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Atmospheric Dispersion Models
ENSEMBLE: Real-time sharing and evaluating long-range predictions on atmospheric dispersion of radioactive gases

Models are important tools in the policy and decision making process. In particular, atmospheric dispersion models have widespread use in situations such as emergency response and the planning of policies and strategies relating to air quality and hazards.

Atmospheric models can simulate the dispersion and chemical reaction of volatile compounds released from point-, line- or area sources. Such models account for the effect of meteorology in the transport, dispersion and deposition of these compounds, and for how they are transformed as a result of radioactive decay, chemical transformation, the interaction with the surface and ecosystems, etc. Models of these kinds can work on a range of time/space scales, from a few hours/kilometers to decades/covering the globe.

  Schematic representation of the ENSEMBLE service. M1 through Mn represents the different models used within a modelling community

Single countries use models for making predictions as part of the planning process. Due to the stochastic nature of the atmosphere and the many different processes involved, models are not perfect tools and different models can produce different results. It is of paramount importance to evaluate models so that their limitations can be taken into consideration.

The IES has a long history of organising model evaluation exercises for atmospheric chemical and transport models. The ENSEMBLE system is a permanent web platform where modelling groups from around the world can come together to simulate common situations, compare model results and evaluate their results against defined measurements. The platform can accommodate all atmospheric dispersion and chemical transport models at all scales. Different communities use the system for carrying out specific research projects or periodic model evaluation exercises.

The advantage of using ENSEMBLE is that it makes all model results submitted, available to all participating groups. Using statistical packages, these model results can be evaluated against common sets of measurements in the system.

ENSEMBLE has been used to support emergency response situations, for example nuclear accidents, chemical spills, volcanic eruptions by gathering several atmospheric dispersion simulations in real-time and providing several model results.



Comparison of dispersion models of the Fukushima radioactive release 






Comparison of dispersion models of the Eyjafjallajökull eruption






Ozone modelling network that can be consulted using ENSEMBLE and used for the Two-continent model evaluation activity (AQMEII) run with the United States Environmental Protection Agency (image on left).  Comparison of models for the Two-continent model evaluation activity (AQMEII) run with the United States Environmental Protection Agency (image on right). 







  • Bianconi R., S. Galmarini and R. Bellasio (2004). Web-based system for decision support in case of emergency: ensemble modelling of long-range atmospheric dispersion of radionuclides, J. of Environmental Modelling and Software, 19, 401-411, 2004.
  • Galmarini S., R. Bianconi, G. de Vries, R. Bellasio (2008). Real-time monitoring data for real-time multi-model validation: coupling ENSEMBLE and EURDEP, Journal of Environmental Radioactivity 99, 1233–1241.
  • Galmarini S. et al. (2001). Forecasting the consequences of accidental releases of radionuclides in the atmosphere from ensemble dispersion modelling. Journal of Environmental Radioactivity, 57, 3, 203-219.
  • Galmarini S. et al. (2004). ENSEMBLE dispersion Forecasting, Part 1: Concept, approach and indicators. Atmospheric Environment, 38, 28, 4607-4617.
  • Gilliam, R.C., Godowitch, J.M., Rao, S.T., Improving the Characterization of Lower Troposphere Transport with Four Dimensional Data Assimilation. Atmospheric Environment. DOI:10.1016/j.atmosenv.2011.10.065.
  • Nopmongcol, U., Koo, B., Tai, E., Jung, J., Piyachaturawat, P. Modeling Europe with CAMx for the Air Quality Model Evaluation International Initiative (AQMEII). Atmospheric Environment. DOI:10.1016/j.atmosenv.2011.11.023.
  • Potempski S., S. Galmarini, R. Addis, P. Astrup, S. Bader, R. Bellasio, R. Bianconi, F. Bonnardot, R. Buckley, R. D’Amours, A. van Dijk, G. Geertsema, A. Jones, P. Kaufmann, U. Pechinger, C. Persson, E. Polreich, M. Prodanova, L. Robertson, J. Sørensen, D. Syrakov (2008), Multi-model ensemble analysis of the ETEX-2 experiment, Atmospheric Environment 42, 7250–7265.
  • Rao, S.T., Galmarini, S., Puckett, K., (2011). Air quality model evaluation international initiative (AQMEII). Bulletin of the American Meteorological Society 92, 23-30. DOI:10.1175/2010BAMS3069.1.
  • Renate Forkel, Johannes Werhahn, et al. Effect of aerosol-radiation feedback on regional air quality - A sensitivity study with WRF/Chem. Atmospheric Environment doi:10.1016/j.atmosenv.2011.10.009.
  • Schere, K., Flemming, J., Vautard, R., Chemel, C., et al. Trace Gas/Aerosol concentrations and their impacts on continental-scale AQMEII modelling sub-regions.  DOI:10.1016/j.atmosenv.2011.09.043.
  • Solazzo, E., Bianconi, R., Pirovano, G., Volker, M., Vautard, R., and et al. Vautard, R., Moran, M.D., Solazzo, E., Gilliam, R.C., Matthias, V., et al. Evaluation of the meteorological forcing used for AQMEII air quality simulations. Atmospheric Environment. DOI:10.1016/j.atmosenv.2011.10.065.
  • Riccio A., G. Giunta S. Galmarini (2007) Seeking for the rational basis of the Median Model: the optimal combination of multi-model ensemble results, Atmos. Chem. Phys., 7, 6085–6098.



Contact Info:

Stefano Galmarini - Tel: +39-0332-785382 E-mail: stefano.galmarini(at)

Science for the Environment Quality  Fire Risk