Pollutant transport between a street canyon and a 3D urban array as a function of wind direction and roof height non-uniformity

Review of Experimental Studies and choice of test case

Air pollution is a major problem in cities, especially in street canyons where tall buildings can trap pollutants and impede ventilation. To better understand the complex flow dynamics in these street canyons and how pollution moves through them, researchers have conducted both experimental (Barlow et al., 2004; Carpentieri et al., 2012; Di Bernardino et al., 2018) and numerical studies (Baik and Kim, 2002; Cai et al., 2008; Liu et al., 2005; Michioka et al., 2014; Yang and Shao, 2008). While experiments are difficult to conduct due to the difficulty of measuring velocity and pollutant concentration simultaneously, numerical simulations have provided valuable insights into the processes taking place.

Previous experimental and numerical studies have focused primarily on simpler quasi-2D canyons, where scalar exchange rates provide equilibrium mass fluxes between the canyon cavity and the free surface layer above the canyon. Both experiments and numerical models have shown that pollutant removal in a 2D canyon at roof level is mainly driven by turbulent transport and that complex turbulent transport cannot be represented by a simple gradient diffusion model. However, real street canyons are three-dimensional and contain intersections. In addition, the roof height is usually not uniform and the wind direction is not only perpendicular to the axis of the street canyon.

To address this research gap, our previous studies (Nosek et al., 2017, 2016) experimentally investigated pollutant transport in 3D street canyons, taking into account the effects of wind direction and non-uniform roof height in all directions. These studies provide valuable data for CFD models and help to better understand the complex flow and pollutant transport dynamics in 3D street canyons. Since architecture and building layout strongly influence the flow within the street canyon, the spatial variability of roof height and shape should be a major concern of future studies.

References

Baik, J.J., Kim, J.J., 2002. On the escape of pollutants from urban street canyons. Atmos. Environ. 36, 527–536. https://doi.org/10.1016/S1352-2310(01)00438-1

Barlow, J.F., Harman, I.N., Belcher, S.E., 2004. Scalar fluxes from urban street canyons. Part 1: Laboratory simulation. Boundary-Layer Meteorol. 113, 369–385. https://doi.org/10.1016/j.atmosenv.2008.03.040

Cai, X.M., Barlow, J.F., Belcher, S.E., 2008. Dispersion and transfer of passive scalars in and above street canyons-Large-eddy simulations. Atmos. Environ. 42, 5885–5895. https://doi.org/10.1016/j.atmosenv.2008.03.040

Carpentieri, M., Hayden, P., Robins, A.G., 2012. Wind tunnel measurements of pollutant turbulent fluxes in urban intersections. Atmos. Environ. 46, 669–674. https://doi.org/10.1016/j.atmosenv.2011.09.083

Di Bernardino, A., Monti, P., Leuzzi, G., Querzoli, G., 2018. Pollutant fluxes in two-dimensional street canyons. Urban Clim. 24, 80–93. https://doi.org/10.1016/j.uclim.2018.02.002

Liu, C., Leung, D., Barth, M., 2005. On the prediction of air and pollutant exchange rates in street canyons of different aspect ratios using large-eddy simulation. Atmos. Environ. 39, 1567–1574. https://doi.org/10.1016/j.atmosenv.2004.08.036

Michioka, T., Takimoto, H., Sato, A., 2014. Large-eddy simulation of pollutant removal from a three-dimensional street Canyon. Boundary-Layer Meteorol. 150, 259–275. https://doi.org/10.1007/s10546-013-9870-6

Nosek, Š., Kukačka, L., Jurčáková, K., Kellnerová, R., Jaňour, Z., 2017. Impact of roof height non-uniformity on pollutant transport between a street canyon and intersections. Environ. Pollut. 227, 125–138. https://doi.org/10.1016/j.envpol.2017.03.073

Nosek, Š., Kukačka, L., Kellnerová, R., Jurčáková, K., Jaňour, Z., 2016. Ventilation Processes in a Three-Dimensional Street Canyon. Boundary-Layer Meteorol. 159, 259–284. https://doi.org/10.1007/s10546-016-0132-2

Yang, Y., Shao, Y., 2008. Numerical simulations of flow and pollution dispersion in urban atmospheric boundary layers. Environ. Model. Softw. 23, 906–921. https://doi.org/10.1016/j.envsoft.2007.10.005

Contributed by: Štěpán Nosek — Institute of Thermomechanics of the CAS, v. v. i.

Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results