Seasonal variation in diffusive exchange of polycyclic aromatic hydrocarbons across the air–seawater interface in coastal urban area

•The strong seasonal pattern of polycyclic aromatic hydrocarbons (PAHs) in air was found with a higher level in cold season.•Equilibrium was found for three-ring PAHs in summer, but the others were in disequilibrium.•More hydrophobic PAHs showed higher fugacity gradients (fA ≫ fW).•The net adsorptive flux to seawater occurred in most seasons with a higher extent in winter.•Atmospheric input is a major source of PAHs to seawater and sediment in this region.

Concentrations of 15 polycyclic aromatic hydrocarbons (PAHs) in air–seawater interface were measured over 1 year in the coastal region of Incheon, South Korea. Most individual PAHs and total PAHs in air displayed statistically significant negative correlations with temperature, but not significant in seawater. Less hydrophobic compounds with three rings were at or near equilibrium in summer, while PAHs with four to six rings were in disequilibrium in all seasons, with higher fugacity gradients in colder seasons and for more hydrophobic compounds. Differently from fugacity gradients, the highest net fluxes occurred for some three- and four-ring PAHs showing the highest atmospheric concentrations. Net gaseous exchange, which was higher in winter, occurred from air to seawater with an annual cumulative flux of 2075 μg/m2/year (for Σ15PAHs), indicating that atmospheric PAHs in this region, originating from coal/biomass combustion, can deteriorate the quality of seawater and sediment.

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