Chapter 4: Air & Atmosphere
वायु एवं वायुमंडल की संरचना (क्षोभमंडल, समतापमंडल में ओजोन, पवन प्रणाली)
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- Atmospheric gas composition: Nitrogen 78%, Oxygen 21%, Argon 0.93%, Carbon Dioxide 0.04%, trace gases and water vapour.
- Greenhouse Effect: Carbon dioxide traps heat radiated from the earth surface, keeping Earth warm enough for life. Without it, Earth would be freezing cold.
- Troposphere: Lowest and most vital layer, average height 13 km; contains the air we breathe; almost all weather phenomena (clouds, rainfall, fog, hailstorms) occur here.
- Stratosphere: Extends from 13 km up to 50 km; cloud-free with stable air, making it ideal for flying jet airplanes; houses the protective Ozone Layer that absorbs harmful solar UV rays.
- Mesosphere: Third layer extending up to 80 km; meteorites burn up upon entering from outer space due to atmospheric friction.
- Thermosphere / Ionosphere: Extends from 80 km to 400 km; contains electrically charged ions; temperature rises sharply; reflects radio waves back to Earth for wireless communication.
- Exosphere: Uppermost layer with extremely thin air; light gases like Hydrogen and Helium float into outer space.
- Classification of Winds: Permanent winds (Trade winds, Westerlies, Easterlies blow constantly year-round); Seasonal winds (Monsoon winds in India); Local winds (blow only during particular periods in small areas, e.g. Loo hot summer wind, sea/land breeze).
- Trap: In which layer do meteorites burn up? Correct: MESOSPHERE (not Stratosphere, not Troposphere).
- Trap: Which layer is ideal for jet airplanes and contains Ozone? Correct: STRATOSPHERE.
- Trap: Which layer enables radio transmission? Correct: THERMOSPHERE / IONOSPHERE.
NCERT Core Facts: Atmospheric Layers, Composition & Wind Systems
In CTET Paper 2 Social Studies (Geography), the 5 atmospheric layers and their distinctive meteorological features are examined in almost every cycle.
1. Composition of the Atmosphere
- Nitrogen ($78\%$): Most plentiful gas; inhaled and exhaled by humans without change; essential for plant protein synthesis (fixed by root bacteria).
- Oxygen ($21\%$): Inhaled by humans and animals for respiration; generated by green plants through photosynthesis.
- Argon ($0.93\%$): Inert noble gas.
- Carbon Dioxide ($0.04\%$): Used by plants to synthesize food; acts as a greenhouse gas by absorbing infrared radiation; excess emissions cause global warming.
2. The Five Concentric Atmospheric Layers
| Atmospheric Layer | Altitude Range | Primary NCERT Features (CTET Exam Benchmarks) |
|---|---|---|
| 1. Troposphere (क्षोभमंडल) | Average height 13 km | Contains the air we breathe. All weather phenomena (rainfall, fog, storm, hailstorm) occur exclusively here. |
| 2. Stratosphere (समतापमंडल) | From 13 km up to 50 km | Free from clouds and turbulent weather; ideal for flying jet airplanes. Contains the Ozone layer (O_3) shielding Earth from UV rays. |
| 3. Mesosphere (मध्यमंडल) | From 50 km up to 80 km | Coldest layer (temperatures plunge down to -100^\circ C). Meteorites burn up in this layer upon entering from space. |
| 4. Thermosphere / Ionosphere (आयनमंडल) | From 80 km up to 400 km | Contains charged ion particles. Reflects radio waves back to Earth, enabling global wireless telecommunication. |
| 5. Exosphere (बहिर्मंडल) | Above 400 km | Uppermost layer merging into space. Extremely thin air; light gases like Hydrogen ($H_2$) and Helium ($He$) float into space. |
3. Wind Systems (पवन प्रणाली)
Wind is the movement of air from high-pressure areas to low-pressure areas:
- 1.Permanent Winds (स्थायी पवनें): Trade winds, Westerlies, and Polar Easterlies. Blow constantly in a fixed direction throughout the year.
- 2.Seasonal Winds (सामयिक पवनें): Winds that reverse their direction in different seasons (e.g., the Monsoon winds of India).
- 3.Local Winds (स्थानीय पवनें): Blow only during a specific period of the day or year in a small local area:
- Sea Breeze & Land Breeze along coastal belts.
- Loo (लू): The hot, dry, dusty local wind that blows across northern plains of India during May and June.
Test Your Mastery: Air & Atmosphere
Authentic CBSE exam questions tested directly from this NCERT chapter.
In which layer of the atmosphere do meteorites burn up upon entering from space?
अंतरिक्ष से प्रवेश करने वाले उल्कापिंड वायुमंडल की किस परत में जलकर भस्म हो जाते हैं?
Which layer of the atmosphere contains the ozone gas layer and is considered ideal for flying jet aeroplanes?
वायुमंडल की किस परत में ओजोन गैस की परत पाई जाती है और जो जेट हवाई जहाजों के उड़ने के लिए आदर्श मानी जाती है?
The hot and dry local wind blowing across the northern plains of India in summer is called:
गर्मियों में भारत के उत्तरी मैदानों में चलने वाली गर्म एवं शुष्क स्थानीय पवन को क्या कहा जाता है?
In which atmospheric layer do meteorites burn up?
Meteorites burn up in the Mesosphere due to atmospheric friction.
Why is the stratosphere ideal for flying jet airplanes?
Because it is cloudless, free from weather turbulence, and contains smooth horizontal airflow.
Which layer reflects radio waves back to Earth?
The Thermosphere (specifically the Ionosphere).