Image: MongabayA 93.3% reduction in PM2.5 particulate emissions. Not from a corporate R&D lab. Not from a billion-dollar startup. From two 17-year-olds, five Nairobi minibuses, and a pile of farm waste. Fredrick Njoroge Kariuki and Miron Onsarigo, students at M-PESA Foundation Academy in Kiambu County, Kenya, built HewaSafi — Swahili for "clean air" — a vehicle exhaust filtration system tested on matatus along the Thika Road corridor, with sensors recording pollution data every six hours under real traffic conditions, according to Mongabay. The results have implications well beyond Nairobi.What's Inside HewaSafiFive compartments, a Kenyan farm's worth of materials, and one surprisingly elegant piece of engineering.Cracking open the device reveals something like a Lego set assembled from local harvest scraps. Five sequential filtration compartments channel exhaust through:AdvertisementAdvertisementMaize cobs and coconut shells converted into activated carbon mediaSteel meshCopperRecycled battery componentsLiving spirulina algae that absorb gases at the back endPM2.5 — particles fine enough to slip past your lungs and into your bloodstream — gets trapped across multiple stages rather than leaving one filter to do all the work.Kariuki has had chronic lung disease since age 10 and still takes weekly medication — this was personal before it was a prototype.The Numbers That MatterThe cost and performance figures are where HewaSafi's case becomes hard to dismiss.At 16,288 Kenyan shillings (~$126), HewaSafi costs less than a third of conventional filters in this market, which run around 50,000 KES (~$390). The performance backs up the price:AdvertisementAdvertisement93.3% PM2.5 reduction42% drop in carbon monoxide21.4% CO₂ absorptionEarth Prize panel chair Agustín Ocaña Escobar called it "a tangible technical pathway using materials that are locally accessible, including agricultural waste and algae," according to Mongabay. The project won the Africa regional Earth Prize 2026, netting $12,500 and a shot at the $100,000 global award.Africa's transport sector has long needed scalable, affordable emissions solutions that don't depend on imported hardware. HewaSafi's expansion playbook is straightforward:1,200 units produced through local artisansA partnership with a matatu owners' association representing around 8,000 driversInstallations on roughly 200 vehicles in the next phaseAdvertisementAdvertisementThe longer-term vision is a franchise model, letting entrepreneurs across Africa manufacture filters using whatever agricultural waste grows locally — think of it as the Substack model for cleantech, but with coconut shells instead of newsletters. Worth flagging: pilot results haven't undergone independent peer review, and long-term durability data remains pending.The WHO estimates air pollution kills approximately 4.4 million people prematurely each year. HewaSafi won't fix that alone. But the raw materials for a meaningful start were already sitting in the field, waiting to be burned or discarded. Kariuki's goal is blunt: no other child should suffer what he did.From the coolest cars to the must-have gadgets, GadgetReview's daily newsletter keeps you in the know. Subscribe - it's fun, fast, and free.
