Deposition of Aerosol Particles

The behavior of aerosol particles in outdoor atmospheres is explained by laws that govern their formation, movement, and capture. These particles are present throughout the planetary boimdary layer and their concentrations depend on a multitude of factors including location, time of day or year, atmospheric conditions, presence of local sources, altitude, and wind velocity. 

The highest concentrations are usually foimd in urban areas, reaching up to 10 and 10 particles per cm, with particle size ranging from around 100 /an to a few nanometer. Size is normally used to classify aerosol because it is the most readily measured property and other properties can be inferred from size information [7]. The highest mass fraction of particles in an aerosol is characterized by particles having a diameter in the range of 8 to 80 /an [8]. 

Some studies have indicated that there is a strong correlation between wind speed and the deposition and capture of aerosols. In such a study of saline winds in Spain a very good correlation was found between chloride deposition rates and wind speeds above a threshold of 3 m s or 11 km h [9]. 

Aerosols can either be produced by ejection into the atmosphere, or by physical and chemical processes within the atmosphere (called primary and secondary aerosol production, respectively). Examples of primary aerosols are sea spray and wind-blown dust. Secondary aerosols are produced by atmospheric gases reacting and condensing, or by cooling vapor condensation. Once an aerosol is suspended in the atmosphere, it can be altered, removed, or destroyed. 

Aerosol particles do not stay in the atmosphere indefinitely, and average lifetimes are of the order of a few days to a week, depending on their size and location. Aerosol particles have a finite mass and are subject to the influence of gravity, wind resistance, droplet dry-out, and possibilities of impingement on a solid surface. Studies of the migration of aerosols inland of a sea coast have shown that typically the majority of the aerosol particles are deposited close to the shoreline (typically 400 to 600 m) and consist of large particles ( 10//m diameter), which have a short residence time and are controlled primarily by gravitational forces [8 9]. 

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Stahlhofen, W., Gebhart, J. and Heyder, J. (1980). Experimental determination of the regional deposition of aerosol particles in the human respiratory tract. Am. Ind. Hyg. Assoc. J. 41 385-398. 

Leong BKJ, Coombs JK, Sabaitis CP, Rop DA, Aaron CS (1998) Quantitative morphometric analysis of pulmonary deposition of aerosol particles inhaled via intratracheal nebulization, intratracheal instillation or nose-only inhalation in rats. J Appl Toxicol 18 149-160. 

A great deal is known about the deposition of aerosol particles in the lung and their later clearance. Less is known about the uptake of gases such as ozone and other oxidants that can react with biopolymers in the... 

Kliment, V., J. Libich, and V. Kaudersova. Geometry of guinea pig respiratory tract and application of Landahl s model of deposition of aerosol particles. J. Hyg. Epidemiol. Microbiol. Immunol. 16 107-114, 1972. 

Purification consists of removal of gaseous impurities by means of absorption or adsorption processes (such as by activated charcoal) Refs 1) F. Fraas O.C. Ralston, I EC 32, v 600—04(1940) (Ekectrostatic sepn of solids from gases) 2) H.F. Johnstone M,H. Roberts, IEC 41, 2417(1949) (Deposition of aerosol particles from moving gas streams)... 

Hounam, R.F., Black, A. Walsh, M. (1971) The deposition of aerosol particles in the nasopharyngeal region of the human respiratory tract. Journal of Aerosol Science, 2, 47-61. 

Kim CS. Methods of calculating lung delivery and deposition of aerosol particles. Respir Care 2000 45(6) 695-711. 

After a brief explanation of the factors governing deposition of aerosol particles in the lung, the common methods of administration of inhalation aerosols have been described. The drugs most frequently delivered by this route are bronchodilators. Correct administration and the use of inhaler accessories, such as spacer devices, enhance the efficacy of inhaled drugs. It is essential that the patient be instructed in the correct use of the devices to optimize the therapeutic effect. 

The dry deposition of aerosol particles (D ) is generally measured by horizontal microscopic slide or so-called dustfall cans and jars. However, the results of such measurements, wide-spread in local pollution studies (Corn, 1976), have to be interpreted with caution because of the disturbance of the laminar and turbulent flow regime by the collector. Furthermore, the laminar layer covering the collector surface may be very different from that over soil and vegetation. In any case, if we also measure the particle concentration N, a parameter with the dimension of velocity can be defined (Junge, 1963) ... 

El-Shobokshy, M.S., Ismail, I.A., 1980, Deposition of aerosol particles from turbuelnt flow onto a rough pipe wall. Atmos. Environ. 14, 3, 297 - 304. 

Figure 4 Scheme of the respiratory aerosol probe for determining total deposition of aerosol particles in the human respiratory tract. 

Heyder J, Armbuster L, Gebhart J, Grein E, Stahlhofen W. Total deposition of aerosol particles in the human respiratory tract for nose and mouth breathing. J Aerosol Sci 1975 6 311-328. 

Kim CS, Brown LK, Lewars GC, Sackner MA. Deposition of aerosol particles and flow resistance in mathematical and experimental airway models. J Appl Physiol 1983 55 154-163. 

Svartengren K, Lindestad P-A, Svartengren M, Philipsson K, ByUn G, Camner P. Added external resistance reduces oropharyngeal deposition and increases lung deposition of aerosol particles in asthmatics. Am 1 Respir Crit Care Med 1995 152 32-37. 

Smirnov L. P., Deryaguin B. V., On inertialess electrostatic Deposition of Aerosol Particles on a Sphere at Flow of viscous Fluid around the Sphere, Colloid J., 1967, No. 3 (in Russian). 

These insights indicate that the presence of excess iodine, chlorine, fluorine and, to a lesser extent, bromine, on the surfaces of Antarctic stony meteorites is attributable to the deposition of aerosol particles (Cl, F, Br) and of methyl iodide from the atmosphere. In other words, the excess halogens on the surfaces of Antarctic meteorites are atmospheric contaminants rather than weathering products. Accordingly, the amount of excess iodine on a meteorite lying on an Antarctic ice field increases primarily as a function of time and is less dependent on the climatic conditions on the ice field and on its distance from the coast. 

Deposition of Particles from a Heated Stream. The reason for deposition of aerosol particles in a hot stream onto cold surfaces is the movement of the particles in a nonuniformly heated medium in a direction opposite to the temperature gradient, i. e., from a high-temperature zone to a lower-temperature zone [265]. Under the influence of thermophoretic force, we find a radial component of velocity from the center of the heated stream to the cooler wall, and an additional possibility of contact between the particles and the surface. 

Papastefanou and Bondietti (1991a, 1991b) performed experiments on the diffusive deposition of aerosol particles on wire screens and, in particular, used Pb deposition as a measure of the collection efficiency of the screens for aerosol-associated attached radionuclides in outdoor air, at Oak Ridge National Laboratory, Oak Ridge, Tennessee (35 58 N, 84 17 W) during the summer period. Stainless steel wire screens (60, 200, as well as 40 and 100 mesh/inch) were used in the experiments to collect the unattached species of radon decay products in ambient aerosols. Glass fibre filters were used as back-up to collect the radon decay products which passed the wire screens. The screens were separated from the back-up filter by a spacer screen (4 mesh/inch) to prevent contamination by the filter deposit (e.g., " Pb atoms) via a-recoil. 

Fig. 5.21. Experimental results of deposition of aerosol particles in alveolar region (open symbols) and whole respiratory tract (closed symbols) (14 or 15 breaths/min by mouth, tidal volume 1.0 to 1.5 1). Error bars are 1 S.E. Lines are theoretical calculations of Yu and Diu (1982).

Liu and Agarwal performed an experimental study on deposition of aerosol particles in turbulent pipe flows. McCoy and Hanratty, Wood, and Papaver-gos and Hedley reported several collections of available data on wall deposition rates. Kvasnak et al. reported their experimental data for the deposition rate of glass beads, various dust components, and glass fibers in a horizontal duct flow. Wood, Hidy, and Papavergos and Hedley reviewed the available methods for evaluating the deposition velocity in turbulent duct flows and discussed different deposition mechanisms. 

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