Structure of Atmosphere UPSC Notes – Layers, Composition & Gases

Atmosphere UPSC Notes: Only on Earth can life be found, making it a special planet. Among the circumstances essential for existence, the air holds a special place. There are many different gases in the air. The planet is surrounded by air on all sides. The term “atmosphere” refers to the air that surrounds the Earth. Due to the earth’s gravitational pull on the gases and aerosols near the surface, their density decreases with height.

What is the Atmosphere?

  • The term “atmosphere” refers to the protective layer of gases that envelops the world. It creates a secure barrier separating the biosphere from space.
  • The atmosphere is a fluid mixture of gases that are continually in motion. Around the Earth, these gases create a number of loosely defined strata based on temperature and composition.
  • The gases that make up the current atmosphere are not a direct by-product of the early stages of the development of the world. They are a result of development brought about by hot springs, volcanic eruptions, chemical breakdown of solid substances, and redistribution from the biosphere.
  • Because life on the surface of the world depends on the atmosphere, without which the globe would have turned into a barren moon, the atmosphere is an important part of the biosphere ecosystem. 
  • It shields the planet from the sun’s damaging radiation. By permitting short-wave radiation from the Sun and trapping long-wave terrestrial radiation from the Earth’s surface, it functions as a greenhouse. 
  • To carry out their biophysical processes, all life forms require a specified range of temperature and a specific range of solar radiation frequencies. 
  • Some solar radiation frequencies are absorbed by the atmosphere, while others are let through. In other words, the atmosphere controls how much solar radiation enters the atmosphere.
  • Additionally, the atmosphere regulates the temperature over the surface of the world. Temperature extremes would exist between day and night over the surface of the world without the atmosphere.

The atmosphere of Earth is composed of:

Our planet’s atmosphere is an essential component. Because of the earth’s gravitational pull, it is bound to the planet. It aids in preventing life-threatening UV rays and preserving the ideal temperature required for survival. Our atmosphere, which is made up of a continually shifting mixture of different gases, envelops earth like a blanket. It covers an area of about 950 km. 

Extra-terrestrial objects like meteorites that are destroyed by friction as they pass through the atmosphere are also taken care of by the atmosphere. There are three components of the Atmosphere as follows:

  1. Gases
  2. Dust particles
  3. Water Vapour


  • Gases like nitrogen, oxygen, and argon may be stable because during the recent history of our planet, their concentrations have stayed relatively constant.
    • The majority of volcanic eruptions (78.09%) produce nitrogen, which is a relatively innocuous gas. 
    • An active gas that naturally forms as a result of photosynthesis in plants is oxygen (20.95%).
    • The inert gas argon (0.93%) is colourless and odourless.
  • Gases that change in quantity include carbon dioxide, methane, and ozone. Despite their minor presence in the atmosphere, they exert strong control over a variety of atmospheric phenomena.
  • Carbon dioxide (0.03%) a greenhouse gas allows solar energy to reach the earth’s surface but prevents that energy to radiate back causing a heat build-up in the atmosphere.
  • Methane, a greenhouse gas rising over several decades has contributed to 18% of global warming. Various anthropogenic changes have contributed to the rise of methane in our atmosphere.
  • While allowing solar energy to reach the earth’s surface, carbon dioxide (0.03%), a greenhouse gas, inhibits that energy from radiating back, leading to a build-up of heat in the atmosphere.
  • Methane, a greenhouse gas that has been on the rise for several decades, is responsible for 18% of global warming. Methane levels in our atmosphere have increased as a result of numerous anthropogenic factors.

Ozone Gas 

  • The stratospheric gas ozone is both beneficial and hazardous to life on earth. Although it stops UV rays from reaching the surface of our planet, its presence in the troposphere’s lower levels of the atmosphere might irritate the eyes and the respiratory system.
  • There is extremely little ozone gas in the atmosphere. Although it just affects the ozone layer, it is quite significant. It shields living things by absorbing the sun’s UV radiation. 
  • On the surface of the world, there would not have been any living things or plants if there was no ozone gas in the atmosphere.

Dust Particles:

  • Typically, dust particles are located in the lowest parts of the atmosphere. Sand, smoke, and sea salt are examples of these abrasives. In the atmosphere, sand particles play a vital role.
  • These dust particles support water vapour condensation. Around these dust particles, water vapour condenses into droplets during condensation.
  • This mechanism creates clouds and makes it feasible for precipitation to occur. Although they are primarily concentrated in the lower layers of the atmosphere, they can travel to great heights because of vertical air currents. 
  • They might come from pollen, soot, soil, etc. They might serve as hygroscopic centres for the development of clouds.

Water Vapour: 

  • Water vapour is largely concentrated on the earth’s surface, close to the equator. As one ascends above the surface, it gradually decreases, and it also decreases as one advances toward the pole.
  • Water vapour refers to the gaseous form of water that exists in the atmosphere. Life on earth is only possible because of the water vapour in the atmosphere, which also causes all precipitation. Its atmospheric concentration could reach a maximum of 4%.
  • The hot, humid regions have the most water vapour, while the dry parts contain the least. 
  • From low latitudes to high latitudes, water vapour concentrations typically continue to decline. In a similar manner, its volume continues to shrink as altitude rises.
  • Evaporation and transpiration are the two ways that water vapour enters the atmosphere. In contrast to transpiration, which occurs from plants, trees, and other living things, evaporation occurs in oceans, seas, rivers, ponds, and lakes.
  • Vapour is temperature-dependent, therefore when temperature lowers toward the poles, it moves away from the equator poleward.
  • Numerous types of condensation and precipitation, such as clouds, fogs, dew, rainfall, frost, hailstorm, ice, and snowfall, are produced by the atmosphere’s moisture content.
  • Since vapour absorbs longwave terrestrial radiation, it serves to heat the earth’s surface and lower atmosphere by making the earth’s surface nearly transparent to incoming shortwave solar radiation, allowing electromagnetic radiation waves to pass through it without encountering many impediments.

Structure of the Atmosphere: 

The atmosphere can be divided into numerous levels depending on its temperature and density. Since there is a significant concentration of gases and dust particles near the earth’s surface, we are aware that the atmosphere is denser there. On the basis of temperature and density, we can interpret the layers as they are presented below.

structure of atmosphere

1. Troposphere:

  • The troposphere, the lowest layer of the atmosphere, has a height range of 8 to 18 km. It is taller near the equator and thinner near the poles. The layer that causes weather changes on the surface is where numerous climatic phenomena take place. 
  • The normal lapse rate, also known as the environmental lapse rate, is the rate at which temperature drops as altitude rises. The Earth’s surface, which affects its temperature, moisture content, and wind speed, has a significant impact on this layer’s lower limit. 
  • Tropopause is the boundary separating the troposphere from the second layer. At the equator, it has a temperature of -80°C, while at the poles, -45°C (at the poles). The term “tropopause” refers to this region’s nearly constant temperature.

2. Stratosphere:

  • The second layer of the atmosphere, located below the mesosphere and above the troposphere, is this one. The word “STRAT” literally means “layer.” Since there is no turbulence or storm to mix the air here, the stratosphere is split into its own set of layers, with the heavier cold layer existing underneath the lighter warm layer. This particular layer has a 50-kilometre thickness. 
  • The OZONE layer, also known as the OZONOSPHERE, which shields us from the sun’s harmful UV rays, is another reason why the layer is important. Without this layer of defence, it would have been challenging to live on Earth. Stratopause separates this layer from the mesosphere.

3. Mesosphere:

  • This layer is located below the thermosphere and above the stratosphere. “MESO” stands for the midway. Instead of being divided according to their masses in this layer, the gases are mixed together. This layer is 80 kilometres thick. 
  • The temperature may drop as low as -100°C in the outermost portion of this layer when we move over it. This layer is where meteors that enter the atmosphere burn up. 
  • To breathe through this layer would be dangerous. Due to the friction and heat produced by the gases present in this layer, the temperature may drop as we move above it to as low as -100°C.
  • This layer’s upper boundary, the Mesopause, is what separates it from the Thermosphere.

4. Thermosphere:

  • This layer is located below the exosphere and above the mesosphere. Heat is the definition of the word “THERMO.” This layer’s temperature could rise as high as 4500°F. 
  • The lack of sufficient gases to transfer heat explains why the layer is so chilly. Because there aren’t enough molecules in this layer, sound waves cannot go there. The layer has a 500 km maximum height. 
  • Although not as thick as the Exosphere, the layer is thicker than the other layers of the atmosphere. There are International Space Stations in this stratum that circle the planet. Low Earth Orbit Satellites are also located in this stratum. The Thermopause separates this layer from the Exosphere.

5. Exosphere:

  • Exosphere is the final layer we encounter as we move through the atmosphere. EXO is short for outdoors. 
  • The exosphere, which separates other layers of our atmosphere from space, is located at the very edge of our atmosphere. 
  • The layer is nearly as large as the earth itself and is around 1000 km thick. To go to space, you must travel through a deeper stratum. 
  • There is a large free space between the gases, such as helium and hydrogen, which are widely dispersed throughout the layer. 
  • Because there isn’t any oxygen available, breathing in this layer is practically difficult. Furthermore, this layer is extremely chilly because of its far-reaching nature.

Importance of the Atmosphere: 

  1. Oxygen is very important for living beings. 
  2. Carbon dioxide is very useful for plants. 
  3. Dust particles present in the atmosphere create suitable conditions for precipitation. 
  4. The amount of water vapour in the atmosphere goes on changing and directly affects the plants and living beings. 
  5. Ozone protects all kinds of life on the earth from the harmful ultraviolet rays of the sun.

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