New level: Milestones in the evolution of the CityTree

It is now a good year since the two founders Peter Sänger and Liang Wu unveiled the new generation of the CityTree in front of the press and many other spectators near the Gedächtnis-Kirche in the centre of Berlin. In the two years prior to the launch, the CityTree underwent significant further development, which was co-financed and thus made possible by the European funding programme Horizon 2020. The seven-figure funding was instrumental in using the knowledge gained from the previous projects to make the moss module smarter and further improve the performance of the CityTree. These are the main four milestones at a glance:

1. The bio-algorithm: best conditions even far away from the natural habitat.

Mosses are capable of amazing things and are also highly adaptable. But in the middle of the city, on a busy square or next to a busy road, our little superheroes need our support to stay vital – that’s the only way they can perform. A specially developed bio-algorithm ensures that the mosses are supplied according to their needs, depending on weather conditions and other factors such as local air quality. With the help of more than 30 built-in sensors and a linked analysis database, factors such as aeration and irrigation are controlled in such a way that the mosses are optimally supplied at all times and can concentrate fully on filtering and refreshing the city air.

2. The moss farm: learning to understand mosses

Mosses have a huge surface area, basically like human lungs. On this surface of moss leaves, stems and hairs, fine dust particles from the air sucked in are held and thus filtered. The particles are attracted electrostatically and absorbed into the interior of the cell with the addition of water. There, the fine dust particles are decomposed and metabolised. For this we need to understand which of the approximately 20,000 known mosses is best suited for the purpose of air purification and freshening and how we can support this super moss in doing so, regardless of location and weather. That is why we have built the world’s first moss farm in Bestensee near Berlin, where the mosses are grown vertically (join our next virtual moss farm tour). Here we explore the green depths of our mosses and are able to cultivate finished mats full of dense, green and hungry moss in just 12 weeks.

3. AirCare: Air quality becomes visible

Nobody would drink a glass of dirty water. But what about breathing dirty air? In addition to air purification and cooling, an essential part of our work is to make air quality visible. For this purpose, we have developed our AirCare dashboard, in which the data measured by the sensors are evaluated and visualised. This allows us to analyse the air quality and the impact of our products on the microclimate in real time and present it in an easy-to-understand way, both on the product itself or in the web interface from anywhere.

4. Scientific validations & CE certification

The verifiability of the performance of our biofilters in outdoor applications is extremely demanding and could only be realised in cooperation with renowned institutes and long-term measurement campaigns. In 2020, the time had finally come. Supported by the European Commission, the Leibnitz Institute for Tropospheric Research Leipzig and the Institute for Air-Conditioning and Refrigeration Dresden, the CityTrees were set up at various locations and accompanied by measurements. These tests were carried out in the laboratory, in a hall and outdoors, and the results were constantly validated. Depending on the particle size, up to 82% of the fine dust can be filtered through the mosses. Since we irrigate the mosses and create a moist surface, there are also significant cooling and moistening effects on the ambient air.

With the CE Lab in Ilmenau, we have also tested the CityTree for safety, quality and compatibility and thus awarded the CE label. In this way, we guarantee that every biofilter complies with the applicable standards and can deliver the promised performance in series production.


[The detailed final report of the European Union on our project can be found here].


Air pollution in urban areas remains a key problem in 2021, limiting health and quality of life. The pandemic has made the urgency of improving air quality in cities abundantly clear. Not only does a high concentration of fine dust increase the risk of cardiovascular and respiratory diseases, but the frequency and severity of COVID-19 diseases is also directly related. This fact continues to drive us forward.

The mission: Create fresh air zones in cities and design the best possible city of the future together with citizens, companies and politicians. We are pioneers in combining living moss with technology to make Europe-wide air pollution visible and to offer city dwellers and visitors places to ‘recharge’. Setbacks cannot be avoided. The milestones, which we were able to achieve thanks to funding from the EU’s Cluster of Excellence, show that we turn failures into insights that allow us to move forward on our path.

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