Measurement of black carbon exposure in urban classrooms during rush hours

Traffic-related air pollutants are predominantly emitted in urban environments; therefore, analyzing their impact on indoor air quality (IAQ) is important. Effectively managing IAQ is vital, given the extensive duration individuals, particularly students, spend indoors. This study conducted a quantitative assessment of black carbon (BC) and indoor and outdoor particulate matter (PM_2.5, particles with diameter ≤2.5 μm) concentrations in five South Korean classrooms to determine the root cause and effects of traffic-related air pollutants on indoor environments. The research specifically focused on indoor BC levels during rush hours, that is, periods marked by increased traffic volume. The analysis revealed that the mean indoor and outdoor BC concentrations in the five classrooms were measured at 1.03 (95% CI: 0.69, 1.36) and 1.38 (95% CI: 0.79, 1.96) μg/m³, respectively, while the mean PM_2.5 concentrations were measured at 17.07 (95% CI: 12.92, 13.62) and 29.89 (95% CI: 10.88, 48.89) μg/m³, respectively. The indoor-to-outdoor (I/O) ratio of BC in the five classrooms during the occupied period was 0.77 (95% CI: 0.69, 0.84) and 0.62 (95% CI: 0.51, 0.72) for PM_2.5. During the unoccupied period, the I/O ratio of BC was 0.68 (95% CI: 0.63, 0.72) and 0.53 (95% CI: 0.42, 0.63) for PM_2.5. The rise in urban traffic increased the BC outdoor level by 47% and the PM_2.5 concentration by 13%. Classrooms situated closer to roadways had higher BC levels than those located at a greater distance. During rush hours, the BC concentration in the classroom closest to the major road was 2.03 (95% CI: 1.78, 2.27) μg/m³, while the furthest classroom recorded a concentration of 0.88 (95% CI: 0.79, 0.96) μg/m³. During commuting times, classroom BC concentrations increased by up to 5.86 μg/m³ owing to student door-opening activities, increasing the I/O ratio by approximately 20%. Consequently, the average BC concentration in classrooms during rush hours was approximately double that recorded during non-rush hours (0.73 μg/m³). These findings are instrumental in developing strategies to enhance IAQ in educational settings and guiding urban planning decisions regarding the location of schools.