Jahn et al. also observed that some particles from the combustion of sawgrass in the laboratory displayed two organic phases under dry conditions (0% RH) using electron microscopy. Two distinct organic phases have also been observed in field-collected BBOA samples under dry conditions. China et al. observed two distinct types of tar balls in field samples, one less oxidized than the other. Hand et al. and Tivanski et al. also found that some types of tar balls in fieldcollected samples had more oxygen in the outer layers. The later observations are consistent with two phases, although the observations of a more hydrophilic phase on the outside of the particles are opposite to our observations. Nevertheless, we do not know if tar balls were present in our field samples and if tar balls are extracted well by our solvent system (methanol-water). Related, Hand et al. observed that some types of tar balls take up water above 75 % RH. In contrast, Semeniuk et al., Adachi and Buseck, and Dusek et al. showed that some types of tar balls are hydrophobic or only weakly hygroscopic. Overall, our results provide additional evidence that field-collected BBOA can contain two phases. Moreover, our results illustrate that the two phases can persist over a wide range of relative humidity values (∼95 to 0 % RH).