Abstract
An alternative formulation for the dispersion parameters in a convective boundary layer is presented. The development consists of a simple algebraic relation for the dispersion parameters, originated from the fitting of experimental data, in which the turbulent velocity variances and the Lagrangian decorrelation time scales are derived from the turbulent kinetic energy convective spectra. Assuming homogeneous turbulence for elevated regions in an unstable planetary boundary layer (PBL), the present approach, which provides the dispersion parameters, has been compared to the observational data as well as to results obtained by classical complex integral formulations. From this comparison yields that the vertical and lateral dispersion parameters obtained from the simple algebraic formulas reproduce, in an adequate manner, the spread of contaminants released by elevated continuous source in an unstable PBL. Therefore, the agreement with dispersion parameters available by an integral formulation indicates that the hypothesis of using an algebraic formulation as a surrogate for dispersion parameters in the turbulent convective boundary layer is valid. In addition, the algebraic vertical and lateral dispersion parameters were introduced into an air pollution Gaussian diffusion model and validated with the concentration data of Copenhagen experiments. The results of such Gaussian model, incorporating the algebraic dispersion parameters, are shown to agree with the measurements of Copenhagen.
Highlights
Our preoccupation about air pollution is a consequence of the explicit evidence that air contaminants negatively affect the health and the welfare of human beings
Degrazia et al [22,23] developed a model for the turbulent spectra in a convective boundary layer and proposed a formulation for the Lagrangian decorrelation time scales and turbulent velocity variances described in terms of the unstable Planetary Boundary Layer (PBL) similarity theory
The overall good agreement between Gaussian model predictions using the algebraic formula for the dispersion parameters and field data of ground-level concentration, as well as the comparison with the integral formulation for the z and y, confirms that the simple algebraic relations (9) and (11) contain a realistic description of the energy-containing eddies that control the turbulent dispersion in the unstable PBL
Summary
Our preoccupation about air pollution is a consequence of the explicit evidence that air contaminants negatively affect the health and the welfare of human beings. Throughout classical statistical diffusion theory [21], it is possible to relate turbulent parameters in the PBL to spectral distribution of the turbulent kinetic energy Following such methodology, Degrazia et al [22,23] developed a model for the turbulent spectra in a convective boundary layer and proposed a formulation for the Lagrangian decorrelation time scales and turbulent velocity variances described in terms of the unstable PBL similarity theory. This paper presents the formulation of a simple short-range Gaussian model which evaluates ground-level concentrations from elevated sources in a boundary layer, dominated by moderate convection The performance of this Gaussian model incorporating simple algebraic relationships and integral formulations for the lateral and vertical dispersion parameters are compared to ground-level concentrations from atmospheric dispersion experiments that were carried out in the Copenhagen area under moderately unstable conditions [24]
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