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Thomas J. Overcamp

Abstract

A Gaussian model for continuous elevated sources is developed which uses a continuous distribution of ground-level sources to replace the use of the image source. For the case of Fickian diffusion with uniform wind, this model is mathematically identical to the conventional Gaussian model with the image source, and therefore, provides a more physically realistic model to justify the use of the image source. For the general, non-Fickian case, the predictions of the surface-corrected model and the conventional model differ.

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Thomas J. Overcamp

Abstract

Many atmospheric contaminants decay or react in the atmosphere. in situations such as the diffusion of radioactive contaminants, certain chemical pollutants and viable microorganisms, a first-order decay rate is considered to be an appropriate model. The conventional method of estimating the downwind concentrations from a continuous point source of these decaying contaminants is to multiply the estimated concentration of an equivalent amount of a conserved pollutant by the factor exp(−kx/ū) in which k is the first- order decay rate, x the downwind distance and ū the wind speed.

In this paper, the statistical diffusion theory is extended to incorporate first-order decay. The statistical theory shows that there is a distribution of the local age of the contaminant at any point downwind. Since this distribution is skewed toward ages less than the travel lime x/ūthe proposed theory predicts higher concentrations than the conventional approach for a pollutant that decays at a first-order rate. The difference is a function of σ x 2 k/ . If this term is very small, the two approaches are in good agreement. If this term is large, the predictions of the proposed model are higher.

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Thomas J. Overcamp

Abstract

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Thomas J. Overcamp

Abstract

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Thomas J. Overcamp

Abstract

A modification of the Gaussian plume model is proposed for the deposition of fine and heavy particulates and gases. It combines a downward-sloping plume to account for settling and the assumption of constant deposition velocity to obtain a solution satisfying an integral mass conservation equation specifying that the decrease in the airborne flux equals the deposition. An example is given comparing this method with the conventional Gaussian model for dry deposition of gases or fine particulates.

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Thomas J. Overcamp

Abstract

Plume models were developed to predict the concentration due to a nonbuoyant release from a source whose strength decreases exponentially with time of a pollutant that reacts in the atmosphere at a first-order rate. Models were developed that combined the conventional Gaussian plume with one of three different one-dimensional models to describe advection and dispersion in the downwind direction: advection without downwind dispersion, advection and dispersion by a Fickian puff, and advection and dispersion by a puff of constant size. In addition to these one-dimensional dispersion models, a model based on three-dimensional Fickian pulls was also developed.

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