NCERT Summary: Pollution of Air & Water - Science Class 8

Introduction

• The layer of air present around the earth is called atmosphere.
• Atmosphere is composed of 78% of nitrogen, 21% of oxygen, and 1% percent other gases such as carbon dioxide, ozone, water vapour, methane, etc.

Air pollution

• The phenomenon of contamination of air with unwanted substances so that it becomes harmful for living organisms and non-living substances is known as air pollution.
• The substances, which cause air pollution, are called air pollutants.

Sources of air pollution
(i) Power plants
(ii) Factories
(iii) Automobiles
(iv) Burning of firewood

Types of air pollutants

(i) Carbon monoxide

• It is a colourless poisonous gas.
• It is produced from incomplete burning of fossil fuels.

(ii) Smog

• It is made up of smoke and fog.

(iii) Sulphur dioxide

• It is produced from combustion of fuels.

(iv) Nitrogen dioxide

• It is produced from incomplete burning of fuels.

(v) Chlorofluorocarbons (CFCs)

• They are released from refrigerators, air conditioners, and aerosol sprays.
• They cause damage to the ozone layer resulting in the formation of ozone hole.

(vi) Suspended particulate matter

• It comprises of tiny particles, which remain suspended in air for a long time.
• They are produced during burning of fossil fuels in power plants, mining, steel making, and other industrial processes.
• They reduce visibility and cause haze.
• They cause respiratory diseases on inhalation.
• Soot released from Mathura refinery has caused yellowing of the marble of Taj Mahal.

Prevention of air pollution

• Use of clear fuels such as CNG, LPG, and unleaded petrol in public and private transport.
• Use of renewable sources of energy such as solar, wind, and hydel energy.
• Planting more and more trees to prevent pollution.
• Prevent burning of dry leaves and use them in composting.
• Kyoto protocol is an agreement between various countries for reducing green house emission.

Acid rain

• It is formed when sulphur dioxide and nitrogen dioxide present in air react with water droplets to form nitric and sulphuric acid.
• When it rains, it brings these acids along with it, which causes damage to plants, animals, and monuments.
• Acid rain has caused corrosion of the marble of Taj Mahal

Water pollution

• The addition of harmful substances to water, as a result of which its physical, chemical, and biological properties get altered, is called water pollution.
• Substances that pollute water are called water pollutants.

Sources of water pollution in Ganga river

• Untreated discharges from textile, paper and sugar mills, and oil refineries.
• Disposal of agricultural discharge from near-by fields, which are rich in pesticides and weedicides, into the river.