Countergradient flow is explained in terms of a nonlocal flux-gradient relationship, obtained through solution of the widely-used BGK or ''relaxation time'' model kinetic equation in one dimension for a layered source in an atmosphere with stationary turbulence. It is also pointed out that the classical formula derived by Taylor [Proc. London Math. Soc. Ser. A 20, 196 (1921)] for dispersion from a point source is fully recoverable from BGK theory.