Class 8 Science



Air Pollution

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.


Effects of Air Pollution:

  • Carbon dioxide cause global warming because it is a potent greenhouse gas.
  • Smog: Smog is a mixture of smoke and fog. Smog reduces visibility, and thus can create problems for drivers at highways. Pilots face problems while landing or taking off; due to smog.
  • Carbon monoxide is a poisonous gas even at low concentration. It reduces oxygen carrying capacity of blood, and a person may die on exposure to carbon monoxide.
  • Acid Rain: Oxides of sulphur and nitrogen mix with rainwater to create acid rain. Acid rain can be harmful for living beings and also for non-living things. Acid rain corrodes the outer surface of buildings. This has caused the Taj Mahal becoming pale.
  • Suspended Particulate Matter in air can cause respiratory problems; like asthma and other respiratory disease.
  • Greenhouse Effect: Greenhouse gases; like carbon dioxide and methane trap solar radiation and thus increase atmospheric temperature. This is called greenhouse effect.
  • Global Warming: Overall increase in temperature of earth is called global warming. Global warming is causing melting of icebergs and glaciers. It is resulting in increased cases of flash floods and a rise in sea level. It is also causing drastic changes in weather patterns.


How to Prevent Air Pollution:

  • We should use CNG; instead of petrol and diesel in automobiles.
  • We should use public transport instead of cars and bikes.
  • We should use bicycle as often as possible.
  • We should walk for short distance commute.
  • Data on air quality can be utilized to assess the situation and to take timely action.
  • More efforts should be made to develop alternate sources of energy, e.g. solar energy, biofuel, etc.
  • We should plant more trees in our surroundings because trees maintain the balance between carbon dioxide and oxygen in atmosphere.
  • Burning of dry leaves should be stopped. Dry leaves should be utilized to make compost.