Ozone layer

The ozone layer or ozone shield is a region of <a href="/facts/Earth/HLLmDfj0">Earth</a>'s <a href="/facts/Stratosphere/taBra67V">stratosphere</a> that <a href="/facts/Absorption_(electromagnetic_radiation)/xBYKt7yS">absorbs</a> most of the <a href="/facts/Sun/CadPCVHh">Sun</a>'s <a href="/facts/Ultraviolet/kncBUqn5">ultraviolet</a> radiation. It contains a high concentration of <a href="/facts/Ozone/o0E5gn2p">ozone</a> (O3) in relation to other parts of the atmosphere, although still small in relation to other gases in the stratosphere. The ozone layer peaks at 8 to 15 <a href="/facts/Parts_per_million/PozRuoLM">parts per million</a> 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 15 to 35 kilometers (9 to 22 mi) above Earth, although its thickness varies seasonally and geographically.
The ozone layer was discovered in 1913 by French physicists <a href="/facts/Charles_Fabry/Tn8nFMV5">Charles Fabry</a> and <a href="/facts/Henri_Buisson/Dab6tcAM">Henri Buisson</a>. Measurements of the sun showed that the radiation sent out from its surface and reaching the ground on Earth is usually consistent with the <a href="/facts/Spectrum/wPUjkpqI">spectrum</a> of a <a href="/facts/Black_body/f0fHghDy">black body</a> with a temperature in the range of 5,500–6,000 K (5,230–5,730 °C), except that there was no radiation below a <a href="/facts/Wavelength/kcJU0ymz">wavelength</a> of about 310 nm at the <a href="/facts/Ultraviolet/kncBUqn5">ultraviolet</a> 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 <a href="/facts/Meteorologist/GDUQ6qxD">meteorologist</a> <a href="/facts/G._M._B._Dobson/pJyyosMC">G. M. B. Dobson</a>, who developed a simple <a href="/facts/Spectrophotometry/hhjdQYvf">spectrophotometer</a> (the <a href="/facts/Dobson_spectrometer/HKuyI6bC">Dobsonmeter</a>) 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 "<a href="/facts/Dobson_unit/cNx6h1DK">Dobson unit</a>" (DU), a convenient measure of the <a href="/facts/Area_density/kFSauAs4">amount</a> 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 <a href="/facts/Nanometer/a98sjHyu">nm</a> to 315 nm <a href="/facts/Wavelength/kcJU0ymz">wavelength</a>), which otherwise would potentially damage exposed life forms near the surface.
In 1985, atmospheric research revealed that the ozone layer was being depleted by chemicals released by industry, mainly <a href="/facts/Chlorofluorocarbon/uLApxm7K">chlorofluorocarbons</a> (CFCs). Concerns that increased UV radiation due to <a href="/facts/Ozone_depletion/ssGWpcx3">ozone depletion</a> threatened life on Earth, including increased skin cancer in humans and other ecological problems, led to bans on the chemicals, and the latest evidence is that ozone depletion has slowed or stopped. The United Nations General Assembly has designated September 16 as the <a href="/facts/International_Day_for_the_Preservation_of_the_Ozone_Layer/trlHHj9K">International Day for the Preservation of the Ozone Layer</a>.
<a href="/facts/Venus/pADnueP6">Venus</a> also has a thin ozone layer at an altitude of 100 kilometers above the planet's surface.

Ozone layer open-in-new

Ozone layer