the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Feb 2024
Biological and dust aerosol as sources of ice nucleating particles in the Eastern Mediterranean: source apportionment, atmospheric processing and parameterization
Abstract. Aerosol-cloud interactions in mixed-phase clouds (MPCs) are one of the most uncertain drivers of the hydrological cycle and climate change. A synergy of in-situ, remote sensing and modelling experiments was used to determine the source of ice nucleating particles (INPs) for MPCs at Mount Helmos in the Eastern Mediterranean. The influences of boundary layer turbulence, vertical aerosol distributions and meteorological conditions were also examined. When the observation site is in the Free Troposphere (FT), approximately 1 in 106 aerosol particles serve as INPs. The INP abundance spans three orders of magnitude and increases following the order of marine aerosols, continental aerosols, and finally, dust plumes. Biological particles are important INPs observed in continental and marine aerosols, whereas they play a secondary yet important role even during Saharan dust events. Air masses in the planetary boundary layer (PBL) show both enriched INP concentrations and higher proportion of INPs in comparison to total aerosol particles, different from cases in the FT. The presence of precipitations/clouds enriches INPs in the FT but decreases INPs in the PBL. Additionally, new INP parameterizations, incorporating the ratio of fluorescent-to-nonfluorescent or coarse-to-fine particles and predicting >90 % of the observed INPs within an uncertainty range of a factor of 10, exhibit better performance than current widely-used parameterizations, and allow ice formation in models to respond to variations in dust and biological particles. The improved parameterizations can help MPC formation simulations in regions with various INP sources or different regions with prevailing INP sources.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-511', Anonymous Referee #1, 20 Mar 2024
The manuscript presents results of an aerosol measurement campaign lasting seven weeks in autumn 2021 at a mountain site on the Peloponnese. Eight contrasting situations were observed during this campaign and characterised using a range of instruments, including an expansion chamber capable to determine in 6-minute intervals the number of ice nucleating particles (INPs) active at around -25 °C. In addition, INPs active at warmer temperatures were collected on filters for offline analysis. Planetary boundary layer height, clouds and rain were observed from a station 0.5 km below the aerosol measurements and potential source regions of the aerosol particles were derived by modelling efforts.
A wealth of data is comprehensively analysed, meaningfully interpreted and discussed in the context of the available literature. Notwithstanding that it encompasses 39 pages of main text the manuscript is pleasant to read, also Figures and Tables are clear.
There is little I would recommend to change in this manuscript. My main concern are general statements about INPs in which their activation temperature is not mentioned. In this study, INPs include those measured by PINE (ca. -25 °C) and others measured by INSEKT (-5 °C to -25 °C). Througout the text, it should always be clear which activation temperature applies in a statement. A first example is in the Abstract, line 25: "...approximately 1 in 10^6 aerosol particles serve as INPs." A much later example is on page 30, lines 753 and 754: "Therefore, the overall effect of precipitation/clouds on INPs observed at (HAC)2 shows a decrease when (HAC)2 lies within the PBL." It should be made clear that this finding relates to INPs active at around -25 °C. Testa et al. (2021; https://doi.org/10.1029/2021JD035186) made a similar observation for INPs active at around -25 °C, but at the same time INPs active at -12 °C were found to have increased (see Figure 5 in Testa et al., 2021). Hence, activation temperature matters not only in terms of the number concentration, but also in terms of atmospheric behaviour.
Minor issues
Page 5, section 2.2.1: Please add to the description of the offline INP observations the filter material, diameter, pore size, and the flow rate of the sampler.
Line 214: "40000 air parcels" probably should be "40000 particles"
Line 245: "take up a large fraction" or "make up a large fraction"?
Lines 253 and 254: "to differentiate the difference" I do not understand the meaning of this expression.
Figure 5: Please add x-axes to the plots, even if they only state the running number of observations in each type of aerosol category.
Figure 8: I wonder why the number of INPs measured with PINE does not increase with decreasing temperature. Please add a note on this issue to the Figure legend.
Figure 9a: The temperature indicated for measurements of "South dust in PBL after marine aerosols" is -2.39. I guess it should be -23.9.
Figure 9c and 9d: The effect of precipitation/clouds on INPs in FT is very similar in direction and magnitude as observed in winter in the Swiss Alps by Mignani et al. (2021; https://doi.org/10.5194/acp-21-657-2021).
Table 2: Readability of p-values would be improved by replacing the scientific notation of very small values (e.g. 9.3e-122) by "< 0.001".
Line 548 to 550: A further explanation of why values reported by Lacher et al. (2021) for Jungfraujoch (3580 m) were smaller than what was found at Mt. Helmos (2314 m) could be the higher elevation of Jungfraujoch.
Lines 588 and 589: Also in the Arctic, fluorescent particles constitute the vast majority of INPs (active at -15 °C), as Freitas et al. have recently reported (2023; https://doi.org/10.1038/s41467-023-41696-7).
Line 725: "...ABCWIBS particles are relevant for biological particles..." I am not sure what is meant by this expression. Do you mean something like "...ABCWIBS particles are related to biological particles..."
Citation: https://doi.org/10.5194/egusphere-2024-511-RC1 -
AC1: 'Reply on RC1', Kunfeng Gao, 30 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-511/egusphere-2024-511-AC1-supplement.pdf
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AC1: 'Reply on RC1', Kunfeng Gao, 30 Jun 2024
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RC2: 'Comment on egusphere-2024-511', Anonymous Referee #2, 05 Jun 2024
Review of Gao et al. Biological and dust aerosol as sources of ice nucleating particles in the Eastern Mediterranean: source apportionment, atmospheric processing and parameterization
This study provides a comprehensive analysis of the sources of Ice Nucleating Particles (INPs) for mixed-phase clouds at Mount Helmos in the Eastern Mediterranean. By integrating in-situ observations, remote sensing data, and modeling experiments, the study examines the influence of boundary layer turbulence, vertical aerosol distributions, and meteorological conditions. It distinguishes among contrasting meteorological situations where aerosol properties and associated INP activities and levels differ. Additionally, the study evaluates existing INP schemes in the literature and proposes new INP parameterizations, constrained by the observations, that outperform previous ones for this specific location.
This is an excellently written and highly relevant study. The extensive experimental data is thoroughly analyzed, and many of the findings are novel. The association between different aerosol properties and INPs is robust, and the inclusion of such dependencies in INP schemes is promising.
I have no major concerns about this paper. One possible consideration is its length—39 pages with a supplementary section containing 35 figures. While the paper is comprehensive and detailed, it might have been more digestible as a two-part paper: one focusing on the thorough analyses and the other on the development and evaluation of the INP schemes.
Specific comments:
- The underestimation of INP concentrations by the INSEKT compared to the PINE is a weakness of the methodology. There is a specific analysis of the differences between the INSEKT and the PINE in the supplemental material and a final discussion in the conclusions. However, it is important to discuss more broadly the implications of such potential systematic error in the evaluation of the INP schemes and the development of new schemes. Providing an estimate of the effect of this underestimation on the evaluation of INP schemes would be helpful. To what extent is this affecting the evaluation of schemes in the literature? How were INPs measured in other studies? This is particularly important when comparing with other studies and for future evaluation of the new schemes proposed with INP data obtained with other methods, as well as when using the new schemes in models.
- Figure 5: Understanding the differences on the proportions of the WIBS channels between the aerosol sources from this Figure is challenging. I suggest that you use box plots as in Figure 3. This would provide a better quantitative comparison of the proportions among sources.
- Section 3.4.1 and Figure 13. I do not fully understand the rationale of comparing existing INP schemes beyond their species-range of applicability. For instance, Niemand and Ulrich focus on dust, McCluskey on marine organics and Tobo on biological particles mostly. While in the supplemental material additional figures are provided for each of the sources and INP schemes, I believe that Figure 13 in the main paper would be more informative if the color coding would refer to the INP source in the observations. Also, please discuss in this section how the uncertainty related to the use of the INSEKT may affect this evaluation.
- Section 3.4.2 and Table 3: An explanation about the selected specific forms for each equation is needed. Also please describe how they were fitted to the measurements. This could be provided in the supplemental material. Also please revise the formulations and check for any potential typo. Given the number of parameters, it would be very unfortunate that potential typos are propagated into future modeling studies.
- Line 463: change to “This means anthropogenic pollution may impact (HAC)2 even when it is in the FT”
- Figure 9. Typo in the x axis of 9a (23.9 instead of 2.39)
- Line 785: revise this sentence. It is not clear.
- Conclusions: how the developed parameterizations could be applied in current climate models? Some models already include dependencies on dust, marine organics and PBAPs. A detailed perspective/recommendation in this sense would be extremely useful for modelers and make even more applicable the results of this paper.
Citation: https://doi.org/10.5194/egusphere-2024-511-RC2 -
AC2: 'Reply on RC2', Kunfeng Gao, 30 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-511/egusphere-2024-511-AC2-supplement.pdf
-
RC3: 'Comment on egusphere-2024-511', Anonymous Referee #3, 11 Jun 2024
I read the manuscript and found it extremely interesting, well organized, clearly written and scientifically sound. The manuscript presents and analyses an extremely valuable observational dataset of INP properties and ancillary information, useful for interpreting INP sources under different circulation regimes in the Mediterranean climate hotspot. I recommend publication, once the following minor comments are addressed.
If I have to make a remark, the authors compare their results with a limited number of previous studies reporting INPs in the Mediterranean basin. Considering that the literature on the subject is not huge, they could have done something more thorough. Nevertheless, I understand that the paper is already long as it is and that the authors selected for comparison the available immersion freezing INP datasets for major comparability with the INSEKT data.
A second remark would regard the paper length. Maybe the authors could have chosen a different publication strategy to disseminate their data (two shorter publications, instead of this very large one).
L280-281. “the distinction of marine aerosols above PBL is indicated by the highest Cl- fraction compared to the other scenarios”: the motivation for this is not clear. Please, explain or support with an appropriate citation.
Fig. 5. It is not clear what the x-axis represents. I guess time? Please add the axis scale and clarify better. Moreover double check this sentence in the caption: “The fraction of each type of particle from an identified aerosol source is shown by the x-axis”. Maybe it should be y-axis?
L556. Remove the symbol #.
L575. I have the feeling that the term “secondary” can be subject to misinterpretations given the different meanings that it can assume in aerosol literature (secondary aerosol, secondary ice formation…); maybe you could use the term “minor” to indicate a lower role of small-sized aerosol particles as INPs. This applies also in L655.
L612. I am not sure that “wrt.” Can be immediately understood by non-native speakers.
Citation: https://doi.org/10.5194/egusphere-2024-511-RC3 -
AC3: 'Reply on RC3', Kunfeng Gao, 30 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-511/egusphere-2024-511-AC3-supplement.pdf
-
AC3: 'Reply on RC3', Kunfeng Gao, 30 Jun 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-511', Anonymous Referee #1, 20 Mar 2024
The manuscript presents results of an aerosol measurement campaign lasting seven weeks in autumn 2021 at a mountain site on the Peloponnese. Eight contrasting situations were observed during this campaign and characterised using a range of instruments, including an expansion chamber capable to determine in 6-minute intervals the number of ice nucleating particles (INPs) active at around -25 °C. In addition, INPs active at warmer temperatures were collected on filters for offline analysis. Planetary boundary layer height, clouds and rain were observed from a station 0.5 km below the aerosol measurements and potential source regions of the aerosol particles were derived by modelling efforts.
A wealth of data is comprehensively analysed, meaningfully interpreted and discussed in the context of the available literature. Notwithstanding that it encompasses 39 pages of main text the manuscript is pleasant to read, also Figures and Tables are clear.
There is little I would recommend to change in this manuscript. My main concern are general statements about INPs in which their activation temperature is not mentioned. In this study, INPs include those measured by PINE (ca. -25 °C) and others measured by INSEKT (-5 °C to -25 °C). Througout the text, it should always be clear which activation temperature applies in a statement. A first example is in the Abstract, line 25: "...approximately 1 in 10^6 aerosol particles serve as INPs." A much later example is on page 30, lines 753 and 754: "Therefore, the overall effect of precipitation/clouds on INPs observed at (HAC)2 shows a decrease when (HAC)2 lies within the PBL." It should be made clear that this finding relates to INPs active at around -25 °C. Testa et al. (2021; https://doi.org/10.1029/2021JD035186) made a similar observation for INPs active at around -25 °C, but at the same time INPs active at -12 °C were found to have increased (see Figure 5 in Testa et al., 2021). Hence, activation temperature matters not only in terms of the number concentration, but also in terms of atmospheric behaviour.
Minor issues
Page 5, section 2.2.1: Please add to the description of the offline INP observations the filter material, diameter, pore size, and the flow rate of the sampler.
Line 214: "40000 air parcels" probably should be "40000 particles"
Line 245: "take up a large fraction" or "make up a large fraction"?
Lines 253 and 254: "to differentiate the difference" I do not understand the meaning of this expression.
Figure 5: Please add x-axes to the plots, even if they only state the running number of observations in each type of aerosol category.
Figure 8: I wonder why the number of INPs measured with PINE does not increase with decreasing temperature. Please add a note on this issue to the Figure legend.
Figure 9a: The temperature indicated for measurements of "South dust in PBL after marine aerosols" is -2.39. I guess it should be -23.9.
Figure 9c and 9d: The effect of precipitation/clouds on INPs in FT is very similar in direction and magnitude as observed in winter in the Swiss Alps by Mignani et al. (2021; https://doi.org/10.5194/acp-21-657-2021).
Table 2: Readability of p-values would be improved by replacing the scientific notation of very small values (e.g. 9.3e-122) by "< 0.001".
Line 548 to 550: A further explanation of why values reported by Lacher et al. (2021) for Jungfraujoch (3580 m) were smaller than what was found at Mt. Helmos (2314 m) could be the higher elevation of Jungfraujoch.
Lines 588 and 589: Also in the Arctic, fluorescent particles constitute the vast majority of INPs (active at -15 °C), as Freitas et al. have recently reported (2023; https://doi.org/10.1038/s41467-023-41696-7).
Line 725: "...ABCWIBS particles are relevant for biological particles..." I am not sure what is meant by this expression. Do you mean something like "...ABCWIBS particles are related to biological particles..."
Citation: https://doi.org/10.5194/egusphere-2024-511-RC1 -
AC1: 'Reply on RC1', Kunfeng Gao, 30 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-511/egusphere-2024-511-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Kunfeng Gao, 30 Jun 2024
-
RC2: 'Comment on egusphere-2024-511', Anonymous Referee #2, 05 Jun 2024
Review of Gao et al. Biological and dust aerosol as sources of ice nucleating particles in the Eastern Mediterranean: source apportionment, atmospheric processing and parameterization
This study provides a comprehensive analysis of the sources of Ice Nucleating Particles (INPs) for mixed-phase clouds at Mount Helmos in the Eastern Mediterranean. By integrating in-situ observations, remote sensing data, and modeling experiments, the study examines the influence of boundary layer turbulence, vertical aerosol distributions, and meteorological conditions. It distinguishes among contrasting meteorological situations where aerosol properties and associated INP activities and levels differ. Additionally, the study evaluates existing INP schemes in the literature and proposes new INP parameterizations, constrained by the observations, that outperform previous ones for this specific location.
This is an excellently written and highly relevant study. The extensive experimental data is thoroughly analyzed, and many of the findings are novel. The association between different aerosol properties and INPs is robust, and the inclusion of such dependencies in INP schemes is promising.
I have no major concerns about this paper. One possible consideration is its length—39 pages with a supplementary section containing 35 figures. While the paper is comprehensive and detailed, it might have been more digestible as a two-part paper: one focusing on the thorough analyses and the other on the development and evaluation of the INP schemes.
Specific comments:
- The underestimation of INP concentrations by the INSEKT compared to the PINE is a weakness of the methodology. There is a specific analysis of the differences between the INSEKT and the PINE in the supplemental material and a final discussion in the conclusions. However, it is important to discuss more broadly the implications of such potential systematic error in the evaluation of the INP schemes and the development of new schemes. Providing an estimate of the effect of this underestimation on the evaluation of INP schemes would be helpful. To what extent is this affecting the evaluation of schemes in the literature? How were INPs measured in other studies? This is particularly important when comparing with other studies and for future evaluation of the new schemes proposed with INP data obtained with other methods, as well as when using the new schemes in models.
- Figure 5: Understanding the differences on the proportions of the WIBS channels between the aerosol sources from this Figure is challenging. I suggest that you use box plots as in Figure 3. This would provide a better quantitative comparison of the proportions among sources.
- Section 3.4.1 and Figure 13. I do not fully understand the rationale of comparing existing INP schemes beyond their species-range of applicability. For instance, Niemand and Ulrich focus on dust, McCluskey on marine organics and Tobo on biological particles mostly. While in the supplemental material additional figures are provided for each of the sources and INP schemes, I believe that Figure 13 in the main paper would be more informative if the color coding would refer to the INP source in the observations. Also, please discuss in this section how the uncertainty related to the use of the INSEKT may affect this evaluation.
- Section 3.4.2 and Table 3: An explanation about the selected specific forms for each equation is needed. Also please describe how they were fitted to the measurements. This could be provided in the supplemental material. Also please revise the formulations and check for any potential typo. Given the number of parameters, it would be very unfortunate that potential typos are propagated into future modeling studies.
- Line 463: change to “This means anthropogenic pollution may impact (HAC)2 even when it is in the FT”
- Figure 9. Typo in the x axis of 9a (23.9 instead of 2.39)
- Line 785: revise this sentence. It is not clear.
- Conclusions: how the developed parameterizations could be applied in current climate models? Some models already include dependencies on dust, marine organics and PBAPs. A detailed perspective/recommendation in this sense would be extremely useful for modelers and make even more applicable the results of this paper.
Citation: https://doi.org/10.5194/egusphere-2024-511-RC2 -
AC2: 'Reply on RC2', Kunfeng Gao, 30 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-511/egusphere-2024-511-AC2-supplement.pdf
-
RC3: 'Comment on egusphere-2024-511', Anonymous Referee #3, 11 Jun 2024
I read the manuscript and found it extremely interesting, well organized, clearly written and scientifically sound. The manuscript presents and analyses an extremely valuable observational dataset of INP properties and ancillary information, useful for interpreting INP sources under different circulation regimes in the Mediterranean climate hotspot. I recommend publication, once the following minor comments are addressed.
If I have to make a remark, the authors compare their results with a limited number of previous studies reporting INPs in the Mediterranean basin. Considering that the literature on the subject is not huge, they could have done something more thorough. Nevertheless, I understand that the paper is already long as it is and that the authors selected for comparison the available immersion freezing INP datasets for major comparability with the INSEKT data.
A second remark would regard the paper length. Maybe the authors could have chosen a different publication strategy to disseminate their data (two shorter publications, instead of this very large one).
L280-281. “the distinction of marine aerosols above PBL is indicated by the highest Cl- fraction compared to the other scenarios”: the motivation for this is not clear. Please, explain or support with an appropriate citation.
Fig. 5. It is not clear what the x-axis represents. I guess time? Please add the axis scale and clarify better. Moreover double check this sentence in the caption: “The fraction of each type of particle from an identified aerosol source is shown by the x-axis”. Maybe it should be y-axis?
L556. Remove the symbol #.
L575. I have the feeling that the term “secondary” can be subject to misinterpretations given the different meanings that it can assume in aerosol literature (secondary aerosol, secondary ice formation…); maybe you could use the term “minor” to indicate a lower role of small-sized aerosol particles as INPs. This applies also in L655.
L612. I am not sure that “wrt.” Can be immediately understood by non-native speakers.
Citation: https://doi.org/10.5194/egusphere-2024-511-RC3 -
AC3: 'Reply on RC3', Kunfeng Gao, 30 Jun 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-511/egusphere-2024-511-AC3-supplement.pdf
-
AC3: 'Reply on RC3', Kunfeng Gao, 30 Jun 2024
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Cited
Franziska Vogel
Romanos Foskinis
Stergios Vratolis
Maria I. Gini
Konstantinos Granakis
Anne-Claire Billault-Roux
Paraskevi Georgakaki
Olga Zografou
Prodromos Fetfatzis
Alexis Berne
Alexandros Papagiannis
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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