Composition and Structure of Atmosphere, UPSC Notes

The atmosphere is the layer of gases surrounding Earth. The air is an essential component of the earth's mass, and 99 percent of the total mass of the atmosphere is concentrated at a height of 32 kilometres above the earth's surface, held in place by gravity. Nitrogen and oxygen account for 99 percent of the gases in dry air, with argon, carbon dioxide, helium, neon, and other gases making up the remaining volume. The combination of gases in the atmosphere forms a complex system divided into layers that support life on Earth. 

The atmosphere can be divided into five layers - Troposphere, Ionosphere, Stratosphere, Exosphere, and Mesosphere. These atmospheric layers are characterised by variations in temperature resulting primarily from the absorption of solar radiation.

Atmosphere Composition

Earth’s atmosphere comprises about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.1 percent other gases. The remaining 0.1% of gases includes a trace amount of neon, water vapour, carbon dioxide, methane and others. Water vapour and Carbon dioxide are found up to 90 km from the earth's surface.

• Nitrogen: Nitrogen is the most prevalent element in the atmosphere's dry composition. At the Earth's surface, nitrogen slows down the rate of burning and dilutes oxygen. Living things require nitrogen to synthesise proteins.
• Oxygen: It is essential for respiration and necessary for combustion (burning). 
• Carbon dioxide:
  • It is essential for photosynthesis by plants, algae and photosynthetic bacteria, to be used by living things as food. 
  • It acts as a blanket that prevents heat from escaping into space called the greenhouse effect. It absorbs some of the terrestrial radiation and reflects some of it toward the surface of the earth.
• Ozone: It serves as a filter and can be found between 10 and 50 kilometres above the surface of the earth which absorbs harmful ultraviolet rays from the sun and stops them from reaching the earth's surface.
• Water Vapour: It is typically present in up to 4% of the total volume, depending on location. With an increase in altitude, water vapour levels decline.
  • When dry winds blow through the Earth's desert regions (30° N/S), the contribution of water vapour to the composition of the atmosphere is nearly zero.
• Dust Particles: In the lower layers of the atmosphere, dust particles are typically concentrated, but convectional air currents can carry them to great heights.
  • They are more concentrated in subtropical and temperate regions than in equatorial and polar regions due to dry winds.

Atmosphere Structure

The atmosphere is divided into five layers, depending on temperature and density. In general, both temperature and density decrease with increasing altitude.

Weather

Weather is a combination of events that occur in our atmosphere daily. The weather varies around the world and changes over a few minutes, hours, days, and weeks. The troposphere, the region of Earth's atmosphere closest to the ground, is where most weather happens.

• Air Pressure and Weather: Changes in atmospheric pressure determine the weather that occurs in a region.
  • Usually, clear, blue skies are present when air pressure is high. The high pressure prevents clouds from forming by causing air to flow down and fan out when it gets close to the ground.
  • Low air pressure causes air to flow together before converging upward, where it rises, cools, and forms clouds.

Climate

Climate refers to an area's average weather pattern over a long period. The weather is what we see outside on any particular day; the climate is the average of that weather. Different regions have different regional climates. 

• Global climate: The average of all regional climates is referred to as the global climate. Weather patterns are anticipated to change along with the global climate.
• Elements of Climate: The main elements of climate are temperature, pressure, winds, and rainfall. All these elements are highly variable and constitute the climate. 
  • They are inextricably linked, and any change in one of them usually causes changes in the others.
  • The variations in climate are largely the result of variations in the amount, intensity, and distribution of these elements over the earth. 
• Climate Controls: The important factors that influence the regional climates are:
  • latitude
  • altitude
  • winds and air masses
  • distribution of land and water, distance from the sea
  • semi-permanent high and low-pressure systems
  • atmospheric disturbances or storms
  • ocean currents
  • mountain barriers
  • natural vegetation

Atmosphere UPSC PYQs

Question 1: Troposphere is a very significant atmosphere layer that determines weather processes. How? (UPSC Mains 2022)

Question 2: Normally, the temperature decreases with the increase in height from the Earth’s surface, because (UPSC Prelims 2012)

1. the atmosphere can be heated upwards only from the Earth’s surface
2. there is more moisture in the upper atmosphere
3. the air is less dense in the upper atmosphere

Select the correct answer using the codes given below 

1. 1 only
2. 2 and 3 only
3. 1 and 3 only
4. 1, 2 and 3

Answer: (c)

Question 2: A layer in the Earth’s atmosphere called Ionosphere facilitates radio communication. Why? (UPSC Prelims 2011)

1. The presence of ozone causes the reflection of radio waves to Earth.
2. Radio waves have a very long wavelength.

Which of the statement(s) given above is/are correct?

1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2 

Answer: (d)

Question 3: The jet aircrafts fly very easily and smoothly in the lower stratosphere. What could be the appropriate explanation?

1. There are no clouds or water vapour in the lower stratosphere.
2. There are no vertical winds in the lower stratosphere.

Which of the statement(s) given above is/are correct in this context?

1. 1 only
2. 2 only 
3. Both 1 and 2
4. Neither 1 nor 2

Answer: (c)

Atmosphere FAQs 

Q1. What is the composition of the atmosphere?

Ans. Earth’s atmosphere is composed of about 78 percent nitrogen, 21 percent oxygen, 0.9 percent argon, and 0.1 percent other gases. The remaining 0.1 percent of gases includes trace amounts of neon, water vapour, methane, carbon dioxide, and methane. 

Q2. What is the Atmosphere and its importance?

Ans. The atmosphere is a mixture of gases that surrounds the Earth. It helps support life by giving us oxygen to breathe, protecting us from the Sun's harmful ultraviolet (UV) radiation, retaining heat to warm the planet, and reducing extreme temperature variations between day and night. 

Q3. How many layers are in the atmosphere?

Ans. The atmosphere is divided into five different layers: Troposphere, Ionosphere, Stratosphere, Exosphere, and Mesosphere varying in density and temperature.