Pollution of Air and Water Class 8 Notes NCERT and MCQs

23-08-2023 17:14 PM IST Priyanka Chaudhary

The chapter discusses about air and water pollution and their effects on human lives. It also discusses about the importance of clean air and water for living beings. Greenhouse effect is also covered in this section along with measures to reduce pollution.

Air Pollution

Air is very important for human survival. Air is a mixture of gases comprising Nitrogen (78% by volume), Oxygen (21%), Carbon dioxide, Argon, Methane, Ozone, and Water vapour in small quantities.

When clean air is contaminated due to the presence of unwanted substances causing harmful effects on both the living and non-living components, then it is termed air pollution.

The unwanted substances that contaminate the air are called air pollutants. Some of the air pollutants are Carbon Monoxide, Nitrogen oxides, Carbon dioxide, Smoke, CFCs, etc.

How does Air gets Polluted?

There are various causes of air pollution. Some of them are listed below:

• Natural Sources: Smoke and Dust arising from forest fires, volcanic eruptions, etc.
• Man made Sources: Factories, Power Plants, Automobile exhausts, Burning of firewood and dung cakes.

Effects of Air Pollution

Air Pollution can lead to many respiratory problems in humans. Incomplete combustion of fuels like petrol and diesel produces carbon monoxide which is a poisonous gas. Carbon Monoxide reduces the oxygen-carrying capacity of the blood.

Smog is made up of smoke and fog. The smoke may contain oxides of nitrogen that combine with other pollutants and fog to form smog. Smog leads to asthma, cough and wheezing in children.

Many gaseous pollutants like Sulphur dioxide, and nitrogen dioxide are released from petroleum refineries and thermal power plants. These pollutants can cause respiratory problems and can even damage the lungs permanently.

Chlorofluorocarbons (CFCs) used in refrigerators, air conditioners and aerosol sprays damage the ozone layer which protects us from harmful UV rays of the Sun.

Tiny particles released from the automobile exhaust and steel making and mining industries remain suspended in the air for a long duration. These are called suspended particulate matter. They reduce visibility and cause diseases if inhaled.

Case Study of Taj Mahal

Taj Mahal in Agra, one of the famous tourist destinations in India, has become a matter of concern. The white marble has discolored due to the presence of air pollutants. This shows that not only living organisms but non-living things are also affected due to air pollution.

The pollutants released by the industries located in and around Agra such as rubber processing, automobile, chemicals and Mathura oil refinery in particular have resulted in corrosion of the marble of the monument. Pollutants like Sulphur Dioxide and Nitrogen Dioxide react with the water vapour to form sulphuric acid and nitric acid. These acids drop down with rain. This is called acid rain. Acid rain destroys the marble of the monument. The phenomenon is called “marble cancer”. The suspended particulate matter has led to the yellowing of the marble.

In order to protect the monument, the Supreme Court ordered industries to move towards cleaner fuels like CNG, LPG, etc. The automobiles were ordered to switch over to unleaded petrol in the Taj zone.

Greenhouse Effect and Global Warming

The sun’s rays reaching the earth's surface are partially absorbed and partially reflected back into space. A part of the reflected radiation is trapped by the atmosphere which further warms the earth. This is called greenhouse effect as it is similar to the greenhouse in a nursery where the sun’s heat is allowed to get in but is not allowed to go out and the trapped heat warms the greenhouse. Greenhouse effect is an essential process as without it life would not have been possible on the earth. But due to the presence of gases like Carbon Dioxide, Methane, Nitrous oxide and Water vapour in excess in the air, this process has become life-threatening. These gases are called greenhouse gases.

Carbon Dioxide is continuously being released due to human activities. Plants use CO₂ for photosynthesis thereby reducing the amount of CO₂ in the atmosphere. But, due to deforestation, the area under forests is decreasing and the amount of CO₂ is increasing in the air. The accumulation of CO₂ in the atmosphere is leading to more trapping of heat. As a result, the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

Impact of global warming

Global warming has become a major concern for everyone. Climate change is one of the major impacts of global warming. It can cause sea levels to rise suddenly. Coastal areas have already been flooded. It has wide ranging effects on Agriculture, Forests, Plants and Animals.

Kyoto Protocol was signed in 1997 to reduce the emission of greenhouse gases. It came into force on 16 February 2005.

Paris Agreement is a legally binding international treaty on climate change that was adopted at COP 21 in Paris on 12 December 2015. The countries commit to reduce their emissions so as to limit global warming to below 2°C.

Measures to reduce Air Pollution

• Switching towards cleaner fuels like Compressed Natural Gas (CNG)
• Prefer public transport like metro, train, bus, or carpooling.
• Say no to crackers
• Regular monitoring of air quality at various locations
• Creating awareness among the people about the ill-effects of air pollution
• Switching over to alternative fuels instead of fossil fuels to meet energy demands
• Promoting renewable sources of energy like Solar energy, hydropower and wind energy
• Planting more and more trees
• Avoid burning of solid wastes

Water Pollution

Water is another precious resource for the existence of life on the earth. Due to the increase in population, industries and agricultural activities, water is becoming scarce. When harmful substances like toxic chemicals, silt, sewage, etc, contaminate water, it is termed water pollution. The substances that pollute water are called water pollutants.

What causes Water Pollution?

People wash clothes, bathe and even defecate in the river. Also, flowers, idols of gods and goddesses and non-biodegradable substances like plastics and polythene bags are thrown into the river. Industrial wastes, washed away fertilisers and pesticides, and toxic chemicals like arsenic, lead and fluorides are directly discharged into the river.

Apart from this, hot water discharged from the power plants and industries into the river raises the temperature of the waterbody, adversely affecting marine life.

Case Study of Ganga

Ganga is one of the major rivers of India. Most of the northern, central and eastern population of India depends on the river Ganga for their daily requirements. But, human activities like littering garbage, untreated sewage, and dead bodies directly into the river have led to the degradation of quality of water in river Ganga. A study by WWF found that Ganga is among the ten most endangered rivers in the world.

Ganga Action Plan was launched by the government in 1985 to reduce the pollution levels and conserve the river. Rising population and industrialization have damaged the Ganga river beyond repair. Ganga at Kanpur in UP is one of the most polluted stretches of the river.

Impact of Water Pollution

Chemicals are directly released by oil refineries, textile and sugar mills, and chemical factories into the river. These chemicals lead to toxicity in plants and animals.

Polluted water causes changes in the acidity of soil, growth of worms, etc. The chemical fertilisers and pesticides used for the protection of crops dissolve in water and seep into the ground and pollute the ground water.

The excessive quantities of chemicals in water act as nutrients for algae leading to algal bloom. When these algae die, they act as food for decomposers like bacteria which leads to the consumption of a lot of oxygen, thereby reducing the oxygen level which may kill aquatic organisms.

Untreated sewage discharged into the water may contain bacteria, viruses, fungi and parasites which cause diseases like cholera, typhoid, jaundice, etc.

Potable Water

Water that is suitable for drinking purposes is called potable water. Water can be made safe for drinking by the following methods:

1. Physical method: Take a plastic bottle and cut it into 2 halves at the centre. Use the upper half as a funnel by putting it upside down in the lower half. Make layers in it with paper napkin or a fine cloth followed by, cotton, sand and then gravel. Now pour dirty water through the filter and after some time you will get filtered water.

2. Boiling method: Boiling impure water kills the germs present in the water.

3. Chemical method: Chlorination is a widely used method for purifying water. Chlorine tablets or bleaching powder is added to the impure water in specified quantity.

Measures to reduce Water Pollution

• Strict implementation of laws for industrial units regarding treating of waste before discharging into rivers.
• Installation of water treatment plants in all industrial areas.
• Installation of Sewage Treatment Plants
• Judicious use of water- Reduce, Reuse and Recycle. Water used for washing vegetables can be used to water plants in the garden.
• Regular monitoring of water quality at various locations
• Creating awareness among the people about the ill effects of water pollution

MCQs based on NCERT Class 8 Science Chapter 18:Pollution of Air and Water

1. Which of the following is NOT a greenhouse gas?

a. Carbon dioxide

b. Sulphur dioxide

c. Methane

d. Nitrogen

Ans. d

Explanation:

The gases that lead to the phenomenon of greenhouse effect are called greenhouse gases. Examples: Carbon Dioxide, Sulphur Dioxide, Methane, Water Vapour, etc.

2. Which of the following air pollutant reduces the oxygen-carrying capacity of the blood?

a. Carbon monoxide

b. Carbon dioxide

c. Nitrogen dioxide

d. Sulphur dioxide

Ans. a

Explanation:

Carbon monoxide is a poisonous gas that reduces the oxygen carrying capacity of the blood.