Modelling air quality in street canyons: a review

Abstract

High pollution levels have been often observed in urban street canyons due to the increased traffic emissions and reduced natural ventilation. Microscale dispersion models with different levels of sophistication may be used to assess urban air quality and support decision making for pollution control strategies and traffic planning. Mathematical models calculate pollutant concentrations by solving either analytically a simplified set of parametric equations or numerically a set of differential equations that describe in detail wind flow and pollutant dispersion. Street canyon models, which might also include simplified photochemistry and particle deposition-resuspension algorithms, are often nested within larger-scale urban dispersion codes. Reduced-scale physical models in wind tunnels may also be used for investigating atmospheric processes within urban canyons and validating mathematical models. A range of monitoring techniques is used to measure pollutant concentrations in urban streets. Point measurement methods (continuous monitoring, passive and active pre-concentration sampling, grab sampling) are available for gaseous pollutants. A number of sampling techniques (mainly based on filtration and impaction) can be used to obtain mass concentration, size distribution and chemical composition of particles. A combination of different sampling monitoring techniques is often adopted in experimental studies. Relatively simple mathematical models have usually been used in association with field measurements to obtain and interpret time series of pollutant concentrations at a limited number of receptor locations in street canyons. On the other hand, sophisticated numerical codes have often been applied in combination with wind tunnel and/or field data to simulate small-scale dispersion within the urban canopy.

Transport processes in and above two-dimensional urban street canyons under different stratification conditions: results from numerical simulation

“…Traffic induced mechanical turbulence is an important source of turbulence in urban street canyons [2,28], but is out of the scope of this paper. Roof geometry effects such as pitched roofs or asymmetric canyons (stepup or step-down notch) will also not be addressed here.…”

Large-Eddy Simulation of Flow and Pollutant Transports in and Above Two-Dimensional Idealized Street Canyons

“…The Reynolds-averaged Navier-Stokes (RANS) equations with the k − ε turbulence model and the large-eddy simulation (LES) are mostly used in the community. The CFD studies for street canyons, including their merits and key findings, are summarized elsewhere (Vardoulakis et al 2003;Li et al 2006). Unlike field or laboratory measurements, the variables in CFD are calculated in the form of spatio-temporal functions, and CFD is often used to examine the fundamental transport mechanisms since idealized conditions can be fully implemented in sensitivity tests.…”

Three-Dimensional Mapping of Air Flow at an Urban Canyon Intersection

“…Air pollution in cities is a major environmental concern and, despite significant improvements in fuel and engine technology, present day urban atmospheric environments are mostly dominated by traffic emissions (Vardoulakis et al, 2003). Human exposure to hazardous substances is expected to be highest especially in those areas where population and traffic density are relatively high.…”

“…The study of urban street canyons has dominated short range dispersion research in urban areas (see the reviews of Vardoulakis et al, 2003;Berkowicz et al, 1997;Britter and Hanna, 2003). However, a number of studies (e.g.…”