Aerosol measurement: principles, techniques, and applications. Willeke K, Baron PA, eds. New York: Van Nostrand Reinhold, 1993 Jan; :8-22
The term aerosol refers to an assembly of liquid or solid particles suspended in a gaseous medium long enough to enable observation or measurement. The term originated as the gas phase equivalent of 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 crystalline particles, which have some regular and some fractured surfaces; asbestos fibers, which are often bundles of finer fibrils, or 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.