Air quality assessment and management is usually performed using atmospheric integrated modelling systems and comparisons with data observed by monitoring stations. In Italy, the Project MINNI (National Integrated Model in support to the International Negotiation on Air Pollution) has been supporting Italian Ministry of Environment for the last ten years within the international negotiation process on Air Pollution and assessing Air Quality policies at national/local level. In order to evaluate the performances of the MINNI atmospheric modelling system, a GIS approach was applied to compare simulated and observed concentrations of different atmospheric pollutants. The geoprocessing workflow integrates GIS tools with external procedures. The study described here includes the collection of detailed information on monitoring networks, their geolocation, the development of a relational database for storage and management of all information collected, the implementation of dedicated procedures for extraction and statistical analysis of observed and modelled data time series and 2D maps. Moreover, management and interpretation of output maps from the air quality model were implemented in GIS environment for specific purpose analyses. This geoprocessing workflow, allows to investigate different aspects of air pollution, evaluating model performances in reproducing real atmospheric processes at local or regional scales and assessing the impact of air quality measures on human health and environment on a national basis.