CBSE Class 8 Science Notes Chapter 18 Pollution of Air and Water
Pollution of Air and Water Class 8 Notes Understanding the Lesson
1. Agents or substances that pollute water, air or soil are called pollutants.
2. The term air pollution is defined as the accumulation of harmful substances or increase in the quantity of any gas in the air above the normal level.
3. Air pollution is harmful for human beings also.
4. In the earth’s atmosphere there is about 78% of nitrogen, 21% of oxygen and the rest are other gases like CO2, methane, ozone and water vapour.
5. The substances which contaminate the air are called air pollutants.
6. There are natural as well as man-made sources of air pollution.
7. Smoke and fog combines to form smog. Smoke may contain oxides of nitrogen which combine with other pollutants and fog to form smog.
8. Smog causes breathing difficulties.
9. Chlorofluorocarbons (CFCs) which are used in refrigerators, air conditioners and aerosol sprays damages ozone layer of the atmosphere.
10. Some pollutants like SO2 and NO2 react with water vapour present in the air to form sulphuric acid and nitric acid. These acids come down with rain as acid rain.
11. A part of the radiation of the sun that falls on the earth is absorbed by it, whereas a part is reflected back into space. A part of the reflected radiation is trapped by the atmosphere. This trapping of radiations by the earth’s atmosphere causes warming of the earth and this is known as greenhouse effect.
12. Human activities contribute to the accumulation of CO2 in the atmosphere. CO2 traps heat and does not allow it to escape into space. As a result of this, the average temperature of the earth’s atmosphere increases gradually and this is called global warming.
13. Gases which contribute to global warming, like CO2, methane, nitrous oxide and water vapour are called greenh’ouse gases.
14. The substances that pollute water are called water pollutants.
15. The harmful substances such as sewage, toxic chemicals, silt, etc., get mixed with water and this leads to water pollution.
16. Water which is suitable for drinking is called potable water.
17. Chlorination is a commonly used chemical method for purifying water. It is done by adding chlorine tablets ‘ or bleaching powder to the water.
18. We must conserve water as it is a precious natural resource.
Class 8 Science Chapter 18 Notes Important Terms
Air pollution: When some unwanted substances get mixed with air and have harmful effect on both living and non-living things, is known as air pollution.
Chemical contamination: Presence of harmful chemicals in air, water and soil causing pollution of water is called chemical contamination.
Global warming: Due to the increasing levels of greenhouse gases, like CO2, the average temperature of earth’s atmosphere is gradually increasing. This is called global warming.
Greenhouse effect: The process of trapping of radiations by the Earth’s atmosphere due to increasing levels of gases like CO2 is called greenhouse effect.
Pollutants: The substances which causes pollution are known as pollutants.
Potable water: Water which is purified and is also fit for drinking is known as potable water.
Water pollution: The contamination of clean water by substances which are harmful to life is called water pollution.