Polycyclic aromatic hydrocarbons (PAHs) in the Mediterranean Sea: atmospheric occurrence, deposition and decoupling with settling fluxes in the water column.

∑(30)PAH gas phase concentrations (13-86 and 22-40 ng m(-3) in the Mediterranean and Black Seas, respectively) dominated the atmospheric levels due to the high contribution of phenanthrene, dibenzothiophene and their alkylated derivates. The high variability of PAH atmospheric concentrations in the different sub-basins is due to several factors (i.e. air-mass trajectory, proximity to sources and losses by deposition). The ∑(30)PAH atmospheric deposition (dominated by low MW PAH net air-water diffusive fluxes) is estimated to be ~3100 ton y(-1) (Mediterranean) and ~500 ton y(-1) (Black Sea). Net volatilization for certain PAHs was estimated. Deposition fluxes (1-2 orders of magnitude higher than reported PAH settling fluxes in the water column) confirm an important depletion/sink of water column PAH in the photic zone, especially for low MW PAHs. Degradation processes in the water column may be responsible for this decoupling. Conversely, high MW PAHs dry deposition fluxes are similar to their settling fluxes.