Ozone

Ozone Layer is a region of the atmosphere from 19 to 48 km (12 to 30 mi) above the earth's surface. Ozone concentrations of up to 10 parts per million occur in the ozone layer. The ozone forms there by the action of sunlight on oxygen. This action has been taking place for many millions of years, but naturally occurring nitrogen compounds in the atmosphere apparently have kept the ozone concentration at a fairly stable level. Concentrations this great at …

… (372 mi), the spacecraft measures ozone variations at different altitudes and is providing the first complete picture of upper atmosphere chemistry. The World Meteorological Organization observed a 45 percent depletion of the ozone layer over one-third of the northern hemisphere, from Greenland to western Siberia, for several days during the winter of 1995-1996. The deficiency was believed to have been caused by chlorine and bromine compounds combined with polar stratospheric clouds formed under unusually low temperatures.