Building Shape and Layout Trap Pollution in Urban Street Canyons

The geometry and arrangement of buildings lining urban streets can strongly control how air moves—and how pollution lingers—in the street canyons between them. A new computational study published in Air Quality, Atmosphere & Health examines how two design factors interact: the length-to-height ratio of buildings (L/H) and whether the buildings are arranged in aligned or staggered rows.

On the central vertical plane of the canyon, the simulations showed that a clockwise vortex drives pollutant accumulation on the leeward side of buildings. Among all cases tested, the aligned layout at L/H = 5 produced the highest pollutant concentration. This finding highlights how stretching buildings longer relative to their height can worsen pollution buildup even in a seemingly regular, aligned street arrangement.

At pedestrian breathing height, the two layouts behaved very differently. In the staggered arrangement, a maze-like flow pattern markedly reduced wind speed and, for L/H = 2, 3, and 5, induced reverse airflow within the building gaps. As a result, pollutants spread both upstream and downstream. In the aligned layout, by contrast, pollutants travelled only downstream.

The study also quantified how increasing the length-to-height ratio degrades ventilation in the central street canyon. Moving from L/H = 1 to L/H = 5 reduced ventilation by 52.1% and raised the maximum pollutant concentration by 210.2%. Notably, the aligned layout at L/H = 1 showed the strongest ventilation of all nine cases examined, suggesting that compact, low-aspect-ratio buildings in a regular arrangement offer the best natural flushing of street-level air.

Wall concentrations revealed another consequence of layout choice. For the common L/H cases, the staggered layout produced averaged leeward wall concentrations that were 36.0% to 71.7% higher than the aligned layout, indicating that staggered arrangements exacerbate pollutant trapping on canyon walls.

The authors frame these results as revealing the coupling mechanism between building proportions and layout, providing a theoretical basis for urban street design and air pollution management.

Subject of Research: How building length-to-height ratio and aligned versus staggered layouts affect airflow and pollutant dispersion in urban street canyons.

Article Title: Coupled effects of building length-to-height ratio and layout on airflow and pollutant dispersion within urban street canyons

Article References: Huang, Y.-D., Yi, S.-Y., Su, M.-J., Chai, M.-X., Wang, K.-X., Cui, P.-Y., & Luo, Y. (2026). Coupled effects of building length-to-height ratio and layout on airflow and pollutant dispersion within urban street canyons. Air Quality, Atmosphere & Health, 19(11), Article 249. https://doi.org/10.1007/s11869-026-02143-w

Image Credits: AI Generated

DOI: 10.1007/s11869-026-02143-w

Keywords: urban air quality, street canyons, CFD modelling, pollutant dispersion, building geometry, ventilation, staggered layout, aligned layout, pedestrian exposure, wind-tunnel validation, Coupled, effects