ozone is a form of oxygen having three instead of the usual two oxygen atoms per molecule. It is formed in the upper atmosphere by the action of ultraviolet light on normal oxygen; and, by being opaque to further incoming ultraviolet light, happily prevents most of the potentially very damaging ultraviolet wavelengths from reaching the earth’s surface.
Some man-made molecules such as the chlorofluorocarbons, once widely used in refrigeration, can, if released into the atmosphere, add to the effects of natural gases from volcanoes, etc. to destroy ozone. This occurs only at very low temperatures, such as occur over the poles in winter, but is nevertheless a matter of concern.