Elevated Anthropogenic Contributions to Trace Elements in Marine Aerosols Compared to Coastal Qingdao in Eastern China

Trace elements (TEs) in aerosols over offshore eastern China originate from both terrestrial and marine emissions. However, their variations with source regions remain poorly understood. During spring and summer 2018, PM_2.5 samples were collected at Qingdao, a coastal city in eastern China, and adjacent Bohai and Yellow Seas. TEs were quantified and analyzed by source region, followed by source apportionment. In spring, TE concentrations were significantly higher over land. Crustal dust contributed 39.2–77.8% of Fe, Mn, Cr and Ni; while waste and industrial emissions contributed 29.4–70.1% of Cu, Zn and Pb. Westerly winds conveyed anthropogenic TEs offshore, with coal combustion contributing 25.9–61.4% to As, Cd, Pb, Zn and Cr, and oil combustion contributing 58.6–84.4% to V and Ni in marine aerosols, indicating efficient long-range pollutant transport. In summer, dust influence declined. Biomass burning contributed 38.2–46.3% of Zn, Cd, Pb and Cr, while vehicular emissions dominated As and Cu (41.7–57.3%) at Qingdao. Over marine areas, anthropogenic elements (Zn, As, and Cd) occasionally exceeded coastal levels, with coal combustion remaining dominant (40.8–75.5%). Ship emissions became especially prominent, contributing 79.3% of V and 63.3% of Ni offshore. Southeasterly winds transported ship-derived pollutants coastward, markedly increasing Fe (21.2%) and Mn (14.0%) compared to spring (1.9% and 1.8%, respectively). These results reveal distinct seasonal shifts in TE source across land-sea gradients, highlighting growing anthropogenic impacts, particularly from coal combustion and maritime shipping on marine aerosols. Quantifying these contributions helps assess marine biogeochemical impacts and supports targeted pollution control.