London mayor Sadiq Khan announced a £1m fund last month for businesses to help tackle air pollution, with green infrastructure measures such as green screens and new green spaces eligible under the scheme. The Air Quality Business Fund is available to individual businesses or groups such as business improvement districts.
Khan has made pollution a very public priority during his first year in office and has accused former mayor Boris Johnson of sitting on a report that showed unacceptably high levels of toxic air near schools, but work on the issue has been going on for some time.
In 2010 Johnson commissioned a study that estimated 4,300 deaths per year in the capital are a result of microscopic airborne particles emitted in exhaust fumes. In 2011 Transport for London (TfL) commissioned Biotecture to build a pollution-mitigating green wall in Edgware Road and in 2013 Johnson launched a £6m Air Quality Fund.
An updated Kings College London study in 2015 included the impact on health of nitrogen dioxide (NO2) in London for the first time. It showed that in 2010 there was the equivalent of up to 5,900 deaths across London associated with long-term NO2 exposure.
The Air Quality Fund financed a three-year research study by Middlesex University and London Borough of Barking and Dagenham Council in 2014 to monitor the effect of living walls on two traffic pollutants - PM10 and NO2 - at a secondary school in the east-London borough.
Surge of interest
Green wall manufacturers and installers have been talking about a London surge of living wall interest for some time. Biotecture director Richard Sabin says he has already spoken to one client about accessing this new fund for a project.
"I think there's an opportunity for green infrastructure. The benefit for green walls of this fund is great. It just shows that they are more than for aesthetics. Whenever we talk to specifiers we're almost tripping ourselves to outline the benefits. The air pollution mitigation is proven. It's proven in studies and also in the field.
"There's an innate understanding that green infrastructure is good for us on many levels. That understanding is becoming clearer. We are getting more and more data that shows us what green infrastructure does. It's not just about living walls, it's also about pocket parks giving people the opportunity to escape city life."
While in the past developers felt the extra cost outweighed the value of adding in green infrastructure, he says they now have a more balanced view. "We are not far away from people saying I can't afford to not have some green infrastructure as part of my development. I need to feel good as a business and demonstrate my green credentials."
Sabin explains that the result of the latest research is that green wall companies now know exactly how which plants are best for mitigating pollution - those that put leaves or fronds out into the air and cause "near surface roughness". Just as vegetation on the banks of a stream catches debris in water as it eddies around, plants can catch particulates from the air as it moves past.
"It's particularly effective in urban street canyons where the width between buildings is less than the height of the buildings," he says. "What happens is the air that gets in there is trapped and finds it quite difficult to get out. It just goes round and round and that's the issue in London. That's exactly where living walls can do some good."
Sabin says big property developers "are massively interested" in reducing pollution and councils are "very interested in air quality. "A lot of schemes need to demonstrate that they are using planting that is reducing air pollution." One such recent scheme was Southampton Row in Holborn, where pollution-reducing plants were chosen. Another Biotecture project, a green wall for TfL in Elephant & Castle, was paid for by clean-air funding.
"Developers are led by their consultants but also by local authorities," he points out. "Some, like Camden and Westminster, are pro living walls. We've done 15 living walls in London over the past five or six years."
Another recent study is by doctoral student Udeshika Weerakkody, who looked at the pollution-capturing abilities of the leaves of 17 different living wall plants and is on the verge of publishing. Her supervisor, Staffordshire University emeritus professor of ecology John Dover, says: "In a few years there will be a lot of information available. We do find that people are starting to listen a bit more. You'll always find one 'it's not for them', but others can see the bigger picture."
Green screens are a quick-fix alternative to green walls that can also be used as fencing systems. Highways England and contractor Costain used 88 1.8m-high Mobilane Green Screens to create a "green bridge" as part of the £192m A556 Knutsford-to-Bowdon dual carriageway.
Landscape supplier Green-tech has seen sales of its ivy green screens take off. The 1.2x1.8m Green-tech Green Screens, the only plant product the company sells, are grown from seed in airpots at its Yorkshire headquarters, with the plant material trained to grow around a mesh over a 12-month period.
"They are selling out the door," says head of sales Richard Gill. "It's a really good idea. You'll see a lot more of them in years to come." Green-tech used to import from Holland but decided to grow its own three years ago. The company sells the screens to landscapers, construction firms and fencing suppliers.
"We were selling hundreds, now we sell 2,000 or 3,000 screens a year. We currently have 5,000 in production. It's the way the world is going. Green infrastructure is huge. We've had a lot of interest in Network Rail and contractors who work for Network Rail." Gill says urban tree planting has also "improved massively".
"One of our biggest markets is in London, especially green roofs and podiums for top landscapers. Companies are interested in green credentials. They want biodiversity, aesthetics, SuDS, a bit of everything. They can get BREEAM points."