The concentration of pollutants within a given political or geographical urban area can arise (1) from combustion or industrial process sources within a given area, (2) from similar sources outside the boundaries of that area or, (3) from natural processes taking place over large areas of the earth's surface or upper atmosphere. The pollution arising from man-made sources outside a given area may come from nearby cities or industrial areas. But the pollutants may also come from distant sites not at all obvious, and perhaps only occasionally offenders, under special meteorological conditions. In the report the methods of production, destruction, and the concentrations of various individual trace gases will be discussed. This can occur as natural releases from the earth's surface, microbiological reactions, and upper atmospheric reactions.