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.