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Driven by a Personal Problem 

Urban air pollution in Kenya is a widespread issue. A study conducted in 2024 revealed that Nairobi, Kenya’s capital, had air particulate pollution (PM2.5) 3.7 times higher than mandated by the World Health Organization. 40% of this pollution was attributed to road transportation. With poor public transit systems, the majority of people travel by boda boda (motorbikes) or matatus (minibuses). Matatus in particular are, on average, 16 years old. Their low fuel efficiency and aged engines contribute significantly to air degradation in the city. 

Even in smaller towns, the problem is still prevalent. When Kariuki was 12 years old, doctors diagnosed him with bronchitis. Growing up, he was constantly exposed to exhaust fumes from nearby vehicles. The air pollution resulted in bouts of coughing and difficulty breathing. “My bronchitis got so bad that I stopped thinking of air pollution as an environmental issue and saw it as something being committed against us,” he said. 

Onsarigo, who grew up in a different city, noticed the same problem where he lived too. “Seeing people get sick as a result of fumes from vehicles has become normal back home in Kisumu County,” he added. “The ‘normal’ did not feel right to me. I wanted to do something about it,” and so they got to work. 

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Innovation with Local Materials 

HewaSafi – Swahili for “clean air” – is a low-cost vehicle exhaust filtration system designed by the teenagers to trap pollutants at the source. By attaching the device directly to the vehicle’s tailpipe, the engine fumes are forced through a chamber that filters out particulates. It contains five filtration compartments; each layer absorbs a different element. 

The device is made from steel mesh, copper, recycled batteries, and agricultural products like corn cobs, coconut shells, and algae. The metal and old batteries neutralize and filter out heavy metallic elements. Whereas the agricultural waste is carbon-rich and acts as an absorption filter, capturing fine particulate matter and soot. Finally, HewaSafi also uses living Spirulina algae, which absorb carbon dioxide via natural biological processing. Using recycled materials and biological waste means the filter only costs $125 to manufacture. 

The results are remarkable. According to the team’s pilot testing, HewaSafi reduced PM2.5 from vehicle exhausts by 93.3%. The device also reduced carbon monoxide by 42% and CO2 by 21.4%. In the next stages, HewaSafi will undergo thorough independent testing to substantiate their evidence.

“From a health perspective, any initiative that leads to reduction of health-damaging pollutants like PM2.5 and CO is commendable and will be supported,” Betty Koech, research officer at Clean Air Africa, told UrbanGeekz exclusively. 

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The Future of Cleaner Air in Kenya 

More than a school project, HewaSafi is looking to scale. Onsarigo and Kariuki entered the African Earth Prize and won a regional prize of $12,500 to start the next phase of production. With this investment, they plan to produce the next 1,200 units alongside local artisans. Through partnering with a local matatu association, they want to install HewaSafi on roughly 200 vehicles. When they advance to commercially selling the filtration device, the team plans to offer payment plans to lower the initial cost of their green tech. 

Beyond solving the problem in their immediate surroundings, Onsarigo and Kariuki are also thinking about how to expand across Africa. Rather than using the same formula in each country, the two are considering ways to adapt the model, allowing entrepreneurs across the country to use whatever agricultural waste is locally available to them.

As Kenya continues to confront the health and environmental consequences of urban air pollution, the project offers an early example of how locally available materials could be used to develop lower-cost climate and clean-air technologies.

The young, tech-savvy generation is building, coding, and innovating solutions for a better tomorrow. Onsarigo and Kariuki are proving that you don’t need expensive materials to build solutions that could mean cleaner air for everyone. 

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