This manuscript generated a lively scientific discussion. As the authors have pointed out, the discussion is now much longer than the manuscript itself. This is clearly an important and timely topic for the HESS readership.
Overall I find that although there is scientific merit in this work, the conclusions are too strong and the assumptions not clearly enough defined.

In particular:
1. I do not agree with the authors that they have "clearly stated our assumptions and presented our results under these assumptions". I do not find the assumptions easy to follow. Many of them are not made explicit and the burden of understanding the assumption is placed on the reader already knowing or reading about it elsewhere. Please can you take more space to identify the consequences of the modelling and parameterizations - i.e. the impacts on and uncertainties in your results and conclusions. Although it is common to say that 'model world' results are applicable to the real world it would be much more robust to present these alongside a clear indication of the main assumptions. I would suggest a whole section on assumptions and their consequences would be one way to address this.
2. I also find the conclusion of 'disproving' LS16's estimates not adequately supported by the evidence provided. Your work does suggest a discrepancy but you do not show evidence that disproves this. I would agree with the comments of the Referees and other comments here. You will need to modify your statements. A much clearer explanation of why there might be differences between different methods would be valuable here.
3. A much clearer review of LS16 and other atmospheric residence time work would no doubt help the readability of the manuscript and assist the reader in following your arguments. Please take some space to undertake this.

Your summary of anticipated changes to your manuscript addresses to some degree most of the main referee comments and my three main concerns made above and thus I look forward to receiving your revised manuscript.

The Referees find your manuscript to be of good quality and suggest only one minor point that requires addressing before publication. Please check this and revise your manuscript accordingly.