Effect of altitude and distance from the sea on fractionation processes of Persistent Organic Pollutants (POPs) associated to atmospheric aerosol from Ross Sea to Dome C, Antarctica

This paper deals with both the transport processes of several classes of organic pollutants in a large area of Victoria Land and Ross Sea (Antarctica) and the role played by marine aerosol which involves the exchange process between the sea surface and the atmosphere. The mechanisms of transfer process from the seawater to the atmosphere and aerosol of three major classes of pollutants (Polycyclic Aromatic Hydrocarbons, PAHs, Polychlorobiphenyls, PCBs, and Organochloride Pesticides, OCPs) were investigated in samples of snow and firn collected during several Italian Expeditions from 1996 to 2014 in a large area of Antarctica. The samples were gathered at different distances from the sea (Rennick Glacier and traverse GV7-Talos Dome-Dome C), at different altitudes (Mt. Melbourne) and at different depths (Evans Nevé). The strategic sampling spots allowed the study of the mechanisms involved in the transfer process that occurs from the seawater to the aerosol and the atmosphere and the consequent diffusion of these pollutants in the environment. Organic compounds linked to sea aerosol showed a fractionation depending on the altitude and on the distance from the sea in agreement with their volatility and affinity to aerosol particles. The results highlighted a decreasing trend of the concentration with the increase of the altitude. This behavior is significant for samples coming from the winter storm, when the very heavy sea produces a high quantity of marine aerosol, where the amount of PCBs, OCPs and PAHs reaches respectively a decrease of 50, 70 and 40% compared to the value found at the lowest altitude. A significant decrease of the concentration of the heavier PAHs and of DDT with the altitude was common in all the samples collected in Mount Melbourne, showing a differentiation in the transportation, and hence in the diffusion, of the analytes on the base of their molecular weight. The dependence of the pollutants on the distance from the sea showed an increase of the contaminant in proximity to the Ross Sea. The samples collected on Evans Nevé and GV7 showed a content of PAHs and DDT 1.5 and 3 times higher on superficial snow than the values found at greater depth. This seems to be connected to a significant flow increase of these pollutants in Antarctica in the last decades.