Size distribution and source apportionment of airborne metallic elements in Nanjing, China

In order to investigate the temporal and spatial variations and the size distribution of atmospheric particulate matter and associated airborne elements, atmospheric particulate matter (TSP, PM_2.5 and size-segregated aerosol particles) were collected monthly for one year from the traditional central district and suburbs of Nanjing, China. Source identification of airborne elements in PM_2.5 was carried out using multivariate statistical analysis. The annual mass concentrations ranged from 49.4 μg/m3 to 391 μg/m3, with a mean of 135 μg/m³ for TSP and from 20.4 μg/m³ to 200 μg/m³ with a mean of 80.5 μg/m³ for PM_2.5. The distribution of annual size-segregated aerosol particles showed a bimodal pattern of coarse and fine particle fractions. Spatial and seasonal variations of elemental composition in atmospheric particulates were observed. The major elements (A1, Ca, Fe, Mg, Na and Mn) were mainly distributed in coarse fractions, while toxic elements, such as As, Cd, Pb and Zn, were significantly enriched in the fine fractions. The enrichment factor indicated anthropogenic inputs of As, Cu, Ni, Pb and Zn in the TSP and PM_2.5 examined in this work. Four potential sources for PM_2.5 were identified by principal component analysis. The source contributions calculated using absolute principal component scores were 37.5% for the first component, 34.1% for the second, 9.0% for the third and 19.8% for the fourth. The Na/Cr/Cu component identified by principal component analysis was divided into Na/Cr and Cu groups using R-mode cluster analysis of PM_2.5, and the Ti in the fourth component was assigned to Cluster 2, indicating a statistical difference in airborne metallic elements. The results of the investigation of element composition, size distribution, and source apportionment carried out in this work can help to better understand and manage the effects of these aerosols on health and air quality.