The ozone layer is a region of the Earth's stratosphere that absorbs most of the sun's ultraviolet (UV) radiation. It contains high concentrations of ozone (O3) relative to other parts of the atmosphere, though Remains small relative to other gases in the stratosphere. The ozone layer contains less than 10 parts per million ozone, while the average ozone concentration in the Earth's atmosphere as a whole is about 0.3 parts per million. The ozone layer is found mainly at the bottom of the stratosphere, about 20 to 30 kilometers (12 to 19 miles) above Earth, although its thickness varies seasonally and geographically.
The ozone layer was discovered in 1913 by French physicists Charles Fabry and Henri Buisson. Measurements of the Sun showed that the radiation emitted from its surface and reaching the ground on Earth is usually consistent with the spectrum of a black body with a temperature in the range of 5,500-6,000 K (5,227 to 5,727 ° C), except That there was no radiation below a wavelength of about 310 nm at the ultraviolet end of the spectrum. It was deduced that the missing radiation was being absorbed by something in the atmosphere. Eventually, the missing radiation spectrum was matched to only one known chemical, ozone. Its properties were explored in detail by the British meteorologist G.M. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958, Dobson established a worldwide network of ozone monitoring stations, which continue to operate to this day. The "Dobson unit", a convenient measure of the amount of ozone overload, is named in his honor.
The ozone layer absorbs 97 to 99 percent of the Sun's average frequency (200 nm to 315 nm wavelength) ultraviolet light, which could otherwise damage near-surface life forms. The United Nations General Assembly has designated September 16 as the International Day for the Preservation of the Ozone Layer. Venus also has a thin layer of ozone at an altitude of 100 kilometers from the surface of the planet.
