Experimental aerosol research frequently requires the controlled generation of an aerosol. A particular property of the aerosol, such as a certain size distribution, may be required to ascertain its transport properties. The control of aerosol generation may extend beyond size distribution and concentration to the physical and chemical properties of the particles. In particular, the effective dose in aerosol therapy is a function of the physical and chemical properties of the aerosol particles in addition to the mass concentration delivered. The size, shape, and structure of the aerosol particles determine their aerodynamic or transport properties and, hence, affect the site and efficiency of deposition. After deposition, these same physical properties of the particles, in addition to the chemical properties, control the surface area of the particles and, hence, the rate of dissolution and absorption of the drug. Consequently, the control of the physical and chemical properties of the aerosol particles and of the number or mass concentration is a prerequisite for the accurate determination of the effective dose in aerosol therapy.

Numerous techniques have been developed to aerosolize liquids, resuspend particles, or generate aerosol particles. Descriptions of these aerosol generation techniques can be found in the literature of diverse fields such as powder technology, chemical engineering, defense technology, and atmospheric science, in addition to the journals of aerosol science, industrial hygiene, and medicine. Several reviews of aerosol generation methods have been published [1-7].

Consequently, some duplication of material in this current review is unavoidable. This chapter discusses aerosol generation methods based on the capability or the need to produce an aerosol with a desired property. Descriptions of generation methods use commercially available models as examples, although endorsement of the instruments is not necessarily to be inferred. This review is not intended to be comprehensive on the variety of aerosol generation methods but focuses on methods that have been proven to produce stable aerosols over a long duration and the parameters that control their stability. Generation methods that produce aerosols intermittently, such as the exploding-wire technique, or methods that are less well controlled or developed, such as generation from chemical reaction of gases, are not covered in this chapter. The reader is referred to the references for details on generation methods that are not discussed.

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