Bed 2nd Year What do you understand by Ozone Layer
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The stratospheric ozone layer mostly concentrated between the altitudes of 12 km to 35 km, is considered a protective shield and earth’s umbrella because it prevents ultraviolet solar radiation from reaching the earth’s surface. Thus, the presence of the ozone layer in the stratosphere is of vital significance for all biota including plants, animals, and man in the biosphere.
In the absence of this layer life is not possible in the biosphere because all the ultraviolet rays of the sun will reach the earth’s surface and consequently the temperature of the earth’s surface and the lower atmosphere will rise to such an extent that the ‘biological furnace’ of the biosphere will turn into a ‘blast furnace’. It is, thus desirable to study the various aspects of this valuable ozone layer viz. the formation of zone laver, the global concern of its depletion, factors, and mechanisms of its depletion, effects of ozone depletion, and maintenance of the ozone layer. (Bed 2nd Year What do you understand by Ozone Layer)
Creation Ozone Layer
Ozone defined as a three-atom isotope’ (one of a set of chemically identical species of the atom which have the same atomic number but different atomic weight is called ISOTOPE of oxygen (0)’ or ‘merely a triatomic form of oxygen (O3), is a faintly blue irritating gas with a characteristics pungent odour. Ozone is a strong oxidizing agent which can at high concentrations decompose with an explosion. There are contrasting opinions about the altitudes of the concentration of ozone.
It presents at almost all altitudes in the atmosphere but the bulk of its concentration is present in a layer from 10 km to 50 km up in the atmosphere and within this zone, the highest concentration of ozone is between the altitudes of 12 km and 35 km in the stratosphere. This zone (12 km to 35 km) of ozone is called Ozonosphere or Ozone Layer or Stratospheric Ozone Layer.
The ozone gas is unstable because it is created as well as destroyed or disintegrated. In other words (the creation and destruction of ozone gas is gradual and continuous natural process. The oxygen molecules are broken up or separated in the atmospheric layer between the altitudes of 80 to 100 km by ultraviolet solar radiation or by an electric discharge in oxygen or air during a thunderstorm in the troposphere in the following manner:
O2 → O + O
(oxygen breaks up into two separate oxygen molecules)
These separated oxygen atoms (O) are then combined with oxygen molecules (O2) and thus ozone (O3) is formed.
O2 + O + M → O3 + M
O2 + O → O3 (Ozone)
Where M denotes energy and momentum balance produced by the collision of oxygen molecules (O2) with another individual atom or molecule. (Bed 2nd Year What do you understand by Ozone Layer)
It may have pointed out that the collisions of 3 atoms or molecules or the collisions of oxy (O2) with the third atom are not very common features of regular occurred between the altitudes of 80 to 100 km (though O2 is very frequently broken up into individual atom or molecule in this layer as referred to above) because the very low density of gas in this part of the atmosphere and such collisions are also very rare in the atmosphere below the altitude of 35 km because most of the solar ultraviolet rays have already been absorbed above this heights. (Bed 2nd Year What do you understand by Ozone Layer)
Depletion of Ozone Layer
There has been much hue and cry about the depletion of stratospheric ozone In the last one or two decades and the issue now has assumed a global dimension because the problem of ozone depletion and its adverse consequences have threatened the existence of all forms of life in the biosphere. (Bed 2nd Year What do you understand by Ozone Layer)
The presence of the ozone layer in the atmosphere is very crucial and significant for plants and animals in general and human beings in particular because it provides a protective cover, known as the earth’s umbrella, to all of the organisms (including plants, animals, micro-organisms and man) in the biosphere ecosystem against their exposure to ultraviolet solar radiation, in fact, the ozone layer filters the solar radiation by absorbing unwanted ultraviolet rays and allowing only those radiation waves to reach the earth’s surface which is essential for the maintenance of life on the planet earth.
Any change in the equilibrium level of ozone in the atmosphere will adversely affect life in the biosphere. Thus the growing concern for the depletion of stratospheric ozone is not without reason and scientific evidence. The following evidence and efforts of scientific communities and governments are sufficient enough to demonstrate the growing awareness about the importance of ozone and the possible adverse effects arising out of its sharp depletion. (Bed 2nd Year What do you understand by Ozone Layer)
By absorption of Ultra Violet radiation O3 layer hurts the stratosphere, causing temperature inversion. This temperature inversion limits the vertical mixing of pollutants. However, in spite of this slow vertical mixing, some pollutants enter the stratosphere and remain there for years until they react with ozone and are converted to other products.
These pollutants deplete the ozone in the stratosphere. Major pollutants responsible for this depletion are chlorofluorocarbons (CFC5), nitrogen oxides (coming from fertilizer), and hydrocarbons. CFC5 has widely been used as coolants in air conditioners and refrigerators, cleaning solvents, aerosol propellants, and foam insulation. CFC is used in fire extinguishing equipment.
They escape as an aerosol in the stratosphere. Jet engines, motor vehicles, nitrogen fertilizers, and other industrial activities are responsible for the emission of CFC5, NOx, etc. Flying at stratosphere heights the supersonic aircraft cause major disturbances in O3 levels. The threat to O3 is mainly from CFC5 known to deplete O3 by 14% at the current emission rate. On the other hand, NOx would reduce O3 by 3.5%. The nitrogen fertilizers release nitrous oxide during denitrification. Depletion of O3 would lead to serious temperature change on the earth and consequent damage to the life-support system.
Factors and Mechanisms of Ozone Depletion and Creation of Ozone Hole
The combining of atmospheric oxygen (O2) with the individual oxygen molecule (O) results in the creation of ozone (O2 + O → O3) whereas the breaking of ozone (O3) into O2 and O or recreation of oxygen due to the collision of ozone (O3) with monatomic oxygen (O) results in the depletion or destruction of ozone (O3 → O2 + O or O3 + O → O2 + O2). The collective process of constant metamorphosis of oxygen into ozone (ozone formation) and ozone back into oxygen (ozone destruction of ozone depletion) is triggered by Photochemical Process.
If this is true, there must be the maximum formation of ozone during June near the equator but the distributional pattern of ozone denotes its maximum concentration in the high latitude (beyond 50° latitude in both the hemispheres) and minimum concentration over the equator. This anomalous distribution of the zone may be explained if we consider the transport of ozone by the atmospheric circulation towards the polar areas. (Bed 2nd Year What do you understand by Ozone Layer)
It is believed that ozone having a maximum concentration between the altitudes of 30 km to 40 km during summer months mainly during June in the low latitudes (equatorial zone) is transported during winter months towards high latitudes (polar areas) between the altitudes of 20 to 25 km. Thus the accumulation of ozone in the polar areas during the winter season results in the development of a rich ozone layer during the early spring season. (Bed 2nd Year What do you understand by Ozone Layer)
It may be pointed out (as referred to earlier) that the creative and destructive of ozone is a regular natural process that never disturbs the equilibrium levels of ozone in the stratosphere but when the destruction of ozone exceeds the level of ozone creation, serious repercussions are bound to crop in due to disequilibrium in the level of ozone.
In the beginning, there was a lot of controversy about the cause and factors of ozone depletion but now a consensus has been reached that the main culprits of ozone depletion are halogenated gases called Chlorofluorocarbons, Halons, and Nitrogen Oxides. The World Meteorological Organization’s (WMO) statement on anthropogenic modification of the stratospheric ozone layer issues in 1976 maintained that a continuous release of chlorofluoromethanes into the atmosphere may be capable of destroying ozone to a considerable extent. (Bed 2nd Year What do you understand by Ozone Layer)
Contrary to this opinion M.L. Parry maintained in 1977 that the ozone concentration in the stratosphere might be rising and chlorine does not necessarily cause depletion of ozone. But the latest NASA report has set aside the controversy about the factors and causes of ozone depletion as Chlorofluorocarbon (CFCs) and Halos have been recognized by most scientists as the main culprits of ozone depletion. (Bed 2nd Year What do you understand by Ozone Layer)
Harmful Effect of Ozone Depletion
The most important function of the stratospheric ozone is to protect the “exosphere and the earth’s surface from most of the ultraviolet solar radiation absorbing ultraviolet rays. (Bed 2nd Year What do you understand by Ozone Layer)
Thus the ozone layer serves as an umbrella or eld against the ultraviolet solar radiation and saves the earth’s surface from ming too hot. (Bed 2nd Year What do you understand by Ozone Layer)
The most dangerous effect of ozone depletion (ozone depletion means thinning of the ozone layer through lowering of its density stratosphere) would be a substantial increase in the ultraviolet solar radiation reaching the earth’s surface.
The increase in ultraviolet solar radiation in turn would raise the temperature of the earth’s surface and the lower atmosphere. This would trigger a chain of effects and counter effects which would adversely affect the life-forms in the biosphere in a variety of ways. Depletion of a stratosphere cause direct as well as indirect harmful effects,
[A] Direct Effect
- Rainfall Failure. Since the temperature rise in the stratosphere is due to heat absorption by ozone, the reduction in ozone would lead to temper change and rainfall failures on earth. (Bed 2nd Year What do you understand by Ozone Layer)
- Increase in Radiation. Moreover, a one percent reduction in O3 increases ultraviolet radiation on earth by 2%. A series of harmful effects are caused by an increase in ultraviolet radiation.
- Cancer. When the O3 layer becomes thinner or has holes, it causes cancer especially related to the skin like melanoma. A 10% decrease in stratospheric on appears likely to lead to a 20-30% increase in skin cancer. Nearly 6,000 people die of such cancers in the USA each year. Such cases increased by 7% in Australia and New Zealand.
- Other Disorder. The other disorders are cataracts, destruction of aquatic life and vegetation, and loss of immunity.
[B] Indirect Effect
- Greenhouse Effect. Under greenhouse effect, conditions, plants exposed to ultraviolet radiation showed a 20-50% reduction in growth, reduction in chlorophyll content, and increase in harmful mutations. Enhanced ultraviolet radiation also impairs fish productivity. (Bed 2nd Year What do you understand by Ozone Layer)
- Indian Scene. In India, the effort has been made to monitor 0, concentration in major cities but the scene is not quite satisfying. Emissions from automobiles are about 1.6 million tons, which are likely to increase in coming years due to increased dependence on coal and oil for several uses. Burning of these fuels causes emissions of NOx and hydrocarbons in ozone depletion. In both instances, human effects are noticed on earth. (Bed 2nd Year What do you understand by Ozone Layer)
Global Efforts to Check Depletion of Ozone Layer
- Vienna Conference. The first Global Conference on the depletion ozone layer was held in Vienna (Austria) in 1985 when scientists discovered a hole in the South Pole. A British team discovered a hole in the ozone layer as large as that of the United States. (Bed 2nd Year What do you understand by Ozone Layer)
- Montreal Protocol. Montreal Protocol in 1987 called for a 50% cut in the use of CFCs by 1998-reducing to the level of 1986. Many countries including India did not sign the Protocol as they did not see any rationale. India’s release of CFC is just 6,00 tonnes a year, equivalent to one and half day’s of the world’s total. In our country per capita consumption of CFC is 0.02 kg. Against 1 kg. Against 1 kg. of the developed world. India has three metropolitan centers- Delhi, Mumbai, and Kolkata-the largest ozone-producing cities. The other cities are Mexico, Los Angeles, and Bangkok.
This gas protects in the atmosphere (20 km above the Earth’s Surface ), but is deadly, if below causing lung disease. Rashmi Mayur, Director, Urban Environment Insitute, Mumbai total that there is nearly 5,000 cause of lung diseases caused by O3 in Mumbai alone.
The protocol endorsed the idea of funding to help the developing world CFCS is mainly the problem of the developed world, as 95% of CFCS is realized by European countries, the U.S.A, Russia, and Japan. The USA alone realize 37% CFCS (producing CFC worth 2 billion dollars.) Dupont alone produces nearly 250,000 tons of CFCs .UK. is a top exporter of CFC, other exporters being the U.S. France, and Japan. Sweden and West Germany plan to eliminate CFC use by 1994.
The European community also decided to cut production by 85%.
- Saving the Ozone Layer Conference. The three say international meet was organized jointly in London in March 1989 by the British Government and the UNEP. It highlighted the global problem created by the developed countries for CFCs Pollution. It stressed the final withdrawal of all these 03 depleting CFCs and other chemicals.Mrs.Thatcher’s idea was supported by 37 more countries while the Montreal Protocol was initially signed by 31 countries while the Montreal Protocol was initially signed by 31 countries. (Bed 2nd Year What do you understand by Ozone Layer)
- Helsinki Conference. In May 1989 was held another international meeting was a conference on ozone in Helsinki to revise the Montreal protocol. As many as 80 nations agreed to have a total ban by 2000 A.D. on chemicals that causes ozone depletion. However, the conference backed away from a plan put forward by Mostafa Toblba, Executive Director, NEP to set up an international climate fund. While the developing countries printed to have the fund the developed ones, including Japan, USA and UK rejected the plan. The agreement for CFC elimination by 2000 A.D. is a major step towards environmental protection.