The Earth is enveloped by a mixture of gases known as the atmosphere, which makes life possible. It provides the air we breathe, shields us from harmful ultraviolet (UV) radiation from the Sun, traps heat to maintain a warm and stable environment, and prevents extreme temperature fluctuations between day and night.
Approximately 97% of the atmosphere's total mass is concentrated within the first 29 kilometres above Earth's surface.
99% of atmospheric mass is within 32 km.
Contents / Index
Gases in the atmosphere
| Gas | Proportion and role |
|---|---|
| Nitrogen (N2) | 78% (Most abundant gas, relatively inert) |
| Oxygen (O2) | 20.9% (Essential for life) |
| Argon (Ar) | 0.93% (Inert noble gas) |
| Carbon dioxide (CO2) | 0.04% (Crucial for plant life, Green House Gas) |
| Neon (Ne) | 0.0018% |
| Helium (He) | 0.0005% |
Vertical distribution of gases
The proportion of gases is not constant throughout the atmosphere.
Carbon Dioxide (CO2) & Water Vapor (H2O) : Found up to about 90 km.
Oxygen (O2) : Present up to about 120 km.
Higher Layers : Gas composition changes significantly, with lighter gases becoming more dominant.
Water vapour: distribution
Water vapour : Constitutes 0% to 5% of atmospheric volume, depending on the location and conditions.
In a warm and humid region, it can reach up to 4%
In cold, arid regions like polar areas and deserts, it is often less than 1%.
The concentration of water vapor decreases with increasing altitude and latitude (toward the poles).
Approximately 50% of atmospheric water vapor is found within the first 2 km of the Earth's surface.
90% of vapor = within 5 km.
Importance of water vapour
It traps outgoing terrestrial radiation, acting as a natural Thermal Blanket and contributing to the Greenhouse Effect.
It significantly influences Atmospheric Stability and instability, affecting weather patterns.
During phase changes (condensation or evaporation), water vapor releases or absorbs Latent Heat, which is critical in driving atmospheric processes, including storms and convection.
Dust: sources and distribution
Dust : a suspension of fine solid particles originating from diverse sources, including – Mineral dust, Salt spray, Biological materials (Pollen, Bacteria, Fungal spores), Smoke (from fires), Volcanic ash (from eruptions), Industrial dust.
It is primarily concentrated in the Lower atmosphere.
Sub-tropical & Temperate regions often exhibiting higher dust concentrations due to ① Dry conditions, ② Strong winds, ③ Larger arid and semi-arid areas compared to polar and equatorial regions.
Importance of atmospheric dust
Cloud formation (hygroscopic nuclei) : Dust particles act as condensation nuclei, providing surfaces for water vapor to condense upon, forming cloud droplets.
Impact on climate : Dust can both cool and warm the atmosphere. It can cool by reflecting solar radiation back into space. However, dark dust particles (like soot) can absorb solar radiation, leading to warming.
Impact on human health : Fine particles (e.g., PM2.5) can be harmful when inhaled, causing respiratory and cardiovascular issues.
High concentrations of dust reduce visibility.
Quick revision
- Nitrogen and oxygen are the most abundant gases listed in the chapter.
- Water vapour varies with location, altitude and latitude.
- Water vapour traps terrestrial radiation and exchanges latent heat during phase changes.
- Dust helps cloud formation and affects climate, health and visibility.
Related concepts from Chapter 1
- Abiotic components of environment
- Photosynthesis and biotic–abiotic interactions
- The interdisciplinary nature of environmental science
Related topics
- Structure of Atmosphere: Layers, Exosphere, Homosphere and Heterosphere
- Troposphere, Stratosphere and Polar Vortex
Chapter 2 index
- Composition of Atmosphere: Gases, Water Vapour and Dust
- Structure of Atmosphere: Layers, Exosphere, Homosphere and Heterosphere
- Troposphere, Stratosphere and Polar Vortex
- Ozone: Formation, Depletion and Effects on Plants
- Mesosphere: Noctilucent Clouds, Meteors and Gravity Waves
- Thermosphere and Ionosphere: Temperature and Radio Communication
- Aurora and Magnetosphere: Solar Wind and Earth’s Magnetic Field
- Sodium Layer: Artificial Guide Stars and Adaptive Optics