应用照相法估算高架点源的污染物浓度

烟流的扩散问题现一般采用高斯模式来描述,高斯烟流模式是在大量实测资料分析的基础上,应用统计理论得到的,提出了解决污染物在大气中扩散的实用模式。本文将利用对高架点源的烟流拍照获得一组烟流照片,把这一组烟流形状在计算机上叠加,可以得到一个采样时间内的烟流边界层,由流体力学理论导出烟流扩散的污染物浓度。 1、模式的建立浮射流高架点源排放的烟流,由于它的起始密度和周围环境大气的密度不等,受到浮力的作用,本文将烟流扩散     

汽车排放污染物浓度的预测

为了预测汽车排放污染物的浓度,应用简化的高斯烟团模式得到静风条件下的线源扩散预测模式。并结合高斯烟流扩散模式,建立了预测汽车污染物在任意风向下和年平均浓度的预测模式,考虑车道上存在车辆行驶的强烈机械扰动湍流和把繁忙的公路视为线源两个因素,提出了计算初始扩散参数的方法。然后,运用Turner和Pasquill扩散参数,建立了线源扩散参数的确定方法。该模式应用于预测高速公路沿途汽车污染物的浓度表明,计算值与监测值吻合较好,可用于我国公路环境影响的评价。     

连续烟流中重金属扩散行为的一致性

<正> 重金属是冶炼厂烟尘中的主要污染物。当随烟流扩散时,各种重金属在某一区域的溅落量是否有一定的关系,是环境评价人员关心的问题。当以高斯模型等数学方法预测连续烟流中重金属的落地浓度和落地距离时,重金属是作为扩散质点对待的。其扩散     

应用发烟照相法研究冲洪积扇秋季大气扩散规律

对秋季冲洪积扇地形下污染物扩散问题的处理,需要加强扩散参数的研究。本文应用发烟照相法研究垂直扩散参数,对其理论曲线与实验曲线进行了比较,对下风向轴线浓度理论值与实验值进行了讨论,认为冲洪积扇的地形和稳定度状况,比平原有利于污染物的扩散稀释;洪积扇地形下研究大气扩散,1km内需用实测的扩散参数来进行计算污染物的扩散,1km以远引用理论值是可以接受的。     

利用电子计算机进行大气稳定度分类

气温的垂直分布与空气污染有着密切地联系,这是因为气温的垂直分布决定了大气稳定度,而大气稳定度又影响着空气运动,进而影响污染物的输送和扩散。扩散理论导出的各种模式又将大气的稳定度状态与污染浓度有机地联系起来,从而将大气对污染物的影响模式化、参数化。如高斯烟流模式中的扩散参数α_v、α_z的取值与大气稳定度的划分有着直接的     

关于高架源浮升烟流扩散参数的探讨

本文根据徐州电厂大气扩散试验,对用同步立体摄影资料计算扩散参数的分析方法与结果进行讨论,为寻求高架源浮升烟流扩散参数估算模式提供依据.     

风向变化对城市大气污染的影响及试验分析

针对城市大气污染的复杂多变状况，在理论分析的基础上，通过风洞实验对城市大气污染扩散模型进行了模拟试验研究，建立了适合一定条件下城市大气污染物扩散的数学和物理模型，并对城市大气污染状况的影响因素进行了分析，在得到特定条件下城市大气污染扩散普遍规律的同时，重点讨论了风向变化对城市大气污染的影响，该方法同时还可以应用于城市大气污染物扩散浓度的估算。     

大气封闭型扩散浓度估算模式细探

从大气封闭型扩散实际反射路径分析入手,引入上下边界不同的反射率与污染物衰减系数,得出比以往公式更具一般意义的大气封闭型扩散的污染物浓度估算公式,特别适用于边界具有一定吸收能力与污染物质有衰减的情况,从而有效改进污染贡献的估算精度.文中展示的示意图,纠正了以往示意图的错误.      

山体绕流和尾流区气态污染物输送扩散规律的研究

采用瞬时烟线仪与迪沙(DISA)热线风速仪相结合的方法探测了山体的绕流区和尾流区结构。试验结果表明,山体的绕流和尾流对低架源排放的气态污染物扩散影响甚大,山体绕流可改变烟流的地面浓度分布.结果还表明,我们所用的探测流向的方法较为有效和准确.     

地下水可溶性污染物迁移的最优估算

对流扩散方程的有限元和有限差方法已经广泛地用来模拟地下水污染物的迁移。由于迁移过程固有的不确定性,模拟方法的不准确性等都会给模型计算带来偏差;另外野外测量的误差也是不可避免的。通过数值模型、量测方程和卡尔曼滤波的结合,作为状态变量的污染物浓度可以优化给出。本文以二维地下水污染物的对流扩散方程为例,应用有限元方法导出卡尔曼滤波的转移矩阵,结果表明,使用滤波技术来估算地下水可溶性污染物浓度的分布比单独使用有限元方法有较大的优越性。     

Plume rise,entrainment and dispersion in turbulent winds

This paper describes a new analytical model which combines within one theoretical framework several aspects of the phenomena of plume rise, dispersion, thermal stratification and ambient turbulence. The model is based in part on knowledge gained from recent investigations of flow within free shear layers. The observations suggest a simple model for the turbulent mixing process, which accounts for the known entrainment of air into smoke plumes by plume-generated turbulence. More importantly, the model also predicts a path by which ambient turbulence causes reverse entrainment of plume material into the surrounding fluids. This gives rise to a new ‘extrainment’ term in each of the plume momentum and buoyancy equations.These equations are solved for a turbulent atmosphere of arbitrary thermal stability, and yield plume trajectories which gradually level off at final rise heights that depend on the degree of thermal stratification and on the scale and intensity of ambient turbulence. A link between plume rise and dispersion is identified by means of the concentration species equation, which is solved to show that the plume acts along its length as a distributed source of passively dispersing material.The new theory, specialized for an adiabatic atmosphere, plus the familiarx^2/3 law and a semi-empirical final rise theory from the literature, are all compared against full-scale data on plume rise in turbulent winds. The new theory significantly improves the accuracy of estimates of plume trajectory and final plume height. The price for this improved predictive ability is the need to evaluate the air temperature and its gradient at plume level, and the corresponding intensity and scale of turbulent air movement. This is no longer a technical obstacle since recently developed SODAR and RASS remote sensors have this capability.     

WRF-Fluent耦合模式的构建及其对城市大气扩散的精细化模拟

为了准确刻画城市环境中的复杂建筑结构对大气运动和污染物输送及扩散过程的影响,结合中尺度模式WRF和微尺度模式Fluent构建了单向耦合的WRF-Fluent模式,并将其应用于榆中县城区高架源排放情景下大气扩散的模拟研究.基于城市气象/示踪外场试验期间获取的气象数据对WRF模式的模拟性能进行验证,发现WRF能够为Fluent提供比较准确的随时间变化的气象驱动场.在此基础上,将榆中县城区三维几何模型嵌入到WRF-Fluent中,对城区内的流场及污染烟羽的时空演变过程进行精细化模拟,并将模拟结果与实测示踪物浓度数据进行比对.结果显示,WRF-Fluent模式可以很好地描述城区内的复杂三维风场结构以及污染烟羽随时间的动态变化特征,而且模拟的地面和城市冠层顶浓度最大值基本位于观测值的0.3~3倍之内,这表明构建的WRF-Fluent模式具有较好的模拟性能,可作为一种有效的工具应用于实际城市规划和空气质量改善以及环境风险评估等方面的研究.     

怠速条件下汽车排气污染物在排气尾流中扩散特性的实验研究

通过实验的方法对怠速条件下汽车排气污染物在排气尾流中的扩散特性进行了研究.测定了怠速条件下汽车排气尾流中的污染物体积分数及其分布,并比较分析了3种不同类型汽车的污染物排放体积分数及其变化.实验结果表明,怠速时汽车排气尾流中的污染物体积分数按照近似指数函数的趋势迅速降低到接近大气背景值;不同类型汽车排气尾流中的污染物体积分数的差别非常明显;排气方向对汽车排放污染物的扩散及其分布具有重要的影响.研究工作可以为怠速工况下汽车排气污染物对周围环境的影响评价提供更多的有用信息.     

特种污染物排放源强反演及可视化分析工具研发及Hg2+分析示例

研发了特种污染物排放源强反演及可视化分析工具,集成利用了WRF气象预报结果及HYSPLIT前向轨迹规划外场监测点,调用CALPUFF模型基于监测数据和对应气象条件快速反算源强并模拟得到排放影响范围,并使用开源GIS平台进行可视化分析.同时,选取大气背景浓度极低的活性气态汞(Hg~(2+))为目标,以李坑垃圾焚烧厂不稳定Hg~(2+)排放为监测主体.结果表明,基于下风向监测数据反演的源强与实测的烟气Hg~(2+)含量有着较好的一致性(R~2=0.801).该工具可作为特种大气污染事故应急辅助决策新手段,提供包含非稳态排放源强、污染扩散影响范围等信息在内的关键依据.     

Preliminary studies of video images of smoke dispersion in the near wake of a model building

A summary of analyses of video images of smoke in a wind tunnel study of dispersion in the near wake of a model building is presented. The analyses provide information on both the instantaneous and time-average patterns of dispersion. Since the images represent vertically-integrated or crosswind-integrated smoke concentration, only the primary spatial and temporal scales of pollutant dispersion can be examined. Special graphic displays of the results are presented to assist in the data interpretation. The video image format is shown to have great potential as an easily quantifiable electronic medium for studying the dispersion of smoke.     

山体对烟羽弥散影响的一种数值模拟方法

本文对山地和丘陵地区中烟羽浓度扩散分布的计算提出一种方法,该方法引用浓度方程的分析解,通过对山地绕流数值计算速度势和流函数,可较简易地求得烟羽浓度分布。作为算例,文中对中条山某工厂烟囟排放的SO2,预测了它在各种风速时被输运扩敢的浓度分布。      

烟羽在夜间雾天状况下的扩散数值研究

用夜间雾的数值模式研究了高架源在雾形成前后的扩散特征。模拟结果表明，雾的出现影响了大气近地层结，使原来很稳定的大气变成不稳定大气，但雾顶以上仍是逆温状态，这样导致雾顶附近的高浓度污染物向地面输送加剧，造成地面污染。这种情况非常类似于日出后出现的地面熏烟。研究结果从大气扩散方面解释了近年来在雾天临测中发现的地面高浓度污染现象，说明雾天是造成地面严重污染的重要天气之一。     

An approximate model of atmospheric plumes produced by large area fires

We develop a simple analytical model to estimate the thickness of a smoke layer formed by a plume of a large area fire and to account for crosswinds. We take advantage of the dominant flow features in the upper part of the rising plume and in the smoke layer far from the plume to model the transition of a vertical flow to a horizontally spread thin smoke (or dust) layer. A one-dimensional approximation is used to model the buoyancy decay and plume overshoot. That solution is matched and combined with a solution based on the work required to establish our asymptotic horizontal smoke layer. The solution estimates the thickness of the spreading smoke layer in a quiescent atmosphere or in an ambient wind field.     

A meso-scale plume dispersion model. Preliminary evaluation in a heterogeneous area

A plume dispersion model for meso-γ-scale applications is developed. The model is formulated with the aim to study plume spreading in moderately complex terrain. An eddy diffusivity analogue is used in order to facilitate future inclusion of chemical transformations. The full diffusivity tensor, obtained from a second-order closure turbulence model, is used to described the dispersion process. The model is driven with simulated meteorological fields, obtained by means of a second-order turbulence closure model. An initial model evaluation has been undertaken using model predictions for an area featuring horizontally inhomogeneous dispersion conditions. Comparison with measurements, as well as with predictions of several other model types for distances out to 40 km, shows that the model is able to describe realistically plume widths and concentration in areas with strongly varying dispersion conditions. Non-negligible errors in plume position were however found for all models compared.