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The method of Fuller, Schettler and Giddings (FSG method) can be used to estimate the air coefficient diffusion for a product from its molecular weight and structure.
For example for toluene (molecular weight = 92.141 g/mol, 7 C, 8 H and 1 ring) at atmospheric pressure at 20°C, the air diffusion coefficient calculated is 0.0781 cm2/s.