This manuscript by Sze et al. measured INPs in the Villum research station in Greenland for more than two years and analyzed various physical properties of these samples. Their study is interesting and significant in our understanding of INPs in the Arctic because of 1) a long-term INP measurement, 2) the measurement location (in the middle of the Arctic (VRS)), and 3) measurements of INP concentration at a different temperature, INP types, and bioaerosol fractions. These detailed and comprehensive measurements of the important region for the climate study are clearly suitable for publication in this journal. I have several suggestions and comments to clarify and improve the readability of this manuscript.

Major comments and suggestions:

Terminology:

1. The authors classified samples using the terms “summer,” “winter,” and “mixed” types. However, these samples were originally classified based on the exponential decay slope values and not by the sampling seasons. Indeed, they initially termed them Fletcher and Cooper types. They were termed because they were more frequent in summer or winter. Then the authors discuss the fraction of “summer” and “winter” types in each season. The terminology is confusing, e. g., line 368 “with summer and winter type dominating summer and winter months, respectively.”
2. The term “bio-ratio” is also somehow misleading. Line 170-172 says, “However, it should be noted that not all biological INPs are equally sensitive to heat. Nevertheless, overall heat-lability is thought to be more associated with biological INPs than mineral INPs, and we will use the term biological INP in this study to refer to heat-labile INP.” The “bio-ratio” is not a real bio-ratio but the fraction of heat-labile INPs. However, in section 3.4., the authors discuss the “bio-ratio” as they are actual bio fraction, e.g., line 395 “that roughly at least half of all INPs during that period were comprised of non-proteinaceous biological material.” The discussion should base on the fraction of heat-labile INPs. Otherwise, more discussion will need to prove that heat-labile INP is equal to biological INPs.

For the above two cases, I agree with the discussion and the interpretation and will be acceptable to mention the “summer” and “winter” types are dominant in summer and winter, respectively, and the bio-ratio mostly represents the fraction of biological particles. On the other hand, the terminology sounds too simplified to interpret the meanings. So, I suggest reconsidering the terminology. Or at least, the discussion should base on these real meanings (e.g., the number fraction of heat-labile INPs but not bio ratio).

Section 3.5 A case study:

The case study section discusses several hypotheses and rejects the first two hypotheses by the authors (line 418 and 434). It is acceptable to discuss any hypotheses, but in my personal view, they use too much space for the discussion to decline their hypotheses, including Figures 9-11, which decreases the readability of the conclusion. At least, they can shorten, and most figures can be replaced in the appendix or supporting information. In addition, this manuscript has so many appendix figures instead of supporting information. I would suggest considering using supporting information as well. This comment is a suggestion that potentially improves the paper and is not mandatory.

Specific comments:

Line 17: “also a higher cloud ice fraction was observed in satellite data for April 2020, compared to April 2019.”

I suggest revising this last sentence in the Abstract, which is somehow awkward and is not a major conclusion of this study.

Line 249 “Hereafter the time period with a snow depth below the threshold is referred to as snow-free months,”

Similar to the general comments, they are not “snow-free month,” but there was snow with < 80 cm. I suggest using a better term here.

Line 350 “And, these are the two slopes…”

Is this sentence “There are two slopes…” (?) Please check it.

Line 371 “60% ot” typo?

Line 408-409 “The altitude threshold of 250m was applied in order to locate potential source regions within the planetary boundary layer”

Over the main part of Greenland, the altitudes from the sea level are mostly > 250m, but the air mass can also pass through near the ground (ice or snow) surface. They may contribute to aerosol sources. Some explanations may be helpful.

Line 475 What is PDF?

Line 489 what is LES?

Line 509. “…value derived from it, is statistically more certain than a low one.”

Is something missing in this sentence?

Figure 1. I suggest indicating the period used in the case study.

Figure 1. During April 2020, there were higher INPs even at -20C than in April 2019, which may suggest that there were significant numbers of aerosol particles in the month. If so, the high number of aerosol concentrations simply increases the number of INP at a high temperature rather than changing particle species. Is there any available data to check the particle concentrations?

Figure 4. I suggest adding a color legend in addition to the text.

Figure 6. It looks like not all samples were plotted (e.g., July 2018). Why?

Figure 11. The colors in the plots are difficult to distinguish.

Figure A5 (November). There are two summer spectra in November; one is the highest INP concentration, and the other is the lowest INP concentration. Is the classification correct?

Review Sze et al. (2022): Ice Nucleating Particles in Northern Greenland: annual cycles, biological contribution and parameterizations

Summary

In this study a two-year dataset of INP concentration measurements from an Arctic site is presented, to better understand the short- and long-term variability of this climate-relevant variable. Currently, only a few INP concentration measurements with a monitoring character exist, especially not in such a  climate-sensitive location as the Arctic, which is why this study is of relevance to the aerosol-cloud interaction community. However, I have some major concerns which should be addressed before publication.

Major comments

• Parameterization: Which fraction of your sample is within a certain factor of the developed parameterization? E.g., are you able to predict the INP concentration accurately within a factor of 10, as deviations larger than this value can impact cloud microphysical and radiative properties (Phillips et al., 2003)?
• Case study: The linkage of an observed higher cloud ice fraction to an increased INP concentration in April 2020 as compared to the previous year is insufficient. First, to my knowledge, there is no evidence that ground-based INP concentrations can impact cloud properties observed on top of the cloud. Second, other parameters differ between April 2019 and 2020, for example, mean wind speed (potential impact from blowing snow) or a lower surface temperature in April 2019 (e.g., a greater impact of pre-activation of INPs; Conen et al., 2015). Moreover, it would be interesting to investigate if there was an enhanced impact from glacial dust sources or a higher biological activity in the ocean. In addition, in the late winter months, the Arctic haze phenomena (e.g., Shaw, 1995) can impact aerosol populations, which is not discussed here.

Minor comments

• What is the relevance of mixed-phase clouds in the Arctic winter regarding the radiative forcing?
• Is there an impact of blowing snow on the aerosol filters?
• In some cases, the mentioned publications are examples and do not represent all existing literature. Please check and make use of "e.g." in such cases or complete the cited literature
• You mention that blank filters were collected weekly, but do not present them here. How high were the INP concentrations from those filters and did you consider using them for a background correction of the INP concentration?
• Lines 35 – 36: Reference for this statement missing.
• Lines 94 – 97: It might be worth mentioning that also the impact of glacial dust is increasing due to retreating glaciers (e.g., AMAP, 2021).
• Lines 125: What is the pore size of the polycarbonate filters?
• Line 152: What is the uncertainty in temperature regarding the 6 second time resolution of the camera and using a 1 °C/min cooling rate?
• Line 253: Can you quantify the variability in INP concentration better, e.g., using the standard deviation?
• Line 277: Statement „Their respective INP parameterizations are often used in atmospheric models“ needs a reference.
• Lines 333 – 334: Are there publications that can strengthen this statement („A common background of mineral dust particles throughout the year may exist“)?
• Lines 354 – 355: It might be worth explaining on which measurements the parameterizations from Cooper (1986) and Fletcher (1962) are based to understand the difference of three orders of magnitudes as compared to your parameterization.
• Line 426: In April 2019 there is a correlation coefficient of 0.86 between INP concentrations at -18°C and surface temperature.

Technical comments

• Line 5: The abbreviation „VRS“ is not used in the abstract, thus should not be introduced here.
• Line 473: „biolgocial“ should be „biological“.
• Check the use of hyphens: I believe it should be „ice-active“, „temperature-dependent“, etc.

References

AMAP, 2021. Arctic Climate Change Update 2021: Key Trends and Impacts. Summary for Policy-makers. Arctic Monitoring and Assessment Programme (AMAP), Tromsø, Norway. 16 pp

Conen, F., Rodríguez, S., Hüglin, C., Henne, S., Herrmann, E., Bukowiecki, N., and Alewell, C.: Atmospheric ice nuclei at the high-altitude observatory Jungfraujoch, Switzerland, Tellus B, 67, 10.3402/tellusb.v67.25014, 2015.

Shaw, G. E.: The Arctic Haze Phenomenon, Bulletin of the American Meteorological Society, 76, 2403-2414, 10.1175/1520-0477(1995)076<2403:TAHP>2.0.CO;2, 1995.