Trajectory Model (non-chemical reactions)

A trajectory model is a mathematical representation of the motion of air mass or parcel as it moves through space and time. It is used for finding pollution connection between receptors and emission source. There are two type of applications for trajectory model, forward trajectory approach and backward trajectory approach. Forward approach finds out the path of air parcel from emission source to its downwind receptors, while backward approach does that from receptor to its upwind sources.

Fig 1. Surface Wind distribution and Trajectory Estimation

The diagram on the left of the above picture is the wind vector at each location. With the wind vector at every location and time, it is possible to calculate the traveling points of the air mass at every time period by forward or backward integration. The trajectories could be obtained by connecting these forward (red) and backward (black) dots, as shown on the right hand side of the figure.