Predictors of particulate matter 2.5 and carbon monoxide levels in government primary schools within Kampala, Uganda

Abstract

Exposure to fine particulate matter (PM₂.₅) and carbon monoxide (CO) poses serious health risks, particularly for children with developing respiratory systems. In Kampala, Uganda, schools are vulnerable to emissions from traffic, industries, biomass fuel use, and open waste burning, yet limited research has examined pollutant levels and their predictors in government primary schools. This study assessed the levels of PM₂.₅ and CO in government primary schools in Kampala and examined the predictors of their concentrations. A convergent parallel mixed-methods design was employed, incorporating quantitative and qualitative data from 39 government primary schools across three divisions. Air quality was measured in five classrooms, one playground, and one kitchen in each school using calibrated portable monitors(Temtop M2000C for PM₂.₅; AS8700A for CO) at three time points daily. Structured questionnaires were administered to 74 school staff to capture school-level characteristics and potential predictors. Quantitative data were complemented by focus group discussions with 23 pupils and detailed field observations. The data were analysed in Jamovi (v2.6.44) using descriptive statistics, t-tests, ANOVA, and regression models to identify significant associations, while qualitative data were analysed thematically. Results: PM₂.₅ concentrations surpassed the WHO 24-hour guideline reference value (15 μg/m³) across all measured school environments (p < .001) with mean differences ranging from 22.5 µg/m³ to 221.7 µg/m³. Morning kitchen CO levels surpassed the WHO guideline reference value (4 ppm) by 11.6 ppm (p < .001). Descriptive assessment against the 2024 Uganda National Air Quality 24-hour guidelines ( 35 μg/m³ for PM₂.₅; 6.11 ppm for CO) similarly showed exceedances for PM₂.₅ across all measured school environments and Morning CO levels in kitchens, respectively. Field observations revealed that biomass fuel use in school kitchens was nearly universal (97.4%), with firewood being the primary fuel (92.3%). Chalk dust was present in all classrooms (100%), and dust from unpaved playgrounds was noted in 76.9% of schools. Structured questionnaires and FGDs highlighted several perceived risk factors, including dusty playgrounds, proximity to busy roads, waste burning within or near school premises, and heavy reliance on biomass fuels in school kitchens. Qualitative data highlighted health concerns, limited resources, and challenges with policy implementation, with a major lack of funding and infrastructure cited as barriers to effective interventions. Linear mixed-effects regression analysis identified time of day as the strongest predictor of both pollutants, with morning concentrations significantly higher than afternoon levels (PM₂.₅: β = 0.586, p < .001; CO: β = 0.742, p < .001). Measurement location explained 25.1% of PM₂.₅ variance and 64.2% of CO variance, with kitchens consistently showing the highest exposures. PM₂.₅ and CO concentrations in Kampala government primary schools surpassed safe thresholds, with several modifiable factors under the time of day as a significant predictor of their levels. Strengthening interventions such as improved ventilation, cleaner cooking fuels, and traffic management around schools is essential to protect children’s health.