Cruise mean ambient air benzene mole fractions were lower than typically observed at terrestrial sites (benzene 14 ± 17 pmol mol -1 ) (25), while toluene mole fractions were essentially near zero and below the limit of detection for most of the cruise track. Such low ambient air mole fractions over the Southern Ocean are similar to observations by Guérette et al. and Rocco et al. , who also observed less than 20 pmol mol -1 benzene and toluene on average over the Southern Ocean. Our observations of higher concentrations of benzene compared to toluene are likely related to the faster reaction with OH and shorter atmospheric lifetime of toluene . Low and homogenous mole fractions as well as the absence of a significant correlation (R=0.01; P=0.1; N=237) between benzene and toluene mole fractions suggest that the concentrations measured during this cruise were largely produced by local and diffuse sources, e.g. many episodes of oceanic outgassing rapidly mixed by winds, and not by transport of polluted air masses.