Development and first evaluation of micro-calgrid: a 3-D, urban-canopy-scale photochemical model

This paper details the development and first application of the MICRO-CALGRID (MCG), micro-scale photochemical model. The MCG model treats individual buildings as obstacles with impenetrable surfaces, rather than as roughness elements; is driven by the flow and turbulence fields generated by the MISKAM Navier–Stokes model, the emissions generated by the German MOBILEV model, and the concentration inflow boundary conditions generated by the urban-scale CALGRID model; includes a detailed treatment of vehicle-induced turbulence; and is equipped with three chemistry schemes (SAPRC-93, CB-4, and an analytic solution for Chapman cycle chemistry). The MCG model is exercised in both its 2-D and 3-D modes. Also described is a MCG application to a 5-day episode measured within a busy street canyon in Berlin, Germany. Concentrations of all measured pollutants (CO, NO, NO2, benzene, SO2 and TSP) were well reproduced by the MCG model. NO2 performance appeared adequate using the simpler analytic chemistry solution; however, inclusion of vehicle-induced turbulence was found to improve model performance statistics.