Bidirectional air–sea exchange and accumulation of POPs (PAHs, PCBs, OCPs and PBDEs) in the nocturnal marine boundary layer

摘要

As a consequence of long-range transported pollution, air–sea exchange canbecome a major source of persistent organic pollutants in remote marineenvironments. The vertical gradients in the air were quantified for 14 species, i.e. four parentpolycyclic aromatic hydrocarbons (PAHs), three polychlorinated biphenyls (PCBs),three organochlorine pesticides (OCPs) and two polybrominated diphenylethers(PBDEs) in the gas-phase at a remote coastal site in thesouthern Aegean Sea in summer. Most vertical gradients were positive (Δ∕Δ  0), indicating downward (net depositional) flux. Significantupward (net volatilisational) fluxes were found for three PAHs, mostly duringdaytime, and for two OCPs, mostly during night-time, as well as for one PCB andone PBDE during part of the measurements. While phenanthrene was deposited,fluoranthene (FLT) and pyrene (PYR) seem to undergo flux oscillation, herebynot following a day–night cycle. Box modelling confirms that volatilisationfrom the sea surface has significantly contributed to the night-time maximaof OCPs. Fluxes were quantified based on eddy covariance. Deposition fluxesranged from −28.5 to +1.8 µg m day for PAHs and −3.4 to+0.9 µg m day for halogenated compounds. Dryparticle deposition of FLT and PYR did not contribute significantly to thevertical flux.