Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Ozone Layer shopping experience:
1. Compare - without doubt the biggest advantage that the Ozone Layer offers shoppers today is the ability to compare thousands of Ozone Layer at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Ozone Layer? Wrong! If the Ozone Layer is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Ozone Layer then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Ozone Layer? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Ozone Layer and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Ozone Layer wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Ozone Layer then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Ozone Layer site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Ozone Layer, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Ozone Layer, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
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. Over 90% of ozone in earth's atmosphere is present here. "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 1 E4 m above Earth's surface, though the thickness varies seasonally and geographically. 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
Spectrophotometry 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.
Origin of ozone
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.
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.
Ultraviolet light and ozone
.
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, resulting in 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.
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 organisms.
DNA sensitivity to UV
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. There is much greater
probability of DNA damage by UV radiation at various wavelengths. 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.
Distribution of ozone in the stratosphere
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.
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.
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.
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.
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. These highly stable compounds are capable of surviving the rise to the
stratosphere, where Cl and Br Radical (chemistry) 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.
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.
On
August 2,
2003, scientists announced that the depletion of the ozone layer may be slowing down due to the international ban on CFCs. 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.
Compounds containing C–H bonds are being designed to replace the function of CFC's (such as
Hydrochlorofluorocarbon), 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.
See also
cool
References
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.
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. Over 90% of ozone in earth's atmosphere is present here. "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 1 E4 m above Earth's surface, though the thickness varies seasonally and geographically. 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 Spectrophotometry 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.
Origin of ozone
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.
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.
Ultraviolet light and ozone
.
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, resulting in 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.
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 organisms.
DNA sensitivity to UV
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. There is much greater probability of DNA damage by UV radiation at various wavelengths. 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.
Distribution of ozone in the stratosphere
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.
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.
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.
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.
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. These highly stable compounds are capable of surviving the rise to the
stratosphere, where Cl and Br Radical (chemistry) 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.
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.
On August 2, 2003, scientists announced that the depletion of the ozone layer may be slowing down due to the international ban on CFCs. 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.
Compounds containing C–H bonds are being designed to replace the function of CFC's (such as
Hydrochlorofluorocarbon), 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.
See also
- Ozone
- Ozone depletion
- Oxygen
cool
References
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.
Ozone Layer
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Ozone layer - Wikipedia, the free encyclopedia
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Geography Site: Ozone layer
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Provides a comprehensive technical primer on the ozone layer and its depletion, as well as access to real-time and historical monitoring data, descriptions of instruments used to ...
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Fears over increase in skin cancer as scientists report that climate change continues to destroy the earth's protection.
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Ozone Layer
The Ozone Layer "The ozone layer" refers to the ozone within stratosphere, where over 90% of the earth's ozone resides.
