We already know that plants are great for the environment, and now there’s more reason to add some more greenery to our cities.

A new report outlining how great they really are has been published in the ACS journal Environmental Science and Technology. Greenery, such as trees and bushes, can help reduce levels of two of the top air pollutants eight times more than previously thought.

Past reports have indicated the connection between pollution and greenery. Pollution and community walkability, specifically, has previously been compared for the degree of ease for walking with local levels of air quality. The exposure to air pollution affects human health, and physical inactivity is linked to an array of negative health effects. If neighbourhoods are designed in ways that can influence air pollution and walkability, those should be harnessed for our health.

The study, which was funded by the UK Engineering and Physical Sciences Research Council Sustainable Urban Environment program, outlined which pollutants are harmful to human health. Thomas Pugh and his team explain in the paper that concentrations of nitrogen dioxide (NO2) and microscopic particulate matter (PM) exceed safe levels on the streets of many cities.

Unlike the previous study regarding walkability, however, adding plants and green life can, yes, improve the air quality in urban areas but the improvement was quite small — under 5 percent. This new study has found that the effects of green plants in the air of city streets, with Pugh and his colleagues dubbed as “urban street canyons” can be better improved–by far more than 5 percent.

The study found that specific placement of grass, climbing ivy, and other green plants in these “urban street canyons” can greatly reduce the concentration at street level of nitrogen dioxide by about 40 percent, and reduced microscopic particulate matter by 60 percent, both of which are much more than previously believed. The authors go as far as suggesting that plant-covered green “billboards” in the canyons can increase the amount of foliage.Trees, though helpful, are not as effective as the grass, ivy, and plant life.

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