Marine biogenic emissions of benzene and toluene and their contribution to secondary organic aerosols over the polar oceans

Natural processes in the polar oceans lead to emission of a variety of reactive gases contributing to atmospheric chemistry and aerosol formation. The identity and air–sea fluxes of most of these gases are poorly characterized, bringing uncertainty to the assessment of pre-industrial aerosol sources. Here we present seawater and atmospheric measurements of benzene and toluene in the open Southern Ocean and the Arctic marginal ice zone. Our data suggest a marine biogenic source for these two compounds, which have typically been associated with anthropogenic pollution. Calculated average emission fluxes were 0.024 and 0.037 μmol m-2 d-1 for benzene and toluene, respectively. Including the observed emissions in a chemistry–climate model increased secondary organic aerosol mass concentrations only by 0.1–1.2 % over the Arctic but by 7.7–77.3 % over the Southern Ocean far from continental sources. Climate models must consider the hitherto overlooked emissions of biogenic benzene and toluene from pristine oceanic regions.