Ozone present in the stratosphere forms a protective layer and known as ozone layer , ozonosphere or ozone umbrella ...... Its concentration in atmosphere is about 10 ppm. In the upper atmosphere, atmospheric gases absorbs the sun's radiation , get ionized , and release molecules . In lower atmosphere , atmospheric oxygen get dissociated and subsequently combines with molecular oxygen of the upper stratosphere, there by producing ozone......
O2-----(UV radiation)----> O+O
O2 + O -----------> O3
The presence of ozone layer in the stratosphere is of vital significance for all biota, as it absorb the harmful ultraviolet radiation which are lethal to
life......O3 + UV radiations--------> O2 + O
The ozone absorbs ultraviolet radiation and prevent them to reach earth's surface . If these radiations are allowed to reach the earth's atmosphere they will increase the temperature of lower atmosphere to such an extent , that it will be impossible for any life to survive on earth. These UV radiations can cause severe radiation damage in human and animals such as DNA mutation and skin cancer........
MECHANISM OF DEPLETION OF OZONE LAYER
Ozone is unstable molecule and maintains a balance between its formation and removal. It occurs in the concentration of about 10 ppm in the form of layer at varying heights in stratosphere..... The thickness of ozone layer is measured in Dobson units , where 1 DU=.01mm of compressed gas at 0 degrees centigrade and 760 mm Hg pressure. When ozone level decreases below 200 DU , the condition is called Ozone hole......
Mechanism of ozone depletion includes two processes , which are -
(1) Natural process : Ozone in the upper atmosphere absorbs UV radiations of short wavelength and release atomic oxygen. This natural mechanism however do not really upset the equilibrium of ozone , because atmospheric oxygen absorbs UV radiation of wavelength of shorter than 240nm and photodissociates into two oxygen atoms. This oxygen combines O2 molecules to form ozone........
(2) Anthropogenic Process : Three important human made sources of ozone depletion are :
(a) Nitrogen Oxide - The supersonic aircrafts fly at ozonospheric cruising altitudes emits NOx which directly enters into the stratosphere ..... Following reactions occurs here in stratosphere:
NO + O3 ----------> NO2 + O2
NO2 + O ----> NO + O2
The net effect of this sequence is the destruction of two ozone molecules, as oxygen atom (O) could have combined with oxygen molecules
to form ozone. Further NO is still not consumed and can produce such sequence many times.....(b) CFC's : They are inert on earth but at high altitudes they get accumulated and release chlorine under the influence of ultraviolet rays .... Chlorine acts as an catalyst in breaking down ozone into oxygen molecules and chlorine molecule. ClO eventually interact with another ozone molecule and give two molecules of O2..... and a free chlorine atom
CFCs + UV -----> Cl
Cl + O3------> ClO + O2
ClO + O3 ------> 2O2 + Cl
Thus chlorine molecule destructs two ozone atoms and again get released , in this way a chlorine atom remain over 100 years in stratosphere and breaks down thousands of ozone molecules..
(3) Sulphates - sulphate aerosols emitted through volcanic eruptions and chimneys of several factories accumulate in the atmosphere mainly between the altitudes of 15 to 22 km . Theses sulphates aerosols catalyse the transformation of ozone to oxygen , thus depleting it's concentration........
HARMFUL EFFECTS OF OZONE LAYER DEPLETION
Now I am going to tell you what are the adverse effects caused by the depletion of the Ozone layer.......
Ozone which accounts for only 3 parts in ten millions of earth's atmosphere , plays several crucial roles in the radiation balance of the planet. It protects us from harmful UV radiations emitted from sun . Depletion of this ozone layer allow UV radiation , to reach on earth which has various adverse effects............
The most adverse effect of UV radistion is on immune system , it may cause the damage to whole immune system. UV rays can cause three kinds of skin cancer - basal cell carcinoma, squamous cell carcinoma and melanoma. UV rays affects the langerhans cells in the epidermis of human skin which are key players in immune serveillance. UV radiation cause blood vessels near the skin's surface to carry more blood , making the skin hot , swollen or red . causing sun burns . UV rays can also cause leukaemia and breast cancer
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