Atmospheric radioactivity from medical isotope production facilities, nuclear power plants and nuclear research reactors has accumulated in the atmosphere. Observations from ground based instruments indicate that the levels can vary significantly, in part due to seasonal changes in the weather patterns and regional differences in sources. In this project we apply for computation time to study the seasonal and regional variations of atmospheric radioactivity from known or assumed sources in the northern hemisphere using Atmospheric Transport Modelling (ATM). ATM tools can be used to study the dispersion of particles from a release point, in both time and space. Furthermore, the project aims to study uncertainties in ATM modelling using an ensemble modelling approach