18- Pollution of Air and Water | Science | NCERT | Class 8

Hello students, in this blog you can find important summary notes from the Chapter 18, Science , NCERT Book of Class 8. These notes can be used for preparation of various school Competitive Exams, Olympiads and also developing strong Fundamentals.

1. We can survive for some time without food, but we cannot survive even for a few minutes without air.

2. Air consists of a mixture of gases, by volume, about 78% of this mixture is nitrogen and about 21% is oxygen.

3. Carbon dioxide, argon, methane, ozone and water vapour are also present in very small quantities in air.

4. Air pollution : 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.

5. Air pollutants : The substances which contaminate the air are called air pollutants.

6. Sources of air pollutants : factories, power plants, automobile exhausts and burning of firewood and dung cakes.

7. Many respiratory problems are caused by air pollution.

8. Vehicles produce high levels of pollutants like carbon monoxide, carbon dioxide, nitrogen oxides and smoke.

9. Carbon monoxide is produced from incomplete burning of fuels such
as petrol and diesel.

10 Carbon monoxide is a poisonous gas and it reduces the oxygen-carrying capacity of the blood.

11. Smog : A thick fog-like layer in the atmosphere, especially during winters is smog and it is made up of smoke and fog.

12. Smoke may contain oxides of nitrogen which combine with other air pollutants and fog to form smog.

13. The smog causes breathing difficulties such as asthma, cough and wheezing in children.

14. Many industries are also responsible for causing air pollution.

15. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide and nitrogen dioxide.

16. Sulphur dioxide is produced by combustion of fuels like coal in power plants.

17. Other kinds of pollutants are chlorofluorocarbons (CFCs) which are
used in refrigerators, air conditioners and aerosol sprays.

18. CFCs damage the ozone layer of the atmosphere.

19. The ozone layer protects us from harmful ultraviolet rays of the sun.

20. Automobiles which burn diesel and petrol, also produce tiny particles which remain suspended in air for long periods, causing reduction in visibility and diseases when inhaled.

21. Tiny particles are also produced during industrial processes like steel making and mining.

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

23. Pollutants in air are discolouring its white marble of Taj Mahal.

24. Pollution affects living organisms and non-living things like buildings, monuments and statues.

25. Acid rain : Pollutants like sulphur dioxide and nitrogen dioxide react with the water vapour present in the atmosphere to form sul-
phuric acid
and nitric acid. When these acids drop down with rain, make the rain acidic and this is called acid rain.

26. Acid rain corrodes the marble of the monuments and the phenomenon is also called Marble cancer.

27. Acid rain affects the soil and plants also.

28. Soot particles emitted by Mathura oil refinery, has contributed towards the yellowing of the marble.

29. The Supreme Court has taken several steps to save the Taj :
– 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.

30. Greenhouse Effect : When sun’s radiation fall on the earth, a part of it is absorbed and a part is reflected back into space. When this
reflected part of radiation is trapped by the atmosphere, it further warms the earth and this effect is called the greenhouse effect.

31. Excess of CO2 in the air is one of the reasons responsible for greenhouse effect.

32. Deforestation leads to an increase in the amount of CO2 in the air because the number of trees which consume CO2 is reduced.

33. Global warming : CO2 traps heat and does not allow it to escape into space. As a result, the average temperature of the earth’s atmo-
sphere is gradually increasing and this is called global warming.

34. Greenhouse gases : Gases like CO2, methane, nitrous oxide and water vapour contribute towards global warming and are known as
greenhouse gases.

35. Global warming can cause sea levels to rise dramatically.

36. Kyoto Protocol : It is an international agreement by many countries to reduce the emission of greenhouse gases.

37. The Gangotri glacier in the Himalayas has started melting because of global warming.

38. There is a need to switch over to alternative fuels like solar energy, hydropower and wind energy instead of the fossil fuels, for our energy requirements.

39. Water is a precious resource.

40 Water is becoming scarce due to increase in population, industries and agricultural activities.

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

42. According to the World Wide Fund for Nature (WWF) Ganga is one of the ten most endangered rivers in the world.

43. Ganga Action Plan : It is an ambitious plan to save the river Ganga, launched in 1985. It aimed to reduce the pollution levels in the

44. National Mission for Clean Ganga (NMCG) : Launched in 2016 by the Government of India, to clean the river.

45. The Ganga at Kanpur in Uttar Pradesh (U.P.), has one of the most polluted stretches of the river.

46. Many industries discharge harmful chemicals into rivers and streams, causing the pollution of water.
Examples :oil refineries, paper factories, textile and sugar mills and chemical factories.

47. The chemicals released from factories include arsenic, lead and fluorides which lead to toxicity in plants and animals.

48. Soil is also affected by impure water, causing changes in acidity, growth of worms, etc.

49. Water contaminated with sewage may contain bacteria, viruses, fungi and parasites which cause diseases like cholera, typhoid and jaundice.

50. Hot water can also be a pollutant, because when hot water (from power plants and industries) is released into the rivers : it raises the temperature of the waterbody, adversely affecting the animals and plants living in it.

51. Water which looks clean may still have disease- carrying microorganisms and dissolved impurities, therefore it is essential to purify water before drinking.

52. Potable water : Water which is suitable for drinking is called potable water.

53. Various physical and chemical processes in the sewage treatment plants help to clean water before discharging it into water bodies.

54. Water can be made safe for drinking:
Filtration : This is a physical method of removing impurities. A popular household filter is a candle type filter.
Boiling as a method for obtaining safe drinking. Boiling kills the germs present in the water.
Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets or bleaching powder
to the water.

55. At our individual levels we should consciously save water and not waste it. We should reduce, reuse and recycle water.



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