|The authors have revised the manuscript appropriately and answered the reviewers’ comments for most part. However, I don’t think the authors answer my major comment that “the authors should include the results of balloon-borne measurements at higher altitudes (~100 m above ground level or more)” in the revised manuscript. I would like to ask the authors to reconsider the following comments before publication.|
# Additional Comments on “Comments/Responses 1 and 2”
Based on the authors’ responses to comments 1 and 2, I could understand the reason why the authors chose 20 m, instead of higher altitudes (100 m or more). I could also understand that you are preparing a detailed analysis for INP measurements at higher altitudes over the High Arctic. However, because the title of this manuscript is “Resolving the size of ice-nucleating particles with a balloon deployable aerosol sampler: the SHARK” and the authors describe that “A critical factor in determining the lifetime and transport of INPs is their size, however very little size-resolved atmospheric INP concentration information exists. This is especially so in the free troposphere (Lines 12-14)” in the Abstract, the most readers will consider that this manuscript should be a technical paper evaluating the performance of the measurements of size-resolved INPs in the free troposphere using a new balloon-borne system.
I assume that the authors have already conducted sized-resolved INP measurements at higher altitude (for example, ~400 m level over the High Arctic, at least). Although the authors mention that “We have already shown that: we can sample when the SHARK is in flight, the INP concentrations are consistent with another filter based sampler, we can communicate with the airborne SHARK when it is above 100 m (Figures 4 and 5), and have described the instrument and the analysis in detail”, it remains unclear whether the authors indeed succeeded to collect ambient aerosol samples at higher altitudes (in the free troposphere) using their impactors and could measure the size-resolved INPs. Unfortunately, they simply evaluated the performance of only OPC and radiosonde (and not impactors) in Figures 4 and 5. Furthermore, although the authors note that “It is not the purpose of this technical paper to present a scientific analysis of INPs at any of the locations from which measurements were obtained, only to demonstrate that the system produces reliable measurements”, I have to say that there are no evidence to demonstrate the reliability of their new system for measuring sized-resolved INPs in the free troposphere. I think there are two potential options, and the authors will need to choose one of them.
Show the preliminary results of the size-resolved INP measurements at higher altitudes (for example, ~400 m level over the High Arctic) in this technical paper. I don’t expect the detailed discussion on the scientific analysis of INPs and new findings (the authors must want to show them in another paper in preparation), but some technical descriptions on the operation of the SHARK system for size-resolved INP measurements at higher altitudes (ideally, free troposphere) should be presented in this technical paper.
Admit that they have not yet included any results of size-resolved INP measurements at higher altitudes in this technical paper. In this case, the authors should clearly explain that “the performance of the SHARK system has been evaluated only near the ground level” and that “its performance in the free troposphere will be evaluated in the future work” in the Abstract (and also in the Introduction!?).
# Additional Comments on “Comments/Responses 6”
In addition to nano-INPs from pollen grains, the authors may need to discuss other potential biological sources causing a steep INP spectrum. Earlier studies have suggested that nanoscale materials that nucleate ice can also be released from soils, as well as pollen grains. For examples, O’Sullivan et al. (2015) quantify the ice-nucleating activity of nano-ice nucleating particles (nano-INPs) washed off pollen and also show that nano-INPs are present in a soil sample. Other studies have also suggested the presence of submicron organic particles serving as INPs from fertile soils (e.g., Tobo et al., 2014; Hill et al., 2016; Wang et al., 2017).
Hill, T. C. J., DeMott, P. J., Tobo, Y., Fröhlich-Nowoisky, J., Moffett, B. F., Franc, G. D., and Kreidenweis, S. M.: Sources of organic ice nucleating particles in soils, Atmos. Chem. Phys., 16, 7195–7211, https://doi.org/10.5194/acp-16-7195-2016, 2016.
O’Sullivan, D., Murray, B., Ross, J., Whale, T. F., Price, H. C., Atkinson, J. D., Umo, N. S., and Web, M. E.: The relevance of nanoscale biological fragments for ice nucleation in clouds, Sci. Rep., 5, 8082, https://doi.org/10.1038/srep08082, 2015.
Tobo, Y., DeMott, P. J., Hill, T. C. J., Prenni, A. J., Swoboda-Colberg, N. G., Franc, G. D., and Kreidenweis, S. M.: Organic matter matters for ice nuclei of agricultural soil origin, Atmos. Chem. Phys., 14, 8521–8531, https://doi.org/10.5194/acp-14-8521-2014, 2014.
Wang, B., Harder, T. H., Kelly, S. T., Piens, D. S., China, S., Kovarik, L. K., Keiluweit, M., and Laskin, A.: Airborne soil organic particles generated by precipitation, Nat. Geosci., 9, 433–437, https://doi.org/10.1038/ngeo2705, 2016.