The manuscript has addressed most of comments by both reviewers. After second review, some minor questions remain, and should be addressed before the paper can be published. The authors are asked to submit a revised version with the suggested minor changes addressed.

After 2nd review, the author response file contains only responses to reviewer #1, but responses to the minor comments and suggestions made by reviewer #2 is missing; no changes appear to have been implemented in the revised paper. The editor considers this a simple oversight, but reviewer #2 should not be ignored.

Both reviewers had raised the likelihood of a connection between PAC and SF < 1, and reviewer #1 had pointed to a missing paper (Ortega et al., 2016) that seems relevant here. Reviewer #2 had recommended to soften language that suggests SF and PAC "can be regarded as independent" (Section 3.4). The editor agrees that such an affirmative statement may be too strong, and can easily be misread; it further seems somewhat at odds with the authors own conclusion that "O4 scaling and PAC were found to have similar impact on the MAX-DOAS AOT results" (Conclusions). Consider to adopt the suggestion made by reviewer #2.

Furthermore, as reviewer #1 points out, the Ortega et al. is not only a "source of bias" (as the current revisions state), but establishes that "lack of sensitivity aloft" (read "AOT-PAC = elevated layers aloft") and SF are plausibly connected. This is currently not said clearly enough in the revised paper. A simple solution may be to add a half sentence "..., consistent with earlier findings (Ortega et al., 2016)." behind the above sentence in the Conclusions. Also consider to cite Ortega et al. 2016 together with Wagner et al., 2019 at the end of that same paragraph.

The changes should be straightforward to implement, and in the interest of time should not need further Editor review.