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aheli and Boojho were very excited You already know that air consists to know that Taj Mahal in of a mixture of gases. By volume, about Pis one of the seven wonders of 78% of this mixture is and the world. But they were disappointed about 21% is . , to hear that the beauty of this argon, , and water monument in white marble is being vapour are also present in very small threatened by in the area quantities. surrounding the Taj. They were eager to know if something can be done to Activity 18.1 control the air and . You may have covered your nose We are all aware that our while passing a brick kiln emitting environment is not what it used to be. or started coughing while Our elders talk about the clean water walking on a busy (Fig. 18.1). and fresh air that was available in their On the basis of your experience, times. Now the media regularly reports compare the quality of air at the on the falling quality of the environment. places given below: We ourselves feel the impact of the falling quality of air and water in our . The l A park and a busy road. number of people suffering from diseases l A residential area and an of the , for example, industrial area. is steadily rising. l A busy traffic intersection at different times of the day e.g. We shudder to imagine a time when clean air and water may no longer be early morning, afternoon and available! You have learnt about the evening. importance of air and water in your l A village and a town. 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 , but we cannot survive even for a few minutes without air. This simple fact tells us how important clean air is to us. Fig. 18.1 : A congested road in a

2021–22 One of your observations in the Activity 18.2 above activity could be the differences You might have read in the in the amount of smoke in the newspapers that respiratory . Do you know where the problems amongst children smoke could have come from? Addition are rising day by day. Conduct a of such substances to the atmosphere survey of in your modifies it. When air is contaminated neighbourhood and among friends by unwanted substances which have to find out how many children are a harmful effect on both the living and suffering from respiratory problems. the non-living, it is referred to as air pollution. Many respiratory problems are caused by air pollution. Let us now try 18.2 How does Air Get Polluted? to find out the substances or which are present in the polluted air. The substances which contaminate the Have you noticed how rapidly the air are called air pollutants. Sometimes, number of vehicles is increasing in our such substances may come from natural ? sources like smoke and arising from Vehicles produce high levels of or volcanic eruptions. pollutants like , carbon Pollutants are also added to the dioxide, nitrogen and smoke (Fig. atmosphere by certain activities. 18.3). Carbon monoxide is produced The sources of air pollutants are from incomplete burning of fuels such (Fig. 18.2), power , as petrol and diesel. It is a poisonous automobile exhausts and burning of gas. It reduces the oxygen-carrying firewood and dung cakes. capacity of the blood.

Fig. 18.3 : Air pollution due to automobiles Do you know? If the vehicles registered in are lined up one after the other, the total length would be nearly equal to the combined lengths of the two longest Fig. 18.2 : Smoke from a in the world, Nile and Amazon!

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2021–22 Boojho remembers seeing a thick Activity 18.3 -like layer in the atmosphere, especially during . This is Prepare a table using the pollutants which is made up of smoke and fog. mentioned above. You may even add Smoke may contain oxides of nitrogen more data to the following Table. which combine with other air pollutants Table 18.1 and fog to form smog. The smog causes Air Pollutants Sources Effects breathing difficulties such as , and wheezing in children. Many industries are also responsible for causing air pollution. refineries are a major source of gaseous 18.3 Case Study— pollutants like sulphur dioxide and The Taj Mahal . Sulphur dioxide is Over the past 2 decades, ’s most produced by of fuels like famous tourist attraction, Taj Mahal in power plants. It can cause located in Agra (Fig. 18.4), has become respiratory problems, including a matter of concern. Experts have permanent damage. You have warned that pollutants in air are already studied about the burning of discolouring its white marble. So, it is fossil fuels in Chapter 5. not only living organisms that get Other kinds of pollutants are affected by polluted air but non-living (CFCs) which are things like buildings, monuments and used in refrigerators, air conditioners statues also get affected. and sprays. CFCs damage the The industries located in and around of the atmosphere. Recall Agra like rubber processing, automobile, that the ozone layer protects us from chemicals and especially the Mathura harmful rays of the sun. Have refinery, have been responsible for you heard of the ozone hole? Try to find producing pollutants like sulphur out about it. Thankfully, less harmful dioxide and nitrogen dioxide. These chemicals are now being used in place gases react with the water vapour present of CFCs. in the atmosphere to form sulphuric In addition to the above mentioned and nitric acid. The drop down with gases, automobiles which burn diesel , making the rain acidic. This is and petrol, also produce tiny called . Acid rain corrodes the which remain suspended in air for long marble of the monument. The periods (Fig. 18.3). They reduce phenomenon is also called “Marble . When inhaled, they cause ”. Suspended particulate matter, diseases. Such particles are also such as the particles emitted by produced during industrial processes Mathura oil refinery, has contributed like steel making and . Power towards the yellowing of the marble. plants give out tiny ash particles which The Supreme Court has taken also pollute the atmosphere. several steps to save the Taj. It has

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2021–22 Fig. 18.4 : Taj Mahal ordered industries to switch to cleaner and a part is reflected back into space. fuels like CNG (Compressed ) A part of the reflected is and LPG (). trapped by the atmosphere. The trapped Moreover, the automobiles should further warm the . If you switch over to unleaded petrol in the Taj have seen a greenhouse in a nursery or zone. elsewhere, recall that the sun’s heat is Discuss with your elders and see allowed to get in but is not allowed to what they have to say about the go out. The trapped heat warms the condition of the Taj, 20 or 30 years ago! green house. The trapping of radiations Try to procure a picture of the Taj Mahal by the earth’s atmosphere is similar. for your book. That is why it is called the . Without this process, would not have been possible on the earth. But

now it threatens life. Excess of CO2 in I am reminded of the the air is one of the gases responsible chapter on crops. I for this effect.

wonder whether acid rain You know that CO2 is one of the affects the and components of air. You have also studied plants also.

18.4 Greenhouse Effect But how does CO content You know that the sun’s rays warm the 2 rise in the atmosphere and earth’s surface. A part of the radiation become excessive? that falls on the earth is absorbed by it

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2021–22 the role of carbon dioxide in plants. But towards this effect. Like CO2, they are if there is excess of CO2 in the air, it also called greenhouse gases. acts as a . Global warming has become a major Can you help Paheli find out the concern for governments worldwide. answer to her question? Many countries have reached an

On the one hand, CO2 is continuously agreement to reduce the emission of being released because of human greenhouse gases. The activities. On the other hand, area under is one such agreement. is decreasing. Plants utilise CO2 Boojho is surprised to hear that an from the atmosphere for , increase in the earth’s temperature by thereby decreasing the amount of CO2 even as little as 0.5 °C can have such a in the air. Deforestation to an serious effect! Paheli tells him that she increase in the amount of CO2 in the air had read in the newspapers recently that because the number of trees which the Gangotri in the Himalayas consume CO2 is reduced. Human has started melting because of global activities, thus, contribute to the warming. accumulation of CO2 in the atmosphere.

CO2 traps heat and does not allow it to 18.5 What can be Done? escape into space. As a result, the average What can we do to reduce air temperature of the earth’s atmosphere pollution? is gradually increasing. This is called There are many success stories in our global warming. fight against air pollution. For example, Other gases like methane, nitrous a few years ago, Delhi was one of the and water vapour also contribute most polluted cities in the world. It was being choked by fumes released from Global Warming automobiles running on diesel and A Serious Threat! petrol. A decision was taken to switch Global warming can cause sea levels to fuels like CNG (Fig. 18.5) and to rise dramatically. In many places, coastal areas have already been flooded. Global warming could result in wide ranging effects on rainfall patterns, , forests, plants and . Majority of people living in which are threatened by global warming are in Asia. A recent change report gives us only a limited time to keep the greenhouse gases at the present level. Otherwise, the temperature may rise by more than 2 degrees Celsius by the end of the century, a level considered dangerous. Fig. 18.5 : A public bus powered by CNG

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2021–22 unleaded petrol. These measures have fuels for our requirements. These resulted in cleaner air for the city. You could be , and might know of some other examples energy. from your area regarding reduction of air pollution. Share these with your Activity 18.4 friends. You have various options of to your school such as Do you know about the “Say no to walking, going by bicycle, travelling crackers” campaign which was by bus or other , organised by children from many schools? This made a big difference using a individually, travelling to the air pollution levels around by car pool. Discuss in your class Diwali. the impact of each of these options on the quality of air. The quality of air at various locations is monitored regularly by government Small contributions on our part can and other agencies. We can use this data make a huge difference in the state of to generate awareness about air the environment. We can trees and pollution among friends and nurture the ones already present in the neighbours. neighbourhood. Do you know about Van There is a need to switch over to Mahotsav, when lakhs of trees are alternative fuels instead of the fossil planted in July every year (Fig. 18.6)?

Fig. 18.6 : Children planting saplings

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2021–22 Boojho and Paheli once happened to Activity 18.5 go to an area where some people were burning dry leaves. They started Try to collect samples of water from a tap, pond, , well and . coughing because the entire area was full Pour each into separate glass of smoke. Paheli thought it would be a containers. Compare these for better option to put them in a smell, acidity and colour. Complete pit rather than burning. What do you the following Table. think? Table 18.2 18.6 Water Pollution Smell Acidity Colour In Class VII you learnt that water is a Tap Water precious . Think and list the various activities in which we need Pond Water water. We saw that water is becoming River Water scarce due to increase in population, Well Water industries and agricultural activities. You have also studied how water Lake Water becomes “dirty” after we use it for washing clothes, bathing, etc. This 18.7 How does Water Get means that we are adding some Polluted? materials to the water, which spoil its quality and change its smell and colour. Case Study Whenever harmful substances such Ganga is one of the most famous rivers as , toxic chemicals, , etc., get of India (Fig. 18.7). It sustains most of mixed with water, the water becomes the northern, central and eastern polluted. The substances that pollute Indian population. Millions of people water are called water pollutants. depend on it for their daily needs and

Gomukh Gangotri Haridwar

NEW UTTRAKHAND DELHI UTT NEPAL BHUTAN AR PRADESH BIHAR BANGLADESH WEST BENGAL

INDIA Kolkata

Bay of Bengal Fig. 18.7 : Course of the river Ganga

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2021–22 livelihood. However, recently a study by People can be seen bathing, washing the World Wide Fund for Nature (WWF) clothes and defecating in the river. found that Ganga is one of the ten most They also throw , flowers, endangered rivers in the world. The idols of gods and goddesses and non- pollution levels have been rising for biodegradable polythene bags into the many years. We have reached this stage river. because the towns and cities, through At Kanpur the amount of water is which the river flows, throw large comparatively small and the flow of the quantities of garbage, untreated sewage, river is very slow. In addition, Kanpur dead bodies, and many other harmful has more than 5000 industries. These things, directly into the river. In fact the include fertiliser, detergent, leather and river is ‘dead’ at many places where the industries. These industrial units pollution levels are so high that aquatic toxic chemical into the life cannot survive. river. An ambitious plan to save the river, Based on the above information called the Ganga Action Plan was think of the answers to the following launched in 1985. It aimed to reduce questions – the pollution levels in the river. However, l What are the factors responsible for the increasing population and pollution of the river ? have already damaged l What steps can be taken to restore this mighty river beyond repair. Now, the the river Ganga to its past glory ? Government of India has launched a new l How would the disposal of garbage, initiative known as National Mission for etc., affect the living organisms in the Clean Ganga (NMCG) in 2016. river ? Let us take a specific example to understand the situation. The Ganga Many industries discharge harmful at Kanpur in Uttar Pradesh (U.P.), has chemicals into rivers and streams, one of the most polluted stretches of causing the pollution of water the river (Fig. 18.8). Kanpur is one of (Fig. 18.9). Examples are oil refineries, the most populated towns in U.P. paper factories, textile and sugar mills

Fig. 18.8 : A polluted stretch of the river Fig. 18.9 : Industrial discharged into Ganga a river

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2021–22 and chemical factories. These industries food wastes, detergents, microor- cause chemical of water. ganisms, etc. Can ground water get The chemicals released include arsenic, polluted by sewage? How? Water and fluorides which lead to contaminated with sewage may contain in plants and animals. There are bacteria, viruses, fungi and parasites to prevent this. Industries which cause diseases like , are supposed to treat the waste typhoid and jaundice. produced before discharging it into The bacteria present in the faeces , but quite often the rules are not of mammals are indicators of the followed. The soil is also affected by quality of water. If water has these impure water, causing changes in bacteria, it means that it has been acidity, growth of worms, etc. contaminated by fecal matter. If such We have learnt in Chapter 1 the water is used by us, it can cause various importance of and weedicides infections. for the protection of crops. However, all these chemicals dissolve in water and Do you know? are washed into water bodies from the Hot water can also be a pollutant ! fields. They also seep into the ground This is usually water from power to pollute ground water. plants and industries. It is released Have you seen ponds which look into the rivers. It raises the green from a distance because they have temperature of the waterbody, a lot of algae growing in them? This is adversely affecting the animals and caused by excessive quantities of plants living in it. chemicals which get washed from the fields. These act as for algae 18.8 What is Potable Water to flourish. Once these algae die, they and How is Water serve as food for decomposers like Purified ? bacteria. A lot of oxygen in the water body gets used up. This results in a decrease in the oxygen level which may Activity 18.7 kill aquatic organisms. Let us construct a water filter with Recall Activity 18.6 simple, everyday materials. Take a plastic bottle and cut it You had investigated the sewage into 2 halves at the centre. Use the disposal system of your locality in upper half as a funnel by putting it Class VII. upside down in the lower half. Make Do you remember how the layers in it with paper napkin or a sewage was collected from your fine cloth followed by, cotton, sand home and where it went thereafter? and then gravel. Now pour dirty water through the filter and observe Sometimes untreated sewage is thrown directly into rivers. It contains the filtered water.

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2021–22 water. Boiling kills the germs present Discuss the following questions in the water. amongst yourselves and with your l Chlorination is a commonly used teacher: chemical method for purifying water. l Why do we need to filter water It is done by adding tablets before drinking ? or bleaching powder to the water. We l Where do you get your drinking must be cautious. We should not water from? use more chlorine tablets than l What will happen if we drink specified. polluted water? 18.9 What Can be Done? Boojho is very upset. He tells Paheli that he drank water which looked clear Activity 18.8 and was without any smell, but still he Investigate the level of awareness fell sick ! about water pollution in your area. Paheli explains that water which Collect data on the sources of looks clean may still have disease- and the methods of carrying and dissolved sewage disposal. impurities. So, it is essential to purify What are the common water-borne water before drinking, for example, by diseases in the community? You can boiling. consult your local doctor/ Water which is suitable for drinking worker for this. is called potable water. You have seen Which are the governmental and how various physical and chemical non-governmental organisations processes in the working in this field? What are the plants help to clean water before measures being taken by them for discharging it into water bodies. generating awareness? Similarly, municipal bodies treat the water before supplying it to households. Laws for industrial units should be Do you know? strictly implemented so that polluted water is not disposed off directly into 25% of the world’s population is without safe drinking water ! rivers and . plants should be installed in all industrial Let us see how water can be made areas (Fig. 18.10). At our individual safe for drinking: levels we should consciously save water l You have already seen how water is and not waste it. Reduce, reuse and filtered. This is a physical method of recycle should be our mantra ! removing impurities. A popular Think of your daily routine – how filter is a candle type can you save water? filter. We can think of creative ideas like l Many households use boiling as a reusing water used for washing and for method for obtaining safe drinking other household tasks. For example,

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2021–22 Fig. 18.10 : Water treatment plant water used for washing vegetables may of our daily lives. Unless we all realise be used to water plants in the . our responsibility and start using Pollution is no longer a distant environment-friendly processes, the very phenomenon. It is affecting the quality survival of our planet is in danger.

Do you know? While brushing your teeth, leaving the tap running may waste several litres of water. A tap that drips once every second wastes a few thousand litres of water every year. Think about it !

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2021–22 KEYWORDS WHAT YOU HAHAOU VE LEARNT AIR POLLUTION Ü Air pollution is the contamination of air by

CHEMICAL impurities which may have a harmful impact CONTAMINATION on the living organisms and the non-living components. GLOBAL WARMING Ü Pollutants are the substances which contaminate air and water. GREENHOUSE Ü Carbon monoxide, nitrogen oxides, carbon EFFECT dioxide, methane and sulphur dioxide are the POLLUTANTS major pollutants of air. Ü Increasing levels of greenhouse gases like CO POTABLE WATER 2 are leading to global warming. WATER POLLUTION Ü Water pollution is the contamination of water by substances harmful to life. Ü Sewage, agricultural chemicals and are some of the major contaminants of water. Ü Water which is purified and fit for drinking is known as potable water. Ü Water is a precious . We must learn to conserve it.

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 ?

(a) Carbon dioxide (b) Sulphur dioxide

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2021–22 (c) Methane (d Nitrogen

8. Describe the ‘Green House Effect’ in your own words. 9. Prepare a brief speech on global warming. You have to deliver the speech in your class.

10. Describe the threat to the beauty of the Taj Mahal. E X R C I S 11. Why does the increased level of nutrients in the water affect the survival of aquatic organisms?

Extended Learning — Activities and Projects

1. In some cities, a pollution check has been made compulsory for vehicles. Visit a petrol pump in order to learn about the process of conducting a pollution check. You may systematically record your findings in the following areas:

l Average number of vehicles checked per month.

l Time taken to check each vehicle.

l Pollutants checked for.

l The process of testing.

l Permissible levels of emission of various gases.

l Measures taken if the emitted gases are above the permissible limits.

l How frequently is a pollution check required ?

2. Conduct a survey in your school to investigate various environment related activities that have been undertaken. The class can divide itself into two groups, with each group looking at a different area. For example, one group can find out whether there is an environment club in the school. What are its objectives ? What is its calendar of events ? How can you become a member ?

If your school does not have such a club, you even think of starting one along with a few of your friends. 3. Organise a field visit to a river in or around your town with the help of your teachers.

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2021–22 Observations followed by discussion could focus on

l the history of the river.

l cultural traditions.

l role of the river in meeting the town’s water needs.

l pollution concerns.

l sources of pollution.

l effects of pollution on the people living by the riverside as well as those living far away. 4. Find out with the help of your teachers and the internet (if possible), whether there are any international agreements to control global warming. Which are the gases covered under these agreements?

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2021–22