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A Moss Wall with the Pollution-Eating Power of 275 Trees

The CityTree is a pop-up moss wall capable of consuming as much air pollution in an urban environment as a small forest.

The CityTree in Oslo at Nordraaks Square between Wergelandsveien and Holbergsgate (© Green City Solutions)

Following President Trump’s withdrawal of the United States from the Paris Agreement, and his avowal to push for the country’s “energy dominance” through a concentration on coal, one issue that will likely worsen in the coming years is air pollution. The only way to truly combat the decreasing quality of our air is by government policy, support for environmental research, and serious attention to sources of carbon dioxide emissions. However, small-scale design projects have the potential to increase awareness and offer solutions for ways to build greener cities.

One such recent green initiative is the CityTree by the Berlin-based Green City Solutions. The name is a bit misleading, as CityTree is really a 13-foot wall of moss, with the possibility for public seating on either side, intended to be a self-sustaining, wifi-ready environment through solar panels and rainwater collectors. Green City Solutions states that the CityTree “has the same effect as up to 275 urban trees” with its “specific moss cultures with vascular plant that eat particulate matter (PM), nitrogen dioxide and ozone — offsetting 240 tons of CO2-equivalents per year in total.”

CNN reported that 20 CityTress have been installed in cities including Paris, Oslo, Hong Kong, and Brussels. Two CityTrees were recently deployed in Glasgow, although the rollout of these pop-up air cleaners has not been without challenges. Co-founder Zhengliang Wu told CNN that in Modena, Italy, “everything was planned and arranged, but now the city is hesitant about the places we can install because of security reasons.” Perhaps a greater hurdle is funding for the devices, which is not cheap. Curbed notes that each costs around $25,000. Arguably, you could plant a lot of hardy street trees for much less money.

Eight CityTrees in front of the Frauenkirche in Dresden (© Green City Solutions)

Yet the CityTree is not meant for parks or to replace street trees, but to add greenery to concrete-heavy spaces where planting is not an option. Paris, one of the inaugural CityTree cities, has a very thin tree canopy; the newly launched Treepedia from MIT’s Senseable City Lab ranked it among the lowest in its tree study of major cities. Nevertheless, as anyone who has attempted to keep a home terrarium knows, even moss requires care for its water needs, and it’s hard to imagine the mini-gardens making it through a harsh winter. Further, the CityTree lacks many benefits of having 275 trees, such as shade.

According to the World Health Organization, seven million deaths were attributed to air pollution exposure in 2012 (resulting from things like strokes, lung cancer, and ischaemic heart disease). There is no easy solution to this global problem. Still, socially conscious design can offer more grassroots responses. For instance, Daan Roosegaarde is partnering with the Beijing-based bike-sharing company Ofo to make smog-inhaling bikes available to the public (Studio Roosegaarde’s previous projects include a 23-foot-tall structure in Rotterdam that vacuums smog and compresses it into jewelry). Air Ink by Graviky Labs in India is transforming airborne pollutants into consumer safe inks and paints. Each of these cannot reverse the environmental catastrophes of climate change and air pollution, but they can draw our attention to them.

The CityTree at Ernst-Abbe-Platz in Jena, Germany, with benches and a wifi hotspot (© Green City Solutions)
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