Measurements of wind speed and plume rise with a rapid-scanning Lidar

A series of 30-min means of plume rise and dispersion parameters were measured at Fawley power station on Southampton Water between May and December 1989 using a rapid-scanning Lidar. Where possible, plume parameters were determined at three distances, typically 250, 750 and 1500 m, from the stack. Simultaneous measurements of temperature profiles were made using model aircraft and of wind speed and direction using a cup anemometer and wind vane at a height of 44 m on a transmission tower. By matching time series of plume heights at different distances, absolute measurements of wind speed at plume height could be made. These measurements gave a more reliable estimate of plume rise than did surface wind speeds. It was found that, for travel distances out to 1.5 km, the Briggs formula gave a robust prediction of plume heights with C₁ = 1.38±0.07 (95% confidence limits). At Fawley, the standard error in the predicted plume height at 500 m was then 21.0 m, or 19% of the 30-min mean plume rise. For plume-level winds of less than 20 m s⁻¹, analysis of the dependence of plume height on distance, wind speed and power-station load gave a virtual source height of 195.2±10.3 m (95% confidence limits). This is identical with the physical stack height of 198.1 m.     

Large-eddy simulation of dispersion in the convective boundary layer

Large-eddy simulation (LES) is used to study the dispersion of a passive scalar downwind of a localized source in a convective boundary layer. The LES turbulent velocity statistics are compared with laboratory data and other LES studies. Two scalar source heights at 0.25 z_i and 0.50 z_i are considered, where z_i is the inversion height, and the mean concentration fields are compared with the experimental data of Willis and Deardorf (1978, Atmospheric Environment12, 1305–1312; 1981, Atmospheric Environment15, 109–117). Emphasis is placed on the fluctuating component of the concentration field due to the random turbulent velocity fluctuations, and amplitudes, temporal and spatial scales, and probability distributions are examined. Concentration fluctuation intensity continually decreases downstream, suggesting zero intensity as the asymptotic limit. Vertical profiles of both mean concentration and fluctuation variance become well mixed downstream. Dissipation and correlation scales increase nearly in proportion to the plume width, so that time- and space-averaging the concentration is less effective in reducing the fluctuations further downstream. Concentration probability distributions show intermittency near the source but become nearly normal as the plume moves downstream. Results are compared and contrasted with the neutral flow study of Sykes and Henn (1992a, Atmospheric Environment26A, 3127–3144).     

Improvement of the modelling of daytime nitrogen oxide oxidation in plumes by using instantaneous plume dispersion parameters

The effect of concentration fluctuations on the modelling of non-linear chemical reactions in the atmosphere will be considerable when hourly mean dispersion parameters are used. This effect can be reduced by introducing instantaneous dispersion parameters, as will be shown in this paper for the modelling of the oxidation of NO emited into an O₃ containing atmosphere.We used the results of atmospheric tracer gas experiments to derive the dimensions of the instanteneous plume. With these results model calculations were carried out for the NOO₃ reaction. Results were compared with airborne measurements of NO oxidation in the plumes of Dutch power plants.The introduction of the instantaneous plume leads to better agreement between model calculations and measurements. It is also found that the deviation from photochemical equilibrium in the plume is considerably smaller when instantaneous, instead of hourly, mean dispersion parameters are used. The dimension of the instantaneous plume did not show a dependence on atmospheric stability.     

Water tank experiment of gas diffusion from a stack in stably and unstably stratified layers under calm conditions

Water tank experiments were conducted to investigate plume rrise and diffusion of gases discharged from a stack under calm conditions with stable and unstable thermal stratifications.First, tracer liquid with fluorescent dye and salt was emitted from a model of a stack in a stably stratified layer and the behavior of a plume was recorded by video camera. Using these results. we obtained formulae for plume rise height, and horizontal and vertical width of a plume as a function of thedensimetric Froude number, stability ratio and time.After the completion of these experiments under stable conditions, an unstably stratified layer was developed from a ground surface by heating a floor and the resulting concentration distribution was measured with electric conductivity probes. Using these results, we analyzed the height of the convection layer and concentration distribution as a function of the overall Richardson number and time.     

Velocity oscillations and plume dispersion in a residential neighborhood during wintertime nights

Measurements of velocity and tracer plume concentrations during stable atmospheric conditions were obtained in the Boise River Valley as part of the EPA Integrated Air Cancer Project during December, 1986. Wind speed, temperature, and wind direction were measured at two levels on a 30 m tower. Spectral and autocorrelation analyses of the velocity component data clearly indicate the occurrence of wave-like oscillations in the flow and the almost complete lack of turbulent energy. The predominate wave-like motion had an oscillation period of about 1000 s. Halogenated atmospheric tracers were released from as many as four houses during the night-time drainage conditions. Hourly averaged horizontal dispersion coefficients were very large compared to the Pasquill-Gifford curves and the urban McElroy-Pooler dispersion curves. The time-averaged dispersion coefficients formed an upper bound on very short-term dispersion coefficients obtained from mobile traverses of the tracer plume with a continuous SF₆ analyzer. These results agree with the concept of a narrow instantaneous plume with a broad meander driven by the observed 1000 s oscillation. Vertical dispersion rates were slightly smaller than the Pasquill-Gifford class F curve. Results from a single tracer release from a side canyon near the neighborhood showed that drainage flow from the tributary impacted the main residential sampling site at Elm Grove Park and represented a significant fraction of the upstream air flow at Elm Grove Park. For sources with equal emission rates, a source in the tributary adds about 10% to the mean of the concentration caused by a neighborhood source.     

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.     

An infrared method for plume rise visualization and measurement

An infrared video camera and recording system were used to record near source plume rise from a low turbine stack at an oil gathering center at Prudhoe Bay, AK. The system provided real-time, continuous visualization of the plume using a color monitor while the images were recorded with a standard video tape recorder. Following the field study, single frame images were digitized using a micro-computer video system. As part of the digitization, the plume centerline was determined as well as an isotherm of the plume outline. In this application, one frame from each 2-min period in the record was digitized. The results were used to calculate the variability in plume centerline during each hour. During strong winds with blowing snow, the mean plume rise for the hour at 15 m downwind was 6±2 m. The observed plume rise from the turbine stack was greater than that calculated using momentum-only or buoyancy-only plume rise models and only slightly larger than that estimated from combined momentum-buoyancy plume rise models.     

卡尔曼滤波方法在地下水污染源反演中的应用

采用卡尔曼滤波方法反演识别地下水污染源的个数和大概位置.借助一个假想算例,建立地下水系统水流和溶质运移模拟模型,利用灵敏度分析方法筛选出对模拟结果影响最大的参数作为随机变量,对该参数进行抽样,运用蒙特卡罗方法将抽样结果输入模拟模型,生成污染质浓度场.采用卡尔曼滤波方法构造迭代过程,逐个利用采样点处浓度的实测值不断更新综合浓度场.引入模糊集理论表示污染羽,对比综合污染羽和单个污染羽的模糊集来更新各潜在污染源的权重,根据潜在污染源权重大小和综合污染羽收敛形状判断真实污染源的个数和大概位置.算例结果表明：采用卡尔曼滤波方法可以成功反演识别出地下水污染中真实污染源的准确个数和大概位置;引入模糊集理论表示污染羽,通过对比综合污染羽和单个污染羽的模糊集,可以确定各潜在污染源的权重.     

Building wake dispersion at an Arctic industrial site: Field tracer observations and plume model evaluations

Ten multi-hour atmospheric dispersion SF₆ tracer experiments were conducted during October and November of 1987 near a large oil gathering facility in the Prudhoe Bay, Alaska, oilfield reservation. The purpose of this study was to investigate dispersion under arctic conditions and in situations where building-generated airflow disturbances dominate downwind distributions of ground level pollutant concentrations. This was accomplished with a network of micrometeorological instruments, portable syringe tracer samplers, continuous tracer analyzers, and infrared visualization of near source plume behavior.Atmospheric stability and wind speed profiles at this arctic site are influenced by the smooth (surface roughness = 0.03 cm), snow covered tundra surface which receives negligible levels of solar isolation in winter. The dispersion of pollutants emitted from sources within the oil gathering facility, however, is dominated by the influence of nearby buildings when high winds generate elevated ground level concentrations. An order of magnitude increase in maximum ground level concentration was observed as wind speeds increased from 5 to 8 m s⁻¹ and another order of magnitude increase was observed as winds increased from 8 to 16 m s⁻¹. Variation in maximum concentrations was also observed with changes in wind direction. Vertical plume diffusion (σ_z) near the buildings was a factor of 2–3 greater than that observed in open terrain and was dependent on both wind speed and the projected building width and location of nearby buildings. Wind tunnel tracer distributions for east winds agree with field observations but also indicate that a significant increase in plume downwash occurs with other wind directions. Concentration distributions were calculated using several versions of the Industrial Source Complex (ISC) model. Model estimates of ground level concentrations were within a factor of three depending on wind direction. The model predictions are extremely sensitive to the ratio of plume height to vertical plume diffusion which is significantly influenced by a complex aerodynamic wake in the field.     

Comparison of measurements and integral model predictions of hot water plume behaviour in a crossflow

Measurements of the trajectory and dilution rate of a hot water jet entering vertically into a crossflow have been made in a water flume. Under various source conditions, thermistor probes at selected downstream locations were used to map out the cross-sectional extent of the plume, and thus to establish mean plume altitude and cross-sectional area as functions of distance from the source. These measurements were compared against the predictions of a simple integral model, similar to well-established models in the literature but modified for use in the flume study by the inclusion of an equation of state for water and an empirical correlation for the length of the potential core. An approximate analytical solution of the integral conservation equations, valid for both gaseous and water plumes, is presented. With entrainment and added mass constants very close to those previously estimated for gaseous plumes, good agreement between measured and predicted plume trajectory and dilution rate was found over the range of source conditions tested.     

Time scales of physical and chemical processes in chemically reactive plumes

The rate of non-linear chemical reactions in a dispersing plume, such as the formation of NO₂, is discussed on the basis of various models and measurements of the oxidation rate of NO. Results of calculations with four different reactive plume models are compared with a set of plume measuremeent and discussed in terms of the ration of the time scales of physical (T_p) and chemical processes (T_c), the Damköhler number:T_p/T_c. In modelling a fast non-linear chemical reaction an interaction between physical processes of dispersion and mixing and chemical reactions can be expected. Models may differ in that they assume either chemical equilibrium (T_p/T_c⪢1) or no chemical equilibbrium (T_p/T_c⪡1).From our study it is concluded that for the first 5 km from a stack concentrations in the plume change more rapidly by dilution due to dispersion of the plume than by chemical reactions. Farther off it is the other way around and the chemistry is fast enough to achieve chemical equilibrum in the plume parcels.Conversion of NO is then inhibited by the mixing rate of the plume with its surrounding air. To incorporate the mixing rate of the plume correctly into a model, in principle the concentration distribution in a momentary plume has to be used. If a non-linear chemical reaction is modelled it is therefore important to establish the averaging times on which the dispersion parameters in the model are based. The contribution of plume meandering to dispersion, which is especially important in the daytime, can be eliminated by taking shorter averaging times. This leads to a marked improvement of modelling results. Further research is required to investigate how the contribution of fluctuations in the concentrations around the mean has to be incorporated into a model of a chemically reactive plume.     

On plume meandering under stable stratification

Under stable stratification and light winds large horizontal wind direction fluctuations have been observed quite often leading to meandering of pollutants plume downwind of elevated point sources. Due to this plume meandering long term concentration levels can be reduced by a factor of 4 or more, compared to straight plume conditions. Some possible mechanisms causing plume meandering under stable conditions are discussed, including gravity waves and vortices with horizontal or vertical axis.     

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.     

应用照相法估算高架点源的污染物浓度

应用流体力学基本原理，导出了烟流扩散新模式，讨论了利用照相法估算烟流污染物浓度的方法及步骤，以高架点源烟流扩散为例，应用新模式结合照相法估算烟流污染物浓度，并与利用高斯模式计算的烟流污染物浓度进行比较，结果表明两者吻合较好．     

Large-eddy simulation of a turbulent reacting plume

The results of large-eddy simulations (LES) of a chemically reacting, dispersing plume in a turbulent boundary layer are presented. The detailed simulations of the dispersion mechanisms are used to investigate the effects of turbulent fluctuations on nonlinear chemical reactions. The idealized single reaction between ozone and nitrogen oxides, NO+O₃→NO₂+O₂, is used as a representative simple, irreversible binary reaction. Effects of different reaction rates are investigated by varying the source NO concentration, while maintaining a constant ambient ozone level. The simulations demonstrate that the rate of production of NO₂ is significantly affected by the turbulent nature of the dispersing plume. The effect of incomplete turbulent mixing of the two reactants on the reaction rate can persist for long distances downstream, particularly for the high NO levels typical of power plant stacks. The LES results also show that the important measure of the turbulent fluctuations, the turbulence segregation coefficient, may be reasonably approximated by a constant value over most of the plume cross-section. This result may prove useful for simplified plume modeling, but will depend on whether the range of constant segregation coefficient covers the whole reaction region since this takes place predominantly in the plumeedges.     

北京市大气中VOCs垂直分布的航测研究

2007年8月在北京市地表水平及地表以上900~3100m采集全空气样品,并用气相色谱(GC-FID)-质谱(MS)对样品中的50种挥发性有机物(VOCs)组分进行了定量分析,研究了北京市大气VOCs的垂直分布特征,并识别了当地排放与周边地区的输送作用对大气VOCs的相对贡献.结果表明,随着高度的增加,各类VOCs浓度均呈现显著降低的趋势,不同物种浓度的垂直梯度与其大气化学活性直接相关.此外,湍流扩散和输送作用也会影响VOCs浓度的垂直梯度.通过对观测期间北京市上空气团反向轨迹的反演以及对惰性VOCs物种的垂直贡献的分析发现,北京市低对流层内大气VOCs受局地源排放主导,亦可能受到天津以及河北廊坊等污染地区的影响.     

Fe0-PRB修复地下水硝酸盐污染数值模拟

基于地下水对流-弥散作用,采用数值分析方法,构建了GMS地下水渗流和硝酸盐污染物迁移三维耦合模型.在污染物迁移过程中,不考虑吸附降解和考虑吸附降解两种工况下,分析了污染物在地下水中的迁移特征.结果表明:地下水和土壤存在天然净化污染物的能力,但不显著,必须采取有效措施控制污染.以零价铁作为PRB墙体介质,并用GMS软件模拟Fe0-PRB修复地下水中硝酸盐的效果.PRB存在时能显著控制污染物的污染范围并降低污染物浓度.PRB厚度为4m时,污染物经过550d开始透过PRB墙,PRB运行10a后,1、2、3号观测井的浓度分别1.712,0.011,0.018mg/L,PRB下游污染羽拖尾明显;PRB厚度为6m时,污染物经过850d开始透过PRB墙,PRB运行10a后,1、2、3号观测井的浓度分别0.52,0.004,0.005mg/L,与4mPRB相比浓度分别降低69.6%、63.6%和72.2%,PRB下游污染羽拖尾仍存在但不明显.污染物迁移数值模拟是评价PRB修复污染地下水效果及确定PRB参数的重要手段.     

Physico-chemical study by two aircraft of a plume from a coal-fired power plant

During the experimental field program that was conducted in October 1985 ton study the physics and chemistry of the Le Havre power plant plume, joints flights were performed with two aircraft from EDF and KEMA. The two episodes with very different meteorological conditions were investigated. The first episode was characterized by fairly constant wind speed and direction with altitude, low solar irradiation and neutral vertical dispersion conditions. The second episode was characterized by low wind speed and changing wind direction, high solar irradiation and stable vertical dispersion conditions. During the latter episode, the concentrations of emitted gases, SO₂ and NO_x remained high, even at several tens of km downwind of the stock. Increased SO₄^2- and NO₃^- concentrations were detected in the power plant plume. In addition, important photochemical activity took p-lace in the plume of a nearby industrial area. The former episode showed more significantly vertical dilution and oxidation of NO but did not reveal any contribution of the power plant plume to aerosol formation.     

An intercomparison of semiempirical diffusion models under low wind speed,stable conditions

The performances of some diffusion models are analysed using concentration data measured at ground level up to 400 m from the emission point, in a series of diffusion tests conducted by U.S. National Oceanic and Atmospheric Administration (NOAA) under inversion conditions with light winds. All tested models are simple semiempirical formulae based on the Gaussian formulation, with different assumptions concerning dispersion parameters; each model utilizes a minimum set of information, i.e. vertical stability category, mean wind speed and standard deviation of the horizontal wind direction over the considered averaging time, σ_θ.Results show that for cases with very low wind speed and large plume spread, explicit consideration of diffusion along the mean wind direction, which is neglected in the standard plume model, significantly improves model results; moreover, when σ_θ is very large (greater than 50–60°), the analysis suggests that standard deviations of the horizontal wind speed may significantly differ from the estimates commonly found in the literature.     

烟气抬升公式计算对比

烟囱的有效烟气高度是计算地面浓度的一个重要因素,目前,有许多烟气抬升公式被用在大气质量模型中,本文介绍了一些烟气抬升公式,即Briggs,Holland.moses和Carson,GB,Lucas.Concawe,Csnady,TVA和静风公式等.其烟囱有小的、中的、大的和极大的各种,这些公式计算的结果在它们适用的范围内做了对比,根据计算的数据,得到了一个新的烟气抬升公式如F:△H=(0.92V,D+5.25F_b0.4H_s0.6)/u,该公式可广泛地应用于大气质量模型。并给出满意的结果