Strategic guidelines for street canyon geometry to achieve sustainable street air quality

This paper is concerned with the motion of air within the urban street canyon and is directed towards a deeper understanding of pollutant dispersion with respect to various simple canyon geometries and source positions. Taking into account the present days typical urban configurations, three principal flow regimes “isolated roughness flow”, “skimming flow” and “wake interference flow” (Boundary Layer Climates, 2nd edition, Methuen, London) and their corresponding pollutant dispersion characteristics are studied for various canopies aspect ratios, namely relative height (h₂/h₁), canyon height to width ratio (h/w) and canyon length to height ratio (l/h). A field-size canyon has been analyzed through numerical simulations using the standard k-ε turbulence closure model. It is found that the pollutant transport and diffusion is strongly dependent upon the type of flow regime inside the canyon and exchange between canyon and the above roof air. Some rules of thumbs have been established to get urban canyon geometries for efficient dispersion of pollutants.     

Influence of cetane improvers on the air quality in an urban street canyon

The concentration distributions of NO_x, PM, HC and CO in an urban street canyon have been estimated using a two-dimensional air quality numerical model based on the k– turbulent model and the atmospheric convection diffusion equation when various cetane improvers were used in diesel fuels. A wind vortex can be found within the street canyon, and the pollutants emitted from the bottom of the street canyon tend to follow the course of the wind field, moving circularly. The addition of cetane improvers can improve the air quality in a street canyon, all of the pollutants were found to decrease with increasing centane number.     

Analysis of air quality within a street canyon using statistical and dispersion modelling techniques

The dispersion model, ADMS-Urban, alongside the statistical modelling technique, generalized additive modelling, have been used to predict hourly NO_x and nitrogen dioxide (NO₂) concentrations at a busy street canyon location and the results compared with measurements. Generalized additive models (GAMs) were constructed for NO₂ and NO_x concentrations using input data required to run ADMS-Urban. Bivariate polar plots have been produced from the wind flow (speed and direction) and pollution data (measured and predicted concentrations) to provide further information regarding the complex wind-pollutant interactions in an urban street canyon. The predictions made with the GAMs show excellent agreement with measured concentrations at this location, reproducing both the magnitude of NO_x and NO₂ concentrations and also the wind speed-wind direction dependence of pollutant sources within the canyon. However, the predictions made with ADMS-Urban under-estimated the measured NO_x by 11% and NO₂ by 21% and there are clear differences in the bivariate polar plots. Several sensitivity tests were carried out with ADMS-Urban in an attempt to produce predictions in closer agreement to those measured at Gillygate. Increasing the primary NO₂ fraction in ADMS-Urban (from 10% to 20%) had a considerable effect on the predictions made with this model, increasing NO₂ predictions by ∼20%. However, the bivariate plots still showed major differences to those of the measurements. This work illustrates that generalized additive modelling is a useful tool for investigating complex wind-pollutant interactions within a street canyon.     

针对街道峡谷内部气流场的参数化研究

为了建立一个能够快速且可靠地模拟街区尺度交通污染物三维分布的模型以应对实时在线模拟的需求,将城区的最小单位假定为两侧建筑物等高的长街区(街道峡谷),基于CFD模型对街道峡谷内部气流场的模拟结果,对街道峡谷内不同区域的气流(U、V、W 3个分量)与街区几何比例(高宽比HW和长宽比LW)、背景风(u和v 2个分量)的数值关系进行了回归分析。分析结果显示,分量U在非靠近边界的区域与街区几何比例和背景风线性相关性较好;分量V则在靠近地面或顶面的区域;分量W则是在靠近墙面的区域。利用回归分析得到的数值关系构建的参数化方法可以计算得到近似于CFD模型模拟结果的街道峡谷内部气流场。在此基础上,基于高斯模型建立了一个参数化模型,并以黑炭气溶胶BC为例对参数化模型进行评估,评估结果表明,参数化模型具有一定的实用价值。     

基于PM2.5全面达标的广东省产业结构调整策略研究

为科学指导广东省进一步开展大气污染综合防治,运用统计分析和空气质量模拟方法,分析广东省实现各城市PM_(2.5)浓度全面达标的污染物减排需求,尤其是产业结构调整的需求。结合各行业的污染物排放强度,识别广东省加强产业结构优化调整工作需要关注的重点行业领域,并提出相应政策建议。结果表明,仅依靠既定的末端治理和能源、交通结构调整措施无法实现2020年广东省各城市PM_(2.5)浓度全面达标的目标,产业结构调整在SO_2、NO_x、挥发性有机物(VOCs)的减排中至少需发挥11%～19%的减排贡献作用,重点应针对区域内的非金属矿物制品、电力热力生产和供应、黑色金属冶炼和压延加工、造纸、纺织印染、化学纤维制造等行业进行调控,主动淘汰落后产能。     

A concentration correction scheme for Lagrangian particle model and its application in street canyon air dispersion modelling

Pollutant dispersion in street canyons with various configurations was simulated by discharging a large number of particles into the computation domain after developing a time-dependent wind field. Trajectory of the released particles was predicted using a Lagrangian particle model developed in an earlier study. A concentration correction scheme, based on the concept of “visibility”, was adopted for the Lagrangian particle model to correct the calculated pollutant concentration field in street canyons. The corrected concentrations compared favourably with those from wind tunnel experiments and a linear relationship between the computed concentrations and wind tunnel data were found. The developed model was then applied to four simulations to test for the suitability of the correction scheme and to study pollutant distribution in street canyons with different configurations. For those cases with obstacles presence in the computation domain, the correction scheme gives more reasonable results compared with the one without using it. Different flow regimes are observed in the street canyons, which depend on building configurations. A counter-clockwise rotating vortex may appear in a two-building case with wind flow from left to right, causing lower pollutant concentration at the leeward side of upstream building and higher concentration at the windward side of downstream building. On the other hand, a stable clockwise rotating vortex is formed in the street canyon with multiple identical buildings, resulting in poor natural ventilation in the street canyon. Moreover, particles emitted in the downstream canyon formed by buildings with large height-to-width ratios will be transported to upstream canyons.     

Three-dimensional modeling of air flow and pollutant dispersion in an urban street canyon with thermal effects

Effects of excess ground and building temperatures on airflow and dispersion of pollutants in an urban street canyon with an aspect ratio of 0.8 and a length-to-width ratio of 3 were investigated numerically. Three-dimensional governing equations of mass, momentum, energy, and species were modeled using the RNG k-epsilon turbulence model and Boussinesq approximation, which were solved using the finite volume method. Vehicle emissions were estimated from the measured traffic flow rates and modeled as banded line sources, with a street length and bandwidths equal to typical vehicle widths. Both measurements and simulations reveal that pollutant concentrations typically follow the traffic flow rate; they decline as the height increases and are higher on the leeward side than on the windward side. Three-dimensional simulations reveal that the vortex line, joining the centers of cross-sectional vortexes of the street canyon, meanders between street buildings and shifts toward the windward side when heating strength is increased. Thermal boundary layers are very thin. Entrainment of outside air increases, and pollutant concentration decreases with increasing heating condition. Also, traffic-produced turbulence enhances the turbulent kinetic energy and the mixing of temperature and admixtures in the canyon. Factors affecting the inaccuracy of the simulations are addressed.     

Dependence of street canyon concentrations on above-roof wind speed - implications for numerical modelling

For microscale numerical modelling of street canyon air pollution, the traffic-related component of the total ambient pollutant concentration is often assumed to be inversely dependent on the wind-speed at rooftops for idealised conditions of neutral stratification, no solar radiation, and no traffic-induced turbulence. Detailed data analyses of two comprehensive datasets from Gottinger Strase (Hannover) and Jagtvej (Copenhagen), including concentration and wind-field measurements in the street and above the rooftops, are presented to test these idealised assumptions, and to improve numerical modelling for a wider range of conditions. The experimental results show systematic deviation from the idealised inverse wind-speed law, when rooftop wind-speeds were less than 10 m/s. It was found that turbulence associated with traffic is a parameter, which is increasingly important for lower wind-speeds.     

Proposed city-specific interim targets for India based on WHO air quality guidelines 2021

Environmental Science and Pollution Research - The World Health Organization has proposed the ambient air quality guidelines 2021. The uniqueness of the guidelines of the World Health Organization...     

Sequential box models for indoor air quality: Application to airliner cabin air quality

In this paper we present the development and application of a model for indoor air quality. The model represents a departure from the standard box models typically used for indoor environments which has applicability in residences and office buildings. The model has been developed for a physical system consisting of sequential compartments which communicate only with adjacent compartments. Each compartment may contain various source and sink terms for a pollutant as well as leakage, and air transfer from adjacent compartments. The mathematical derivation affords rapid calculation of equilibrium concentrations in an essentially unlimited number of compartments. The model has been applied to air quality in the passenger cabin of three commercial aircraft. Simulations have been performed for environmental tobacco smoke (ETS) under two scenarios, CO₂ and water vapor. Additionally, concentrations in one aircraft have been simulated under conditions different from the standard configuration. Results of the simulations suggest the potential for elevated concentrations of ETS in smoking sections of non-air-recirculating aircraft and throughout the aircraft when air is recirculated. Concentrations of CO₂ and water vapor are consistent with expected results. We conclude that this model may be a useful tool in understanding indoor air quality in general and on aircraft in particular.     

Fractal geometry and applicability to biological simulation shapes for sustainable architecture design in Vietnam

Environmental Science and Pollution Research - Sustainability is the biggest goal that all areas including building architecture aim at. Sustainability is created by the harmony of buildings to the...     

Critical evaluation of approaches in setting indoor air quality guidelines and reference values

The importance of good indoor air quality for the health of the individual was recognized as long as 150 years ago and that period also saw recommendations, which essentially related to questions of ventilation and carbon dioxide. The first evaluation standards for organic and inorganic substances were laid down in the 1970s, often on an empirical basis. It was in the mid-1980s of the 20th century that a shift occurred towards systematically evaluating the results of indoor air measurements, carrying out representative environmental surveys and deriving guideline values and reference values on the basis of toxicological, epidemiological and statistical criteria. Generally speaking the indoor environment is an area which can only be assessed with difficulty since its occupants are in most cases exposed to mixtures of substances and there can be great local and temporal variations in the substance spectrum. Data are available today for a large number of substances and this makes it possible, with the aid of statistically derived reference values and toxicologically based guideline values, to make useful recommendations regarding good indoor air quality. Nevertheless, it is still difficult to evaluate reactive compounds and reaction products. What is disadvantageous, however, is the fact that different guideline values may be published for one and the same substance, whose justification and area of application are often not transparent. A guideline or reference value can only be regarded as rational when necessary and when a strategy for its verification is available.     

Simulations of the impacts of building height layout on air quality in natural-ventilated rooms around street canyons

Numerical simulations were conducted to investigate the effects of building height ratio (i.e., HR, the height ratio of the upstream building to the downstream building) on the air quality in buildings beside street canyons, and both regular and staggered canyons were considered for the simulations. The results show that the building height ratio affects not only the ventilation fluxes of the rooms in the downstream building but also the pollutant concentrations around the building. The parameter, outdoor effective source intensity of a room, is then proposed to calculate the amount of vehicular pollutants that enters into building rooms. Smaller value of this parameter indicates less pollutant enters the room. The numerical results reveal that HRs from 2/7 to 7/2 are the favorable height ratios for the regular canyons, as they obtain smaller values than the other cases. While HR values of 5/7, 7/7, and 7/5 are appropriate for staggered canyons. In addition, in terms of improving indoor air quality by natural ventilation, the staggered canyons with favorable HR are better than those of the regular canyons.     

Damage costs due to automotive air pollution and the influence of street canyons

Using the methodology of the ExternE Project of the European Commission, we have evaluated the damage costs of automotive air pollution by way of two case studies in France: a trip across Paris, and a trip from Paris to Lyon. This methodology involves an analysis of the impact pathways, starting with the emissions (e.g., g/km of particles from tailpipe), followed by local and regional dispersion (e.g., incremental μg/m³ of particles), calculation of the physical impacts using exposure-response functions (e.g., cases of respiratory hospital admissions), and finally multiplication by unit costs factors (e.g.,

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per hospital admission). Damages are aggregated over all affected receptors in Europe. In addition to the local and regional dispersion calculations carried out so far by ExternE, we also consider the increased microscale impacts due to the trapping of pollutants in street canyons, using numerical simulations with the FLUENT software. We have evaluated impacts to human health, agricultural crops and building materials, due to particles, NO_x, CO, HC and CO₂. Health impacts, especially reduced life expectancy, dominate in terms of cost. Damages for older cars (before 1997) range from 2 to 41 Euro cents/km, whereas for newer cars (since 1997), the range 1–9 Euro cents/km, and there is continuing progress in reducing the emissions further. In large cities, the particulate emissions of diesel cars lead to the highest damages, exceeding those of gasoline cars by a factor of 7. For cars before 1997 the order of magnitude of the damage costs is comparable to the price of gasoline, and the loss of life expectancy is comparable to that from traffic accidents.     

interpretation of air quality data with respect to the national ambient air quality standards

San Diego Gas &; Electric has developed a quality assurance program for continuous emission monitors (CEM). Extractive, rather than in situ, monitors were selected as a result of an in-house evaluation program. Two extractive systems have been certified and a good operating and maintenance record has been established on these systems. A successful program requires the involvement and support of all affected personnel. It is desirable to have one or two key personnel coordinate the development of the program. It is also highly desirable to have good in-house source testing capabilities.     

Strategic environmental assessment of mining activities: A methodology for quantification of cumulative impacts on the air quality

Environmental impact assessments in Brazil have usually focused solely on project-related issues without considering the regional context. Although required by current environmental legislation, cumulative impact assessments have not been included in the overall environmental assessment of projects. However, in recent Strategic Environmental Assessment (SEA) studies of policies, plans, and programs undertaken on a voluntary basis in support of the decision-making process, this kind of assessment has been performed especially with respect to air quality. This paper presents the application of a methodology for the quantification of cumulative impacts on air quality under high uncertainty caused by various mining activities in a single region that is recommended for SEA studies. In this way, the methodology presented here is suitable for areas lacking detailed modeling information. The developed approach uses a relatively simplified mathematical model, lowering information gathering costs and requiring little processing time. The application of the methodology is illustrated in the case of a SEA of the Corumbá Mining and Industrial Complex Development Program. Despite the lack of data needed for a minimum characterization of conditions of the area surrounding the region modeled, the quantification of impact cumulativeness on air quality has played an important role in the context of the SEA.     

PM10 emission factors for non-exhaust particles generated by road traffic in an urban street canyon and along a freeway in Switzerland

Recent studies have shown clear contributions of non-exhaust emissions to the traffic related PM10 load of the ambient air. These emissions consist of particles produced by abrasion from brakes, road wear, tire wear, as well as vehicle induced resuspension of deposited road dust. The main scope of the presented work was to identify and quantify the non-exhaust fraction of traffic related PM10 for two roadside locations in Switzerland with different traffic regimes. The two investigated locations, an urban street canyon with heavily congested traffic and an interurban freeway, are considered as being typical for Central Europe. Mass-relevant contributions from abrasion particles and resuspended road dust mainly originated from particles in the size range 1–10 μm. The results showed a major influence of vehicle induced resuspension of road dust. In the street canyon, the traffic related PM10 emissions (LDV: 24 ± 8 mg km^?1 vehicle^?1, HDV: 498 ± 86 mg km^?1 vehicle^?1) were assigned to 21% brake wear, 38% resuspended road dust and 41% exhaust emissions. Along the freeway (LDV: 50 ± 13 mg km^?1 vehicle^?1, HDV: 288 ± 72 mg km^?1 vehicle^?1), respective contributions were 3% brake wear, 56% resuspended road dust and 41% exhaust emissions. There was no indication for relevant contributions from tire wear and abrasion from undamaged pavements.     

Water quality guidelines for chemicals: learning lessons to deliver meaningful environmental metrics

Many jurisdictions around the globe have well-developed regulatory frameworks for the derivation and implementation of water quality guidelines (WQGs) or their equivalent (e.g. environmental quality standards, criteria, objectives or limits). However, a great many more still do not have such frameworks and are looking to introduce practical methods to manage chemical exposures in aquatic ecosystems. There is a potential opportunity for learning and sharing of data and information between experts from different jurisdictions in order to deliver efficient and effective methods to manage potential aquatic risks, including the considerable reduction in the need for aquatic toxicity testing and the rapid identification of common challenges. This paper reports the outputs of an international workshop with representatives from 14 countries held in Hong Kong in December 2011. The aim of the workshop and this paper was to identify ‘good practice’ in the development of WQGs to deliver to a range of environmental management goals. However, it is important to broaden this consideration to cover often overlooked facets of implementable WQGs, such as demonstrable field validation (i.e. does the WQG protect what it is supposed to?), fit for purpose of monitoring frameworks (often an on-going cost) and finally how are these monitoring data used to support management decisions in a manner that is transparent and understandable to stakeholders. It is clear that regulators and the regulated community have numerous pressures and constraints on their resources. Therefore, the final section of this paper addresses potential areas of collaboration and harmonisation. Such approaches could deliver a consistent foundation from which to assess potential chemical aquatic risks, including, for example, the adoption of bioavailability-based approaches for metals, whilst reducing administrative and technical burdens in jurisdictions.