Deposition of Ultrafine Aerosols and Thoron Progeny in Replicas of Nasal Airways of Young Children

The deposition efficiencies of ultrafine aerosols and thoron progeny were measured in youth nasal replicas. Clear polyester-resin casts of the upper airways of 1.5-yr-old (Cast G), 2.5-yr-old (Cast H), and 4-yr-old (Cast I) children were used. These casts were constructed from series of coronal magnetic resonance images of healthy children. The casts extended from the nostril tip to the junction of the nasopharynx and pharynx. These casts were similar in construction to those used in previous studies (Swift et al. 1992; Cheng et al. 1993). Total deposition was measured for monodisperse NaCl or Ag aerosols between 0.0046 and 0.20 (Jim in diameter at inspiratory and expiratory flow rates of 3, 7, and 16 L min^?1 (covering a near-normal range of breathing rates for children of different ages). Deposition efficiency decreased with increasing particle size and flow rate, indicating that diffusion was the main deposition mechanism. Deposition efficiency also decreased with increasing age at a given flow rate and particle size. At 16 L min^?1, the inspiratory deposition efficiencies in Cast G were 33% and 6% for 0.008- and 0.03-μm particles, respectively. Nasal deposition of thoron progeny with a mean diameter of 0.0013 μm was substantially higher (80%-93%) than those of the ultrafine aerosol particles, but still had a similar flow dependence. Both the aerosol and thoron progeny data were used to establish a theoretical equation relating deposition efficiency to the diffusion coefficient (D in cm² s^?1) and flow rate (Q in L min^?1) based on a turbulent diffusion process. Data from all casts can be expressed in a single equation previously developed from an adult nasal cast: E = 1 - exp(-aD ^0.5 Q ^?0.125). We further demonstrated that the effect of age, including changes to nasal airway size and breathing flow rate, on nasal deposition can be expressed in the parameter “a” of the fitted equation. Based on this information and information on minute volumes for different age groups, we predicted nasal deposition in age groups ranging from 1.5- to 20-yr-old at resting breathing rates. Our results showed that the nasal deposition increases with decreasing age for a given particle size between 0.001 to 0.2 μm. This information will be useful in deriving future population-wide models of respiratory tract dosimetry.     

Deposition of Ultrafine Aerosols in a Human Oral Cast

This paper reports experimental measurements of the total deposition of ultrafine aerosols in a human oral airway cast. A clear polyester resin cast of the upper airways of a normal human adult, including the nasal airways, oral cavity, tongue, nasopharynx, and larynx, was made from a postmortem solid cast. Measured pressure drop in the oral airway was slightly lower than in the nasal airway. The measured oral flow resistance was similar to the values reported for human volunteers breathing through the mouth at rest and for spontaneously opening of the mouth. Aerosol deposition data in the cast for monodisperse NaCl aerosols between 0.2 and 0.005 μm in diameter deposited in the cast were obtained for inspiratory and expiratory flow rates of 4, 20, and 40 L/min. Deposition efficiency increased with decreasing particle size and flow rate indicating that turbulent diffusion was the dominant mechanism for deposition. Higher deposition efficiency was observed for inspiratory flow in the oral airway than for expiratory flow. Oral deposition and nasal deposition for inspiratory flow were similar, but oral deposition was lower for expiratory flow. Deposition efficiency can be expressed as a function of the flow rate and diffusion coefficient of the particle.     

Characterization of Submicrometer Aerosol Deposition in Extrathoracic Airways during Nasal Exhalation

Submicrometer and especially fine aerosols that enter the respiratory tract are largely exhaled. However, the deposition of these aerosols under expiratory conditions is not well characterized. In this study, expiratory deposition patterns of both ultrafine (<100 nm) and fine (100–1000 nm) respiratory aerosols were numerically modeled in a realistic nasal-laryngeal airway geometry. Particle sizes ranging from 1 through 1000 nm and exhalation flow rates from 4 through 45 L/min were considered. Under these conditions, turbulence only appeared significant in the laryngeal and pharyngeal regions, whereas the nasal passages were primarily in the laminar regime. Exhaled particles were simulated with both a continuous-phase drift flux velocity correction (DF-VC) model and a discrete Lagrangian tracking approach. For the deposition of ultrafine particles, both models provided a good match to existing experimental values, and simulation results corroborated an existing in vivo–based diffusion parameter (i.e., D ^0.5 Q ^?0.28). For fine particles, inertia-based deposition was found to have a greater dependence on the Reynolds number than on the Stokes number (i.e., St^0.1 _kRe^0.9), indicating that secondary flows may significantly influence aerosol deposition in the nasal-laryngeal geometry. A new correlation was proposed for deposition in the extrathoracic airways that is applicable for both ultrafine and fine aerosols over a broad range of nasal exhalation conditions. Results of this study indicate that physical realism of the airway model is crucial in determining particle behavior and fate and that the laryngeal and pharyngeal regions should be retained in future studies of expiratory deposition in the nasal region.     

Deposition of Ultrafine Particles in Human Tracheobronchial Airways of Adults and Children

Inhalation exposure to ultrafine particles, including radon progeny and other combustion aerosols, has been implicated in potential health risks of ambient and indoor environments. These particles deposit in the respiratory tract mainly by diffusion. The purpose of this study was to determine the deposition pattern of nanometer-sized particles in the human tracheobronchial (TB) airways of children and young adults. The deposition was determined for 1.75, 10, and 40 nm ²¹²Pb particles at flow rates corresponding to respiratory minute volumes at rest and during moderate exercise. The 1.75 nm particles were unattached clusters, whereas the 10 and 40 nm particles were silver particles with attached ²¹²Pb clusters. Replicate casts of the upper TB airways of 3, 16, and 23 year old humans were used, including the larynx, trachea, and bronchial airways down to generations 5-8. Deposition in each generation and total deposition were measured by counting the ²¹²Pb gamma photopeak in a NaI (Tl) detector. The effects of airway geometry, particle size, and flow rate on deposition efficiency were studied. The deposition of the 1.75 nm particle, corresponding to unattached indoor radon progeny, was substantially higher than that of the 10 and 40 nm particles. The dependence of particle deposition on the flow rate was relatively weak, and deposition efficiencies were only slightly higher at the lower flow rates. The deposition models for diffusion from parabolic flow underestimated aerosol deposition, whereas the diffusion deposition predicted for plug flow overestimated the TB deposition. The deposition models resulting from this study can be used for developing lung deposition models and in the risk assessment of radon progeny and ultrafine ambient particles.     

Effects of Age on Deposition of Inhaled Aerosols in the Human Lung

Department of Mechanical and Aerospace Engineering, State University of New York at Buffalo, Amherst NY 14260 Theoretical calculations have been made for the deposition of inhaled aerosol particles in the respiratory tract of humans from birth to adulthood. Variations of both airway structure and respiratory condition with age have been taken into consideration. It is found that these variations do not lead to any significant changes in the mechanisms of deposition in the air passages. For all particle sizes, total deposition in the respiratory tract and deposition in the head region are found to be higher for children than that for adults. However, depositions in the tracheobronchial and alveolar region in a child could be larger or smaller, depending upon the particle size.     

Deposition of Ultrafine Particles at Carinal Ridges of the Upper Bronchial Airways

Bifurcations of the upper bronchial airways are primary hot spots for deposition of inhaled particles and noxious gases. Deposition of coarse particles in the carinal ridges results from inertial impaction, and deposition distal to these sites is attributed to secondary flows. Diffusional deposition of ultrafine particles on carinae surfaces is studied here. Similarity solutions for both the flow and concentration fields at the respective boundary layers that develop near the surface of a wedge are presented, corresponding to a relatively high Re number. The expressions developed for the deposition efficiency compare favorably to those obtained by rigorous computational fluid dynamics simulations. Yet unlike simulation-derived expressions that pertain to the specific geometry and flow conditions studied, our expressions are robust and can account for different branching angles, airflow rates, and particle sizes. The average diffusive flux toward the carina walls is in good agreement with experimental deposition data, as well as with simulation results specifically designed to account for deposition hot spots at airway bifurcations. The expressions obtained can be easily implemented in algebraic inhalation dosimetry models to estimate deposition profiles along the whole respiratory system.     

Total Deposition of Ultrafine Hydrophobic and Hygroscopic Aerosols in the Human Respiratory System

The deposition of ultrafine particles in the human respiratory system was studied under a variety of steady breathing conditions. The monodisperse aerosols tested were hydrophobic kerosene heater, aluminosilicate, and hygroscopic NaCl in the size range of 0.03 to 0.4 μm in diameter. The results for all aerosols show that particle deposition increases with an increase in tidal volume, but with a decrease in breathing frequency. Also, deposition during breath holding increases nearly exponentially with an increase in time. However, particle deposition as a function of particle size is different between hydrophobic and hygroscopic aerosols in the size range tested. The hydrophobic aerosols increase with a decrease in particle size, while hygroscopic aerosols show minimum value in the size range of 0.06 to 0.09 μm. The hydrophobic kerosene heater and aluminosilicate particle deposition confirms the recent theoretical calculations of Yeh and Schum (1980), Yu and Diu (1982), and Yu and Hu (1983). The NaCl particles show a 3.5 to 4.5 fold growth under conditions approximating the respiratory tract.     

Hygroscopic Growth and Deposition of Inhaled Secondary Cigarette Smoke in Human Nasal Pathways

To ascertain the threat to human health posed by the inhalation of the particulate phase for secondary cigarette smoke (SCS), it is necessary to determine the doses delivered to airway cells. The risk assessment of SCS particles is complicated by their hygroscopic properties. Inhaled particles that are hygroscopic may absorb the water vapor that is present in a warm, humid environment such as that found in the human respiratory system. As a direct result, the physicochemical characteristics of a particle such as size, shape, density, and composition may experience significant changes. Herein, the effects of hygroscopicity and deposition of SCS particles are examined in the nasopharyngeal region of the respiratory tract through which particles travel before entering the lung. To accomplish this goal, a computer model is defined to describe the anatomical features of the airways within the human head and throat. Then the effects of water vapor uptake and deposition on inhaled particle size distributions are formulated. The results of the simulations indicate that hygroscopicity is a critical factor affecting the dynamics of inhaled SCS.     

Modeling Particle Deposition in Extrathoracic Airways

The extrathoracic (ET) airways filter, warm, and humidify the inspired air and provide olfactory function. These multiple functions are reflected in its complex anatomy and physiology. The ET airways form the first line of defense against inhaled pollutants, both gaseous as well as particulate. To accurately assess the risk posed by inhaled particulate matter to the lung, it is essential to understand the filtering efficiency of the ET airways. In this paper computational fluid dynamics is used to simulate the airflow patterns and the thermodynamics of the ET airways. We detail the procedure to develop a computer reconstruction of the ET airways and the computer model to simulate the flow variable. Using this information we compute the particle trajectories, for both hygroscopic and nonhygroscopic aerosols, and use this data to evaluate the particle deposition pattern in the ET airways. The model predicts high relative humidity conditions in the ET airways. The model also shows that the high relative humidity conditions are conducive for rapid growth of hygroscopic particles and dramatically alter the deposition characteristics of ambient (hygroscopic) aerosol.     

Generation and Characterization of Ultrafine Chain Aggregate Aerosols

Continuously stable, well-characterized chain aggregate aerosol sources generated from a flame aerosol generator are described. To characterize the length of the chain aggregate, a new image processing software was developed to measure the length distribution of aggregates. This program measures the path length of the aggregate that has been skeletonized into one pixel in width while maintaining its length and shape. In order to generate monodisperse chain aggregate sources, a differential mobility analyzer was used to classify aggregates according to electrical mobility. A series of experiments were conducted to generate singly charged, monodisperse chain aggregate aerosol sources. The operational range of the system for generation of monodisperse chain aggregates is described. Single-mode chain aggregates with a geometric mean particle length between 1.50 and 3.20 μm and a length standard deviation around 1.3 were generated.     

Particle Deposition in a Cast of Human Tracheobronchial Airways

Abstract

Regional particle deposition efficiency and deposition patterns were studied experimentally in a human airway replica made from an adult cadaver. The replica includes the oral cavity, pharynx, larynx, trachea, and four generations of bronchi. This study reports deposition results in the tracheobronchial (TB) region. Nine different sizes of monodispersed, polystyrene latex fluorescent particles in the size range of 0.93–30 μm were delivered into the lung cast with the flow rates of 15, 30, and 60 l min^{? 1}. Deposition in the TB region appeared to increase with the increasing flow rate and particle size. Comparison of deposition data obtained from physical casts showed agreement with results obtained from realistic airway replicas that included the larynx. Deposition data obtained from idealized airway models or replicas showed lower deposition efficiency. We also compared experimental data with theoretical models based on a simplified bend and bifurcation model. A deposition equation derived from these models was used in a lung dosimetry model for inhaled particles, and we demonstrated that there was general agreement with theoretical models. However, the agreement was not consistent over the large range of Stokes number. The deposition efficiency was found as a function of the Stokes number, bifurcation angle, and the diameters of parent and daughter tubes. An empirical model was developed for the particle deposition efficiency in the TB region based on the experimental data. This model, combined with the oral deposition model developed previously, can be used to predict the particle deposition for inertial effects with improved accuracy.     

Particle Deposition in a Cast of Human Oral Airways

Oral and nasal airways are entryways to the respiratory tract. Most people breathe through the nasal airway during rest or light exercise, then switch to oral/nasal breathing during heavy exercise or work. Resistance through the oral airways is much lower than through the nasal airways, so fewer aerosol particles are deposited in the oral airways. Aerosol drugs are usually delivered by inhalation to the lung via the oral route for that reason. Oral deposition data from humans are limited, and those available show great intersubject variability. The purpose of this study was to investigate the effects of particle size and breathing rate on the deposition pattern in a human oral airway cast with a defined geometry. The airway replica included the oral cavity, pharynx, larynx, trachea, and 3 generations of bronchi. The oral portion of the cast was molded from a dental impression of the oral cavity in a human volunteer, while the other airway portions of the cast were made from a cadaver. Nine different sizes of polystyrene latex fluorescent particles in the size range of 0.93-30 mu m were used in the study. Regional deposition was measured at a constant inspiratory flow rate of 15, 30, and 60 L min^-1. Deposition in the oral airway appeared to increase with an increasing flow rate and particle diameter. Deposition at the highest flow rate of 60 L min^-1 was close to 90% for particles >20 mu m. Particles> about 10 mu m deposited mainly in the oral cavity. Deposition efficiency has been found to be a unique function of the Stokes number, suggesting that impaction is the dominant deposition mecha nism. Oral deposition can be approximated by a theoretical deposition model of inertial impaction in a 180 degrees curved tube, assuming perfect mixing in a turbulent flow. Our model suggests that the minimum dimension near the larynx and the average cross-sectional area are important parameters for oral airway deposition; however, additional data from the oral airway replica are needed to ascertain whether these are indeed the critical dimensions. Information from the present study will add to our knowledge of the deposition mechanism, the correlation of particle deposition with airway geometry, and eventually the best way to deliver aerosol drugs.     

Differences in Diffusion Charging of Dielectric and Conducting Ultrafine Aerosols

The effect of the dielectric constant on unipolar and bipolar charging rates is investigated. This effect is manifested through the image potential. Bulk dielectric constants of aerosol materials range from 2.5 to 50. The corresponding image potentials range from about 40% to about 96% of the image potential for a perfect conductor. Charging simulations were carried out for this parameter range and typical results are presented. For dielectric constants greater than 2.5 the charging behavior shows a strong image potential effect, and may be approximated by calculations for a perfect conductor. This suggests that charging models that do not allow for image potential effects are likely to be inaccurate except, perhaps, for larger particles, where the Coulomb potential dominates the image potential. The simulations are compared with unipolar charging data from recent experiments, which tend also to support this conclusion.     

Ultrafine Particle Deposition in a Human Tracheobronchial Cast

The deposition of 0.20, 0.15, and 0.04 μm diameter particles was measured in a human central airway cast using a variable larynx with cyclic inspiratory flow. Data were compared with theoretical predictions for deposition from laminar flow for the first seven airway generations. With the exception of tracheal deposition, which on average exceeded predictions by a factor of 9, the measured deposition was about twice that predicted. The enhanced deposition is attributable to secondary swirling flows. Less enhancement is observed at higher inspiratory flow rates as turbulence increases. The surface density of particles deposited at bifurcations was approximately 20% greater than along the airway lengths. This increased deposition at bifurcations should be considered when calculating tissue dose for particles which act before the initial deposit is removed by clearance processes.     

Deposition of Fiber in the Human Nasal Airway

Inhalation is the main route for aerosol entering the human body. Many occupational lung diseases are associated with exposure to fiber aerosol in the workplace. However, very few studies to date have been conducted for investigating fiber deposition in the human airway. As a result, there is a notable lack of information on the nature of the fiber deposition pattern in the human respiratory tract. With this in mind, this research consisted of a large number of experimental works to investigate the effects of fiber dimension on the deposition pattern for a human nasal airway. Carbon fibers with uniform diameter (3.66 μm) and polydispersed length were adopted as the test material. Deposition studies were conducted by delivering aerosolized carbon fibers into a nasal airway replica (encompassing the nasal airway regions from vestibule to nasopharynx) at constant inspiratory flow rates of 7.5, 15, 30, and 43.5 l/min. Fibers deposited in each nasal airway region were washed out and the length distribution was determined by microscopic measurement. The results showed that impaction is the dominant deposition mechanism. Most of the fibers with high inertia deposited in the anterior region of the nasal airway (vestibule and nasal valve). In contrast, fibers with low inertia were found to pass through the entire nasal airway easily and collected on the filter at the outlet. Comparing the deposition results between fibers and spherical particles, our data showed that the deposition efficiencies of fibers are significantly lower than that of spherical particles, which implies that the inhaled fibers could pass through the entire nasal airway comparatively easier than spherical particles. Thus, relatively more fibers would be able to enter the lower respiratory tract.     

Generation of Radiolabeled Soot-Like Ultrafine Aerosols Suitable for Use in Human Inhalation Studies

We have developed a method for radiolabeling ultrafine carbon particle aggregates with technetium-99m. The carbon aggregate aerosol was chosen to mimic the physical properties of urban combustion or ''soot-like'' particulate. The radioisotope is a short lived (t_1/2 = 6.02 h) gamma emitter commonly used in human studies where scintigraphic methods are employed. Primary carbon parti cles, the aggregation of which is controlled by concentration and time, were produced by arcing between graphite electrodes under an argon atmosphere. Radiolabeling of particles was accomplished by applying a pertechnetate solution onto the tips of electrodes prior to arcing. The activity median diameter of experimental aerosols could be varied from 50 to 150 nm. The specific activity of aerosols increased with the amount of activity applied to the electrodes and decreased with time of generator operation. In-vitro leaching of the radioisotope from particles into solution was also measured. Leaching appeared to increase with the specific activity of the aerosol but was not affected by particle size.     

Analytic Solutions to Diffusional Deposition of Polydisperse Aerosols in Fibrous Filters

Deposition of polydisperse aerosols by Brownian diffusion was studied analytically using the penetration efficiency of monodisperse aerosols combined with the correlations among the moments of lognormal distribution functions. The analytic solutions, so obtained were validated using the exact solutions, which were applied to recalculate the filtration efficiencies of the existing experimental data for various filtration conditions. It was found that the collection efficiency of a fibrous filter should be corrected with respect to the position in the filter, if the particles are polydisperse. By considering the effect of the polydispersity of particle size, the analytic solutions showed good agreement with existing experimental data. It is believed that the present work makes it possible to determine the filtration efficiency of polydisperse aerosols in fibrous filters and to estimate errors associated with the degree of polydispersity of the particles quickly and accurately for the diffusion dominant regime.     

广州大气颗粒物与酸沉降的关系研究

本文研究了大气颗粒物的酸度和酸缓冲能力,实验证实广州大气颗粒物中存在着游离的硫酸,其水溶性离子中SO4^2-及NO3^-占很大的比例。颗粒物中的碱性成分含量大于酸性成分,对酸性降水有一定的缓冲能力。气溶胶中细颗粒物的酸性大于粗颗粒物,且酸缓冲能力远低于粗颗粒物。     

Deposition of Man-Made Fibers in a Human Nasal Airway

Many occupational lung diseases are associated with exposure to aerosolized fibers in the workplace. The nasal airway is a critical route for fiber aerosol to enter the human respiratory tract. The fiber deposition efficiency in the nasal airway could be used as an index to indicate the fraction of the inhaled fibers potentially transported to the lower airways. In this research, experiments of fiber deposition in the human nasal airway were conducted. Man-made carbon, glass, and titanium dioxide fibers in the inertia regime were used as the test fiber materials. The deposition studies were carried out by delivering aerosolized fibers into a human nasal airway replica at constant human inspiratory flow rates ranging from 15 l/min to 43.5 l/min. The deposition results were compared in detail between these fiber materials to study how the fiber characteristics affected the nasal airway deposition. The results showed that the deposition efficiency of the carbon fiber increases as the fiber impaction parameter increases. Many carbon fibers deposited in the anterior region of the nasal airway. In contrast, very few glass or titanium dioxide fibers deposited in the nasal airway, but relatively more of these two fibers deposited in the turbinate region. This result implies that, if a fiber in the inertia regime is inhaled during normal human breathing, the smaller the fiber, the more easily it could enter the human lower respiratory tract, possibly causing harm to the human respiratory tract.     

北京大气气溶胶干沉降和质量浓度的季节变化特征

本文利用北京地面气溶胶观测资料,分析了北京气溶胶质量浓度、谱分布和干沉降的季节变化.结果表明,北京总悬浮颗粒物浓度(TSP)质量浓度有明显的季节变化.春季最高,TSP质量浓度为509μg/m3,秋冬次之,分别为319和281 μg/m3,夏季最低,仍然达到245μg/m3.全年TSP平均339μg/m3.北京气溶胶分粒径质量浓度观测结果表明,粗粒子质量浓度占的比例很高.春季在沙尘天气条件下,气溶胶中粗粒子(直径＞2.1 μm)占总浓度的83%.在4月,8月,10月和12月的非沙尘季节,粗粒子分别占74%,71%,54%和85%,平均值为71%.北京在3月和4月的干沉降通量为最大,分别为1.17和1.44g/(m2.d),其他月份较小,在0.12～0.42 g/(m2·d)之间,年均值为0.42 g/(m2·d).