WHAT IS AIR POLLUTION?

WHAT IS 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. 

You already know that air consists of a mixture of gases. By volume, about 78% of this mixture is nitrogen and about 21% is oxygen. Carbon dioxide, argon, methane, ozone and water vapour are also present in very small quantities.

Activity 18.1:

You may have covered your nose while passing a brick kiln emitting smoke or started coughing while walking on a busy road (Fig. 18.1).

Figure 18.1: A congested road in a city

On the basis of your experience, compare the quality of air at the places given below:

*   A park and a busy road.

*   A residential area and an industrial area.

*   A busy traffic intersection at different times of the day e.g. early morning, afternoon and evening.

*   A village and a town.

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.

Source: This topic is taken from NCERT TEXTBOOK

HOW DOES AIR GET POLLUTED?

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 certain human activities. The sources of air pollutants are factories (Fig.18.2), power plants, automobile exhausts, and the burning of firewood and dung cakes.

Activity 18.2:

*  You might have read in the newspapers that respiratory problems amongst children are rising day by day.

*  Conduct a survey of households in your neighbourhood and among friends to find out how many children are suffering from respiratory problems.

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 the incomplete burning of fuels such as petrol and diesel. It is a poisonous gas. It reduces the oxygen-carrying capacity of the blood.

Figure 18.3: Air pollution due to automobiles

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 rivers in the world, Nile, and Amazon.

Boojho remembers seeing a thick fog-like layer in the atmosphere, especially during winters. This is smog 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 and nitrogen dioxide. Sulphur dioxide is produced by the 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 the 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 the air for long periods (Fig. 18.3). They reduce visibility. When inhaled, they cause diseases. Such particles are also produced during industrial processes like steelmaking 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:

Source: This topic is taken from NCERT TEXTBOOK

CASE STUDY – THE TAJ MAHAL

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 the 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 present 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 the yellowing of the marble.

Figure 18.4: Taj Mahal

The Supreme Court has taken several steps to save the Taj. It has ordered industries to switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas). Moreover, the automobiles should switch over to unleaded petrol in the Taj zone.

Discuss with your elders and see what they have to say about the condition of the Taj, 20 or 30 years ago! Try to procure a picture of the Taj Mahal for your scrapbook   

Source: This topic is taken from NCERT TEXTBOOK

GREENHOUSE EFFECT

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 and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. The trapped radiations further warm the earth. If you have seen a greenhouse in a nursery or elsewhere, recall that the sun’s heat is allowed to get in but is not allowed to go out. The trapped heat warms the greenhouse. The trapping of radiations by the earth’s atmosphere is similar. That is why it is called the greenhouse effect. Without this process, life would not have been possible on earth. But now it threatens life. Excess of CO₂ in the air is one of the gases responsible for this effect.

You know that CO₂ is one of the components of air. You have also studied 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, the 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 an increase 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.

Other gases like methane, nitrous oxide, and water vapour also contribute towards this effect. Like CO₂, they are also called greenhouse gases.

Global warming has become a major concern for governments worldwide. Many countries have reached an agreement to reduce the emission of greenhouse gases. The Kyoto Protocol is one such agreement.

Boojho is surprised to hear that an increase in the earth’s temperature by even as little as 0.5°C can have such a serious effect! Paheli tells him that she had read in the newspapers recently that the Gangotri glacier in the Himalayas has started melting because of global warming.

Global Warming A Serious Threat!

Global warming can cause sea levels to rise dramatically. In many places, coastal areas have already been flooded. Global warming could result in wide-ranging effects on rainfall patterns, agriculture, forests, plants, and animals. Majority of people living in regions which are threatened by global warming are in Asia. A recent climate 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.

Source: This topic is taken from NCERT TEXTBOOK

WHAT CAN BE DONE?

WHAT CAN BE DONE?

What can we do to reduce air pollution?

There are many success stories in our fight against air pollution. For example, a few years ago, Delhi was one of the most polluted cities in the world. It was being choked by fumes released from automobiles running on diesel and petrol. A decision was taken to switch to fuels like CNG (Fig. 18.5) and unleaded petrol. These measures have resulted in cleaner air for the city. You might know of some other examples from your area regarding the reduction of air pollution. Share these with your friends.

Figure 18.5: A public transport bus powered by CNG

Do you know about the “Say no to crackers” campaign which was organised by children from many schools? This made a big difference to the air pollution levels around Diwali.

The quality of air at various locations is monitored regularly by the government and other agencies. We can use this data to generate awareness about air pollution among friends and neighbours.

There is a need to switch over to alternative fuels instead of fossil fuels for our energy requirements. These could be solar energy, hydropower and wind energy.

Activity 18.4:

*  You have various options of commuting to your school such as walking, going by bicycle, travelling by bus or other public transport, using a car individually, travelling by carpool.

*  Discuss in your class the impact of each of these options on the quality of air.

Small contributions on our part can make a huge difference in the state of the environment. We can plant trees and nurture the ones already present in the neighbourhood. Do you know about Van Mahotsav, when lakhs of trees are planted in July every year (Fig. 18.6)?

Figure 18.6: Children planting saplings

Boojho and Paheli once happened to go to an area where some people were burning dry leaves. They started coughing because the entire area was full of smoke. Paheli thought it would be a better option to put them in a compost pit rather than burning. What do you think?

Source: This topic is taken from NCERT TEXTBOOK