This manuscript presents a sensitivity study of dust aerosols’ minerology, loading, vertical distribution, and the background atmosphere to FIR (15-100 μm) observation from FORUM mission and compares the sensitivity to the MIR (2.5-15 μm) observation from IASI, using a pseudo-observation simulator. It demonstrates a significant FIR spectral signature of dust (up to 50% of the longwave spectrum), which can complement the MIS observation, especially for relatively thick dust in the free and upper troposphere. The manuscript is well-written with detailed demonstrations of the methodology. The science merits publication in AMT, I have some minor suggestions listed as follows.

Line 102: The PO is limited at nadir viewing angle, which should be recognized in the last section, as it is relatively important.

Line 107: The two atmospheric profiles representing tropical and polar regions should be shown in either the manuscript or the supplementary documents, especially the water vapor profile, which is directly related to Section 3.3.

Line 115: What is the assumption of the two vertical distributions of dust (e.g., normal distribution with a central height)? The plot for dust vertical distributions is needed in either the manuscript or the supplementary documents.

Line 120: As this study is using a PO for the FORUM observations, why not use a more realistic particle size distribution (SD) (e.g., from in-situ measurements as presented in Formenti and Di Biagio (2024)) instead of using a monomodal lognormal size distribution?

Line 160: Using Mie calculation with spherical assumption for dust needs to be justified, for example, by providing the evidence (or direct references) that dust optical properties are insensitive to particle shape in MIR and FIR spectrum.

Line 173 and Table 1: At which wavelength is the AOD used as the input for the RTM in this study? It should be presented in text and in Table 1. It is also a bit confusing for “average value in the FORUM spectral range” in Table 1. Does it mean the spectral AODs in the entire FORUM spectral range are constant? If yes, it would not be appropriate, and it is suggested to follow the spectral extinction coefficients based on the CRI and SD. If not, the AOD at which specific wavelength is needed.

In Section 3.2, the Jacobian calculated in this study is the radiance to the number concentration, which is optically to the AOD with the fixed particle size distribution assumption. Therefore, the sensitivity of dust in MIR and FIR is with respect to the aerosol burden, which is similar in terms of spectral behaviors in MIR and FIR. Therefore, using either MIR or FIR could have similar spectral radiance sensitivity to the AOD or number concentrations. The FIR does not provide additional information content in terms of retrieving AOD. Therefore, the contribution of FIR to the total sensitivity in infrared is not appropriate to be simply divided by the add-up sensitivity, as the information content between them is similar.

Based on Figures 3 and 4, the FIR sensitivity to dust CRI is more distinguishable from the CRI sensitivity in MIR. Thus, it is suggested to calculate Jacobians with respect to the different mineral fractions (e.g., Quartz and Feldspar) to further look at the sensitivity contribution of the FIR.

According to the size parameter differences in different wavelengths with the same particle SD, the sensitivity of spectral radiances to dust particle SD would also be different between FIR and MIR, which is also suggested for the authors to consider.

Reference:

Formenti, P. and Di Biagio, C.: Large synthesis of in situ field measurements of the size distribution of mineral dust aerosols across their life cycles, Earth Syst. Sci. Data, 16, 4995-5007, 10.5194/essd-16-4995-2024, 2024.

In this article, the authors test the sensitivity to dust aerosols of the instrument planned to operate during the upcoming FORUM ESA EE9 mission. They extended an existing radiative transfer model to simulate satellite pseudo-observations in different atmosphere and dust layer configurations for FORUM and related measurements from IASI-NG. Their results show how FORUM measurements will complete IASI-NG in the far infrared in situations involving dust aerosols.

The subject is appropriate to AMT and scientifically relevant, useful and novel. The article is well-written and easy to follow. The figures are clear and well described. The discussion draws clear conclusions. 

From my point of view the article could be published as-is. I have a few small points below.

Technical comments

1. l. 185; "on the other hands"
2. l. 207, fig. 3c and 3d: the NESR curve is so thin it is easy to miss
3. l. 231: "decrease" should be "decreases"
4. l. 238: "which covers" 
5. l. 247: "please find spectral intervals in the figure" -- this is a weird phrasing, please rephrase.
6. l. 290: "Even if Fig. 7..." shouldn't this be Fig. 6?
7. l. 310: "Going upper..." -> "higher"