Photograph by Bertrand Garbel, Hemis.fr/Getty Images
Air pollution in cities is rapidly increasing but living walls on buildings can help to mitigate the damage to human health.
Over the past couple of weeks, London has experienced extreme air pollution including high nitrogen dioxide levels and heavy photochemical smog. Polluted air can cause severe health problems. In addition to triggering asthma attacks, it can cause irritation of the eyes, nose and throat, bronchitis, pneumonia, and over a longer period, lung disease, heart attacks, and damage to the liver, kidneys and brain.
Using what is called a ‘street canyon,’ a recent study has shown that green walls reduce air pollution by a significant amount. Living walls planted in street canyons, or corridors between tall buildings, are not only visually pleasing but offer several benefits including reducing noise, improving the energy efficiency of the building, and cooling city blocks.
Air pollution is reduced when green walls lower extreme summer temperatures through photosynthesis by capturing gases and trapping particulate matter. Vegetation-laden walls also provide buildings with thermal insulation which results in less of a dependence on power and a reduction in harmful emissions.
Biochemist Thomas Pugh and colleagues at the Karlsruhe Institute of Technology in Germany conducted the street canyon study by utilising a computer model of a green wall with vegetation generic to a Western European city. Noting factors such as building placement and wind speed, they recorded the chemical reactions taking place on the living wall.
A clear pattern emerged showing the street canyon absorbed large amounts of particulate matter and nitrogen dioxide.
“Compared with reducing emissions from cars, little attention has been focused on how to trap or take up more of the pollutants,” said Pugh, adding “[the green wall study] is putting forward an alternative solution that might allow governments to improve air quality in these problem hot spots.”
Taking advantage of under-utilised spaces in urban areas, leafy green walls could very well be integrated into every city block.
Pugh hopes the study will show policy makers a viable way to reduce pollution that is neither overly expensive or complicated, providing a clear and simple strategy to mitigate negative health effects caused by polluted air.