The release
of undesirable substances such as dust, smoke and harmful gases in the
atmosphere is called air pollution and these undesirable substances are called
pollutants.
One of the
major causes of pollution of the atmosphere is the combustion of fossil fuels
to meet our daily requirements of energy.
Fossil fuels cause air pollution in the following ways:
1. The combustion of fossil fuels results in the formation of
carbon dioxide, which is released into the atmosphere. Thus, concentration of
CO2 is
increasing in the atmosphere. Carbon dioxide has to ability to absorb infrared
radiation emitted by the earth and re-radiate it back. This effect is known as
‘greenhouse effect’. It is speculated that if the concentration of CO2 in atmosphere increases significantly this
could have thee effect of increasing the average temperature of the earth.
2.
Combustion of coal, gasoline and other fossil fuels in the presence of
insufficient supply of oxygen liberates carbon monoxide and unburnt
hydrocarbons. Carbon monoxide (CO) combines with hemoglobin in the blood to
form carboxy-haemoglobin and makes it incapable of transporting oxygen. Many
hydrocarbons are carcinogenic and hence, are serious health hazards.
3. Coal
contains some compounds of sulphur and nitrogen. During combustion these
compounds are oxidized to from the oxides of sulphur and nitrogen, which are
corrosive and poisonous. During rains these oxides dissolve in rain water and
are known to cause ‘acid rain’.
4. When gasoline burns in internal combustion engines, a very
high temperature is produced, at this high temperature, nitrogen and oxygen
combine to form oxides of nitrogen such as NO and NO2. These
oxides are highly poisonous and cause many respiratory problems. Moreover,
gasoline also contains some additives such as a tetraethyl lead [(C2H5)4Pb].
Tetraethyl lead is added to gasoline to reduce knocking (irregular combustion).
During combustion it produces volatile lead compounds which are released in the
air. These compounds are highly poisonous and cause serious pollution.
It may be
mentioned here that the pollution caused by burning oil based products is more
difficult to control than that produced by burning of coal. This is due to the
reason that oil based fuels such as gasoline and diesel are burnt in moving
vehicles. On the other hand coal is burnt mainly in factories and thermal
plants which cause pollution at a particular place. This pollution can be
controlled more easily by installing tall chimneys and electrostatic
precipitators. In addition, burning of gasoline also produces poisonous lead
compounds. This type of pollution is not caused by burning of coal.
