Thank you for your questions and feedback on the manuscript. Detailed responses to the comments and related manuscript revisions will be addressed together with input from other comments and formal reviews.

Regarding the difference between the AIOMFAC-Equil. and AIOMFAC-CLLPS models we will provide references and a more detailed characterization in a revised version of the manuscript. Briefly, these are two thermodynamic model variants for the computation of droplet surface tension as a function of composition, size, and temperature, introduced by Ovadnevaite et al. (2017) (see their supplementary information) and also discussed and applied by Davies et al. (2019).   AIOMFAC-Equil is a full “bulk” equilibrium model, including gas–particle partitioning and liquid–liquid phase separation (LLPS), but without consideration of bulk–surface partitioning. In the context of surface tension predictions, a procedure for the postprocessing of model outputs has been introduced in Ovadnevaite et al. (2017), which assumes a core–shell droplet morphology in the case of LLPS.  The AIOMFA-Equil model treats the droplet surface tension as the surface-area-fraction-weighted average of the surface tensions of  the present liquid phases. The initial surface tensions of those phases are computed based on a volume-fraction-weighted mean of the pure component surface tensions. The “AIOMFAC-CLLPS with organic film” model variant assumes complete LLPS among organics and inorganics (except for water) at all RH levels. It further assumes that all organic species in the droplet are present in a water-free layer at the surface of the droplet while  all electrolytes are present in a core phase of the droplet. The surface tension of the droplet in this model is equal to the surface tension of the organic film (phase), assuming complete coverage by the organic phase, or the surface-area-fraction-weighted average of the organic phase and the electrolyte-rich aqueous phase, should there be insufficient organic material to completely cover the droplet (Davies et al., 2019).

Regarding the second comment on the AFM measurements of sub-micrometer scale droplets, these studies are indeed promising as a source of measurement data at that size scale. In the present study, such measurements were not analyzed because placing the droplet on a glass substrate introduces a second interface, the substrate–droplet interface, which may modify the partitioning behavior of different species as well as affect the geometry of the droplet from spherical to approximately semi-spherical. At the moment, the framework laid out in this manuscript is only capable of handling spherical geometries with a single gas–droplet surface; the inclusion of interfaces between two condensed phases and the treatment of non-spherical geometries is the subject of future work.

References

Davies, J. F., Zuend, A., and Wilson, K. R.: Technical note: The role of evolving surface tension in the formation of cloud droplets, Atmos. Chem. Phys., 19, 2933-2946, 10.5194/acp-19-2933-2019, 2019.

Ovadnevaite, J., Zuend, A., Laaksonen, A., Sanchez, K. J., Roberts, G., Ceburnis, D., Decesari, S., Rinaldi, M., Hodas, N., Facchini, M. C., Seinfeld, J. H., and O’ Dowd, C.: Surface tension prevails over solute effect in organic-influenced cloud droplet activation, Nature, 546, 637-641, 10.1038/nature22806, 2017.

We would like to thank the referee for reviewing our manuscript and for their positive feedback on our work.

We would like to thank the referee for taking the time to review our manuscript and for their helpful feedback on our work. We have attached detailed responses to the referee's comments in the document below.