NCERT Class 11 Geography Chapter 8: Composition and Structure of Atmosphere YouTube Lecture Handouts

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NCERT Class 11 Geography Part 1 Chapter 8: Structure and Composition of Atmosphere

Frequency: (hence air is crucial)

99 % of mass of atmosphere is confined in 32 km from earth՚s surface

Air is colorless & odorless and felt only when it blows as wind

Composition of Atmosphere

  • Oxygen would be negligible beyond 120 km
  • not found beyond 90 km
Constituent and Its Formula

: Interesting Gas

  • Transparent to incoming solar radiation but opaque to outgoing terrestrial radiation
  • Absorbs a part of terrestrial radiation and reflects back some part of it towards the earth՚s surface
  • Responsible for greenhouse effect
  • Volume increasing due to burning of fossil fuels
  • Leads to rise of temperature


  • Lies between 10 to 50 km
  • Act as filter and absorbs ultra-violet rays

Water Vapor

  • Varies in atmosphere
  • Decreases with altitude
  • Account for 4 % by volume (warm & tropical area) & 1 % by volume (in cold desert and polar areas)
  • Decreases from equator to poles
  • Absorbs insolation and act as blanket
  • Contributes to stability and instability of air

Dust Particles

  • Concentrated in lower layers
  • Convectional air currents transport them to more heights
  • High concentration in subtropical and temperate regions due to dry wind as compared to equatorial and polar regions
  • Act as hygroscopic nuclei around which water vapor condenses to produce clouds

Structure of Atmosphere

Density decreases with altitude


  • Lowermost layer with average height of 13 km (8 km at poles and 18 km at equator)
  • Maximum thickness at equator as heat transported by convection currents
  • Temperature fall of for every 165 meters
  • Major layer for biological activities


  • Separates troposphere and stratosphere
  • Ranges from at equator to at poles
  • Temperature is constant
Structure of Atmosphere


  • Height upto 50 km
  • Has ozone layer – absorbs UV rays


  • Upto 80 km
  • Temperature decreases with height and reach at 80 km


  • Between 80 to 400 km
  • Electrically charged particles as ions
  • Reflects radio waves
  • Temperature increases with height


  • Outermost layer
  • Extremely rarified

Elements of Climate

  • Temperature
  • Pressure
  • Winds
  • Humidity
  • Clouds
  • Precipitation