The biggest sample of gas readily accessible to us is the atmosphere, a mixture of gases
with the composition summarized in Table 1.3. The composition is maintained
moderately constant by diffusion and convection (winds, particularly the local turbulence
called eddies) but the pressure and temperature vary with altitude and with the
local conditions, particularly in the troposphere (the ‘sphere of change’), the layer
extending up to about 11 km.