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Stratospheric Pollution

Stratosphere is the layer of earth’s atmosphere just above troposphere and below mesosphere. The upper stratosphere consists of considerable amount of ozone (O3), which protects us from the harmful ultraviolet (UV) radiations coming from the sun. These radiations cause skin cancer  in humans. Therefore, it is important to maintain.

  • Formation of ozone layer in stratosphere.

In stratosphere (10-50 km from earth surface) , the O2 is partially converted into O3. It is a two step process.

Step 1: The UV radiation coming from the sun has sufficient energy to split the O2 into 2 oxygen radicals.

O2 + UV → 2O.

Step 2:  The oxygen radicals react with more oxygen molecules to form ozone.

O2 + O.  + UV → O3

Ozone absorbs U.V radiation and again breaks into oxygen molecule and oxygen radical.

 O3 + UV → O2 + O.  

Heat is also given out in this process which warms up stratosphere. For this reason, stratosphere is a zone of increasing temperature.

O2 + UV → O+ O.+ x kcal

In this way , O3 cycle is completed in this region.

  • Depletion of ozone layer in stratosphere

?Due to human activity two compounds NO and CFC, are responsible for depletion of ozone layer.

(a) NO( Nitric Oxide)

NO + O3 → NO2 + O2

NO2 + O. → NO + O2

The NO reacts with O3 causing decrease in the amount of O3 and forms NO2 which reacts with oxygen radicals for regeneration of  NO. Thus there is no net decrease in amount of NO while amount of O3 decreases.

(b) Chlofofluoro carbons (CFC) or freons

The ferons decompose in the presence of U.V. radiation coming from the sun.

CF2Cl2 + hv → .CF2Cl + .Cl

CFCl3 + hv → Cl + CFCl2

The reactive chlorine atoms then destroy  the ozone layer through the following sequence of reactions which are repeated because chlorine atoms are regenerated in the second reaction.

Cl. + O3 → ClO. + O2

ClO. + O → Cl. + O2

One molecule of cfc can destroy more than one thousand o3 molecules in stratosphere.

Refer to the following video for depletion of ozone layer

  • Effects of Depletion of ozone layer in stratosphere

Due to depletion of O3 layer, U.V. radiations fall on the earth surface

  1. UV radiations damage the cornea and lens of the eyes.

  2. The UV radiations affect plants proteins and thus reduce the chlorophyll..

  3. The UV radiations , disturb the heat balance of the earth.

  4. The influx of UV radiation reaching the surface of earth would increase which would increase in risk to skin cancer due to exposure to UV radiation, UV radiations also tend to damage the immune system.

You can also refer   JEE Organic Chemistry Syllabus,  Environmental Chemistry Notes & Reference books of Organic Chemistry

To read more, Buy study materials of Environmental Chemistry comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.


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