Cooking with biomass fuel is an important source of household air pollution in developing countries, and a leading risk factor for ill-health. Although various designs of “improved cookstoves” (ICS) have been promoted as interventions in these settings, few of them have undergone in-field evaluation, partly due to the challenge of conducting field measurements in remote settings.

This study assessed the change in carbon monoxide (CO) exposure following the replacement of the traditional three-stone fire with a popular ICS in 49 homes in Western Kenya. It also assessed the suitability of using kitchen CO as a proxy for kitchen PM2.5. Reduction in 48-hour mean kitchen CO was 3.1 ppm (95% confidence interval: − 8.1, 1.8) and in personal CO was 0.9 ppm (95% confidence interval: − 4.3, 2.6) following stove replacements.

Overall, 48-hour kitchen and personal CO exposures were lower after stove replacement (28% and 12%, respectively) but with wide confidence intervals that also suggested possible increases in exposure. There were statistically significant reductions in peak kitchen and personal CO concentrations represented by the 8-hour 95th percentile: reductions of 26.1 ppm (95% confidence interval: − 44.6, − 7.6) and 8.0 ppm (95% confidence interval: − 12.2, − 3.8), respectively. This is equivalent to a 53% reduction in kitchen CO and a 39% reduction in personal CO.

The study found good correlation between kitchen CO and PM2.5 concentrations overall (r = 0.73, n = 33 over averaging periods approximating 1 day), which varied by time of day and exposure setting. These variations limit the applicability of CO as a proxy measure for PM2.5 concentrations. A combination of interventions, including better designed stoves, improved ventilation and cleaner fuels, may be needed to reduce household air pollution to levels that are likely to improve health.

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