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News Article

Trees improve pollutant dispersal in cities

Study found trees reduced traffic pollution in Leicester by up to 7%

A recent study by the University of Leicester’s Department of Physics and Astronomy and aerial mapping company Bluesky, has found that trees in cities can have a regionally beneficial impact on the air quality.  Using Leicester city as the study area, the team found that the presence of trees increased turbulence and reduced ambient concentrations of road traffic emissions by 7 percent, at pedestrian height on average. 

Previous research has suggested that trees trap pollution; however, the new study focuses on the effectiveness of trees at dispersing emissions arising from road traffic.  Leicester was chosen for the study because up to 90 percent of some atmospheric pollutants in the city, such as NO2 are emitted by traffic. 

The team used a range of geographic datasets, including Bluesky’s National Tree Map, in order to create a 3D representation of Leicester with buildings, roads and trees.  Air quality measurements from a number of mobile and fixed sensors were then added to the model to provide data on pollution in different locations at different times of the day.  

Commenting on the results of the study, lead author and PhD researcher Antoine Jeanjean said, “Our fears of trees trapping pollution around streets were revealed to be unfounded.  In some situations they can increase pollution locally but on average, their impact is beneficial in terms of pollutants dispersion.” 

The researchers noticed that while trees reduced air quality in some street canyons in the city by trapping pollutants, as a whole, they decrease the amount of pollutants around pedestrians.  They also observed that while trees reduce the wind speed over the city, they produce more turbulence, which helps disperse the pollution emitted by traffic, resulting in a lower exposure for the public. 

James Eddy, Bluesky’s Technical Director said: “Basing this type of study on the most up to date and accurate geographic data, such as the National Tree Map, allows for the results to be validated and the studies replicated for other locations and types of environment further enhancing our understanding of air pollution and the important role played by trees.”

The study is published in the journal Atmospheric Environment.

Further information is available to subscribers of the Forest Science Database.  For example, using the search string trees AND "air pollution" AND cities, yields over 130 results.  Some of these are provided in the further reading section below.



A.P.R. Jeanjean, G. Hinchliffe, W.A. McMullan, P.S. Monks, R.J. Leigh. A CFD study on the effectiveness of trees to disperse road traffic emissions at a city scale. Atmospheric Environment, 2015; 120: 1 DOI: 10.1016/j.atmosenv.2015.08.003

Article details

  • Author(s)
  • Stephanie Cole
  • Date
  • 28 September 2015
  • Source
  • University of Leicester
  • Subject(s)
  • Forest trees