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Class 8th Science
Class 8 Social Science History
Online Class For 8th Standard Students (CBSE) (English Medium)
About Lesson

Introduction to Air Pollution

In chapter 18 of class 8 Science, we study the harmful changes taking place in our surroundings and their effects on our lives. The substance that contaminates air and water are known as pollutants. Air gets polluted from natural sources smoke and dust arising from forest fires or volcanic eruptions. Pollutants such as power plant and automobile exhaust and burning of firewood are man-made pollutants. Carbon dioxide, nitrogen oxides, carbon monoxide, methane and sulphur dioxide are the major pollutants of air. Increasing levels of carbon dioxide lead to global warming.


Environmental pollution refers to undesirable changes in the surroundings that have adverse effects on plants, animals and other biological and physical components of the environment.

  • A substance that causes pollution is called a pollutant. Pollutants can be in liquid, solid or gaseous form.
  • A substance becomes a pollutant when its concentration is greater than the natural abundance and this increase in concentration is either due to human activities or natural phenomenon.
  • Types of pollution: Air pollution, water pollution, soil pollution, sound pollution, light pollution, etc.

Air Pollution

Air pollution is the introduction of pollutants, organic molecules, or other hazardous substances into earth’s atmosphere.

a) Natural – forest fire, dust storms, and volcanic activity
b) Man-made – power plants, homes, industries, oil refineries, and  transportation


  • Causes allergies, diseases and even death to humans.
  • Causes birth defects in new-born babies.
  • Endangers animal health and welfare of plants and vegetation.


How Crucial Is Air and Water?


  • The major sources of water are streams, rivers, lakes, oceans on the earth’s crust.
  • It plays a significant role in sustaining life on earth.
  • It is widely used for human activities such as agriculture, drinking, washing, cleaning, etc.


  • Air is inevitable in our lives.
  • The oxygen in the air is essential for the animals to survive.
  • Oxygen helps to produce energy in their bodies.

Air Pollution – What and How

Air Pollutants

The substances, which accumulate in the air in high enough concentration that is hazardous to all organisms or to materials exposed to the air are called air pollutants.

  • These may be present as solid particles, liquid droplets or gases.
  • Examples: Methane, chlorofluorocarbons, particulate matter, sulphur dioxide, nitrogen dioxide, carbon monoxide, lead, etc.

Carbon Dioxide and Carbon Monoxide

Sources of carbon dioxide: cement production, deforestation and burning of fuels like gasoline, natural gas, oil, coal, and wood.
Sources of carbon monoxide (a toxic air pollutant): incomplete combustion of carbon-containing compounds especially fuels.

Sulphur and Nitrogen

Nitrogen dioxide (NO2) and sulphur dioxide (SO2) are major air pollutants.
Sources: Petroleum refineries, combustion of fossil fuels like coal in power plants.

  • Respiratory problems, including permanent lung damage.
  • Acid rain.
  • Photochemical smog, which causes breathing difficulties.

Particulate Matter

Particles of solid or liquid that remain suspended in air, water or gas are called particulates.

Example: dust, pollen, debris, soot, acid droplets and smoke.
Causes: Combustion, construction, road dust, power plants, industries, deforestation and agricultural activities.

  • Respiratory and heart diseases.
  • Asthma
  • Birth defects


Smog is made up of smoke and fog.

Types: Classical smog, Photochemical smog

1.Classical smog:

  • This type of smog occurs in areas with a humid climate and high concentrations of sulphur oxides in the air.
  • It is a mixture of smoke, fog, and mainly sulphur dioxide gas.
  1. Photochemical smog:
  • This type of smog is prevalent in areas with dry and sunny climate and large numbers of automobiles.
  • It is formed primarily as a result of chemical interactions among nitrogen oxides and sunlight.


  • Breathing difficulties such as asthma, cough, and wheezing.
  • Inhibits plant growth and can cause widespread damage to crops and forests.
  • Photochemical smog leads to the corrosion of metals, building materials, and painted surfaces.


Chlorofluorocarbons (CFCs) are compounds of chlorine, fluorine, and carbon.

Components of aerosol sprays.
Refrigerants in refrigerators, ACs, and cooling plants.


  • CFCs destruct ozone layer that protects the earth from the sun’s ultraviolet (UV) radiation.
  • UV exposure can lead to skin cancer, suppression of the immune system and eye damage.

Taj Mahal

Effects of Air Pollution on the Taj Mahal

  • Carbon dioxide, sulphur dioxide, and nitrogen dioxide react with the water vapour present in the atmosphere to form, carbonic acid, sulphuric acid, and nitric acid respectively.
    These acids drop down with rain, making it acidic in nature.
    Reactions involved:
    CO2(g) + 2H2O(l)→2H2CO3(aq)
    2SO2(g) + O2(g) + 2H2O(l)→2H2SO4(aq)
    4NO2(g) + O2(g) + 2H2O(l)→4HNO3(aq)                                                    

Effects on Taj Mahal:

  • Acid rain corrodes the marble of the monument.
  • Air pollution is turning the white marble into the black.

Global Warming

Greenhouse Gases

  • The gases, which are responsible for greenhouse effect are called as greenhouse gases.
  • Examples: Water vapour, nitrous oxide, carbon dioxide and methane.

Greenhouse Effect

  • Most of the solar radiation passes through the atmosphere.
  • The earth’s surface radiates heat back toward space.
  • A part of it is trapped by the greenhouse gases in the earth’s atmosphere.
  • This effect maintains the liveable temperature on the earth’s surface.

Global Warming

  • The increase in the average temperature of the earth’s atmosphere due to excess of greenhouse gases is called as global warming.
  • Causes: Deforestation, industries, oil refineries, power plants, excess burning of fossil fuels like natural gas, oil, and coal, etc.

Effects of Global Warming

  • Warmer climate: On average, the earth’s temperature has become warmer than earlier.
  • Natural calamities: There is an increase in occurrence and severity of natural calamities such as floods, cyclones, earthquakes, etc.
  • Rise of sea level: Due to global warming, there is a rise in sea levels due to the melting of the polar ice caps.
  • Severe weather events: Shifting of the climatic pattern has been observed across the globe.

What Can We Do

Measures to Reduce Air Pollution

  • Encourage use of CNG: It is a cleaner fuel as compared to petrol and diesel.
  • Use of unleaded petrol: The unleaded petrol does not emit harmful gases into the environment.
  • Proper waste management: Maintains hygiene by proper disposal of waste to areas where they can be left, incinerated or disposed of in a safe manner.
  • Use of public transport or carpooling: It is economical, eases congestion on roads and also reduce emissions to large extent.

Water Pollution – Introduction

Water Pollution

Water pollution is the contamination of water bodies with harmful waste.

  • Urbanization
  • Industries
  • Agriculture
  • Religious and Social Practices etc.

Not so Holy Ganga

Water Pollutants

  • The substances that pollute water are called water pollutants.
  • Examples: Detergents, chemicals dumped by hospitals, Insecticides and herbicides etc.

Effects of Water Pollution on the River Ganga

  • Towns and cities, through which the river flows, throw large quantities of garbage, untreated sewage, dead bodies, and many other harmful things, directly into the river.
  • Pollution in Ganga is choking the aquatic life and hindering the growth of plants.
  • Ganga is one of the ten most endangered rivers in the world.

Potable Water

Potable Water

  • Water, which is suitable for drinking is called potable water.
  • The potable water is free from all the contaminants and harmful bacteria.
  • The water, which is not potable or fit for drinking is called raw water.

Boiling Water

  • Boiling the water kills all the microbes.
  • It protects us from waterborne diseases.

Filtering Water

  • Filtration is the process of separating suspended solid matter from a liquid.
  • Filtering water can take away all microbes and impurities up to a certain extent.


  • Chlorination is done by adding chlorine tablets or bleaching powder to the water.
  • This method is used to kill certain bacteria and other microbes in tap water.


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