the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Mar 2022
The ocean fine spray
Abstract. A major fraction of the atmospheric aerosols come from the ocean spray originated by the bursting of bubbles from breaking waves. A theoretical framework that incorporates the latest knowledge on film and jet droplets from bubble bursting is proposed. Assuming that their relics constitute the ultimate origin of primary and secondary sea aerosols through a diversity of physicochemical routes, the model can be reduced to a single controlling parameter to predict the global probability density distribution (pdf) of the ocean spray. The bursting and collapse of small bubbles on the sea surface from about 10 to 100 microns produces an extreme energy focusing and the ejection of a rapid liquid spout whose size reaches the free molecular regime of the gaseous environment. In these rarefied conditions, simulations show that this spout yields a jet of sub-micrometer and nanometric scale droplets whose number and speed can be far beyond any previous estimation, overcoming by orders of magnitude alternative mechanisms recently proposed. The one-parameter model fits remarkably well published experimental measurements along five orders of magnitude of spray size, from about 5 nm to about 0.5 mm. According to this proposal, the majority of aerosols determining the life on our planet would have their extremely elusive birth in the uterus-like nano-shape of small bursting bubbles on the ocean surface at the very latest instants of collapse.
Status: closed
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CC1: 'Comment on egusphere-2022-27', carlos bordons, 13 Apr 2022
It seems to be a very interesting and disruptive theoretical framework. I can help to understand the origin and behaviour of aerosols in the atmosphere. Looking forward to reading the complete study.
Citation: https://doi.org/10.5194/egusphere-2022-27-CC1 -
AC1: 'Reply on CC1', Alfonso Ganan-Calvo, 13 Apr 2022
Thank you indeed. As you say, these results may help to understand the origin of the aerosol content of the atmosphere. First of all, it would not only help to explain the ultimate origin of most nanoscale seeds that form clouds from supersaturated atmospheric vapor (cloud condensation nuclei), but knowing their precise mechanical birth process would help to understand the role of organic matter and pollutants at the sea surface (sea surface layer) in that atmospheric aerosol content and its microphysics. Secondly, the detailed statistical description provided can be a helpful tool to identify and experimentally verify the different components of the theoretical proposal.
Citation: https://doi.org/10.5194/egusphere-2022-27-AC1
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AC1: 'Reply on CC1', Alfonso Ganan-Calvo, 13 Apr 2022
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RC1: 'Comment on egusphere-2022-27', Anonymous Referee #1, 25 Apr 2022
The paper “The ocean fine spray” by A. Ganan-Calvo discusses the production of sea spray aerosols at the sea surface. Specifically, the author focuses on the bubble-bursting mechanism, in which an air bubble entrained in the water rises to the surface, breaks, and expels aerosols into the atmosphere. It is thought that this process generates two types of droplets: sub-micrometer film droplets, and larger jet droplets. In his paper, the author argues that the size range of jet droplets may extend well into the sub-micrometer regime, and that their contribution to this fraction could be orders of magnitude larger than the total film contribution.
I found it difficult to review this paper, because I lack the in-depth knowledge of fluid mechanics required to challenge the author’s line of thoughts or his calculations of streamlines etc. Having said this, I find the paper clear and convincing. The paper is well-organized, and the author properly introduces each step in his line of thoughts. The author also provides ample references (75), which allows the interested reader to verify all underlying work. I find the discussion of the data and the conclusions drawn from it convincing. The author pays attention to many details, such as the properties of the underlying literature data, or the sensitivity of the model he derives. In all, I find this a very good paper.
The paper is difficult to read because of its complexity, but I found the textual quality quite acceptable. I normally have a list of minor textual hiccups, but I did not find it necessary to do so in this case.
In summary, I recommend this paper for acceptance.
Citation: https://doi.org/10.5194/egusphere-2022-27-RC1 -
AC2: 'Reply on RC1', Alfonso Ganan-Calvo, 25 Apr 2022
I sincerely appreciate the encouraging comments of the anonymous Referee.
Citation: https://doi.org/10.5194/egusphere-2022-27-AC2
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AC2: 'Reply on RC1', Alfonso Ganan-Calvo, 25 Apr 2022
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RC2: 'Comment on egusphere-2022-27', Anonymous Referee #2, 25 Apr 2022
The author proposes that a single mechanism is responsible for most sea spray aerosol, ranging from 5 nm to about 0.5 mm and due to bursting bubbles from 10um through the jet drop process. I consider that this paper is of interest to the community as it presents a new vision of the problem. However, I have several comments that I believe need to be addressed before the paper can be published. It is also worth mentioning that the paper is relatively hard to read and follow.
I think the author needs to be clearer on what has been proven by experimental data at this point and which part of its theory remains hypothetical. This is not necessarily a problem but it needs to be made very clear that several statements are not backed up by data at this point (as far as I understand). If I followed correctly, the discussion on rarefaction remains highly hypothetical since no experimental data can back the claims from the author. I remain particularly impressed by the 2017’s paper from the author on jet drop, but that theory was backed by many data. I am also unclear why the author did not consider any of the dry particles measurements by bursting from many other authors (e.g. Forestieri et al, Salter et al, Prather et al; Frossard et al, Sellegri et al etc). The literature is huge and I understand it is hard to keep track but it seems that the choice of data set might be at least discussed, so that the reader can understand why certain data are used and not others.
As a general point of discussion, I am not convinced that a single mechanism can explain all of the sea spray aerosols for two main reasons: a) there is plenty of chemical evidence of the importance of film drops, as it is expected to have more organic material in the film drops than the jet drops; and b) can the author clarify how the bubble population down to 10um at the surface is justified? Again, this is not a show stopper but hypothesis and limitations should be discussed more openly.
Major comments:
1/ When discussing sizes, the author needs to specify if they mention the size at production, the size at 80% humidity or the dry aerosol size (all of which are being used in various parts of the literature). There are typically factor 2 to 4 variations for sea salt which make a big difference when arguing about “100nm” drops/particles. I do not recall jet drop data demonstrating 200nm drop size, as Brasz et al 2018 show a 1um drop (which would be about 250 dry radius for a salt particle (so not a drop but a solid salt particle). This needs to be clarified throughout the text. Is the author talking about salt dry size? Liquid size? If considering salt, then field data suggest that particles below 10nm are essentially organic (see literature cited in the introduction).
2/ Several papers have analyzed the composition of atmospheric aerosols. I am not a chemist but it seems that organic aerosol mostly originate from film drops (see recent work by Quinn, Prather, etc). How would the author reconcile its claim with the atmospheric chemistry literature? (some of it being cited in the manuscript). This is also related to my previous point as the link between organic aerosol and initial drop size is not obvious (at least to me).
3/ Do we have observations of bursting bubbles of 10-1000um at the surface of the ocean? Such small bubbles are observed down in the water column as they can be transported by turbulent processes. Simulations of bubble dynamics in upper ocean by JH. Liang and coauthors show significant transport of the small bubbles down in the mixed layer, leading to their full dissolution. There are discussions in papers on bubble gas exchange by Thorpe and Woolf which assume that bubbles below a certain size fully dissolve as their rise velocity would be too small to overcome turbulence fluctuations and those bubbles might never reach the surface. It seems that these questions deserve some discussion as they will be important to test the applicability of the proposed theory.
4/ I am not sure that the current literature “describes in great detail the chemical composition of ocean aerosols and their dependence on ambient (wind temperature)” There is a lot of uncertainties in the role of temperature, with some studies predicting an increase in ssa while other predict a decrease (see for example figure 1 in Forestieri et al 2018). Scatter in the role of wind spans two to three orders of magnitude (see review from deLeeuw et al 2011). This is a topic of intense scrutiny due to the difficulty of the field measurements.
5/ When the author mentions “Two basic mechanisms are responsible of this droplet emission: bubble film breakup” (p Lhuissier and Villermaux (2012); Jiang et al. (2022)),” I would encourage to cite previous work by Spiel, Blanchard, and others. The cited papers are not (by far) the first ones to describe film drops. The review of Lewis and Schwartz 2004 does an excellent job at summarizing the film drop evidence in the literature, in particular with respect to sub-micron aerosols. This part of the literature should not be overlooked as the Lhuissier and Villermaux (2012); Jiang et al. (2022) papers (while wonderful) present a specific vision of the problem (in the same way as the present paper presents the specific vision of the author). All of this is fine and part of the scientific process but the introduction should not focus on a specific subset of authors.
6/ The fitting and reanalysis done in figure 2 needs to be clarified. I would encourage the author to first show the dimensional data and then the rescaling as the rescaling is not obvious/common in the aerosol literature. I would also encourage to provide a plot of the mean diameter/radius of the drops as a function of the bubble, as it seems to emerge from that rescaling and is not presented in the original paper (I think). The measurements from Jiang et al 2022 are presented in dry size so the scaling factors used in the reanalysis need to be mentioned.
7/ The discussion on the rarefaction effect is rather unclear to me. I would encourage the author to explain this better. Figure 7 is used as proof of the rarefaction effect but if I understand correctly comes from simulations. Does the author have any experimental evidence of this effect? I see this as a major issue with the claims of the author. They propose a theory leading to very strong claims but have no data to back it up. I would be more clear on some of the hypothesis that remain to be tested.
Other comments:
8/ In 2.1.; “rd<0.5” is that micron?
9/ I do not understand the statement: “The super-micron size range is comprised by wet aerosols and its presence is fundamentally reduced to marine and coastal regions Boyce (1954)”
10/ I do not understand the statement “From this study and entirely attributing the fitted pdfs to micron- and submicron film droplets, one would conclude that (i) the droplet generation by film flapping will be distributed according to a lognormal for the nondimensional variable η = χdLa−1/5 , which reflects a reasonable dependency on the bubble size, while (ii) the more “ classical” film rim fragmentation Lhuissier and Villermaux (2012) would yield droplets distributed according to a generalized inverse Gaussian as (1) independently of La.”
Could the author be more explicit?
11/ The discussion on enrichment for very small bubbles seems interesting but I am not sure I am fully following. It also seems to contrast with some other papers. I would encourage the author to discuss this in more details and clarify its hypothesis compared to other work in the literature (see the work from W.C. Keene, P. Quinn, A. Frossard, K. Prather, etc).
12/ I am not sure that the first sentence of the abstract is accurate. It is true in remote marine environment but probably wrong as a general statement.
Citation: https://doi.org/10.5194/egusphere-2022-27-RC2 - AC3: 'Reply on RC2', Alfonso Ganan-Calvo, 06 May 2022
Status: closed
-
CC1: 'Comment on egusphere-2022-27', carlos bordons, 13 Apr 2022
It seems to be a very interesting and disruptive theoretical framework. I can help to understand the origin and behaviour of aerosols in the atmosphere. Looking forward to reading the complete study.
Citation: https://doi.org/10.5194/egusphere-2022-27-CC1 -
AC1: 'Reply on CC1', Alfonso Ganan-Calvo, 13 Apr 2022
Thank you indeed. As you say, these results may help to understand the origin of the aerosol content of the atmosphere. First of all, it would not only help to explain the ultimate origin of most nanoscale seeds that form clouds from supersaturated atmospheric vapor (cloud condensation nuclei), but knowing their precise mechanical birth process would help to understand the role of organic matter and pollutants at the sea surface (sea surface layer) in that atmospheric aerosol content and its microphysics. Secondly, the detailed statistical description provided can be a helpful tool to identify and experimentally verify the different components of the theoretical proposal.
Citation: https://doi.org/10.5194/egusphere-2022-27-AC1
-
AC1: 'Reply on CC1', Alfonso Ganan-Calvo, 13 Apr 2022
-
RC1: 'Comment on egusphere-2022-27', Anonymous Referee #1, 25 Apr 2022
The paper “The ocean fine spray” by A. Ganan-Calvo discusses the production of sea spray aerosols at the sea surface. Specifically, the author focuses on the bubble-bursting mechanism, in which an air bubble entrained in the water rises to the surface, breaks, and expels aerosols into the atmosphere. It is thought that this process generates two types of droplets: sub-micrometer film droplets, and larger jet droplets. In his paper, the author argues that the size range of jet droplets may extend well into the sub-micrometer regime, and that their contribution to this fraction could be orders of magnitude larger than the total film contribution.
I found it difficult to review this paper, because I lack the in-depth knowledge of fluid mechanics required to challenge the author’s line of thoughts or his calculations of streamlines etc. Having said this, I find the paper clear and convincing. The paper is well-organized, and the author properly introduces each step in his line of thoughts. The author also provides ample references (75), which allows the interested reader to verify all underlying work. I find the discussion of the data and the conclusions drawn from it convincing. The author pays attention to many details, such as the properties of the underlying literature data, or the sensitivity of the model he derives. In all, I find this a very good paper.
The paper is difficult to read because of its complexity, but I found the textual quality quite acceptable. I normally have a list of minor textual hiccups, but I did not find it necessary to do so in this case.
In summary, I recommend this paper for acceptance.
Citation: https://doi.org/10.5194/egusphere-2022-27-RC1 -
AC2: 'Reply on RC1', Alfonso Ganan-Calvo, 25 Apr 2022
I sincerely appreciate the encouraging comments of the anonymous Referee.
Citation: https://doi.org/10.5194/egusphere-2022-27-AC2
-
AC2: 'Reply on RC1', Alfonso Ganan-Calvo, 25 Apr 2022
-
RC2: 'Comment on egusphere-2022-27', Anonymous Referee #2, 25 Apr 2022
The author proposes that a single mechanism is responsible for most sea spray aerosol, ranging from 5 nm to about 0.5 mm and due to bursting bubbles from 10um through the jet drop process. I consider that this paper is of interest to the community as it presents a new vision of the problem. However, I have several comments that I believe need to be addressed before the paper can be published. It is also worth mentioning that the paper is relatively hard to read and follow.
I think the author needs to be clearer on what has been proven by experimental data at this point and which part of its theory remains hypothetical. This is not necessarily a problem but it needs to be made very clear that several statements are not backed up by data at this point (as far as I understand). If I followed correctly, the discussion on rarefaction remains highly hypothetical since no experimental data can back the claims from the author. I remain particularly impressed by the 2017’s paper from the author on jet drop, but that theory was backed by many data. I am also unclear why the author did not consider any of the dry particles measurements by bursting from many other authors (e.g. Forestieri et al, Salter et al, Prather et al; Frossard et al, Sellegri et al etc). The literature is huge and I understand it is hard to keep track but it seems that the choice of data set might be at least discussed, so that the reader can understand why certain data are used and not others.
As a general point of discussion, I am not convinced that a single mechanism can explain all of the sea spray aerosols for two main reasons: a) there is plenty of chemical evidence of the importance of film drops, as it is expected to have more organic material in the film drops than the jet drops; and b) can the author clarify how the bubble population down to 10um at the surface is justified? Again, this is not a show stopper but hypothesis and limitations should be discussed more openly.
Major comments:
1/ When discussing sizes, the author needs to specify if they mention the size at production, the size at 80% humidity or the dry aerosol size (all of which are being used in various parts of the literature). There are typically factor 2 to 4 variations for sea salt which make a big difference when arguing about “100nm” drops/particles. I do not recall jet drop data demonstrating 200nm drop size, as Brasz et al 2018 show a 1um drop (which would be about 250 dry radius for a salt particle (so not a drop but a solid salt particle). This needs to be clarified throughout the text. Is the author talking about salt dry size? Liquid size? If considering salt, then field data suggest that particles below 10nm are essentially organic (see literature cited in the introduction).
2/ Several papers have analyzed the composition of atmospheric aerosols. I am not a chemist but it seems that organic aerosol mostly originate from film drops (see recent work by Quinn, Prather, etc). How would the author reconcile its claim with the atmospheric chemistry literature? (some of it being cited in the manuscript). This is also related to my previous point as the link between organic aerosol and initial drop size is not obvious (at least to me).
3/ Do we have observations of bursting bubbles of 10-1000um at the surface of the ocean? Such small bubbles are observed down in the water column as they can be transported by turbulent processes. Simulations of bubble dynamics in upper ocean by JH. Liang and coauthors show significant transport of the small bubbles down in the mixed layer, leading to their full dissolution. There are discussions in papers on bubble gas exchange by Thorpe and Woolf which assume that bubbles below a certain size fully dissolve as their rise velocity would be too small to overcome turbulence fluctuations and those bubbles might never reach the surface. It seems that these questions deserve some discussion as they will be important to test the applicability of the proposed theory.
4/ I am not sure that the current literature “describes in great detail the chemical composition of ocean aerosols and their dependence on ambient (wind temperature)” There is a lot of uncertainties in the role of temperature, with some studies predicting an increase in ssa while other predict a decrease (see for example figure 1 in Forestieri et al 2018). Scatter in the role of wind spans two to three orders of magnitude (see review from deLeeuw et al 2011). This is a topic of intense scrutiny due to the difficulty of the field measurements.
5/ When the author mentions “Two basic mechanisms are responsible of this droplet emission: bubble film breakup” (p Lhuissier and Villermaux (2012); Jiang et al. (2022)),” I would encourage to cite previous work by Spiel, Blanchard, and others. The cited papers are not (by far) the first ones to describe film drops. The review of Lewis and Schwartz 2004 does an excellent job at summarizing the film drop evidence in the literature, in particular with respect to sub-micron aerosols. This part of the literature should not be overlooked as the Lhuissier and Villermaux (2012); Jiang et al. (2022) papers (while wonderful) present a specific vision of the problem (in the same way as the present paper presents the specific vision of the author). All of this is fine and part of the scientific process but the introduction should not focus on a specific subset of authors.
6/ The fitting and reanalysis done in figure 2 needs to be clarified. I would encourage the author to first show the dimensional data and then the rescaling as the rescaling is not obvious/common in the aerosol literature. I would also encourage to provide a plot of the mean diameter/radius of the drops as a function of the bubble, as it seems to emerge from that rescaling and is not presented in the original paper (I think). The measurements from Jiang et al 2022 are presented in dry size so the scaling factors used in the reanalysis need to be mentioned.
7/ The discussion on the rarefaction effect is rather unclear to me. I would encourage the author to explain this better. Figure 7 is used as proof of the rarefaction effect but if I understand correctly comes from simulations. Does the author have any experimental evidence of this effect? I see this as a major issue with the claims of the author. They propose a theory leading to very strong claims but have no data to back it up. I would be more clear on some of the hypothesis that remain to be tested.
Other comments:
8/ In 2.1.; “rd<0.5” is that micron?
9/ I do not understand the statement: “The super-micron size range is comprised by wet aerosols and its presence is fundamentally reduced to marine and coastal regions Boyce (1954)”
10/ I do not understand the statement “From this study and entirely attributing the fitted pdfs to micron- and submicron film droplets, one would conclude that (i) the droplet generation by film flapping will be distributed according to a lognormal for the nondimensional variable η = χdLa−1/5 , which reflects a reasonable dependency on the bubble size, while (ii) the more “ classical” film rim fragmentation Lhuissier and Villermaux (2012) would yield droplets distributed according to a generalized inverse Gaussian as (1) independently of La.”
Could the author be more explicit?
11/ The discussion on enrichment for very small bubbles seems interesting but I am not sure I am fully following. It also seems to contrast with some other papers. I would encourage the author to discuss this in more details and clarify its hypothesis compared to other work in the literature (see the work from W.C. Keene, P. Quinn, A. Frossard, K. Prather, etc).
12/ I am not sure that the first sentence of the abstract is accurate. It is true in remote marine environment but probably wrong as a general statement.
Citation: https://doi.org/10.5194/egusphere-2022-27-RC2 - AC3: 'Reply on RC2', Alfonso Ganan-Calvo, 06 May 2022
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