Modelling concentration heterogeneities in streets using the street-network model MUNICH

Abstract. Populations in urban areas are exposed to high local concentrations of pollutants, such as nitrogen dioxide and particulate matter, because of unfavorable dispersion conditions and the proximity to traffic. To simulate these concentrations over cities, models like the street-network model MUNICH (Model of Urban Network of Intersecting Canyons and Highways) rely on parameterizations to represent the air flow and the concentrations of pollutants in streets. In the current version MUNICH v2.0, concentrations are assumed to be homogeneous in each street segment. A new version of MUNICH where the street volume is discretized is developed to represent the street gradients and better estimate people exposure. Three vertical levels are defined in each street segment. A horizontal discretization is also introduced under specific conditions by considering two zones with a parameterization taken from the Operational Street Pollution Model (OSPM). Simulations are performed over two districts of Copenhagen, Denmark, and one district of Greater Paris, France. Results show an improvement of the comparison to observations with higher concentrations at the bottom of the street, closer to traffic, of pollutants emitted by traffic (NO_x, black carbon, organic matter). Finally, a sensitivity analysis to the influence of the street network highlights the importance to use the model MUNICH with a network rather than with a single street.