- Karlsruhe Institute of Technology, Institute for Water and Environment, Laboratory of Building and Environmental Aerodynamics, Germany (gromke@kit.edu)
The dispersion of traffic pollutants in a street canyon with roadside hedges was investigated in an atmospheric boundary layer wind tunnel. Two types of hedge arrangements were studied: (1) one central hedgerow between the main traffic lanes, and (2) two eccentric hedgerows sidewise of the main traffic lanes. Hedges differing in height and porosity were tested. Pollutant concentrations were sampled at the lower half of the building facades and at pedestrian level on the sidewalks in front of the buildings for perpendicular approach wind.
The results reveal overall improvements in air quality at the lower half of the building facades and on the sidewalks in street canyons with hedges compared to the hedge-free case. The reductions are larger for the central hedgerow arrangements than with the sidewise hedgerow arrangements. At the leeward facade of the windward building in the central street canyon zone - where traffic pollutant concentrations are highest for the given approach wind - zone-averaged reductions of up to 61% are achieved with central hedgerows and up to 39% with sidewise hedgerows. At the lateral end zones of the street canyon, reductions in traffic pollutant concentrations are found with central hedgerows but increases with sidewise hedgerows. However, since the concentrations of traffic pollutants in the lateral end zones are considerably lower compared to those in the central zone, in total an improvement in air quality dominates.
The study shows that roadside hedgerows can beneficially affect the dispersion of traffic pollutants in urban street canyons. Overall, they lead to a reduction of concentrations and in particular to a strong reduction in the central street canyon zone were typically the highest pollutant levels occur. Hence, they can therefore be employed in a targeted manner to considerably remedy the exposure of residents and pedestrians to traffic pollutants in urban street canyons.
How to cite: Gromke, C.: Modification of traffic pollutant dispersion and concentration levels by hedgerows in urban street canyons, 12th International Conference on Urban Climate, Rotterdam, The Netherlands, 7–11 Jul 2025, ICUC12-217, https://doi.org/10.5194/icuc12-217, 2025.
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