Kanawade et al. reported the observation an interesting phenomenon of nanoparticle shrinkage and explored the potential underlying mechanisms, which is different from the well-known U-shaped evolution of PNSD. Such a phenomenon has been reported in previous studies, yet this is the first time that the underlying processes are examined with the simultaneous measurements of particles, ions, and gaseous precursors. The authors proposed that these events were governed by atmospheric dilution, and reversible partitioning of LVOCs and SVOCs led to rapid nanoparticle shrinkage. Although the hypothesis can be valid and the manuscript is easy to follow, its evidence was organized in a perhaps unbalanced structure. Overall, I recommend the publication of this manuscript in Atmospheric Chemistry and Physics, and hope the authors can address my comments below.

Major comments

1. The core analysis (Figs. 3-5 and related text) investigates potential causes of NPS events using gas and particulate data from the measurement site. However, as clearly indicated by the particle size distributions, new particles observed during NPS events did not originate at the observation site but were transported post-formation. The rapid shifts in size distributions further indicate a significant change in meteorological conditions/air masses. Given the geographical conditions of the Cyprus site, it is reasonable to anticipate a significant influence of transport on the observed particle evolution, whereas local measurements of precursors may not be sufficient to explain particle formation. Therefore, I recommend the following structure of the results and discussion section:

a) Analyzing particle origins via meteorological parameters and back-trajectory analysis. Current discussions are mainly in in the SI (with discussions on anthropogenic tracers in main text). The analysis should be enhanced with a focus on the short periods when the shift in size distribution were observed.

b) Investigating rapid particle shrinkage through local precursor observations and particle size evolution analysis.

2. Beyond NPS events, what causes particle shrinkage in DMD events? Could this contribute to elucidate the NPS phenomena?

3. The evaporation discussion appears contradictory. It is stated that “observed differences in particle behavior were not driven by the availability of condensing vapours......” However, particle shrinkage is latter attributed to “evaporation of condensable species under atmospheric dilution”. If vapor concentrations do not govern gas-particle equilibrium, what are the governing factors (e.g., temperature, particle size)? Please elaborate; alternatively, please consider softening or removing relevant sentences in the abstract and conclusions.

General

The authors present a set of three nanoparticle shrinkage (NPS) events at rural Cyprus during a 2,5 Month measurement campaign. Even though such events were few during the campaign, previous measurements at the same site show that the phenomenon occurs repeatedly at the site, especially in April. To the authors’ (and to the reviewer’s) knowledge such events have not been reported or analyzed earlier in the literature. Therefore, the topic of the manuscript is both relevant and new.

Both new particle formation (NPD) and NPS events are relatively short (only 5-8 hours) before they become hard to follow. This is expected, considering the site being on a large island. Particles originating from further away come through very different conditions.

Analysis and conclusions

The set of instruments used at the measurement campaign is comprehensive, allowing a proper analysis of the events, and enabling confirming or ruling out of several hypothesis. Part of the relevant information is unfortunately in the supplementary material instead of the main manuscript.

The authors conclude that the particles observed during NPS events are not emitted as (anthropogenic) primary particles locally. However, the possibility of the particles originating via NPF upwind of the measurement site and advecting to the site (Kivekäs et al., 2016, Hakala et al., 2023) is not thoroughly examined. Analysis of trajectories in the main manuscript would provide valuable information here.

The authors come to the conclusion that entrainment and evaporation of SVOC and LVOV matter in the particles would be the main explanation of the observed NPS events. If this was the case, the observed shrinkage of the particle mean diameter from 20 nm to 5 nm (7.4. obtained from NAIS -p) would require 98% of the material in the particles to evaporate. The different volatility distribution of the particles is presented only in Figure 5f, which is somewhat difficult to understand. Also the increase of nucleation mode particle number concentration during NPS day is difficult to explain by entrainment and partitioning, unless the particles break apart physically.

Please add these points in the updated discussion of the results and resulting conclusions.

Presentation

The manuscript is well structured with clear introduction, methods including instrumentation, results and discussion, and finally conclusions. Earlier work is mainlyproperly acknowledged and cited.

The figures have generally two issues:

1. Since there are so many simultaneous measurements of different parameters, the figures contain a lot of information. This is tackled by splitting them in several sub-figures. The result of this is, however, that the text and information in the sub-figures are too small and difficult to read / interpret. The same issue is visible in the supplementary material. Please make these more clear
2. The choise of colours in the figures is very difficult to a colour blind person (most commonly red-green). Please re-select the colours and / or line types to make them more readable.

References:

For the international networks listed on line 98 and around, it would be good to provide references, if available. Eg. for ACTRIS Laj et al., 2024, DOI: https://doi.org/10.1175/BAMS-D-23-0064.1