  In the turbulent boundary layer of multicomponent fluid mixtures, the
species-specific mass flux is determined by the combination of
turbulent-diffusiophoretic diffusion and diffusion due to gradients in
supplementary fields (e.g. temperature). For inert mixtures, a balance must
exist between all the diffusive transport mechanisms so that the net diffusive
mass flux normal to the wall is zero everywhere. This may require non-constant
composition profiles. Implications are discussed, and mathematical modelling is
employed to demonstrate how this may affect fluid property profiles, wall heat
flux, and wall shear stress in a Newtonian ternary gas mixture ($H_2 + N_2 +
CO_2$) subject to a temperature gradient.
