Dear authors,

I do not feel that all comments of reviewer #1 have been adequately addressed. In particular:

Major comment #1 is hardly addressed. Paraphrasing the manuscript changes a bit, the new statements of "sulfate increased by 50% which improved the SO2/sulfate ratio", and "increase in simulated surface PM2.5 by 15-25%" are not enough. The reviewer's question was: "It’s not clear from the manuscript whether the ability of the model to capture PM concentrations in the Southeast in 2013 is a result of the extensive model modifications and if so, which factor(s) are most important". It appears that only the minor comment #5 has been answered by the text changes.

Major comment #3 is also not addressed. The expansion of the discussion in Section 7 mentioned in the reply, is only limited to an addition of a statement in a parenthesis. I understand that the main point is the seasonal cycle of surface PM vs. AOD, however an underestimation of the seasonal cycle itself needs to be discussed, for the reader to be convinced that the model provides an answer for the correct reasons.

Major comment #4 is also not properly addressed. The new statement in the abstract, as well as the short new sentence in lines 312-313, are not answering the most interesting part of the reviewer's comment: "Does this study suggest that SOA is non-volatile, and models should eliminate the use of partitioning theory and NOx-dependent yields?". Even if this is the case only in the SEUS, it is worth mentioning. If not, a statement that speculates on why the model is better with non-volatile SOA should be introduced. Maybe the model behaves as it is, due to the changes mentioned in major comment #1? Combined with minor comment #4, why only reference Marais et al. 2015, which has the more mechanistic approach, without elaborating on why the two approaches differ, and (if at all possible) recommend on the best one to use?

On a last remark, please mention when concluding which results are driven from (and are only applicable to) the SEUS, as opposed to the global scale.

Please adequately address the major comments of reviewer #1, as outlined above, and provide a detailed answer and track-changes text that addresses these points.

Kind regards
Kostas Tsigaridis