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城市复杂环境下涡度相关通量观测的适用性分析 总被引:2,自引:0,他引:2
利用涡度相关技术,于2008—2009年对北京325 m铁塔47 m、140 m和280 m高度处CO2和能量通量进行了观测.研究了涡度相关技术应用于城市环境通量长期观测中的理论问题和方法适用性.结果表明,平面拟合方法受地面建筑物的影响明显,不同的坐标旋转方法所计算CO2通量差异在15%以内,这种差异随着观测高度的增加而减小.稳态检验表明,城市环境下低质量的数据分布没有明显的日变化趋势.CO2通量在各自通量贡献区内明显受到平流输送的影响,47~140 m之间的平流约占140 m日累计CO2通量的33%.白天对流混合,污染物浓度梯度很小,垂直平流不大,水平平流占据了平流输送的绝大多数,夜间水平平流和垂直平流则具有相同量级. 相似文献
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Environmental Persistence of Chemicals 总被引:1,自引:0,他引:1
- DOI: http://dx.doi.org/10.1065/espr2006.01.008
Background The hazard criterion of persistence as it applies to chemicals in the environment is reviewed and discussed. This quantity
can not be measured directly in the environment, thus it must be estimated using models that synthesise information on chemical
half-lives and partitioning properties, the nature of the environment and how the chemical is released into the environment.
Main Features It is suggested that the preferred criterion is the average residence time of the chemical in the environment, i.e. conceptually
the sum of the life-times of all molecules (attributable only to losses by degrading reactions) divided by the number of molecules.
If all chemical fate processes are first order, this persistence is independent of the quantity of chemical introduced and
whether introduction is steady- or unsteady-state in nature. It is shown that in a multimedia environment persistence is affected
not only by degradation kinetics, but also by mode-of-entry and partitioning. For screening level purposes a Level II equilibrium
model may be adequate but a Level III model is generally preferable for estimating the average persistence. If a distribution
of persistences is required a dynamic Level IV model must be used.
Discussion The implications for regulating chemicals on the basis of persistence are discussed.
Conclusion It is concluded that the preferred strategy is to use Level II, III, and IV models and that the use of only degradation kinetics
or media-specific half-lives can be misleading and uneconomical. 相似文献
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The purpose of this study is to present a library of analytical solutions for the three-dimensional contaminant transport in uniform flow field in porous media with the first-order decay, linear sorption, and zero-order production. The library is constructed using Green’s function method (GFM) in combination with available solutions. The library covers a wide range of solutions for various conditions. The aquifer can be vertically finite, semi-infinitive or infinitive, and laterally semi-infinitive or infinitive. The geometry of the sources can be of point, line, plane or volumetric body; and the source release can be continuous, instantaneous, or by following a given function over time. Dimensionless forms of the solutions are also proposed. A computer code FlowCAS is developed to calculate the solutions. Calculated results demonstrate the correctness of the presented solutions. The library is widely applicable to solve contaminant transport problems of one- or multiple- dimensions in uniform flow fields. 相似文献
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IntroductionWiththedevelopmentofmodernindustry ,variouspollutantsdischargeintotheair,rivers,lakesandoceans,whichmakestheenvironmentalqualitiesworsenandhasbadeffectonthemankind’shealthandthesustaineddevelopmentofindustryandagriculture .Theenvironmentalpo… 相似文献
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Amvrossios C. Bagtzoglou Andrei Novikov 《Journal of the American Water Resources Association》2007,43(1):207-219
Abstract: This paper presents a numerical investigation of approaches to enhance the mixing and dispersion processes in tidal areas by effecting changes in the natural estuary system. It compares the impact of various estuary modifications stemming from human intervention to pollutant dispersion and chaotic flow within the estuary including the implications of alteration of the original channel shape, change of the channel bathymetry, and modification of the tidal signal. Our findings indicate that chaotic flow analysis is similar in many regards, but not all, to conventional dispersion analysis. Specifically, we conclude that (1) simplification of the flow regime reduces chaotic flow patterns and tracer particle dispersion, (2) creation of extensively protruding barriers and/or installation of barriers on opposite sides of the main stem of the estuary enhances particle dispersion and chaotic mixing, (3) installation of underwater berms has relatively minor beneficial, but highly localized, effects on chaotic regime and particle dispersion, and (4) increasing the tidal signal amplitude was shown to increase chaotic and dispersion properties of the estuarine system. A parametric study investigating the effect of several geometrical configurations and tidal signals on characteristics of chaotic flows concludes the paper. 相似文献
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Analytical solutions of three-dimensional contaminant transport in uniform flow field in porous media: A library 总被引:1,自引:0,他引:1
Hongtao Wang Huayong Wu 《Frontiers of Environmental Science & Engineering in China》2009,3(1):112-128
The purpose of this study is to present a library of analytical solutions for the three-dimensional contaminant transport
in uniform flow field in porous media with the first-order decay, linear sorption, and zero-order production. The library
is constructed using Green’s function method (GFM) in combination with available solutions. The library covers a wide range
of solutions for various conditions. The aquifer can be vertically finite, semi-infinitive or infinitive, and laterally semi-infinitive
or infinitive. The geometry of the sources can be of point, line, plane or volumetric body; and the source release can be
continuous, instantaneous, or by following a given function over time. Dimensionless forms of the solutions are also proposed.
A computer code FlowCAS is developed to calculate the solutions. Calculated results demonstrate the correctness of the presented
solutions. The library is widely applicable to solve contaminant transport problems of one- or multiple- dimensions in uniform
flow fields. 相似文献
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北京冬季雾日大气污染结构特征 总被引:4,自引:1,他引:3
运用激光雷达和大气污染监测网络观测了2007年2月北京地区2次平流雾大气污染过程. 通过分析雾生消过程中大气颗粒物消光性的垂直结构、地面大气污染物质量浓度的水平分布及其演变,研究了北京市雾日大气污染的空间结构特征. 结果表明:雾生成前及持续阶段大气扩散条件较差,污染积累明显,但高湿度雾能加速污染物的湿沉降,雾生成后污染会略有回落. 雾生成前后大气污染垂直分布变化显著,但静稳气象条件下,大气污染的水平分布受雾的影响较小. 相对湿度是影响雾日大气污染变化的重要因素,决定了污染物湿沉降量的大小. 在2007年2月21—22日的平流雾过程中,SO2和NO2浓度与雾生成前相比分别下降了56%与47%,湿沉降量分别为48.0和30.8 g/km2;而在25—27日的平流雾过程中,SO2和NO2湿沉降量分别为16.3和14.3 g/km2. 相似文献