In our case of nanoparticles as potential migrants, we use the volume (size) of spheric particles as a point of departure to transfer it into a size dependent quasi-molecular weight, Mr,i*, which allows then to apply the above Eq. (2) for calculation of diffusion coefficients. For this purpose, we consider nanoparticles to be quasi-molecules and assume spherical particles chemically consisting of elemental carbon with a density of 1 g cm3. In this way we calculated the volume, mass, number of carbon atoms and the quasi-molecular weight of carbon based particles in dependence of their size by following equations: