Eulerian Dispersion Model Research Articles

Comparação entre coeficientes de difusão derivados do espectro de energia turbulenta e coeficientes de difusão que dependem da razão entre os fluxos de entranhamento e os de superfície

Uma grande parte das pesquisas em dispersão turbulenta de contaminantes na Camada Limite Planetária (CLP) é relacionada com a especificação dos fluxos turbulentos de concentração. A aproximação para estes termos desconhecidos permite resolver a equação de difusão-advecção. O processo de especificação da parametrização dos fluxos turbulentos de concentração é conhecido como o problema de fechamento do transporte turbulento. O esquema matemático mais comum que conduz à uma solução da equação de difusão-advecção emprega coeficientes de difusão que relacionam os fluxos turbulentos de concentração ao gradiente da concentração média. Neste estudo, empregando-se um modelo Euleriano de dispersão e dados de concentração, coeficientes de difusão derivados do espectro de energia turbulenta e aqueles que dependem da razão entre o fluxo de entranhamento e o de superfície, serão usados na simulação do campo de concentração superficial.

Simulation of Dry Deposition Rates of Acidic Pollutants—An Assessment of Deposition Pathways in Hiroshima, Japan

A eulerian grid photochemical transport and dispersion model was used to simulate the dry deposition rates of nitrogen (as HNO3) and sulfur (as SO2) in Hiroshima, west Japan. Seasonal patterns of predicted dry deposition fluxes reveal that HNO3 is most prevalent at more remote locations while SO2 is deposited near to and slightly downwind from the major emission sources. The predicted dry deposition rates of HNO3 and SO2 were compared to the values measured at Mt. Gokurakuji (located in Hatsukaichi) and in Hiroshima City. The simulation results show that the model under-predicted (about 44% and 80%, respectively) both nitrogen and sulfur deposition rates at Mt. Gokurakuji and in Hiroshima City, indicating that the acid deposition in Hiroshima prefecture is possibly affected by long-range transboundary transport of acidic pollutants. Comparison of wet to dry deposition ratios (4.5 and 8.7 for nitrogen and 4.6 and 7.0 for sulfur) from the two observation sites above indicates that wet deposition maybe the most important acid deposition pathway in Hiroshima, Japan.

Influência da constante de Corrsin no cálculo dos coeficientes de difusão turbulentos

In this work, expressions for the eddy diffusivities are obtained using differents values from the Corrsin’s constant (γ= 0,44; γ= 0,55 and γ= 0,7). These eddy diffusivities are derived from the convective similarity theory and from the one dimensional vertical turbulent velocity spectrum, for unstable conditions. To test the influence of Corrsin’s constant in the evaluation of the eddy diffusivities, was utilized an Eulerian dispersion model that permits the pollutants concentration simulation and uses the eddy diffusivities here presented. The simulations of the concentrations were confronted with the observed concentrations in the Copenhagen experiment. The best results were obtained when the values for the Corrsin’s constant γ= 0,44 and γ= 0,55 are utilized in the eddy diffusivities.

Intercomparison of different regulatory and Eulerian dispersion models: an application for the electric power plant in Rhodes Island

This study tries to inform the user of the abilities and limitations of dispersion models by comparing their differences in air pollution estimations. In particular, an intercomparison between the results of Eulerian and regulatory dispersion models for the new electric power plant in Rhodes Island is carried out, in order to emphasise their differences. The Eulerian models used in this study are Airpol and UAM, the latter also incorporating photochemistry. The input meteorological parameters and diffusion coefficients for both of these models are provided from the non-hydrostatic prognostic mesoscale meteorological model TVM. The regulatory models that have been used are Plumes and CTDMPLUS which are both Gaussian models and use hourly routine meteorological data as input. The simulations have been carried out for one year, and the worst results have been compared. A satisfactory agreement was found among the results for long-term predictions, while a spatial variation was observed for short-term predictions.

A scheme for black carbon and sulphate aerosols tested in a hemispheric scale, Eulerian dispersion model

Production, transport and deposition of sulphate and black carbon (BC) are simulated separating aerosol modes by production mechanisms, thus facilitating calculation of aerosol physical properties. The scheme uses explicit sulphur chemistry with prescribed oxidants and aerosol transformation based on Brownian coagulation rates, and is implemented in a 3-D, hemispheric-scale transport model with off-line meteorology from ECMWF. The components are DMS, SO 2, sulphate and BC. Simulations are made for the year 1988. Predicted results for sulphate agree well with the measurements, except for considerable underestimations in the Arctic. In Europe SO 2 is slightly overestimated and sulphate is slightly underestimated in cold seasons, whilst trends are less clear in North America. Compared to many other models, we estimate a smaller effective oxidation rate for SO 2 due to reduced rates in cold clouds; a shorter turnover time for sulphate (3.7 d) due to a probably too large below-cloud scavenging ratio; and slightly smaller sulphate column burdens. Our BC results are similar to Liousse et al.’s (1996, J. Geophys. Res. 101, 19.411–19.432) except in USA, whilst the concentrations in remote areas and the turnover time (3.7 d) are considerably smaller than Cooke and Wilson’s (1996, J. Geophys. Res. 101, 190.395–19.409). Agreements with available measurements are quite close to large anthropogenic emissions (including USA), but they are considerably underestimated in Arctic winter. Transition from hydrophobic to hydrophilic BC due to coagulation is swift (6% h -1). Sensitivity tests emphasize that sub-cloud scavenging coefficients rely on careful assumptions about size distributions, and that more research is needed on sulphate production in ice-clouds. Emphasis should also be put on production of sulphate and hydrophilic BC boundary-layer clouds; inclusion of hydrophobic accumulation mode BC and sub-grid transition to hydrophilic BC in emitting grid squares.

A computationally efficient Kalman smoother for the evaluation of the CH 4 budget in Europe

Two data assimilation methods of the Kalman filtering approach are applied to the evaluation of the methane (CH 4) distribution in the atmosphere of Europe. The long term historical observation data of CH 4 concentration are integrated with the dynamical Eulerian dispersion model (EUROS). In each proposed method a specific algorithm is employed to avoid the heavy computation burden and huge storage requirement of the conventional Kalman filter for large scale systems. Moreover, a smoother algorithm is developed to identify the emission input. The feasibility of proposed data assimilation methods is verified by the application results.

Bulgarian emergency response models–validation against ETEX first release

In the paper, the performance of two Bulgarian dispersion models is tested against European Tracer Experiment (ETEX) first release data base. The first one is the LED puff model which was the core of the Bulgarian Emergency Response System during all releases of ETEX. The second one is the newly created Eulerian dispersion model EMAP. These models have two important features: they are PC-oriented and they use quite a limited amount of input meteorological information. First, a number of runs with various source configurations are made on meteorological data produced by ECMWF. The aim of these runs is to verify the models’ ability to simulate reliably ETEX first release. To this end, a set of statistical criteria selected in ATMES (Atmospheric Transport Models Evaluation Study, see Klug et al., 1992are used. The best runs for both models are obtained when the source is presented as a column towering from the ground to heights of 400–700 m. These runs took part in the second phase of ETEX (ETEX-II), the so called ATMES-type exercise where EMAP ranked ninth and LED - fourteenth among 34 models. Here, additional sets of EMAP are presented where in the first run the value of the horizontal diffusion coefficient is varied and in the other runs different meteorological data sets are tested. The results obtained from the first run show that the values of K h =4–6×10 4 m 2 s -1 produce fields which fit experimental data best. The other sets of runs show that the higher the frequency of the meteorological data, the better the simulation. The results can be improved by linear interpolation of the meteorological parameters with time, the best fitting obtained with interpolation at each time step.

Dispersion of an Elevated Release in a Coastal Region

Abstract This paper presents a study on air pollutant dispersion from an elevated accidental release from the space shuttle tower at the Kennedy Space Center in Florida under the influence of a stratified onshore flow. The temperature difference between land and ocean can generate a local sea-land circulation and a thermal internal boundary layer. Both play a significant role in the coastal dispersion. Results from a Gaussian dispersion model and those from numerical simulations show that the concentrations obtained from these two distinctly different methods are of the same order of magnitude and have similar patterns. Numerical simulations were performed by combining the Advanced Regional Prediction System with an Eulerian pollutant dispersion model. Numerical sensitivity experiments were conducted to investigate the effects of upwind stability, coastal topography, and calm wind condition. Numerical results also show that the dispersion pattern from a continuous release is significantly different from t...

Towards deducing regional sources and sinks from atmospheric CO 2 measurements at Spitsbergen

In order to quantify the role of oceanic and terrestrial CO 2 exchange on the atmospheric record collected at Ny-Ålesund, Spitsbergen, we have employed a high resolution, regional atmospheric transport model. The three-dimensional Eulerian dispersion model has been developed at the Swedish Meteorological and Hydrological Institute, and is driven by observed meteorology. The model has a detailed description of the atmospheric boundary layer, which is allowed to vary during the course of the day. The domain is located over the Arctic and covers the Northern Atlantic down to circa 50°N and large parts of Siberia and the regions affected by anthropogenic activities in Europe and Russia. In the model we can test different oceanic and terrestrial uptake scenarios, and by comparing with the measurements at Ny-Ålesund we may constrain the regional budget of CO 2. The model is successful in discriminating between the different processes affecting CO 2 measured at Spitsbergen while the absolute values, which depend on the chosen source functions, and boundary conditions, remains to be determined.

Calculation of water exchange times in the ICES-boxes with a eulerian dispersion model using a half-life time approach

The transport of passive, dissolved and conservative matter is calculated with a three-dimensional Eulerian transport model in order to estimate the water exchange times for the ICES-Boxes. Daily flow fields calculated with a baroclinic circulation model (Pohlmann [1991]) are used to drive the transport model. The half-life time of water exchange in a box is defined analogously to the half-life time of radioactive substances. To determine the half-life time for every ICES-Box, the water in this specific box is marked by a constant concentration, whereas the concentration outside the box is set to zero. The calculation stops when the concentration of matter in the box reaches 50% of its initial value. In the classical approach the total exchange of water in a box is characterized by the time that is needed for the total box mass to flow through the open boundaries of the respective box (flushing-time approach). The advantage of the half-life time approach introduced in this study is the fact that it takes into account the structure of the underlying flow field as well as horizontal and vertical diffusion processes. Moreover, it is possible that matter leaves a box and returns, following a change in the flow field. In such a situation the concentration in the box may increase, inducing a longer exchange time compared to the flushing-time. Depending on the starting time there are significant inter-annual deviations between the half-life times for individual boxes. In comparison with the classical flushing-time approach used by Davies [1982], Backhaus [1984], Lenhart [1990] and Lenhart & Pohlmann [1996], the results of the method presented here show that in boxes with a predominantly inhomogeneous flow field (i.e. the ICES-Boxes 3a, 4, 5a, (6b), 7a and 7b) the time needed to reduce the concentration of a contaminant is longer than was to be expected from earlier studies. This is due to the fact that in these boxes the flushing depends not only on the strength of the flow but also on the structure of the flow field, which is not taken into account in the classical flushing-time approach.

Concentration and deposition of acidifying air pollutants over Sweden: Estimates for 1991 based on the match model and observations

The MATCH (Mesoscale Atmospheric Transport and CHemistry) model has been developed as a tool for air pollution assessment studies on different geographical scales. MATCH is an Eulerian atmospheric dispersion model, including physical and chemical processes governing sources, atmospheric transport and sinks of oxidized sulfur and oxidized and reduced nitrogen. Using a combination of air and precipitation chemistry measurements and the MATCH model, the national and long-range transport contributions to air pollution and deposition can be quantified in the model region. The calculations for the year 1991 show that the Swedish import was about 4.5 times larger than the export for sulfur and about six times larger for reduced nitrogen, while the Swedish import of oxidized nitrogen only exceeded the export by 10%. Using the MATCH system we estimate the long-range transport in an independent way compared to EMEP. Comparison between the EMEP and MATCH calculations for 1991 show that the total deposition of oxidized nitrogen over Sweden is similar, while the EMEP-values for total deposition of oxidized sulfur and reduced nitrogen are 25% respectively 40% smaller than what is obtained from MATCH.

Simulation of elevated long-range plume transport using a mesoscale meteorological model

A three-dimensional mesoscale meteorological model was used to construct a modeling system in order to investigate atmospheric dispersion in mesoscale flow fields. The mesoscale model was first coupled to a three-dimensional Monte Carlo (Lagrangian particle) dispersion model, and then an Eulerian dispersion model was embedded into the mesoscale model. Both the Eulerian model and the Monte Carlo model are based on the wind and turbulence fields simulated by the mesoscale model. The modeling system was then applied to the Tennessee Plume Study field experiments on 23 August 1978. The field experiments were basically designed to provide information on the dynamics of plume transport over long distances, and primarily targeted the plume from the Cumberland steam plant. Wind and turbulence fields were first simulated by the mesoscale model. The transport and diffusion of pollutants from the Cumberland steam plant were then simulated by the dispersion models, using these wind and turbulence fields. The results demonstrated that the modeling system generally performed satisfactorily, reproducing the trajectory and spread of the Cumberland plume.

Estimation of seasonal dimethyl sulphide fluxes over the North Atlantic Ocean and their contribution to European pollution levels

A monthly resolved emission budget which aims to reproduce the observed seasonal variations of dimethyl sulphide (DMS) production over the oceans is derived for the North Atlantic Ocean. The monthly cycle of DMS concentrations in seawater and their distribution over the North Atlantic Ocean was determined from a collation of available field measurements. DMS fluxes are calculated on the basis of Liss and Merlivat's (1986) formulation of sea‐to‐atmosphere gas exchange, using six‐hourly meteorological data from the European Center for Medium‐Range Forecasts for the year 1988. This allows to show the influence of meteorological conditions on the DMS fluxes to the atmosphere. Results show averaged fluxes over the North Atlantic Ocean in the range 39–390 μg S m−2 d−1, with a monthly summer maximum between 67 and 1260 μg S m−2 d−1, about 20 times larger than the winter minimum. The contribution of natural oceanic sulphur to the acidic deposition levels over Europe is evaluated with the help of a three‐dimensional Eulerian dispersion model and is compared to the separate contributions of European and North American anthropogenic sources. The relative contribution of biogenic sulphur to total sulphur deposition over the west coast of Europe does not exceed 2% on a yearly basis although it can be close to 10% during the summer months. Considering the uncertainty ranges associated both to the estimation of DMS fluxes and to the subsequent dispersion in the atmosphere, the actual contribution of North Atlantic DMS to European pollution levels can vary by a factor of 3.

Vertical profiles of ozone during the EMEFS I experiment in Southern Ontario

Vertical profiles of ozone from the surface to over 15 km altitude were obtained with a combination of free-flying and tethered ozonesondes and differential absorption lidar. During the Eulerian Model Evaluation Field Study (EMEFS I) of July–August 1988, these profiles were compared with the output of a sophisticated regional-scale three-dimensional Eulerian dispersion and chemistry model, the Acid Deposition and Oxidant Model (ADOM). The results show that ADOM predicts the ozone concentration profiles with accuracy only in the lower troposphere and particularly well during simple synoptic situations. In the upper troposphere, the model does not predict the intrusions of ozone from the stratosphere which appear to be extremely important in determining the ozone concentration profile.

Dispersion modelling of nitrogen oxides in the United Kingdom

This paper describes the construction and application of an Eulerian-dispersion model for the calculation of NO 2 and NO x concentrations in the U.K. Model results are compared with measurements from 44 U.K. sites. The sensitivity of the model results to chemical and dispersion parameterisations is assessed. The model is also used to verify the validity of ‘instantaneous mixing’ assumptions used in trajectory models. Finally, the distribution of ground-level NO x concentrations from power stations, motor vehicles and other stationary sources is calculated across the U.K., including a preliminary assessment of the possible contribution from natural sources.

Modelling of the air pollution in the cracow area

Short-term SO 2 concentrations in Cracow, Poland are calculated, using a three-level Eulerian dispersion model, and verified with data from the MONAT-84 experiment. A comprehensive package or methods to evaluate model performance is suggested.

Generalization ofKTheory for Turbulent Diffusion. Part II: Spectral Diffusivity Model for Plume Dispersion

Abstract Further development of the spectral turbulent diffusivity concept is presented with the aim of obtaining an Eulerian dispersion model applicable for multiple interacting sources. The theory is applied for studies of plume dispersion in a field of a homogeneous and stationary turbulence. A continuous plume is considered as consisting of an infinite number of expanding puffs. The puffs' center of mass fluctuates following the long-wave range of the turbulent velocity fluctuation spectrum. The center-of-mass fluctuations are assigned to phases of the Fourier coefficients of the concentration distribution. The standard deviation of the velocity of the phase fluctuations is dependent on the wave vector of the Fourier coefficient. Time-averaging results in a spectral phase diffusivity coefficient. It is shown that the rate of growth and the center-line concentration obtained by the spectral diffusivity model are in agreement with results predicted by the Lagrangian statistical theory. For a narrow plum...