4.Other Pollutants :

           One of the most important of these pollutants is carbon dioxide which increases in percentage in the atmosphere due to the usage of organic fuel (petroleum and  coal). This gas absorbs some of the heat which is radiated from earth and prevent its loss to outer space. This leads to the gradual increase of the earth's temperature.

        Some scientists believe that the increase of temperature will lead to the melting of ice at the two poles. Water would flow from the poles to submerge some parts of the continents. Another opinion states that the opposite would occur. When strange particles accumulate in the air they absorb the heat of the sun and this leads to a gradual decrease in the temperature of the earth and approach of a new ice age.

        Various kinds of pollen grains are considered as pollutants. The amount increases in air during spring time. They become more effective with the effect of strong wind. They may cause various allergies to man and some animals.

        Insecticides and herbicides, which may be carried by air, also show harmful side-effect in far away places.