Protective effect of reduced particulate matter exposure on pulmonary function and cognitive performance among school children: a cross-over trial

Children spend substantial time in classrooms, where particulate matter (PM) may adversely affect respiratory and cognitive health. However, the incremental health benefits of higher clean air delivery rate (CADR) or multiple air purifiers under real-world classroom conditions remains poorly understood. We evaluated the effects of air purifier CADR and the number of devices on PM reduction, pulmonary function, airway inflammation, and cognitive performance in schoolchildren. Period crossover intervention trial was conducted over 6 weeks in three classrooms, involving 66 children aged 8–9 years. Participants underwent three 1-week intervention conditions: 1) two devices with a CADR of 520 m 3 /h (higher-CADR/multiple condition), 2) one device with a CADR of 400 m 3 /h (lower-CADR/single condition), and 3) two devices with a CADR of 400 m 3 /h (lower-CADR/multiple condition), each separated by a 1-week washout. PM concentrations were monitored during school hours. Pulmonary function, fractional exhaled nitric oxide (FeNO), and cognitive attention scores were assessed before and after each intervention period. Linear mixed-effects models with false discovery rate correction were used to estimate intervention effects and the associations between PM reduction and health outcomes. In condition-specific analyses, only the higher-CADR/multiple condition was associated with significant improvements in cognitive performance, except for particle number concentration. In contrast, the lower-CADR/single condition was associated with significant reductions in FeNO across all PM size fractions. In between-condition comparisons, the FeNO reduction associated with an interquartile range decrease in PM 1.0 was significantly greater under the lower-CADR/single condition than under the higher-CADR/multiple condition by 29.4% (95% CI: 7.8–55.2%). In pooled analyses across intervention conditions, each interquartile-range reduction in PM was associated with improvements in all health outcomes except forced vital capacity. Higher-capacity air purification may provide greater benefits for children's cognitive performance and pulmonary function, whereas lower-capacity systems may be sufficient to reduce airway inflammation in school settings.