This work reports 15 years of direct measurements of aerosol number size distribution and CCN concentrations at a remote mountaintop observatory. The combination of simultaneous measurements allows to investigate long-term impact of new particle formation events on CCN budget. It is a complex and extended dataset and the results will fit with the scope of ACP, being of interest for the international research community. However, I recommend to improve and correct some issues before it is published in ACP.

Major comments

1. I suggest the authors to improve methodology section (specific comments below). Specially, it is not clear how the authors account the contribution of NPF to CCN, and only the timing of the events is presented.
2. This manuscript presents a new methodology to classify NPF events, however it has been only applied at SPL site and validation, success ratio and/or comparison with other methods in detail are not provided. Despite it is a visual classification and can lead to human biases, Dal Maso et al 2005 has been used for years as an standardized method to classify NPF events. This methodology is presented as new, however it is based on Dal Maso et al methodology. Why not comparing results in deep? This is not the first automatic method in the literature (e.g. Su et al., 2022) and no comparison, benefits or improvements are shown. Finally, the authors don’t provide the procedure to calculate the GR, the formation rate is calculated with a formula that is simplified (and not correct), the diffusion coefficient is assumed to be 0.077 cm2 s-1 (this factor depends on the temperature and pressure, how representative is for SPL?) and the factor beta is also considered to be unity (why?). Kulmala et al 2012 provided guidelines to compare different NPF studies.
3. When talking about the impact of NPF to CCN concentrations, this method is not well explained and further explanations are needed. In addition, this method does not show clear advantages with those previously presented in the literature and I suggest the authors to look in deep some of the issues discussed in previous works (e.g. Dameto de España et al., 2017; Rejano et al., 2021; Rose et al., 2017). 1) We can assume that all the particles >100nm will act as CCN, however not all particles below 100nm come from NPF events, so you can explore some subtracting method to account for that? 2) SPL is a mountain site, the difference between event and non-event days will probably be affected by the transport from lower altitudes, I suggest to add some results/discussion about free troposphere conditions, influence from boundary layer, and the differences during event and non-event days. 3) Free troposphere conditions will probably reduce the number of NPF events, and boundary layer conditions will lead to higher event frequency, why not using same atmospheric conditions to subtract the effect from lower sizes? 4) SMPS measures from 8 to 340 nm, if above 100nm we have the largest contribution to CCN concentrations, which errors have the increase factors that you present here?
4. The abstract doesn’t provide new findings. 1) NPF occurs 50% of all days (if you use a new method to classify NPF events and you compare results with previous methods, it could be a highlight); 2) Events with persistent growth are common in spring and winter; 3) NPF enhances CCN by a factor 1.36, that combined with previous work at SPL, suggests the enhancement of CCN?. These three new findings pointed in the abstract could be results of a measurement report (not for a research paper). The results 1) and 2) have been already reported previously by Hallar et al. 2011.

Minor comments

L24-70 – There is a lack of references that have previously investigated the impact of NPF on CCN concentrations, some of them on mountain sites and combining PNSD and CCN and/or using monodisperse (e.g., Kalkavouras et al., 2019; Dameto de España et al., 2017;  Kalkavouras et al., 2019; Kalivitis et al. 2015; Kecorius et al. 2019; Rejano et al., 2021; Rose et al. 2017) and some NPF studies in mountain sites.

L91-99 – CPC model? Do you routinely calibrate the instrumentation? Please, include both information.

L104, L107, 108 – These references are mainly based on the methodology presented by Dal Maso et al. (2005).

Figure 1 – “Is the average concentration below 25 nm above the 10th percentile of all data?” What means? All data serie, 10^th percentile of total particle concentration of that 5min data, daily concentrations?

L127-136 – The Gaussians are calculated following the equation 1, however, I can not see the diameter parameter. Are you using lognormal distribution?  The time index, where is that index? “k” is the maximum aerosol number concentration” for each of the modes I guess?. Please check some references as Huusein et al. 2008 (equations) or Hussein et al. 2005 (DO-FIT algorithm) and rewrite this explanation, difficult to understand which fit method are you applying. In addition, 5 different maximum points? 5 different Gaussians? why that number?

Figure 2 – specify what the black lines indicate (and red ones).

Figure 3 – the authors identify the bottom figure as a weak event, why? There is no new mode appearing below 25 nmor growing.

Figure 4 – please use log-scale (or log-log)

References

Dameto de España et al. 2017: Long-term quantitative field study of New Particle Formation (NPF) events as a source of Cloud Condensation Nuclei (CCN) in the urban background of Vienna, Atmos. Environ., 164, 289-298.

Hallar et al. 2011: Persistent daily new particle formation at a mountain-top location, Atmospheric Environment, 45, 4111-4115.

Hussein et al. 2005: Evaluation of an automatic algorithm for fitting the particle number size distributions. Boreal Environ. Res. 10, 337–355.

Hussein et al. 2008: Observation of regional new particle formation in the urban atmosphere, Tellus B, 60, p509-521.

Kalkavouras et al. 2019: Regional new particle formation as modulators of cloud condensation nuclei and cloud droplet number in the eastern Mediterranean, Atmos. Chem. Phys., 19, 6185–6203.

Kalivitis et al. 2015: Atmospheric new particle formation as a source of CCN in the eastern Mediterranean marine boundary layer, Atmos. Chem. Phys., 15, 9203–9215.

Kecorius et al. 2019: New particle formation and its effect on cloud condensation nuclei abundance in the summer Arctic: a case study in the Fram Strait and Barents Sea, Atmos. Chem. Phys., 19, 14339–14364.

Kulmala et al. 2012: Measurement of the nucleation of atmospheric aerosol particles, Nat Protoc, 7, 1651–1667.

Rejano et al. 2021: Activation properties of aerosol particles as cloud condensation nuclei at urban and high-altitude remote sites in southern Europe, Sci. Tot. Env., 762, 143100.

Rose et al. 2017: CCN production by new particle formation in the free troposphere, Atmos. Chem. Phys., 17, 1529– 1541.

Su et al. 2022: New particle formation event detection with Mask R-CNN, Atmos. Chem. Phys., 22, 1293-1309.

This work uses a newly developed algorithm to analyse 15 years of new particle formation (NPF) and growth events observed at the Storm Peak Laboratory, located 3210 metres above sea level.  It couples the NPF events with coincident measurements of cloud condensation nuclei (CCN) concentrations to enable estimates of the role of NPF in producing CCN at this site.  The paper is well within the scope of ACP, and the addition of CCN measurements to the size distribution measurements and analysis gives this work a unique look at an important issue.  The paper is generally well written and organized, but I feel there is need of some clarification of details.  Also, I find that the discussion needs to be broadened.  Most of my initial comments are very minor.  Some of comments 10-18 require more attention.

1.    Line 86 – BVOCs can impact aerosol formation and growth.

2.    Line 93-94 – Define Level 1, Level 2 and EBAS.

3.    Line 127 – what is “ample”?

4.    Line 181 – ΔN8,Dmax rather then N

5.    Line 212 – It is unclear here why you bother with CCN for non-event days.  Presumably, it is because you use this as a reference point for comparison of CCN impacted by events.  The reason should be made clear here.

6.    Line 213 – NPF and growth are impacted by sunlight as well as many other factors.  Rather than “NPF and growth are largely impacted by sunlight, therefore…”, I suggest something like “Sunlight is generally necessary for NPF and growth, and therefore…”

7.    Line 214-215 – Here you state that you “obtain four different values of CCNstart”.   I assume, but may be wrong, that you mean one for each season, but not four for each event, which is how it sounds.  Clarify please.

8.    Line 223-224 – It is written to sound like this is novel, yet surely it is obvious that you must allow a long enough time.

9.    Lines 248- 250 - Is 53% significantly lower than 56% in this case?  

10.    Lines 260-263 - What is the method of production of particles on non-event days, and are they truly new particles or just the result of a meteorological change, such as a developing boundary layer (since you are at a mountain site)?

11.    Line 265 – I suggest changing “produce” to “indicate”.

12.    Lines 266-267 - I’m having trouble understanding the apparent use of non-events as a reference.  Why is it necessary to use non-events this way.  Are you assuming that days with events would be the same as non-event days, IF there was no event?  Presumably, one of the triggers for the event could be that the aerosol immediately preceding the event was particularly low in number and size (i.e., low CS).  Would the non-event reference be appropriate in that case?  Also, it is possible that the aerosol sampled on non-event days may well have been influenced by NPF at some time in its history.  Would you clarify your reasons behind this, please?

13.    Line 283 - Here, the summer result again suggests the "non-event" may not be a suitable reference.

14.    Line 303 – What about condensable organics?  Do higher temperatures somehow inhibit growth by organics?  How would your CCN number concentrations react if organics played a major role in growth of the newly-formed particles, compared with sulphate?  What do you think are the main precursors leading to particles growth at SPL?

15.    Lines 310-333 - You have more bursts in summer and fall that suggests H2SO4 is being produced.  Are you suggesting that it ends up condensing on existing larger particles, thereby improving their ability to act as CCN?  In the first paragraph here, you say that a reduced CS is important for your SPL observations of NPF, and that is shown in Table 2.  However, then you lead off the second paragraph stating that one phenomenon is influencing NPF and CCN on event days at SPL in the summer: temperature.  I feel that this is misleading without a detailed analysis of the many things that might affect NPF: including, temperature, CS, SO2 concentrations, irradiance, available condensable species.  In relatively clean environments with low concentrations of precursors (e.g., Arctic), a low CS can be to be a trigger for NPF.  Higher concentrations of SO2 superimposed on regions with a low CS will result in higher number concentrations of NPF.  Higher SO2 concentrations in regions with a higher CS will tend to have lower NPF.  In other words, the CS is important, along with other factors.  Unless you can present more evidence or a stronger argument that temperature is the primary factor controlling NPF here, I think the focus on one factor may be misleading and the discussion should be made a little more objective.

16.    The paper would be helped by putting the present results in perspective through a simple tabled comparison with other estimates of the contribution from NPF to CCN in the literature.

17.    Lines 397-398 – Scale is an important factor when comparing remote regions with areas of strong anthropogenic influence.  There has been a reasonable amount of work examining NPF in the Arctic (a remote region).  I think before concluding with this statement, you should look at some related literature: for example, Nieminen et al. (ACP, 2018; https://doi.org/10.5194/acp-18-14737-2018); Abbatt et al. (ACP, 2019; https://doi.org/10.5194/acp-19-2527-2019 ), and references therein.