The seawater measurement noise is slightly higher in the Arctic compared to the Southern Ocean cruise due to less frequent blanks and different PTR-MS quadrupole data collection settings. Measurement noise and LOD are low enough to detect these gases in seawater while air mole fractions were often close to the LOD. We test for diurnal variability in the measured seawater concentrations from the Southern Ocean by using the local solar time to remove the influence of the ship track crossing multiple time zones. The measured seawater concentrations were binned in 24 hourly bins and the standard deviation and standard error was calculated for each bin (Figure ). Figure shows that measurements of benzene and toluene during solar zenith are generally a little higher than the other measurements, but there is no substantial diurnal variability in seawater benzene and toluene concentrations and this variability is not statistically significant. The Arctic data was not tested for diurnal variability due to 24 h light during the sampling period and the relatively smaller dumber of data points compared to the Southern Ocean cruise. Table . Antarctic, <-55ºS: 0.0236 μmol m -2 d -1