NCERT Class 8 Geography Chapter 17: Pollution Of Air And Water YouTube Lecture Handouts

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Watch Video Lecture on YouTube: NCERT Class 8 Science Chapter 18: Pollution of Air and Water (NSO/NSTSE)

NCERT Class 8 Science Chapter 18: Pollution of Air and Water (NSO/NSTSE)

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Air Pollution

Factories and automobiles

Factories and Automobiles

Factories and automobiles

  • Respiratory diseases

  • Air is essential – we need clean air

  • 78% is nitrogen; 21% is oxygen

  • When air is contaminated by unwanted substances which have a harmful effect on both the living and the non-living, it is referred to as air pollution.

Smoke from a Factory & Air Pollution Due to Automobiles

Pollution from factories and automobiles

Pollution from Factories and Automobiles

Pollution from factories and automobiles

  • The substances which contaminate the air are called air pollutants.

  • Smoke Dust

  • Factories, power plant, automobiles, burning of firewoods

  • Vehicle – CO, CO2, Nitrogen oxide and smoke

  • Carbon monoxide is produced from incomplete burning of fuels such as petrol and diesel. It is a poisonous gas. It reduces the oxygen-carrying capacity of the blood If the vehicles registered in Delhi are lined up one after the other, the total length would be nearly equal to the combined lengths of the two longest rivers in the world, Nile and Amazon!


  • Smoke + Fog (in winters)

  • Asthma, cough and wheezing

  • 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. It can cause

  • respiratory problems, including permanent lung damage

  • Chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays. CFCs damage the ozone layer of the atmosphere.

  • Automobiles which burn diesel and petrol, also produce tiny particles which remain suspended in air for long periods. They reduce visibility.

  • Power plants give out tiny ash particles which also pollute the atmosphere

Acid Rain Affects the Soil and Plants




Green House Effect

  • A part of the radiation that falls on the earth is absorbed by it and a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. The trapped radiations further warm the earth

  • The trapped heat warms the green house. The trapping of radiations by the earth’s atmosphere is similar. That is why it is called the greenhouse effect

  • CO2 is constantly been released and area under forest is decreasing – it increases CO2 in atmosphere

  • the average temperature of the earth’s atmosphere is gradually increasing. This is called global warming.

  • Greenhouse gases - methane, nitrous oxide and water vapour - control it by Kyoto Protocol

A Public Transport Bus Powered by CNG

  • Delhi was one of the most polluted cities in the world. It was being choked by fumes released from automobiles running on diesel and petrol. A decision was taken to switch to fuels like CNG and unleaded petrol

  • Quality is monitored by government agencies

  • Alternate sources – solar, hydropower and wind

  • Van Mahotsav – planting trees in July

Children Planting Saplings

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Planting Trees

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It is not right to burn dry leaves as it causes air pollution. The right way to dispose off the dry leaves is to convert them into compost.

Course of the River Ganga

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River Ganga

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  • Water Pollution – industry and agriculture

  • Whenever harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water, the water becomes polluted. The substances that pollute water are called water pollutants

  • Source or place of pollution is called as point source, e.g.– municipal and industrial discharge pipes, where pollutants enter the water source. Non–point sources of pollution are those where a source of pollution can not be easily identified, e.g.– agricultural run off, acid rain.

A Polluted Stretch of the River Ganga

Clean Ganga

Clean Ganga

Clean Ganga

  • World Wide Fund for Nature (WWF) found that Ganga is one of the ten most endangered rivers in the world. The pollution levels have been rising for many years.

  • river flows, throw large quantities of garbage, untreated sewage, dead bodies, and many other harmful things, directly into the river. In fact the river is ‘dead’ at many places where the pollution levels are so high.

A Polluted Stretch of the River Ganga

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Pollution in Ganga

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  • Ganga Action Plan was launched in 1985. It aimed to reduce the pollution levels in the river

  • National Mission for Clean Ganga (NMCG) in 2016.

  • The Ganga at Kanpur in Uttar Pradesh (U.P.), has one of the most polluted stretches of the river. Kanpur has more than 5000 industries. These include fertiliser, detergent, leather and paint industries.

  • Industries discharge harmful chemicals into rivers and streams – oil refinery, petrol, chemical, textile, sugar

  • The chemicals released include arsenic, lead and fluorides which lead to toxicity.

Water Treatment Plant

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Water Treatment Plant

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  • Why pond look green from a distance – due to algae growth. This is caused by excessive quantities of chemicals which get washed from the fields. These act as nutrients for algae to flourish. Once these algae die, they serve as food for decomposers like bacteria. A lot of oxygen in the water body gets used up. This results in a decrease in the oxygen level which may kill aquatic organisms

  • The bacteria present in the faeces of mammals are indicators of the quality of water

  • Water which is suitable for drinking is called potable water. You have seen how various physical and chemical processes in the sewage treatment plants help to clean water before discharging it into water bodies.

  • Physical method to remove impurity – filtration

  • Boiling to kill germs

  • Chlorination – add chlorine

  • Distillation – free of all impurities

  • Reduce (brushing your teeth), reuse (washing vegetables) and recycle (dirty water for purification)

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