PM₂.₅ Concentrations among Rural Biomass-Fuel and Urban Mixed-Fuel Households in Eastern Ethiopia: A Comparative Cross-Sectional Study

Background Household air pollution is an important source of exposure to fine particulate matter (PM₂.₅), particularly in households that rely on solid fuels and traditional cooking technologies. However, direct measurements of household PM₂.₅ concentrations and their temporal and seasonal variability remain limited in Ethiopia. This study assessed household kitchen PM₂.₅ concentrations and examined differences between rural and urban households, seasonal variation, and factors associated with PM₂.₅ concentration in Eastern Ethiopia. Methods A community-based comparative cross-sectional study was conducted among households in selected rural and urban kebeles under the Haramaya University Health and Demographic Surveillance System. A total of 923 households (573 rural and 350 urban) were included. Kitchen PM₂.₅ concentrations were measured continuously using 20 PurpleAir II-Secure Digital (SD) optical sensors for three to five consecutive days per household between January 2023 and December 2024. Twenty-four-hour mean PM₂.₅ concentrations were calculated from minute-level measurements. Seasonal variation was assessed using repeated measurements from 96 kitchens (60 rural and 36 urban) monitored during both wet and dry seasons. Independent and paired t-tests were used to compare rural–urban and seasonal concentrations, respectively. Kernel regression was used to assess factors associated with household PM₂.₅ concentrations. Results The mean 24-hour PM₂.₅ concentration was substantially higher in rural kitchens than in urban kitchens (473 ± 255 µg/m³ versus 80 ± 92 µg/m³), with an observed mean difference of 393 µg/m³ (95% CI: 370–416; p < 0.0001). All rural households used unclean fuels and open-fire stoves, whereas 58.3% of urban households used electricity as their primary cooking fuel. Among the 96 kitchens monitored in both seasons, rural mean PM₂.₅ concentration increased from 343 µg/m³ during the dry season to 732 µg/m³ during the wet season, corresponding to a mean within-kitchen difference of 388 µg/m³ (95% CI: 348–430; p < 0.0001). In urban kitchens, mean concentrations increased from 47 to 105 µg/m³, with a mean difference of 59 µg/m³ (95% CI: 39–78; p < 0.0001). In the adjusted kernel regression model, rural residence was the strongest factor associated with PM₂.₅ concentration (estimate = 383.21 µg/m³; 95% CI: 357.52–406.65; p < 0.001). Rich households had lower concentrations than very poor households (estimate = − 7.80 µg/m³; 95% CI: −14.62 to − 0.84; p = 0.031), while lack of ventilation was associated with higher concentrations (estimate = 4.81 µg/m³; 95% CI: 0.30–9.46; p = 0.040). Clean-fuel use was associated with lower PM₂.₅ concentrations (estimate = − 4.12 µg/m³; 95% CI: −6.48 to − 2.07; p < 0.001). Conclusion Household kitchen PM₂.₅ concentrations were very high, particularly among rural households relying on unclean fuels and open-fire cooking. Concentrations also varied substantially by season, with markedly higher levels during the wet season in both rural and urban kitchens. Rural residence showed the strongest association with PM₂.₅ concentration, while wealth, ventilation, and fuel type showed smaller independent associations. The findings highlight the importance of expanding access to clean cooking energy and appropriate cooking technologies and of considering seasonal and temporal variability when assessing household PM₂.₅ concentration. Future research should incorporate longer monitoring periods, personal exposure assessment, and validation against reference or gravimetric instruments. Clinical Trial Registration Clinical trial registration was not applicable because this was an observational household-based study.