PAHs in air and seawater along a North-South Atlantic transect: Trends, processes and possible sources

Polycyclic aromatic hydrocarbons (PAHs) were simultaneously measured in air and surface seawater between 49° N and 25° S in the open Atlantic Ocean. Elevated concentrations of PAHs (Σ₁₀ PAHs ≈ 1.4-2.5 ng m^-3 air, and 0.7-1 ng L^-1 seawater) occurred in the Biscay Bay and off the northwest coast of Africa. The unexpectedly high concentrations off NW Africa were discussed assessing the possible contribution of the emerging oil industry along the African shore, the role of biomass burning and natural sources of PAHs. In the southern Atlantic, concentrations of PAHs were close to detection limits (Σ₁₀ PAHs ≈ 0.02-0.5 ng m^-3 air, and 0.06-0.5 ng L^-1 seawater) and showed decreasing trends with increasing latitudes. Correlations of PAHs' partial pressures versus inverse temperature were not significant, in contrast to results for polychlorinated biphenyls from the same transect. This could have been due to the importance of ongoing primary sources and the shorter atmospheric life-times of PAHs. Air-water fugacity ratios (f_a/f _w) were calculated for selected compounds. They were close to 1 for fluoranthene and pyrene in remote open ocean areas suggesting air-water partitioning near equilibrium. Ratios for anthracene and phenanthrene were <0.3 in the remote tropical Atlantic, suggesting net volatilization.