Review: Validation of ATLID stratospheric aerosol retrievals using SAGE III/ISS and ground-based lidar observations

The purpose of this paper is to validate the stratospheric aerosol observations from ATLID on EarthCARE through comparison with observations from SAGE III/ISS and two ground-based lidars. Overall, the paper is well written and an important contribution for any users of the ATLID data. I recommend publication after minor revisions.

I have two main suggestions:

1. Choice of lidar ratio: the lidar ratio directly scales the backscatter coefficient when calculating the extinction, so using an accurate value is important. The manuscript mentions that a full analysis of the lidar ratio choice is a topic of future work. However, the method this paper proposes to anyone who wishes to use stratospheric ATLID data is highly dependent on the lidar ratio, so I think the impact of the lidar ratio on the biases with SAGE should be explored further here. At the very least, it would be helpful to see the impact of varying the lidar ratio within a reasonable range on the bias between the ATLID and SAGE extinctions for some example profiles, like those in Figure 3. This would also help with verifying the statement on lines 352-354, which suggests that the larger bias in the NH is due to smoke particles that have a lidar ratio other than 50 sr.
2. Organization of results (Section 3): As a user of the ATLID data, my initial thought would be to use the L2 product, and I believe this paper is the first to clearly demonstrate the problems with the L2 aerosol retrieval in the stratosphere. Therefore, I think it would be helpful to show the L1/L2 comparison at the start of the paper, which would then motivate the detailed validation of the L1-derived extinction. This could be done by moving Figures 3 and 7 and the surrounding discussion to the start of Section 3, so that the issues with the L2 product are immediately clear.

Specific comments:

• Line 62: An explanation of the baselines and the difference between them would be helpful.
• Section 2.2: I think it is worth providing more details on the method used to calculate the extinction coefficient, even if it is a repeat of Khaykin et al (2026), given that one of the main recommendations in this paper is to derive extinctions from the L1 observations instead of using the official ATLID product.
• Comparison with ground-based observations: What is the impact of using a fixed lidar ratio of 50 sr to convert these observations to extinction/SAOD, when the ATLID observations are (at least sometimes) converted to extinction using the retrieved L2 lidar ratio?
• Are data points below the tropopause removed before calculating the relative difference in extinction? (Figures 1 and 2)
• Figure 2 caption: the meaning of daytime and nighttime SAGE III occultations is not clear, given that the measurements are at sunrise and sunset. Also, the text on line 189 says that the split is based on the EarthCARE overpass time, not the SAGE III occultation time. Please clarify this.
• Line 194: Was it unexpected for the day and night bias to have a similar vertical structure? If so, this should be explained, and if not, I would remove the word “remarkably”.
• Figure 3 caption: this figure is very insightful, but discussions of the bias between L1/L2 and SAGE should be in the main text, not the figure caption.
• Section 3.3: Do you have any theories as to why ATLID overestimates the SAOD in cases with more aerosol?
• Figures 4 and 7: displaying the comparison with SAGE III in a histogram form, as was done for Figure 1a, would be helpful for understanding these figures. Currently, it is difficult to determine the range of SAOD values where the agreement is best.
• Line 267: it looks like the gray shaded region is the broadest in the NH tropics/midlatitude (10N-30N) and narrowest at higher latitudes. Is this sentence phrased backwards?

Technical corrections:

• Line 148: Change “the following metrics” to “the metrics in Table 1.”
• Line 154: remove comma after “independent”
• Section 3.2.2: Include “=” sign between “lat” and the value in all cases.