11th Class Chemistry Environmental Chemistry

  • question_answer 10) What do you mean by ozone hole? What are its consequences?


    Two types of compounds, nitric oxide and chlorofluorocarbons (Freons) have been found to be most responsible for depleting ozone layer and creating a hole into it (known as ozone hole). Nitric oxide reacts with ozone in stratosphere forming oxygen and\[N{{O}_{2}}\].\[N{{O}_{2}}\]further reacts with free oxygen atoms available in the stratosphere producing back NO. \[NO+{{O}_{3}}\to {{O}_{2}}+N{{O}_{2}}\] \[N{{O}_{2}}+O\to NO+{{O}_{2}}\] Thus, NO is not consumed but depletion of ozone occurs. CFC first undergo photochemical decomposition to give chlorine atoms or free radicals. \[C{{F}_{2}}C{{l}_{2}}\xrightarrow{hv}\overset{\centerdot }{\mathop{C{{F}_{2}}}}\,Cl+\overset{\centerdot }{\mathop{Cl}}\,\] \[CFC{{l}_{3}}\xrightarrow{hv}\overset{\centerdot }{\mathop{CF}}\,C{{l}_{2}}+\overset{\centerdot }{\mathop{Cl}}\,\] Chlorine atoms destroy the ozone layer through a sequence of reactions which are repeated over and again. \[\overset{\centerdot }{\mathop{Cl}}\,+{{O}_{3}}\to {{O}_{2}}+Cl\overset{\centerdot }{\mathop{O}}\,\] \[Cl\overset{\centerdot }{\mathop{O}}\,+O\to \overset{\centerdot }{\mathop{Cl}}\,+{{O}_{2}}\] Although above reactions take place in all parts of stratosphere, yet ozone hole has mainly been observed in the stratosphere over Antarctica on account of strange climatic conditions. Consequences of depletion of ozone layer: UV-radiation filter into troposphere. These lead to ageing of skin, cataract, sunburn, skin cancer, killing of phytoplanktons, damage to fish productivity, etc. Plant proteins are easily affected by UV-radiations. It also increases evaporation of surface water through stomata of leaves and decreases the moisture content of soil. UV-radiations damage paints and fibres. Ozone depletion has very strong effect on climate and ecology.  

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