atmo-metre

[Etymology: metre-atmosphere] physics A measure of areal concentration of gas, being the length in metres of a column of the gas when at s.t.p. Numerically it is the partial pressure of a gas relative to that exerted by a 1-metre column at s.t.p. Since the pressure exerted by a collection of gas molecules is independent of the particular gas, the number of molecules in the column per square metre of cross-section equals the atmo-metres times Loschmidt's number.