Spectral Aerosol Optical Depth Retrievals by Ground-Based Fourier Transform Infrared Spectrometry

Round 1

Reviewer 1 Report

This paper is a thorough description of wavelength dependent and AOD measurements of aerosol in remote location, including application of FTIR measurements compared with AERONET spectrophotometry.

The paper is well written and represents a complete discussion of a useful experimental program at the IZO observatory. The paper is in good form in its current form for publication.

There are few minor details that the authors could consider in final editing of this paper

1. Might note the references that indicate little or no marine aerosol at the observatory elevation (Presumably the results later for no. concentrations and mass concentration are modeled values? Can these be verified with added references to aerosol studies?--see below)
2. Line 306 --might spell out PWV early rather than later.
3. Line 319--might distinguish optical air mass from meteorological definition for reader appreciation.
4. Line 370 might add a reference to recent studies of size distributions hat support Junge subrange from broader multimodal distribution forms defining the accumulation range and the coarse range.
5. Line 618 As above the number and mass concentrations are determined by modeling--verified with observations at the observatory?
6. L641 Statement that there is no marine aerosol  is probably too simplistic--here is the water soluble component--There may be a good reference for aerosol composition at the observatory that could support this statement?

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments Reviewer

I would like to thank the authors for such an interesting and meaningful work.

I only have two comments that probably the authors already consider for future papers.

• I encourage the authors to go deeper into FTIR instrumental issues (like SNR in SWIR region where light is low, etc). Although the FTIR is isolated for environmental conditions (Temperature, Humidity, etc), this morning (am) and afternoon (pm) different estimations could better explained with that deeper understanding.
• You cross-validate the AOD obtained with SWIR bands of the FTIR (B5,B6, and B7)?

I read the manuscript carefully and I only have to notify that the OPD acronym is not explained.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

General comment

 

The paper is focused on the retrieval of aerosol optical depth using FTIR approach that is generally a measurement system used for gases. Measurements were taken in a high altitude site that is more suitable for this approach. The topic is interesting and suitable for the Journal. There are some elements of novelty even if the approach discussed has sever limitations for routine use in other sites that should be put in a better evidence. Some other aspects need some corrections/explanations. In conclusions, I would suggest minor revisions (see my specific comments) before publications.

 

 

Specific comments

 

The approach proposed seems to have a relatively low efficiency of measurements (about 43% line 516) and it is difficult to find suitable conditions for calibrations even at this site that could be more suitable for this application compared to sea level sites in which several sources act simultaneously. This severely limits the applicability at different sites and should be clearly stated in the conclusions.

 

Looking at Figure 4 it appears that there could be specific events that quickly deteriorate the performance of the system and this limit the usability of the approach in routine conditions. Could authors suggest how frequently should the system be cleaned and recalibrated for a reasonable long-term use?

 

Table 1. Why median values were accompanied by standard deviation? Generally, standard deviations are coupled with average values and median values with some choice of percentiles.

 

It is not very clear what the last column of Table 1 reports. Please explain better in the caption or in the text.

 

Lines 430, 467    please remove “…”. If authors want to add something it is better to do it explicitly.

 

Line 433. What is a “scientific container”? It is not sufficient to say container?

 

Figure 3. X-axis. It is not very clear “air mass”.

 

Figure 6. It would be better to use a second scale for the pristine conditions because it is not possible to see much of variability in the current figure. Furthermore, it is sure that an exponential fit is the best way? It seems that a constant value will be probably better than an exponential. I mean that with the variability shown there is not any measurable difference at the different wavelength for this case. Please discuss this aspect and justify your choice of fitting formula.

 

In the conclusions it should be clearly stated what are the advantages when this system is used compared to more widely accepted approaches for AOD detection. This should help in focusing if these advantages overcome the disanvantages.

Author Response

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Author Response File: Author Response.pdf