ABSTRACT
This chapter reviews basic physical quantities and the tools used to describe and interpret them. It is on this basis that all quantitative evaluation of environmental processes is built. Central to all engineering calculations is a system of units. All physical quantities are not pure numbers but instead have dimensions expressible in a system of units. The most important environmental measurement is generally the density or concentration of a pollutant. The impact of a particular pollutant is typically assumed or observed to have a direct relation to its prevalence in the system, or concentration. One of the most important distributions in environmental work is the Gaussian or normal distribution. The Gaussian distribution is bell-shaped and symmetric. Another very important distribution encountered in environmental engineering is the log-normal distribution. This is a modification of the Gaussian distribution in that the logarithm of the observations is distributed normally about the logarithm of the mean.
