Composition and Structure of Atmosphere Class 11 Geography Notes

This chapter explains the composition of the atmosphere and its layered structure. It highlights the importance of gases like oxygen, carbon dioxide and ozone, explains the role of water vapour and dust particles, and discusses the major atmospheric layers such as troposphere, stratosphere, mesosphere, thermosphere and exosphere. (NCERT Pages 64–66)

Major Topics Covered

• Meaning of atmosphere
• Composition of atmosphere
• Gases in atmosphere
• Role of carbon dioxide
• Importance of ozone layer
• Water vapour
• Dust particles
• Structure of atmosphere
• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere/Ionosphere
• Exosphere
• Elements of weather and climate

Meaning of Atmosphere

• Atmosphere is a mixture of different gases surrounding the Earth.
• It envelopes the Earth from all sides.
• It contains life-supporting gases like oxygen and carbon dioxide.
• Atmosphere is essential for survival of all organisms.
• 99% of atmospheric mass is confined within 32 km from Earth’s surface.
• Air is colourless and odourless.

Importance of Atmosphere

• Provides oxygen for respiration.
• Provides carbon dioxide for photosynthesis.
• Protects Earth from harmful solar radiation.
• Regulates temperature.
• Supports weather and climate processes.

Composition of Atmosphere

The atmosphere consists of:

Major Atmospheric Gases

Carbon Dioxide

• Carbon dioxide is transparent to incoming solar radiation.
• It is opaque to outgoing terrestrial radiation.
• It absorbs terrestrial radiation and reflects heat back to Earth.
• Responsible for greenhouse effect.

Causes of Increase in CO₂

• Burning of fossil fuels
• Industrialisation
• Human activities

Effects

• Increase in atmospheric temperature
• Global warming

Importance of Ozone

• Ozone layer is found between 10 km and 50 km above Earth’s surface.
• It absorbs harmful ultraviolet rays from the Sun.
• Prevents harmful radiation from reaching Earth.

Importance for Life

• Protects humans from skin diseases
• Protects plants and animals
• Maintains ecological balance

Water Vapour

• Water vapour is a variable gas.
• Amount decreases with altitude.
• Highest in warm and humid tropics.
• Lowest in deserts and polar regions.

Importance of Water Vapour

• Absorbs solar radiation
• Preserves Earth’s radiated heat
• Prevents extreme heating and cooling
• Helps in cloud formation
• Influences stability and instability of air

Sources of Dust Particles

• Sea salts
• Fine soil
• Smoke soot
• Ash
• Pollen
• Meteor particles

Characteristics

• Mostly concentrated in lower atmosphere
• Transported upward by convection currents
• Higher concentration in subtropical and temperate regions

Importance

• Act as hygroscopic nuclei
• Help in condensation
• Essential for cloud formation

Features of Troposphere

• Lowest layer of atmosphere
• Average height: 13 km
• 8 km near poles
• 18 km near equator
• Contains dust particles and water vapour
• Weather and climate changes occur here
• Most important layer for biological activities

Temperature Change

• Temperature decreases with height.
• Rate: 1°C per 165 m.

• Extends up to 50 km
• Contains ozone layer
• Absorbs ultraviolet radiation
• Protects life on Earth
• Stable atmospheric conditions
• Suitable for jet aircraft

• Extends up to 80 km
• Temperature decreases with altitude
• Temperature reaches nearly -100°C at 80 km

Mesopause

• Upper limit of mesosphere

• Located between 80 km and 400 km
• Contains electrically charged particles called ions
• Reflects radio waves back to Earth
• Temperature increases with height

• Uppermost layer of atmosphere
• Atmospheric gases are extremely rarefied
• Gradually merges with outer space
• Very little is known about this layer

Very Short Answer Questions

1. What is atmosphere? (NCERT Page 64)
2. Name the major gases of atmosphere. (NCERT Page 64)
3. What is greenhouse effect? (NCERT Page 64)
4. Which layer contains ozone layer? (NCERT Page 65)
5. What is tropopause? (NCERT Page 65)
6. Which atmospheric layer reflects radio waves? (NCERT Page 65)
7. Name the uppermost layer of atmosphere. (NCERT Page 66)
8. What are hygroscopic nuclei? (NCERT Page 65)

Short Answer Questions

1. Explain the importance of atmosphere. (NCERT Page 64)
2. Describe the role of carbon dioxide in atmosphere. (NCERT Page 64)
3. Explain the importance of ozone layer. (NCERT Page 64)
4. What is the role of water vapour in atmosphere? (NCERT Page 64)
5. Describe the structure of atmosphere. (NCERT Pages 65–66)
6. Why is troposphere important for human life? (NCERT Page 65)

Long Answer Questions

1. Describe the composition of atmosphere in detail. (NCERT Pages 64–65)
2. Explain the layered structure of atmosphere with diagram. (NCERT Pages 65–66)
3. Discuss the importance of atmospheric gases. (NCERT Page 64)
4. Explain the role of dust particles and water vapour in atmosphere. (NCERT Pages 64–65)

1. What is atmosphere?

Atmosphere is a mixture of gases surrounding the Earth. (NCERT Page 64)

2. Which gas is responsible for greenhouse effect?

Carbon dioxide is mainly responsible for greenhouse effect. (NCERT Page 64)

3. Why is ozone layer important?

It absorbs harmful ultraviolet rays from the Sun. (NCERT Page 64)

4. Which layer is most important for weather changes?

Troposphere is most important because all weather changes occur there. (NCERT Page 65)

5. Which layer reflects radio waves?

Ionosphere reflects radio waves back to Earth. (NCERT Page 65)

• Atmosphere surrounds Earth.
• 99% atmospheric mass lies within 32 km.
• Carbon dioxide causes greenhouse effect.
• Ozone absorbs UV rays.
• Water vapour regulates temperature.
• Dust particles help in condensation.
• Troposphere is weather-making layer.
• Stratosphere contains ozone layer.
• Mesosphere extends up to 80 km.
• Ionosphere reflects radio waves.
• Exosphere merges with outer space.
• Main weather elements:
  • Temperature
  • Pressure
  • Winds
  • Humidity
  • Clouds
  • Precipitation