The main focus of this paper is the description of a methodology for probabilistic or long-term evaluation of the atmospheric transport and deposition of harmful (for example radioactive) releases from risk sites based on a dispersion modelling approach. This work was realised as a part of the multidisciplinary 'Arctic Risk' study; the purpose of which was the development of a methodology for environmental risk and vulnerability assessments and the testing of this methodology through estimation of the nuclear risk to the population in the Northern European countries in case of a severe accident at a nuclear risk site. The following research tools were applied for probabilistic atmospheric studies:(1) dispersion modelling -Danish Emergency Response Model of the Atmosphere and Danish Meteorological Institute HIgh Resolution Limited Area Model -for long-term simulation and case studies of radionuclide transport for hypothetical accidental releases at sites; (2) probability fields analysis -to construct annual, monthly and seasonal indicators based on dispersion modelling results to identify the most impacted geographical regions.