ABSTRACT
In previous chapters the quality of ambient air was discussed in the context of major pollutants, sources, effects, and atmospheric dispersion processes. Air quality, of course, is ever changing. It varies greatly over the course of the year or over 24 hours and from one location to another. The quality of ambient air for a specific time and place depends on a combination of factors including the magnitude of emissions from individual sources, source emission density, topography, and the state of the atmosphere.
