CLIM2614 Theme 2 Notes

Atmospheric Composition
and
Structure




CLIM2614
Theme 2

, Atmospheric Composition
Permanent gases Variable gases
Gas Symbol % per volume Gas Symbol % per volume Parts per
dry air dry air million
(ppm)¤

Nitrogen N2 78.08 Water vapour H2O 0–4
Oxygen O2 20.95 Carbon dioxide CO2 0.037 374¤
Argon Ar 0.93 Methane CH4 0.00017 1.7
Neon Ne 0.0018 Nitrous oxide N2O 0.00003 0.3
Helium He 0.0005 Ozone O3 0.000004 0.04*
Hydrogen H2 0.00006 Particles 0.000001 0.01 – 0.15
(dust, soot,
etc.)
Xenon Xe 0.000009 Chlorofluoro- CFCs 0.00000002 0.0002
carbons




Greenhouse Gases
• Absorb the outgoing infrared radiation and trap
the heat in the atmosphere
• Over time, the amount of energy sent from the
sun to the Earth’s surface should be about the
same as the amount of energy radiated back
into space, leaving the temperature of the
Earth’s surface roughly constant
• Many gases exhibit these “greenhouse”
properties - some of them occur in nature (water
vapour, carbon dioxide, methane, and nitrous
oxide), while others are exclusively human-
made (like gases used for aerosols)

, Natural Greenhouse Effect