CLIMATE | Class 11 Geography Notes

COMPOSITION OF THE ATMOSPHERE

The atmosphere is composed primarily of gases, water vapour, and dust particles. The major gases include nitrogen (about 78%) and oxygen (about 21%), with other gases like argon, carbon dioxide, and trace gases making up the remainder. The proportion of these gases remains relatively constant up to about 90 km altitude, except for water vapour and carbon dioxide which decrease with height. Carbon dioxide, though a minor component, is meteorologically significant because it is transparent to incoming solar radiation but absorbs outgoing terrestrial radiation, contributing to the greenhouse effect. Its concentration has increased in recent decades due to human activities such as burning fossil fuels, leading to global warming. Ozone, another important gas, is concentrated between 10 and 50 km altitude in the stratosphere. It absorbs harmful ultraviolet radiation from the sun, protecting living organisms on Earth. Water vapour is a variable gas, constituting up to 4% of the atmosphere in warm, humid tropical regions but less than 1% in cold, dry polar and desert areas. It decreases with altitude and latitude and plays a crucial role in weather and climate by absorbing solar radiation and preserving Earth's heat. Water vapour also influences atmospheric stability and instability, affecting cloud formation and precipitation. Dust particles in the atmosphere originate from various sources such as sea salts, soil, smoke, ash, pollen, and meteoric debris. These particles are mostly concentrated in the lower atmosphere but can be transported to higher altitudes by convection. Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to form clouds, playing a vital role in the water cycle and weather phenomena.

📊 Diagram: No separate diagram in this subsection, but Figure 7.1 shows the ozone layer within the stratosphere and the distribution of gases with altitude.

🧪 Activity: No specific activity in this section.

🔗 Connection: Understanding atmospheric composition is essential for studying atmospheric processes such as insolation, heat budget, and weather elements detailed in following sections.