Innovation & Technology

Of Course, Nature Can Save Our Hot, Polluted Cities:
Meet the CityTree

Green City Solutions has combined air-purifying moss with IoT technology in a smart biotech filter that can clean 82% of fine dust particles from the air, and humidify and cool it by up to 4°C.

By Scarlett Buckley | Published 1 year ago | About a 4 minute read

Image: A CityTree in Cork, Ireland | Green City Solutions

Global air quality has been declining over the years; and the effects are hard to ignore: According to the World Health Organization, 99 percent of the population is now breathing in polluted air; and it is responsible for 7 million premature deaths annually.

More than 50 percent of the population lives in cities — which are hotspots for air pollution — a number predicted to reach 68 percent by 2050. Incredibly harmful to human health, air pollution is linked to public health concerns including cancer, cardiovascular disease, respiratory diseases, diabetes mellitus; and various reproductive, neurological and immune disorders.

Urban areas can also become “heat islands” — where temperatures are higher, thanks to the abundance of concrete surfaces absorbing, rather than reflecting, the sun's heat. With climate change, heat-island temperatures will be hotter each year; and as more people migrate to cities, the number of people vulnerable to the health effects of air pollution will also increase.

German startup Green City Solutions (GCS) is, much like its name suggests, on a mission to clean city air by bringing nature back. Combining pollution-absorbing plants with digital technology, Green City’s solution merges air-purifying moss with smart sensors, active ventilation and irrigation technology. The company spent years researching and developing its solution — with a key breakthrough involving the identification of the most suitable species of moss (out of 16,000 potential candidates), which is now growing at the company’s vertical moss farm.

“As the first green plant on our planet, moss can absorb and bind particles from the air like no other plant. It stores water and serves as a natural air conditioner through evaporative cooling,” founder and CEO Peter Sänger told Sustainable Brands®. “Because it absorbs everything it needs via the air, it can reduce pollutants like fine dust. Most of the absorbed fine dust is metabolized, which means that the moss grows on the dirt in the air. These properties make moss a perfect ally in the fight against air pollution and heat islands in cities.”

Green City’s solution works with the help of vertical moss mats inserted into biofilters. A ventilation system then draws in polluted and heated city air and passes it through the dense layer of moss, which leaves the air much cleaner and cooler — the filters humidify the air and cool it by up to 4° Celsius, creating fresh air zones. The system can help drastically improve urban air quality — where the population is dense and where greenery might have a hard time taking root thanks to all the paved surfaces.

The moss-filter technology is integrated into different formats that offer multiple benefits in areas where space may be limited: The CityTree with its seating, for example, also functions as street furniture; while the CityBreeze combines the moss filter with a large, digital screen that can serve as a sustainable advertising or information pillar. They can also work as charging stations for e-bikes or electric vehicles, or provide an open WLAN hotspot.

CityBreeze in Leipzig's Allee-Center | Image credit: Green City Solutions

With the cleverly integrated IoT technology, GCS can supervise the status and performance of every filter in the field. The technology ensures the vitality of the moss and makes the moss filter a low-maintenance, long-lasting system. The technology also makes it possible to measure the amount of air filtered and collect relevant data on air quality.

“Since air pollution is not always visible to the human eye, we visualize air-quality-related data and provide them as part of performance reports to our customers,” Sänger explains. “The temperature and air humidity of the inflowing and outflowing air can also be determined. The data can also be shown on screens right on the biofilter itself. This helps a great deal to make an intangible problem more relatable for the public.”

CityTrees have been successfully planted in cities including Berlin, Leipzig, London and Cork, Ireland. In third-party assessments, GCS was able to demonstrate a fine-dust filter effect of up to 82 percent for its moss filters, with air improvement still detectable at a distance of 5 meters. Sänger says the CityTree can clean the air for 10,000 people per hour.

GCS’ goal is for its products to be part of a multipronged solution to provide clean and fresh air for 500 million people by 2030 and contribute to the decarbonization of urban infrastructure.

“Our products can be an important element in the transformation of cities to be healthier, more sustainable and climate resilient. Of course, there is no single cure-all here — ideally, our products are always embedded in an overall strategy consisting of various measures. For this purpose, we like to work together with different stakeholders during the implementation to achieve an optimal result.”