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• Air: Mixture of gases
• Composition of air: Air is composed of 78% of nitrogen, 21% of oxygen, carbon dioxide, argon, methane, ozone and water vapor
• Air pollution: Undesirable changes in properties of air due to mixing of toxic gases and other minute particles.
• Air Pollutants: Harmful substances that causes water pollution.
  • Natural pollutants: Volcanic Eruption, Sand and Dust Storm, Forest Fires etc.
  • Manmade pollutants: Vehicles, Industries, Factories, Agriculture and power plants.
• Air pollutant that causes pollution:
  • Burning of fossil fuels due automobile causes air pollution by releasing harmful gases
  • Refining of crude oil obtained from earth’s crust releases harmful gases like sulphur oxide, nitrogen dioxide, etc.
  • Chlorofluorocarbons (CFCs) that are released from refrigerators, air conditioners, etc causes damage to the ozone layer.
  • Open field burning, burning of coal, firewood, cow dung cakes, etc are some other causes of air pollution.

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• Acid Rain: When pH of rain water drops below 5.6, it is called acid rain.
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• Carbon cycle: Process in which carbon from the atmosphere is used for various process and is returned back to the atmosphere.
  • Photosynthesis: Plants use atmospheric carbon dioxide or carbon dioxide from water and converts it glucose, which is stored as food in plant body.
  • Respiration: While breathing animal body takes in oxygen and removes carbon dioxide in atmosphere.
  • Decomposition: During the decomposition of dead plants and animal carbon from body is released in atmosphere.
  • Combustion: Burning of fossil fuels emit large amount of carbon dioxide in the atmosphere.
• Greenhouse effect: Greenhouse gases have the ability to trap heat energy emitted by sun and maintain temperature of earth. Carbon dioxide is one the greenhouse gases. Due to human activities there is increase in percentage of carbon dioxide in atmosphere. Hence, large amount of heat gets trapped in atmosphere causing increase in global temperature resulting in global warming. Such effect of greenhouse gas is called as greenhouse effect.
• Oxygen Cycle:
  • Combustion: Burning of substance in presence of atmospheric oxygen releases carbon dioxide.
  • Respiration: Animal use atmospheric oxygen to breath and produce carbon dioxide.
  • Decomposition: Plants and animal die and release carbon dioxide, oxygen and nitrogen in atmosphere.
  • Photosynthesis: Plants use atmospheric carbon dioxide and oxygen is released out of plant body as a waste product.
• Ozone Layer: Stratosphere contain a separate layer of ozone called as ozone layer. This layer protect living organisms from harmful ultraviolet rays emitted by sun. Due to various human activities, there is release of compound chlorofluorocarbons i.e. CFC’s in the air. These are stable compounds. After reaching to ozone layer they form compound with oxygen present in ozone. This causes reduction in ozone molecules causing depletion. If depletion of ozone layer continues human life may suffer from various diseases, e.g skin cancer.
• Ways to reduce air pollution:
  • Use of CNG and unleaded petrol
  • Use of alternative sources of energy like solar energy, hydropower, etc
  • Say no to crackers
  • Adopt environment friendly practices like use of public transport systems, bicycles, etc.
  • Promote tree plantation
  • Do not burn dry leaves or garbage, garbage should be properly disposed and dry leaves should be buried in the ground.
• Water pollution: Harmful substances added in water like chemical waste, household waste, etc causes water pollution.
• Reasons of water pollution:
  • Addition of unwanted substances to water sources
  • Removal of important substances from water resources
• Ganga River Case Study: Ganga river is among the ten most endangered rivers in the world because of water pollution. To clean river Ganga in 1985 Ganga Action Plan was launched, that aimed to reduce the level of pollution of water.
• Sources of water pollution:
  • Water from household or domestic waste is let into the water bodies, which contains suspended impurities, phosphates, organic waste of food and vegetables, etc.
  • Waste from industries and construction sites containing acids, alkalis, toxic metals, gypsum, cement, etc.
  • Radioactive wastes from industrial, scientific and medical purposes.
  • Agricultural runoff containing excess of chemicals and fertilizers.
  • Oil spills from oil rig, tankers or underwater pipelines.
  • Thermal pollution in which river water is used for cooling purposes and is then released into the water.

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• Purification of water: To obtain pure water following methods are used –
  • Use of household filters. It has candle type structure, this allow only water to pass and impurities are held back
  • Boiling of water kills germs in it.
  • Addition of chlorine liquids, tablets or bleaching powder into water helps in purification. This method is known as chlorination of water.
  • Sewage treatment plants helps in the treatment of waste water before releasing it into the water bodies.
  • Treatment of water before supplying for household use must be ensured by municipal bodies.