Units offer relief from air pollution

Funding sought by living wall specialist Treebox to produce Air Pollution Units for use in cities.

Air Pollution Units: can be bolted to walls or bus stops to purify air (credit Treebox)
Air Pollution Units: can be bolted to walls or bus stops to purify air (credit Treebox)

Living wall company Treebox has invented a portable green wall that sucks in pollution and blows out purified air - and director Armando Raish believes it could have big implications for cities.

The Air Pollution Units (APUs) create an artificial breeze that draws polluted air into the plants' root zone. There, microbes work 24/7 to process pollutants into harmless organic molecules. Each unit churns through one million litres of air per day.

Normal planting schemes and even green walls keep dust down and leaves can process some pollution but they are not very effective at cutting pollutants, said Raish. "The problem with passive planting is that trees respond to the environment. Whether the wind's blowing or the sun's out, or it's a certain time of year, they perform very differently and at times have very little impact."

Attempts to use a fan system to bring polluted air into the root zone have so far failed because high airflow dries out plants' roots. But new aerogation technology developed by American company AgroSci brings water in as well, hydrating the air and keeping roots, substrate and microorganisms at an ideal moisture level and temperature.

Indoor tests by AgroSci have shown aerogation units can process highly polluted air to 99 per cent purity. But Treebox, which has the EU licence for the technology, is the first to use it outdoors.

Staffordshire University researchers are testing the technology's effectiveness at reducing nitrogen dioxide outside. Cities in France and Germany are also signed up for on-street trials.

Raish is now seeking funding of between £500,000 and £1m to produce the first 1,000 APUs. The business has workers across the South East, with a logistics centre in Essex, manufacturers in Kent and assembly by a business in Radlett, north of London. The plants will be UK-grown, with Chichester living wall company Biotecture one of the companies being considered as a supplier.

Once produced, Raish intends for bus companies and other businesses to lease the boxes for around £180 per month, covering all costs including maintenance. He estimated that London's zones 1 and 2 would require at least 10,000 APUs to make a serious dent in pollution.

Specifications - Air Pollution Units in detail

Each 1m x 1m x 20cm Air Pollution Unit contains 30 plants and uses 0.5 litres of water per day. Interchangeable pots are filled with a substrate of crushed volcanic rock, expanded clay, mica and organic material.

They are planted with herbaceous species including ferns, grasses and small shrubs such as sarcococca that have the additional benefit of scent. Units can be bolted to walls or bus stops, with rainwater collection and a reservoir top-up providing irrigation. All mechanical elements are solar-powered.

Maintenance staff will remove and swap any poorly performing plants. They could also change plants seasonally to add colour and interest.

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