Atmospheric Data - Composition of Air

Dry air is a mechanical mixture of gases.

**Composition of Dry Air**
Gas	By volume (%)	By weight (%)
Oxygen	21.00	23.2
Nitrogen	78.03	75.5
Carbon dioxide	0.03	0.046
Hydrogen	0.01	0.007
Rare gases	0.93	1.247
Water vapour	-	-

**Atmospheric Composition at Sea Level**
Gas	By volume (%)
Oxygen	20.75
Nitrogen	77.08
Carbon dioxide	0.03
Hydrogen	0.01
Rare gases	0.93
Water vapour	1.20

The composition of air is unchanged to a height of approximately 10,000 metres. The average air temperature diminishes at the rate of about 0.6°C for each 100 m of vertical height.