Hedges around playgrounds keep schoolchildren safe from air pollution
“Tredges” (trees managed as head-high hedges) installed at Manchester schools in the UK were shown to prevent toxic traffic-derived air from reaching school children by a substantial amount. Exposure to fine particulate matter (PM) in air pollution is reportedly the largest environmental risk factor contributing to cardiovascular deaths and disease globally, and is linked to around six to nine million premature deaths each year. Children are more susceptible to air pollution than adults as the former have a higher breathing rate, on account of their still-developing organs.
The team of researchers behind this experiment deduce that roadside vegetation can significantly decrease air pollution-related health risks.
The tredges in question each composed of an ivy screen, western red cedar, and mixture of western red cedar, Swedish birch, and an inner juniper hedge. A fourth primary school with no planting of vegetation between roads and the school playground was used as a control – all tredges were installed during the summer school holidays of 2019.
The school with the ivy screen, which have smooth and waxy leaves, saw a substantial reduction in playground particulate matter concentrations, but an increase in black carbon. The playground with the mixture of planting saw lower reductions in air pollution to that of the western red cedar.
The biggest overall reductions in particulate matter and black carbon were shown at the school with western red cedar planted. The results showed almost half (49%) of black carbon and around 46% and 26% of the fine particulates, PM2.5 and PM1 emitted by passing traffic were captured by the western red cedar tredges.
In addition, the tredges also significantly reduced the magnitude and frequency of acute “spikes” in air pollution reaching the playgrounds.
According to research lead Barbara Maher, Emeritus Professor at Lancaster University, “Western red cedar tredges work well because this species’ leaves form millions of tiny rough corrugated projections, each of which can bump into the particulates suspended in the air and ‘capture’ them in their ridges, furrows and pores.
“This takes them out of the local atmosphere and therefore reduces the exposure to these traffic-sourced air pollution particulates of the children and staff in the playground.”
The researchers believe that western red cedar performed best at preventing the particulate air pollution from reaching the playground because its prolific, small, rough, evergreen leaves act like a filter, capturing particulate pollution and stopping it circulating in the atmosphere. When it rains, the particulates wash off – ending up in the soil or drains – enabling the leaves to then capture more particulate pollution.
“Our findings show that we can protect school playgrounds, with carefully chosen and managed tredges, which capture air pollution particulates on their leaves. This helps to prevent at least some of the health hazards imposed on young children at schools next to busy roads where the localised air quality is damagingly poor, and it can be done quickly and cost-effectively,” Professor Maher.
The researchers are quick to suggest these benefits highlighted are not just limited to schools and that carefully selected and managed tredges could be used in other parts of urban areas to reduce the damaging health impacts of exposure to traffic pollution.
[Groundwork Greater Manchester had installed the tredges and also ran “citizen science” workshops in classes from the select primary schools to highlight issues around air quality and steps young people and their families can take to make a difference.] Image source:
Category: Education
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