Maritime and coastal observations of ambient PM_2.5 and its elemental compositions in the Bohai Bay of China during spring and summer: Levels, spatial distribution and source apportionment

This study conducted a ship-based observation to measure the concentrations of PM_2.5 (particulate matter with aerodynamic diameters ≤ 2.5 μm) and PM_2.5-bound trace elements (TEs) in China's Bohai Bay, encompassing the coastal and offshore regions. Results revealed that while observed PM_2.5 concentrations were comparatively lower in the offshore area than the coastal region, average TEs concentrations were higher, possibly indicating the differences in emission sources between the two regions. However, the top six elements found in PM_2.5 were consistent in both areas, including Si, S, Al, Fe, Ca and K. Notably, higher levels of Ni and V in this study region than in the coastal cities of developed countries. In this study, ship emissions were identified as the primary contributor of TEs in the study region, with the V/Ni ratio indicating a higher contribution in offshore areas. Moreover, TEs levels during daytime in maritime region were significantly higher than those in the coastal areas. Eight sources of TEs were identified, including dust, sulfur from emission and chemical conversion, biomass burning, steel industry, vehicular and ship emissions, coal combustion, nonferrous metal smelting, and vessel emissions. Overall, coastal and offshore pollution emissions had significant impacts on the study region. This research provides valuable insights into the evolution and sources of PM_2.5-associated TEs, helping researchers understand the potential impact of particulate TEs on maritime and atmospheric environments so as to improve pollutant management practices in these regions.