Respiratory Benefits of Multisetting Air Purification in Children

Importance: Particulate matter exposure has been linked to impaired respiratory health in children, but the respiratory benefits of air purification have not been fully elucidated. Objectives: To assess the respiratory health outcomes among children exposed to multisetting air purification vs sham purification. Design, Setting, and Participants: This cluster randomized, double-blind, crossover trial was conducted among healthy school-aged children (10-12 years) in China from April to December 2021. Data were analyzed from December 2021 to July 2024. Interventions: A multisetting (both in classrooms and bedrooms) air purification intervention compared with sham purification in a 2-stage intervention with more than 2 months (76 days) for each period and a washout period (88 days) to estimate the respiratory benefits of air purification. Main Outcomes and Measures: The primary outcomes were pulmonary function, airway inflammation markers, and metabolites in exhaled breath condensate (EBC) before and after the air purification intervention. Linear mixed-effects models were used to estimate the respiratory benefits of children related to air purification. Differential metabolites in EBC were identified using metabolomics analysis to explore their possible mediation roles. Results: A total of 79 children (38 male [48%]; mean [SD] age, 10.3 [0.5] years) were included in the statistical analyses. During the study period, the mean (SD) concentration of outdoor fine particulate matter (PM2.5) at the school site was 32.53 (24.06) μg/m3. The time-weighted personal PM2.5 concentration decreased by 45.14% during the true air purification period (mean [SD], 21.49 [8.72] μg/m3) compared with the sham air purification period (mean [SD], 39.17 [14.25] μg/m3). Air purification improved forced expiratory volume in 1 second by 8.04% (95% CI, 2.15%-13.93%), peak expiratory flow by 16.52% (95% CI, 2.76%-30.28%), forced vital capacity (FVC) by 5.73% (95% CI, 0.48%-10.98%), forced expiratory flow at 25% to 75% of FVC by 17.22% (95% CI, 3.78%-30.67%), maximal expiratory flow at 75% of FVC by 14.60% (95% CI, 0.35%-28.85%), maximal expiratory flow at 50% of FVC by 17.86% (95% CI, 3.65%-32.06%), and maximal expiratory flow at 25% of FVC by 18.22% (95% CI, 1.73%-34.70%). Fractional exhaled nitric oxide in the true air purification group decreased by 22.38% (95% CI, 2.27%-42.48%). Several metabolites in EBC (eg, L-tyrosine and β-alanine) were identified to mediate the effect of air purification on respiratory health. Conclusions and Relevance: This randomized clinical trial provides robust and holistic evidence that indoor air purification notably improved pulmonary health in children, highlighting the importance of intensified indoor air purification in regions with high air pollution levels. Trial Registration: ClinicalTrials.gov Identifier: NCT04835337.