Dear Authors,

Thank you for your revised manuscript that has satisfactorily addressed the questions raised by the referees. I am happy to accept it for publication in ACP.

Regarding the organic phase being assumed to form the outer shell phase around the aqueous phase. Further support for this can be found from spreading coefficient theory, and also from aerosol optical tweezers experiments, and x-ray microscopy measurements. The following are some suggested references that support the segregation of the organic phase to the air interface, with the aqueous phase forming the inner core phase. Although most or all of these experiments did contain inorganic solutes, while these experiments are free of inorganic salts, that should not change the preference of the organic phase for the outer shell phase.

Reid, J. P., Dennis-Smither, B. J., Kwamena, N.-O. A., Miles, R. E. H., Hanford, K. L. and Homer, C. J.: The morphology of aerosol particles consisting of hydrophobic and hydrophilic phases: hydrocarbons, alcohols and fatty acids as the hydrophobic component., Phys. Chem. Chem. Phys., 13(34), 15559–72, doi:10.1039/c1cp21510h, 2011.
Kwamena, N.-O. A., Buajarern, J. and Reid, J. P.: Equilibrium morphology of mixed organic/inorganic/aqueous aerosol droplets: investigating the effect of relative humidity and surfactants., J. Phys. Chem. A, 114(18), 5787–95, doi:10.1021/jp1003648, 2010.
Gorkowski, K., Donahue, N. M. and Sullivan, R. C.: Emulsified and Liquid–Liquid Phase-Separated States of α-Pinene Secondary Organic Aerosol Determined Using Aerosol Optical Tweezers, Environ. Sci. Technol., 51(21), 12154–12163, doi:10.1021/acs.est.7b03250, 2017.
Gorkowski, K., Beydoun, H., Aboff, M., Walker, J. S., Reid, J. P. and Sullivan, R. C.: Advanced aerosol optical tweezers chamber design to facilitate phase-separation and equilibration timescale experiments on complex droplets, Aerosol Sci. Technol., 50(12), 1327–1341, doi:10.1080/02786826.2016.1224317, 2016.
O’Brien, R. E., Wang, B., Kelly, S. T., Lundt, N., You, Y., Bertram, A. K., Leone, S. R., Laskin, A., Gilles, M. K., O’Brien, R. E., Wang, B., Kelly, S. T., Lundt, N., You, Y., Bertram, A. K., Leone, S. R., Laskin, A. and Gilles, M. K.: Liquid–Liquid Phase Separation in Aerosol Particles: Imaging at the Nanometer Scale, Environ. Sci. Technol., 49(8), 4995–5002, doi:10.1021/acs.est.5b00062, 2015.


Ryan Sullivan
ACP Co-Editor