5. 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 coming from the sun.
10. Too much ultra-violet-b on human beings Skin cancer:90% of the skin carcinomas are attributed Eye damage such as cataracts : Increases the risk of cataracts Induces type of protein that provokes cleaving (splitting) in the lens Leading cause of blindness The prevalence of cataract after age 30 is doubling each decade Immune system damage : Enhanced susceptibility to infection
11. Dna and uv DNA absorbs UV-B radiation Changes shape in DNA Changes in the DNA molecule mean that enzymes cannot “read” the DNA code Results in mutated cells or the cells die Cells have developed the ability to repair DNA A special enzyme arrives at the damage site removes the damaged section of DNA replaces it with the proper components This makes DNA somewhat resilient to damage by UV-B
12. The influence of the UV-b radiation on plant process. In experimental series the following observationswere determined: number of leaves, tillering of plants recordedafter three weeks and before harvest plant height,biomass of plants, specific leaf weightsleaf: shoot dry ratio, shoot dry matterof chlorophyll. Leaf area was measured using a LICOR LI-30004 portable leaf area meter and the content oftotal chlorophyll was measured with a Minolta SPAD-502meter5.
13. Phytoplankton UV-B penetrates water columns to depths of 30m Increased UV-B exposure Reduces productivity by interfering with processes of photosynthesis Damages DNA Inhibits mobility Studies (1993) conducted in the Weddle Sea Evaluated effects of photosynthesis to UV exposure in the presence of vertical mixing, found: photosynthesis by phytoplankton was strongly inhibited near the surface of the water
15. The DISCOVERYIn 1985, using satellites, balloons, and surface stations, a team of researchers had discovered a balding patch of ozone in the upper stratosphere, the size of united states, over Antarctica. Team who discovered the hole 1985. From left: Joe Farman, Brian Gardiner, and Jonathan Shanklin
16. What is being done to counter the effects of ozone depletion ??? Montreal Protocol (adopted in 1987) – panel of experts was formed to investigate substances responsible for hole formation Established policies that prevent future use of certain types of chemicals Stipulated that the production and consumption of compounds contributing towards depletion of ozone in the stratosphere were to be phased out by the year 2000 (2005 for methyl chloroform)
17. Signs of recovery ??? There have been some signs of recovery Since the Montreal Protocol came into effect, the atmospheric concentrations of the most important chlorofluorocarbons and related chlorinated hydrocarbons have either levelled off or decreased. 1997 satellite showed a decline of several known ozone-depleting gases Satellite images show some slowing down of ozone loss
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20. Ozone loss resulted from human produced ozone destroying substances (ODS: CFCs ). These chemicals have extremely long lifetimes.
21. ODSs have been regulated under international agreements and are slowly decreasing.
22. Ozone levels are not getting worse, but we can’t say that things are getting better (yet).
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Notes de l'éditeur
The Earth’s atmosphere can be divided into various distinct layers. Troposphere is the one closest to surface of earth. Then comes stratosphere then the thermosphere and outermost is the exosphere. Ozone is spread all over the atmosphere . But Almost 90% of the ozone exists in the stratosphere.
What is ozone
What is ozone???Ozone is a triatomic form of oxygen (O3) a no of ozone molecules come together at high conc they form the ozone layer. This layer absorbs 97–99% of the Sun's high frequency ultraviolet light, which is damaging to life on Earth.
What chemicals cause ozone loss????Most ozone damage inflicting chemicals abbreviated as cfc’s. Cfc’s aren’t naturally existing compounds. These were invented in the year 1920 by scientist named Thomas Midgley . And were extensively used in air conditioning units and in refrigerators and even as some cleaning chemicals.
Chemical mechanismThe structure of cfc’s contain central carbon atom which is bonded to 3 cl and 1 Fl atom by covalent bonds. They are found to be highly non toxic and inflammable in the troposphere . But once they reach the stratosphere in the presence of UV radiations the cl and c bond is broken. This cl released acts as a catalyst and breaks down ozone molecules to oxygen. Making the earth’s surface vulnerable to UV radiation.
UV radiations are electromagnetic radiations having wavelength range 100 to 400nm. Based on wavlength UV rays are divided as UV-A , UVB and UVC where Uva are lease dangerous to human beings and Uvc are most dangerous but are completely absorbed by ozone.
Ozone destruction impactOn human beings : over exposure can cause skin cancer, and can also cause cleaving in the lens and also can damage retina cells leading to blindness. They can also cause damage to immune system making human body vulnerable to various diseases.
Dna and UV ray’s : WhenDna is exposed to UV- b rays it absorbs these rays resulting in change of dna shape further resulting in creation of mutated cells and dying of cells. But if the UV-b ray exposure is low then a special enzyme gets created which can repair the damage.
Influence of uv-b radiation on plants growth : To find effect of Uv-b radiaton on plant growth experiments were conducted in which similar plants species were made to grow exposed to various UV conc. And it was found that the plant which was most exposed to UV radiation was found to have stunted growth and chlorophyll content was found to be very low thus hindering photosynthesis.
Phytoplankton: These are microscopic plants which were considered to initially store the thermosphere with oxygen and are primary source of food and energy for the ocean eco system. Phytoplankton exposure to Uv-b rays was found to inhbit the photosythesis process, damaged dna.
The ozone hole discovery
The ozone hole was discovered in the year 1985 by a group of scientists named Brian , Joe , Jonathan using satellites, balloons and space stations over antartica . And the size of this ozone was found to be almost of the size of United States.
To counter the effects of ozone depletion the Montreal protocol a treaty was signed to prevent further damage of ozone and for ozone recovery . As per the Montreal protocol all the clorofluorocarbns were banned and it demanded the replacement of these of ozone depleting chemicals. And balloons were sent to extract the cfc’s already present in the stratosphere.
Signs of recovery . After the signing of Montreal protocol treaty the atmosphereicconc of clc’s was found to be levelled off. Satllites showed decline the recovery of ozone . But however the recovery is very slow….
This is the graph showing cfc decrease after implementing the montreal protocol . As you can find the progress is very low.
Ozone layer is very much vital to human beings. It absorbs most of Uv radiations . Ozone loss by human produced chemicals such as Cfc’s have caused serious damage to human beings and various other living organisms. Though the present rate of recovery of ozone is very low , things are still getting better . And if the effort to protect the ozone is continued ozone is said sure to recover by 2068. Thank you
