K-model description of probabilistic long-range atmospheric transport in the Northern Hemisphere

Predictions obtained from a simple Eulerian K-model are compared to a full-year ensemble average of long-range transport and deposition data, obtained from a numerical weather prediction model coupled to a 3D Lagrangian dispersion model. Five release sites located in different climate regions in the Northern Hemisphere were investigated. In all cases, the K-model is found qualitatively to account for the gross structure of the mean deposition patterns, and as such, it is providing a simple means for a first qualitative description of site-specific, averaged long-range atmospheric dispersion and deposition. An embedded stochastic gamma model can be used to describe the large-scale spatial fluctuations around the mean values. The parameters of both the K-model and the stochastic gamma distribution model have been obtained through maximum likelihood estimation. For 1 μm diameter aerosols, the effective deposition length is found to be of the order of 500 km. We argue that the K-model may be used as a practical tool for qualitative probabilistic safety assessment, where it is suggested that climatological data of e.g. mean wind can be used to estimate the model parameters.