Figure 1b: Illustration of the coupling between the Lagrangian model and the Eulerian model. The square indicates the area where the Lagrangian model is applied. The Eulerian model is applied in the whole model area. The source is located in the center of the square. The figure shows a single puff located at the boundary of the Lagrangian model area where the puff is incorporated into the Eulerian model (see Brandt et al., 1996).