Chemical composition and health risk indices associated with size-resolved particulate matter in Pearl River Delta (PRD) region, China

Size-resolved particulate matter (PM) was collected at the Heshan Super-Station in the Pearl River Delta (PRD) region, China, to evaluate their chemical characteristics and potential health risks. The chemical mass closures illustrate that the dominant fraction in coarse (2.5 μm < Dp < 10 μm) PM was dust, while organic matter made up a substantial portion of both fine (0.1 < Dp < 2.5 μm) and ultra-fine (Dp < 0.10 μm) PM fractions. The size distribution of most PM components varied substantially. PM, NO3−, K+, Cl−, Na+ and most of the transition/redox metals displayed bimodal size distributions with the dominant peak at 0.32–0.56 μm plus a small peak at 1.8–3.2 μm. In contrast, unimodal size distributions were found for the rest of the species, such as water-soluble organic carbon (WSOC), NH4+, and SO42− and the majority of oxyanion metals with a single peak at 0.32–0.56 μm, and Mg2+, Ca2+, and dust tracer elements which mainly accumulated in coarse particles. Based on the crustal enrichment factor (CEF) analysis, Cd, Zn, Sb, Sn, As, Pb, Mo, Cu, and Cr primarily originated from anthropogenic activities, while Ti in all size fractions and Sr, Mg, Na, and Fe in fine and ultra-fine particles were mainly emitted from natural sources. The potential health risk assessment of trace metals was performed using the hazard quotient (HQ) and excess lifetime cancer risk (ELCR) indices. Although the adverse health effects of most metals were limited, significant potential carcinogenic risks were found for As and Cr in both fine and coarse particle size fractions, which contributed more than 95% of total ELCR. Therefore, considering that these two elements were mainly emitted from industrial processes, improvements in air quality and health risks in the PRD region can be largely achieved by reducing the emissions of local industrial sources.