Class 8 Science
Air: Air is a mixture of gases. About 78% of air is composed of nitrogen, 21% is composed of oxygen, and the rest 1% is composed of carbon dioxide, argon, methane, ozone, water vapour, etc.
Air Pollution: When air is contaminated with unwanted substances and becomes harmful for the living and non-living, this is called air pollution.
Air Pollutants: Substances which contaminate air are called air pollutants.
Causes of Air Pollution:
Natural Causes: Smoke and dust from forest fire and volcano
Automobile Exhaust: Petrol and diesel are used as fuel in automobiles. Combustion of these fuels produces many polluting gases; like carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide, etc. Automobile engines also produce minute particles which remain suspended in air. These particles are called Suspended Particulate Matter (SPM).
Factories: Fossil fuel is also used in factories and hence factories produce pollutants; like carbon dioxide, sulphur dioxide and nitrogen dioxide.
Construction sites and Stone Quarries: Construction sites and stone quarries produce lot of dust particles. Mining activities and power plants also produce dust particles.
Households: Many fuels are used in kitchens, and thus kitchen is a significant source of air pollution.
CFC: Chlorolfuorocarbon (CFC) is used in refrigerators and in aerosol sprays. It is a non-toxic and non-inflammatory compound of chlorine, fluorine and carbon. CFCs react with ozone to produce oxygen and thus damage the ozone layer.
Ozone Layer: Ozone layer is a protective layer in the atmosphere. It contains a higher amount of ozone than any other layer of the atmosphere. However, compared to other gases; ozone still forms a negligible part of air in ozone layer. This layer prevents harmful ultraviolet radiations from the sun from entering our atmosphere. Ultraviolet radiations can cause skin cancer in humans and animals, and is also harmful for plants. Any damage to the ozone layer can be highly detrimental to the living beings.