Evaluation on ventilation and traffic pollutant dispersion in asymmetric street canyons with void decks

Chung Hyok Sin; Peng-Yi Cui; Kwang Song Jon; Yang Luo; Jiao-Wen Shen; Yuan-Dong Huang

doi:10.1007/s11869-023-01314-3

Evaluation on ventilation and traffic pollutant dispersion in asymmetric street canyons with void decks

Air Qual Atmos Health. 2023;16(4):817-839. doi: 10.1007/s11869-023-01314-3. Epub 2023 Feb 13.

Authors

Chung Hyok Sin^{1

2}, Peng-Yi Cui¹, Kwang Song Jon^{1

3}, Yang Luo¹, Jiao-Wen Shen^{1

4}, Yuan-Dong Huang¹

Affiliations

¹ School of Environment and Architecture, University of Shanghai for Science and Technology, Yangpu District, No. 516, Jungong Road, Shanghai, China.
² Natural Science Center, Democratic People's, Kim Il Sung University, Taesong District, Pyongyang, Democratic People's Republic of Korea.
³ School of Metallic Engineering Central District Democratic People's, Kim Chek University of Technology, Pyongyang, Democratic People's Republic of Korea.
⁴ School of Resources and Environmental Engineering, Shanghai Polytechnic University, Shanghai, 201209 China.

Abstract

With continuous global warming, growing urban population density, and increasing compactness of urban buildings, the "void deck" street canyon design has become increasingly popular in city planning, especially for urban streets located in tropical areas. Nevertheless, research on traffic pollutant dispersion in street canyons with void decks (VDs) is still at its early stage. This study quantitatively evaluates the effects of void deck height and location on the canyon ventilation and pollutant dispersion in asymmetric street canyons with void decks, and the pollutant exposure risk level for pedestrians and street dwellers. Void decks introduce more fresh air, thereby greatly improving the ventilation properties of the asymmetric canyon. The air exchange rate (ACH: 147.9%, 270.9%) and net escape velocity (NEV*: 416.7%, 915.8%) of the step-up and step-down canyons with VDs (3 m high at full scale) at both buildings are higher than those of regular asymmetric canyons. Moreover, the mean dimensionless pollutant concentration (K) on the building wall and pedestrian respiration plane in which VDs are located stands at a low level, because pollutants are removed by the airflow entering or exiting through the void decks. Increased VD height (4.5 m at full scale) enhances the strength of airflow flowing into and out of the canyon, significantly increasing ACH (177.3%, 380.9%) and NEV* (595.2%, 1268.4%) and decreasing the mean K on both pedestrian respiration planes and canyon walls. In particular, the K values on both pedestrian respiration planes and both walls are almost zero for the canyons with VDs at both buildings. Therefore, among the three VD locations, both VDs provide the best living environment for pedestrians and near-road residents. These findings can help to design urban street canyons for mitigating traffic pollution risk and improving ventilation in tropical cities.

Keywords: CFD; Lift-up building; Street canyon; Traffic pollution; Ventilation; Void deck.

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