Deposition of polycyclic aromatic hydrocarbons in the North Pacific and the Arctic

Eighteen polycyclic aromatic hydrocarbons (PAHs) were simultaneously measured in surface seawater and boundary layer air from the North Pacific toward the Arctic Ocean during the Fourth Chinese National Arctic Research Expedition in the summer of 2010. Atmospheric sigma(18)PAH ranged from 910 to 7400 pg m(-3), with the highest concentrations observed in the coastal regions of East Asia. Correlations of PAHs' partial pressures versus inverse temperature were not significant, indicating the importance of ongoing primary sources on ambient PAH levels in the remote marine atmosphere. The relatively high atmospheric concentrations observed in the most northerly latitudes of the Arctic Ocean suggest the influence of regional sources. For example, higher levels of particle-bound PAHs were observed in the air of the Arctic Ocean than the North Pacific, indicating forest fire and/or within-Arctic sources. Concentrations of PAHs in surface seawater were within a range of 14-760 pg L-1 and generally decreased with increasing latitude. The observed air-sea gas exchange gradients strongly favored net deposition of PAHs along the entire cruise, with increasing deposition with increasing latitude, while the particle-bound dry deposition fluxes (particularly for the high molecular weight PAH) were highest at sample sites close to East Asia. Based on characteristic PAH ratios, atmospheric PAHs originated from the combustion of biomass or coal, while the ratios observed in seawater reflected a mixture of sources. Given the dominance of primary emissions to the atmosphere and the relatively fast removal of PAHs from the water column, then PAHs will continue to load into the surface waters of the remote marine environment via atmospheric deposition.