POLLUTION OF AIR AND WATER | SPEED NOTES | SCIENCE | CBSE | CLASS 8

Chapter – 18 Pollution of Air and Water

Pollution: An undesirable change in the physical, chemical or biological characteristics of air, water and landthat may beharmful to human life and otheranimals, living conditions, industrial processes andcultural assets.

Pollutants: The agents thatpollute our environment are called pollutants. Pollutants are thesubstances which contaminate air, water andland. For eg.smoke ,dust,fog andgases like sulphur dioxide andnitrogen dioxide.

Air pollution is the contamination ofair by impurities which may havea harmful impact on the living organisms and thenon-living components. Sources of Air Pollution:

Natural Sources: Smoke and dust arising from forest fires or volcanic eruptions. Methane gas arising from decaying organic matter.

Man-made Sources: Exhaust gases fromfactories, power plants and automobiles. Carbon monoxide, nitrogen oxides, carbon dioxide, methane and sulphur dioxide are the major pollutants of air. Smog is a mix in the air of smoke and chemicals with fog. The chemical components of smog can include ozone, sulphur dioxide, nitrogen dioxide and carbon monoxide. Smog can trigger breathing difficulties likeasthma and coughing.

Steps to prevent airpollution: Use of fuels like CNG andunleaded petrol inautomobiles. Switching to alternative fuels, like solar energy, hydropower andwind energy. Planting trees. Travelling to school on a bicycle or on public transport or carpooling. Avoiding theburning of leaves, trash and vegetable matter. • Restricting cigarette smoking. Increasing levels ofgreenhouse gases like CO2 ,CFC (Chloroflorocarbon) areleading to global warming.

Excessive useof CFCs damages ozone layer whichprotects the earthfrom harmful UVrays emitted bythe sun.

Greenhouse Effect and Global Warming: The sun's rays warm the earth's surface. A part of the radiation that falls on the earth is absorbed byit and apart is reflected back into space. A part ofthe reflected radiation is trapped by the atmosphere due to presence of gases likewater vapor, carbon dioxide, methane, nitrous oxide etc known asgreenhouse gases. Thisis known asgreenhouse effect. The trapped radiations further warm theearth and haveadverse effects suchas melting of glaciers andincreasing sea levels. This phenomenon isknown as global warming.

Water pollution is the contamination ofwater by objectionable and harmful substances such assewage, toxic chemicals, silt, etc. Sewage, agricultural chemicals and industrial waste are some ofthe major contaminants of water. Water which is purified andfit for drinking is known as potable water. Water is a precious natural resource. We mustlearn to conserve it.