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Rob MacKenzie shares insight into new research that might complicate assumptions about the role of trees in urban environments. The problem, writes MacKenzie: "some recent studies have suggested that trees may in fact worsen urban air quality by trapping pollutants at street level."
It's not that simple, of course, and Mackenzie insists that a closer look at the evidence "can help us come to a more nuanced understanding of the impacts of trees on our urban environment."
It all has to do with effect of the cocktail of buildings, structures, and landscapes that make up the city, of which trees have a unique role to play. "Trees affect the urban environment in several subtle ways. From altering air flows, to collecting pollution deposits, to affecting the chemical make up of the atmosphere, their impacts are both pervasive and difficult to pinpoint," writes MacKenzie.
So while MacKenzie goes into more detail about the several different pollution processes tress take part in, no studies have so far managed to put all the pieces of a city together. In lieu of a comprehensive model, MacKenzie uses the article as an opportunity to suggest strategies for piecing together different studies to create a more complete picture.
For more on the complex questions posed by the role of trees in the urban environment, an earlier article by John Gallagher first raised some of the same discussion points.