Dear Author,

Your revised manuscript # amt-2018-40 has received additional comments from the two anonymous reviewers. Both reviewers have suggested a number of minor corrections and sought for some specific explanations to further improve the quality and accuracy of the research content presented in the paper. Given below are the corrections suggested by the two reviewers. Please consider these comments while revising the manuscript. The final decision on the paper is contingent upon receiving a satisfactory response which addresses reviewers' concerns accompanied with the updated manuscript.

If you have any questions, please don't hesitate to contact me.

Thanks,

Hiren Jethva
Associate Editor, AMT.


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Report # 1
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Summary
This manuscript uses a case study to illustrate the derivation of the aerosol single scattering albedo (SSA) using observations from the OMI sensor of a large biomass-burning event in south Chile in 2017.
UV remote sensing of aerosols has not received the same level of attention as other sensors (such as MODIS/VIIRS) and studies like this one are a welcome addition to the general body of knowledge regarding the measurement of aerosol absorption from space. The paper is well laid out and its novelty resides in the combination of sensors utilized, its focus on single scattering albedo and aerosol height retrievals (as opposed to AOD and SSA) and its application using OMI observations. Overall, I think this paper can be published in its present form after some clarifications and corrections are included (mostly technicallso, I second the Editor’s comments that the Satheesh et al and the Gassó and Torres papers should be consider in this analysis plus the lack of mentioning of the recent SSA studies using OMI done by Jethva and Torres.
Details



L325-326: the explanation provided does not make much sense to me. If there is little sensitivity to deltaZ , why the claim that there is an amplification of absorption in the layer?. My interpretation is that if there is an amplification of absorption, the AAI increases which means there is sensitivity to deltaZ. Please, revise the sentence.

Line 332-333: A similar conclusion was reached by Colarco et al (2017) when analyzing the sensitivity of OMI UVAI . Colarco, P. R., Gassó, S., Ahn, C., Buchard, V., da Silva, A. M., and Torres, O.: Simulation of the Ozone Monitoring Instrument aerosol index using the NASA Goddard Earth Observing System aerosol reanalysis products, Atmos. Meas. Tech., 10, 4121-4134, https://doi.org/10.5194/amt-10-4121-2017, 2017.

Lines 343-347: It should be mentioned that while the sensitivity is exists, in this case, it is very small; color range in the respective figure is from 0 to 1% which is negligible for practical purposes.

Section 3.1.1 Include the time difference between GOME-2 and OMI overpasses the respective type of orbits (ascending/descending)

Line 378: please remove this sentence unless you can make a more convincing case. The data set used in this study is not good enough for making assessments of the MODIS SSA assumption (which certainly needs to be addressed). You need at least well-collocated CALIPSO and Aeronet data. This does not mean that the comments regarding MODIS biases should be removed. The results are suggestive at most and it should be included.

Line 444: what is a “ ground pixel”? in this context it seems like the word pixel is enough.

Line 540: This method does not “retrieve an aerosol profile”, it retrieves an average aerosol height. Please correct this case and other that are included in the paper.

Figure 2: I see very little value in including a single-phase function in the figure. At reference to a paper should be enough and publication charges will be saved. Alternatively, you may want include additional phase functions to point out differences between aerosol models.

Figure 5: a) and b) seem to be inverted

Figure 6a: Put the same ticks in both x and y axis.

Figure 6: caption does not include reference or explanation of figure 6b.

Figure 7: since the colorbar is not the standard colorbar used in the official CALIPSO quicklooks, can you clarify if the dark red are cloud? The contrast between in smoke and cloud appears to be between orange and red but a clarification will be appreciated.

Figure 8 Caption: nowhere in the caption mentions the word AI. Is this the parameter displayed?

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Report # 2
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This manuscript presents a technique to retrieve aerosol SSA from satellite data by simulating near UV AAI and constraining AOD. This is similar to- and draws from the same philosophical lines as the study of Satheesh et al., 2009. The authors have chosen to retrieve SSA at 550 nm by using MODIS-AOD at 550 nm from the simulated AAI. This makes the UV-Vis spectral dependency of aerosols under investigation a key parameter. Since the simulation of AAI is driven by aerosol microphysics, complex refractive index from the nearest AERONET site which determines this spectral dependency. This raises a flag on its representativeness on the simulation and in-turn the retrieved properties far away from the site (at least for the case presented here – smoke plume travels up to 3000 km away from source fires and AERONET site). I think the authors should include some discussion in the manuscript about this representativeness and reliability of technique for studying such long-range transport of aerosols.

Few general points (in no specific order) the author should take care of, before the paper is ready for a final publication.
1) The purpose of the study mentioned in L 73 – 74, should also be presented in the abstract before they say “In the first part of this study…….and later we present….” with the reference wavelength of the SSA retrieval.
2) Line 17 : This sentence sounds like it is the instrument’s deficiency. It is not. Please make it clear. Something like “The CALIOP overpasses over the region failed to capture the complete evolution….”
3) Line 21 : replace ‘observations’ with ‘satellite observations’
4) Line 69 – 71 : Poorly phrased. Please re-write it.
5) Line 108 :‘linearly’ should be ‘linear’.
6) Line 207 – 209 : Poorly phrased. Please re-write it.
7) Line 234 – 235 : I am not sure what the authors are saying here. Firstly, the
Santiago_Beauchef site has near-UV AERONET measurements. Secondly, the
aerosol complex refractive index is provided in their Inversion product that is always only for 440, 675, 880 and 1020 nm. So, what does “site only covers the visible band” and “absence of observations” mean there ?
8) Line 286 : Please mention the wavelength of SSA retrieval.
9) Line 295 : What do mean by “may even fail to capture the elevated plume” ?
10) Line 305, 307 : It should be ‘... for 26 January ….’.
11) Line 306 : low RMSE ? Not really. For a quantity like AAI which is varying from 0– 4, an RMSE of 0.5 or 0.6 is not low. Further the measures RMSE and correlation alone cannot confirm an agreement or disagreement between model and observations. Probably one could try using a T-test and say at what confidence level the agreement is statistically significant, I am not sure if your sample size allows for it ?
12) In Table 2, please also provide RMSE for the SSA to be consistent with the AAI report.
13) Please provide the sample size (number of pixels) for which statistics are derived in the Table 2 and also in figure 8 (i – l).
14) Line 313 : Is this ‘accounting’ or ‘contributing’ ?

15) Line 319 – 321 : I think, the authors should also report absolute difference in SSA with the AERONET before drawing parallels with the study mentioned here. It is confusing to compare percent difference in ni and absolute difference in SSA.
16) The spectral dependency retrieved in the study should also be compared with the insitu measurements and other studies on biomass burning in the literature and include in the discussion (L 320 – 330).
17) Line 374 : “The retrieved SSA is out of typical uncertainty….” this statement does not make sense and should be removed or re-phrase appropriately. At least for the case presented here the authors did not come up with a quantitative estimate of the uncertainty in SSA and clearly it is difficult if not impossible because of the multiple error sources.

Dear Author,

Re: amt-2018-40

Your response and revised manuscript have been received and evaluated. The revision looks in much better shape with increased clarity and quality of the content presented in the paper. The response to each concern raised by the two reviewers adequately resolves the ambiguities found in the earlier version of the manuscript.

However, an inconsistent statement found in your response, which is also cited in the revised manuscript, needs to be corrected. In response to a question raised by the Reviewer # 3 (comment # 16), it is mentioned that "This 20% spectral dependence adopted in their work is associated with findings of Hoffer et al. (2006).", which is untrue. The relative spectral dependence in the imaginary index between 354 and 388 nm assumed in the OMAERUV algorithm was derived from Kirchstetter et al. (2004) results, not Hoffer et al. (2006), although the latter has found similar results (large values of AAE for organics). Please correct this part of the description in the paper and upload the revised manuscript to AMT. Also, it is advised that the manuscript undergoes a careful reading one more time to eliminate any minor language and/or grammar related issue, which might have missed during the revision. The final decision on the manuscript is contingent upon the suggested corrections.

In case of any questions, please get back to me.

Best,

Hiren Jethva
Associate Editor, AMT