Sources and fate of polycyclic aromatic hydrocarbons in the Antarctic and Southern Ocean atmosphere

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a geochemically relevant family of semivolatile compounds originating from fossil fuels, biomass burning, and their incomplete combustion, as well as biogenic sources. Even though PAHs are ubiquitous in the environment, there are no previous studies of their occurrence in the Southern Ocean and Antarctic atmosphere. Here we show the gas and aerosol phase PAHs concentrations obtained from three sampling cruises in the Southern Ocean (Weddell, Bellingshausen, and South Scotia Seas), and two sampling campaigns at Livingston Island (Southern Shetlands). This study shows an important variability of the atmospheric concentrations with higher concentrations in the South Scotia and northern Weddell Seas than in the Bellingshausen Sea. The assessment of the gas-particle partitioning of PAHs suggests that aerosol elemental carbon contribution is modest due to its low concentrations. Over the ocean, the atmospheric concentrations do not show a temperature dependence, which is consistent with an important role of long-range atmospheric transport of PAHs. Conversely, over land at Livingston Island, the PAHs gas phase concentrations increase when the temperature increases, consistently with the presence of local diffusive sources. The use of fugacity samplers allowed the determination of the air-soil and air-snow fugacity ratios of PAHs showing that there is a significant volatilization of lighter molecular weight PAHs from soil and snow during the austral summer. The higher volatilization, observed in correspondence of sites where the organic matter content in soil is higher, suggests that there may be a biogenic source of some PAHs. The volatilization of PAHs from soil and snow is sufficient to support the atmospheric occurrence of PAHs over land but may have a modest regional influence on the atmospheric occurrence of PAHs over the Southern Ocean. Key Points The atmospheric occurrence of PAHs over the Southern Ocean is mainly the result of long-range atmospheric transportThe observed gas-particle partitioning of PAHs suggest a modest influence of elemental carbon due to its low concentrationsAntarctic soils and snow are secondary sources of some PAHs to the terrestrial atmosphere