve deposition equations, which incorporate characteristic airway dimensions to address intersubject variability of deposition during nasal breathing. Deposition in the nasal and oral airways is dominated by the inertial mechanism for particles >0.5 mum and by the diffusion mechanism for particles <0.5 mum. Deposition data from adult and child nasal airway casts with detailed geometric data can be expressed as E(n) = 1 - exp(-110 Stk), where the Stokes number is a function of the aerodynamic diameter (d(a)), flow rate (Q), and the characteristic nasal airway dimension, the minimum cross-sectional area (A(min)). In vivo data for each human volunteer follow the equation when the appropriate value of A(min) is used. For the diffusion deposition, in vivo deposition data for ultrafine particles and in vivo and cast data for radon progeny were used to derive the following deposition: En=1-exp(-0.355Sf4.14D0.5Q-0.28), where S(f) is the normalized surface area in the turbinate region of the nasal airway, and D is the diffusion coefficient. The constant is not significantly different for inspiratory deposition than for expiratory deposition. By using the appropriate characteristic dimension, S(f), one can predict the variability of in vivo nasal deposition fairly well. Similar equations for impaction and diffusion deposition were obtained for deposition during oral breathing. However, the equations did not include airway dimensions for intersubject variability, because the data set did not have airway dimension measurements. Further studies with characteristic airway dimensions for oral deposition are needed. These equations could be used in lung deposition models to improve estimates of extrathoracic deposition and intersubject variability.
Intensive Short Term Measurements of the Ambient Aerosol in the Greater Cincinnati Airshed.
McDonald R, Hu S, Martuzevicius D … +3 more , Grinshpun SA, Lemasters G, Biswas P
Aerosol Sci Technol · 2004 · PMID 18259606 · Full text
As part of a larger study undertaken in the Greater Cincinnati area to determine if diesel truck emissions are adjuvant to naturally occurring bioaerosols in the initiation of allergies in children, a more detailed inten...
As part of a larger study undertaken in the Greater Cincinnati area to determine if diesel truck emissions are adjuvant to naturally occurring bioaerosols in the initiation of allergies in children, a more detailed intensive measurement campaign was undertaken to elucidate the characteristics of the ambient aerosol and compare to the regular, integrated measurements being conducted. The mass concentration, total number concentration, size distributions, and morphologies were established at several locations including a residential area far from major traffic (Mernic), a suburban area on both sides of a major highway (I-275, Blue Ash), a site in the city center very close to the highway (I-75, Findlay), and an enclosed oval track at a Truck Driving School.Differences between real-time tapered element oscillating microbalance (TEOM) average mass concentrations and integrated Harvard impactor (HI) measurements were observed, with the magnitude of the difference being dependent on location and the organic compounds (OC) concentrations in the sample. Qualitative variation of the peaks in real-time PM 2.5 concentrations were observed with variation in truck traffic at the Findlay site; and no peaks in real-time PM 2.5 levels were observed at Mernic. Minimal variation in PM 2.5 was observed with distance from the highway at the Blue Ash site (fewer trucks). The site at Mernic had a smaller fraction of aggregated particles in comparison to the other sites. The two-dimensional fractal dimensions measured at the Findlay, Blue Ash, and Truck Driving School sites were statistically identical (1.58-1.61) but were higher than that measured at the Mernic site (1.41). Implications of the intensive measurement campaign vis-à-vis the epidemiological study are discussed briefly.
A model of ventilation distribution in the human lung.
Chang YH, Yu CP
Aerosol Sci Technol · 1999 Mar · PMID 11676446 · Publisher ↗
A thorough analysis of aerosol particle deposition in the human lung requires the knowledge of the distribution of inspired air at respiration. In this paper, a mathematical model of ventilation distribution has been dev...
A thorough analysis of aerosol particle deposition in the human lung requires the knowledge of the distribution of inspired air at respiration. In this paper, a mathematical model of ventilation distribution has been developed using a five-lobe airway model. The model accounts for the nonlinear effects of compliance and resistance on airway dynamics. Ventilation distributions were determined under different gravitational force conditions. A larger gravity leads to a greater nonuniformity of ventilation between the upper and lower lobes of the lung. Ventilation distributions in different lobes of the lung at various inspiratory flow rates were also calculated. At slow inspiratory flow rates, ventilation was found to be nonuniform with more air entering the lower lobes. As the flow rate increases, this nonuniformity became smaller. The calculated results compare favorably with existing experimental data. When a different gas is inspired instead of air, a preferential distribution of ventilation to the upper lobes was found if the density of the inspired gas is greater than that of the air.
Sampling stratospheric aerosols with impactors.
Oberbeck VR
Aerosol Sci Technol · 1989 · PMID 11542175 · Publisher ↗
Derivation of statistically significant size distributions from impactor samples of rarefied stratospheric aerosols imposes difficult sampling constraints on collector design. It is shown that is is necessary to design i...
Derivation of statistically significant size distributions from impactor samples of rarefied stratospheric aerosols imposes difficult sampling constraints on collector design. It is shown that is is necessary to design impactors of different size for each range of aerosol size collected as as to obtain acceptable levels of uncertainty with a reasonable amount of data reduction.
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