Class 11 Geography Chapter 8 Composition and Structure of Atmosphere Notes in English

Chapter - 8

Composition and Composition of Atmosphere

️ Atmosphere :-

The cover of air around the earth is called atmosphere. This cover of air is stuck around the earth as a blanket due to the gravitational force of the earth and is an important part of the earth. Part of life on Earth is possible because of such an atmosphere. Air is important for all living beings to survive. 99% of the atmosphere is confined to a height of 32 km above the earth's surface .

️ Air :-

The mixture of different gases is called air. Air is colourless, odorless and tasteless. Many important gases such as nitrogen, oxygen, argon, carbon dioxide, neon, helium, ozone, hydrogen, methane, krypton, xenon, etc. are found in the air.

Apart from gases, water vapor and dust particles are also present in the atmosphere.

️ Aerosols :-

Water particles, carbon dioxide, ozone, xenon, krypton, neon, argon and large solid particles in the atmosphere together are called aerosols.

Layers of Atmosphere :-

On the basis of temperature and air pressure, the atmosphere is divided into five layers – troposphere, stratosphere, mesosphere, ionosphere and outer mantle . All the circles have different characteristics.

Briefly explain the composition of the atmosphere :-

The atmosphere is mainly composed of some gases, water vapor and dust particles.

Gases :-

Most of the gases in the atmosphere consist of nitrogen (78.8%) and oxygen (20.95%). Apart from this, the main gases are carbon dioxide, argon and ozone etc. All gases have their own importance. The definite proportion in which these gases are present should be maintained.

Water vapor :-

The amount of water vapor in the atmosphere depends on the climate of a place. Water vapor absorbs some of the insolation and also absorbs the heat emitted from the earth. In this way, it protects the earth from getting too hot and too cold.

Dust Particles :-

Dust particles act as nuclei to absorb moisture and help in the formation of clouds.

Importance of dust particles in the atmosphere :-

Due to the movement of air in the atmosphere, fine particles of dust keep flying. These dust particles are obtained from various sources. These include fine soil, dust, sea salt, smoke soot, ash and meteorite particles. These dust particles are very useful for our life. By this process clouds are formed and it rains. Dust particles also work to prevent insolation and reflect it. They form shades of red and orange in the sky at sunrise and sunset.

Description of the important gases of the atmosphere :-

The atmosphere is a mixture of many gases. In addition to gases, water vapor and dust particles are also present in the atmosphere.

The distribution of some important gases is as follows:

Nitrogen :-

The highest percentage of this gas is 78.8 percent. It is one of the important gases in the atmosphere. Nitrogen is used to make proteins for plants, which are the main part of food.

Oxygen :-

Oxygen gas is considered to be the life-giving gas because without it we cannot breathe. The amount of oxygen in the atmosphere is 20.95 percent. We cannot burn fuel in the absence of oxygen.

Carbon dioxide gas :-

It is the heaviest gas and due to this it is found only in the lowest layer. Despite being only 0.03 percent in the atmosphere, carbon dioxide is an important gas because it is essential for plants.

Ozone gas :-

It is found in the atmosphere in very less quantity only at higher altitudes. It absorbs dangerous ultraviolet radiation coming from the sun.

Aerosols :-

Water particles, carbon dioxide, ozone, xenon, krypton, neon, argon and large solid particles in the atmosphere are called aerosols.

Description of the composition of the atmosphere :-

On the basis of temperature and air pressure, the atmosphere is divided into five major layers. On the basis of chemical composition, the atmosphere is divided into two broad layers homosphere and heterosphere.

But on the basis of temperature and composition of gases, the atmosphere is divided into the following layers:-

🔶 क्षोभमंडल ( Troposphere ) :-

It is the lowest layer of the atmosphere. Its average altitude is 13 km. Its height is 18 km at the equator and 8 km at the poles. All the events related to seasons and seasons happen in this layer. This layer is useful for humans.

🔶 समतापमंडल ( Stratosphere ) :-

This layer is up to 50 km wide. There is no change in temperature in its lower part up to a height of 20 km, hence it is called stratosphere. Above this, the temperature rises up to a height of 50 kilometers, the ozone gas is present in the lower part of this layer, which absorbs the ultraviolet radiation coming from the Sun.

🔶 मध्यमंडल ( Mesosphere ) :-

The extent of this layer is from 50 to 90 km high. The temperature in this layer decreases with height.

Ionosphere :-

The extent of this layer is from 90 km to 400 km. The particles of the gas present here are electro-charged, they are called ions. The ionosphere reflects the radio waves transmitted from the earth and sends them back to the earth.

🔶 बाह्यमंडल ( Exosphere ) :-

Above the ionosphere is the uppermost layer of the atmosphere, which is called the exosphere. Air is very rare in this layer, which gradually merges into outer space.

Why is the troposphere considered to be the most important layer of the atmosphere?

The troposphere is the lowest layer of the atmosphere. Its average altitude is 13 km. Its height is 18 km at the equator and 8 km at the poles. The reason for the high height of the troposphere at the equator is due to the convective currents running there which carry the heat to a sufficient height. In addition to these

In the troposphere, all weather-related events like cloud formation, rain, condensation, etc. take place.
The temperature in this zone decreases with altitude.
Dust particles and water vapor are in maximum quantity in this layer.

Why is the troposphere called the life-giving layer?

The troposphere is considered to be the life-giving layer because all the favorable conditions for survival occur in this layer, apart from this, all the weather related events like wind, rain, lightning and formation of clouds, etc. take place in this layer.

Difference between weather and climate :-

Weather: The average of the elements like temperature, rainfall, air pressure, humidity, wind direction and speed etc. is called weather. It expresses short duration or daily atmospheric conditions over a small area.

Climate: The average of the elements of the weather is a general expression of atmospheric conditions based on studies of many years over a long time period and over a large area.

Main elements of weather and climate :-