Characterization of trace elements and Pb isotopes in PM2.5 and isotopic source identification during haze episodes in Seoul, Korea

Abstract

Trace elements in fine particulate matter (PM2.5) exacerbate human health problems owing to exposure to PM2.5 and its toxic components. Samples of PM2.5 collected in Seoul, Republic of Korea, during typical haze episodes between November 2017 and April 2018, were analyzed for trace elements and Pb isotopes to characterize PM2.5 trace elements and their sources. The concentrations of Cu, Zn, As, Cd, Sb, Tl, and Pb showed statistically significant increases with ambient PM2.5 levels under their negative relationships with wind speed. High enrichment factor values provided evidence of significant inputs from anthropogenic sources. We assigned the dominant source regions of PM2.5 mass and chemical composition during individual sampling periods by coupling the Pb isotopic composition with the air mass back trajectories. The results identified three major categories of domestic, Chinese, and mixed domestic/Chinese source contributions, accounting for about 39%, 38%, and 21%, respectively, during the entire sampling period, which reflects a significant Chinese contribution. Principal component analysis (PCA) identified the major domestic sources for individual elements: coal/oil combustion and vehicle exhaust (Zn, As, Cd, Sb, Tl, and Pb), non-exhaust traffic emissions (Cu and Sb), and soil/road dust (Fe and Mn). Using a Pb isotopic mixing model, the relative contributions from coal combustion, oil combustion, and vehicle exhaust to associated trace elements were estimated to be 35 ± 11%, 35 ± 8%, and 29 ± 16%, respectively. Our results highlight that beyond addressing climate change, driving the transition from fossil fuels to renewable energy sources in the power, heat, and road transport sectors can help greatly reduce air pollution and achieve healthy environment.