ABSTRACT
A new model was proposedby using separation of variables to solve the diffusion equation in three dimensions, considering that the eddy diffusivity depends on the vertical height z. Comparisons between calculated, observed and previous data in neutral and stable conditions were carried out. Model performances were evaluated using observed data and another model. Results show that both models performance well in calculating activity concentrations with different degree of accuracy. From the statistical evaluations in neutral and stable conditions, one finds that the two models are inside a factor of two with observed data. Regarding NMSE and FB, the correlation for the present model is well with observed data than the previous work. We can conclude that our model shows more accuracy in neutral and stable cases than the previous work.