POLLUTION OF AIR AND WATER aheli and Boojho were very excited You already know that air consists to know that Taj Mahal in Agra of a mixture of gases. By volume, about Pis one of the seven wonders of 78% of this mixture is nitrogen and the world. But they were disappointed about 21% is oxygen. Carbon dioxide, to hear that the beauty of this argon, methane, ozone and water monument in white marble is being vapour are also present in very small threatened by air pollution 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 water pollution. 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. smoke or started coughing while Our elders talk about the clean water walking on a busy road (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 lives. The l A park and a busy road. number of people suffering from diseases l A residential area and an of the respiratory system, 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 food, 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 city 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 atmosphere. 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 households 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 pollutants 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 cities? sources like smoke and dust arising from Vehicles produce high levels of forest fires or volcanic eruptions. pollutants like carbon monoxide, carbon Pollutants are also added to the dioxide, nitrogen oxides and smoke (Fig. atmosphere by certain human activities. 18.3). Carbon monoxide is produced The sources of air pollutants are from incomplete burning of fuels such factories (Fig. 18.2), power plants, 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 Delhi 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 factory rivers in the world, Nile and Amazon! 240 SCIENCE 2021–22 Boojho remembers seeing a thick Activity 18.3 fog-like layer in the atmosphere, especially during winters. This is smog 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 asthma, cough and wheezing in children. Many industries are also responsible for causing air pollution. Petroleum refineries are a major source of gaseous 18.3 Case Study— pollutants like sulphur dioxide and The Taj Mahal nitrogen dioxide. Sulphur dioxide is Over the past 2 decades, India’s most produced by combustion of fuels like famous tourist attraction, Taj Mahal coal in power plants. It can cause located in Agra (Fig. 18.4), has become respiratory problems, including a matter of concern. Experts have permanent lung 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 chlorofluorocarbons (CFCs) which are things like buildings, monuments and used in refrigerators, air conditioners statues also get affected. and aerosol sprays. CFCs damage the The industries located in and around ozone layer of the atmosphere. Recall Agra like rubber processing, automobile, that the ozone layer protects us from chemicals and especially the Mathura oil harmful ultraviolet 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 acid In addition to the above mentioned and nitric acid. The acids drop down with gases, automobiles which burn diesel rain, making the rain acidic. This is and petrol, also produce tiny particles called acid rain. 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 visibility. When inhaled, they cause cancer”. Suspended particulate matter, diseases. Such particles are also such as the soot particles emitted by produced during industrial processes Mathura oil refinery, has contributed like steel making and mining. 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 POLLUTION OF AIR AND WATER 241 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 Natural Gas) A part of the reflected radiation is and LPG (Liquefied Petroleum Gas). trapped by the atmosphere. The trapped Moreover, the automobiles should radiations further warm the earth. 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 scrap book. That is why it is called the greenhouse effect. Without this process, life 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 soil 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 242 SCIENCE 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 pollutant. 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 Kyoto Protocol activities. On the other hand, area under is one such agreement. forests is decreasing. Plants utilise CO2 Boojho is surprised to hear that an from the atmosphere for photosynthesis, 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 leads 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 glacier 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.