Dear Authors,

You have a final opportunity to revise your manuscript with a possibility for publication in ACP after the revision. Your last round of revisions was not sufficiently responsive to the referee's comments. Please revise the manuscript again, addressing the second round of reviewer comments and taking care to thoroughly address the comments of both reviewers from the first round. Be careful to ensure that your responses in the author's response document are carried through to changes in the manuscript.

As one example of meaningfully modifying the text in response to the first round of reviewer comments (and there are more instances where this needs to be done), in the Responses you wrote, “Previous studies investigated the hygroscopicity of organic-inorganic mixtures of representative model compounds from biomass burning (Cruz and Pandis, 1998, 2000; Raymond and Pandis, 2002; Abbatt et al., 2005; Henning et al., 2005; Svenningsson et al., 2006; Carrico et al., 2008; Dusek et al., 2011). For example, water uptake of surrogate mixtures containing a representative water-soluble organic fraction and inorganic compounds were studied by Svenningsson et al. (2006). They used the ZSR relation to compare and successfully explain the observed hygroscopic growth factors for 3 out of 4 mixtures. In addition, Carrico et al. (2008) and Dusk et al. (2011) investigated CCN activity and hygroscopic growth behavior of ambient biomass burning aerosols. “ This text, which provides a thorough review of the literature, is the type that should be incorporated in the manuscript, rather than the abridged version that you added.

A specific point regarding reviewer 2's comment in the first round: the effect of particle size on hygroscopicity should be discussed. You made a minor text change on Page 11628 line 21-23 to include the word "size distribution" but this is not a true discussion.

- V. Faye McNeill, editor