Production and Characterization of Aerosols

Abstract

The production and characterization of aerosols are essential processes in experimental studies of the toxicity of inhaled particles. Certain methods for producing monodisperse aerosols are especially useful for studying the mechanics of deposition and short-term clearance from the lung and for calibration of sampling instrumentation. Polydisperse aerosols are encountered in practical studies of inhalation toxicity and in medical applications of aerosols. The aerodynamic properties of particles are especially significant in bringing about their deposition in the respiratory tract. They can be measured directly with appropriate instrumentation.The conversion of bulk liquids or solids to airborne droplets or particles is an essential process in studies concerned with the hazards associated with inhalation of toxic particles and in medical treatment re¬ quiring the deposition of water drop¬ lets or particulate medication in the respiratory tract. It is possible to use monodisperse aerosols, ie, aerosols in which all of the particles have very nearly the same size, under certain circumstances. They have been used to marked advantage to study depo¬ sition in, and early clearance from, the respiratory tract and are espe¬ cially useful for calibrating the in¬ struments with which to characterize other aerosols. For studies of inhala¬ tion toxicity and for medical appli-cations, however, it is often impos¬ sible to obtain monodisperse aerosols of the substance of interest. It is then necessary to rely on polydisperse aerosols, which are more easily pro¬ duced but are more difficult to charac¬ terize than are monodisperse aerosols. Following are some of the common methods for producing both types of aerosols and the principles underlying those methods. Monodisperse AerosolsFor any given study, an aerosol would be ideally monodisperse if de¬ viations of particle size from the mean value were too small to contrib¬ ute significantly to the overall error in whatever experimental measure¬ ments are necessary. Thus, a particu¬ lar aerosol is more monodisperse for some studies than for others, and the definition of monodispersity should be related to the purpose for which the aerosol is produced. In practice, the definition is seldom explicit or, if given at all, is qualitative. One of the few quantitative definitions ad¬ vanced is that of Fuchs and Sutugin,1 who limited their review of monodis¬ perse aerosols to those having coeffi¬ cients of variation (standard devia¬ tion +· mean diameter) < 0.2, which is equivalent to a geometric standard deviation of 1.22 when particle sizes are distributed lognormally, as they very frequently are. This definition is arbitrary and allows too broad a spec¬ trum of sizes for some applications, but it is reasonable for this discus¬ sion. Several methods of production provide aerosols that satisfy this definition.Controlled Condensation of Vapors.-Sinclair and LaMer2 obtained par¬ ticles in a narrow size range by the controlled condensation of organic vapors in the apparatus shown in Fig 1. T...

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