NCERT Book Class 8 Science Pollution Of Air And Water

POLLUTIION OF AIIR AND WATER

Paheli and Boojho were very excited to hear the news that Taj Mahal in Agra is now one of the seven wonders of the world. But they were disappointed to hear that the beauty of this monument in white marble is being threatened by air pollution in the area surrounding the Taj. They were eager to know if something can be done to fight the air and water pollution.

We are all aware that our environment is not what it used to be. Our elders talk about the blue sky, clean water and fresh air that was available in their times. Now the media regularly reports on the falling quality of the environment. We ourselves feel the impact of the falling quality of air and water in our lives. The number of people suffering from diseases of the respiratory system, for example, is steadily rising. We dread to imagine a time when clean air and water may no longer be available! You have learnt about the importance of air and water in your previous classes. In this chapter, we will study about the harmful changes taking place in our surroundings and their effects on our lives.

18.1 Air Pollution

We can survive for some time without food, but we cannot survive even for a few minutes without air. This simple fact tells us how important clean air is to us. One of your observations in the above activity could be the differences in the amount of smoke in the atmosphere. Do you know where the smoke could have come from? Addition of such substances to the atmosphere modifies it. When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as air pollution.

18.2 How does Air Get Polluted?

The substances which contaminate the air are called air pollutants. Sometimes, such substances may come from natural sources like smoke and dust arising from forest fires or volcanic eruptions. Pollutants are also added to the atmosphere by human activities. The sources of air pollutants are factories (Fig. 18.2), power plants, automobile exhausts and burning of firewood and dung cakes. Many respiratory problems are caused by air pollution. Let us now try to find out the substances or pollutants which are present in the polluted air. Have you noticed how rapidly the number of vehicles is increasing in our cities? Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke (Fig. 18.3). Carbon monoxide is produced from incomplete burning of fuels such as petrol and diesel. It is a poisonous gas. It reduces the oxygen-carrying capacity of the blood. Boojho remembers seeing a thick fog-like layer in the atmosphere, especially during winters. This is smo which is made up of smoke and fog. Smoke may contain oxides of nitrogen which combine with other air pollutants and fog to form smog. The smog causes breathing difficulties such as asthma, cough and wheezing in children. Many industries are also responsible for causing air pollution. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide andnitrogen dioxide. Sulphur dioxide is produced by combustion of fuels like coal in power plants. It can cause respiratory problems, including permanent lung damage. You have already studied about the burning of fossil fuels in Chapter 5. Other kinds of pollutants are chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays. CFCs damage the ozone layer of the atmosphere. Recall that the ozone layer protects us from harmful ultraviolet rays of the sun. Have you heard of the ozone hole? Try to find out about it. Thankfully, less harmful chemicals are now being used in place of CFCs.  In addition to the above mentioned gases, automobiles which burn diesel and petrol, also produce tiny particles which remain suspended in air for long periods (Fig. 18.3). They reduce visibility. When inhaled, they cause diseases. Such particles are also produced during industrial processes like steel making and mining. Power plants give out tiny ash particles which also pollute the atmosphere.

Activity 18.3 

Prepare a table using the pollutants mentioned above. You may even add more data to the following Table. Table 18.1 Air Pollutants Sources Effects

18.3 Case Study : The Taj Mahal

Over the past 2 decades, India’s most famous tourist attraction, Taj Mahal located in Agra (Fig. 18.4), has become a matter of concern. Experts have warned that pollutants in air are discolouring its white marble. So, it is not only living organisms that get affected by polluted air but non-living things like buildings, monuments and statues also get affected. The industries located in and around Agra like rubber processing, automobile, chemicals and especially the Mathura oil refinery, have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide. These gases react with the water vapour presen in the atmosphere to form sulphuric acid and nitric acid. The acids drop down with rain, making the rain acidic. This is called acid rain. Acid rain corrodes the marble of the monument. The phenomenon is also called “Marble cancer”. Suspended particulate matter, such as the soot particles emitted by Mathura oil refinery, has contributed towards yellowing of the marble. The Supreme Court has taken several steps to save the Taj. It has

18.4 Greenhouse Effect

You know that the sun’s rays warm the earth’s surface. A part of the radiation that falls on the earth is absorbed by it the role of carbon dioxide in plants. But if there is excess of CO2 in the air, it acts as a pollutant. Can you help Paheli find out the answer to her question? On the one hand, CO2 is continuously being released because of human activities. On the other hand, area under forests is decreasing. Plants utilise CO2 from the atmosphere for photosynthesis, thereby decreasing the amount of CO2 in the air. Deforestation leads to anincrease in the amount of CO2 in the air because the number of trees which consume CO2 is reduced. Human activities, thus, contribute to the accumulation of CO2 in the atmosphere. CO2 traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

Exercises

1. What are the different ways in which water gets contaminated ?

2. At an individual level, how can you help reduce air pollution?

3. Clear, transparent water is always fit for drinking. Comment. 

4. You are a member of the municipal body of your town. Make a list of measures that would help your town to ensure the supply of clean water to all its residents.

5. Explain the differences between pure air and polluted air.

6. Explain circumstances leading to acid rain. How does acid rain affect us?

7. Which of the following is not a greenhouse gas?

(a) Carbon dioxide

(b) Sulphur dioxide

(c) Methane

(d Nitrogen

8. Describe the ‘Green House Effect’ in your own words.

9. Prepare a brief speech on global warming that you have to make in your class.

10. Describe the threat to the beauty of the Taj Mahal.

11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Please refer to attached file for NCERT Class 8 Science Pollution Of Air And Water