| Summary: | A school environment with good indoor air quality contributes to the children's performance and learning efficacy. This study aims to determine indoor and outdoor PM2.5 concentrations in school environments and its possible sources and exposure levels. Daily measurements of PM2.5 samples were collected for 24 h using low volume samplers from 19 primary schools in densely populated areas of Kuala Lumpur. Chemical species of the PM2.5 were determined for trace metals, water soluble inorganic ions (WSII) and polycyclic aromatic hydrocarbons (PAHs) for both indoor and outdoor. The results showed that classroom indoor PM2.5 levels had an average concentration of 42.0 ± 23.1 μg m−3, which was not much different from outdoor levels, which have an average concentration of 39.9 ± 21.9 μg m−3. However, there was a significant difference between indoor and outdoor chemical constituents for Fe, Zn, Cu, Mn, Na+, B[b]F and B[a]P (p < 0.05). The major components of PM2.5 mass indoors and outdoors were SO42− (3.9% and 3.6%) and NO3− (2.4% and 2.4%), respectively. The results from Positive Matrix Factorization (PMF) identified building materials (34%) as the major source for indoors, while secondary pollutants (38%) were identified as the major source for outdoors. Hazard quotient (HQ) values for all metals were <1 indicated low non-carcinogenic risk to school children, while the excess lifetime cancer risk (ELCR) values were in the sequence of Cr > Ni > Cd > Pb. Overall, PM2.5 concentrations impacted the air quality in schools and posed health risks to children, which means measures need to be taken to reduce PM2.5 pollution in school environments. © 2022 Elsevier Ltd
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