We will discuss below one of the most widely used models in air pollution, the Gaussian Plume Model and also look at how it might be considered as a form of a box model. Before that let us take a step back, some would say into reality, and consider a very simple model which can produce results well within factor of 2 when compared to field observations.

We should say at the outset that a model which produces results within a factor of 2 is usually seen as a good model and it is not until it is within a factor of 3 that it is seen as a bad model. This should also point us to the fact that it is not worth reporting resultant pollution concentrations to more than one significant figure, whatever the model used.