1,721,052 research outputs found
Spatial distribution of air pollutants in cities
No full textThis chapter discusses the spatial distribution of air pollutants in cities in light of progress made by the scientific community in the field of flow and pollutant dispersion around buildings and within complex urban geometries. With the rate of urbanisation expected to increase in the next years, countries are forced to face challenges in addressing air pollution. Starting from the process of urbanisation and the problem of outdoor air pollution, the discussion focuses on main factors affecting flow and pollutant dispersion in cities. The dynamic of the urban atmosphere is sensitive to a large number of factors related to meteorology, building geometry and city density as well as to the presence of urban obstacles such as trees, parked cars and other barriers, buoyancy effects due to thermal exchanges at urban surfaces, traffic-induced turbulence and others. Some of them are reviewed here. The recent research towards unregulated pollutants, such as airborne ultrafine particles, which are considered to show higher health impacts compared with fine particles, is briefly addressed
CFD modelling of tree-atmosphere interaction and assessment of air quality in street canyons
No full textCharacterizing the morphology of real street models and modeling its effect on thermal environment
No full textA numerical study on the correlation between sky view factor and summer microclimate of local climate zones
No full textCFD modelling: The most useful tool for developing mesoscale urban canopy parameterizations
No full textIndices employed for the assessment of “urban outdoor ventilation” - A review
No full textIn recent years, several ventilation indices have been proposed and applied to assess the efficiency of “urban outdoor ventilation”, i.e. the ability of an urban area to dilute pollutants, heat and moisture by exchanging air between inside and above of the urban canopy. Here, focusing on the pollutant dispersion, the definition of 13 ventilation indices is given, which includes indoor-initially proposed and outdoor directly proposed. Then, 63 literature studies (published until 2018) applying the ventilation indices are selected, analysed and summarized in terms of the types of geometry investigated, the timeline and the frequency of employment of each index, the turbulence models employed. Based on the analysis of such studies, advantages and limitations of each index are provided, which may help the scientific community to choose the most appropriate one depending on the specific application and objective. Future perspectives are also given, suggesting the necessity to correlate ventilation indices with urban morphological parameters, to apply indices in real urban areas characterized by building height variability and complex morphology, as well as to provide threshold values useful for urban planning purposes
The influence of vegetation and street layouts on pollutant dispersion and population exposure in idealized two-dimensional urban street canyon
No full textIndoor air quality in the near-road buildings largely depends on the urban flow patterns and vehicular pollutant dispersion which are greatly affected by urban vegetation configurations and street layouts like building morphologies and aspect ratios (AR, i.e. building height/street width). Trees are usually settled to relieve the burden from urban heat island and maintain urban zoology system, however, trees also tend to reduce urban windiness and further provide adverse impacts on pollutant dilution
Scale-adaptive morphometric analysis for urban air quality and ventilation applications
Full text linkA novel, flexible method to derive urban morphometric parameters is presented. Through selected examples, it demonstrates its employability in a wide range of applications. This method builds upon an extension of an image-based technique for the treatment of building data to discuss objective criteria for model grid choice and related consequences. Starting from an estimation of aerodynamic parameters, and their validation by computational fluid dynamics using an existing simulation of downtown Oklahoma City in the US, the method is used to evaluate improvements in the performance of an operational dispersion model. Results are applied to flow over a neighbourhood for the determination of ventilation parameters. It is suggested that the grid used for calculation of morphometric parameters provides the best agreement with data from laboratory experiments when the selection of grid size is made upon the spatial profile of building height standard deviation and maximum building height. The implication is that when a mesoscale numerical model is employed, morphometric parameters should be calculated by positioning the computational grid based on physical boundaries, while for finer resolution (namely, smaller scale) numerical models, morphometric parameters should be calculated using the street grid as external boundary, and the maximum building height criterion performs well
On the drag force distribution over arrays of cubical buildings: wind tunnel experiments
No full textNature-Based Solutions Planning for Urban Microclimate Improvement and Health: An Integrated Ecological and Economic Approach
Full text linkNature-based Solutions (NbSs) play a pivotal role in mitigating the impact of microclimates on human well-being. The effectiveness of NbSs is contingent upon the synergy between natural capital, defined by the ecological structure and functions of the ecosystem, and human-derived capital, encompassing the economic investments required for implementation. This study introduces a decision-making framework designed to evaluate the impact of NbSs and advocate for optimal solutions for human health at the local scale, amalgamating ecological and economic assessments. Physiological Equivalent Temperature (PET) was chosen as a key urban parameter to assess the efficacy of NbSs in mitigating urban microclimates and enhancing human health. The PET analysis was conducted using ENVI-met 5.0.3 software across diverse urban scenarios in Gallipoli city, Italy. Integrated with a cost–benefit analysis of NbSs considering various investment scenarios, the study aimed to identify the most effective solution. Results indicated positive effects of NbSs in open spaces and around building blocks where the PET levels remained below 30 °C. Conversely, scenarios without NbSs exhibited PETs exceeding 40 °C, with peaks of 50 °C, posing potential risks to human health. Considering the social and economic benefits associated with PET mitigation, the cost–benefit analysis suggests that implementing NbSs using a mix of young and mature plants in the initial phase is advantageous compared to using only young plants. Thus, in establishing NbSs, it is crucial to consider not only the quantity of vegetation but also the strategic timing of implementation. In conclusion, our work offers an innovative framework that combines ecological and economic perspectives, providing valuable insights for decision-makers in urban planning and promoting the practical application of NbSs for enhanced human well-being
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