Please see attached file.

The paper analyzes significant reductions in European lower tropospheric ozone (O₃) levels during and after the COVID-19 pandemic (2020–2022), using satellite data and modeling. It attributes these reductions to decreased emissions from lockdown-related activity reductions, with the remainder influenced by meteorological factors. The study highlights persistent anomalies in spring and summer ozone levels, with the largest reductions observed in 2022. I find the paper very interesting and suitable for publication after the following comments are taken into consideration:

General comment:

1. Meteorology is used as a broad term to explain and quantify its effect on the ozone reduction. In the section about the TOMCAT, no details about the met fields are provided. For example, I assume you use average tropospheric met fields? But what if you use near surface ones? Are transport/winds included? See a more specific comment hereafter
2. The sections about IASI/GOME is independent from the one with the simulation. The conclusion section does not attempt to link both neither. No mention of applying the AK to the model simulation so no comparison is attempted. Why is so?
3. It would have been nice to see a map of the decrease or a map of the decreasing trends to see if it is negative everywhere in Europe.
4. Not sure if the paper’s data is included in TOAR but it would be interesting to use the module recommended by TOAR to calculated the trends shown in SI: https://gitlab.jsc.fz-juelich.de/esde/toar-public/toarstats.

Specific comments:

1. Was the RAL product validated? If so please add a reference
2. Line 126: "The MetOp-B record was adjusted according to monthly differences with the MetOp-A record in the overlap year of 2018". The community has always supposed that the two instruments are the same. If anything, IASI B is a reference radiance instrument because of its stability (and before that it was IASI A), how come there are differences? This is the first time I read about a possible difference between the two instruments’ products.
3. Line 220. This phrase is confusing. You investigate the effect of meteorology in the following sentence and state here that it is emission dependent. Rephrase?
4. Line 240. “Meteorology” is very broad. Does this include long range transport? What is the meteorological factor that is driving the year-to-year difference? It would be interesting to make a simple test on the sole influence of the temperature or cloud cover (or other?). Since temperature/photochemistry drives the O3 concentrations, you can check/validate if the simulations with the pre COVID years meteorology are in line with the temperatures over Europe in 2020 vs 2017 to 2019 (even if from ERA5). IASI for example, has a L2 NRT temperature product that can be retrieved from EUMETSAT.
5. Figure 3/STE discussion/Line 260: the discussion of the STE should come way earlier, before talking about Figure 4. Please rearrange or simply remove the STE from Figure 3

minor remarks:

This abstract phrase is weird/not necessary because it is self-explanatory in the following phrase: “Rutherford Appleton Laboratory (RAL) retrieval products show large negative anomalies in the spring-summer periods of 2020–2022, with the largest in 2022, and smaller reductions in 2023.”

The first phrase of the text should read “tropospheric ozone (O3)”

L60: “Based on activity data », what does this even mean?

 MetOp is, since few years, it spelled Metop (no capital O)

L160-162. This phrase should come earlier

Figure 3. Spell STE in the legend