Composition of the Atmosphere

The atmosphere is a mixture of several gases that surround the Earth and make life possible. Each gas has a specific role in maintaining environmental balance and supporting living organisms.

Major Components of Air

1. Nitrogen (N₂)
   • Nitrogen is the most abundant gas in the atmosphere.
   • It forms a major part of the air and is essential for plant growth.
   • Plants absorb nitrogen indirectly from the soil for the formation of proteins and other nutrients.
2. Oxygen (O₂)
   • Oxygen is the second largest component of the atmosphere.
   • Human beings and animals require oxygen for respiration.
   • It is also necessary for combustion and various biological processes.
3. Carbon Dioxide (CO₂)
   • Carbon dioxide is present in a smaller quantity but plays a vital role in nature.
   • Green plants use carbon dioxide during photosynthesis to prepare food.
   • In this process, plants release oxygen back into the atmosphere.
4. Argon and Other Gases
   • Argon is an inert gas found in small amounts in the atmosphere.
   • Apart from argon, traces of gases such as helium, neon, hydrogen, and ozone are also present.

Structure of the Atmosphere

The atmosphere is divided into different layers based on changes in temperature and altitude. These layers protect Earth and support various natural processes.

Layers of the Atmosphere

1. Troposphere

• The troposphere is the lowest and most significant layer of the atmosphere.
• Its average height is around 13 km from the Earth’s surface.
• Almost all weather-related activities such as rainfall, clouds, storms, and snowfall occur in this layer.
• The air required for breathing is mainly found here.

2. Stratosphere

• The stratosphere lies above the troposphere and extends up to nearly 50 km.
• This layer contains the ozone layer, which protects life on Earth from harmful ultraviolet rays of the Sun.
• Since weather disturbances are absent here, aeroplanes often fly in this region.

3. Mesosphere

• The mesosphere is located above the stratosphere.
• It extends up to about 80 km above the Earth’s surface.
• Meteors entering Earth’s atmosphere usually burn up in this layer due to friction.

4. Thermosphere

• In the thermosphere, temperature increases rapidly with height.
• The ionosphere forms a part of this layer and extends approximately between 80 km and 400 km.
• This region is important for radio communication because it reflects radio waves back to Earth.

5. Exosphere

• The exosphere is the outermost layer of the atmosphere.
• It gradually merges into outer space.
• The air is extremely thin in this layer.

Weather and Climate

Weather

• Weather refers to the short-term or day-to-day condition of the atmosphere at a particular place.
• It changes frequently and includes conditions such as temperature, rainfall, humidity, and wind.

Climate

• Climate represents the average weather conditions of a place observed over a long period of time.
• It remains relatively stable compared to weather.

Important Elements of Weather and Climate

Temperature

• Temperature indicates the degree of hotness or coldness of the atmosphere.
• It is measured using a thermometer.

Air Pressure

• Air pressure is the force exerted by the weight of air on the Earth’s surface.
• Differences in air pressure influence weather patterns and wind movement.

Wind

• Wind is the movement of air from areas of high pressure to areas of low pressure.

Types of Winds

1. Permanent Winds

• Permanent winds blow continuously throughout the year in a fixed direction.
• Examples include:
  • Trade Winds
  • Westerlies
  • Easterlies

2. Seasonal Winds

• Seasonal winds change their direction according to seasons.
• The monsoon winds of India are the best example.

3. Local Winds

• Local winds affect small regions and blow for a short duration.
• Examples:
  • Land Breeze
  • Sea Breeze
  • Loo – a hot and dry wind that blows over the northern plains of India during summer.

Key UPSC Points to Remember

• Nitrogen is the most abundant gas in the atmosphere.
• Ozone layer is located in the stratosphere.
• Weather changes frequently, whereas climate is long-term.
• The ionosphere helps in radio communication.
• Winds always move from high-pressure regions to low-pressure regions.