POLLUTION

INTRODUCTION
    The contamination of environment with harmful (toxic and poisonous) substances due to the certain natural phenomena and human activities is called environmental pollution or simply as pollution.
    Any substance that cause pollution is called a pollutant. A substance becomes pollutant when its concentration increases beyond a certain permissible limit in the environment.
    Pollutants may belong to any of the following classes.
(A)     Gaseous Pollutants : Such as Carbon monoxide, Oxides of Sulphur and Nitrogen, Chlorine gas etc.
(B)     Particulate Pollutants : Such as Dust, Smoke, Fumes, Mist, Fly ash, Pesticides, Insecticides, Cement dust, etc.

AIR POLLUTION
    Our atmosphere contains many gases. Some of these gases are necessary for the existance of life on the earth. Due to urbanization and industrialization, many harmful compounds are released by the factories into the atmosphere. The presence of such undesirable substances in the air makes it unfit for breathing and is called as air pollution. Thus, the contamination of air with harmful toxic gases, smoke and dust, etc., is called air pollution. 
    The substance which cause pollution of the air are called air pollutants. Major air pollutants are:
    (i)      Carbon monoxide    (ii)     Carbon dioxide    (iii) Sulphur dioxide
    (iv)     Nitrogen oxides    (v)     Smoke             (vi) Dust


Burning of Fossil Fuels
    The pollutants released during the burning of these fossil fuels are:

    
    
    All these pollutants released during the burning of fossil fuels cause air pollution. So, burning of fossil fuels causes air pollution.

Sources of Air Pollution
    Air gets polluted due to various human activities as summarized below.
(i)    Burning/combustion of fuel: Burning of fuel for household purposes generates gases like carbon dioxide, carbon monoxide as well as soot and particulate matter. 
(ii)    Vehicular emission: Gases emitted from the exhausts of motor vehicles contribute significantly to air pollution. These gases are nitrogen oxides, sulphur dioxide, carbon monoxide, carbon dioxide, hydrogen sulphide, etc.
(iii)    Industrial emission: With the increase in population, the number of industries is increasing day by day. they emit harmful gases and smoke. For example, operations like mining of coal release coal dust into the atmosphere.
(iv)    Emmissions from power plants: Thermal power plants and nuclear power plants release harmful gases, smoke and radioactive pollutants.
(v)    Deforestation: Trees absorb substantial amount of carbon dioxide from the atmosphere. Hence, cutting of trees pullutes the environment by increasing the amount of carbon dioxide in the atmosphere.
(vi)    Use of chlorofluorocarbons (CFCs) in refrigerators, fire extinguishers, aerosol sprays, etc. leads to release of harmful gases that deplete the ozone layer.

Effects of Air Pollution
    The harmful effects of some air pollutants on living and non-living things.
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