The ozone layer or ozone shield is a region of Earth's stratosphere that absorbs most of the Sun's ultraviolet (UV) radiation. It contains high concentrations of ozone (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer contains less than 10 parts per million of ozone, while the average ozone concentration in Earth's atmosphere as a whole is about 0.3 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, although its thickness varies seasonally and geographically.
The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Measurements of the sun showed that the radiation sent out 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 5,500Ð6,000 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 spectrum of the missing radiation was matched to only one known chemical, ozone. Its properties were explored in detail by the British meteorologist G. M. B. 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 overhead, is named in his honor.
The ozone layer absorbs 97 to 99 percent of the Sun's medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength), which otherwise would potentially damage exposed life forms near the surface.
The United Nations General Assembly has designated September 16 as the International Day for the Preservation of the Ozone Layer. Read more ...
The Hole in Earth's Ozone Layer Is Healing Live Science - January 8, 2018
Efforts to heal the hole in Earth's ozone layer over Antarctica appear to be paying off, according to a new, first-of-its-kind study that looked directly at ozone-destroying chemicals in the atmosphere. Earth's ozone layer protects the planet's surface from some of the sun's more harmful rays that can cause cancer and cataracts in humans, and damage plant life, according to NASA. In the mid-1980s, researchers identified a massive hole in the ozone layer over Antarctica and determined that it had been caused largely by human-produced chemicals called chlorofluorocarbons (CFCs). Previous satellite observations have observed changes in the size of the ozone hole, noting that it can grow and shrink from year to year. But the new study is the first to directly measure changes in the amount of chlorine - the main CFC byproduct responsible for ozone depletion - in the atmosphere above Antarctica, according to a statement from NASA. The study showed a 20-percent decrease in ozone depletion due to chlorine between 2005 and 2016.
Antarctic Ozone Hole Hits 2013 Peak Size Live Science - October 22, 2013
= The Antarctic ozone hole reached its biggest extent for the year on Sept. 26, 2013, the National Oceanic and Atmospheric Administration announced yesterday. At its maximum, the ozone hole over the South Pole measured a whopping 7.3 million square miles (18.9 square kilometers), making it almost twice the area of Europe.
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