Coastal terrestrial emissions modify the composition and optical properties of aerosols in marginal seas

Aerosols originating from marginal seas significantly contribute to regional and global air pollution burdens and climate regulation. However, the responses of marine aerosols to terrestrial transport remain uncertain. In this work, we investigated chemical composition and properties of aerosols over Bohai Sea (BS) and Yellow Sea (YS). Our observation results indicate that in the BS and YS regions in summer, the proportion of terrestrial boundary layer air masses is lower than that of marine boundary layer air masses. But the terrestrial characteristics of aerosols in these two regions are still apparent. The characteristics of carbon component ratios (mean: 5.58–12.11 for OC/EC, 0.48–0.58 for WSOC/OC) in aerosols are similar to those in coastal cities, and the proportion of non-sea salt ions ( > 80 %) is significantly higher than that of sea salt ions. Humic–like substances (HULIS) and water–insoluble organic compounds (WISOC) mainly contain anthropogenic components (oxygenated aromatic compounds, nitrogen-containing aromatic compounds, anthropogenic surfactants, fossil fuel-derived SOA). The δ 13 C TC characteristics and positive matrix factorization model (PMF) reveal that biomass burning contributes 60 %–80 % to carbonaceous species and marine primary emissions contribute 20 % to aerosols. According to the height of air mass trajectories and the half-life (15–20 h) of light-absorbing components, we determined the coastal region within 190–260 km of the coastline and the coastal waters as key regions controlling the composition of BS and YS aerosols. Our results emphasize that during summer when the influence of marine air masses increases, the terrestrial characteristics of BS and YS aerosols remain evident, being related to air mass transport from coastal terrestrial regions.