1. AIR

2. INTRODUCTION
Air is a mixture of several gases and it forms the atmosphere around us. Air is essential for life. Without food we can live for several weeks, without water we can live for several days but without air we cannot live for more than few minutes.

3. COMPOSITION OF AIR The following is the normal composition of air
nitrogen 78.09%
oxygen 20.94%
carbon dioxide 0.03%
hydrogen, helium, argon and neon – traces

4. USES OF AIR
INSIDE THE BODY Inside body air takes part in oxidation of food material i.e. utilization of food by tissues and removal of waste products in the form of carbon dioxide.

5. USES OF AIR
OUTSIDE THE BODY Air is responsible for regulation of body temperature. Under normal conditions the temperature of the adult human body remains constant at 98.4 F irrespective of the external conditions. Temperature regulation of human body is done by a thermoregulatory centre in the brain.

6. HEAT LOSS MECHANISMS
Air helps in the regulation of the body temperature by following processes:
Conduction-convection
Radiation
Evaporation

7. CONDUCTION-CONVECTION
Heat loss by this mechanism depends upon temperature of the air that surrounds the body. If this temperature is lower than that of body, then heat loss may takes place but if the temperature of the air is either equals to or higher than the body temperature than this mechanism will not takes place.

8. RADIATION
Heat loss by radiation depends upon the temperature of the objects surrounding the body such as walls and roofs of the room. If the temperature of these objects is lower than that of the body, then heat loss takes place otherwise it will not. The surrounding air does not part in this mechanism except by altering the temperature of the surrounding objects.

9. EVAPORATION
Heat is lost from the body by evaporation of sweat from its surface. This heat loss depends upon the difference between the vapour pressure over the body surface and that of surrounding air. If the humidity of air is 100% then no heat loss takes place by this mechanism. The air movement can help in heat loss by this method, by replacing humid air in contact with the body, with drier air.

10. CAUSES OF IMPURITIES IN AIR
These includes
Respiration of living organisms
Combustion of coal, gas, oil etc
Decomposition of organic matter
Traffic pollution
Dust, fumes, vapours and gases from industries.
Nuclear pollution

11. FACTORS RESPONSIBLE FOR NATURAL PURIFICATION OF AIR
WIND
These cause uniformity by dispersal.
MOVEMENT OF AIR AT DIFFERENT TEMPERTURE
Warm air rises constantly and cold air rushes to take its place.
DIFFUSION OF GASES
The different gases in the atmosphere diffuse with one another at a rate which is inversely proportional to the square root of their densities.

12. CONTD.
RAIN
When the rain falls it washes down the suspended impurities of air along with it.
PLANTS
The plants help in purifying the atmosphere by giving off oxygen and taking up carbon dioxide during the day.
SUNLIGHT
Sunlight helps in oxidizing the impurities and killing bacteria.

13. CONTD. OXIDATION OF ORGANIC MATTER
This helps in purifying the atmosphere.