A Microscale Model for Air Pollutant Dispersion Simulation in Urban Areas： Presentation of the Model and Performance over a Single Building

A microscale air pollutant dispersion model system is developed for emergency response purposes. The model includes a diagnostic wind field model to simulate the wind field and a random-walk air pollutant dispersion model to simulate the pollutant concentration through consideration of the influence of urban buildings. Numerical experiments are designed to evaluate the model＇s performance, using CEDVAL （Compilation of Experimental Data for Validation of Microscale Disper- sion Models） wind tunnel experiment data, including wind fields and air pollutant dispersion around a single building. The results show that the wind model can reproduce the vortexes triggered by urban buildings and the dispersion model simulates the pollutant concentration around buildings well. Typically, the simulation errors come from the determination of the key zones around a building or building cluster. This model has the potential for multiple applications; for example, the prediction of air pollutant dispersion and the evaluation of environmental impacts in emergency situations; urban planning scenarios; and the assessment of microscale air quality in urban areas.

Numerical and Experimental Studies on Flow and Pollutant Dispersion in Urban Street Canyons

In this study numerical simulations and water tank experiments were used to investigate the flow and pollutant dispersion in an urban street canyon. Two types of canyon geometry were tested. The studies indicate that in a step-up notch canyon （higher buildings on the downstream side of the canyon）, the height and shape of the upstream lower buildings plays an important role in flow pattern and pollutant dispersion, while in a step-down notch canyon （lower buildings on the downstream side）, the downstream lower buildings have little influence. The studies also show that the substitution of tall towers for parailelepiped buildings on one side of the canyon may enhance the street ventilation and decrease the pollutant concentration emitted by motor vehicles.

Effects of a rooftop wind turbine on the dispersion of air pollutant behind a cube-shaped building

The concentration distribution of urban air pollutants is closely related to people’s health.As an important utilization form of urban wind power,rooftop wind turbines have been widely used in cities.The wake effect of the rooftop wind turbines will change the flow behind buildings and then affect the pollutant dispersion.To this end,the pollutant dispersion behind the building is studied via the computational fluid dynamics method.The actuator disk model and idealized cube are adopted to model the wind turbine and the building,respectively.The study shows that the rooftop wind turbine can reduce the pollutant mass fraction near the ground and the pedestrian level.Due to the wake effect of the rooftop wind turbine,the turbulent fluctuation behind the building is weakened,and the spanwise pollutant dispersion is suppressed.Besides,the rooftop wind turbine weakens the downwash movement of the building,which enhances the vertical pollutant dispersion.

ADAPTIVE FINITE ELEMENT METHOD FOR ANALYSIS OF POLLUTANT DISPERSION IN SHALLOW WATER

A finite element method for analysis of pollutant dispersion in shallow water is presented. The analysis is divided into two parts ： （ 1 ） computation of the velocity flow field and water surface elevation, and （2） computation of the pollutant concentration field from the dispersion model. The method was combined with an adaptive meshing technique to increase the solution accuracy, as well as to reduce the computational time and computer memory. The finite element formulation and the computer programs were validated by several examples that have known solutions. In addition, the capability of the combined method was demonstrated by analyzing pollutant dispersion in Chao Phraya River near the gulf of Thailand.

Modeling the Dispersion and Atmospheric Mitigation of Pollutants in the Dibamba-Douala Thermal Power Plant

This work simulates the dispersion and atmospheric attenuation of pollutants from the Dibamba-Douala thermal power plant. The objective of this research is to study the dispersion of air pollutants and mitigate the impact of pollutants on the populations living around the power plant. The methodology used is as follows: the Gaussian model is used for the representation of the dispersion in the form of a plume, the finite difference method for digital resolution. Finally, dispersion charts are constructed which allow the heights of the chimneys to be fixed for which the concentrations of pollutants discharged comply with ambient air quality standards. The results obtained using the simulation made in the MATLAB software version 2016 show that, for a wind regime of 1.5 m/s;we have a predicted distance of 150 m at which the concentration is canceled out. Then, for the wind speed of 2 m/s;we had a predicted distance of 125 m and finally for a wind speed of 2.5 m/s;we observed the 120 m distance at which the concentration is canceled. In addition, for the same wind regimes, the attenuation of pollutants at ground level is obtained for a height of 60 m.

Impact of Noise Barriers on Air-Pollution Dispersion

The impact of noise barriers on gaseous air-pollution dispersion was examined using the high-resolution CLMM (Charles University LES (Large Eddy Simulation) Microscale Model). The dispersion of a mixture of nitrogen oxides (denoted as NOx—a mix of NO and NO2) was computed, providing the simulation in which wind direction is approximately perpendicular to the noise barriers. The barriers were assumed to be straight and infinitely long, with a height of 3 m. Dispersion of NOx was modeled for situations with no noise barriers along the highway, barriers on both sides, and for a single barrier on the upwind and downwind sides of the highway. The modelling results are presented and discussed in relation to previous studies and the implications of the results are considered for pollution barriers along highways.

Random walk modeling of wake dispersion for the exhaust tower of an underground tunnel in urban area

In this paper, some experimental studies on the impact of effluent from an exhaust tower of an underground tunnel with special construction are reported. By measuring the flow field downstream of the tower in NJU meteorological wind tunnel, some flow characteristics in the make area were established. Based on these, an advanced random\|walk dispersion model was set up and applied successfully to the simulation of dispersion in the wake area. The modelling results were in accordance with wind tunnel measurements. The computed maximum of ground surface concentration in the building case was a factor of 3-4 higher than that in the flat case and appeared much closer to the source. The simulation indicated that random walk modelling is an effective and practical tool for the wake stream impact assessment.

Volatile Organic Compound Emissions from Surface Coating Facilities: Characterization of Facilities, Estimation of Emission Rates, and Dispersion Modeling of Off-Site Impacts

Surface coating facilities are major sources of volatile organic compounds (VOCs) in urban areas. These VOCs can contribute to ground-level ozone formation, and many are hazardous air pollutants (HAPs), including xylene, ethylbenzene, and toluene. This project was conducted in order to provide information for updating the Texas Commission on Environmental Quality (TCEQ), USA, permit by rule for Surface Coating Facilities. Project objectives were: 1) To develop a database of information regarding surface coating facilities in Texas;2) To estimate maximum emission rates for various VOC species from surface coating facilities in Texas;3) To conduct dispersion modeling to estimate off-site impacts from surface coating facilities. The database was developed using 286 TCEQ permit files authorizing surface coating facilities in Texas during 2006 and 2007. The database was designed to include information important for estimating emission rates, and for using as inputs to the dispersion model. Hourly and annual emissions of volatile organic compounds (VOCs), particulate matter (PM), and exempt solvents (ES) were calculated for each permitted entity/ company in the database, according to equations given by TCEQ. Dispersion modeling was then conducted for 3 facility configurations (worst-case stack height, good practice stack height, and fugitive emissions), for urban and rural dispersion parameters, for 8-hour and 24-hour operating scenarios, and for 1-hour, 24-hour, and annual averaging times, for a total of 36 scenarios. The highest modeled concentrations were for the worst-case stack height, rural dispersion parameters, 24-hour operation scenario, and 1-hour averaging time. 108 specific chemical species, which are components of surface coatings, were identified as candidates for further health impacts review.

Viscoelastic modeling of the diffusion of polymeric pollutants injected into a pipe flow

This study focuses on the transient analysis of nonlinear dispersion of a polymeric pollutant ejected by an external source into a laminar pipe flow of a Newtonian liquid under axi-symmetric conditions.The influence of density variation with pollutant concentration is approximated according to the Boussinesq approximation and the nonlinear governing equations of momentum,pollutant concentration are obtained together with and Oldroyd-B constitutive model for the polymer stress.The problem is solved numerically using a semi-implicit finite difference method.Solutions are presented in graphical form for various parameter values and given in terms of fluid velocity,pollutant concentration,polymer stress components,skin friction and wall mass transfer rate.The model can be a useful tool in understanding the dynamics of industrial pollution situations arising from improper discharge of hydrocarbon pollutants into,say,water bodies.The model can also be quite useful for available necessary early warning methods for detecting or predicting the scale of pollution and hence help mitigate related damage downstream by earlier instituting relevant decontamination measures.

Physio-chemical modeling of the NO_(x)-O_(3) photochemical cycle and the air pollutants’ reactive dispersion around an isolated building

A numerical physio-chemical model of the NO_(x)-O_(3) photochemical cycle in the near-wake region of an isolated residential/office building has been presented in this study.The investigation delves into the dispersion of reactive air pollutants through the lens of fluid phenomenology and its impact on chemical reactivity,formation,transport,deposition,and removal.Computational fluid dynamics(CFD)simulations were conducted for the ground-point-source(GES)and roof-pointsource(RES)scenarios.Results show that the Damköhler number(Da),which quantifies pollutants’physio-chemical timescales,displays a strong inverse proportionality with the magnitude and spread of NO–increasing Da reduces human exposure to the toxic NO and NO_(2) substantially.When different wind directions were considered,the dispersion range of NO exhibited varying shrinking directions as Da increased.Furthermore,as Da increases,the concentration ratio KNO_(2)/KNO_(x),which quantifies the production of NO_(2) resulting from NO depletion,forms sharp high-low gradients near emission sources.For GES,the dispersion pattern is governed by the fluid’s phenomenological features.For RES,the intoxicated area emanates from the building’s leading-edge,with the lack of shielding inhibiting pollutant interactions in the near-wake,resulting in scant physio-chemical coupling.The NO_(2)/NO_(x) distribution follows a self-similar,stratified pattern,exhibiting consistent layering gradients and attributing to the natural deposition of the already-reacted pollutants rather than in-situ reactions.In the end,building design guidelines have been proposed to reduce pedestrian and resident exposure to NO_(x)-O_(3).

内河航道船舶大气污染物扩散模拟研究

为探究内河航道船舶大气污染物在沿岸建筑物群的扩散规律,基于船舶自动识别系统数据构建南京市内河某航道段船舶大气污染物排放计算模型,采用“自下而上”方法计算得到船舶SO_(2)、NO_(2)、PM_(10)、PM_(2.5)、CO和挥发性有机物6种大气污染物排放量。通过Revit软件与Fluent软件建立船舶大气污染物在沿江居民区的扩散模型并进行可视化模拟分析。结果表明:在常风向全年平均风速条件下,污染物扩散与建筑群布局密切相关,在密集建筑物群背风面易出现负压区,该处污染物浓度较低,但在整体建筑物群背风面稍远处,出现气流旋涡区,导致较高浓度的污染物聚集,短期内产生持续污染影响。研究思路与结果可为航道沿岸居民区规划建设,降低船舶大气污染物影响提供理论依据。

住院病房的暖通分析与基于SEIR模型疾病传染分析

基于CFD软件对住院病房进行暖通分析。通过建立物理模型和数学模型的方法,分析温度云图、气流组织云图以及污染物扩散云图总结规律。从暖通的角度出发利用SEIR模型在MATLAB软件中对比无防控措施下病毒传播与有防护措施下病毒传播人数感染情况,从而以小窥大反应暖通专业在控制疾病传播上有一定作用。

高海拔隧道施工期污染物扩散规律

为了探究高海拔隧道施工通风过程中的污染物扩散规律,依托川藏铁路芒康山隧道工程,采用数值模拟和现场测试的方法,研究高海拔隧道施工通风过程中粉尘和CO的扩散规律.研究结果表明,粉尘主要是以贴壁流动的形式向洞外扩散,在该过程中会聚集成为“粉尘团”.粉尘扩散主要是受到重力影响发生沉降,隧道内风速过大,不利于降低粉尘质量浓度.CO以“气团”的形式从掌子面附近向洞口迁移,在迁移过程中CO气团体积逐渐扩大,质量浓度峰值不断下降,逐渐形成“U形”的分布趋势,CO质量浓度的现场测试结果与数值模拟结果基本吻合.随着海拔高度的上升,隧道内的CO质量浓度会增大,隧道内同一位置CO质量浓度达到规范要求的时间会增加.推导基于海拔高度的隧道通风过程中CO质量浓度修正系数计算公式,对当前规范中CO的海拔高度修正系数进行很好的补充.

小清河入海污染物扩散特征及其对近岸工程建设的响应

河流入海污染物是近海污染物的主要来源之一。小清河是莱州湾西南部主要入海河流和污染物来源,近年来小清河口两侧近岸工程建设规模不断扩大,其对小清河入海污染物扩散的影响如何有待深入研究。采用MIKE21数值模型模拟了近岸工程建设对潮流场的影响及小清河入海污染物(无机氮、活性磷酸盐)的扩散特征,探讨了入海污染物扩散对近岸工程建设的响应。研究结果表明:小清河口两侧近岸工程的建设,导致小清河河口附近海域流速有所减小,减小值介于2~21 cm/s。河口两侧的堤坝、防波堤等工程阻挡了污染物向东南、西北方向扩散,使小清河入海污染物扩散范围有所减小,不利于污染物扩散,导致河口附近海域污染物浓度有所增加,从而加剧了小清河河口附近海域的水质污染。因此,近岸工程建设会造成工程附近海域的潮流减弱,削弱近海海域的污染物扩散能力。

论含水层非均质性对地下水污染特征的控制——以某山谷型垃圾填埋场为例

以某山谷型垃圾填埋场垃圾渗漏液泄漏的地下水污染调查与污染风险管控过程为例,探讨山谷型水文地质条件小尺度场地下含水层非均质性对地下水污染特征的控制作用。通过对研究区水文地质勘查、地下水污染的精准消源控羽和含水层强径流带的高效刻画等实践结果表明:山谷区非均质含水层中“非菲克弥散”现象明显;场地含水层非均质的掌控是地下水污染管控与修复工程成败与优化的关键所在;含水层非均质的把控可明显提高地下水污染精准管控效果,同时还可大大降低管控成本。本案例可为山谷型地下水污染风险管控工作提供可供借鉴的实践经验和技术参考。

道路交通排放对周边环境影响的分析——以兰州市安宁区学府路为例

探究城市道路中机动车污染物的排放对周边环境的影响,对环境治理起着至关重要的作用。通常通过分析污染物的影响因素,来建立排放模型。根据研究尺度的不同,将应用较广泛的模型进行划分,并对模型原理、应用及存在不足等方面进行归纳和总结。为了探究学府路道路污染状况,选取COPERT模型进行污染物排放量的测算,并使用ANSYS软件模拟了道路交通排放对学府路周边环境的影响,得出了污染物地图。结果表明:学府路工作日内4项主要大气污染物NO_(2)、CO、PM_(2.5)、PM_(10)排放量分别为67.7、269.1、15.1和22.8 t。数量占10.0%的轻型货车排放贡献较大,分别占机动车NO_(2)和PM排放总量的50.5%和69.1%。通过模拟值与实测值的对比发现,COPERT模型对于中观尺度的研究具有较好的支撑。

绿化空间布局及壁面加热条件对街道峡谷内污染物扩散的影响

采用经风洞实验验证的标准k−ε数值模型,模拟了绿化空间布局及壁面加热条件对街道峡谷内流场和污染物扩散的影响。考虑了3种绿化组合方式与4种壁面加热条件,并采用无量纲浓度K与空气交换率RACH分别对街道峡谷内污染情况与通风性能进行评估。结果表明,不同的绿化空间布局和壁面加热条件会改变街道峡谷内流场和污染物浓度分布。选择绿化结合布局时,应尽量选择绿墙和绿篱的组合以减弱绿化阻塞作用对污染物扩散的不利影响。背风面加热和迎风面加热对街道峡谷的通风能力提升作用并不明显,而三壁加热能明显改善街道峡谷的通风性能。

城市景观绿化设计布局对扬尘污染的弱化影响研究

为了设置出最合适的城市景观绿化布局,缓解城市扬尘污染,降低空气颗粒物浓度,减少空气污染,分析城市景观绿化设计布局对扬尘污染的弱化影响。计算不同类型尺度的绿化指标,确定景观优势元素和绿化类型的多样性标准。依据空气污染历史数据,获得扬尘污染质量浓度水平。经过实例分析可知,根据多样性标准设计的城市景观绿化布局能够弱化扬尘污染,且弱化效果随时间推移不断增强;通过城市景观绿化设计布局优化,能改变风速与扬尘间的正相关关系,降低二次扬尘污染,稀释了30%以上的污染浓度。