2022 No https://doi.org/10.1016/j.scitotenv.2022.156824 Zhang, Ting Asia Observational Epidemiology Study Students Elementary (K-5) Particulate Matter (PM) Ozone (O3) Absenteeism Fine particulate matter Ozone (O3) Children's health Illness-related school absenteeism Hospital visit record Analyzed 687,748 illness-related absences from 2,564 Chinese elementary schools. PM2.5 and O₃ exposure increased risk of absence, with home care cases undercounted in hospital data. Supports pollution control and school-based illness tracking.