If you get too excited, “Just take a slow deep breath,” they say. The sense of cool, clean air entering our lungs has a calming effect on anyyone. But what if the air we breathe is neither cool … nor clean?

The BBC’s Melissa Hogenboom reports, “Emerging studies show that air pollution is linked to impaired judgement, mental health problems, poorer performance in school and most worryingly perhaps, higher levels of crime … In the future, police and crime prevention units may begin to monitor the levels of pollution in their cities, and deploy resources to the areas where pollution is heaviest on a given day.”

“Wherever the cloud of pollution travels, crime increases.”

So, what can we do about air pollution?

Trees “breathe” in carbon dioxide and “breathe” out oxygen. They remove contaminants from the air in the process. Ben Wilson, in The New York Times, notes, “Green spaces offer another form of much needed protection from the elements.”

Journalist Vittoria Traverso says, “Trees are particularly effective at removing particulate matter. But trees also play a vital role in directly removing pollutants from the air. Plants are often seen as the “lungs” of an ecosystem because they absorb carbon dioxide and emit oxygen … But they also act as an ecosystem’s “liver” too, filtering atmospheric pollutants like sulphur dioxide and nitrogen dioxide through their leaves.”

Treehugger’s Lloyd Alter quotes Roland Ennos, a professor of biomechanics at the University of Hull, “Theoretically, trees can help provide cooling in two ways: by providing shade, and through a process known as evapotranspiration. Locally, trees provide most of their cooling effect by shading.” 

Ben Wilson — historian and author — elaborates, “If cities are to survive a hotter, wet, less predictable climate it is in their interests to strike an accommodation with nature. Urban centers like Louisville, Ky., denuded of tree canopy and foliage, can be 20 degrees Fahrenheit hotter than the lusher surrounding areas. Green spaces offer another form of much needed protection from the elements.”

Alter explains, “All up, the shade provided by trees can reduce our physiologically equivalent temperature (that is, how warm we feel our surroundings to be) by between seven and 15°C, depending on our latitude.” 

“Trees have a remarkable range of traits that can help reduce urban air pollution, and cities around the world are looking to harness them,” Traverso expands. “Trees can improve air quality in direct and indirect ways. Indirectly, they can help by shading surfaces and reducing temperatures … by reducing the need for conventional air conditioning, and the emissions of greenhouse gases that come with it. Plus, lower temperatures decrease risk of harmful pollutants like ground level ozone that commonly spike on hot days in urban areas.”

“But increasingly, greenery has been edging its way back into modern urban landscapes, and for good reason. Vegetation helps cities become better habitats for wildlife and for people, and it helps to make city air safer.”

Wilson looks to the future, “Imagine a city latticed with lightly cultivated wild spaces, microforests and roadside meadows. (For that matter, imagine the manicured neatness of suburbia blooming with wildlife gardens in place of ecologically impoverished, pesticide-soaked lawns.) That would be a different kind of city, where the human and the natural coil together and where the conventional cityscape is visually enriched by exuberant wildlife.”

Additional information:

Lloyd Alter, The Best Way to Cool Our Cities Is to Plant More Trees, July 25, 2022, TreeHugger

Melissa Hogenboom, How Air Pollution is Doing More than Killing Us, 16 April 2019, BBC Future

Vittoria Traverso. The Best Trees to Reduce Air Pollution, 4th May 2020, BBC FUTURE PLANET

Ben Wilson, Let the Postpandemic City Grow Wild, May 9, 2023, The New York Times