Interesting work. Well done. See attached file for comments. Good luck.

Congratulations to the authors on their preparation of this interesting work. Review notes are attached.

Lapere et al present an important modeling study of the contribution of leads to sea spray aerosol in the high Arctic. This work is particularly important in the context of rapidly declining sea ice in the Arctic. The manuscript is well-written. A main concern is that it seems from the methods that areas with sea ice concentration less than 80% are not considered for sea spray aerosol production in this study (according to my understanding of the statement on lines 178-179). While I understand this threshold for defining sea spray aerosol from leads, it is not clear how sea spray aerosol from sea ice regions with less than 80% sea ice concentrations is considered (according to my understanding of the statement on lines 178-179, it appears to be ignored/not considered). This needs to be clarified throughout, especially in the context of comparing lead-based sea spray aerosol and blowing snow aerosol %s, as sea spray aerosol emissions from within the Arctic, including the MIZ regions, are expected to increase the contribution of fresh sea spray aerosol to the high Arctic. In addition, as discussed below, the authors choice of sea ice lead satellite product also impacts the sea spray aerosol produced from leads, and this needs to be clear in the abstract and conclusions in particular. Given the lack of consideration of MIZ and choice of sea ice lead product (as shown in Figure 3), this means that the modeled sea spray aerosol %s are likely lower bounds. This is important as Arctic sea ice is declining and thinning, making sea spray aerosol emissions expected to be increasing across the Arctic, especially in the lower Arctic latitudes. Since the authors seem to focus on the High Arctic (e.g. Fig 2), it is then confusing when the authors then compare to coastal locations (e.g. Fig. 7), while not including sea spray aerosol from regions of sea ice conc < 80% (which it seems the authors had defined as such in Fig 2?). These points need to be considered and clarified in this modeling study. Additional detailed comments are provided below.

Abstract: It is important that the authors clarify here that “sea ice regions” here pertains only to regions with >80% sea ice concentration, according to Section 2.2.1. It is also not clear here how “open ocean” is defined – is it <80% sea ice concentration? The definition of “high Arctic” in Figure 2 is different than in many studies and needs a statement in the abstract for clarification. Overall, these points need clarification in the abstract and elsewhere, for the reasons noted above.

Section 2.1.2 and Figure 8 discussion: This section parameterizes the organic fraction of marine aerosols based on chlorophyll-a. However, Quinn et al. (2014, Nat. Geosc.) found through observations that the organic content of sea spray aerosol does not vary with chlorophyll-a levels. Rocchi et al. (2024, Environ. Sci. Technol.) also found no correlation with chlorophyll for Arctic sea spray aerosol. Both Kirpes et al. (2019, ACS Central Sci.) and Zeppenfeld et al. (2021, ACS Earth Space Chem) found increased seawater and sea spray aerosol organic content associated with the presence of sea ice. Given these findings, it is critical that the authors add discussion of the uncertainties and caveats associated with parameterizing the organic fraction as a function of chlorophyll.

Lines 128-130: The authors assume that the size distribution of marine organics is the same as inorganic sea salt, but this is not in line with sea spray aerosol studies (Prather et al., 2013, PNAS), including in the Arctic (Kirpes et al., 2019, ACS Central Sci.). Increased marine organics are present in smaller particles produced from film drops (Wang et al. 2017, PNAS).

Sections 2.1.3 and 3.2: Prior sections generally do a good job discussing uncertainties associated with uncertainties in parameterizing sea spray aerosol from leads and the need for more measurements. However, similar discussion of the uncertainties associated with parameterizing blowing snow sea salt aerosol emissions is missing here. As written it comes across that sea salt aerosol fluxes from leads are more uncertain than blowing snow, when in actuality sea spray aerosol from leads have been studied for decades, whereas Arctic blowing snow parameterizations are missing observational evaluation and flux measurements. Therefore, the authors should add discussion of the blowing snow sea salt aerosol uncertainties just as they have for sea spray aerosol. This includes discussion of the uncertainties associated with their assumptions and the need for measurements to evaluate these.

Section 3.1: The authors state that “we cannot consider ArcLeads as viable surface information”, but a proper, thorough sea ice evaluation study is not conducted to support this statement and others in this section. Is there a paper that compare the accuracy of ArcLeads vs TOPAZ and neXtSIM? My understanding is that satellite sea ice product evaluation is outside of the expertise of the authors, and therefore it is inappropriate to discuss the accuracy of the sea ice products without referencing other studies dedicated to this purpose. It is clear from Figure 2 that the choice of sea ice lead product will have a major impact on the sea spray aerosol emissions so this discussion is critical to the results presented. Therefore, the authors need to add additional sea ice literature and further discuss caveats/assumptions.

Line 240: This sentence states that blowing snow occurs in the summer. What is the justification for this at the time when melt ponds are present? What evaluation was completed to evaluate the presence of blowing snow and support this sentence?

Lines 248-249, 257-258, & 427-428: To my knowledge, the size distribution of aerosols produced from blowing snow sublimation in the Arctic is highly uncertain and not yet observationally determined. This caveat needs to be discussed here, as the phrasing makes it sound like the blowing snow aerosol size distribution is known. Furthermore, Nilsson et al. (2001) and May et al. (2016) did not measure the aerosol size distribution from blowing snow, as implied.

Lines 281-282 and 444: It is stated that the largest uncertainty is the uncertainty/scarcity of emission flux measurements, but it would seem, based on Figure 3, that the sea ice lead product used could result in even greater uncertainty. This should be discussed.

Section 3.4: According to Figure 2 and associated discussion, both Alert and Utqiagvik are outside of the High Arctic where leads are considered in this modeling study, and therefore, my understanding is that the MIZ mask would be relevant for these locations. But, according to Figure 7, it seems that local leads are considered, so this is confusing. Please clarify.

Figure 7: The boxes around Alert and Utqiagvik in Figure 7 are very small – equivalent to maybe an hour or so of transport time (i.e. very little transport), when at least 24 h of transport time would be more appropriate. This is problematic for the comparison to local sodium aerosol, as a larger domain should be considered. What is the sensitivity of the results shown to the box chosen? Also, how is open water (i.e. sea ice conc > 80%) considered for these model-observational comparisons? It seems like this is ignored? Please also add to the caption what size range is shown for the sodium surface conc.

Additional Comments:

Lines 61-63: Chen et al. (2022) did not prove resuspension of snowpack deposited sea spray aerosol, but could not rule it out because of leads directly upwind of the snowpack.

Lines 91: Held et al. (2011) also measured fluxes, but only at lower wind speeds.

Line 176: Add the clarification that the “all areas of open water” is only in areas with sea ice >80%.

Line 197: Please clarify what is meant by “transport from the lower latitudes”. Does this include the MIZ and coastal Arctic?

Lines 209-210: It is important to note that freezing and opening of leads are processes that are faster than the timescale of the satellite observations.

Lines 218-219: See also Rheinlænder et al 2024, JGR-Ocean, doi:10.1029/2023JC020395, “Breaking the Ice: Exploring the Changing Dynamics of Winter Breakup Events in the Beaufort Sea”.

Lines 220-221: Wouldn’t the low spatial resolution of TOPAZ compared to typical lead sizes explain the lack of “discernible lead spaces”.

Lines 266-267: Does “lower latitudes” here include within the Arctic? Please clarify.

Line 274: This lacks acknowledgement of the uncertainty in blowing snow aerosol emissions.

Line 326-327: Kirpes et al. (2019) did not measure concentrations and only considered nascent (locally produced) sea spray aerosol – not those transported from open ocean.

Figure 9: Why is the Utqiagvik box bigger here than in Fig 7?

Figure 10: The grey band is difficult to see.