Atmosphere : Gases Composition

B.Sc.Part 3 Botany Semester v

1. SEMESTER V UNIT V Atmosphere – Gases Composition BY Dr.Vanita Uttamrao Pochhi Shri Shivaji Science and Arts College,Chikhli Dist.Buldana

2. Atmosphere Each and every living organism has its specific surrounding medium of environment to which it continuously interacts and remain fully adopted. The life supporting environment of planet earth the biosphere is composed of three chief media. Atmosphere (air) Hydrosphere(Water) Lithosphere (Soil)

3. Structure of Atmosphere There are five concentric layers within the atmosphere which can be distinguished on the basis of Temperature.These are as follows. 1.Troposphere 2.Stratosphere 3.Mesosphere 4.Thermosphere 5.Exosphere

4. Troposphere 1. It is the lowermost layer. 2. The earths atmosphere from the surface upto about 20km. 3. Troposphere concerns us most because it is the only that supports Plants and Animals . 4. The important weather events such as cloud formation lightning, thundering, etc. take place in troposphere. 5. Air temperature in the zone gradually decreases with height at the rate of about 6.5 c per km. 6. The temperature might decrease upto -60 c towards the upper layer of the troposphere. 7.The water vapour in the atmosphere and most of the air is confined to the troposphere. Troposphere merges into the next zone which is known as Tropopause.

5. Stratosphere 1. It is the Second zone of about 30 km.in height where temperature are about 90 c . 2. In this zone the temperature shows an increase from a minimum of about 5 c. 3. Increase in temperature is due to ozone formation under the influence of ultraviolet rays of solar radiation such a layer of ozone is called Ozonosphere. 4. A large concentration of ozone (o 3 ) is found in the stratosphere.This Ozone layer absorbs much of the ultraviolet radiation emitted by the sun. 5. Stratosphere is above clouds ,violent stroms and precipitation. The upper layer of the stratosphere form the stratopause

6. Mesosphere 1.It is the third layer of the atmosphere about 40 km in height 2. It extends to about 85 km. 3. This layer is often referred to as the cold layer .In this zone temperature shows a decrease upto -- 90 c . 3. The upper limit of the mesosphere is termed as mesopause. 4. Temperature once again grow colder as you rise up through the mesosphere . 5.The air in the mesosphere is far too thin to breathe , 6.Air pressure at the bottom of the layer is below 1% of the pressure at sea level and continues dropping as you longer.

7. Thermosphere 1. Above the mesosphere the region is the Thermosphere . 2. This region is also called as Ionosphere . 3. The height is about 300km.which extends up to 500km above the earths surface . Most of the gaseous component which become ionised . They are rarely present in molecular form. Thus radiant energy brings about considerable changes in the atmosphere. 4. The layer of very rare air above the mesosphere is called thermosphere. 5. High energy x rays and UV radiation from the sun are absorbed in the layer

8. Exosphere Exosphere is the region above the thermosphere . It lacks atoms except that of hydrogen and Helium and extends Up to 32190 km from the earth . Exosphere has a very high temperature due to solar radiation. It contains mainly oxygen and Hydrogen atoms.