My review is attached a PDF document.

general comments

Much work went into this simulation study to develop a basis for the potential impact on ozone from EUMETSAT’s high spectral IR sounder. Overall, the manuscript is a great first step in showing the benefits of geostationary advanced sounders regarding Ozone, and a pathway for investigating other species. Seems like the manuscript script could have been much shorter if the authors had used different models for the simulations and assimilation steps. For example, maybe http://raqms-ops.ssec.wisc.edu/, but this was not the path taken, so much on the calibration of the OSSE had to be included.

specific comments

For more on the instrument, this reference on the IRS could be added: Sylvain Abdon, Hubert Gardette, Cyril Degrelle, Jean-Michel Gaucel, Patrick Astruc, Patrice Guiard, Antonio Accettura, Daniel Lamarre, Donny M. Aminou, Didier Miras, "Meteosat third generation infrared sounder (MTG-IRS), interferometer and spectrometer test outcomes, demonstration of the new 3D metrology system efficiency," Proc. SPIE 11852, International Conference on Space Optics — ICSO 2020, 118521F (11 June 2021); https://doi.org/10.1117/12.2599240

Line 8. Since the IRS uses the IR part of the EM, the various gases can be monitored at night as well as during the day. This fact should be note somewhere before the summary. Stated another way, advanced IR sounders in geo can complement UV/visible sensors. Maybe add this reference: https://journals.ametsoc.org/view/journals/bams/104/3/BAMS-D-22-0266.1.xml

Line 15. Define that NR is the Natural Run. Currently defined on line 208.

Line 20. This statement would be equally true in operations, not just in research.

Line 57. Could include this overview article on the MTG: Holmlund, K., and Coauthors, 2021: Meteosat Third Generation (MTG): Continuation and Innovation of Observations from Geostationary Orbit. Bull. Amer. Meteor. Soc., 102, E990–E1015, https://doi.org/10.1175/BAMS-D-19-0304.1.

Line 318. What local zenith angle cut-off was used?

Line 350. The reader could be reminded that the IRS will be providing data over Europe every 30 min, while only hourly data were included in this study.

Line 335. As a start, only clear sky values were used, but for low clouds, won’t the sensor still observe most of the ozone?

technical corrections

Line 27. Replace trough with through.

Line 37. Consider changing to “wide spectral range”.

Line 203. This kind of experiments comply a series of steps should be These kind of experiments comply a series of steps

Line 247. Remove ‘it’ … At the same time, it the same surface emissions as ….

Line 219. The text states “observations are more dense over land and in the South-East portion of the instrument disk”, yet the figure (8) is mostly just covering Europe.

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