EU Science Hub

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

The first comprehensive assessment of gas and aerosol phase PAH concentrations and deposition fluxes across the Mediterranean Sea and in the South West Black Sea is presented. Σ30PAH 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 observed in the different Mediterranean sub-basins is due to several factors such as air-mass trajectory, proximity to potential sources and losses by deposition. The Σ30PAH atmospheric deposition (dominated by low molecular weight PAH net air-water diffusive fluxes) to the Mediterranean and Black Seas are estimated to be ~3100 and ~500 ton y-1 , respectively. In addition, net volatilization for certain PAHs was estimated. Atmospheric deposition fluxes are 1-2 orders of magnitude higher than reported PAH settling fluxes in the water column, confirming the existence of an important depletion/sink of water column PAH concentrations 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 than their settling fluxes.