Chapter No.14Chemistry 10

Compounds of sulphur are air pollutants. Describe the sources of these compounds along with their effects.

. No.7. Compounds of sulphur are air pollutants. Describe the sources of these compounds along with their effects.

Answer. Naturally occurring sulphur containing compounds are emitted in the bacterial decay of organic matter, in volcanic gases and forest fires. But the concentration of sulphur containing compounds in the atmosphere because of natural sources is very small as compared to the concentration of those compounds emitted by fossil fuel combustion in automobiles and industrial units. About 80% of the total SO2 is released by the combustion of coal and petroleum products as shown her

Fossil fuels contain Sulphur

Effects of SO2

(i)        SO2 is a colorless gas having irritating smell. It causes suffocation, irritation and severe respiratory problems to asthmatic people.

(ii)      SO2 forms sulphuric acid which damages buildings and vegetations.


  1. No. 8. Where does ozone layer lie in atmosphere? How it is depleting and how we can prevent its depletion?

Answer. Ozone is present throughout the atmosphere. But its maximum concentration called ozone layer lies in stratosphere region about 25 to 30 Km away from the Earth’s surface.



Under normal conditions ozone concentration in stratosphere remains nearly constant through a series of complex atmospheric reactions. Two reactions that maintain a balance in ozone concentrations are as follows:

O2 + O                     O3   (formation)


O2 + O                       2O2 (decomposition)

But this ozone layer is being depleted through various chemical reactions, such as:

(i)        The ozone molecule absorbs solar radiations and dissociate readily i.e., self dissociation of ozone takes place.

(ii).      However, chlorofluorocarbons (CFCs) (used as refrigerants in air conditioners and refrigerators) are major cause of depletion of ozone layer. These compounds leak in one way or other; escape and diffuse to stratosphere. There ultraviolet radiation breaks the C-C1 bond in CFCl3 and generates chlorine free radicals as


CFCI3                         CFCI2+Cl·

These free radicals are very reactive. They react with ozone to form oxygen as

O3+ Cl            O2 + OCl·

OCl·            O· + Cl·

O· + O·            O2

A single chlorine free radical released by the decomposition of CFCs is capable of destroying up to 1 lac ozone molecules. The region in which ozone layer depletes is called ozone hole. Depletion of ozone layer can be prevented by controlling the use of CFCs.

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