Air Pollution- Biology Guide for Class 8

Air Pollution- Class 8 Science Guide

Information about Air Pollution


Air Pollution


Class 8


Class 8 Biology

Topics Covered

  • Air Pollution
  • Causes of Air Pollution
  • Carbon Monoxide
  • Nitrogen dioxide
  • Smog
  • Chlorofluorocarbons
  • Acid Rain
  • Methods to control Air Pollution

We all are dependent on the environment for our survival. Clean environment is vital for the maintenance of life of all living organisms. An increase in the population has created an extra burden on our environment.
  • More and more forests are being cut to meet the increasing demand of houses.
  • More food is needed to feed the increasing population.
  • More industries have to be set-up to manufacture items of daily use. Many of these industries release harmful gases in the atmosphere and liquid waste in water.
  • Number of vehicles has also increased on the roads.
These release harmful gases in the atmosphere. All these activities have led to the contamination of our environment. In this Chapter, we will learn more about contamination of air and the remedial measures necessary to free our environment from pollution. 


    The term pollution has been derived from Latin word pollotioneum which means 'to make dirty'. 
    • Any substance, present in the environment in proportions greater than its natural abundance, and causing harmful effects, is called a pollutant; this phenomenon is known as pollution
    This implies that the presence of many of the substances, in undesirable concentrations, causes, pollution. Also, there are some harmful substances, which when released into the atmosphere due to various human activities, cause pollution. 

      Air Pollution 

        Air is a mixture of very many gases. Two of the most prominent of these gases are nitrogen (78%) and oxygen (21%). Other gases, like carbon dioxide, argon, methane, helium, ozone and water vapours, are also present in very small amounts. 
        • The contamination of air, by unwanted substances having harmful effects on both the living and the non-living things, is referred to as air pollution
        • All such substances, that contaminate air, are called air pollutants.

        Causes of Air Pollution

        Following are some major causes of air pollution:
        1. Excessive burning of fossil fuels, like coal, kerosene, petrol or diesel.
        2. Smoke, from factories and vehicles.
        3. Use of certain harmful substances, like chlorofluorocarbons.

        Let us know the basic details about some air pollutants.

        Carbon monoxide

        Carbon monoxide, formed by incomplete combustion of fuels, is a major source of pollution.

        Harmful effects of carbon monoxide

        1. Carbon monoxide, when inhaled, passes through the lungs into the blood. It combines with the haemoglobin (in the blood) to form a complex substance known as carboxy haemoglobin. This complex is unable to transport oxygen to various parts of the body. This causes suffocation and ultimately death.
        2. A high concentration of carbon monoxide in air affects the growth of plants causing the leaves to drop. It is worthwhile to note here that another well-known gas, carbon dioxide, when present in excess, also causes pollution of air.

          Nitrogen dioxide

          Nitrogen dioxide is mainly produced by combustion of petrol/gasoline in automobiles.

          Harmful effects of nitrogen dioxide

          1. High concentration of nitrogen dioxide in air is harmful to plants. It results in retardation of their photosynthetic activity.
          2. It results in respiratory problems in human beings.


            In winters, a thick fog-like layer envelops the atmosphere. This layer is made up of smoke and fog. 
            • When smoke, containing oxides of nitrogen, combines with other air pollutants and fog, it forms smog

            Harmful effects of smog

            It leads to diseases related to lungs (such as bronchitis, asthma, etc.). 2. It prevents the sunlight from reaching the earth; this affects the normal functioning of plants.

              Chlorofluorocarbons (CFCs)

              They are mostly used as refrigerants, solvents and foaming agents. When released in the atmosphere, they decompose under the ultraviolet (UV) radiations, present in sunlight. 

              Harmful effects of CFCs

                CFCs cause the depletion of ozone layer by decomposing ozone to oxygen. This results in an increased amount of ultraviolet radiations, from the sun, reaching the earth. This can cause skin cancer and damage to eyes.

                  Acid Rain 

                    Normal rain is slightly acidic due to the dissolution of atmospheric carbon dioxide in water.
                    • Excessive carbon dioxide, smoke and nitrogen dioxide, when released in the atmosphere, come in contact with the water vapours present there.
                    • This results in the formation of sulphuric acid and nitric acid. These acids then fall down with rain, making it acidic; such rain is called acid rain

                      Harmful effects of acid rain

                      1. Statues and structures, made from marble and limestone, get slowly corroded when rain water, containing the acids, falls on them.
                      2. Both sulphuric acid and nitric acid can dissolve marble to form salts; acid rain, hence, corrodes the marble of the monument. This phenomenon is also called marble cancer. The pollutants in air can, thus, cause discolouring of white marble.
                      3. Articles made of metals, and gold and silver ornaments, slowly lose their lustre when they are affected by acid rain. Acid rain washes away a number of essential minerals from the soil.
                      4. Acid rain has an adverse effect on aquatic life, particularly, that in the lakes. 
                        Acid rain is, therefore, quite harmful to both plant and animal life.

                        Methods to Control Air Pollution

                        1. Use of smokeless chulhas, solar cookers and biogas (instead of the fossil fuels) for cooking purposes.
                        2. Use of unleaded petrol in vehicles.
                        3. Use of CNG in automobiles.
                        4. Use of alternative sources of energy (like solar energy, hydropower, wind energy and nuclear energy) instead of conventional sources of energy (such as coal and petrol).
                        5. Sticking to pollution emission norms from automobile exhausts and continuous upgrading to the relevant Euro standards.
                        6. Avoid burning of crackers; they cause a lot of air and noise pollution.
                        7. Install tall chimneys, with filters, in factories; locate them away from residential areas. 
                        8. Plant more trees (afforestation).
                        9. Undertake more Vanmahotsava like programmes (normally celebrated every year in the month of July).
                        10. Enforce strict anti-pollution measures.
                        11. Regular monitoring of air quality (by the Government and other agencies) at various locations. 
                        12. Avoid the burning of dry vegetable wastes; collect it in a pit and make compost.

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