A non-Gaussian puff model

A model for the dispersion of passive non-Gaussian puffs is presented. The model is based on a general technique for solving the K-equation on the basis of the truncated Gram-Charlier expansion of the concentration field. The model performances are evaluated against experimental ground-level concentrations, using meteorological data collected near the ground

Sensitivity analysis of an operational advanced Gaussian model to different turbulent regimes

A non-reactive air pollution model evaluating ground level concentration is presented. It relies on a new Gaussian formulation (LUPINI R. and TIRABASSI T., J. Appl. Meteor., 20 (1981) 565-570; TIRABASSI T. and RIZZA U., Atmos. Environ., 28 (1994) 611-615) for transport and vertical diffusion in the Atmospheric Boundary Layer (ABL). In this formulation, the source height is replaced by a virtual height expressed by simple functions of meteorological variables. The model accepts a general profile of wind u(z) and eddy diffusivity coefficient Kz . The lateral dispersion coefficient is based on Taylor’s theory (TAYLOR G. I., Proc. London Math. Soc., 20 (1921) 196-204). The turbulence in the ABL is subdivided into various regimes, each characterized by different parameters for length and velocity scales. The model performances under unstable conditions have been tested utilizing two different data sets

A surface energy-budget model coupled with a Skewed Puff Model for investigating the dispersion of radionuclides in a sub-tropical area of Brazil

An air pollution model (Skewed Puff Model, SPM) based on the Monin-Obukhov similarity theory was applied to investigate the atmospheric radionuclide dispersion at Iperó in Brazil, the location of a nuclear industrial installation. The SPM numerical simulations were carried out using as input 5-minute averaged wind speed and direction observed at 11.5 m, friction velocity and the Monin-Obukhov length supplied by the surface energy-budget model, along with PBL height, estimated from empirical equilibrium expressions for the nighttime and Mixed-Layer model for the daytime. The agreement between the observed and simulated sensible and latent heat fluxes, friction velocity and Monin-Obukhov length, within a level of confidence of 99.9% indicates that the internal parameters chosen for the surface energy-budget model are representative of the interface soil-vegetation conditions at Iperó. The mean concentration field at the surface was estimated assuming that a hypothetical accident at Iperó produced a continuous emission from a 10 m high point source for 18 hours during the summer of 1993 and for 36 hours during the winter of 1992. The results indicated that, in the case of an accident, the highest concentration values are located near to the source and most of the contaminated area is within a 5 kilometers range, in both seasons. The shape of the contaminated area is defined by the wind speed pattern

Development of a grid-dispersion model in a large-eddy-simulation–generated planetary boundary layer

Numerical simulations of dispersion experiments within the planetary boundary layer are actually feasible making use of Large Eddy Simulations (LES). In Eulerian framework, a conservation equation for a passive scalar may be superimposed on LES wind/turbulence fields to get a realistic description of timevarying concentration field. Aim of this work is to present a numerical technique to solve the Eulerian conservation equation. The technique is based on Fractional Step/Locally One-Dimensional (LOD) methods. Advection terms are calculated with a semi-Lagrangian cubic-spline technique, while diffusive terms are calculated with Crank-Nicholson implicit scheme. To test the grid model, the dispersion of contaminants emitted from an elevated continuous point source in a convective boundary layer is simulated. Results show that the calculated concentration distributions agree quite well with numerical and experimental data found in the literature

A model for the estimation of standard deviation of air pollution concentration in different stability conditions

We propose to estimate the standard deviations of the air pollution concentration in the horizontal and vertical direction, σy and σz, based on Pasquill’s well-known equation, in terms of the wind variance and the Lagrangian integral time scales, on the basis of an atmospheric turbulence spectra model. The main advantage of the spectral model is its treatment of turbulent kinetic energy spectra as the sum of buoyancy and a shear produced part, modelling each one separately. The formulation represents both shear and buoyant turbulent mechanisms characterizing the various regimes of the Planetary Boundary Layer, and gives continuous values at any elevation and all stability conditions from unstable to stable. As a consequence, both the wind variance and the Lagrangian integral time scales in the dispersion parameters are more general than those found in literature, because they are not derived from diffusion experiments as most parameterizations. Furthermore, they provide a formulation continuous for the whole boundary layer resulting more physically consistent. The σy, σz parameters, included in a Gaussian model have been tested and compared with a dispersion scheme reported in the literature, using experimental data in different emission conditions (low and tall stacks) and in several meteorological conditions ranging from stable to convective. Results show that the dispersion model with the sigmas parameterisation included, produces a good fitting of the measured ground-level concentration data in all the experimental conditions considered, performing slightly better than other state-of-art models

A GIS BASED AIR QUALITY SYSTEM FOR THE APULIA REGION, SOUTHERN ITALY

Apulia region in the Southern Italy is frequently characterised by high photochemical pollution levels in the warm period and by high levels of PM10 and NO2 in the winter season. Emissions in the area derive essentially from urban, shipping and industrial activities. The main industrial activities are related to the iron and steel industry (one of the largest in Europe) on the western coast and to two coal power plants on the eastern coastline. A GIS based air quality system has been developed to support local authorities in air quality management for the region. The proposed modeling system is based on RAMS (Pielke et al., 1992) and CALMET (Scire et al., 2000) meteorological models and on CALPUFF (Scire et al., 2000)/ CALGRID (Yamartino et al., 1989) dispersion models. Diffuse emissions for the domain were obtained from the national CORINAIR data base (www.sinanet.apat.gov.it) and were preprocessed by a new-developed tool GEM-PP (Gis EMission Pre-Processor) based on open source GIS. Point sources emissions are obtained by local inventory. Meteorological and dispersion simulations were performed for the year 2005. Predictions have been compared with concentration data from the air quality monitoring network. Results evidence a good correlation between predictions and measurements for O3, NOx, SO2 with most of data in factor of two of the measurements for rural stations and a tendency to underestimate measured data in urban stations. Overall the model tends to underestimate CO measurements. The uncertainty of the predictions are analysed and discussed in terms of the emission calculations, dispersion modelling and monitoring site

The role of subsidence in a weakly unstable marine boundary layer: a case study

The diurnal evolution of a cloud free, marine boundary layer is studied by means of experimental measurements and numerical simulations. Experimental data belong to an investigation of the mixing height over inner Danish waters. The mixed-layer height measured over the sea is generally nearly constant, and does not exhibit the diurnal cycle characteristic of boundary layers over land. A case study, during summer, showing an anomalous development of the mixed layer under unstable and nearly neutral atmospheric conditions, is selected in the campaign. Subsidence is identified as the main physical mechanism causing the sudden decrease in the mixing layer height. This is quantified by comparing radiosounding profiles with data from numerical simulations of a mesoscale model, and a large-eddy simulation model. Subsidence not only affects the mixing layer height, but also the turbulent fluctuations within it. By analyzing wind and scalar spectra, the role of subsidence is further investigated and a more complete interpretation of the experimental results emerges

Turbulent dispersion from tall stack in the unstable boundary layer: a comparison between Gaussian and K-diffusion modelling for non buoyant emissions

Most air quality dispersionmo dels used for regulatory applications are based onGaussianan d K-diffusionform ulations. The reliability of such models strongly depends on how dispersion parameters and eddy diffusivities are computed on the basis of the update understanding of the Planetary Boundary Layer (PBL) meteorology. In this paper, we compare the performances in simulating pollutants released from continuous point source, by using some Gaussian and K-diffusion models with different assumptions concerning the parameterisation of the dispersionpro cesses. Results show that the Gaussianmo del, inwhic h the dispersion parameters are directly related to spectral peak of turbulence energy, gives the best overall performances. This could be due to a more realistic description of spreading processes occurring into the PBL. This suggests that, in the context of the regulatory applications, this model cangiv e the best combinationb etweengroun d level concentration estimates and computer requirements

A Derivation of a Variable Vertical Mesh Spacing for Les Models: Application To a CBL

A derivation of a variable vertical mesh spacing for LESmodels: application to a CB