1. carbon dioxide
1.1. the percentage of carbon dioxide in the air: 0.03%-0.04%
1.2. significance of carbon dioxide
1.2.1. it acts as food for plants
1.2.2. it does not allow the heat to radiate rapidly at night
2. water vapour
2.1. the percentage of water vapour: 0.4%-4%
2.2. significance of water vapour
2.2.1. it determines the climatic conditions
2.2.2. it controls the rate of evaporation
2.2.3. it is essential for the growth of plants
3. noble gases
3.1. a group gases which chemically do not react
3.2. significance of noble gases
3.2.1. helium is used for filling weather observation balloons
3.2.2. argon is used for filling electric bulbs
3.2.3. neon is used for the glowing of the advertisment
4. nitrogen
4.1. the percentage of nitrogen in air: 77.9%-78.03%
4.2. significance of nitrogen
4.2.1. it dilutes the activity of oxygen
4.2.2. they take nitrogen indirectly through nitrogen compounds
4.2.2.1. the compounds of nitrogen are of vital importance to plants to manufacture proteins.
4.2.2.1.1. During lightning an electric spark passes through the air
4.2.2.1.2. some bacteria directly absorb nitrogen
5. oxygen
5.1. the percentage of oxygen: 20.8%-20.9%
5.2. significance of oxygen
5.2.1. it supports all animal and plant life
5.2.2. it is essential for the combustion of fuels
5.2.3. it is present in water also so marine animals can take the oxygen in the water
6. impurities
6.1. the percentage of impurites is never constant, but increases near industrious areas
6.2. they consist of
6.2.1. dust particles
6.2.2. smoke particles
6.2.3. sulphur dioxide
6.2.4. nitrogen dioxide
6.2.5. carbon monxide
6.2.6. hydrogen sulphide