Aerosol Measurement: Principles, Techniques, and Applications. Second Edition, PA Baron, K Willeke, eds., New York: John Wiley and Sons, Inc., 2001 Sep; :31-43
An aerosol is an assembly of liquid or solid particles suspended in a gaseous medium, for example, air, long enough to be observed and measured. The need to measure aerosols has increased dramatically in recent years. This need has arisen in various disciplines. Although much information is available in the published literature, the scientists and practitioners making aerosol measurements in one application may have little or no awareness of the knowledge and experience gained in other applications. For instance, environmental engineers and industrial hygienists make aerosol measurements in order to ensure that the public and the industrial work force are not exposed to hazardous aerosols at undesirable concentration levels. Faced by increasingly complex and demanding regulations, the aerosol measurements are becoming more costly in equipment and in time to perform, and they may require more than elementary knowledge to perform and interpret. The results are critical as expensive control measures may have to be put in place as a result of such measurements. In contrast, the scientists and engineers concerned with industrial materials are developing an ever-increasing number of manufacturing processes in which the material passes through an aerosol phase that needs to be monitored and controlled. For instance, powders and pigments may be produced by passing the feed materials into a flame, plasma, laser, or flow furnace where they evaporate. Upon cooling, a very high concentration of very small particles is formed. With time, the aerosols may agglomerate to a lower concentration of larger particles. At any time, the trajectories of these particles may be directed by external forces, for example, diffusion or an applied electric field, to deposit the particles in a predetermined manner, thus forming products such as ceramics or optical fibers. While producing desirable materials in this manner, the aerosol may have to be measured not only to ensure an optimum amount of uniform product but also to avoid exposure of humans to processing materials that may be quite hazardous.