In this work, the advection-diffusion equation was solved in two dimensions to calculate the normalized crosswind integrated concentration by Laplace technique. Considering that the wind speed is constant and we have two models of the vertical eddy diffusivity, one depends on downwind distance and the other model depends on vertical distance. A comparison between our proposed two models, Gaussian, previous work and observed data measured at Copenhagen, Denmark, have been carried out. One finds that there is a good agreement between predicted (2) model and the observed concentrations than predicted (1), Gaussian and previous work. From the statistical technique, one finds that all models are inside a factor of two with observed data. Regarding to Normalized mean square error (NMSE) and Fraction Bais (FB), proposed model (2) is performance well with observed data than the predicted (1), Gaussian and previous work in unstable condition.

In this paper, comparing between Gaussian plume models and the solution of Advection-diffusion equation in three dimensions using different shapes of dispersion parameters and eddy diffusivities respectively. After that, comparing between Gaussian plume model, proposed model and observed concentrations data which measuring on Egyptian Atomic Energy Authority EAEA for Iodine-135 (I135) in unstable condition.

Natur The vertical fraction variation of eddy diffusivity was taken into consideration in the dispersion of pollutants from a point source. A power-law profile was used to describe the variation of wind speed and vertical eddy diffusivity with height above ground surface. The dry deposition of the diffusing particles at the ground surface is taken into account through the boundary conditions. The concentration of pollutants was derived assuming that the vertical diffusion is limited by an elevated inversion layer located at the top of the boundary layer "h". Also, the decay distance of a pollutant along the wind direction was estimated. The resulting analytical solutions have been applied on the emissions from Egypt's First Research Reactor at Inshas in unstable condition and Hanford diffusion experiment in stable condition. Comparisons between proposed and observed concentrations show a good agreement between the proposed and observed concentrations when α=0.81than other fractions and integer value. The results are discussed and presented in illustrative figures.

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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.