ABSTRACT
Particles in the atmosphere may be primary or secondary, solid or liquid. They come into the atmosphere, and leave it again, by a wide variety of routes. After looking at general aspects of particles such as definition of size and the way they behave in the atmosphere, this chapter describes the sources of particles and methods for controlling emissions. If all the particles in a volume of gas are the same diameter, the size distribution is said to be monodisperse. Monodisperse aerosols are only found when they have been made artificially for calibrating sampling equipment; even then they soon start to become polydisperse, due to collisions and agglomeration between the original particles. When there is relative movement of particles within a cluster by Brownian or turbulent diffusion, there will be collisions between particles and this will sometimes result in their combination to form a single new larger particle.
