Study Notes : All about the Atmosphere

•About 99% of total mass of atmosphere is within the height of 32 km from earth surface, rest above merges with outer space 

Atmospheric Air → Colourless, Tasteless, Odourless, Compressible, Mobile & Expandable

Atmospheric air mainly consists of -  

Nitrogen   →  78.03 % 

Oxygen     →  20.99 % 

Argon       →  .94 %

CO2         →  .03 % 

H             →   .01 % 

• Rest are Neon, Helium, Ozone, Xenon & Krypton in very minute percentage 
• Nitrogen
• Major cause of atmospheric pressure, Force of wind & reflection of light 
• Regulates combustion & avoids quick burning 
• Dilutes oxygen and prevents rapid burning at the earth’s surface 
• Nitrogen cannot be used directly from the air. 
• The Nitrogen Cycle is nature’s way of supplying the needed nitrogen for living things
• Get fixed to soil & generates protein in plants (Major source of food)
• CO2.
• Heaviest gas in atmosphere, essential for growth of vegetation 
• Transparent to incoming solar radiations but opaque to terrestrial radiations radiated from earth surface which keeps air near the ground warmer 
• Responsible for global warming, as alarming increase in level of CO2 in past few years due to burning of fossil fuels 
• Water Vapour 
• Form in atmosphere due to evaporation from surface water bodies 
• Absorbs part of insolation from the sun & reduces its amount reaching the earth →Preserves earth’s radiated heat 
• Hence, acts as a blanket, allowing the earth to neither become too hot or too cold 
• Amount of water vapour decrease with altitude 
• Amount of water vapour decreases from equator to poles 
• Dust Particles 
• Derived by strong winds from different sources on earth surface
• Acts as hydroscopic nuclei around which water vapour condense & form clouds 
• Intercept & reflect sun rays giving orange colour at sunrise, red colour at sunset & blue colour of clear sky 
• Molecules (Dust particles) in air scatter blue light (shorter wavelength) more than red light (longer wavelength) in every direction, hence sky looks blue 
• At sunrise & sunset, sky appears orange & red because blue light has already been scattered out by molecules in the air, out of sight & longer wavelength light reaches out to us 
• Dense Haze & smog (smoke + fog) are also caused due to presence of dust particles in the air 
• Structure of Atmosphere.
• On the basis of chemical composition atmosphere can be divided into 2 parts viz. 

Homosphere → Upto 90 km (Uniformity in chemical composition) 

Troposphere 

Stratosphere

Mesosphere 

Heterosphere → Above 90 Km (non-uniformity in chemical composition) 

Ionsphere

Exosphere   

Each sublayer mentioned in these 2 layers is further divided by a shallow transitional zone ending with term “Pause” 

Troposphere

• Average height is 16 Km → 10 km at Poles &upto 18 km at Equator.
• Greatest at Equator due to upward transportation of heat by strong conventional currents.
• That is why height of troposphere at a given latitude is greater in summer Temperature decreases with height, roughly at 1*C for every 165 meters → Normal Lapse Rate.
• Lowest, Densest & contains 75 % of earth’s atmosphere with 90% of water vapours & dust particles.
• All major atmospheric processes take place in this layer.

Tropopause 

Shallow transitional zone (Unstable zone) b/w Troposphere & Stratosphere (Approx. 1.5 Km) 

Temperature stops falling in this layer → – 80*C over equator & – 45*C over poles 

Stratosphere 

• This layer rises upto 50 km (Thicker at Poles than at Equator) 
• Temperature remains constant in its lower portion upto 20 Km & then gradually increases to 0*C till its upper limit i.e. 

Tropopause 

• Increases mainly due to the presence of ozone gas, which absorbs sun’s UV rays
• Practically no clouds, convection currents, Thundering or lighting, water vapours or dust particles hence airplane fly in this region
• Few clouds called “Mother of Pearls / Narcreas” can be seen over Antarctica
• Its lower portion (15 – 35 Km) constitutes Ozone layer which prevents us from harmful UV rays 
• Amount of Ozone gas is found at Stratopause i.e. uppermost limit of Stratosphere

Mesosphere

• Upto 80 ~ 90 Km, Temp. Decreases gradually with height until – 100 *C at 80 km 
• Displays wispy clouds at high altitudes due to reflected sunlight from meteoric dust particles 
• Most weather balloons are placed in this region 
• Most meteors burn up in this layer; Upper limit Mesopause