- Atmosphere: The gaseous mixture surrounding the surface of the Earth.
- The dry atmosphere is composed of the following gases:
|Gas||% by volume
- The dried atmospheric composition varies little with altitude.
- The percentage of carbon dioxide in the atmosphere has been increasing over the last 150 years, largely due to the burning of fossil fuels.
- The percentage of water vapour in the atmosphere varies considerable, particularly in the troposphere, where it ranges from 0.5 % to 5 %.
- The atmosphere consists of a series of layers, the boundaries between which are defined by marked changes in the rate of change of temperature.
|Troposphere||Earth’s surface to ~15 km||Temperature decreases with altitude|
|Stratosphere||~15 km to ~50 km||• Temperature increases with altitude
• Contains ozone layer, with maximum concentration at altitude of ~25 km
|Mesosphere||~50 km to ~85 km||Temperature decreases with altitude|
|Thermosphere||~85km to ~500 km||Temperature increases with altitude|
|Exosphere||~500 km outwards||• Particles can overcome the Earth’s gravity an escape into space
• Diffuses into space
|Ionosphere||~60 km outwards||• Incorporates the thermosphere and part of the mesosphere
• Contains free ions, atoms and electrons