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Challenge / Goal

Air pollution can seriously hinder children's health. A study showed that roadside air pollution in London stunts lung growth in children by 12.5%. Furthermore, on high air pollution days, 143 more children with asthma in London experience asthma symptoms than on lower pollution days. 
A busy road runs beside Hampstead Hill School, making air pollution a problem. A key priority of schools is to ensure a safe environment for students during their time at school. Protecting the students from harmful air pollution is therefore of high importance to the school council. 


The independent school has installed two innovative air filters on the playground that use living moss to clean fine dust particles from the air and enrich it with oxygen. These innovative biotech filters combine natural moss with innovative technology. One of these filters, dubbed CityTree, can purify up to 3,500 cubic metres of air per hour — roughly equivalent to the hourly breathing volume of 7,000 people. In addition, a CityTree removes up to 82% of especially harmful fine dust from the air. The positive effects go beyond air purification. Due to the ability of mosses to store large amounts of water, moss filters can also cool the air flowing through them — a refreshing effect that students and teachers will surely appreciate, especially in the warm summer months. 

Citizen participation

The CityTrees on the schoolyard can educate about environmental issues, such as air pollution, and show children how everyone can do something to improve the environment. Furthermore, the children can learn something about technology and biology by understanding how the CityTree cleans the air. Together with the school council we organised a drawing competition with the children and asked them to show us how they imagine the superhero moss in the fight against bad air. Below, you can find a few of the wonderful results.


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Time period

Planning time: 6 months to 1 year

Implementation time: Less than 6 months


Hampstead Hill School

Service providers

Green City Solutions

End users

Students; School Staff

    Main benefits

  • Single access point for information

  • Enhanced data collection

  • Reducing local air pollution

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