CBSE Notes for Class 8 Science Chapter 18 – Pollution of Air and Water

Important Notes for CBSE Class 8 Science Chapter 18 – Pollution of Air and Water. Pollution of Air and Water Class 8 Notes and Study Material Download in PDF form.

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Pollution of Air and Water Class 8 Notes

  • Air pollution:

Air is a mixture of gases. It is made up of about 78% nitrogen, about 21% is oxygen. The remaining 1% has Carbon dioxide, argon, methane, ozone and water vapor present in very small quantities.

  • Air pollution: Air contaminated with unwanted substances which are harmful for living and nonliving things.

How does air get pullulated?

Air pollutants:

  • Contaminants of air are called air pollutants.
  • They can be having varied sources such as natural sources like smoke and dust arising from forest fires or volcanic eruptions or man-made sources like factories, power plants, automobile exhausts and burning of firewood and dung cakes.
  • Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke.
  • Carbon monoxide is a produced from incomplete burning of fuels such as petrol and diesel
  • Smog: It is a thick fog-like layer in the atmosphere, especially during winters. It made up of smoke and fog
  • Smoke contains oxides of nitrogen which combine with other air pollutants and fog to form smog.
  • Many industries are 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 combustion of fuels like coal in power plants.
  • Chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays.

 Effects of air pollution:

  1. Respiratory problems are associated with air pollution.
  2. Carbon monoxide is a poisonous gas which reduces the oxygen-carrying capacity of the blood.
  3. Smog causes breathing difficulties such as asthma, cough and wheezing in children.
  4. Sulphur dioxide can cause respiratory problems, including permanent lung damage.
  5. CFCs are known to damage the ozone layer of the atmosphere. The ozone layer protects from harmful ultraviolet rays of the sun.
  6. Small particles are also produced during industrial processes like steel making and mining can cause disease when inhaled.
  7. Powerplants give out tiny ash particles which also pollute the atmosphere

Case Study—The Taj Mahal

  • The taj mahal is one of the seven wonders of the world. It is a world heritage site and major tourist attraction.
  • Air Pollutants are discoloring its white marble.
  • The industries located in and around Agra such as rubber processing, automobile, chemicals and oil refinery, have been responsible for producing pollutants like Sulphur dioxide and Nitrogen dioxide.
  • The gases react with the water vapors present in the atmosphere to form sulphuric acid and nitric acid, making the rain acidic.
  • Acid rain corrodes marble of the monument. This is called “Marble cancer”.
  • Suspended shoot particulate matter emitted by oil refinery have contributed towards the yellowing of the marble.
  • 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).
  • The automobiles should switch over to unleaded petrol in the Taj zone.

Greenhouse Effect:

  • A part of the radiation (Sun light) that falls on the earth is absorbed and a part is reflected back into space.
  • The reflected part of radiation is trapped by the atmosphere which further warm the earth.
  • The trapping of radiations by the earth’s atmosphere so that it is not emitted out is called the green house effect.
  • Life on earth is dependent on this effect.
  • But now it threatens life. Excess of CO2 in the air is responsible for this effect.
  • CO2 is continuously being released because of human activities, area under forests is decreasing.
  • CO2 traps heat and does not allow it to escape into space due to the average temperature of the earth’s atmosphere is gradually increasing.
  • This is called global warming.
  • Gases like methane, nitrous oxide and water vapors also contribute towards this effect. These 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.

What can be done to prevent greenhouse effect?

  • Individuals should switch to fuels like CNG and unleaded petrol. There is a need to switch over to alternative fuels instead of the fossil fuels for our energy requirements.
  • These could be solar energy, hydropower and wind energy.
  • These measures have resulted in lowering of the air pollution.
  • Generate awareness about air pollution among friends and neighbors.
  • Plant a number of trees and protect the ones already present in the neighborhood.

Water Pollution:

  • Clean water in the environment is becoming scarce due to increase in population, industries and agricultural activities.
  • Use of water for washing clothes, bathing, etc. has led to its pollution which spoil its quality and change its smell and color.
  • Harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water causing its pollution
  • The substances that pollute water are called water pollutants.

How does Water Get Polluted?

  • World Wide Fund for Nature (WWF) found that Ganga is one of the ten most endangered rivers in the world.
  • The pollution levels in ganga have risen for many years.
  • Large quantities of garbage, untreated sewage, dead bodies, and many other harmful things, directly into the river.
  • The increasing population and industrialization have already damaged this mighty river beyond repair.
  • The Government of India has launched a new initiative known as National Mission for Clean Ganga (NMCG) in 2016.
  • Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water
  • Examples include oil refineries, paper factories, textile and sugar mills and chemical factories.
  • These industries cause chemical contamination of water.
  • The chemicals released include arsenic, lead and fluorides which lead to toxicity in plants and animals.
  • Industries are supposed to treat the waste produced before discharging it into waters, but quite often the rules are not followed.
  • The soil is affected by impure water, causing changes in acidity, growth of worms, etc.
  • Pesticides and weedicides are used for the protection of crops. All these chemicals dissolve in water, are washed into water bodies from the fields.
  • They also seep into the ground to pollute ground water.
  • Algal growth can be seen on the surfaces of water when excessive quantities of chemicals which get washed from the fields.
  • These act as nutrients for algae to flourish.
  • On dying, algae serve as food for decomposers like bacteria.
  • A lot of oxygen in the waterbody gets used up which results in a decrease in the oxygen level which may kill aquatic organisms.
  • Untreated sewage is thrown directly into rivers contains food wastes, detergents, microorganisms, etc.
  • Water contaminated with sewage may contain bacteria, viruses, fungi and parasites responsible for causing diseases like cholera, typhoid and jaundice.
  • The bacteria present in the faeces of mammals are indicators of the quality of water.
  • If water has these bacteria, it means that it has been contaminated by fecal matter. Such water is used by us can cause various infections.
  • Hot water from power plants and industries can also be a pollutant
  • If released into the rivers can raises the temperature of the water body, adversely affecting the animals and plants living in it.


Potable Water and How is Water Purified?

  • Water which is suitable for drinking is called potable water.
  • Water looks clean but can have disease carrying microorganisms and dissolved impurities.
  • Boiling it can reduce the pollutant load.
  • A number of various physical and chemical processes in the sewage treatment plants help to clean water before discharging it into water bodies.
  • Municipal bodies treat the water before supplying it to households.


Making water safe for drinking:

  • Filter water before use which is a physical method of removing impurities.
  • Candle filters are commonly used in homes to filter water.
  • Boiling water is a safe method to obtain safe drinking water.
  • Boiling kills the germs present in the water.
  • Chlorination is a commonly used chemical method for purifying water.
  • Chlorine tablets or bleaching powder is added to the water.


What Can be Done?

  • Strict implementation of policies so that polluted water is not disposed of directly into rivers and lakes.
  • Water treatment plants should be installed in all industrial areas.
  • At individual levels consciously save water and should not waste it.
  • Reduce, reuse and recycle water. One can do this by reusing water used for washing and for other household tasks


  • Pollution is no longer a distant phenomenon and is affecting the quality of our daily lives.

Pollution of Air and Water Class 8 Notes in PDF

Pollution of Air and Water

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