Since coal and petroleum have been formed from biomass (plant and animal material), therefore, in addition to carbon and hydrogen, they also contain nitrogen and sulphur elements. When coal, and petroleum based fuels (like petrol and diesel) are burnt, the products of combustion are: Carbon dioxide, Water, Sulphur dioxide and Nitrogen oxides. And if combustion takes place in an insufficient supply of air (or oxygen), then some carbon monoxide is also produced. Out of all the products of combustion of these fuels, only water is harmless and does not affect the environment. All other products are harmful and hence pollute the environment. For example:
(i) Sulphur dioxide attacks the lungs causing bronchitis and other diseases. Sulphur dioxide also dissolves in rainwater making it acidic. The acid rain thus produced damages trees, plants, aquatic organisms, buildings and metal structures.
(ii) Just like sulphur dioxide, nitrogen oxides attack the breathing system and also cause acid rain.
(iii) Carbon monoxide is a very poisonous gas. If carbon monoxide gets into our blood stream, it stops red blood cells from carrying oxygen from lungs to the rest of the body causing suffocation. Too much carbon monoxide causes death.
(iv) Though carbon dioxide is not a poisonous gas but it is a greenhouse gas which traps sun’s heat energy falling on the earth. The burning of more and more of fossil fuels is increasing the amount of carbon dioxide in the atmosphere causing increased greenhouse effect leading to global warming.
From the above discussion we conclude that: We need to use fossil fuels (coal and petroleum) judiciously because:
(i) Fossil fuels (coal and petroleum) left in the earth are limited which will get exhausted soon, and
(ii) The products of combustion of fossil fuels (coal and petroleum) pollute the environment.