Atmospheric Signature and Potential Sources of Rare Earth Elements in Size-Resolved Particulate Matter in a Megacity of China

ABSTRACT

The atmospheric signature and potential sources of rare earth elements (REEs) in ambient particulate matter (PM) collected at urban (ZH) and background sites (ZWY) between February 2011 and January 2012 in the Yangtze River Delta region were investigated in this study. The average total concentrations of REEs for TSP, PM₁₀ and PM_2.5 were measured to be 11.98, 9.37, 2.24 ng m^–3 in ZH, which were 1.9, 1.8, 1.3 times higher than those measured in ZWY. The size distribution pattern of the REEs shows that they are significantly fractionated into coarse particles (e.g., approximately 50% in PM_2.5–10). However, La, Ce and Sm are even more enriched in PM with respect to each other and other REEs. It is also shown that Ce contamination is prevalent throughout the study area, which is particularly exemplified in the finer particulate matter fraction; this significant Ce contamination could be primarily attributed to vehicle emissions. Additionally, the REEs’ pollution events during the sampling campaign were identified by the time series of the REE ratios. And the contaminations of La, Sm and Ce show clearly wind-induced variations. The enrichment factors for REEs indicate that La, Ce, Nd and Sm originated from a mix of anthropogenic and natural emission sources with small EF values.