Children's exposure to particulate matter air pollution in indoor and outdoor school environments in the city of Bukavu, Democratic Republic of the Congo, Central Africa

School-age children are particularly vulnerable to the negative health impacts of air pollution, since early exposure can have lasting effects. This is especially alarming in sub-Saharan Africa, where children frequently exposed to diesel fumes, biomass burning, and resuspended road dust emissions during their travel s to and fromschools. Although these health risks are well known, research on children's exposure in school settings is limited. This study, the first of its kind in the Democratic Republic of the Congo (DRC), simultaneously measured indoor and outdoor concentrations of fine (PM 2.5 ) and coarse (PM 10 ) particulate matter across three primary schools in different land-use contexts. Measurements were conducted continuously for three months using low-cost sensors. Across schools, mean PM 2.5 levels were 60.0–74.5 μg/m 3 indoors and 54.5–85.4 μg/m 3 outdoors, while PM 10 ranged from 71.0 to 82.2 μg/m 3 indoors and 58.0–91.1 μg/m 3 outdoors. These average levels exceeded the World Health Organization's 24-h guideline limits by more than 5 times, highlighting a serious public health issue for schoolchildren in Bukavu. Daily data showed that PM 2.5 levels peaked in the morning and afternoon, often exceeding 140 μg/m 3 . The indoor-to-outdoor (I/O) concentration ratios ranged from 0.8 to 1.1 for PM 2 . 5 and from 0.8 to 1.2 for PM 10 , indicating that outdoor sources have a predominant influence on indoor air quality. Higher indoor concentrations in some schools were linked to nearby traffic, unpaved roads, and poor classroom ventilation. This study highlights the short-term elevated levels of particulate matter in school environments and the potential exposure of schoolchildren to both indoor and outdoor air pollution, providing a valuable baseline for future research in the Democratic Republic of the Congo. The findings emphasize the urgent need for school-based interventions, improved urban planning, and the incorporation of air quality considerations into national education, environmental, and public health policies.