A mathematical model of diffusion from a steady source of short duration in a finite mixing layer

This paper presents an analytical unsteady-state solution to the atmospheric dispersion equation for substances subject to chemical-physical decay in a finite mixing layer for releases of short duration. This solution is suitable for describing critical events relative to accidental release of toxic, flammable or explosive substances. To implement the solution, the Modello per Rilasci a Breve Termine (MRBT) code has been developed, for some characteristics parameters of which the results of the sensitivity analysis are presented. Moreover some examples of application to the calculation of exposure to toxic substances and to the determination of the ignition field of flammable substances are described. Finally, the mathematical model described can be used to interpret the phenomenon of pollutant accumulation.     

A three-dimensional steady-state atmospheric dispersion-deposition model for emissions from a ground-level area source

An analytical solution to the steady-state three-dimensional atmospheric dispersion equation has been developed for the transport of non-buoyant emissions from a continuous ground-level area source. The model incorporates power law profiles for the variation of wind speed and vertical eddy diffusivity with height, represents the lateral eddy diffusivity as a function of wind speed and the crosswind dispersion coefficient, and includes dry deposition as a removal mechanism. The model is well suited for accurate prediction of emission concentration levels in the vicinity of an area source, as well as farther downwind, under neutral or stable atmospheric conditions. The impact of the important model parameters on contaminant dispersion is examined. The results from several simulations, compared with point and line sources of equivalent source strength, indicate that at short downwind distances, predictions of contaminant concentrations emitted from area sources may be unacceptably inaccurate unless the structure of the source is properly taken into account.     

Predicting atmospheric debris transport in real-time using a trajectory forecast model

An experiment is described in which a trajectory forecast model was used in real-time to estimate the transport of debris associated with a large chemical explosion in the south-western U.S. The forecast trajectories were used to vector sampling aircraft into a position favorable for intersecting the debris cloud. The forecasts are evaluated and compared with three independent measures of debris transport: diagnostic trajectories calculated after the experiment using observed wind fields; transport of a tracer balloon; and aircraft measurements of the debris cloud.Trajectory forecasts originating as early as 39 h before the explosion successfully predicted the downwind atmospheric drift pathway of the cloud. The forecast trajectories agreed well with diagnostic trajectories, confirming the high quality of the meteorological forecast data upon which the trajectories are based. The forecast trajectories also proved skilful in predicting real-rime atmospheric motion at short notice. The results support our conclusion that forecast trajectory models are valuable tools for vectoring sampling aircraft in long-range atmospheric dispersion experiments and operations. These models should prove useful in the future when real-time estimates of atmospheric transport are needed.     

A surface-layer similarity model for the dispersion of a skewed passive puff near the ground

A model for the dispersion of a passive puff near the ground is developed. The model is based on the Monin-Obukhov similarity theory for the atmospheric surface layer, which is used to specify eddy diffusivities and the wind speed profile. Starting from the diffusion equation in a puff-following coordinate-system, rate equations are derived for the standard deviations of the concentration distribution and for its skewness. Approximate solutions are obtained for the shape of the concentration distribution and for the puff velocity.     

Simulation of dispersion in moderately complex terrain—Part B. The higher order closure dispersion model

A three-dimensional higher-order closure dispersion model is presented. The model is used to simulate dispersion from point sources in complex terrain. The model uses mean and turbulence quantities simulated with the fluid dynamic model presented in Part A to simulate dispersion in a polar coordinate system with its origin in the point source. Different turbulent length scales are used for the vertical and horizontal fluxes. Simulation results are compared with data from tracer experiments performed in southern Sweden, the Vänersborg-Trollhättan region. The tracer experiments were performed during convective atmospheric conditions as well as during very stable conditions. The geographical area has terrain features that exert forcing on the meso-γ-scale. Within the area there is a relatively flat agricultural area, forested hills, a river valley and an extended lake area. The terrain height relief is typically 80 m.The simulations with the dispersion model performed in the Vänersborg-Trollhättan region show good agreement with measured data in the region for convective atmospheric conditions as well as for very stable conditions.     

一种大气CO2源汇反演模式方法的建立及应用

在一个二维全球大气化学传输模式的基础上,通过对模式的修改和调整,建立了一个简单二维扩散、传输模式,用于CO2源汇的反演研究.在验证了模式的有效性之后,将其应用于大气CO2源汇分布的研究.大气CO2的源主要集中在赤道地区和北半球中高纬度地区.其中,海洋和陆地生态系统(热带雨林的破坏)是赤道地区的主要碳源;北半球中高纬度的陆地生态系统是重要的碳汇,而南半球中纬度地区则表现为CO2的弱汇.对El Nino年(1982年)和其他年份的碳源汇分布情况作了比较,两者之间存在显著的差异,由于化石燃料燃烧排放并无明显波动,因此认为碳通量的年际变化是由于El Nino事件对陆地和海洋碳循环产生影响而造成的.     

A long-range dispersion model evaluation study with Chernobyl data

The Chernobyl accident outlined the need for improving the capability of the real-time estimate of long-range atmospheric dispersion and provided an opportunity to test numerical models against the radiological data collected over Europe. The APOLLO model, which became recently operational in the Accidental Release Impact Evaluation System (ARIES) at ENEA-DISP, has been tested based on meteorological and radiological data made available during and after the joint IAEA/CEC/WMO Atmospheric Transport Model Evaluation Study (ATMES). In the present paper a model evaluation and a sensitivity test with respect to the mixing depth and horizontal diffusion parameterizations are presented. The quantities involved in the validation are Cs-137 air concentrations paired in space and time, time-integrated concentrations and time of arrival of the cloud at each locality. The results show that the treatment of space and time variability of the mixing depth improves the model estimates, and that a linear trend in time of the horizontal dispersion coefficient gives better results than a square-root trend in terms of scattering between observed and computed values.     

Model calculating annual mean atmospheric dispersion factor for coastal site of nuclear power plant

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对封闭型大气扩散模型应用的探讨

在建设项目的环境影响评价中 ,对高架点源排出的大气污染物扩散进行模拟预测 ,不同的扩散模型代表着不同污染气象条件下的扩散结果。选择有代表性的扩散模型客观地反映污染物对环境影响的结果才有助于指导建设项目的实施。本文通过对封闭型扩散模型的使用条件分析 ,提出了正确使用该模型的方法。     

A fast long-range transport model for operational use in episode simulation. Application to the Chernobyl accident

A simple Lagrangian puff trajectory model and its software implementation, STRALE, are described. Standard meteorological data are used as input for the simulation of the three-dimensional atmospheric transport and dispersion of a pollutant released by a point source. The schemes adopted to describe the vertical diffusion and the interaction with the mixing layer are discussed on the basis of the comparison between simulated and measured ¹³⁷Cs activities for the Chernobyl nuclear accident.     

小风条件下大气扩散模式发展回顾研究

由于小风对污染事件的潜在影响,以及与中等风速和大风条件相比边界层结构、湍流和扩散的特殊性,常规的稳态高斯烟流模式在这种条件下具有局限性,建立适用于小风条件的大气扩散模式具有重要的理论和实际意义。本文回顾了近年来小风条件下大气扩散模式的建立和发展,从较简单的解析模式到复杂的数值模式,并对不同模式的参数化方案、与示踪物实验的比较结果、适用性和不足之处进行了总结。综合考虑不同模式的优劣,在应用方面有利于根据实际情况选择合适的模式,在模式开发方面,有助于建立更加完备的大气扩散模式。     

AERMOD大气扩散模型研究综述

AERMOD模型是美国环保局和美国气象学会联合开发的一种大气扩散模型,它采用了最新的大气边界层和大气扩散理论,替代ISC(Industrial Source Complex)模型成为美国的新一代法规模型,该模型已被列入我国环境影响评价技术导则--大气环境(HJ/T2.2-2008)推荐模型之一。国内外针对该模型开展了很多研究,主要集中在:AERMOD模型与其它大气扩散模型的对比研究和评价;AERMOD模型运行所需气象数据的模拟以及AERMOD模型在某些领域中的具体应用。AERMOD模型较我国旧版环境影响评价技术导则--大气环境(HJ/T2.2-93)推荐模型更能反映污染物的实际扩散规律,但由于目前该模型系统在国内的应用不算广泛,而且该模型本身也一直在不断完善当中,因此,为验证它的可靠性、合理性及实用性并确定其预报准确率,建议在该模型推广应用到一个新的地区或城市之前应当经过模型评估过程。     

对熏烟扩散模式应用的探讨

工程上应用的大气污染物扩散模式中 ,熏烟模式由于其非定常性而与其他扩散模式有很大的区别。正确处理模式中各参数及变量的相互关系才能客观地反映污染物对环境影响的结果。本研究通过对熏烟模式的非定常性和各参数、变量相互关系的分析 ,提出了正确使用该模式的方法     

Parallel processing of a random-walk model of atmospheric dispersion

Algorithms for random-walk models of atmospheric dispersion take considerable processing time on sequential computers. Such algorithms are, however, more suited to parallel computers as they contain a high degree of parallelism. In this paper, to show this suitability and to investigate the improvement in the processing time with the use of a parallel computer, the model algorithm developed and applied in Luhar and Britter (1989, Atmospheric Environment23, 1911–1924) has been implemented on a Distributed Array of Processors (DAP). The results show a 14-fold improvement in the processing time over a sequential machine.     

城郊道路交通带状多线源污染扩散模式研究

为研究适用于路面宽,等级高的城郊道路大气污染扩散模式,以Ｃａｌｉｎｅ－３有阴长线源污染扩散模式为基础,并以上海浦东新区道路网为实例,将带状线源的概念引入线源扩散模式研究,建立了新的带状多线源污染扩散模式,分析了气象条件,初始扩散,道路基本工程参数对大气污染扩散的影响,引用实例数据,对所建立的ＢＭＬＳＭ模式进行了检验,并与Ｃａｌｉｎｅ－２模式进行了对比。结果表明,采用本研究建立的带状多线源污染扩散模     

中国法规大气扩散模式及其与其他模式的比较

介绍了中国法规性大气扩散模式(CRADM),分析了CRADM和西方一些模式(如HPDM,AMS)的差别。采用同样条件作为输入,比较并讨论了CRADM,HPDM和AMS在各方面的性能差异。分析了中国大气扩散模式在环境影响评价应用中出现的一些问题,提出了改进建议。特别地,研究表明中性条件下Briggs烟气抬升公式对实际抬升有过高估计,原因是没有考虑环境湍流对烟羽的累积作用      

工业园区典型VOCs污染过程精细化溯源

以上海某化工工业园区为目标区域,针对典型的大气VOCs污染过程,通过耦合高时间分辨率GC-MS在线监测、拉格朗日大气扩散模型、VOCs源谱及相似度分析等技术手段,开展了小尺度大气VOCs的精细化溯源.结果表明,针对敏感点监测到的VOCs高值时刻,拉格朗日大气扩散模型能够追踪主要的气团来向及企业潜在贡献,空间分辨率达到1...     

路旁土壤公路源重金属含量空间分布数值模型的探讨

公路源重金属产生后,赋存于大气颗粒物中,随颗粒物在大气中迁移沉降,最终沉降于路旁土壤中.本研究通过对公路源重金属迁移机理的分析,以高斯污染物扩散模型为基础,构建公路源重金属在路旁土壤中空间分布的数值模型,并用G310国道杏花营断面路旁土壤重金属(Cd、Cr、Cu、Ni、Pb和Zn)含量空间分布实测数据对模型预测能力进行验证.结果表明:土壤Cr和Cu含量呈指数分布,土壤Cd、Ni、Pb和Zn含量呈偏态分布,指数分布实质上是偏态分布的峰值十分接近路基的一种特例.研究表明,本文构造的数值模型可以较好地拟合上述两种路旁土壤重金属空间分布形式,模拟情景数n的取值越大,模拟结果越准确.     

北京地区FLEXPART模式适用性初步研究

FLEXPART是挪威大气研究所开发的拉格朗日粒子扩散模式.为客观地评价该模式在北京地区的适用性,以北京上甸子大气本底站为例,模拟了CO浓度变化及其源区分布特征,并与该站实测CO浓度和2006年排放源清单进行了比对.结果表明:①模式模拟的CO浓度变化趋势可以较好地反映上甸子地区CO浓度的日变化规律,CO浓度的模拟值与实测值的相关系数在春夏两季分别达到0.42和0.41;②春夏两季北京市污染气团主要源地分布在西-西南和西西南-南-南南东扇区,模式结果较好地体现了北京及周边地区CO源区的分布特征.初步研究表明,FLEXPART模式在北京地区是基本适用的.     

Particle model simulation of diffusion in low wind speed stable conditions

A Lagrangian particle model (LAMDA), previously developed and applied to the simulation of atmospheric dispersion in neutral and convective windy conditions, was modified to deal with stable low wind speed conditions. These last are among the most difficult to be treated. In fact, on the one hand, nearly calm situations, associated to strong stability and air stagnation, make the lower layers of the atmosphere poorly diffusive, and, on the other hand, the large fluctuations in the wind direction (meandering), spread the airborne pollutants over wide angular sectors. An ad hoc algorithm to simulate the effect of meadering on the dispersion is proposed. The model is validated by comparing its simulation results to three tracer experiments held in stable low wind speed conditions by the Idaho National Engineering Laboratory (U.S.A.) in 1974. These experiments present plume spread of different width (48, 138 and 360°, respectively, at an arc located 200 m downwind from the source) and are comprehensive of a wide set of conditions, ranging from strong to weak stability and from low wind speed to calm. The results of the comparison are discussed. The ability of the model to simulate the g.l.c. distributions with a good degree of confidence is illustrated.