Hereford Council’s high tech, natural approach to improving air quality

The English cathedral city is installing three moss filters in a bid to bring down levels of atmospheric pollution. 

Hereford Council is hoping to improve local air quality through what are believed to be among the most powerful natural tools with which to combat harmful emissions. 

Three moss filters – known as City Trees, produced by Germany’s Green City Solutions – will be installed in the city, the first of which went live on 15th June at Eign Gate. Moss is considered particularly effective at tackling air pollution thanks to its ability to metabolise dust and particles, store and evaporate large amounts of moisture, in turn cooling the air. 

The so-called ‘city trees’ are around the size of an average tree, but have a far greater impact because the moss itself covers a much bigger surface area than leaves. 80% of fine dust particles in the immediate area can be absorbed, and when combined with ventilation technology – as Hereford has done – there is potential to filter breathing for up to 7,000 people per hour. 

In order to maximise efficiency, all three moss filters will be installed in busy traffic areas, with mosses specially selected for their high absorption qualities. Integrated smart sensors will monitor performance and equipment condition, meaning the public can monitor the effect on air quality via Hereford Council’s website. 

‘Moss works differently to trees. Like trees, moss is great at converting carbon dioxide into oxygen, however moss also actually absorbs pollution particles from the air – metabolising and converting them into natural and harmless biomass. The particles it cannot use are bound in the sediment of the moss. And with their excellent moisture storing ability, the moss filters also work more efficiently to cool the air around them,’ said Cllr John Harrington.

‘I understand one moss filter captures carbon dioxide equivalent to 28 beech trees and cools the air around it like three mature winter lime trees. While trees are also playing an important role in our efforts to improve air quality across the city, the moss filters provide a boost in busy traffic areas where there is higher pollution but little space,’ he continued. 

In 2018, Westminster City Council trialled the use of a ‘living wall’ made with moss in a bid to address its own air pollution problems.