A parametric study of the effect of roof height and morphology on air pollution dispersion in street canyons

Abstract

 Parametric study of airflow and pollution in street canyons of different morphologies  Conventional pitched roofs increase pollution concentration for most morphologies  Pollution and airflow sensitive to roof slope and roof arrangement morphology  Morphology of upstream streets affects pollution concentration downstream  Interaction between parameters complex; results are variable and case specific ABSTRACT We investigate the effect of conventional pitched roofs on ventilation and pollution in street canyons using Computational Fluid Dynamics and a parametric approach. We studied parallel street canyons with several street morphologies, created by assigning a set of streets with pitched roofs, and varying their pitch and arrangement for three different height-to-width aspect ratios. The distribution of flow properties and pollution concentrations within the street canyons are examined and the effect of different parameter combinations is assessed. We find the relationship between these properties and the street morphology to be complex and case specific. For most morphologies, the pitched roofs lead to higher average pollution concentrations, and in some cases to pollution hotspots near emission sources especially on the leeward side. The pitched roofs are rarely beneficial to ventilation of the street canyons, but a few roof arrangements lead to reduced concentrations on the windward side. Roof slope is shown to significantly relate to both average pollution concentrations and their distribution inside the street; in some street geometries more than others. The results have implications for pedestrian and residential pollution exposure, and for conservation of building facades on historical buildings.

Recent advances in modeling turbulent wind flow at pedestrian-level in the built environment

“…Among the studies investigated in this review, SRANS is broadly Fig. 1 CFD applications in PLW studies published in recent 5 years applied to investigate PLW flow fields in different urban settings, ranging from an isolated building (Huang et al, 2021;Jia et al, 2021;van Druenen et al, 2019;Weerasuriya et al, 2018;Zhang, Yang, et al, 2021) to more complex geometries such as building arrays (Allegrini & Carmeliet, 2017;Hang, Chen, et al, 2018;Hang, Xian, et al, 2018;Lin et al, 2019;Sattar et al, 2018;Sha et al, 2018), generic street canyons (Liu et al, 2021;Sun & Zhang, 2018;Wen & Malki-Epshtein, 2018;Yang et al, 2020;Zhang et al, 2019;Zhang, Chen, et al, 2020), and realistic urban areas (Ricci et al, 2020;Santiago et al, 2021;Sousa & Gorle, 2019;Tsichritzis & Nikolopoulou, 2019;Vervoort et al, 2019).…”

Computational Fluid Dynamics Simulation of Airflow and Air Pattern in the Living Room for Reducing Coronavirus Exposure

“…For mesh independency study, five different numbers of meshes with characteristics shown in table 1 have been tested. Mesh independency analysis ensured that the flow fields at the computational domain were not affected by mesh dimension (Wen and Malki-Epshtein 2018). As shown in figure 3, the final number of the mesh is set to 1,416,884 elementary cells.…”

CFD evaluation of mean pollutant concentration variations in step-down street canyons

“…It should be noted that the value of 0.2 could not be the best for all the geometric ratios considered in this work. However, it was decided to always use the same Sct in the whole study, which is a common practice done by the scientific community (Takano and Moonen, 2013 ;Wen and Malki-Epshtein, 2018 ;Cui et al, 2016), in order to only compare the influence of the geometric properties of the buildings on the mean concentrations and to avoid multi parameter comparisons.…”

“…The effects of street geometry on pollutant dispersion have already been studied extensively with both experimental (Gerdes and Olivari, 1999;Hotchkiss and Harlow, 1973;Pavageau and Schatzmann, 1999;Vardoulakis et al, 2003) and numerical methods (Aristodemou et al, 2018;Bijad et al, 2016;Santiago and Martin, 2005;Tominaga and Stathopoulos, 2017;Vardoulakis et al, 2003) and also at full-scale with in situ measurements (Qin and Kot, 1993;Vardoulakis et al, 2002). Some authors have even studied the effects of roof shape on pollutant dispersion (Takano and Moonen, 2013;Wen and Malki-Epshtein, 2018). However, most of these works were conducted in symmetrical street canyons using buildings with the same height.…”