This study presents an improved methodology for analysing atmospheric pollution around airports using Gaussian-plume numerical simulation integrated with Geographical Information Systems (GIS). The new methodology focuses on streamlining the lengthy analysis process for Airport Environmental Impact Assessments by integrating the definition of emission sources, simulating and displaying the results in a GIS environment. One of the objectives of the research is to validate the methodology applied to the Athens International Airport, "Eleftherios Venizelos", to produce a realistic estimate of emission inventories, dispersion simulations and comparison to measured data. The methodology used a combination of the Emission Dispersion and Modelling System (EDMS) and the Atmospheric Dispersion and Modelling system (ADMS) to improve the analysis process. The second objective is to conduct numerical simulations under various adverse conditions (e.g. scenarios) and assess the dispersion in the surrounding areas. The study concludes that the use of GIS in environmental assessments provides a valuable advantage for organizing data and entering accurate geographical/topological information for the simulation engine. Emissions simulation produced estimates within 10% of published values. Dispersion simulations indicate that airport pollution will affect neighbouring cities such as Rafina and Loutsa. Presently, there are no measured controls in these areas. In some cases, airport pollution can contribute to as much as 40% of permissible EU levels in VOCs.