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”

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