emergency response; and long-term environmental impact analysis. It is an integrated model that includes boundary layer dispersion modelling. UDM – Urban dispersion model is a Gaussian puff based model for predicting the dispersion of atmospheric pollutants in the range of 10m to 25 km throughout the urban environment. It is developed by the Defense Science and Technology Laboratory for the UK Ministry of Defence. It handles instantaneous, continuous, and pool releases, and can model gases, particulates, and liquids. The model has a three regime structure: that of single building (area density < 5%), urban array (area density > 5%) and open. The model can be coupled with the US model SCIPUFF to replace the open regime and extend the model's prediction range. Models developed in continental Europe The European Topic Centre on Air and Climate Change, which is part of the European Environment Agency (EEA), maintains an online Model Documentation System (MDS) that includes descriptions and other information for almost all of the dispersion models developed by the countries of Europe. The MDS currently (July 2012) contains 142 models, mostly developed in Europe. Of those 142 models, some were subjectively selected for inclusion here. Anyone interested in seeing the complete MDS can access it here. Some of the European models listed in the MDS are public domain and some are not. Many of them include a pre-processor module for the input of meteorological and other data, and many also include a post-processor module for graphing the output data and/or plotting the area impacted by the air pollutants on maps. The country of origin is included for each of the European models listed below. AEROPOL (Estonia) – The AERO-POLlution model developed at the Tartu Observatory in Estonia is a Gaussian plume model for simulating the dispersion of continuous, buoyant plumes from stationary point, line and area sources over flat terrain on a local to regional scale. It includes plume depletion by wet and/or dry deposition as well as the effects of buildings in the plume path. Airviro Gauss (Sweden) – A gaussian dispersion model that handles point, road, area and grid sources developed by SMHI. Plumes follow trajectories from a wind model and each plume has a cutoff dependent on wind speed. The model also support irregular calculation grids. Airviro Grid (Sweden) – A simplified eulerian model developed by SMHI. Can handle point, road, area and grid sources. Includes dry and