Air

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Atmosphere

A huge blanket of air that surrounds earth is called atmosphere.
It provides us the air we breathe and protects us from the harmful effects of the sun’s rays which is essential for our survival.

Composition of the Atmosphere

Nitrogen and oxygen are two gases which make up the bulk of the atmosphere.
Carbon dioxide, helium, ozone, argon and hydrogen are found in lesser quantities.
Tiny dust particles are also present in the air.

→ Nitrogen: 78%

→ Oxygen: 21%

→ Argon: 0.93%

→ Carbon Dioxide: 0.03%

→ All Others: 0.04%

Nitrogen

→ Plants need nitrogen for their survival but they cannot take it directly from air.

→ Bacteria in soil and plant roots convert nitrogen into usable form.

Oxygen

→ Humans and animals take oxygen from air for breathing.

→ Green plants produce oxygen during photosynthesis, keeping oxygen levels constant.

Carbon Dioxide

→ Green plants use CO₂ to make food and release oxygen.

→ Humans and animals release CO₂ which is balanced by plant usage.

→ Burning fuels like coal and oil increases CO₂, disturbing weather and climate.

Structure of Atmosphere

The atmosphere is divided into five layers starting from the Earth’s surface:

→ Troposphere

→ Stratosphere

→ Mesosphere

→ Thermosphere

→ Exosphere

Troposphere

→ Most important layer as it contains air we breathe and weather events like rainfall, fog, hailstorm.

→ Average height is 13 km.

Stratosphere

→ Lies above troposphere, up to 50 km height.

→ Free from clouds, ideal for aircraft.

→ Contains ozone layer that protects from harmful sun rays.

Mesosphere

→ Third layer, lies above the stratosphere up to 80 km.

→ Meteorites burn up in this layer.

Thermosphere

→ Temperature rises rapidly with height in this layer.

→ Ionosphere is part of this layer (80–400 km).

→ Helps in radio transmission.

Exosphere

→ Uppermost layer of the atmosphere.

→ Air is very thin; helium and hydrogen float into space.

Weather and Climate

→ Weather: Hour-to-hour, day-to-day condition of the atmosphere; changes quickly.

→ Climate: Average weather condition of a place over long periods.

Temperature

→ Temperature is the degree of hotness or coldness of the air.

→ Varies from day to night and season to season.

Insolation

→ Insolation is the incoming solar energy intercepted by Earth.

→ Decreases from equator to poles, hence temperature decreases similarly.

Temperature in Cities

→ Cities are hotter than villages due to heated concrete, metal, and asphalt surfaces.

Air Pressure

→ Air pressure is the pressure exerted by air on Earth's surface.

→ Highest at sea level, decreases with height.

Temperature & Pressure Relation

→ High temperature: Air rises → Low pressure area → Cloudy, wet weather.

→ Low temperature: Air sinks → High pressure area → Clear, sunny skies.

→ Air moves from high to low pressure areas.

Wind

→ Wind: Movement of air from high to low pressure.

→ Three types of winds:

Permanent Winds

→ Trade winds, westerlies, easterlies blow all year in same direction.

Seasonal Winds

→ Change direction with season, e.g., monsoons in India.

Local Winds

→ Blow during a particular time in a small area, e.g., land and sea breeze.

→ Loo: Hot, dry wind in northern Indian plains.

Moisture

→ Evaporation from land/water becomes water vapour.

→ Humidity is moisture in air.

→ Warm air holds more vapour, becomes humid.

→ As vapour rises, it cools and condenses into water droplets.

→ Clouds are masses of such droplets.

→ When droplets get heavy, they fall as precipitation (rain).

Types of Rainfall

→ Convectional rainfall

→ Orographic rainfall

→ Cyclonic rainfall

Importance of Rainfall

→ Essential for survival of plants and animals.

→ Provides fresh water to Earth’s surface.

→ Less rain → Drought; Too much rain → Floods.

MCQs

1. Green plants use ____ to make their food and release ___

(a) Oxygen, helium

(b) Carbon dioxide, hydrogen

(d) Carbon dioxide, oxygen

► (d) Carbon dioxide, oxygen

2. The air pressure is highest at

(a) Plain level

(b) Plateau level

(d) Mountain level

► (c) Sea level

3. As we ___ the layers of atmosphere, the pressure ___

(a) go up, rise

(b) go down, falls

(d) go up, falls

► (d) go up, falls

4. Our earth is surrounded by a huge blanket of

(a) Sand

(b) Air

(d) Water

► (b) Air

5. ____ is this hour-to-hour, day to day condition of the atmosphere

(a) Wind

(b) Weather

(d) Climate

► (b) Weather

6. Which is the second most plentiful gas in the air

(a) Nitrogen

(b) Argon

(d) Hydrogen

► (c) Oxygen

7. Carbon dioxide released in the atmosphere creates a

(a) Green house effect

(b) Carbon effect

(d) Dioxide effect

► (a) Green house effect

8. Meteorites burn up in this layer on entering from the space

(a) Thermosphere

(b) Mesosphere

(d) Stratosphere

► (b) Mesosphere

9. The ___ winds blow constantly throughout the year in a particular direction.

(a) Directional

(b) Local

(d) Seasonal

► (c) Permanent

10. On the Celsius scale the water freezes at ___ and boils at ___

(a) 32ºC, 232ºC

(b) 10ºC, 90ºC

(d) 0ºC, 100ºC

► (d) 0ºC, 100ºC

11. Cold air is ____ than hot air

(a) Small and heavy

(b) Less denser and light

(d) Small and light

► (c) Denser and heavy

12. Which layer is almost free from clouds

(a) Troposphere

(b) Mesosphere

(d) Thermosphere

► (c) Stratosphere

13. When water evaporates from land and different water bodies, it becomes

(a) Ice

(b) Snow

(d) Water Vapour

► (d) Water Vapour

14. The degree of hotness and coldness of the air is known as

(a) Weather

(b) Temperature

(d) Season

► (b) Temperature

15. The standard unit of measuring temperature is

(a) Fahrenheit

(b) Meter

(d) Celsius

► (c) Kelvin

16. Which of the following is not the types of rainfall

(a) Orographic rainfall

(b) Cyclonic rainfall

(d) Seasonal rainfall

► (d) Seasonal rainfall

17. Jet planes flying in the sky leave a ____ trail behind them

(a) Black

(b) Blue

(d) Grey

► (c) White

18. Green House gas is

(a) Nitrogen

(b) Oxygen

(d) Carbon dioxide

► (d) Carbon dioxide