November 10, 2021 – Air pollution from traffic can build up where buildings line city roads, creating the effect of a polluted urban canyon. But new research suggests that the shrubs along the streets may mitigate exposure for pedestrians and cyclists. But the trick is to figure out the best place to put the hedge.
Researchers from the UK used instruments to measure particles in the air in 13 areas around a hedge along Du Cane Road near White City in west London. The hedge runs along the sidewalk between the road and residential buildings.
After collecting daily readings for nearly 7 weeks in late summer 2020, investigators mapped the particle concentrations against the hedge. They found that the concentration of polluting particles was lowest at a height of 1 to 1.7 meters (39.4 to about 67 inches) in front of the hedge, where many pedestrians and cyclists were breathing.
But the wind direction affected where the pollution has accumulated around the hedge, with higher levels in some areas behind the roadside greenery. The researchers, whose work has been published in International environment, assume that other non-hedged vegetation nearby could trap the pollution.
For city planners, the implication may be that randomly planting greenery, even with the best of intentions, risks worsening air pollution in some areas. Local weather conditions, the layout of streets and buildings, and the surrounding areas are all factors that can determine the best hedge placement for air pollution mitigation.
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