Identification of Fine Dust in Schools through Comprehensive Chemical Characterization

The chemical characteristics of particulate matters collected from 53 schools in 2019 through 2022 were closely investigated to determine the main sources of classroom PM_2.5. On average, indoor PM_2.5 measured during class hours distributed from 3.3 μg/m³ to 45.97 μg/m³, and it consisted of 45% of ions, 33% of carbons, 17% of metals and others. The average indoor-to-outdoor ratio (I/O) of PM_2.5 was 0.73. Values for I/O ranged from 0.6 to 0.91 for inorganic elements; 0.3 to 0.8 for ions; 0.50 to 2.69 for elemental carbons (EC), and 0.52 to 8.50 for organic carbons (OC). The linear correlation of indoor EC with concentrations of K⁺ and NO₃⁻ indicates that the contribution of combustion-related sources to classroom PM_2.5 is significant in roadside schools. The findings from this study should help establish construction guidelines for urban schools near high-traffic areas.