Quantifying indoor PM2.5 levels and its sources in schools: What role does location, chalk use, and socioeconomic equity play ?

This study examines children's exposure to PM_2.5 in the classroom environment of spatially and administratively distributed schools. For this purpose, we monitored PM_2.5 levels inside and outside 40 classrooms in public and private schools located in urban and rural settings, while exploring the magnitude of indoor sources and correlations between the indoor and outdoor environment. A high correlation between indoor and outdoor PM_2.5 levels across most schools was evident (Spearman correlation = 0.82). The usage of chalkboards as well as the re-suspension of settled particles due to indoor activities, high occupancy, and infrequent classroom cleaning increased indoor exposure. Concentrations of indoor PM_2.5 (20–180 μg/m³, and a mean of 62 μg/m³) showed differences between urban and rural as well as between private and public schools. Some rural schools exhibited greater exposure than urban schools, depending on their immediate surrounding environment and their internal PM_2.5 sources. IAQ simulation results indicated that internal sources may be as high 15.9 mg/h. Schools using chalkboards tended to have higher net PM_2.5 sources as compared to schools that had shifted to whiteboards. Among the chalk-based classrooms, the mean net indoor source emission rate for public schools (4.8 mg/h) was significantly higher (>2.5 folds) than that determined for their private counterparts (1.8 mg/h). The consideration of urban versus rural settings, socioeconomic differences, as well as the quantification of the contribution of indoor sources are of significance in the context of improved management of IAQ in schools and protecting school-aged children.