Reduced Black Carbon Concentrations following a Three-Year Stepped-Wedge Randomized Trial of the Wood-Burning Justa Cookstove in Rural Honduras

Household air pollution from cooking-related biomass combustion remains a leading risk factor for global health. Black carbon (BC) is an important component of particulate matter (PM) in household air pollution. We evaluated the impact of the engineered, wood-burning Justa stove intervention on BC concentrations. We conducted a three-year stepped-wedge randomized controlled trial with six repeated visits among 230 female primary cooks in rural Honduras. Participants used traditional stoves at baseline and were randomized to receive the Justa after visit 2 or after visit 4. During each visit, we measured 24 h gravimetric personal and kitchen fine PM (PM2.5) concentrations and estimated BC mass concentrations (Sootscan Transmissometer). We conducted intent-to-treat analyses using linear mixed models with natural log-transformed 24 h personal and kitchen BC. BC concentrations were reduced for households assigned to the Justa versus traditional stoves, e.g., personal BC geometric mean (geometric standard deviation) of 3.6 μg/m3 (6.4) versus 11.5 μg/m3 (4.6), respectively. Following the intervention, we observed 53% [95% confidence interval (CI) of 35-65%] lower geometric mean personal BC concentrations and 76% (95% CI of 66-83%) lower geometric mean kitchen BC concentrations. The Justa stove intervention substantially reduced BC concentrations, mitigating household air pollution and potentially benefiting human and climate health.