Dispersion in a rectangular network

I'll be discussing recent work with A Tzella (Birmingham) on the dispersion of a diffusive scalar released in a fluid flowing through a rectangular network. (The spreading of a pollutant released in the streets of a city with a grid plan like Manhattan illustrates the problem.) A large-deviation approach provides a coarse-grained description that captures both the Gaussian core and non-Gaussian tail of the scalar distribution. The approach, which is remarkably simple and explicit, captures a subtle interplay between flow, diffusion and geometry.