2024 No Trace elements in outdoor and indoor PM2.5 in urban schools in Xi'an, Western China: characteristics, sources identification and health risk assessment https://pubmed.ncbi.nlm.nih.gov/35978258/ Wang, Runyu Asia Observational Teachers Students Middle/Jr High (6-8) Particulate Matter (PM) Heavy metals Dust Indoor/outdoor fine particulate matter (PM2.5) Heavy metals middle school Health risk assessment In two Xi’an middle schools, indoor and outdoor PM2.5-bound elements were elevated, with Ca, K, Fe, S, Zn, and Cl most abundant. Sources included coal, dust, and industry. Health risks from As and Cr were noted, with non-cancer risks exceeding safe levels. 2022