It may sound like a no-brainer to say that trees improve air quality. After all, we know that trees absorb the greenhouse gas carbon dioxide (CO₂), and that their leaves can trap the toxic pollutants nitrogen dioxide (NO₂), ozone, and harmful microscopic particles produced by diesel vehicles, cooking and wood burning.
Yet some recent studies have suggested that trees may in fact worsen urban air quality by trapping pollutants at street level. A closer look at the evidence – and how it was collected – reveals the root of this dispute, and can help us come to a more nuanced understanding of the impacts of trees on our urban environment.
Asking whether cities should have trees in it is a bit like asking whether a suit should have a person in it. There is every chance that urban trees could provide a “nature-based solution” to several pressing problems with the urban environment, but perhaps not in the way scientists and policy-makers seem currently to be thinking. Rather than providing a technical fix that disguises our obsession with the diminishing returns of the internal combustion engine, increasing urban tree numbers could change our entire perspective on cities, facilitating the creation of livable cities that value nature as an integral part of social, economic and environmental capital. (2015) By Rob MacKenzie on The Conservation.