ABSTRACT
This chapter presents virtually all the definitions and physical laws that describe the behavior of gases and vapors within the environment. It starts with practical differences among the meanings of “normal” and between absolute and relative units of temperature and pressure (two intrinsic properties of all gases and vapors), and works its way to a definition of vapor pressure (a term that is very important within industrial hygiene) and to the distinction between gases and vapors. The temperature of a solvent is often assumed equal to that of the environment, although it can vary independently of the nearby ambient temperature. The actual behavior of any particular heated vapor plume is difficult to predict because the mechanisms that control molecular and turbulent dispersion turn out to be related to (but are somewhat different from) those mechanisms that control thermal cooling.
