Enviropedia
Climate Change
Global Warming
Ozone
Air Pollution
Weather & Climate
Sustainability
Kids
INFORMATION
Climate System
Climate Change
Empirical Study
Climate Models
Palaeoclimates
Global Warming
Introduction
Greenhouse Effect
Enhanced G-Effect
Greenhouse Gases
 - Carbon Dioxide
   - Sources
   - Sinks
   - Carbon Cycle
   - Concentrations
   - Equilibrium
 - Methane
   - Sources
   - Sinks
   - Concentrations
 - Nitrous Oxide
   - Sources
   - Sinks
   - Concentrations
 - Halocarbons
   - Sources
   - Sinks
   - Concentrations
 - Ozone
 - Other Trace Gases
 - Adjustment Time
 - Summary
Greenhouse Forcing
 - Forcing Factors
 - GWPs
 - ΔF-ΔC Relationships
 - 1765 to 1990
 - Ozone
Aerosols
 - Aerosols
 - Radiative Forcing
   - Direct
   - Indirect
 - Total Forcing
Climate Variations
 - Surface Temperature
 - Precipitation
 - Other Variations
   - Stratosphere
   - Cryosphere
   - Circulation
   - Cloudiness
Detection
 - Modelling
 - Attribution
   - Latitudes
   - Stratosphere
   - Precipitation
   - Sea Level Rise
   - Fingerprints
 - When?
Future Climate
 - GCM Simulations
 - Feedbacks
   - Water Vapour
   - Clouds
   - Ice Albedo
   - Greenhouse Gases
 - 21st Century
Impacts
 - Agriculture
 - Forestry
 - Ecosystems
 - Water Resources
 - Oceans & Coasts
 - Humans & Health
Responses
 - Stabilising
 - FCCC
 - Kyoto Protocol
 - UK Programme
   - Energy Demand
   - Energy Supply
 - Evaluation
Conclusion
LINKS
Navigate

1.2.1. The Composition of the Atmosphere

Let us consider first the atmospheric gases. Table 1.1 illustrates the average gaseous composition of dry air below 25km. Although traces of atmospheric gases have been detected well out into space, 99% of the mass of the atmosphere lies below about 25 to 30km altitude, whilst 50% is concentrated in the lowest 5km (less than the height of Mount Everest).

Table 1.1. Average composition of the atmosphere below 25km

Component Chemical Abbreviation Volume % (dry air)
Nitrogen N2 78.08
Oxygen O2 20.98
Argon Ar 0.93
Carbon dioxide CO2 0.035
Neon Ne 0.0018
Helium He 0.0005
Hydrogen H 0.00006
Krypton Kr 0.0011
Xenon Xe 0.00009
Methane CH4 0.0017
Ozone O3 0.00006

Strictly speaking, the concentration of ozone in the atmosphere is variable.
Inert gases.

This gaseous mixture remains remarkably uniform in composition, and is the result of efficient biogeochemical recycling processes and turbulent mixing in the atmosphere. The two most abundant gases are nitrogen (78% by volume) and oxygen (21% by volume), and together they make up over 99% of the lower atmosphere. There is no evidence that the relative levels of these two gases are changing significantly over time (Kemp, 1994).

Despite their relative scarcity, the so-called greenhouse gases play an important role in the regulation of the atmosphere's energy budget.