A decision support tool for evaluating the air quality and wind comfort induced by different opening configurations for buildings in canyons

Developing a Health-Spatial Indicator System for a Healthy City in Small and Midsized Cities

A recent examination of the significant role of public health has prompted calls to re-investigate how the urban environment affects public health. A vital part of the solution includes Healthy City initiatives that have been the subject of extensive policies, implications, and practices globally. However, the existing literature mainly focuses on big cities and metropolitan areas, while investigations into small and midsized cities (SMCs) are lacking, and thus reflect the underlying issues of health inequity. This study develops an indicator system for evaluating Healthy City initiatives in SMCs, linking urban design and public health, supported by the analyzed opinions from experts collected using both questionnaires and interviews. The indicator system includes six primary dimensions and 37 variables: urban form and transportation (UFT); health-friendly service (HFS); environmental quality and governance (EQG); community and facility (CF); green and open space (GOS); and ecological construction and biodiversity (ECB). A fuzzy synthetic evaluation technique was used to assess the relative importance of factors, emphasizing the importance of UFT, HFS, and EQG, with importance indexes of 0.175, 0.174, and 0.174, respectively. This indicator system is helpful for SMCs seeking to construct a Healthy City in the future, and is based on urban design and governance inputs and for enhancing the Healthy City knowledge base of cities of varied scales.

Genotoxic assessment of selected native plants to deferentially exposed urban ecosystems

The aim of this study is to provide an analysis of the impact of ecogenotoxicity on native flora abortivity in various urban areas. In which, there was an analysis of 5 groupings of locations with a differing environmental load intensity within the city of Bratislava (Slovakia) over a 2-year period. Our results show varying data depending on the proximity of each site relating to a direct source of pollution and the potential impact of localized wind currents on the distribution of pollutants in the urban environment. The highest value of pollen abortivity in the city was observed in a group of locations exposed to heavy traffic pollution loads. Abortivity of native flora near heavy traffic road areas correlated with the imissions data measured in the same area. Wind-exposed uncovered sites also experienced higher values of native flora abortivity. These results confirmed the varying intensity of genotoxic impact in differing localities and also suggest that xenobiotic effects on flora can occur remotely from the original source of pollution.

Numerical evaluations of urban design technique to reduce vehicular personal intake fraction in deep street canyons

High-rise deep street canyons usually experience poor ventilation and large vehicular pollutant exposure to residents in near-road buildings. Investigations are still required to clarify the flow and dispersion mechanisms in deep street canyons and explore techniques to reduce such large pollutant exposure. By conducting computational fluid dynamics (CFD) simulations validated by wind tunnel data and scale-model outdoor field measurements, we investigate the integrated impacts of aspect ratios, first-floor and second-floor elevated building designs, viaduct settings, height variations and wind catchers on the flow, personal intake fraction (P_IF) of CO (carbon dioxide) and its spatial mean value 〈P_IF〉 in two-dimensional (2D) street canyons. Results show that cases with H/W = 5 experience two counter-rotating vortices, much poorer ventilation and 1-2 orders larger 〈P_IF〉 (43.6-120.8 ppm) than H/W = 1 and 3 (3.8-4.3 and 5.6-5.8 ppm). Moreover, in cases with H/W = 5 the height variation results in three vertically-aligned vortices and much weaker wind, subsequently produces greater 〈P_IF〉 (1402-2047 ppm). To reduce 〈P_IF〉 with H/W = 5, various urban designs are evaluated. The first-floor elevated building design creates more effective ventilation pathways than the second-floor elevated type does and reduces 〈P_IF〉 at H/W = 5 by five orders (1402 to ~0.01 ppm) or two orders (43.6 to ~0.1 ppm) in cases with or without the height variation. However, such reductions at H/W = 1 and 3 are only 76.8%-81.4% and 22.4%-36.2% respectively. Wind catchers destroy the multi-vortex flow pattern as H/W = 5, produce a contra-clockwise main vortex and reduce 〈P_IF〉 by 1-2 orders for cases with or without the height variation.

Improving pedestrian level low wind velocity environment in high-density cities: A general framework and case study

An acceptable pedestrian level wind environment is essential to maintain an enjoyable outdoor space for city residents. Low wind velocity environment can lead to uncomfortable outdoor thermal experience in hot and humid summer, and it is unable to remove the pollutants out of city canyons. However, the average wind velocity at pedestrian level is significantly lowered by closely spaced tall buildings in modern megacities. To improve the low wind velocity environment at pedestrian level in high-density cities, a general framework and detailed guidelines are needed. This study is the first time to develop such a framework, and provide detailed guidelines for improving pedestrian level low wind velocity environment in high-density cities. Additionally, a detailed review and summarisation of evaluation criteria and improvement measures are presented in this paper, which provide additional options for urban planners. To investigate the performance of the framework, the Hong Kong Polytechnic University campus was utilised as a case study. Results showed that pedestrian level wind comfort was greatly improved with the developed framework. The outcomes of this study can assist city planners to improve the low wind velocity environment, and can help policy makers to establish sustainable urban planning policies.

A review on the study of urban wind at the pedestrian level around buildings

Urbanization is leading towards the change of local wind climate in the vicinity of tall buildings, which influences the pedestrian level wind environment to an uncomfortable or even dangerous level. Therefore nowadays, building design should not be limited only for the consideration of wind load and indoor environment, but outdoor wind environment should also be considered. This study presents a review of the methods for the assessment of pedestrian level wind climate, different wind comfort criterion and various techniques to evaluate the wind speed at the pedestrian level. In later sections, brief review for the influence of different parameters related to building design and configuration on pedestrian level wind is presented. After analyzing previous literature it is suggested that there is a strong need for the homogenization of different wind comfort criterion, as it may lead to different consequences for the architects. Among various wind tunnel measurement techniques, use of Irwin probe is simple and accurate compared to hot-wire anemometry and it can be installed at numerous locations for simultaneous measurement of pedestrian level wind speed. For numerical simulation, Reynolds Averaged Navier Stokes based technique has been used by various researchers, although this technique is not accurate as much as large eddy simulation and detached eddy simulation. But this technique is cost effective and requires less computing resources.

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Wind comfort due to high as well as low wind speeds should be considered.

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Irwin probes provide relatively accurate measurements of wind speed.

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Reynolds Averaged Navier Stokes based method is economic to simulate urban wind flow.

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Corner modified and lift-up buildings and use of podiums are positive design approach.

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Building width at 1/3rd height from ground affects the pedestrian wind mostly.