Question

(a) Why is the ozone layer required in the stratosphere ? How does it get degraded ? Explain. 

(b) Why is the ozone depletion a threat to mankind ?

Answer 1

(a) The ozone formed in the stratosphere is called 'good' ozone, as it acts as a shield and absorbs the ultraviolet radiation from the sun.

The major ozone-depleting substances are chlorofluorocarbons, which release active chlorine in the presence of UV. The chlorine atoms degrade ozone into molecular oxygen.

CFCl₃ + UV(C) → CFCl₂ + Cl

CFCl₂ + UV(C) → CFCl + Cl

Cl + O₃ → ClO + O₂

ClO + O₃ → Cl + 2O₂  

(b) (i) The thinning of the ozone layer results in an increase in the UV radiation reaching the earth's surface. A 5 per cent increase in UV radiation.

(ii) In humans, the increased UV radiation increase the incidence of cataract and skin cancer (including melanoma) and diminishes the functioning of the immune system.

(iii) Elevated levels of UV radiation affect photosynthesis as well as damage nucleic acids in living organisms. UV radiation inhibits photosynthesis in most phytoplankton as it penetrates through the clear open ocean water.

(iv) This, in turn, can affect the whole food chain of organism that depends on the phytoplankton.