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
Ozone Depletion<br />By : Brian Antony D'Souza<br />
O3 both heats the stratosphere by absorbing UV and is a greenhouse gas (absorbing and emitting in the Infrared).</li></li></ul><li>What chemicals cause ozone loss ???<br />
Ozone Depleting Substances<br /><ul><li>Chlorofluorocarbons (CFC’s)Freon from old air conditioners and refrigerators and from industry is one of the big sources.Chlorofluorocarbons (cfcs) were invented by Thomas Midgley in the 1920s. They were used in air conditioning/cooling units, as aerosol spray propellants prior to the 1980s, and in the cleaning processes of delicate electronic equipment. They also occur as by-products of some chemical processes. No significant natural sources have ever been identified for these compounds — their presence in the atmosphere is due almost entirely to human manufacture. </li></li></ul><li><ul><li>CHEMICAL MECHANISM Chlorofluorocarbon's: - CFC’s contain : Cl, Fl, C - Non-toxic, non-flammable i.e. inert in the troposphere. - In the stratosphere are photolysed, releasing reactive chlorine atoms. - The chlorine atoms act as a catalyst, and each can break down tens of thousands of ozone molecules to oxygen. </li></li></ul><li>Stratospheric Ozone and Ultraviolet Radiation (UVR)<br />Ultra-violet radiation (UVR) high energy electromagnetic wave emitted from the sun. It is made up of wavelengths ranging from 100nm to 400nm. <br />UV radiation includesUV-A, the least dangerous form of UV radiation, with a wavelength range between 315nm to 400nm, UV-B with a wavelength range between 280nm to 315nm, and UV-C which is the most dangerous between 100nm to 280nm. UV-C is unable to reach Earth’s surface due to stratospheric ozone’s ability to absorb it.<br />
Too much ultra-violet-b on human beings<br />Skin cancer:90% of the skin carcinomas are attributed <br />Eye damage such as cataracts : Increases the risk of cataracts<br />Induces type of protein that provokes cleaving (splitting) in the lens<br />Leading cause of blindness<br />The prevalence of cataract after age 30 is doubling each decade<br />Immune system damage : Enhanced susceptibility to infection<br />
Dna and uv<br />DNA absorbs UV-B radiation <br />Changes shape in DNA<br />Changes in the DNA molecule mean that enzymes cannot “read” the DNA code <br />Results in mutated cells or the cells die<br />Cells have developed the ability to repair DNA<br />A special enzyme arrives at the damage site<br /> removes the damaged section of DNA<br /> replaces it with the proper components<br />This makes DNA somewhat resilient to damage by UV-B<br />
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. <br />
Phytoplankton<br />UV-B penetrates water columns to depths of 30m<br />Increased UV-B exposure<br />Reduces productivity by interfering with processes of photosynthesis<br />Damages DNA <br />Inhibits mobility<br />Studies (1993) conducted in the Weddle Sea <br />Evaluated effects of photosynthesis to UV exposure in the presence of vertical mixing, found:<br />photosynthesis by phytoplankton was strongly inhibited near the surface of the water<br />
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.<br />Team who discovered the hole 1985. <br />From left: Joe Farman, Brian Gardiner, and Jonathan Shanklin<br />
What is being done to counter the effects of ozone depletion ???<br />Montreal Protocol (adopted in 1987) – panel of experts was formed to investigate substances responsible for hole formation<br />Established policies that prevent future use of certain types of chemicals <br />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)<br />
Signs of recovery ???<br />There have been some signs of recovery<br />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.<br />1997 satellite showed a decline of several known ozone-depleting gases<br />Satellite images show some slowing down of ozone loss<br />