Influence of kitchen design, fuel use, and seasonality on household air pollution across agro-ecological zones in Kenya

Household air pollution (HAP) remains a serious environmental health risk, particularly in low- and middle-income countries, where it is strongly associated with non-communicable diseases. In Kenya, interventions have emphasized clean fuels and improved cookstoves, yet persistently unsafe pollutant levels highlight the importance of kitchen design and ventilation in HAP reduction. This study investigated how kitchen design, ventilation practices, fuel use, and seasonal and regional factors influence HAP levels and personal exposures across nine agro-ecological zones in Kenya. A cross-sectional survey sampled 384 households, with 37 monitored for air quality during wet and dry seasons. Household, kitchen, and fuel data were collected using questionnaires, assessments, and 24 h fuel measurements. Indoor and personal exposures were measured with calibrated monitors. Data were processed in R and SPSS, using Spearman’s correlation analysis with significance set at p < 0.05. Findings from 372 households showed significant regional disparities in kitchen characteristics and ventilation practices, including number of doors, chimney presence and type, and window opening during cooking ( p < 0.05). Most households exceeded safe pollutant thresholds in both seasons, with higher pollution intensities in the wet/cold season. Mean 24 h kitchen PM 2.5 concentrations were 463.27 µ g m −3 in the wet/cold season and 265.12 µ g m −3 in the dry/warm season, exceeding the WHO safe limit of 15 µ g m −3 by 30.9 and 17.7 times, respectively. Mean personal CO exposure among cooks was also higher in the wet/cold season than in the dry/warm season (5.09 mg m −3 vs 3.97 mg m −3 ). Significant associations were observed between ventilation and PM 2.5 ( p = 0.037), kitchen floor area and PM 2.5 ( p = 0.047), and daily fuel consumption and PM 2.5 ( p = 0.007). The Lake Agrarian Lowland Region consistently recorded the highest pollutant concentrations and exposures for PM 2.5 and PM 10 ( p = 0.005). Mean kitchen PM 2.5 concentrations were also substantially higher than ambient PM 2.5 concentrations, by 29.5 times in the wet/cold season and 7.9 times in the dry/warm season. Seasonal and regional disparities in HAP are strongly influenced by kitchen design and ventilation. Targeted interventions integrating ventilation behavior and kitchen design, particularly in high-risk zones, are essential for effective HAP reduction and should be prioritized in national clean cooking strategies.