Energy balance models for urban areas (e.g. Masson, 2000) need to incorporate transfer from all active surfaces in an urban landscape. On the scale of a street canyon, this requires separate consideration of transport from (i) roads and walls into the street canyon air, and (ii) from the street canyon and roofs into the boundary layer. Understanding and quantifying the net transfer out of the canyon is particularly important in establishing the difference between the canyon air temperature and the boundary layer above. At present, the resistances to transfer through these pathways are not known, nor is it known how they depend upon geometry.

We have used the naphthalene sublimation technique (Barlow and Belcher, 2001) to measure the resistance network for a street canyon using a windtunnel model. By coating different combinations of surfaces and measuring the transfer of naphthalene vapour, all the resistances can be inferred. The variation of resistances as a function of geometry has been investigated. The results will be useful in developing further energy balance models for urban areas.