Among the local impacts which are considered within the Sub Program 9.3 of the ULCOS project for the assessment of technologies sustainability, air quality is a key issue for the evaluation of the environmental impact of a steel plant in its surrounding area. In this paper a method based on the use of air dispersion modelling is proposed for the assessment of the ULCOS technologies on the basis of the concentration in the atmosphere of the main pollutants (NOx, SO2, TSP, PM10, PM25, CO, Pb, PCDD) produced by the plant. For performing this task the AERMOD model, a widely used model belonging to class of Gaussian models, was used. For exploiting AERMOD it was necessary to characterize the case base plant specifying the positions and dimensions of its main parts and its stacks as well as the characteristics of their emissions. Furthermore it was necessary to collect information on the meteorological conditions and the terrain of the considered zone. The results, measured in terms of average concentration of the pollutants at ground level, show that such concentrations are below the limits established by current legislation. In the future these results will be used for comparisons of the case base with new technologies.