Size distribution and source-specific risks of atmospheric elements in Dalian, a coastal city in north China

Trace elements in particles play an essential role in particle-related health and environmental effects and were recognized as primary source tracers. An understanding of the size-segregated elemental composition is critical for accurate source attribution and risk evaluation. The present study investigated the characteristics of 28 elements in the size-fractioned particles of a coastal megacity in north China. The size distribution of element concentration posed bimodal peak mode, and the proportion of most trace elements tended to increase with the decreasing particle size, especially toxic metals like Hg, Ga, Tl, As, Pb, Se, and Cd. Source attribution based on the size-segregated concentrations was conducted by positive matrix factorization. Natural sources such as crust and sea spray aerosol dominated the trace element concentration in the large particles, while anthropogenic sources such as traffic, biomass, coal combustion, and industry contributed the majority in the fine particles. The source-specific exposure risk calculation based on the size-segregated dataset showed a noncarcinogenic risk (HQ) of 6.62 for children, mainly contributed by Tl and As from biomass burning, petrochemical refining, and coal combustion. Compared with larger particles, the finer particles generated a higher HQ and carcinogenic risk, especially particles smaller than 0.49 mu m. Fine particles primarily emitted from the petrochemical industry and coal combustion brought out the largest HQ, while fine particles from vehicle traffic and the petrochemical industry contributed the largest carcinogenic risk. Transport of sea spray aerosol contributed a considerable amount of the carcinogenic risk in the coastal urban area.