General comments

The manuscript investigates the seasonal and diurnal variability in ice nucleating particle concentration (INP) measured over a year at the High Altitude Research Station Jungfraujoch.  It represents the longest continuous measurement of INPs to date with a high time resolution of 20 minutes.  A seasonal trend in INPs is observed with highest concentrations occurring in Spring and lowest concentrations occurring in Winter. A diurnal trend in INPs is also identified for air masses with boundary layer intrusions. The study identifies long term trends in INP concentrations and is a valuable contribution to the field of INP research. However, I believe that the discussion of the data represented in the figures could be clearer and further links between potential INP sources and with previous literature studies could be made. I therefore recommend the manuscript for publication in ACP following appropriate response to the following comments.

Specific comments

1.  The results section contains very detailed analysis and lots of information is contained within each figure. It would be clearer and easier for the reader to follow the discussion if the panel or the section of the figure that is being discussed is regularly referred to in the text.

e.g. for Figure 2:

• page 8, line 204: ‘Dividing BG periods into FT_BG and BLI_BG…’ Please refer to panel c).
• Page 8, line 216: ‘…is apparent in April for the total particle concentration.’ Please refer to panel f).
• Page 8, line 217: ‘…total particle number concentrations remained at summer levels also in September’ Please refer to panel d).

This comment applies to all figures but especially to figures 2, 5 and 6.

Additionally it would also help the reader if colours were referred to in the text when discussing the data, e.g. in Figure 5, page 14, line 322-323: ‘…shows a weak diurnal cycle, with a maximum of 629 std cm^-3 at 13 h UTC and a …’ Please add (black line in panel a)).

2.  Pages 9-11 contains a detailed discussion of pollen as the potential INP source for the high INP concentrations measured in April. Whilst this discussion is interesting, I believe it could be reduced as the overall conclusion is that it is unlikely that pollen is responsible for the high INP concentrations in April (without further pollen measurements at JFJ). Why do you not comment on any other potential sources for the high INP concentration in April? Was any back trajectory analysis of air masses performed that could inform on potential INP sources? Were any samples collected (gas or filters) and analysed for chemical composition?

3.  The introduction discusses trends in seasonal and diurnal variability in INP measurements in the literature from various studies using mostly offline analysis. It would be good to make links back to the findings of these studies during the results section for comparison i.e. similar seasonal dependences were observed.

4.  The introduction states that knowledge of seasonal and diurnal variability will help to understand the sources and sinks of INPs. The conclusion only briefly mentions that the observed seasonal variation of INP concentrations could be linked to partitioning of particles in different seasons. As this appears to be the main motivation for the measurements, this discussion should be expanded in either the results or conclusion section. Can any further information on sources and sinks of INPs at JFJ be obtained from this study?

5.  Comment: The only other study to have observed diurnal variation in INPs over a longer time period is mentioned on page 3, lines 65-69 (Wieder et al., 2021 in prep.). It would be useful to make further comparisons between this study (data in Figure 5) and that of Wieder et al., however, as the manuscript is in prep this is not possible.

Technical corrections

Page 7, line 196-7: the text states that ‘June had the most active SDE of the investigated period with a duration of 116 h’ whereas in Figure 2 it appears that the SDE in June lasts for 123 hours. Please correct.

Page 16, line 352: the text states ‘The large particle concentrations continue to decrease between 9-12 h UTC…’ which I think should be 21-24 h UTC from the data presented in Figure 6, panel f). Please correct.

Figure A3 is not mentioned in any part of the paper. Is this needed?

Typing errors/grammar:

Page 1, line 13: ‘…is with a factor of…’ should be changed to ‘is within a factor of’.

Page 3, line 81: ‘Furthermore, the remote location allows to study…’ should be ‘Furthermore, the remote location allows the study of…’

Page 4, line 98: unites should be units.

Page 6, line 181: ‘There were two exceptionally dry period in the end…’ should be ‘There were two exceptionally dry periods at the end…’

Page 11, line 291: ‘…uncertainty can alter the frequency distributing…’ should be ‘…uncertainty can alter the frequency distribution…’

Review of “The diurnal and seasonal variability of ice nucleating particles at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland” by Brunner et al.

The paper from Brunner et al, reports seasonal variability and diurnal variability of INP concentration at the JFJ site during the year 2020. This is this year the third paper in this series of INP measurements at JFJ. The first technical paper appeared earlier this year in AMT, describing the auto-HINC, a new CFDC device enabling continuous INP measurement at the JFJ. “Continuous online monitoring of ice-nucleating particles: development of the automated Horizontal Ice Nucleation Chamber (HINC-Auto)”. A second paper, “The contribution of Saharan dust to the ice nucleating particle concentrations at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland” currently in ACPD presents one year (2020) data of INP attributed to Sarahan dust and measured at JFJ. This current third paper is pushing the analysis further by looking more carefully at the seasonal variation of the INP during the same time, extracting the INP seasonality and diurnal variation by excluding the SDE. The data are first cleaned from local pollution (roughly 25% of the data removed) and then data is classified in 4 different air masses: FT with or without SDE and BLI with/without SDE. This paper is well written and very pleasant to read. It is a nice continuation of the first two papers published/under review this year. It presents an impressive work of high temporal resolution of INP concentration for 1 year of continuous measurement. The fact that the authors could use this high temporal resolution HINC instrument compared to “classical” daily filter measurement allow the authors to remove from the data any short local pollution, which I’m not sure would have been feasible with 24hr filter. For sure, much more of this type of high temporal INP measurement is very appreciated, and hopefully more in the future will be done (also at different locations).

I have only one main comment and a few small comments, and I recommend the paper to be published once these comments are addressed.

Main comment:

PL369: “Based on our observations, it is unlikely that pollen or subpollen particles are responsible for the observed high background INP concentrations in April,”

Looking at the data, I would arrive at a different conclusion (or at least less affirmative about the non-influence of pollens on INP at JFJ).

A) Like Sarahan dust, pollens are known to be a very good candidate to act as INP as the authors explained, and this is why the authors investigated this specific source of INP. However, the authors do not have a direct measurement of pollen directly on site, so they have to speculate. The data presented here show that there is a peak of pollen measured 60 km away from the station (at Bern, 3 km lower in altitude) just a few days (1-3 days, hard to read from the figure FA1.a) before the measured “peak” of the INP at JFJ. Pollens are released first before INP increases, which therefore does not rule out the possibility of Pollen reaching JFJ and increasing INP concentration (the other way round would not work). Similar to SDE, pollen transported to JFJ could have departed days earlier before arriving on this high altitude site?

B) Then there is the estimation of how many pollen particles would reach the station:

P11L261 “. If every pollen grain would be ice-active at 243 K, and the same pollen concentration were present at the JFJ as measured in Bern, i.e., the PBL was perfectly mixed and the JFJ was within the PBL, pollen would only contribute up to 3.6 INP std L−1 (4 INP L−1 ), 5 times less than the Q95% INP concentration for BLIBG conditions during the same time period. “

However, pollen concentration measured at Bern is an average of 24hrs, whereas INP concentration measured at JFJ is a snapshot of 20 min of measurement. So for me, this will not exclude the possibility of pollens arriving in a batch at JFJ, therefore explaining this higher concentration. Also, pollen concentration measured at Bern may not be the representative concentration of pollens arriving at JFJ as another site (Visp) at a roughly similar distance from JFJ reported half of the concentration around the same day (April 20^th ?).

C) Air mass origin. I wonder if an analysis of the air mass origin could help in understanding this spring peak of INP. Where the air mass is coming from during the INP peak? Could this air mass have collected pollen from somewhere in Europe? Could pollen be transported from further away than Bern or Visp (like SDE)? The authors state that an anti-cyclone was present until April 16^th. Could it have influenced the non-transportation of pollen to JFJ at that time (low INP)? Could the peak of INP arriving just after the end of the anti-cyclone be a result of transportation of air mass from mainland Europe (which was full of pollen)?

Small comments:

It would be good to have Brunner et al. accepted 2021 in ACP to use the same notation as in this paper (if it is still possible to edit the manuscript). For example table 1 in both paper show the same results but with different notation.

P3L87-88 “(CPC), TSI 3772, lower cut-off size: 14 nm) and size distribution (scanning mobility particle sizer (SMPS); optical particle sizer (OPS)”

What is the size range of the SMPS (which is then used to calculate N90) and the size range of the OPS?

Fig 3: “with the Q10% of PFT of a given day” what is the right axis BLI/FT %? I m a bit confused about how to read this scale. I am assuming that data close to BLI correspond to 0% and close to FT correspond to 100%. is that correct?

Fig 3: What is the meaning of the dash black line around mid-April in panel a) and b).

Reference Schneider, J. et al. 2020 is from ACPD, Schneider et al. 2021 is the final version. Please correct in the text and in the reference list.

Reference Brunner et al. 2021 in ACPD might be available at the time of the publication of this article.

if other references of manuscripts in “preparation” are now available, please add them.