| 28 Sep 2026
Charge-regulated aerosol survival from new particle formation to cloud condensation nuclei
Abstract. Cloud condensation nuclei (CCN) links atmospheric aerosol particles to cloud droplet formation, yet the electrical charge carried by these particles is not represented in aerosol-cloud models. Previous studies linking ionisation to CCN have focused on ion-induced particle production and found small effects. Here we test whether charge instead modifies particle survival and redistribution during growth to cloud-active sizes. Using the charge- and size-resolved ELSA-ICAM box model, we perform matched neutral and charged simulations in two regimes: a polluted urban regime dominated by sulfuric acid-dimethylamine nucleation and a clean boreal regime dominated by biogenic highly oxygenated organic molecule nucleation. In the polluted regime, bipolar charging reduces total particle number by 3.1 % relative to the neutral case at 72 h while increasing CCN at 0.2 % supersaturation by 2.5 %. By 120 h, the number response reverses to +4.1 % and the CCN enhancement increases to +5.8 %. In the clean regime, the charge-resolved case increases CCN by +8.9 % at 120 h relative to the neutral case. Process attribution shows that charge-dependent coagulation is the largest shared contribution, increasing CCN by +5.8 % in polluted air and +5.3 % in clean air through size-selective survival and redistribution. Ion-induced nucleation is negligible in polluted air but contributes an additional +3.6 % to CCN in clean air, despite producing a larger increase in particle number. The CCN response is therefore less sensitive to ion production than particle production. These results identify charge-regulated aerosol survival as a microphysical pathway linking atmospheric ionisation to CCN.
This study by Gosh et al. investigates the effect of charge on aerosol particle survivability to CCN in polluted and clean scenario using model simulations. The results show a 5.8 to 8.9% enhancement of CCN concentrations in the charge-resolved case compared to neutral case. The survivability of newly formed particles to CCN is one of the key issues for the climate-relevancy of new particle formation, and this study brings new insight into this topic. The study is also well-written and the methodology and results are clearly presented. However, there are some concerns regarding the assumptions for the different cases and the atmospheric relevance of the results. Thus, I recommend the manuscript for publication after minor revision.
Specific comments
Introduction:
L13 “The CCN response is therefore less sensitive…” This sentence is slightly confusing, I suggest clarifying what is meant by it.
L23: The following paragraph is very heavy to read due its length, I would suggest dividing it into two.
L35: What size range is meant by cluster regime in this context?
Methods
Fig. 1: In the lower part of the schematic, there is a phrase “Particle born charged”, which I recommend to be replaced by “Particle formed charged”
L100: I am slightly questioning the accuracy of the two configurations and whether that can impact the results. Ali et al. (2025) showed that organic compounds likely play an important role in the growth of particles in Delhi, in addition to sulfuric acid. Mishra et al. (2023) showed the presence of organic driven particle growth Delhi. In Hyytiälä, the growth is certainly driven by organic compounds as assumed, however nucleation is typically not biogenic but driven by sulfuric acid, unlike what is assumed here. As described in Sect. 2.5, these choices affect the rates of ion-induced nucleation.
Therefore, the choice of these two configurations and their assumptions should at least be better justified. In addition, I recommend a brief discussion on how these assumptions might affect the results.
Ali, U., Singh, V., Faisal, M., Kumar, M., & Gani, S. (2025). Exploring the influence of physical and chemical factors on new particle formation in a polluted megacity. Environmental Science: Atmospheres, 5(1), 25-47.
Mishra, S., Tripathi, S. N., Kanawade, V. P., Haslett, S. L., Dada, L., Ciarelli, G., ... & Prevot, A. S. (2023). Rapid night-time nanoparticle growth in Delhi driven by biomass-burning emissions. Nature Geoscience, 16(3), 224-230.
L197: Please include a reference to justify the chosen value of the ion-pair production rate q.
L249: What is the justification for applying the charge-enhancement only for sulfuric acid, but not HOM, condensation?
Results and discussion
As a general comment, I am left wondering if the results are consistent with atmospheric observations. For example, these results show a large increase in number of formed particles in the clean environment when IIN occurs, while in most environments the proportion of IIN to neutral nucleation has been observed to be relatively minor (Gagné et al., 2010; Hirsikko et al., 2011). If the model overestimates the relative contribution of IIN to particle number in the clean environment, this might change the results significantly. In general, I find the discussion on atmospheric relevance and the implications of the results to be a bit lacking.
L566: As aforementioned, particle growth driven by sulfuric acid-dimethylamine chemistry does not seem to be the most realistic choice as suggested by previous studies.
Fig. A2: The concentrations for the small ions in the clean environment are quite low compared to observations in similar environments (Hirsikko et al., 2011). What is the reason for this?
Gagné, S., Nieminen, T., Kurtén, T., Manninen, H. E., Petäjä, T., Laakso, L., ... & Kulmala, M. (2010). Factors influencing the contribution of ion-induced nucleation in a boreal forest, Finland. Atmospheric Chemistry and Physics, 10(8), 3743-3757.
Hirsikko, A., Nieminen, T., Gagné, S., Lehtipalo, K., Manninen, H. E., Ehn, M., ... & Kulmala, M. (2011). Atmospheric ions and nucleation: a review of observations. Atmospheric Chemistry and Physics, 11(2), 767-798.