The reliance of sub-Saharan African households on inefficient biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More stoves in poorly ventilated kitchens is a major contributor to indoor air pollution and associated health risks. A study by James Kinyua Gitau and co-authors, published in Sustainability, assessed the performance of biochar-producing gasifier cookstoves across 150 smallholder farms in three diverse agro-ecological regions of Kenya: Embu (highlands), Kwale (coastal), and Siaya (mid-lowlands). The research, which included participatory cooking tests with 75 households, quantified the stoves’ impact on indoor air quality, fuel use efficiency, and char production under real-world cooking conditions.

The study compared the gasifier cookstove (a Top-Lit Updraft, or TLUD, model branded “GASTOV”) to the traditional three-stone open fire. The gasifier significantly reduced concentrations of key indoor air pollutants across all sites. The reduction in fine particulate matter (PM2.5​), which is strongly linked to respiratory illness, was most pronounced in Embu, achieving a 97% reduction compared to the three-stone open fire. Reductions in Kwale and Siaya were 79% and 95%, respectively. Despite these large reductions, average PM2.5​ concentrations from the gasifier were still above the 25μg/m3 World Health Organization (WHO) 24-hour limit at all three sites, indicating a need for stove improvement before scaling up. Reduction in carbon monoxide (CO), another major pollutant, was also highest in Embu at 82%. Siaya achieved an 81% reduction, while Kwale’s reduction was 57%. Gasifier-produced CO concentrations were below the 30 ppm WHO critical limit at all three sites. The largest reduction in carbon dioxide (CO2​) was recorded in Kwale at 41%. CO2​ concentrations were below the 5000 ppm permissible exposure limit at all sites.

The gasifier consistently consumed less firewood than the three-stone open fire at all sites. The efficiency calculations demonstrated substantial fuel savings, depending on how the produced char byproduct is valued. The stove converts biomass to char with an efficiency of 17-18%. Siaya showed the highest fuel savings (43% net and 65.2% gross), which is statistically significant and likely due to the limited firewood availability in Siaya, where households prioritize saving what little wood they have. If households use the produced char as a soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More (biochar), they could save 24-43% of fuel compared to the three-stone open fire. If the char is considered a fuel source, the potential savings increase to 42-65%. This reduction in firewood use translates into a reduced burden of fuel collection, which has been shown to be time-consuming and a major source of physical and mental stress.

Between 86% and 100% of households were using the gasifier stove 2–3 months after being issued, with use highest in Siaya (100%) and lowest in Embu (86%). However, there was a high variation in frequency, with some households using it only 1–5 days per week, a practice known as stacking, where multiple stoves are used. The produced char was of good quality, with average moisture content and volatile matterVolatile matter refers to the organic compounds that are released as gases during the pyrolysis process. These compounds can include methane, hydrogen, and carbon monoxide, which can be captured and used as fuel or further processed into other valuable products.   More below FAO-recommended maximums of 30% and 10% respectively, although ashAsh is the non-combustible inorganic residue that remains after organic matter, like wood or biomass, is completely burned. It consists mainly of minerals and is different from biochar, which is produced through incomplete combustion.   Ash Ash is the residue that remains after the complete More content was above the recommended 3% for lump charcoalCharcoal is a black, brittle, and porous material produced by heating wood or other organic substances in a low-oxygen environment. It is primarily used as a fuel source for cooking and heating.   More. Char from Embu had the highest calorific value and fixed carbon, and the lowest ash content. The gasifier’s char byproduct can be used as biochar for soil amendment, a known practice that can improve crop yields and consequently household food security. At all the study sites, the wives were the main cooks and the ones who prepared the firewood for the gasifier. The adoption and frequent use of gasifier cookstoves by households is a viable way to help them tackle the issues of fuel use efficiency, exposure to indoor air pollutants, the burden of firewood collection placed on women, and the expenditure on cooking fuel.

Source: Gitau, J. K., Sundberg, C., Mendum, R., & Njenga, M. (2025). Comparative assessment of gasifier cookstove performance on smallholder farms in three regions in Kenya. Sustainability, 17(13), 5872