At barely 12 years old, Fredrick Njoroge Kariuki began experiencing breathing difficulties and was later diagnosed with bronchitis, an inflammation of the airways (bronchial tubes) that causes mucus buildup, wheezing, and a persistent cough.
According to doctors, Kariuki’s illness was a result of vehicle fumes, the thick grey exhaust released by matatus and boda bodas on roads.
The experience would inspire a journey that would later see Kariuki and his classmate, Miron Onsarigo, build an invention that went on to win a continental award.
What began as a personal struggle slowly turned into a shared mission between the two students at M-PESA Foundation Academy. While many had grown used to the choking fumes hanging over busy roads and bus stops, Kariuki and Onsarigo could no longer ignore the damage they were causing. For Kariuki, it was the weekly medication and painful memories of struggling to breathe. For Onsarigo, it was watching communities in Kisumu treat illnesses linked to pollution as something ordinary. Together, they started asking a simple question during their chemistry lessons: what if the same materials people throw away every day could be used to clean the air they breathe?
In an attempt to address the problem, they built HewaSafi, a low-cost vehicle exhaust filtration system designed using locally available materials, including maize cobs, coconut shells, steel mesh, recycled battery components, agricultural waste, and living algae.
Five years after Kariuki’s diagnosis, the innovation earned the duo continental recognition after they were named Africa Winners of the 2026 Earth Prize, one of the world’s largest environmental competitions for teenagers.
For the two 17-year-olds, the award represents validation after years of research, testing, setbacks, and persistence. The recognition also sends a message that young Africans can create practical solutions to problems affecting millions of people across the continent. Their journey reflects how personal struggles can evolve into ideas capable of impacting entire communities.
“I did not choose this problem. It chose me,” Kariuki said in an exclusive interview with a Kenyan daily.
“Growing up in Naivasha, 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 noted.
The problem they are trying to solve is difficult to ignore. Across major African cities, thick exhaust fumes have become part of daily life for millions of commuters. Public transport systems continue to rely heavily on aging diesel engines that release harmful pollutants into the air. In many urban centres, people inhale contaminated air every day without fully understanding the long-term health effects. It is this reality that pushed the students to search for an affordable and accessible solution.
Air pollution remains one of the world’s deadliest environmental health threats, with the World Health Organisation (WHO) estimating that the combined effects of household and effects of household and outdoor air pollution contribute to about 6.7 million premature deaths globally every year.
In Africa, rapid urbanisation, fossil fuel dependence, aging transport systems, and industrial emissions continue to worsen air quality in many cities, exposing millions to dangerous levels of pollution daily. In Kenya, the crisis is becoming increasingly visible, particularly in Nairobi, where traffic congestion and vehicle fumes dominate everyday life. Recent findings published in 2024 showed that Nairobi’s annual PM2.5 concentration averages 18.4 micrograms per cubic metre, more than three times the World Health Organisation’s recommended threshold of 5 micrograms. Researchers linked these pollution levels to between 400 and 1,400 premature deaths in the capital in 2021 alone, with vehicle emissions identified among the leading contributors.
These statistics, according to Kariuki, stopped being abstract figures after his experience with bronchitis.
There were days he struggled to breathe comfortably. Hospital visits became part of his childhood. Medication became routine. Yet beyond the discomfort and treatment, one thing stayed in his mind: the source of the problem was everywhere.
The same fumes that triggered his condition continue to float through bus stops, schools, estates, highways, and marketplaces every day.
An estimated 70 per cent of Nairobi’s 4.5 million commuters, for example, rely on matatus for transport, with many vehicles running on old diesel engines with little or no emission controls.
For years, catalytic converters remained one of the recognised solutions to harmful emissions. However, the technology is expensive and inaccessible to many small transport operators.
That gap is what the HewaSafi team believes they are addressing. The students realised that many matatu operators could not afford existing emission control technologies despite understanding the dangers associated with vehicle fumes. They also understood that any successful solution had to be practical enough to fit into Kenya’s public transport system without significantly increasing operational costs. Instead of relying on imported materials, they focused on resources that were locally available and relatively affordable. Their goal was to build a solution that ordinary transport operators could realistically adopt.
“Our filter goes for just Sh16,288,” Kariuki explained.
The system, he said, employs multiple stages of locally sourced materials, including a living algae component, to capture more than 90 per cent of particulate matter and reduce toxic carbon monoxide and carbon dioxide emissions.
The innovation works by inserting the filtration system directly into a vehicle’s exhaust pipe.
“It does the filtering as the vehicle moves,” Onsarigo said.
The design separates exhaust flow into different compartments, each targeting a different pollutant before the fumes are released into the atmosphere.
One of the most unique parts of the invention is the algae component.
“When a wall becomes damp and there is mould on it, that is the algae we use,” Onsarigo explained.
The use of algae introduces an element of bioremediation into the system, helping absorb harmful gases before they are released into the air.
What further distinguishes the invention is its affordability. In many developing countries, environmental technologies often remain out of reach because of high production and maintenance costs. The students wanted to avoid creating another innovation that communities could admire but never afford to use.
They have significantly reduced the cost of production by incorporating agricultural waste, recycled materials, and natural components.
The result was a filtration system that balances both environmental impact and economic practicality.
Existing emission control systems can cost up to Sh50,000, making them unrealistic for many operators in the public transport sector.
The pair carried out pilot tests with matatus operating along Nairobi’s Thika Road corridor. Sensors were installed to monitor air quality readings under real operating conditions.
The results exceeded their expectations. The students had initially hoped to prove that low-cost materials could contribute meaningfully toward reducing vehicle emissions. However, the performance of the filters during pilot tests demonstrated that the concept had even greater potential than they had first imagined. The data strengthened their confidence that the technology could work effectively under real transport conditions. It also gave them stronger evidence as they presented the project to judges, researchers, and potential partners.
According to the students, the filters achieved a 93.3 per cent reduction in PM2.5 emissions, a 42 per cent reduction in carbon monoxide, and a 21.4 per cent absorption of carbon dioxide.
“We all know greenhouse gases are one of the main causes of climate change,” Kariuki said.
“The moment we can filter carbon dioxide, we can reduce the amount of these gases entering the atmosphere,” he added.
For Onsarigo, the project was deeply personal too.
Growing up in Kisumu County, he watched people develop respiratory complications linked to pollution, yet many considered the problem normal.
“Seeing people get sick as a result of fumes from vehicles had become normal back home in Kisumu County,” he said, adding that the “normal” did not feel right to him.
The pair said the project initially started as a school idea before growing into a serious engineering solution.
Like many student innovations, the first conversations around HewaSafi happened in ordinary classroom settings during discussions about pollution and environmental sustainability. At the time, neither of them imagined the concept would eventually attract continental recognition. The deeper they researched the problem, the more determined they became to build something practical. What started as curiosity slowly transformed into a mission driven by both science and personal experience.
They spent months researching existing filtration systems, experimenting with locally available materials, and redesigning prototypes after failed attempts.
Some versions did not work as expected. Others became too expensive to produce. There were also challenges balancing academics with testing and development.
The students credit their chemistry lessons at M-PESA Foundation Academy for shaping the scientific foundation behind the innovation.
“It would be unfair to judge me by my age,” Kariuki said.
“This is not my first project. I have done several things since I was 14.”
Their determination would soon attract international attention. After months of testing, redesigning, and improving the prototype, the students submitted HewaSafi to the Earth Prize competition. Competing against young innovators from different parts of Africa meant their project had to demonstrate both originality and practicality. The judges were particularly interested in the way the students combined environmental science with locally available materials. The project’s strong community relevance also helped distinguish it from many conventional climate solutions.
This year, HewaSafi was shortlisted among Africa’s top student-led environmental innovations under the Earth Prize.
The Switzerland-based Earth Foundation runs the annual competition, which supports young innovators aged between 13 and 19 working on solutions to environmental challenges.
Now in its fifth year, the competition has reached more than 21,000 students across 169 countries.
The judges said what made HewaSafi stand out was not just the concept itself, but the practicality behind it.
“What made their project strong was that they were not presenting only an idea, but a tangible technical pathway using materials that are locally accessible, including agricultural waste and algae,” Agustín Ocaña Escobar, chair of the adjudicating panel, said.
“That combination of realism, experimentation, and potential community impact made us believe this is a project worth backing. I’m really looking forward to seeing where they take it over the next year.”
Winning the Africa regional award came with a $12,500 grant, approximately Sh1.6 million, alongside mentorship opportunities and access to networks that can help scale the technology.
The students noted that the support is arriving at a critical moment. Developing environmental technologies often requires extensive testing, specialised equipment, and access to manufacturing resources. Without financial support, many promising student-led innovations struggle to move beyond the prototype stage.
Despite the promise shown by the project, funding had remained one of their biggest obstacles.
Like many young innovators across Africa, they often struggled to access the resources needed to fully develop their ideas.
M-PESA Foundation Academy provided access to the internet, research facilities, guidance, legal support during the patenting process, and raw materials used in developing the prototypes.
The support, they noted, is a privilege that many young people in Kenya still do not have.
Now, the pair hopes to move beyond prototypes into full production. Their focus is no longer limited to proving the technology works. Instead, they are thinking about manufacturing, partnerships, and long-term sustainability. They want to ensure the filters can be produced consistently and installed across large sections of the public transport industry. Scaling the innovation successfully could significantly reduce harmful emissions in densely populated urban areas.
Their long-term plan is to develop a full product family under the HewaSafi Emission Control System.
The line is expected to include HewaSafi Lite, HewaSafi Pro, and HewaSafi Mobile, each designed for different users and transport categories.
Public transport remains their primary target market.
The students are already in discussions with a matatu sacco and hope to scale testing across more vehicles.
Beyond Kenya, they envision expanding the technology across African cities struggling with dangerous pollution levels.
Their dream is not only to reduce emissions but also to make clean air solutions affordable and accessible.
