Filter-like trees improve city air
Trees in London improve air quality by filtering out pollution particulates which cause problems such as asthma.
New research found that the urban trees of the Greater London Authority (GLA) area remove somewhere between 850 and 2,000 tonnes of particulate pollution (PM10), which can be inhaled by humans, from the air every year.
The University of Southampton research found that the targeting of tree planting in the most polluted areas of the GLA area and particularly the use of a mixture of trees, including evergreens such as pines and evergreen oak, would have the greatest benefit to future air quality in terms of PM10 removal.
One of the paper's authors, Professor Gail Taylor, said: "Trees have evolved to remove CO2 from the atmosphere, so it's not surprising that they are also good at removing pollutants.
"Trees which have leaves the whole year are exposed to more pollution and so they take up more. Using a number of different tree species and modelling approaches, the effectiveness of the tree canopy for clean air can be optimised."
The study also looked at predictions of particulate volumes in future climate and for five tree planting scenarios in London.
Using seasonal rather than hourly data was shown to have little impact on modelled annual deposition of pollution (PM10) to urban canopies, suggesting that pollution uptake can be estimated in other cities and for the future where hourly data are not available.
Co-author Peter Freer-Smith, chief scientist for Forest Research (Forestry Commission), said: "We know that particulates can damage human health, for example exacerbating asthma, and this reduction in exposure could have real benefits in some places, such as around the edge of school playgrounds.
"Urban green space and trees give a wide range of benefits and this study confirms that improving air quality is one of them and will also help us to get the most out of this benefit in future."