The Ozone Layer
The earth’s atmosphere is made up of several layers. The troposphere is the lowest part of the earth’s atmosphere that extends from earth surface up to 10km in altitude. All human activities occur in the troposphere. The next layer is the stratosphere that continues from 10km to about 50km. Ozone is concentrated in a layer in the stratosphere from 15 to 30 km above the earth’s surface. The ozone layer in the stratosphere, absorbs the portion of the radiation from the Sun, preventing it from reaching the surface of Earth.
When sunlight reaches to the stratosphere , the ultraviolet rays of sunlight split up oxygen molecule(O2) into its two atoms. The hight reactivity of oxygen atom forces it to combine with oxygen molecules resulting in the formation of ozone molecule.
O2 → O + O
Ozone(O3) is a molecule formed [by three atoms of oxygen. While O2.which we normally refer to as oxygen, is essential for all aerobic forms of life.Ozone performs an essential function. It shields the surface of the earth from ultraviolet(UV) radiation from the Sun. This radiation is highly damaging to organisms, for example,it is known to cause skin cancer and cataract in human beings, UV rays also has its harmful effects on plant life and marine life.
Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule.The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms.These atoms then combine with the molecular oxygen to form ozone as shown –
Depletion of Ozone Layer
The ozone molecule is destroyed when it comes with the contact of chlorine atom, one chlorine atom can destroy 100000 ozone molecules. It occurs when compounds containing chlorine exposed to ultraviolet rays the compounds chich releases chlorine or similar elements like bromine are responsible for the depletion of ozone layers. The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers, such compounds which causes depletion of the ozone layer are known as Ozone Depletion Substance(ODS), the other ODS are Hydrochlorofluorocarbon(HDFCs) , Carbon tetrachloride and Methyl chloroform which releases chlorine, the ODS which releases bromine are Halons and Methyl bromide. n 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels and controlling the production of other ODS.
Nature contribution in depletion of O3 layer.
The volcano’s eruption also affects the ozone layer indirectly. The aerosol produced as a result of volcano eruption when reaches to stratosphere it boosts up the activity of chlorine or bromine atoms although its contribution in depletion of the ozone layer is very less as compared to human-created ODS.
The example of the ozone hole is the Annual ozone ‘hole’ over Antarctica, it is not that ozone is completely absent in that particular region, actually, the amount of ozone is exceptionally low in that region. This happens in the begining of the southern hemisphere spring (august-October) . The scientist has surveyed that ozone depletion is not limited to the region over the south pole, some of the latitudes over North America, South America, Europe, Asia, and much area of Africa are also have been seen a decrease in the amount of ozone.