Dear authors,

Thank you very much for your revised manuscript.

The reviewer and I are generally satisfied with your changes. However, there are still many language and grammar issues in the current version. Therefore, the manuscript needs another thorough editorial read (preferable by a native speaker). Although it is not the work of the editor, I marked a few issues below (but not all of them due to limitations in time).

In addition, there are some other minor content issues which need clarification or improvement.

• Line 22: It should be “resolutions”.
• Line 28: Please remove the ‘…’ (you already say ‘e.g.’ at the beginning of the parenthesis).
• Line 32: Add ‘the’ before ‘atmosphere’.
• Line 34 and 36: Alpha and MAC are already defined in Line 19 and 20.
• Line 38: Suggest to move ‘approach' behind ‘here presented’.
• Line 46: Suggest to replace ‘At the state of the art’ with ‘Currently' or ‘As the state of the art’.
• Line 49: ‘proved’ -> ‘proven’. There should probably be a comma after ‘In the late 1990s’.
• Line 64: The variable of the absorption coefficient was already defined in line 58. Please add ‘to be’ before ‘proportional’.
• Line 76, line 81 and later: The word ‘source apportionment optical models’ sounds like a weird construct that is probably not correct. Strictly speaking, it is a model dealing with source apportionment and not with optics. Could you maybe rephrase it as e.g. “Source apportionment models based on optical measurements” or “Source apportionment models using optical measurements as input”?
• Line 82: ‘fuels’ -> ‘fuel’
• Line 84: Add ‘the’ before ‘atmosphere’.
• Line 85: ‘need a priori assumption about alpha values’ -> ‘need a priori assumptions on the alpha values’
• Line 94: This sentence is very long a hard to read. In addition, I would replace ‘In the frame’ by ‘In the framework’.
• Line 95: Also this sentence is difficult to understand. I guess you want to say “Instead of using alpha as an a priori input, this approach even allows to retrieve alpha as a source-dependent value.’?
• Line 102 (and throughout the manuscript): The word ‘that’ should not be preceded by a comma.
• Line 103: Please remove the ‘…’.
• Line 104: Alpha has already been introduced many times before.
• Paragraph starting in line 106: This paragraph is a bit confusing and I suggest to rephrase it.
• Line 121: ‘in activity’ -> ‘active’
• Line 178: ‘Jülich Forschungszentrum’ -> ‘Forschungszentrum Jülich’
• The citation of ‘Valentini et al.’ is not an accepted or peer-reviewed publication and as such should be avoided as reference. I suggest to remove these sentences. It is sufficient that the comparison of the instrument is mentioned in the reply to the reviewers.
• Line 248 and 263: Add ‘such’ before ‘as’.
• Line 265: What do you mean with under-weighed? Less weighed? How?
• Line 297: Suggest to replace ‘Opposite’ with ‘In contrary’.
• Line 304: Add ‘the’ before ‘factor’.
• Line 310: Alpha has been defined already many times before.
• Figure 1: Please add proper y-axis labels (e.g. ‘Concentration’ or ‘Concentration Fe’).
• Figure 2: Please add y-axis labels to the unit.
• Line 346: I suggest to add ‘the’ or ‘a’ before ‘multi-time resolution model’
• Figure 3: It would be helpful to the reader if you describe ‘F’ and ‘EVF’ once more in the caption.
• Line 446: The reference to figure S3 is missing in this paragraph.
• Figure 4: As in the right axis, please also add the word ‘concentration’ or ‘conc.’ to the y-axis label in the left axis.
• Figure 5: The number on the y-axis for the biomass burning component are somehow wrong. Please check. The font size of the axis numbers is very small (it should be similar to the caption font size).
• Line 511: Alpha was already defined several times before.
• Line 539: Suggest to put a hyphen between alpha and value.
• Line 560: ‘At’ -> ‘For’ and add a comma after ‘nm’.
• Line 561: Suggest to change it to ‘report a MAC value of …’.
• Line 581: Suggest to add a ‘the’ or ‘a’ before ‘Multiliniear’.
• Line 604: Remove the word ‘works’.
• Figure S2: What does ”scaled residuals” mean? Normalized by the mean/median? Please clarify in the caption. The y- and x-axis are also missing their proper labels and units.
• Figure S2: Suggest to also mention the year.

Please also consider and reply to the comments by reviewer #1.

Thanks and kind regards

Paul Zieger.

Dear authors

Thank you for your last changes and the additional language improvements. The manuscript is now ready to be published in ACP.

Kind regards

Paul.