ABSTRACT
An understanding of the atmosphere and its basic properties is vital in aeromedical practice. The physics of that part of the atmosphere where life can exist (the biosphere) provides the framework upon which a working knowledge of altitude and aviation physiology is based. The mixture of gases which surrounds the Earth in a flexible, elastic envelope is called the atmosphere; it extends to an upper limit of around 50 miles (80 km). Conventionally there are three layers which are of variable depth, depending where on the Earth's surface the measurement is taken. A fluency in the application of Dalton's Law is necessary for the understanding of altitude physiology, for it describes how the effects of a fall in pressure are reflected in a reduction in oxygen availability. When ultra-violet rays from solar radiation hit the atmosphere, ozone (triatomic oxygen, O3 ) is formed from normal molecular oxygen (O2 ).
