At international level, in the frame of the UN-ECE Convention on Long-Range Transboundary Air Pollution (CLRTAP), as well as, in the context of the Community Environmental policies of the EU Commission, the RAINS-Europe model provides one of the most relevant examples of successful application of Integrated Assessment Modelling (IAM). Some European countries like Italy, among others, have tackled the issue of downscaling, introducing higher spatial resolution in similar models, pursuing the ultimate objective of a more adequate response to the need of evaluating, at national level, cost-effective policy measures to reduce air pollutant emissions, and, consequently, the pressure on environment and human health. As a result, the issue of adequate scaling in IAM becomes of the utmost importance to achieve the desired objective of a comprehensive representativeness of all the peculiar aspects, at each of the several stages of the modelling process: emissions estimates, application of abatement technologies, atmospheric pollutant dispersion, effects on ecosystems and human health. A number of issues which need to be carefully evaluated to finally establish to what extent downscaling has to be carried out, due to the difficulties in gathering detailed and accurate input data, and their consistency at the different scales. In this study, advantages and disadvantages of downscaling are explored, through a comparative analysis between impact scenarios over Italy, generated by the RAINS-Europe and RAINS-Italy models. The effects of the different resolution, 50 x 50 (km) vs. 20 x 20 (km) are highlighted, compared and discussed, in terms of impact on environment and human health, on the basis scenarios developed for the revision of the National Emission Ceiling Directive (NECD) of the European Union.