The air quality assessment and the impact evaluation of emission reduction policies cause an increasing interest on long term simulations with Chemical Transport Models. For this reason the CityDelta open model intercomparison exercise has been organized by the Joint Research Centre of Ispra as a contribution to the modelling activities in the CAFE (Clean Air For Europe) Programme (6th EU Environmental Action Programme). In this frame two atmospheric chemistry-transport models, CAMx [1] and TCAM [2], have been applied over the Milan area for yearly PM10 simulations. The computational domain ([300 x 300] km2) includes a large flat area surrounded by mountains along three sides. It is a complex test bench in which low wind speeds and summery elevated solar radiation cause high ozone and PM concentration levels. Models have shared the same input fields, provided by JRC (local emission inventory), EMEP (emission fields and boundary concentrations) and Météo France (Aladin meteorological fields). The meteorological data used by the chemical models have been computed mainly by CALMET diagnostic model on the basis of the local observations and the Aladin fields. Some future emission scenarios have been simulated, based on the combination of a CLE (Current LEgislation) case, related to the emission reduction obtained in the 2010 year by the application of Current Legislation, and a MFR (Most Feasible Reduction) case, related to the emission reduction obtained by taking into account the use of the best available technologies for NOx, SO2, PM, VOC, CO and NH3. The evaluation of the scenario impact for the two models has been performed evaluating the differences with respect to the base case in PM10 concentrations and the inorganic components. The analysis has been performed for 9 points distributed over all the domain. [1] ENVIRON Corporation (2004). User’s guide to the Comprehensive Air quality Model with extension (CAMX) ver 4.0. Technical report. [2] Decanini, E., Volta, M. Application to Northern Italy of a new modelling system for air quality planning: a comparison between different chemical mechanisms. International Journal of Environment and Pollution, 20: 85-95, 2003.