Australia: The Land Where Time Began

A biography of the Australian continent 

Southern Ocean – Factors that Affect the Occurrence in the Atmosphere, and Deposition of, Polychlorinated Biphenyls (BCPs)

Long range atmospheric transport of persistent organic pollutants such as polychlorinated biphenyls carries them to the Southern Ocean atmosphere. In this study Galbán-Malagón et al. have reported the largest dataset available for the presence in the atmosphere of PCBs above the Southern Ocean around the Antarctic Peninsula from samples obtained during 3 cruises in 2005, 2008 and 2009. It was found that the concentrations of the aerosol phase of the total PCBs were 0.04 to 0.4 pg/m³, but the gas phase of total PCBs (Σ₂₅PCBs) were significantly higher, ranging from 1 to 70 pg/m³. The aerosol phase is consistent with the predictions of gas-particle partitioning for the model, being enriched in the more hydrophobic congeners. Galbán-Malagón et al. found that there is a net air-to-water diffusive flux of PCBs to the Southern Ocean that is up to 100 times higher than the dry deposition flux of PCBs that are bound to aerosols. The air-water disequilibrium is consistent with the role of the biological pump removing PCBs from the water column by settling the PCBs bound to organic matter as the disequilibrium is higher for the hydrophobic congeners. The half-lives in the atmospheric of PCB 52 and 180 are 3.8 and 1 days, respectively, as calculated from the measured concentration and depositional fluxes. Higher concentrations of the gas phase of PCBs in the atmosphere above Antarctica during the warmer periods are driven by the volatilisation of PCBs from the soils of Antarctica during the austral summer. This temperature dependence has not been observed for PCBs over the adjacent Southern Ocean, Galbán-Malagón et al. suggesting this is probably due to the importance of atmospheric occurrence of PCBs being modulated by long-range atmospheric transport and atmospheric deposition.

Conclusion

This study reported the largest dataset on the occurrence in the atmosphere of PCBs over the part of the Southern Ocean that surrounds the Antarctic Peninsula. Compared to other oceanic regions the concentrations are low and a net flux from the atmosphere to the ocean is shown by estimations of atmospheric deposition. The large air-to-water disequilibrium for the more hydrophobic compounds is consistent with the sequestration of atmospheric PCBS in the region being driven by the biological pump. In the aerosol phase the concentrations are extremely low due to the concentrations of organic aerosol in the Antarctic atmosphere being extremely low, and the dry deposition accounting for a small fraction of the total deposition fluxes. Over the Southern Ocean concentrations in the atmosphere do not correlate with temperature above the Southern Ocean, which contrasts with the clear temperature dependence of gas phase PCB concentrations above land. These distinct trends suggest the major contribution of long-range atmospheric transport as well as local secondary sources for the marine and terrestrial atmosphere, respectively.

Sources & Further reading

Galbán-Malagón, C. J., S. Del Vento, A. Cabrerizo and J. Dachs (2013). "Factors affecting the atmospheric occurrence and deposition of polychlorinated biphenyls in the Southern Ocean." Atmos. Chem. Phys. 13(23): 12029-12041.