In the frame of the urban air quality modelling exercise promoted by the CTN-ACE (Italian National Topic Centre on Air, Climate and Emission) Earth Tech’s CALPUFF lagrangian puff model has been applied with three different configurations in order to evaluate NOx and CO ground level concentrations. The selected domain covered a 12×12 km2 area centred over the city of Brescia (northern Italy), nearby the Alps. The area is characterised by low wind regime with frequent stagnation conditions. The meteorological data were obtained from CALMET output. Emissions referred to year 1999 and were provided for 7 industrial stacks and a network of 948 roads. The simulations shared the same domain and input data. Industrial stacks were treated as point sources with CALPUFF in all simulations, while different choices were made to simulate emissions from road transport. A first option was to simulate these emissions with CALPUFF as a regular emitting grid of 500x500m2 volume sources. A second choice was to represent roads as about 6.000 volume sources following the road network. Finally, traffic emissions were treated as linear sources with CALINE model. Model results have been evaluated by means of a comparison with measured concentrations at one urban station. The analysis concerned mean days, percentiles, bias, correlation and other statistical indexes. Patterns of annual mean ground level concentrations maps have been also compared. This work has two main purposes. First, to highlight CALPUFF capability (eventually integrated by CALINE) to correctly reproduce the mean temporal behaviour of selected pollutants in an urban area (not a frequent use of the model). Then, to investigate the uncertainty related to the different ways to apply the same model to the same inputs. PUBBLICATO A5018631 (PAD – 640237)PUBBLICATO A5018631 (PAD – 644049)