In the frame of the CityDelta open model intercomparison exercise, three chemistry-transport models, CALGRID (Yamartino et al. 1991), CAMx (Environ 2004) and STEM-FCM (Silibello et al. 2001) have been applied to simulate emission scenarios expected up to 2010. The selected domain covered a 300×300 km2 area in the Northern Italy. The simulations concerned the hourly ozone concentrations during six month in the summer of 1999. The input data set for the base case was provided by the Joint Research Centre and EMEP. Four emission scenarios, suggested by JRC-IIASA (http://www.iiasa.ac.at/rains/index.html), have been simulated: the first one (CLE) is related to the emission reduction obtained in the 2010 year by the application of Current Legislation; the others are three Most Feasible emission Reduction scenarios, obtained by taking into account the use of the best available technologies for NOx (MFR(NOx)), VOC (MFR(VOC)) and both of them (MFR(NOx,VOC)). The assessment of the impact of the scenarios has been performed evaluating the differences with respect to the base case in ozone concentrations. The analysis has been performed for 9 points distributed over the domain. The simulations show that the three models supply very similar behaviours and agree in suggesting that the more efficient control policy is to strongly reduce VOC emissions. * Pirovano Guido, CESI Research Centre, V.le Rubattino 54, Milano, Italy. +39 02.2125.4625. guido.pirovano@cesi.it PUBBLICATO A5021386 (PAD – 644093)