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CORPUS Magazine

A square for fresh air

To solve the problem of increasing air pollution, four young entrepreneurs in Dresden, Germany have developed the CityTree. Occupying little space, the intelligent, low-maintenance square “tree” containing an Internet connection cleans and cools the air of smog-plagued cities.

The idea of stepping outside and starting the day with a deep breath of fresh air is more of a vain hope than reality for many city dwellers. Our cities and their populations are faced with in some cases serious air pollution. This has been shown again by a study by the World Health Organization (WHO) updated in 2016. More than 80 % of people in urban areas with air quality checks are exposed to pollution above the WHO ceilings. Worldwide, air pollution rose by 8 % from 2008 to 2013, with the problems becoming more acute in countries with mainly low and middle incomes. This is where 90 % of cities with populations of over 100,000 fail to meet WHO air-quality targets. In countries with higher incomes, the figure is declining noticeably but is still at 56 %. On the positive side, awareness of the issue is growing and with it the number of cities monitoring emissions, taking action, and reducing air pollution.

Pollution goes to the wall

A simple solution with a big effect is the CityTree of Dresden startup Green City Solutions. The smart “tree” takes up just 3 square meters of space but is capable of reducing air pollution by up to 30 % within a radius of up to 50 meters. To put this into perspective: A mere 116 CityTrees would be sufficient to reduce the particulate concentration
in the center of Berlin by 10 micrograms per cubic meter. A single CityTree matches the particulate filter performance of 275 conventional trees, while costing about 95 % less and occupying 99 % less space. It is precisely this that makes the intelligent trees so attractive for cities – because even where there’s a will, the space and funding for urban tree-planting are often lacking.

1: Billboard and seating in one: The side walls of the CityTree can be used as information panels by companies or also by the municipality.
2: The space-saving CityTree is only about 4 meters high and occupies a 3 square meter footprint.


The CityTree is self-sufficient and only needs a few hours of care each year. Concealed behind the square carpet of foliage is advanced technology: Powered by solar panels, sensors measure all functions and parameters such as water consumption and sunlight and feed this information into a cloud application. Integrated rainwater tanks provide regular irrigation. These miracle trees have already been “planted”, as permanent and temporary installations, at Dresden’s Frauenkirche and in Oslo, Hong Kong, and Paris.

People make use of the CityTrees in their town and consciously seek them out. When we relocated a CityTree in Dresden, the people moved with it.

Peter Sänger
COO of Green City Solutions


Masterminding this environmental innovation is an interdisciplinary team: Peter Sänger, whom CORPUS met for an interview, Dénes Honus, Victor Splittgerber, and Liang Wu founded Green City Solutions two years ago. Along with architecture and urban design, the young entrepreneurs also cover the disciplines of mechanical engineering, informatics, and horticulture. Their goal is to make the city of the future a little greener – and hence a little more hospitable.

1: Peter Sänger
2: Victor Splittgerber
3: Dénes Honus
4: Zhengliang Wu

Four university students start thinking about how they can make tomorrow’s world a little better. A short while later they found their own startup that effectively combines high tech and sustainability. Being an interdisciplinary team, their projects are influenced by ideas from architecture and urban design as well as mechanical engineering, informatics and horticulture.  

Peter Sänger, COO of Green City Solutions, talks to CORPUS about the CityTree and its concept, provides insight into the project’s early days and shares with us what drives him and his co-founders.

CORPUS: Mr. Sänger, the idea of CityTrees is right in line with today’s thinking – but how did it come about?

PETER SÄNGER: It all started in 2013, when we were sharing our ideas about our personal futures and careers and about the future of cities in general. The WHO report in particular had awakened us to the fact that high air pollution is one of the most critical environmental problems. It is responsible for more than seven million deaths each year and thus for more fatalities than road accidents. And even if the problem is best-known from Asia, it still affects London, Paris, and Rio de Janeiro. And there’s a huge imbalance between pollutant emissions and their elimination.

CORPUS: And this is how you arrived at the CityTree?

PETER SÄNGER: First we developed the basic concept of the CityTree and defined its initial features – so we designed it vertically because of the shortage of space in cities. Then we did some research. How can we reduce pollutants? Can plants do this and what kinds of plants do they have to be? With the aid of a startup grant and after a lot of time for thought, we got the project off the ground.

CORPUS: Who are you mainly targeting with your product: Commercial enterprises or municipalities?

PETER SÄNGER: We now know that it’s municipalities. Unfortunately, many cities don’t have any money for new greenery. So we approach larger locally resident businesses and bring them to the table. The CityTree helps cities to act and develop sustainably – and that’s also good news for business.

CORPUS: Your CityTrees can be found in different places worldwide. How does the location affect the selection of plants?

PETER SÄNGER: We know which plants are suitable for which location and draw on our own plant database. This way we can develop our planting strategy – taking account of the climate zone, maximum temperatures, and, of course, special features desired for esthetic or practical reasons. Does the CityTree have to flower in the city’s colors? Or is maximization of air cleaning performance the main goal?

Behind each CityTree lies a planting strategy to assure the plants are suitable for the particular location.

CORPUS: How does the CityTree work? Are the plants alone responsible for cleaning the air?

PETER SÄNGER: A combination of different processes is decisive. Sure, it’s important to choose plants that are capable of absorbing particulates and nitrogen oxides and that cope with them so well that they aren’t destroyed by higher pollution levels. Mosses in particular are not used to the hot and stifling conditions in cities, but the CityTree creates the ideal environment for them. With the aid of integrated sensors, a fully automated watering system obtains all the data and supplies the plants with water and nutrients – even though there are as many as 1,700 plants covering the surface.

CORPUS: How does the Internet of Things (IoT) come into play?

PETER SÄNGER: Of course we want to know the effect of the CityTrees locally and whether they’re working efficiently. So each CityTree has its own Internet connection so that we can obtain data independently of the location and also send data to it. We know its particular environmental performance and can call off further data from particulate and temperature sensors. If necessary, we are capable of making adjustments for the weather. If a heat wave is on its way, we can order extra watering the night before it arrives.

CORPUS: So can CityTrees also collect environmental data for the municipalities?

PETER SÄNGER: A big problem is that most cities have just three or four monitoring stations, which is hardly a blanket network. But this is something we could remedy by furnishing a district in a city with CityTrees. We are currently developing an app for this that also involves local residents, shows environmental effects, and explains how the system works: The AirCare project.

CORPUS: Mr. Sänger – Thank you for the Interview

Biography in brief 
Peter Sänger, born in 1991, completed his Masters in Horticulture at Dresden’s University of Applied Sciences. Alongside his studies, he gathered practical experience in various gardening and landscaping businesses. He has been Managing Partner and COO of Green City Solutions since 2014. In addition, Sänger works free-lance as a consultant and designer for gardening firms.

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