Pollution of Air and Water – Study module with Revision Notes

These CBSE Class 8 Science – Chapter Wise Study Materials Based on NCERT are specially designed to help you understand every concept of Chapter 18: Pollution of Air and Water in a simple and systematic way. The study module strictly follows the NCERT textbook and is ideal for CBSE Class 8 board exam standard preparation.

Introduction – Pollution of Air and Water

Our environment provides us with basic necessities of life such as air and water. For healthy living, both air and water must be clean and pure. However, due to careless human activities, the quality of air and water is getting spoiled. When harmful substances are added to air or water, they make them impure and unsafe for living beings. This unwanted change is called pollution.

In this chapter, you will learn about:

• What is air pollution and water pollution?
• Major causes and harmful effects of pollution.
• Methods to control and prevent pollution.
• How you, as a student, can contribute to a cleaner environment.

What is Air Pollution?

Air pollution is the presence of harmful and unwanted substances in the air that can harm humans, animals, plants and materials. These harmful substances are called air pollutants. When their concentration increases beyond a safe limit, the air becomes polluted.

The atmosphere of Earth contains mainly nitrogen, oxygen, carbon dioxide, water vapour and some other gases. In pure air, these gases are present in a fixed proportion. Pollution changes this proportion and adds dust, smoke and other harmful gases.

Major Air Pollutants and Their Sources

Important air pollutants and their common sources are:

• Carbon monoxide (CO): Produced by incomplete burning of fuels in vehicles and industries.
• Carbon dioxide (CO₂): Released during respiration, burning of fuels, deforestation and industries.
• Sulphur dioxide (SO₂): Produced by burning coal and oil in power plants and factories.
• Nitrogen oxides (NO and NO₂): Released from vehicle exhausts and factories.
• Suspended Particulate Matter (SPM): Tiny solid particles like dust, smoke, soot and ash.
• CFCs (Chlorofluorocarbons): Earlier used in refrigerators, air-conditioners and aerosol sprays.

Smog, Acid Rain and Global Warming

Smog is a thick fog-like layer formed when smoke mixes with fog in the air. It reduces visibility and causes breathing problems. Smog is common in big cities with heavy traffic and industries.

Acid rain occurs when gases like sulphur dioxide and nitrogen oxides mix with rainwater to form acids. This acidic rain can:

• Damage leaves of plants and reduce crop yield.
• Corrode buildings and monuments (for example, marble of Taj Mahal).
• Make lakes and rivers acidic, harming aquatic life.

Global warming is the gradual rise in the average temperature of the Earth due to increased concentration of greenhouse gases like carbon dioxide and methane. It leads to melting of glaciers, rise in sea level and changes in climate.

Harmful Effects of Air Pollution

Air pollution can cause serious health and environmental problems such as:

• Irritation in eyes, throat and nose.
• Respiratory diseases like asthma and bronchitis.
• Increased risk of allergies and lung infections.
• Reduced visibility leading to accidents.
• Damage to crops and forests.

Ways to Reduce Air Pollution

Some important measures to control and reduce air pollution are:

• Using public transport, carpooling, walking or cycling instead of using personal vehicles for short distances.
• Using cleaner fuels like CNG, LPG and electricity instead of petrol and diesel.
• Planting more trees because they absorb carbon dioxide and release oxygen.
• Using chimneys with filters or electrostatic precipitators in factories to reduce smoke and dust.
• Banning burning of dry leaves, waste and crop residues in open fields.

What is Water Pollution?

Water pollution is the contamination of water bodies such as rivers, lakes, ponds, seas and oceans due to the addition of harmful substances. Water becomes unfit for drinking, washing, bathing or for aquatic life.

Just like air, pure water also has a definite composition. However, when harmful substances such as chemicals, sewage, plastics and industrial wastes are added, the quality of water decreases and it becomes polluted.

Common Water Pollutants and Their Sources

Important water pollutants include:

• Sewage: Wastewater from homes, offices, hospitals and markets containing soaps, detergents and human excreta.
• Industrial effluents: Chemical waste, dyes, acids and heavy metals from factories.
• Agricultural runoff: Fertilisers and pesticides washed away by rain from fields.
• Oil spills: Leakage from ships and oil tankers in seas and oceans.
• Plastics and solid waste: Polythene bags, bottles and garbage thrown into water bodies.

Eutrophication and Its Effects

When extra fertilisers from fields reach water bodies, the water becomes rich in nutrients like nitrates and phosphates. This causes rapid growth of algae on the water surface, forming a green layer known as algal bloom. This process is called eutrophication.

Algal bloom blocks sunlight from reaching deeper water, and when algae die and decompose, they use up a lot of dissolved oxygen. As a result, fish and other aquatic animals die due to lack of oxygen.

Potable Water and Its Characteristics

Water that is safe for drinking is called potable water. It should be:

• Clear and colourless.
• Free from harmful germs (microorganisms).
• Free from harmful dissolved substances and pollutants.
• Possessing a small amount of useful salts and minerals.

For CBSE Class 8 exams, remember that potable water must be free from disease-causing organisms and toxic chemicals, not totally free from all dissolved salts.

Purification of Water at Home

At home, we can make water potable by using simple methods. Important methods are:

• Boiling: Kills most disease-causing germs present in water.
• Filtration: Using filters or candle-type filters to remove suspended impurities.
• Chlorination: Adding the correct amount of chlorine tablets or bleaching powder to kill germs.
• Modern water purifiers: Use processes like UV treatment and RO (Reverse Osmosis) to purify water.

Sewage Treatment and Wastewater Management

Sewage is wastewater from homes, industries and other buildings that contains urine, faeces, soaps, detergents and other wastes. It must be treated in sewage treatment plants (STPs) before being released into rivers or other water bodies.

Basic steps in sewage treatment include:

• Primary treatment: Removal of large solid particles, sand and grit by screening and sedimentation.
• Secondary treatment: Use of microorganisms to decompose organic matter in aeration tanks.
• Disinfection: Killing harmful pathogens using chlorine or ozone before discharge.

Proper sewage treatment helps in reducing water pollution and protects aquatic life and human health.

Prevention and Control of Water Pollution

Some important measures to control water pollution are:

• Treating sewage and industrial effluents before releasing them into water bodies.
• Using organic manure instead of excessive chemical fertilisers.
• Using eco-friendly pesticides and reducing their usage.
• Spreading awareness and avoiding throwing garbage, plastics and religious waste into rivers and lakes.
• Cleaning and maintaining ponds, lakes and rivers regularly.

Government Laws and Public Awareness

The government has made several laws and programmes to control pollution. Examples include pollution control boards, restrictions on factory emissions and campaigns for cleaning major rivers. However, laws alone are not enough. Public awareness and active participation of citizens are very important.

As students, you can help by saving water, saying no to plastic, planting trees and educating others about the ill effects of pollution.

Key Terms – At a Glance

• Pollution: Undesirable change in the environment that harms living beings.
• Pollutant: Any substance that causes pollution.
• Air pollution: Contamination of air by harmful gases, dust and smoke.
• Water pollution: Contamination of water bodies by harmful substances.
• Smog: A mixture of smoke and fog.
• Acid rain: Rainwater containing acids formed from SO₂ and NOx.
• Global warming: Increase in average temperature of Earth due to greenhouse gases.
• Potable water: Water that is safe for drinking.
• Sewage: Wastewater containing human and domestic waste.
• Eutrophication: Excessive growth of algae in water bodies due to extra nutrients.

Exam-Oriented Tips & Question Hints

• Always support your answers with examples like vehicle exhaust, factory smoke, sewage, fertilisers, etc.
• Learn at least 3–4 measures to control both air and water pollution separately.
• Definitions of pollution, smog, acid rain, potable water and global warming are very important.
• Practice drawing and labelling simple diagrams (for example, water purification at home, sewage treatment steps).
• Use simple, clear language as used in the NCERT textbook for writing answers.

Summary of the Chapter

In this chapter, you studied how human activities are disturbing the natural balance of air and water. Air pollution is mainly caused by vehicle exhaust, industrial smoke and burning of fuel, which release harmful gases and particles into the atmosphere. It leads to health problems, smog, acid rain and global warming.

Water pollution occurs when untreated sewage, industrial waste, fertilisers, pesticides and plastics enter rivers, lakes and seas. This makes water unfit for drinking and harms aquatic life.

You also learnt about potable water, methods to purify water at home and the importance of sewage treatment plants. The chapter highlights that laws, technology and above all, responsible behaviour of every citizen are required to control pollution.

These CBSE Class 8 Science – Chapter Wise Study Materials Based on NCERT provide a complete, exam-ready revision of Chapter 18: Pollution of Air and Water. If you revise these notes regularly and practice textbook questions, you will be well prepared for school tests and CBSE Class 8 board exam standard papers.