Evaluation of Downwash Modifications to the Industrial Source Complex Model

The Industrial Source Complex (ISC) model has been modified to account for Improved understanding of plume rise and downwash around buildings. Two sets of observations are used to compare the modified and the original ISC models, showing that the new model better simulates the observed concentrations during high-wind conditions when downwash usually occurs.     

Case study of plume dispersion over elevated terrain

A study was conducted to evaluate the ability of a steady-state Gaussian model to simulate plume dispersion over elevated terrain. MULTIMAX, a multisource model equivalent to the Environmental Protection Agency's CRSTER model, was used in the study.The effects of using different combinations of onsite and offsite meteorological data with six different terrain treatment techniques were investigated. The modeling results are compared with measured data obtained during an intensive field study conducted at the Tennessee Valley Authority's Widows Creek Steam Plant. Although the model initially failed to simulate the various dispersion conditions, the results improved significantly after modifications were made to the model and the meteorological preprocessor program.     

A complex terrain dispersion model for regulatory applications

This paper demonstrates the development of a model designed to estimate concentrations associated with a source situated in complex terrain. The model is designed to provide estimates of concentration distributions and is thus primarily suitable for regulatory applications. The model assumes that the concentration at a receptor is a combination of concentrations caused by two asymptotic states: the plume remains horizontal, and the plume climbs over the hill. The factor that weights the two states is a function of the fractional mass of the plume above the dividing streamline height. The model has been evaluated against data from four complex terrain sites. The evaluation shows that the model performs at least as well as CTDMPLUS (Perry, S.G., 1992. CTDMPLUS, a dispersion model for sources near complex topography. Part I: technical formations. Journal of Applied Meteorology 31, 633–645), a more comprehensive model designed for complex terrain applications.     

Performance of a time-dependent dispersion model in elevated terrain

A study was conducted to evaluate the ability of the TVA quasi-steady model (QSM) to simulate plume dispersion over high terrain. QSM is a time-dependent, plume-segment model. The modeling results are compared with measured data obtained from a field study conducted at the Tennessee Valley Authority's (TVA) Widows Creek Steam Plant. Also, the results obtained using a steady-state Gaussian model are compared to give an indication of the advantages of a time-dependent method compared to a steady-state method.Although the results from both models agree well with the measured values, QSM, which provides better temporal and spatial resolution, more successfully modeled inversion-breakup and plume-impingement conditions.     

A complex terrain dispersion model for regulatory applications at the Westvaco luke mill

A data set for studying transport and dispersion in complex terrain was collected at the Westvaco Corporation's Luke Mill, located in the Potomac River valley in western Maryland. Meteorological analyses indicate very strong channeling of winds and the presence of strong inversions and wind shears in a shallow layer at the height of the surrounding mountaintops (300 m above the valley floor). Wind velocities observed near the valley floor are unrepresentative of wind velocities at plume height. Observed turbulence intensities at plume height are about twice as large as those observed over flat terrain. Standard stability classification schemes generally underestimate plume dispersion at this site. When high 3-h and 24-h average SO₂ concentrations are observed, winds are usually light and an inversion is present. These instances of relatively high concentrations are often associated with periods when the wind shifts direction 180° from up-valley to down-valley or vice versa, and the nearly stagnant polluted air mass blows against the mountainsides.A dispersion model was developed that is Gaussian in form but uses observed meteorological data to the maximum extent possible. For example, observed turbulence intensities at plume height are used to estimate dispersion. Plume impaction on terrain is calculated if the plume height is below a critical height dependent on the Hill Froude number. Evaluation of the model with the full 2-y data set shows that it can estimate the second highest 3-h and 24-h average concentrations (of regulatory significance) with a mean bias of less than 7%.     

Evaluation of a long-range lagrangian dispersion model with ETEX

Performance of a Lagrangian dispersion model was examined in connection with its dependency on the boundary layer modelling and the input data resolution. The European Tracer Experiment (ETEX) data were used as reference. According to the sensitivity analysis of the model performance, the long-range dispersion model with the sparse input data was not noticeably different from that with the finer resolution data. The assumption of the prescribed constant mixing depth did not largely degrade the prediction results as compared with the simulation results with the temporally changing boundary layer. It is, therefore, concluded that the model is practical, considering the limited input data in the operational mode. However, it was also pointed out that the parameterization for the horizontal and vertical diffusion processes used in the present model enhanced the growth of plume. The improvement of input data resolution in time and space caused further dispersion of tracer deterministically. These resulted in the underestimation of the maximum concentration and the unfocussed concentration distribution map although the mean concentration was predicted fairly well.     

An examination of gaussian plume dispersion parameters for rough terrain

Two key parameters in the Gaussian plume model for estimating downwind concentrations of airborne pollutants are the coefficients of lateral and vertical dispersion, σ_y(x) and σ_z(x), respectively. Values of σ_y(x) and σ_z(x) generally used were originally derived from data gathered over relatively smooth terrain. Theoretical attempts have been made to correct σ_y(x) and σ_z(x) values for roughness. The results of experiments at two sites in Germany were compared to these theoretical methods. It was found that, in general, higher values of σ_y(x) and σ_z(x) were found in the field than were predicted. Use of these experimentally-determined σ_y(x) and σ_z(x) values results in predictions of lower long-range concentrations of airborne material, but larger maximum concentration values located closer to the source may be predicted, when compared to predictions using the theoretical methods. The use of all of the values of σ_y(x) and σ_z(x) presented herein for estimating air pollutant impact is discussed.     

Performance evaluation of four grid-based dispersion models in complex terrain

Four numerical grid-based dispersion models (Mathew/ADPIC, SMOG, Hybrid, and 2DFLOW) were adapted to the Geysers-Calistoga geothermal area in northern California. The models were operated using five intensive meteorological and tracer diffusion data sets collected during the 1981 ASCOT field experiment at the Geysers (three nocturnal drainage and two daytime valley stagnation episodes). The 2DFLOW and Hybrid Models were found to perform best for drainage and limited-mixing conditions, respectively. These two models were subsequently evaluated using data from five 1980 ASCOT drainage experiments. The Hybrid Model was also tested using data from nine limited-mixing and downwash tracer experiments performed at the Geysers prior to the ASCOT program. Overall, the 2DFLOW Model performed best for drainage flow conditions, whereas the Hybrid Model performed best for valley stagnation (limited-mixing) and moderate crossridge wind conditions. To aid new source review studies at the Geysers, a series of source-receptor transfer matrices were generated for several different meteorological regimes under a variety of emission scenarios using the Hybrid Model. These matrices supply ready estimates of cumulative hydrogen sulfide impacts from various geothermal sources in the region.     

Development of a livestock odor dispersion model: part II. Evaluation and validation

A livestock odor dispersion model (LODM) was developed to predict odor concentration and odor frequency using routine hourly meteorological data input. The odor concentrations predicted by the LODM were compared with the results obtained from other commercial models (Industrial Source Complex Short-Term model, version 3, CALPUFF) to evaluate its appropriateness. Two sets of field odor plume measurement data were used to validate the model. The model-predicted mean odor concentrations and odor frequencies were compared with those measured. Results show that this model has good performance for predicting odor concentrations and odor frequencies.     

修订版大气导则与现行大气导则推荐模式实例对比验证分析

介绍了现行大气导则推荐预测模式的不足及修订版大气导则推荐模式AERMOD与ADMS的特点,并分析了不同推荐模式的功能及适用范围.以美国环境保护署两个试验场(Clifty Creek(简单地形)和Epri Bowline(建筑物下洗))的数据资料为基础,分别用修订版大气导则推荐模式AERMOD与ADMS及现行大气导则推荐模式计算小时浓度、日均浓度及年均浓度,并采用统计法(最大值比较法、高端值比较法、相对偏差比较法)和图形法(Q-Q对比图)进行模式比较分析.结果表明,在简单地形下,3种预测模式小时浓度预测精度接近,修订版大气导则推荐模式在可靠性上要优于现行大气导则推荐模式;在考虑建筑物下洗的复杂条件下,AERMOD、ADMS模式的预测结果普遍比现行大气导则推荐模式要好;现行大气导则推荐模式无法应用于计算建筑物下洗的模拟条件.     

Lagrangian dispersion modeling of vehicular emissions from a highway in complex terrain

Transit traffic through the Austrian Alps is of major concern in government policy. Pollutant burdens resulting from such traffic are discussed widely in Austrian politics and have already led to measures to restrict traffic on transit routes. In the course of an environmental assessment study, comprehensive measurements were performed. These included air quality observations using passive samplers, a differential optical absorption spectroscopy system, a mobile and a fixed air quality monitoring station, and meteorological observations. As was evident from several previous studies, dispersion modeling in such areas of complex terrain and, moreover, with frequent calm wind conditions, is difficult to handle. Further, in the case presented here, different pollutant sources had to be treated simultaneously (e.g., road networks, exhaust chimneys from road tunnels, and road tunnel portals). No appropriate system for modeling all these factors has so far appeared in the literature. A prognostic wind field model coupled with a Lagrangian dispersion model is thus presented here and is designed to treat all these factors. A comparison of the modeling system with results from passive samplers and from a fixed air quality monitoring station proved the ability of the model to provide reasonable figures for concentration distributions along the A10.     

Ozone fluxes in the nocturnal planetary boundary layer over hilly terrain

The mean day-night ozone variation in fine weather situation is determined for the planetary boundary layer above a flat bottomed valley by means of a tethered balloon. The nighttime flux of atmospheric ozone into the ground is found not to be negligible as assumed for flat terrain, but even larger than normally quoted values for daytime fluxes, due to the occurrence of a local closed cellular cross valley wind system, in which destruction processes occur within a layer of downslope winds.     

A model of wet deposition to complex terrain

A two dimensional model of the seeder-feeder mechanism of orographic rainfall enhancement has been developed. The model has been extended to include the deposition of aerosol material incorporated into the orographic feeder cloud by nucleation scavenging. Parameterizations of any changes in the concentration of SO₄²⁻ in the cloud due to chemical reactions have also been included. The model is used to predict the rainfall enhancement and SO₄²⁻ deposition over terrain consisting of two parallel ridges oriented perpendicular to the wind. A wide range of spatial scales has been used of up to 150 km. It is found that the patterns of rainfall enhancement and deposition are strongly dependent on the spatial scales, the atmospheric structure and the cloud chemistry.     

Numerical simulation of the urban boundary layer over the complex terrain of Hong Kong

Due to the complexity of the underlying surface, urban boundary layers may exhibit very different wind-temperature field structures compared with rural areas. In this study, an urban boundary layer model with a resolution of 500 m is applied to Hong Kong, a place characterized by complex topography with high mountains and dense urban developments. Five surface land use types are considered; grass and shrub land, trees, water, old urban areas and new town developments. The urban boundary layer model is embedded into the National Center for Atmospheric Research (NCAR) Mesoscale Model, version 5 (MM5). The initial and boundary conditions are obtained from the National Centers for Environmental Prediction (NCEP)/NCAR reanalysis dataset. The modeling approach therefore takes into account both the mesoscale background field and the urban underlying surface. The model is applied to the simulation of a pollution episode in Hong Kong. Results show good agreement with meteorological data for the surface winds and temperature. The model successfully simulates the urban heat island and the occurrence of a sea–land breeze circulation, and their impact on air pollutant transport and dispersion.     

基于复杂地形的高斯烟羽模型改进

针对复杂地形条件下化工行业气体泄漏的污染扩散难以预测的问题,基于传统大气扩散的高斯烟羽模型结合空间插值对原有算法进行了改进。以研究区的数字高程模型(DEM)数据为基础,采用C#语言和ArcGIS Engine作为开发工具实现了复杂地形条件下的污染扩散模拟的可视化表达。通过分析不同参数条件下的大气扩散影响,发现地形起伏明显影响地表气体扩散浓度值。相较于传统研究方法,此模拟结果更符合实际大气扩散规律。     

Comparison of the complex terrain algorithms incorporated into two commonly used local-scale air pollution dispersion models (ADMS and AERMOD) using a hybrid model

ADMS and AERMOD are the two most widely used dispersion models for regulatory purposes. It is, therefore, important to understand the differences in the predictions of the models and the causes of these differences. The treatment by the models of flat terrain has been discussed previously; in this paper the focus is on their treatment of complex terrain. The paper includes a discussion of the impacts of complex terrain on airflow and dispersion and how these are treated in ADMS and AERMOD, followed by calculations for two distinct cases: (i) sources above a deep valley within a relatively flat plateau area (Clifty Creek power station, USA); (ii) sources in a valley in hilly terrain where the terrain rises well above the stack tops (Ribblesdale cement works, England). In both cases the model predictions are markedly different. At Clifty Creek, ADMS suggests that the terrain markedly increases maximum surface concentrations, whereas the AERMOD complex terrain module has little impact. At Ribblesdale, AERMOD predicts very large increases (a factor of 18) in the maximum hourly average surface concentrations due to plume impaction onto the neighboring hill; although plume impaction is predicted by ADMS, the increases in concentration are much less marked as the airflow model in ADMS predicts some lateral deviation of the streamlines around the hill.     

High-resolution simulation of volcanic sulfur dioxide dispersion over the Miyake Island

After severe eruptions of the volcano at Miyake Island in August 2000, a large amount of volcanic gas was released into the atmosphere. To simulate flows and dispersion of sulfur dioxide (SO₂) over Miyake Island, a set of numerical models was developed. The multi-nesting method was adopted to reflect a realistic meteorological field and to sufficiently resolve the flow over the island with a diameter of 8 km. The outermost model was the Regional Spectral Model (RSM) of the Japan Meteorological Agency (JMA) with a horizontal grid size of 10 km. Finer atmospheric structure was simulated with the nonhydrostatic model jointly developed by the Meteorological Research Institute and the Numerical Prediction Division of JMA (MRI/NPD-NHM) with grid intervals of 2 km, 400 m and 100 m. Realistic topography of the island was represented in the innermost model. The Lagrangian particle method was applied to the dispersion model, which is driven by the meteorological field of the 100 m grid MRI/NPD-NHM. The random walk procedure was used to represent the turbulent diffusion. The model was verified in four cases. Simulated SO₂ concentrations agreed well with observed concentrations at a monitoring station including temporal variation. Under a large synoptic change, however, accurate prediction became difficult. Further numerical experiments have been done to investigate characteristics of the flow and the distribution of SO₂. Steady inflows, classified according to the surface wind speed and direction, were assumed. Simulated SO₂ distribution on the ground apparently depends on the surface wind. Under relatively weak inflow, there is a large diurnal change in SO₂ distribution, affected by the thermally induced flow. SO₂ gas is widely spread downstream in the nighttime but hardly reaches the coastal area in the daytime. On the other hand, SO₂ gas steadily reached the downstream coast with little diurnal variation under the stronger inflow. Ground temperature, as well as the static stability of the inflow, also influences downstream wind, turbulent diffusivity and SO₂ distribution.     

Dispersion of carbon dioxide released from buried high-pressure pipeline over complex terrain

Environmental Science and Pollution Research - To quantitatively assess the risks associated with Carbon Capture and Storage (CCS) technology, a better understanding of the dispersion...