西北典型工矿型城市街道尘埃重金属污染的环境磁学响应

以甘肃省白银市为研究区域,系统采集43个城区街道尘埃样品,并对其进行环境磁学和重金属元素特征分析.结果表明,白银市街道尘埃磁性特征以低矫顽力的磁铁矿和磁赤铁矿为主导,磁晶体粒径为较粗的假单畴(PSD)和多畴(MD)颗粒;样品低频磁化率(χlf)变化范围为(43.75~1 340.08)×10-8m3·kg-1,平均值为245.98×10-8m3·kg-1,与国内综合型大城市相比,白银市街道尘埃磁性矿物含量相对较低,但呈现明显的空间分布差异,表现为工业区高于带状交通区,带状交通区高于商业区,新城区磁性矿物含量较低;白银市各功能区污染源相对单一,工业污染对强磁性矿物的贡献占主导,污染程度空间分异显著.白银市街道尘埃样品中Cu、Pb、Zn整体含量较高,污染负荷指数(PLI)与低频磁化率(χlf)、非磁滞剩磁化率(χARM)、饱和等温剩磁(SIRM)、"软"剩磁(SOFT)相关性较高,且空间变化特征较为一致,表明反映磁性矿物含量的参数可以有效监测城市重金属污染,进而圈定重金属综合污染区域和范围,为进一步的城市污染治理工作提供快速有效的证据支持.     

城市街道峡谷气流和污染物分布的数值模拟

应用计算流体力学(CFD)软件中的FLUENT软件模拟了典型城市街道峡谷中的气流和污染物分布状况.建立的模型包括不同形状的建筑物所构成的街道峡谷和存在高架桥的街道峡谷.研究结果表明:①不同形状的建筑物改变了街道峡谷内的风和湍流分布,从而对街道峡谷内污染物的分布产生很大的影响,在几何比例相同的街道峡谷里,建筑物外形越趋向于流线型,街道峡谷里污染物的地面浓度越小;②高架桥对街道峡谷内污染物浓度的影响取决于高架桥相对于街道峡谷的高度和宽度,高度越高、宽度越窄的高架桥其地面污染物的浓度越低;③ FLUENT软件对街道峡谷大气环境的模拟结果基本合理,可用于研究城市大气环境问题.      

三峡工程对重庆环境的主要影响及对策建议

本文详细地叙述了三峡工程对重庆的环境影响。其影响程度尽量做到定量化,对于一时难以定量的影响也作了较详尽的说明。本文还提出了消除不利影响可能采取的对策措施,以及今后的工作建议。     

孤立与非孤立城市街道峡谷内污染物扩散

通过求解二维不可压N-S方程、k-ε方程及污染物对流扩散方程,模拟了孤立街道峡谷与非孤立街道峡谷内的流场及交通污染物浓度场.计算结果与风洞试验结果总体趋势一致.非孤立街道峡谷内污染物壁面浓度要大于孤立街道峡谷内的壁面浓度.通过计算街道峡谷建筑屋顶高度处的垂直方向污染物通量,说明了湍流扩散是污染物扩散出街道峡谷的主要原因,其污染物通量总为正,而平均流通量可以为负.非孤立街道峡谷由于平均流流动和湍流流动的总扩散通量减少,造成污染物在街道峡谷内集聚,从而理论上解释了非孤立街道峡谷与孤立街道峡谷污染扩散的差别.     

The Modelling of Turbulence from Traffic in Urban Dispersion Models — Part I: Theoretical Considerations

The modelling of pollutant dispersion at the street scale in an urban environment requires the knowledge of turbulence generated by the traffic motion in streets. In this paper, a theoretical framework to estimate mechanical turbulence induced by traffic in street canyons at low wind speed conditions is established. The standard deviation of the velocity fluctuations is adopted as a measure of traffic-produced turbulence (TPT). Based on the balance between turbulent kinetic energy production and dissipation, three different parameterisations for TPT suitable for different traffic flow conditions are derived and discussed. These formulae rely on the calculations of constants that need to be estimated on the basis of experimental data. One such estimate has been made with the help of a wind tunnel data set corresponding to intermediate traffic densities, which is the most common regime, with interacting vehicle wakes.     

Fractionation and Biotoxicity of Heavy Metals in Urban Dusts Collected from Hong Kong and London

Samples of urban dusts, road site dusts and car park dusts, were collected at two selected sites each in Hong Kong and London. Sequential extraction was used to characterise the chemical compositions of these urban dusts. Copper, lead, zinc, pH, electrical conductivity and organic content were measured. Biotoxicity tests of urban dusts were conducted on higher plants (Brassica chinensis and Lolium perenne), a dinoflagellate green alga (Dunaliella tertiolecta) and luminescent bacteria (Photobacterium phosphoreum). A significant correlation was found between total lead (r =; – 0.70, p < 0.01) and zinc (r =; – 0.74, p < 0.05), and the 20 min – EC50 using P. phosphoreum. In addition, there was a significant correlation (r = – 0.72, p < 0.01) between the exchangeable lead content in dust and the 48 h- EC30 using D. tertiolecta. No specific trend was obtained for higher plants. Total lead and zinc contents were higher in dusts from London while the percentage of exchangeable fraction of metal contents was higher in those from Hong Kong.     

A framework for evaluation of flood management strategies

The resulting impact of disasters on society depends on the affected country's economic strength prior to the disaster. The larger the disaster and the smaller the economy, the more significant is the impact. This is clearest seen in developing countries, where weak economies become even weaker afterwards. Deliberate strategies for the sharing of losses from hazardous events may aid a country or a community in efficiently using scarce prevention and mitigation resources, thus being better prepared for the effects of a disaster. Nevertheless, many governments lack an adequate institutional system for applying cost effective and reliable technologies for disaster prevention, early warnings, and mitigation. Modelling by event analyses and strategy models is one way of planning ahead, but these models have so far not been linked together. An approach to this problem was taken during a large study in Hungary, the Tisza case study, where a number of policy strategies for spreading of flood loss were formulated. In these strategies, a set of parameters of particular interest were extracted from interviews with stakeholders in the region. However, the study was focused on emerging economies, and, in particular, on insurance strategies. The scope is now extended to become a functional framework also for developing countries. In general, they have a higher degree of vulnerability. The paper takes northern Vietnam as an example of a developing region. We identify important parameters and discuss their importance for flood strategy formulations. Based on the policy strategies in the Tisza case, we extract data from the strategies and propose a framework for loss spread in developing and emerging economies. The parameter set can straightforwardly be included in a simulation and decision model for policy formulation and evaluation, taking multiple stakeholders into account.     

The underutilization of street markets as a source of food security indicators in famine early warning systems: a case study of Ethiopia

Famine Early Warning Systems (EWS) are reliant on data aggregated from multiple sources. Consequently, they are often insensitive to localized changes in food security status, leading to delayed response or interventions. While price and infrastructural data are often gathered, this case study suggests that local street markets and vendor knowledge are underutilized. Few efforts have been made to monitor systematically the street markets as an indicator of local stressors. Findings from Ethiopia show that knowledge generated by expanding food security indicators in this sector can be used in combination with EWS to facilitate earlier intervention in, or to monitor more effectively, on-going humanitarian crises. Indicators developed from this study are accurate, cost effective, and sensitive to local climatic and food stressors.     

Giving parks back to people: a transportation study of New Orleans City Park with implications for improving public health

Park planning, once at the root of the profession during the nineteenth century, can again provide cities with a means to improve public health through restricting access to automobiles. This intercept study, conducted in New Orleans City Park, found that two-thirds of users support weekend street closures to automobiles. Widespread support (63%) exists even among the 72% of people who arrived by automobile. This study also found measurable stated benefits from restricting car access. For more than 53% of the sample that stated that they would walk more in a car-free zone, respondents noted that they would walk nearly 30?min more per month. These findings suggest that planners and policy-makers have a cost-effective option to improve cities and public health – taming the automobile in urban parks.     

Dispersion in Urban Environments; Comparison of Field Measurements with Wind Tunnel Results

A wind tunnel study was performed to determine the dispersion characteristics of vehicle exhaust gases within the urban canopy layer. The results were compared with those from a field monitoring station located in a street canyon with heavy traffic load. The agreement found was fair. In the second part of the paper it is shown how wind tunnel data can be utilized to supplement and thereby enhance the value of field data for model validation purposes. Uncertainty ranges were quantified which are inherent to mean concentration values measured in urban streets.