Dear Authors

Thank you for providing the revised manuscript “AOD trends during 2001–2010 from observations and model simulations” as well as your responses to the issues raised during the reviews.

Based on the reviewer’s comments and my own assessment I have concluded to reconsider your manuscript for publication in Atmospheric Chemistry and Physics after minor revisions.

Most of the reviewer’s comments have been resolved in your response; however, I would kindly ask you to address some outstanding issues listed below.

I am looking forward to your revised manuscript.

Kind regards,

Philip Stier
Co-Editor
Atmospheric Chemistry and Physics

Issues:

1. The analysis of component AODs plays a central role in this manuscript, yet the calculation of component extinction is an approximation based on the component volume fraction of total extinction. This needs to be included in the model description and potential implications clearly stated.

2. As discussed by the reviewers, also the aerosol water uptake calculation plays a central role so that it should be mentioned in the model description. The water uptake calculation eluded to in section 4 is one factor but it is important to state all relevant assumptions, such as the relative humidity calculation (clear-sky vs. grid-box mean) and any assumed maximum relative humidity.

3. Your response to the reviewer comments regarding temporal sampling is insufficient. In your response you state that this is mitigated by the use of satellite overpass time sampling. However, this does not prevent significant temporal sampling biases – it is only possible to retrieve AOD reliably for a small fraction of the globe at any given day due cloud cover and other factors. Use of daily L3 AOD products and temporal sampling of corresponding daily model values could have largely mitigated this issue. It is important to discuss the limitations of this assumption if you decide keep the analysis to monthly mean data.

4. In your conclusions you write “The differences between the two simulations show that the observed AOD increases over Middle East and North Africa are caused mostly due to meteorological effects.” This is a bit misleading as over both of these areas dust emissions are a significant contributors to AOD. As you do not vary dust emissions you mix potential emission trends into “meteorological effects”. This should be clarified throughout the conclusions.

Dear Authors

Thank you very much for your revised submission that addressed all outstanding issues. Thank you for choosing ACP!

Best regards,
Philip Stier