Chapter: Air: Composition and Structure

I. Introduction
- The Earth's atmosphere is a mixture of gases that surround the planet.
- The composition and structure of the air play a vital role in supporting life and influencing weather patterns.

II. Composition of Air
- Air is primarily composed of nitrogen (78%) and oxygen (21%).
- Other gases present in smaller amounts include carbon dioxide, water vapor, and trace gases like argon, helium, and neon.

III. Nitrogen (N₂)
- Nitrogen is the most abundant gas in the atmosphere.
- It is a non-reactive gas that plays a crucial role in the growth of plants and animals.
- Nitrogen-fixing bacteria in the soil convert atmospheric nitrogen into a usable form for plants.

IV. Oxygen (O₂)
- Oxygen is essential for the survival of most living organisms.
- It supports respiration, combustion, and the formation of ozone (O₃).
- Plants and trees produce oxygen through the process of photosynthesis.

V. Carbon Dioxide (CO₂)
- Carbon dioxide is a greenhouse gas that plays a significant role in climate change.
- It is produced through respiration, combustion, and the decay of organic matter.
- Plants absorb carbon dioxide during photosynthesis.

VI. Water Vapor (H₂O)
- Water vapor is the gaseous form of water present in the atmosphere.
- It influences weather patterns and plays a crucial role in the water cycle.
- Water vapor condenses to form clouds and precipitation.

VII. Other Gases
- The atmosphere also contains small amounts of argon, helium, neon, and trace gases.
- These gases are present in minute quantities but still contribute to the overall composition of the air.

VIII. Structure of the Atmosphere
- The atmosphere is divided into different layers based on temperature variations.
- The layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
- Each layer has distinct characteristics and plays a role in various atmospheric phenomena.

IX. Troposphere
- The troposphere is the closest layer to the Earth's surface.
- It contains most of the Earth's weather and is where we live and breathe.
- Temperature decreases with height in the troposphere.

X. Stratosphere
- The stratosphere is located above the troposphere.
- It contains the ozone layer, which absorbs harmful ultraviolet (UV) radiation from the Sun.
- Temperature increases with height in the stratosphere due to the presence of ozone.

XI. Mesosphere, Thermosphere, and Exosphere
- The mesosphere is the layer above the stratosphere and is characterized by low temperatures.
- The thermosphere is the layer above the mesosphere and experiences high temperatures due to the absorption of solar radiation.
- The exosphere is the outermost layer, where the atmosphere gradually merges into space.

XII. Conclusion
- Understanding the composition and structure of the air is essential for comprehending atmospheric processes and their impact on life and climate.
- The Earth's atmosphere is a dynamic system that continuously interacts