Fundamentals of Physical Geography

Composition and Structure of Atmosphere Class 11 Geography Notes

Class 11 Geography Chapter 7 – Composition and Structure of Atmosphere Notes

These Composition and Structure of Atmosphere Class 11 Notes explain the meaning, composition, importance and layers of the atmosphere. The chapter discusses gases, water vapour, dust particles and the vertical structure of the atmosphere along with the significance of different atmospheric layers. (NCERT Page 64)

These notes are useful for UPSC, SSC, Railways, State PSC, CUET, CBSE Board Exams and other competitive examinations because atmosphere-related concepts are frequently asked in Geography, Environment and General Science sections. Exact NCERT page references are included throughout the notes for revision and exam preparation. (NCERT Pages 64–66)

Table of Contents

Chapter Overview

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 (NCERT Page 64)

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 (NCERT Page 64)

Composition of Atmosphere

The atmosphere consists of:

Component Importance
Gases Support life and regulate temperature
Water Vapour Controls humidity and rainfall
Dust Particles Help in cloud formation

Gases of Atmosphere (NCERT Page 64)

Major Atmospheric Gases

Gas Importance
Nitrogen Largest proportion in atmosphere
Oxygen Essential for respiration
Carbon Dioxide Greenhouse effect
Ozone Absorbs ultraviolet rays

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

Ozone Layer (NCERT Page 64)

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 (NCERT Page 64)

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

Dust Particles (NCERT Page 65)

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

Layers of Atmosphere (NCERT Pages 65–66)

Layer Approximate Height
Troposphere Up to 8–18 km
Stratosphere Up to 50 km
Mesosphere Up to 80 km
Thermosphere/Ionosphere 80–400 km
Exosphere Above thermosphere

Troposphere (NCERT Page 65)

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.

Stratosphere (NCERT Page 65)

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

Mesosphere (NCERT Page 65)

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

Mesopause

  • Upper limit of mesosphere

Thermosphere / Ionosphere (NCERT Page 65)

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

Exosphere (NCERT Page 66)

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

Elements of Weather and Climate (NCERT Page 66)

Element Importance
Temperature Controls heat conditions
Pressure Controls air movement
Winds Distribute heat and moisture
Humidity Determines moisture content
Clouds Associated with precipitation
Precipitation Rainfall, snowfall etc.

Important Topics

Important Topic NCERT Page
Composition of atmosphere 64
Carbon dioxide and greenhouse effect 64
Ozone layer 64
Water vapour 64
Dust particles 65
Structure of atmosphere 65

Important Scientific Concepts / Terms

Concept Explanation NCERT Page
Greenhouse Effect Trapping of heat by gases 64
Ozone Layer Absorbs UV rays 64
Tropopause Boundary between troposphere and stratosphere 65
Mesopause Upper boundary of mesosphere 65
Hygroscopic Nuclei Dust particles aiding condensation 65

Important Questions

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)

FAQs

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)

Quick Revision Summary

  • 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
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