Ozone layer

The ozone layer, or ozonosphere, is that part of the Earth's stratosphere which contains relatively high concentrations of ozone (O{{sub|3}}). "Relatively high" means a few parts per million, much higher than the concentrations in the lower atmosphere but still small compared to the main components of the atmosphere. The ozone layer was discovered in 1913 by the french physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G.M.B. Dobson, who developed a simple spectrophotometer that could be used to measure stratospheric ozone from the ground.

Ultraviolet light and ozone

While the ozone concentrations are very small, it is vitally important to life because it absorbs biologically harmful ultraviolet radiation from the Sun. There are three different types of ultraviolet (UV) radiation, based on the wavelength of the radiation. These are referred to as UV-A, UV-B, and UV-C. UV-C is entirely screened out by ozone around 35 km altitude. On the other hand, most UV-A reaches the surface, but it is not as genetically damaging. It is the UV-B radiation that can cause sunburn and that can also cause genetic damage, resulting in things like skin cancer, if exposure to it is prolonged. Ozone screens out most UV-B, but some reaches the surface. Were the ozone layer to decrease, more UV-B radiation would reach the surface, causing increased genetic damage to living things.

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Because of ozone, it is virtually impossible for solar ultraviolet to penetrate to Earth's surface. For radiation with a wavelength of 290 nm, the intensity at Earth's surface is 350 million times weaker than at the top of the atmosphere.

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