Aerosol Measurement: Principles, Techniques, and Applications. Second Edition, PA Baron, K Willeke, eds., New York: John Wiley and Sons, Inc., 2001 Sep; :45-60
The term aerosol refers to an assembly of liquid or solid particles suspended in a gaseous medium long enough to be observed or measured. The term originated as the gas phase equivalent to the term hydrosol, which refers to a suspension of particles in a liquid ( from the Greek word combination "water particle"). Manufactured and naturally produced particles, found in ambient and industrial air environments or in industrial process gas streams, may have a great diversity in size, shape, density, and chemical composition. The diversity of microscopic particles, includes what we might think are ideal shapes, such as spheres (droplets of water or oil) or cylinders (glass fibers). However, it also includes more complex shapes such as crytalline particles, which have some regular and some fractured surfaces; asbestos fibers, which are often bundles of finer fibrils but may be matted clumps of fibrils; and carbon black particles, which often consist of an extended framework of very small spheroids. All these have a different chemical constitution. Even if all these particles have the same microscopically observed diameter, the mass, surface area, and other properties of each particle are likely to be quite different. Part III, the Applications Section of this book, discusses a wide range of particulate types in many different environmental and industrial settings.