Pollution of Air and Water
Welcome to HSLC Guru! In this lesson on Class 8 General Science Chapter 9, you will study how human activities pollute the air we breathe and the water we drink. Following the ASSEB syllabus, this English-medium guide explains the sources, pollutants, harmful effects, and control measures for air and water pollution, along with complete textbook question answers, additional MCQs, fill in the blanks, true or false statements, and a glossary to help you score full marks.
Chapter Summary
Air Pollution: The contamination of air by harmful substances is called air pollution. Major sources include exhaust from vehicles (cars, buses, trucks), smoke from factories and thermal power plants, burning of fossil fuels like coal, petrol, diesel and wood, oil refineries, and brick kilns. The chief air pollutants are oxides of sulphur (SOx), oxides of nitrogen (NOx), oxides of carbon (COx — carbon monoxide and carbon dioxide), smog, suspended particulate matter (SPM), and chlorofluorocarbons (CFCs) released from refrigerators and aerosol sprays.
Effects of Air Pollution: Polluted air causes serious respiratory diseases such as asthma, bronchitis and lung cancer. SOx and NOx dissolve in rain water to form acid rain, which damages plants, soil, buildings and historical monuments — the white marble of the Taj Mahal at Agra is gradually turning yellow due to acid rain and SPM, a problem known as the “Marble Cancer”. Carbon dioxide traps the heat of the Sun causing the greenhouse effect, leading to global warming, melting of glaciers and rise in sea level. CFCs damage the protective ozone layer of the atmosphere, allowing harmful UV rays to reach the Earth. Air pollution can be controlled by using clean fuels like CNG and LPG, switching to public transport, using catalytic converters, planting more trees, and shifting to renewable sources of energy.
Water Pollution: The contamination of water by harmful substances is called water pollution. Sources of water pollution include domestic sewage, industrial wastes from factories, agricultural run-off containing fertilisers and pesticides, oil spills from tankers in seas and oceans, and disposal of garbage and dead bodies in rivers. Water pollutants are classified as chemical (pesticides, heavy metals like mercury and lead), biological/organic (bacteria, sewage, animal waste), and physical (heat, silt). The river Ganga, considered holy in India, is one of the ten most polluted rivers in the world.
Effects and Control: Polluted water spreads water-borne diseases such as cholera, typhoid, jaundice and diarrhoea. Excessive nutrients from fertilisers cause rapid growth of algae in water bodies — this phenomenon is called eutrophication, which kills aquatic animals due to lack of oxygen. Water that is fit for drinking is called potable water; it can be made safe by filtration, boiling, distillation, and chlorination (adding chlorine tablets). To save the river Ganga, the Government of India launched the Ganga Action Plan in 1985. Every citizen should adopt the 3 Rs — Reduce, Reuse and Recycle — to keep our environment clean.
Textbook Questions and Answers
Very Short Answer Questions (1 Mark)
Q1. What is air pollution?
Answer: The contamination of air by harmful substances such as gases, smoke and dust which adversely affect living beings is called air pollution.
Q2. Name two gases responsible for acid rain.
Answer: Sulphur dioxide (SO2) and nitrogen dioxide (NO2) are responsible for acid rain.
Q3. What is potable water?
Answer: Water that is fit for drinking and free from harmful impurities is called potable water.
Q4. Expand CNG and CFC.
Answer: CNG stands for Compressed Natural Gas and CFC stands for Chlorofluorocarbon.
Q5. Which monument is being damaged by acid rain?
Answer: The Taj Mahal at Agra is being damaged by acid rain — its white marble is turning yellow, a problem called Marble Cancer.
Q6. Name one greenhouse gas.
Answer: Carbon dioxide (CO2) is the major greenhouse gas. Methane and water vapour are also greenhouse gases.
Q7. What is global warming?
Answer: The gradual increase in the average temperature of the Earth’s atmosphere due to the greenhouse effect is called global warming.
Q8. Name the action plan launched to clean the river Ganga.
Answer: The Ganga Action Plan was launched in 1985 by the Government of India to reduce pollution in the river Ganga.
Q9. Which gas damages the ozone layer?
Answer: Chlorofluorocarbons (CFCs) released from refrigerators, air conditioners and aerosol sprays damage the ozone layer.
Q10. What is eutrophication?
Answer: Excessive growth of algae in water bodies due to nutrients from fertilisers, which depletes oxygen and kills aquatic life, is called eutrophication.
Short Answer Questions (2-3 Marks)
Q1. Mention four major sources of air pollution.
Answer: Four major sources of air pollution are: (i) exhaust gases from vehicles like cars, buses and trucks, (ii) smoke released from factories and thermal power plants, (iii) burning of fossil fuels such as coal, petrol, diesel and wood, and (iv) oil refineries and brick kilns. Forest fires and volcanic eruptions are natural sources of air pollution.
Q2. What is acid rain? How is it formed?
Answer: Rain water containing dissolved acids such as sulphuric acid and nitric acid is called acid rain. When sulphur dioxide and nitrogen oxides released from factories and vehicles mix with water vapour in the atmosphere, they form sulphuric and nitric acids which fall back to the Earth as acid rain. It damages plants, soil, aquatic life and historical monuments like the Taj Mahal.
Q3. Explain the greenhouse effect.
Answer: The trapping of the Sun’s heat by greenhouse gases like carbon dioxide, methane and water vapour in the atmosphere is called the greenhouse effect. These gases allow sunlight to enter the Earth but prevent the heat from escaping back into space, just like the glass walls of a greenhouse. This raises the temperature of the Earth and is responsible for global warming.
Q4. Why is the Taj Mahal turning yellow?
Answer: The Taj Mahal is built of white marble (calcium carbonate). Acid rain and suspended particulate matter from nearby industries, refineries and vehicles react with the marble and corrode it, turning the white surface yellow. This deterioration is known as “Marble Cancer”. To protect the Taj Mahal, the Supreme Court has ordered industries around Agra to switch to cleaner fuels.
Q5. List four sources of water pollution.
Answer: Four sources of water pollution are: (i) domestic sewage and garbage from houses, (ii) industrial waste discharged by factories containing harmful chemicals and heavy metals, (iii) agricultural run-off carrying fertilisers and pesticides into rivers, and (iv) oil spills from ships and tankers in seas and oceans.
Q6. What is meant by 3 Rs? How do they help reduce pollution?
Answer: The 3 Rs stand for Reduce, Reuse and Recycle. Reduce means using less of natural resources such as water and electricity. Reuse means using items like bottles and plastic bags more than once. Recycle means converting waste materials such as paper, glass and metal into new products. Practising the 3 Rs reduces waste, saves resources and helps in keeping the environment clean.
Long Answer Questions (5-6 Marks)
Q1. Describe the major air pollutants and their harmful effects on human health and the environment.
Answer: The major air pollutants are: (i) Oxides of sulphur (SOx) released from burning of coal in factories — they cause respiratory problems and acid rain. (ii) Oxides of nitrogen (NOx) released from vehicles — they cause smog and acid rain. (iii) Carbon monoxide (CO), an extremely poisonous gas from incomplete burning of petrol/diesel, reduces the oxygen-carrying capacity of blood and can cause death. (iv) Carbon dioxide (CO2) increases the greenhouse effect and global warming. (v) Suspended particulate matter (SPM) like dust, smoke and ash causes asthma, bronchitis and lung diseases. (vi) Chlorofluorocarbons (CFCs) from refrigerators damage the ozone layer. These pollutants together cause respiratory diseases, eye irritation, acid rain damage to monuments, global warming and depletion of the ozone layer.
Q2. What measures can be taken to control air pollution?
Answer: Air pollution can be controlled by the following measures: (i) Use of clean fuels such as Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG) in vehicles instead of petrol and diesel. (ii) Encouraging people to use public transport, bicycles or to walk for short distances. (iii) Fitting catalytic converters in vehicles to convert harmful gases into less harmful ones. (iv) Installing tall chimneys with filters and electrostatic precipitators in factories. (v) Planting more trees, as plants absorb carbon dioxide and release oxygen. (vi) Using renewable sources of energy like solar, wind and hydroelectric power instead of fossil fuels. (vii) Avoiding burning of dry leaves, garbage, crackers, etc. (viii) Spreading awareness about air pollution among citizens.
Q3. Explain water pollution, its causes, harmful effects, and methods of purification of water.
Answer: The contamination of water bodies by harmful substances making the water unfit for use is called water pollution. Causes: Discharge of untreated sewage, industrial effluents containing heavy metals (mercury, lead, arsenic), agricultural run-off carrying fertilisers and pesticides, oil spills, and dumping of garbage and dead bodies into rivers. Effects: Polluted water causes water-borne diseases like cholera, typhoid, jaundice, diarrhoea and dysentery. It causes eutrophication, kills fish and aquatic plants, and disturbs the food chain. Heavy metals enter the human body through fish and cause long-term illness. Purification methods: (i) Filtration using a clean cloth or candle filter to remove visible impurities. (ii) Boiling water for at least 10 minutes to kill germs. (iii) Chlorination by adding chlorine tablets or bleaching powder to disinfect water. (iv) Distillation for the purest form of water. (v) Modern purifiers using UV rays and reverse osmosis (RO).
Q4. What is the Ganga Action Plan? Why was it launched?
Answer: The Ganga Action Plan (GAP) is a project launched by the Government of India in the year 1985 to reduce pollution and improve the water quality of the river Ganga. It was launched because the Ganga, considered a sacred river by Hindus, had become one of the ten most polluted rivers in the world due to dumping of sewage from cities like Kanpur, Varanasi, Allahabad and Patna, discharge of industrial waste from tanneries and chemical factories, immersion of half-burnt dead bodies, and disposal of religious offerings in the river. Under GAP, sewage treatment plants have been set up, public awareness campaigns are organised, and laws are enforced against industrial pollution. Later, the project was expanded as Namami Gange to cover the entire river basin.
Q5. Differentiate between air pollution and water pollution with examples of pollutants and effects.
Answer: Air pollution is the contamination of air by harmful gases and particles, while water pollution is the contamination of water bodies by harmful substances. Air pollutants include SOx, NOx, COx, CFCs, smog and SPM; water pollutants include sewage, pesticides, heavy metals, oil and detergents. Air pollution causes respiratory diseases, acid rain, greenhouse effect and ozone depletion; water pollution causes cholera, typhoid, jaundice and eutrophication. Sources of air pollution are vehicles, factories and burning of fuels; sources of water pollution are sewage, industries, agricultural run-off and oil spills. Both can be controlled by using clean technology, treating waste, and creating public awareness.
Additional Questions
Multiple Choice Questions (MCQs)
Q1. Which of the following is a clean fuel?
(a) Petrol (b) Diesel (c) CNG (d) Coal
Answer: (c) CNG
Q2. The gas chiefly responsible for global warming is —
(a) Oxygen (b) Carbon dioxide (c) Nitrogen (d) Hydrogen
Answer: (b) Carbon dioxide
Q3. Acid rain is caused by —
(a) CO and CO2 (b) SO2 and NO2 (c) CFC (d) Methane
Answer: (b) SO2 and NO2
Q4. Marble Cancer affects —
(a) Red Fort (b) Qutub Minar (c) Taj Mahal (d) India Gate
Answer: (c) Taj Mahal
Q5. The ozone layer is depleted by —
(a) CO2 (b) CFC (c) SO2 (d) NO2
Answer: (b) CFC
Q6. Ganga Action Plan was launched in —
(a) 1975 (b) 1985 (c) 1995 (d) 2005
Answer: (b) 1985
Q7. Water fit for drinking is called —
(a) Hard water (b) Heavy water (c) Potable water (d) Distilled water
Answer: (c) Potable water
Q8. Excessive growth of algae in water bodies is called —
(a) Photosynthesis (b) Eutrophication (c) Filtration (d) Distillation
Answer: (b) Eutrophication
Q9. Which one is not a greenhouse gas?
(a) CO2 (b) Methane (c) Oxygen (d) Water vapour
Answer: (c) Oxygen
Q10. Boiling water kills —
(a) Salts (b) Germs (c) Heavy metals (d) Pesticides
Answer: (b) Germs
Q11. Which disease is caused by drinking polluted water?
(a) Asthma (b) Cholera (c) Bronchitis (d) Cancer
Answer: (b) Cholera
Q12. The most polluted river in India that needed an action plan is —
(a) Yamuna (b) Brahmaputra (c) Ganga (d) Godavari
Answer: (c) Ganga
Fill in the Blanks
Q1. _________ rain damages the marble of the Taj Mahal.
Answer: Acid
Q2. CNG stands for _________ Natural Gas.
Answer: Compressed
Q3. The gradual rise in Earth’s temperature is called global _________.
Answer: Warming
Q4. The 3 Rs are Reduce, Reuse and _________.
Answer: Recycle
Q5. Adding chlorine tablets to water is called _________.
Answer: Chlorination
Q6. _________ are used in refrigerators and damage the ozone layer.
Answer: CFCs
True or False
Q1. Carbon monoxide is a poisonous gas.
Answer: True
Q2. CFC is used in fire extinguishers only.
Answer: False (CFCs are used in refrigerators, air conditioners and aerosol sprays.)
Q3. Plants help in reducing air pollution.
Answer: True
Q4. Sewage water is safe for drinking.
Answer: False (Sewage water contains harmful germs and must be treated.)
Q5. Ganga is one of the most polluted rivers in the world.
Answer: True
Q6. Carbon dioxide does not contribute to the greenhouse effect.
Answer: False (Carbon dioxide is the main greenhouse gas.)
Q7. Filtration removes germs from water completely.
Answer: False (Filtration removes only solid impurities; boiling or chlorination is needed to kill germs.)
Glossary
| Term | Meaning |
|---|---|
| Air Pollution | Contamination of air by harmful substances like gases, smoke and dust. |
| Pollutant | A substance that contaminates air, water or soil. |
| SPM | Suspended Particulate Matter — fine dust and ash particles in air. |
| CFC | Chlorofluorocarbon — gas that depletes the ozone layer. |
| Smog | A mixture of smoke and fog seen in polluted cities. |
| Acid Rain | Rain water containing dissolved sulphuric and nitric acids. |
| Greenhouse Effect | Trapping of Sun’s heat by gases like CO2 in the atmosphere. |
| Global Warming | Rise in average temperature of Earth due to greenhouse effect. |
| Ozone Layer | Layer in stratosphere that blocks harmful UV rays from the Sun. |
| CNG | Compressed Natural Gas — a clean fuel used in vehicles. |
| Water Pollution | Contamination of water bodies by harmful substances. |
| Sewage | Waste water from houses containing organic and human waste. |
| Potable Water | Water that is safe and fit for drinking. |
| Eutrophication | Excessive growth of algae in water due to nutrients, killing fish. |
| Chlorination | Adding chlorine to water to kill germs. |
| Filtration | Process of removing solid impurities from water using a filter. |
| Ganga Action Plan | Project launched in 1985 to reduce pollution of river Ganga. |
| 3 Rs | Reduce, Reuse and Recycle — principles to save environment. |
| Marble Cancer | Yellowing and corrosion of Taj Mahal’s marble due to acid rain. |
| Renewable Energy | Energy from sources that do not get exhausted, like solar and wind. |