Air is the mixture of gasses found in the atmosphere.
Composition of Air
Air is composed of the following gasses:
Other gases (including carbon dioxide) 1%
The oxygen content of the air is vital for life support on aircraft and for the combustion of fuel in the aircraft engines.
Air also contains water vapour which condenses into cloud from which precipitation subsequently falls in the form of rain, snow, etc.
Maritime and Continental Air Masses
Air originating over the ocean is known as maritime air whilst air originating over a continent is known as continental air. Maritime air masses absorb moisture from the oceans and so contain more water vapour than a continental air mass. The amount of water vapour in the air (humidity) affects the performance of an aircraft; aircraft performance is slightly poorer in more humid air. In-Flight Icing is also more likely to occur in air masses with a high humidity. For further information see the separate article on Air Masses.