The work discusses the application potential of a hybrid modeling system, developed by combining an Eulerian model—applied at the regional scale—with a Lagrangian model—applied at the local scale—for estimating both the concentrations of atmospheric pollutants in urban areas and the contribution of the different emission sources to these concentrations. In detail, the system is made up of the Eulerian model CAMx and the Lagrangian model AUSTAL2000, together with the WRF and TALdia models—for the preparation of the related input meteorological data—and the SMOKE model—for processing and preparing the emission data starting from emissions inventories. The application presented refers to a case study of the center of Milan for the atmospheric concentrations of fine particulate matter (PM2.5) and nitrogen dioxide (NO2), which are the pollutants that determine the main critical issues for compliance with air quality limits. The results show a good ability to reconstruct concentration fields with high spatial resolution in urban areas, consistently with the structure of the built environment which influences both the spatial distribution of the sources—in this case the structure of the road network—and how their emissions are dispersed. The comparison with the observed data, however, shows shortcomings in the correct reconstruction of the concentration levels, especially in the case of dust, not so much in the annual average values but rather in the daily trends, in particular in the winter period, when the meteorological component of the system struggles to reproduce persisting conditions of atmospheric stability that favor the accumulation of pollutants.

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