ABSTRACT
Air is a mixture of gases, and although the notion that air has weight might seem slightly strange, air in the atmos
BOX 9.6 ATMOSPHERIC PRESSURE
It is estimated that the total weight of the atmosphere is about 5,000 million million tonnes, and half of this lies within the lowest 5 km (recall from p. 229 that the atmosphere extends out perhaps as far as 1,000 km). The lower layers are compressed, and average density decreases from about 1.2 kg m-3 at sea level to about 0.7 kg m-3 at about 5 km height
phere exists under pressure (Box 9.6). Atmospheric pressure is a physical pressure created by the interaction of the molecules that make up the gases in the air.
