the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 05 Aug 2024
Charging, Aggregation, and Electrostatic Dispersion of Radioactive and Nonradioactive Particles in the Atmosphere
Abstract. Electrostatic dispersion can significantly impact the microphysical behavior of charged particles and ions until reaching zero space charge. However, although radioactive particles can be strongly charged in air, the influence of electrostatic dispersion has been neglected in understanding their behavior. This study is aimed at investigating time-evolution of the charge and size distributions of radioactive and nonradioactive particles in air and developing simple approaches for applications. Involving charging, aggregation, and electrostatic dispersion, a comprehensive population balance model (PBM) has been developed to examine particle charge/size distribution dynamics. It is shown that, compared to nonradioactive particles, the charge and size distributions of radioactive particles may evolve differently with time because radioactivity and electrostatic dispersion can significantly affect the charging and aggregation kinetics of the particles. It is found that, after the Fukushima accident, background aerosols in the pathway of radioactive plumes might be highly charged due to ionizing radiation, suggesting that radiation fields may strongly influence in-situ measurements of charged atmospheric particles. The comprehensive PBM is simplified, and then the verification and application of the simplified PBMs are discussed. This study provides useful insight into how radioactivity can affect the dynamic behavior of particles in atmospheric systems including radiation sources.
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RC1: 'Comment on ar-2024-19', Anonymous Referee #1, 23 Sep 2024
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General comments:
In this study by Kim et al. the authors investigate the time-evolution of radioactive particles, taking into account charging, aggregation, and electrostatic dispersion of the particles. A comprehensive population balance model has been developed and used in studying the effects of radioactivity on the time-evolution of both radioactive particles and non-radioactive background particles. In addition, simplified forms of the population balance model are developed and verified. The scope of the manuscript is suited for publication in Aerosol Research.
The manuscript itself has clearly been carefully prepared. It is quite well written and easy to follow. The results are presented in a logical manner.
I would suggest this manuscript to be accepted for publication after my comments, which are mainly technical corrections, have been addressed.
Specific comments and technical corrections:
Introduction:
1. (L38) “Because such radiation sources can affect the particle charge and size distributions, understanding the influence of radioactivity is necessary to investigate many microphysical processes in atmospheric systems including radiation sources.” I suggest reformulating this sentence slightly, as I found it difficult to follow whether it referred to microphysical processes, including radiation sources or to microphysical processes, which include radiation sources.
2. 3.4 Simulation: What was the time step used?
Results:
3. L220: The word “respectively” is unnecessary.
4. L230: I suggest adding figures of these other comparisons mentioned as a supplementary.
5. L241 and L244: Incorrect use of respectively. I suggest replacing it with e.g., separately.
6. L285: The results not shown here could be added as a supplementary information.
7. L375: How much is “slightly”?
Conclusions
8. L408: “monovariate” should read “bivariate”
Citation: https://doi.org/10.5194/ar-2024-19-RC1 -
RC2: 'Comment on ar-2024-19', Anonymous Referee #2, 10 Oct 2024
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Review of „ Charging, Aggregation, and Electrostatic Dispersion of Radioactive and Nonradioactive Particles in the Atmosphere” by Kim et al. 2024
The study deals with the behaviour of radioactive particles in the atmosphere. A temporal component is taken into account and the focus is on the particle concentration and number of elementary charges per particle in the atmosphere.
The manuscript has been thoughtfully written and deals with a challenging topic which is presented in a comprehensible way.
I vote in favour of the publication of the manuscript, but I would still like to have some questions answered
Remarks/Questions
In a previous publication, reference was also made to experiments. in this publication, experiments and data from observations are quite rare. (as in : Kim, Y.-H., Yiacoumi, S., Nenes, A., and Tsouris, C.: Charging and coagulation of radioactive and nonradioactive particles in the atmosphere, Atmos. Chem. Phys., 16, 3449–3462, https://doi.org/10.5194/acp-16-3449-2016, 2016.)
Radioactive decay is often a chain reaction to other unstable nuclei, which have a different activity. has this been sufficiently taken into account?
General Comments
Line 77 - transport […] decrease their concentration: Please explain what the mechanism. Sedimentation/Collision and Agglomeration is important aswell
Line 90f - the volume size of the particle ensures a greatly increased number of atmoe and thus also a much higher activity. can you explain the size bin dependency in more detail?
Line 105f - the height of the atmosphere plays a major role for the ion concentration, if this has not been taken into account, please narrow down to the relevant height range (Stozhkov 2003)
Line 142f – charges of particles…. : The average charges of particles is largely a multi modal distribution with a size dependency. (Wiedensohler 1987) May you explain the differences?
Line 171f: the selected radioactive elements themselves decay into radioactive atoms and can change their type of radiation. has this been taken into account?
Line 176 – “we assumed” : how was this justified, also with regard to the source
Line 230f; Figure 4: Why was a particle size of one micrometre chosen? the accumulation of particles in the atmosphere is around 200 nm (sedimentation-driven). the calculations can be redone/added with this relevant variable (Rose et al. 2021)
Line 272f: the changed behaviour with regard to the charge distribution may also have something to do with the electronegativity/affinity of the elements?
Line 294 137Cs vs 131I - the electron affinity differs greatly for these elements and is also reflected in the charge distribution as the corresponding ions are strongly favoured (positive charged alkali metals and negatively halogens). can this be the explanation?
Line 375f: can you please add numbers and percentages to your statements?
Line 379/Figure9: please add a legend in all your graph for the colored lines (the arrows do not point unambiguously to the lines)
Minor Comments
Line 67 – can easily change to favored
References:
Y I Stozhkov 2003 J. Phys. G: Nucl. Part. Phys. 29 913 DOI:10.1088/0954-3899/29/5/312
A Wiedensohler 1987 J. Aerosol Science, 19 3 387-389 https://doi.org/10.1016/0021-8502(88)90278-9
C Rose 2021 Atmos. Chem. Phys., 21, 17185–17223 https://doi.org/10.5194/acp-21-17185-2021
Citation: https://doi.org/10.5194/ar-2024-19-RC2
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