Network models of dispersion in urban areas

The roads through urban areas and their connections at intersections provide important pathways for dispersion in urban areas over the neighbourhood scale. Network models aim to capture these processes by dividing the street network into boxes around each street, connected at the intersections. Following from earlier work (Soulhac & Perkins; Hamlyn, Hilderman & Britter), and as shown in this talk, the resulting models are computationally cheap and capture important processes observed in dispersion in urban areas. In addition, we will show that in simple geometries, the network model can be solved analytically, which then shows how the parameters of the model combine to determine the salient features of the solution, such as the lateral spread, and the detrainment into the boundary layer above. This in turn enables quantitative estimates to be made of the range of validity and usefulness of the network approach, and therefore the neighbourhood scale, before a "far field" Gaussian-plume solution takes over.