Debate on robot trees looks to clear the air: What are other countries doing?

IN 2021, Cork City Council installed five ‘CityTrees’ in the city centre, as part of Cork City Council’s strategy to tackle air pollution across the city.

The 4m tall units, known as “robot trees”, are covered in a mixture of moss cultures. These filter harmful pollutants out of the air.

Earlier this week, councillors were furnished with a lengthy report on the trees which stated that the data on their effectiveness at improving air quality, is inconclusive.

The report, which runs to 185 pages, sets out Cork City Council’s rationale for installing the CityTrees, or “moss walls” as they are also referred to.

It stated that Cork City Council now has a number of options available to them regarding the future of the installations, including leaving the units in situ and in operation, setting the units up elsewhere in different indoor or outdoor locations, or engaging further research into the effectiveness of the units.

The report is due to come before a meeting of the full council on Monday, where it will be further debated.

Cork isn’t the only city to look into technological solutions to air pollution, with the same moss walls appearing all over the world over the last five years and several of these CityTrees installed in London in 2020.

Other projects with the same aim have popped up around the globe, such as The BioUrban 2.0 air purification system in Puebla, Mexico.

Designed by a Mexican start-up, the BioUrban system measures nearly 14ft tall and nearly 3m wide and is made up of a steel trunk, with a tank of green algae on top, surrounded by steel rings to imitate branches.

Serbia had a creative solution to achieving cleaner air in the city, where two very large coal power plants have made air pollution a huge problem.

In 2019, the Global Alliance for Health and Pollution published the Global, Regional, and Country Analysis of Pollution and Health Metrics, which placed Serbia as the country in Europe with the highest pollution-related deaths: 175 per 100,000 people.

The city of Belgrade, in Serbia, is currently ranked 24th in the world for worst air quality. The population density there means there is a lack of space to plant trees.

Dr Ivan Spasojevic, from the Institute for Multidisciplinary Research at the University of Belgrade, developed a solution to improve air quality: The liquid tree.

Known as Liquid 3, the creation is Serbia’s first urban photo-bioreactor, a tank that contains 600l of water and works by using microalgae to bind carbon dioxide.

The microalgae replace two 10-year-old trees or 200 sq m of lawn, but the company says the advantage of microalgae is that it is 10-50 times more efficient than trees and grass at photosynthesising and creating pure oxygen.

The team explained that they are not aiming to replace trees with these tanks of green water, but that they are a substitute for areas where there is no space to plant them, or they would not survive due to the air quality.

The Liquid 3 is situated in front of the Municipality of Stari Grad in Makedonska St in Belgrade.

This is a busy urban area where CO2 emission concentrations are highest and, similar to Cork’s robot trees, Liquid 3 cleans the air and also serves as a bench in the city centre.

The controversial robot trees in Cork were unveiled in August 2021.

The total cost of the purchase was €355,106, while the total cost of regular inspection and maintenance of the robot trees for the period of August 10, 2022, to September 9, 2023, was €17,880.

By contrast, the maintenance for the Liquid 3 costs €60 a month, meaning €1,440 has been spent in the two years since it was installed, which equates to 21 times less per month than Cork’s robot trees.

The Liquid 3 website measures the volume of heavily polluted urban air cleaned off of metals in houses.

Their website states that the average volume of a house is 700 cubic metres, revealing that four houses worth of aluminium, two of cadmium, and one each of both strontium and vanadium, are cleaned each month.

Lorna Bogue, a councillor for the Green Party in Cork city, pointed out that the environment in Belgrade is very different to that of Cork.

She has been critical of Cork’s robot trees.

“Belgrade would have a different environment to Cork, our climate would be more conducive to real trees”, she argued.

“In Cork city, there are problems with the air quality, but also a lack of biodiversity and a lack of green spaces.”

Ms Bogue explained that in addition to just cleaning the air, trees provide shade — which is key for regulating temperatures — and according to many studies, they are good for mental wellbeing.

Referencing the robot trees, which she called “a vanity project” and “an investment into unproven technology”, she said: “These things just appeared and we were not told about them … we would have told them it was not a good idea in comparison to just putting up real trees.”

Ms Bogue added: “There’s always going to be new technology, but we have these naturally occurring things that are popular.

“People have the right to a nice public space and to be in nature,” she said, suggesting that “rather than privatising out to technology companies, we should be concentrating more on making the city a liveable space to be in,” and that real trees are the key to this.