Seasonal variations, sources, and health risks of heavy metals in atmospheric PM 2.5 in Ulaanbaatar, Mongolia

Abstract To assess the seasonal variations, potential sources, and health risks of heavy metals in fine particulate matter (PM 2.5 ), PM 2.5 samples (n = 90) were collected between December 2019 and February 2022 in Ulaanbaatar, Mongolia. Fourteen metals (Al, Ti, Ca, Mg, Fe, As, Co, Sb, Ni, Ba, Cr, Cu, K, Mn, Pb) were determined by inductively coupled plasma mass spectrometer and inductively coupled plasma optic emission spectrometry (ICP-MS, ICP-OES). Results showed that the average annual mass concentration of the PM 2.5 was 62.7 µg m –3 and 13.6 ± 4.2 µg m –3 at urban site in winter and summer, respectively. PM 2.5 in winter exceeded the permissible limit in the Mongolian National Ambient Air Quality Standards (NAAQS, MNS4585:2016) for all days studied 1.1 to 4.6 times. The higher total concentrations of metals occurred in winter, whereas the lower concentrations were observed in summer with the winter to summer ratio of 12 (for summer)-1358 (for winter). Enrichment factor (EF) values high ( > 100 ) indicated that the As, Sb, Cr, Cu, and Pb were mainly from combustion sources. Additionally, source apportionment by PCA identified three major sources for the studied metals: coal combustion, motor vehicles and resuspended dust of crustal source and ash particles. The carcinogenic risk (CR) of three heavy metals (As, Cr and Pb) in Ulaanbaatar exceeded the safe level (1 × 10 -6 ) of exposure for both children and adults in winter, while within the limit of tolerable levels for summer.