A layer of haze in the atmosphere, usually bounded at the top (haze line) by a temperature inversion and frequently extending downward to the ground. Necessary for the existence of this phenomenon are, of course, a source of haze particles and a relatively stable stratification of temperature in the atmosphere either within or immediately above the haze layer. A haze layer may vary in extent from the type developed locally over an urban area at night to a layer covering thousands of square miles as within an old and stable air mass.