This manuscript presents sensitivity estimates for Br- and I- CIMS using the voltage scanning method. It follows several earlier studies where this approach has been utilized, and it is likely a useful addition to the growing literature on the subject. I recommend publication after revisions, and list my main comments and concerns below, with the major one relating to lack of novelty.

General comment

It is not very clear to what the novelty in this specific work is. Lopez-Hilfiker et al. presented a very similar set of results for I- CIMS in 2016, and there have been several other papers following up with additional details after that. I started reading this manuscript with high hopes for some new insight, methodologies, or guidelines. In particular as the title said “From Signal to Sensitivity”, suggesting that the manuscript would contain new and in-depth methodology. However, now I have to suggest to the authors to more clearly showcase what this manuscript presents that is actually new in the context of “Atmospheric Measurement Techniques”. The authors themselves note in the introduction that “voltage scanning is one of the most frequently used semi-quantitative calibration methods”.

This is my only general comment, since in general the manuscript reads well and is quite straightforward, but this is partly because the authors are following similar steps as earlier studies.

Specific comments

Page 1, Line 17: How is the feasibility of the method actually shown? There is a figure with time series of different molecules, but those are not compared against anything else.

Page 2, Line 3: This reference seems limited concerning to generality of the sentence. Perhaps the authors could cite some recent review touching the subject, e.g. Zhang et al., 2023 (https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/mas.21857), or some CIMS comparison, e.g. Riva et al., 2019 (https://amt.copernicus.org/articles/12/2403/2019/).

Page 3, lines 5-8. This is a key sentence of the manuscript, but it is now very long and hard to follow. I suggest splitting it in two and making it clearer. In addition, this paragraph is followed by two more, which read more as summaries and feel a bit misplaced at the end of an introduction.

Page 4, line 7: What does it mean that the VUC sources were switched?

Page 4, lines 8-9. Please add citation since you say it is well-known.

Page 4, lines 18-21. I had to re-read these sentences several times and am still not sure I understood the details. Please try to make this more clear and easy to understand.

Fig. 1, caption: I am used to seeing “SSQ”, but is the first quadrupole not segmented in this instrument? In addition, quadrupole is misspelled in the figure.

Page 5, line 4: Which are these “other voltages”. The last mentioned one was the orifice plate, and if also all others were kept constant, then there would not be much changed at all? In addition, Table S1 provides voltages that were varied, but using nomenclature that is not used elsewhere, making it hard to relate to.

Page 6, line 12: KDE was applied to investigate the oxygen levels. How does KDE serve that particular purpose? And in the SI it says “We introduced it to ensure the completeness of the manuscript", which also confused me.

Figure 2: 1) The figures have two lines that refer to “uncertainty”, and they are very different, and on different axes. 2) nitrophenol is misspelled in panel a. 3) Having the “I” in the formulas in panel b in the middle of the formulas, although they are adducts with I-, seems incorrect.

Page 11, lines 17-18: Is this information on fragments not something that could be utilized for other types of analyses? Not in this manuscript, but it seems like an interesting topic to explore.

Page 11, line 22: “more than 2” would be “>2”.

Page 12, line 14: I am not sure what this sentence means.

Page 14, lines 12-14: This reads as if also the latter series of compounds would have bene injected, but from later sentences, this seems not to be the case. Please make sure it is clear and correct.

Page 14, lines 18-21: What is the purpose of this sentence? If only to list the VOCs, it is unnecessarily complicated to list what they were injected as. Also, the following sentence then starts “All of these oxidation products”, although they are not oxidation products.

Technical comments

Page 1, Lines 3 and 21: Sensitivities of adduct ions are mentioned. Is it really the sensitivity of those that you are reporting, or is it the sensitivity of the CIMS to different molecules?

Page 1, Line 6 and elsewhere: Sensitivities are given with four significant digits in many cases. Is this possible? Given e.g. that standard gas concentrations are typically accurate to two significant digits.

Page 2, lines 35 and 36. Why not simple add the year to the first mention of Lopez-Hiilfiker et al and Song et al, instead of separately adding the full citations again in the end of the sentence?

Page 3, line 24: “SAPHIR”

Page 3, lines 40-42: Seems like some repetition from what was already said concerning definitions and acronyms.

Page 5, line 3: Please rephrase “primarily purely”

Page 6, line 37: S4?

Page 9, line 6: Check the sentence.

Overall, the manuscript is well-written and presents a valuable methodology for estimating the sensitivity of a wide range of atmospheric trace gases using the Multi-Reagent Chemical Ionization Mass Spectrometer (MR-CIMS) platform. By combining collision-limit determinations with a voltage scanning approach, the authors address the challenges of quantifying diverse compounds in the atmosphere. The authors identify three gaps that motivate this work: the evaluation of bromide CIMS chemistry in scanning, the application to a new Ion-Molecule Reactor (IMR) design, and the determination of the signal-to-noise ratio (SNR) required for this approach. However, since bromide voltage scanning is fundamentally similar to iodide chemistry and SNR requirements are often implied in previous literature, I believe that the true novelty of this work should lie in investigating how the unique Vocus AIM IMR design and Vocus B fast-switching capabilities influence standard voltage scanning protocols. Currently, the manuscript does not clearly articulate the implementation of the voltage bias in the new Vocus AIM IMR or how this specific IMR configuration changes the scanning procedure. Furthermore, the methodology as presented feels equally applicable to a standard Vocus AIM with slower switching, potentially failing to highlight the unique electrical and chemical challenges posed by the rapid polarity and reagent switching of the Vocus B. My major comments are as follows:

As pointed out by the authors, one main difference between the VOCUS-AIM-IMR and the traditional CIMS is that we can no longer change a set of voltages at the same time upstream of the BSQ. Instead, there is a voltage bias setting. This changes a lot of the difference in how we should do voltage scanning. I think there is still a lack of explanation on how this voltage bias changes the de-clustering, even though the authors have a short paragraph in the supporting information

Page 5 line 1-15. While I appreciate the authors explaining the use of voltage bias in the new IMR, it's still not quite clear to me whether they change the voltage bias between a regular sampling mode and a voltage scanning mode. I think one of the reasons for the confusion is the use of different terminology for the same voltage setting (for example, Quad DC(bias) in Table S1 vs voltage bias on Page 5). My understanding is that the voltage bias was adjusted at each step during scanning, but why does the change in voltage bias not influence the transmission efficiency (i.e., reduce TIC as suggested by Figure S3)? Also, should the voltage bias setting be different between Vocus AIM and Vocus B during voltage scanning?

Page 5 Line 16-19. Rapid switching between four reagent ions at a frequency of 1 Hz is impressive but introduces the risk of chemical interference or competition. Given that the authors indicate that benzene and acetone dimer chemistries can overlap, I think that it is important to demonstrate whether this fast-switching environment leads to residual "cross-talk" that might corrupt the dV50 determination for any single reagent ion.

Table S1. What is Quad linac? Is this specific to Vocus B? My recollection is that this setting is not on a Vocus AIM. On Page 3 Line 42, the authors state that the MR-CIMS uses the Vocus AIM IMR. These additional settings suggest minor differences between the AIM and Vocus B platforms that are not clearly documented. The manuscript might be easier to follow if the methodology focused entirely on the Vocus AIM, as the Vocus B details increase complexity without necessarily helping to validate the scanning approach.

With over 260 compounds identified in chamber experiments, structural isomers are highly probable, particularly as oxygen content increases. The manuscript would be strengthened by a discussion on the capability, or inherent limitations, of this voltage scanning approach to differentiate between isomers that share a molecular formula but possess different binding energies.

Minor comments:

There is a typo on Page 2, Line 68, where a double period follows the phrase "voltage scanning methods..".

The reference to Figure S1 in Section S1 regarding Total Ion Counts (TIC) appears incorrect, as Figure S1 in the text pertains to IMR stability; the authors likely intended to reference Figure S3.

It would be clearer if Figure 1 could be annotated to show exactly where the specific voltage settings mentioned in Table S1 are applied within the instrument, which would clarify how the electrical gradient differs in the AIM IMR compared to older designs

In summary, this is a strong paper that merits publication. However, I found the methodology difficult to follow from the perspective of a user looking to implement voltage scanning on their own instrumentation. This is partly due to the nuanced differences between the Vocus AIM and Vocus B. The manuscript would benefit from a clearer differentiation between these two inlets/instruments, or perhaps a reorganization specifically tailored to the implementation of voltage scanning within the Vocus AIM framework.