2021 No https://www.sciencedirect.com/science/article/abs/pii/S0304389421004945 Heo, Sujeong Asia Experimental Elementary (K-5) Dust School air quality Particulate matter (PM) Fine particulate matter (PM 2.5) Emission source Chemical constituent The indoor PM2.5 was lower than that of the outdoors as indicated by an I/O ratio of 0.52–0.92 based on mass concentration, and it was maintained below the National Guideline. Heavy metals such as Cr, Mn, Ni, Cu, Zn, As, Sn and Pb were lower in indoor PM2.5 than outdoors. On the contrary, carbons including OC and EC were higher in indoor PM2.5. As a result of source apportionment analysis, an outdoor emission source was responsible for 58.5% of the classroom PM2.5.