The ozone layer is a layer in Earth's atmosphere which contains relatively high concentrations of ozone (O₃). This layer absorbs 97-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on Earth.^[1] Over 90% of ozone in earth's atmosphere is present here. ^[1]"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. It is mainly located in the lower portion of the stratosphere from approximately 15 km to 35 km above Earth's surface, though the thickness varies seasonally and geographically.^[2] 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. Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations which continues to operate today. The "Dobson unit", a convenient measure of the total amount of ozone in a column overhead, is named in his honor. Air redirects here. ... For other uses, see Ozone (disambiguation). ... Sol redirects here. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... Atmosphere diagram showing stratosphere. ... To help compare different orders of magnitude this page lists lengths between 10 and 100 km (104 to 105 m). ... Year 1913 (MCMXIII) was a common year starting on Wednesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Tuesday of the 13-day-slower Julian calendar). ... Charles Fabry Maurice Paul Auguste Charles Fabry (June 11, 1867 / Marseille, France – December 11, 1945 / Paris, France) was a French physicist. ... Henri Buisson (1873 – 1944) was a French physicist. ... Gordon Miller Bourne Dobson FRS (25 February 1889 - 11 March 1976) was a British physicist and meteorologist who did important work on ozone. ... Spectrophotometer In physics, spectrophotometry is the quantitative study of electromagnetic spectra. ... Year 1928 (MCMXXVIII) was a leap year starting on Sunday (link will display full calendar) of the Gregorian calendar. ... Jan. ... Dobson units (DU) are the standard way to express ozone amounts in the atmosphere. ...

Origin of ozone

Ozone-oxygen cycle in the ozone layer.

The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930. Ozone in the earth's stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (O₂), splitting them into individual oxygen atoms (atomic oxygen); the atomic oxygen then combines with unbroken O₂ to create ozone, O₃. The ozone molecule is also unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O₂ and an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle, thus creating an ozone layer in the stratosphere, the region from about 10 to 50 km (32,000 to 164,000 feet) above Earth's surface. About 90% of the ozone in our atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 15 and 40 km, where they range from about 2 to 8 parts per million. If all of the ozone were compressed to the pressure of the air at sea level, it would be only a few millimeters thick. Image File history File links Ozone_cycle. ... Image File history File links Ozone_cycle. ... Ozone-oxygen cycle in the ozone layer. ... Sir Sydney Chapman (politician) Sydney Chapman (astronomer) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Year 1930 (MCMXXX) was a common year starting on Wednesday (link will display 1930 calendar) of the Gregorian calendar. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... Properties For other meanings of Atom, see Atom (disambiguation). ... Ozone-oxygen cycle in the ozone layer. ... Atmosphere diagram showing stratosphere. ... A millimetre (American spelling: millimeter), symbol mm is an SI unit of length that is equal to one thousandth of a metre. ...

Ten percent of the ozone in the atmosphere is contained in the troposphere, the lowest part of our atmosphere where all of our weather takes place. Tropospheric ozone has two sources: about 10 % is transported down from the stratosphere while the remainder is created in situ in smaller amounts through different mechanisms. Atmosphere diagram showing the mesosphere and other layers. ... Seasonal average concentrations of tropospheric ozone in Dobson units over the period 1979 to 2000. ... Atmosphere diagram showing stratosphere. ...

Ultraviolet light and ozone

Levels of ozone at various altitudes and blocking of ultraviolet radiation.

Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation emitted from the Sun. UV radiation is divided into three categories, based on its wavelength; these are referred to as UV-A, UV-B, and UV-C. UV-C, which would be very harmful to humans, is entirely screened out by ozone at around 35 km altitude. However it is interesting to note that ozone gas is a pollutant at lower levels and cause severe problems like oedema, hemorrage etc. UV-B radiation can be harmful to the skin and is the main cause of sunburn; excessive exposure can also cause genetic damage, as a result problems such as skin cancer. The ozone layer is very effective at screening out UV-B; for radiation with a wavelength of 290 nm, the intensity at Earth's surface is 350 billion times weaker than at the top of the atmosphere. Nevertheless, some UV-B reaches the surface. Most UV-A reaches the surface; this radiation is significantly less harmful, although it can potentially cause genetic damage. Levels of ozone at various altitudes, and related blocking of several types of ultraviolet radiation. ... Levels of ozone at various altitudes, and related blocking of several types of ultraviolet radiation. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... Skin cancer is a malignant growth on the skin which can have many causes. ...

Depletion of the ozone layer allows more of the UV radiation, and particularly the more harmful wavelengths, to reach the surface, causing increased genetic damage to living creatures and organisims.

DNA sensitivity to UV

UV energy levels at several altitudes. Blue line shows DNA sensitivity. Red line shows surface energy level with 10% decrease in ozone.

To appreciate the importance of this ultraviolet radiation screening, we can consider a characteristic of radiation damage called an action spectrum. An action spectrum gives us a measure of the relative effectiveness of radiation in generating a certain biological response over a range of wavelengths. This response might be erythema (sunburn), changes in plant growth, or changes in molecular DNA. Certain wavelengths of UV radiation have a much greater probability of DNA damage than others. Fortunately, where DNA is easily damaged, such as by wavelengths shorter than 290 nm, ozone strongly absorbs UV. At the longer wavelengths where ozone absorbs weakly, DNA damage is less likely. If there were a 10% decrease in ozone, the amount of DNA damaging UV insolation increases, in this case, by about 22%. Considering that DNA damage can lead to maladies like skin cancer, it is clear that this absorption of the sun's ultraviolet radiation by ozone is critical for our well being.^{[citation needed]} UV energies at various altitudes. ... UV energies at various altitudes. ... An action spectrum is the rate of a physiological activity plotted against wavelength of light. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... Probability is the likelihood that something is the case or will happen. ... Not to be confused with insulation. ... Skin cancer is a malignant growth on the skin which can have many causes. ...

Distribution of ozone in the stratosphere

Global monthly average total ozone amount

The thickness of the ozone layer—that is, the total amount of ozone in a column overhead—varies by a large factor worldwide, being in general smaller near the equator and larger as one moves towards the poles. It also varies with season, being in general thicker during the spring and thinner during the autumn. The reasons for this latitude and seasonal dependence are complicated, involving atmospheric circulation patterns as well as solar intensity. Image File history File links TOMS_Global_Ozone_65N-65S.png Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Ozone layer Ozone depletion User:SEWilco/Images ... Image File history File links TOMS_Global_Ozone_65N-65S.png Summary Licensing File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Ozone layer Ozone depletion User:SEWilco/Images ...

Since stratospheric ozone is produced by solar UV radiation, one might expect to find the highest ozone levels over the tropics and the lowest over polar regions. The same argument would lead one to expect the highest ozone levels in the summer and the lowest in the winter. The observed behavior is very different: most of the ozone is found in the mid-to-high latitudes of the northern and southern hemispheres, and the highest levels are found in the spring, not summer, and the lowest in the autumn, not winter. During winter, the ozone layer actually increases in depth. This puzzle is explained by the prevailing stratospheric wind patterns, known as the Brewer-Dobson circulation. While most of the ozone is indeed created over the tropics, the stratospheric circulation then transports it poleward and downward to the lower stratosphere of the high latitudes.

Brewer-Dobson circulation in the ozone layer.

The ozone layer is higher in altitude in the tropics, and lower in altitude in the extratropics, especially in the polar regions. This altitude variation of ozone results from the slow circulation that lifts the ozone-poor air out of the troposphere into the stratosphere. As this air slowly rises in the tropics, ozone is produced by the overhead sun which photolyzes oxygen molecules. As this slow circulation bends towards the mid-latitudes, it carries the ozone-rich air from the tropical middle stratosphere to the mid-and-high latitudes lower stratosphere. The high ozone concentrations at high latitudes are due to the accumulation of ozone at lower altitudes. Brewer-Dobson circulation in the ozone layer. ... Brewer-Dobson circulation in the ozone layer. ...

The Brewer-Dobson circulation moves very slowly. The time needed to lift an air parcel from the tropical tropopause near 16 km (50,000 feet) to 20 km is about 4-5 months (about 30 feet per day). Even though ozone in the lower tropical stratosphere is produced at a very slow rate, the lifting circulation is so slow that ozone can build up to relatively high levels by the time it reaches 26 km.

Ozone amounts over the continental United States (25°N to 49°N) are highest in the northern spring (April and May). These ozone amounts fall over the course of the summer to their lowest amounts in October, and then rise again over the course of the winter. Again, wind transport of ozone is principally responsible for the seasonal evolution of these higher latitude ozone patterns.

The total column amount of ozone generally increases as we move from the tropics to higher latitudes in both hemispheres. However, the overall column amounts are greater in the northern hemisphere high latitudes than in the southern hemisphere high latitudes. In addition, while the highest amounts of column ozone over the Arctic occur in the northern spring (March-April), the opposite is true over the Antarctic, where the lowest amounts of column ozone occur in the southern spring (September-October). Indeed, the highest amounts of column ozone anywhere in the world are found over the Arctic region during the northern spring period of March and April. The amounts then decrease over the course of the northern summer. Meanwhile, the lowest amounts of column ozone anywhere in the world are found over the Antarctic in the southern spring period of September and October, owing to the ozone hole phenomenon. Image of the largest antarctic ozone hole ever recorded in September 2000. ...

Ozone depletion

Main article: Ozone depletion

The ozone layer can be depleted by free radical catalysts, including nitric oxide (NO), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine (Br). While there are natural sources for all of these species, the concentrations of chlorine and bromine have increased markedly in recent years due to the release of large quantities of manmade organohalogen compounds, especially chlorofluorocarbons (CFCs) and bromofluorocarbons.^{[citation needed]} These highly stable compounds are capable of surviving the rise to the stratosphere, where Cl and Br radicals are liberated by the action of ultraviolet light. Each radical is then free to initiate and catalyze a chain reaction capable of breaking down over 100,000 ozone molecules. Ozone levels, over the northern hemisphere, have been dropping by 4% per decade. Over approximately 5% of the Earth's surface, around the north and south poles, much larger (but seasonal) declines have been seen; these are the ozone holes. Global monthly average total ozone amount Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earths stratosphere since around 1980; and a much larger, but seasonal, decrease in stratospheric ozone over Earths... R-phrases , , , , S-phrases , , , Except where noted otherwise, data are given for materials in their standard state (at 25 Â°C, 100 kPa) Infobox disclaimer and references Nitric oxide or Nitrogen monoxide is a chemical compound with chemical formula NO. This gas is an important signaling molecule in the body of... // Hydroxyl group The term hydroxyl group is used to describe the functional group -OH when it is a substituent in an organic compound. ... General Name, symbol, number chlorine, Cl, 17 Chemical series halogens Group, period, block 17, 3, p Appearance yellowish green Standard atomic weight 35. ... Bromo redirects here. ... An organic halide is an organic compound containing one or more halogen atoms. ... For other uses, see CFC (disambiguation). ... Atmosphere diagram showing stratosphere. ... In chemistry, radicals (often referred to as free radicals) are atomic or molecular species with unpaired electrons on an otherwise open shell configuration. ... Northern hemisphere highlighted in yellow. ... Image of the largest antarctic ozone hole ever recorded in September 2000. ...

Regulation

On January 23, 1978, Sweden became the first nation to ban CFC-containing aerosol sprays that are thought to damage the ozone layer. A few other countries, including the United States, Canada, and Norway, followed suit later that year, but the European Community rejected an analogous proposal. Even in the U.S., chlorofluorocarbons continued to be used in other applications, such as refrigeration and industrial cleaning, until after the discovery of the Antarctic ozone hole in 1985. After negotiation of an international treaty (the Montreal Protocol), CFC production was sharply limited beginning in 1987 and phased out completely by 1996. is the 23rd day of the year in the Gregorian calendar. ... Year 1978 (MCMLXXVIII) was a common year starting on Sunday (link displays the 1978 Gregorian calendar). ... CFC, cfc, or Cfc may stand for: Chlorofluorocarbon : a class of chemical compounds known to inflict great damage to the ozone layer. ... Aerosol spray can Aerosol spray is a type of canister that sprays an aerosol when its button is pressed or held down. ... Image of the largest antarctic ozone hole ever recorded in September 2000. ... The largest Antarctic ozone hole recorded as of September 2000 For other similarly-named agreements, see Montreal Protocol (disambiguation). ...

On August 2, 2003, scientists announced that the depletion of the ozone layer may be slowing down due to the international ban on CFCs.^[3] Three satellites and three ground stations confirmed that the upper atmosphere ozone depletion rate has slowed down significantly during the past decade. The study was organized by the American Geophysical Union. Some breakdown can be expected to continue due to CFCs used by nations which have not banned them, and due to gases which are already in the stratosphere. CFCs have very long atmospheric lifetimes, ranging from 50 to over 100 years, so the final recovery of the ozone layer is expected to require several lifetimes. is the 214th day of the year (215th in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... The American Geophysical Union (or AGU) is a nonprofit organization of geophysicists, consisting (as of 2006) of over 49,000 members from over 140 countries. ...

Compounds containing C–H bonds are being designed to replace the function of CFC's (such as HCFC), since these compounds are more reactive and less likely to survive long enough in the atmosphere to reach the stratosphere where they could affect the ozone layer. This article should be merged with Freon, Halon, CFC, and Hydrochlorofluorocarbon and added to Alkyl halide Hydrochlorofluorocarbons (HCFCs) is one of a class of fluorocarbon compounds that are used primarily as chlorofluorocarbon (CFC) substitutes. ...

References

1. ^ ^{a b} Ozone layer (English). Retrieved on 2007-09-23.
2. ^ Science: Ozone Basics. (English). Retrieved on 2007-01-29.
3. ^ Independent Online (2006-09-23). Independent Online. (English). Retrieved on 2006-09-23.

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 29th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ...

Further reading

• Seinfeld, John H.; Pandis, Spyros N (1998). Atmospheric Chemistry and Physics - From Air Pollution to Climate Change. John Wiley and Sons, Inc. ISBN 0-471-17816-0

External links

• Stratospheric ozone: an electronic textbook
• http://www.unep.org/ozone/Public_Information/4Aii_PublicInfo_Facts_OzoneLayer.asp
• NASA. Studying Earth's Environment From Space. June 2000. (accessed April 14, 2005) http://www.ccpo.odu.edu/SEES/index.html.