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- Author or Editor: G. A. Degrazia x
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Abstract
A new formulation for the lateral dispersion parameter is presented. The model is valid for unstable atmospheric conditions and based on the turbulent kinetic energy spectra and Taylor diffusion theory. It has been tested and compared, through an experimental dataset, with other formulations taken from the literature. The statistical evaluation shows that the proposed σ y parameterization is suitable for application in advanced air quality regulatory models.
Abstract
A new formulation for the lateral dispersion parameter is presented. The model is valid for unstable atmospheric conditions and based on the turbulent kinetic energy spectra and Taylor diffusion theory. It has been tested and compared, through an experimental dataset, with other formulations taken from the literature. The statistical evaluation shows that the proposed σ y parameterization is suitable for application in advanced air quality regulatory models.
Abstract
An integral parameterization of the dispersion coefficients σ y and σ z in a shear–buoyancy-driven atmospheric boundary layer is developed by using a model for the frequency spectrum of eddy energy. The formulation relies on Taylor classical diffusion theory and further developments by Pasquill. The statistical independence of Fourier components for distant frequencies allows the specification of the turbulent kinetic energy spectrum as the sum of a buoyancy- and a shear-produced part. For both components the dispersion parameters are described in terms of the frequency of spectral peak and dissipation function. In this way they are directly related to energy-containing eddies that are most responsible for turbulent transport of any scalars in an atmospheric boundary layer generated by mechanical and thermal forcing mechanisms. As a consequence, the resulting dispersion parameters are more general than those found in the literature, because they do not utilize measurements of turbulent dispersion as most parameterizations do and provide a formulation valid for the whole unstable regime. The formulations are compared with field diffusion data, along with other schemes. The new parameters are well suited for application in air pollution modeling under unstable conditions.
Abstract
An integral parameterization of the dispersion coefficients σ y and σ z in a shear–buoyancy-driven atmospheric boundary layer is developed by using a model for the frequency spectrum of eddy energy. The formulation relies on Taylor classical diffusion theory and further developments by Pasquill. The statistical independence of Fourier components for distant frequencies allows the specification of the turbulent kinetic energy spectrum as the sum of a buoyancy- and a shear-produced part. For both components the dispersion parameters are described in terms of the frequency of spectral peak and dissipation function. In this way they are directly related to energy-containing eddies that are most responsible for turbulent transport of any scalars in an atmospheric boundary layer generated by mechanical and thermal forcing mechanisms. As a consequence, the resulting dispersion parameters are more general than those found in the literature, because they do not utilize measurements of turbulent dispersion as most parameterizations do and provide a formulation valid for the whole unstable regime. The formulations are compared with field diffusion data, along with other schemes. The new parameters are well suited for application in air pollution modeling under unstable conditions.
Abstract
An analytical method to evaluate the Lagrangian length scales for a turbulent planetary boundary layer (PBL) under stable and convective conditions is described in this paper. The method is based on the Taylor's diffusion theory. Agreement with the mixing lengths found in the literature indicates that the hypothesis of using Lagrangian length scale as a surrogate for mixing length scale in the turbulent PBL is valid.
Abstract
An analytical method to evaluate the Lagrangian length scales for a turbulent planetary boundary layer (PBL) under stable and convective conditions is described in this paper. The method is based on the Taylor's diffusion theory. Agreement with the mixing lengths found in the literature indicates that the hypothesis of using Lagrangian length scale as a surrogate for mixing length scale in the turbulent PBL is valid.
Abstract
A 140-m micrometeorological tower has been operating since August 2016 at 4 km from the coastline and 250 m from a thermal power plant that releases heat from its 20-m stacks in southeastern Brazil. The measurements include 11 levels of turbulence observations and 10 levels of slow-response temperature and humidity. The observed atmospheric structure is largely dependent on the wind direction with respect to the power plant. When winds blow from the plant to the tower, the air layer between 20 and 60 m of the atmosphere may be warmed by as much as 2°C. In these circumstances there are events when the emissions pass directly by the tower. They allow the analysis of turbulence structures of thermal plumes generated from the plant’s heat release in comparison with those generated by the surface heating. In the more common case of winds blowing from the tower to the plant, the observations allow a detailed description of the local atmospheric boundary layer. During the day, vertical profiles of turbulent quantities and their spectral distributions show a cycle controlled by interactions between the land and oceanic surfaces, such as a thermal internal boundary layer. At night, there is a systematic tendency of progressive stabilization throughout the period, suitable for the analysis of the boundary layer transition from weakly to very stable conditions. The data also grant the inference of detailed vertical profiles of turbulent diffusion coefficients directly from observations.
Abstract
A 140-m micrometeorological tower has been operating since August 2016 at 4 km from the coastline and 250 m from a thermal power plant that releases heat from its 20-m stacks in southeastern Brazil. The measurements include 11 levels of turbulence observations and 10 levels of slow-response temperature and humidity. The observed atmospheric structure is largely dependent on the wind direction with respect to the power plant. When winds blow from the plant to the tower, the air layer between 20 and 60 m of the atmosphere may be warmed by as much as 2°C. In these circumstances there are events when the emissions pass directly by the tower. They allow the analysis of turbulence structures of thermal plumes generated from the plant’s heat release in comparison with those generated by the surface heating. In the more common case of winds blowing from the tower to the plant, the observations allow a detailed description of the local atmospheric boundary layer. During the day, vertical profiles of turbulent quantities and their spectral distributions show a cycle controlled by interactions between the land and oceanic surfaces, such as a thermal internal boundary layer. At night, there is a systematic tendency of progressive stabilization throughout the period, suitable for the analysis of the boundary layer transition from weakly to very stable conditions. The data also grant the inference of detailed vertical profiles of turbulent diffusion coefficients directly from observations.
