General comments

This paper presents and discusses the contribution of Fe from combustion and natural sources to atmospheric aerosols over the ocean on the basis of Fe isotope ratios to evaluate the combustion Fe that may affect fractional Fe solubility. The authors show multiple data of the fractional solubility and Fe species in addition to Fe isotope ratios. They also compared the observed data with the output of a model calculation. Overall, the paper is well written and provides new insights into our understanding of sources of aerosol Fe and the solubility in particles by using Fe isotope ratios. While the data presented are valuable, there are some issues that need to be worked out and clarified before its publication in ACP.

Specific comments

(1) One of my concern is on the two different sets of the samples obtained by the two cruises: one obtained in winter (KH-13-7) and the other in summer (KH-14-3). The authors combined the data sets of the two cruises and classified into three groups by the trajectory analysis in terms of possible source regions. This classification is based on the emission area and transport pathways, while photochemical activities that may have affected photochemical and acidification processes (L. 458) during the transport of aerosols, are expected to be different between the periods of the two cruises. Is there any possibility that such difference in the photochemical fields of the atmosphere may have affected Fe fractional solubility, fraction of iron species, and Fe isotope ratios, even within the same group? I think the authors should add some more discussion on this point.

(2) I suppose that the fractions of group I, II, and III in each cruise samples reflect the difference in the metrological conditions (wind fields) as well as the differences in the geographical locations where the aerosol samplings were made between winter (KH-13-7) and summer (KH-14-3). If this is true, I think the authors should mention it in the text.

(3) L.328: “Fe oxides were only found in the group III samples,” while they are dominant ion species identified in the group III (Figure 5e). Is this attributable to the oceanic region where the aerosols were sampled, or is this related to the specific season? Not only saying “different sources,” but also additional discussion on possible sources or processes of this fraction should be made.

(4) In the text, it would be helpful to show the averages and standard deviations of the concentrations, fractional solubility, and isotope ratios of Fe in each group (I, II, and III) in addition to the ranges. I understand that the number of data would become limited in each classification, but still the average values and the variation provide some basic information.

(5) The authors show the term “East Asia” quite often (e.g., six times in the abstract). Maybe they intend to say that East Asia is characterized by anthropogenic sources, while they also discuss possible effect of biomass burning in Siberia which is not included in East Asia. According to Figure 2(a), some air masses are coming from far west and passed over eastern part of the Eurasian continent, while some pathways in the south of 30 degree north are not clear to me. Please briefly characterize “East Asia” in terms of sources (terrestrial natural source is also expected) and clarify the pathways of the trajectory in Figure 2(a).

Minor comments

(6) L.360: “..suggesting an importance of aerosols with low δ56Fe values”: importance in terms of what?

(7) The word “transportation” generally refers to a system or method for carrying passengers or goods by a vehicle or a vessel or an airplane. For atmospheric aerosol or air masses, “transport” is generally used and is more appropriate word.

(8) Figure 11: The authors should mention what the size of the pie chart indicates. Maybe the magnitude of the concentrations and flux?

This work is a well written manuscript describing size-fracionated aerosol data collected on two cruises in the Pacific Ocean. The authors report total and ultrapure water soluble iron concentrations, calculate fractional solubility, and δ56Fe isotopic values . The study focuses on determining the relative contribution of combustion Fe and the impact on the observed fractional solubility. The results are also compared with outpus from the IMPACT model.

I only have minor comments and have determined the manuscript to be nearly ready for final publication. This is a timely contribution to the literature as stable isotope studies are still rare in the marine aerosol community.

Minor Comments:

Line 91: In reference to Myriokefalitakis et al (2018), the authors state, "such as the relative fraction of combustion and dust Fe to the soluble Fe that is present over oceanic regions...". I believe this intends to refer to the relative contribution of combustion and dust Fe to the soluble Fe. The term fraction was a bit confusing in this context. 

Line 104-105: It is not clear what is meant by "which is not directly associated with the observed T-Fe and S-Fe concentrations". I belive the authors mean that we are unable to determine the relative contributions of combustion Fe and natural Fe (assumed to mean mineral dust). Suggest rewording to "which is not possible from the observed T-Fe and S-Fe concentrations".

Line 142: Were certified reference materials digested and analyzed to assess the efficacy of the digests? This data should be included if available.

Line 150: >18.2 MΩ·cm

Line 156: What Fe isotope was measured by the quadrupole ICPMS? Were any measures taken to remove polyatomic interferences?

Line 274: What were the sources of the large errors?

Line 279: How were the EF values tested to determine if there statistical differences across the groups?

Line 299 Fig3 caption: Delete "was not enough"

Line 380: change "sorely" to "solely"

Line 398-399: The final sentence does not fit here. The same statement follows at Line 421 after it has been more fully justified. Suggest delete the first use where the claim appear overly confident.

Line 459: Parantheses around acidic are not necessary

Line 560: Perhaps remind the reader what Comp 3 refers to.

Line 581-582: Change both uses of "is" to "are" for correct subject/verb agreement.