Reviewer's Comments in bold, our reply in bold italics

The manuscript "Measurement Report: Comparative Analysis of Fluorescing African Dust Particles in Spain and Puerto Rico" reports measurements taken at two sites during episodes of African dust using two Wideband Integrated Bioaerosol Spectrometers (WIBS), which show that bioaerosol-like fluorescing aerosol particles (FAP) that can be associated with these dust episodes.  Satellite and back trajectory analyses confirm that dust from Northern Africa was the source of the particles during both events. The WIBS measures the size of individual particles in the range from 0.5 µm to 30 µm, derives a shape factor and classifies seven types of fluorescence from the FAP. Some new indicators are introduced to provide a more quantitative way to compare the FAP characteristics derived from particles measured under different environmental conditions. The analysis highlights the similarities and differences at the two locations and reveals differences that can be attributed to the age and history of the dust plumes.

In general, the paper is well written and presented in a logical way. It is a timely and important piece of work. I therefore recommend publication of this paper in Esphere after minor revisions. My comments are listed as follows:  

Major Comments:

1. In Table 1, a lot of data is used in this paper. How does the author consider the differences between laboratory and field data in different spatial and temporal resolutions? How does comparison ensure accuracy?

Response: We appreciate this question from the reviewer; however, perhaps we don’t understand the nature of the questions. Laboratory measurements of bioaerosols are designed to document the response of the WIBS to different taxa of bacteria, fungi and pollen. They are not meant to replicate what happens in ambient conditions. Although elevated humidity can cause plants to emit spores, as far as we know, there is no reason to think that the fluorescing characteristics of bioaerosols in the laboratory will differ from those in the ambient. The relative magnitudes of Type A, B or C fluorescence intensity for Colorado yellow pine pollen, for example, should be the same regardless of whether these are measured in the laboratory or ambient air.  We understand that laboratory aerosol measurements are under controlled conditions as compared to field measurements which are rather more complex with respect to their temporal and spatial distribution of aerosols. As far as fluorescent aerosol measurements using WIBS are concerned, the lab measurements provide different taxa of bioaerosols or fluorescent aerosols representative of those in the ambient. Numerous airborne fluorescent aerosols have been tested in the laboratory (Hernandez et al., 2016; Savage et al., 2017) to provide databases of bioaerosol fluorescing aerosol particles that can be compared to ambient particles. That being said, however, we understand the point that the reviewer is making and have added extra verbiage to declare that we are making the assumption that a taxa of bioaerosol measured in the laboratory will exhibit the same fluorescence characteristics as the same taxa in the field.

We have added this sentence in section 2.3.2 “Here we are making the assumption that ambient conditions like temperature and humidity do not change the fluorescence properties of a particular taxa from those measured in the laboratory for the same taxa.”

1. Inline 443-444 of the manuscript, “The pre-dust size distributions of non-FAP aerosol (Fig. 6a) are almost identical at both sites, with a small fraction of the León particle population larger than those in PR.” How does Figure 6a arrive at this conclusion without showing non-FAP concentrations?

Response: The reviewer makes a valid point. Figure 6a is the FAP+non-FAP whereas 6b is just the FAP. The total aerosol population is dominated by the non-FAP particle population, particularly during the dust event as size larger than 5 µm, as can be seen when comparing with the FAP-only size distribution shown in Fig. 6b. The large difference between the total and FAP distributions brings us to the conclusion that we have now expanded a bit to read:

“ The pre-dust size distributions of all aerosol particles, non-FAP and FAP (Fig. 6a), are almost identical at both sites, with a small fraction of the León particle population larger than those in PR. The arrival of dust leads to almost two orders of magnitude increase in both the PR and León concentrations, over all sizes, and brings significant numbers of particles larger than 10 µm.”

1. In Figure 11b, The ordinate in the figure is the absorption coefficient, and the following text explanation is the extinction coefficient, please unify the statement.

Response: Thanks to Reviewer for catching this error, which has now been corrected in the revised manuscript, replacing all references to “extinction” with “absorption”.

1. Inline 364 of the manuscript, Leon is misspelled.

Response: Thanks to Reviewer for catching the typo error. This has been corrected.

1. PM in the manuscript pay attention to modify the subscript.

Response: We have now rectified the subscript error.

1. In Figure 15, abscissa 2400 is displayed incorrectly.

Response: Thanks to Reviewer for catching the error in the abscissa. We have corrected it in the revised manuscript.

1. In line 674 and 826 of the manuscript, the HYSPLIT model was run for thirteen and five days for PR and León, respectively. Why did the author choose these two time periods?

Response: As we described already in the manuscript, the satellite data was used to determine the amounts of time that it was taking for the dust to travel from Africa to Puerto Rico and León, respectively.

1. In line 828 of the manuscript, as for figures 8 and 9, figures 18 and 19 show basically opposite results, which the author believes are the result of the mixing of aerosols internally and externally. This statement is very novel, please add some testimony.

Response: We would like to direct the reviewer to the section in the discussion where we address the question of internal vs external mixing. We copy it here as a reminder and think that we have already explained our reasoning clearly:

“Referring back to Fig. 10a we observe a clear difference between PR and León when comparing the changes in the MEODs, over all FAP types, when dust arrives. The MEODs decrease by 20-30% in PR and increase by 30-50% in León. These opposite changes were also seen in the size distributions shown in Figs. 8 and 9, i.e., in general, FAP concentrations in sizes <5 µm increased in PR and decreased in León. These differences can be explained, to some degree, by differences in the mixing state of FAP and dust during AD events. The large decrease in the FAP MEOD in PR suggests that the dust is bringing many more small FAPs than are found in the background; however, the increase in the larger FAPs indicates that some of these FAP are also internally mixed with the larger dust particles. Hence, the PR dust may be more externally than internally mixed (Fig. S8a). On the other hand, the AD event in León increased the MEODs over all the sizes; however, the larger particles (>5 µm) increased proportionately more than those <5 µm. This leads to the conclusion that the FAP in the León AD event are more internally mixed, i.e., that a large fraction of the AD FAP are attached to or mixed with the AD, as illustrated in Fig. S8b.”

1. It is suggested to add references in introduction.

Recommend citation:

Wang, Y. et al.,2023: Identification of fluorescent aerosol observed by a spectroscopic lidar over northwest China, Optics Express, 31, 13.

Sugimoto, N. et al.,2012: Fluorescence from atmospheric aerosols observed with a multi-channel lidar spectrometer. Optics Express, 20 (70), 20800-7.

Citation: https://doi.org/10.5194/egusphere-2024-446-RC1

Response: We thank the reviewer for reminding us that lidar can also measure fluorescence and we have added the following to the introduction: “Fluorescence from dust particles has also been detected with lidar, such as the measurements reported Sugimoto et al. (2012) and by Wang et al. (2023)  who report relatively strong, broad fluorescence from Asian dust and air-pollution aerosols transported from urban and industrial areas at wavelengths between 343nm and 526nm.”

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