General comments;

The paper entitled “Vanadium-containing ship exhaust particles detected in and above the marine boundary layer in the remote atmosphere” analyzed the PALMS instrument of the NASA DC-8 aircraft during 2016-2018. The authors found that PM emitted by ships is widespread in the atmosphere, and also demonstrated that vanadium-containing ship exhaust particles were observed up to 13 km because not all ship exhaust particles are removed by wet deposition. Overall, the manuscript is well-written and concluded an important result for the air quality/climate, and health impact. I have several specific points as follows, and please address these questions and comments.

Specific comments;

• Line 9 (Abstract): Here the authors introduced 1.2 Tg ship emissions, whereas it is introduced as 1.67 Tg in Line 31. This might indicate different contents (I am not sure about PM10 or PM2.5 in the abstract), but it will be better to be consistent within this manuscript.
• Line 21-23 (Abstract): If possible, the short comment on the IMO 2020 sulfur regulation will be important attention to the readers.
• Line 55-57: Needs appropriate reference(s) regarding this analysis to support the importance of ship emissions.
• Line 96-105: In Line 102 to 105, how to distinguish the mineral dust has been presented. However, I understand that the authors used V, Ni, Fe, SO4, and organics for ship exhaust. For example, SO4 may also produced via anthropogenic sources and volcanoes. How to detect the ship emissions? More information is required here.
• Line 173-175: I am also wondering about the effect of Asian dust when the DC-8 flight passed over the Pacific Ocean. Was there no dust event in Asia during this analyzed period?
• Line 186-187: For heavy metals, is there no possibility of the removal by dry deposition process?
• Line 196: From here, the analysis focusing on MBL has been discussed; however, there seems to be no explicit definition of MBL. How to calculate MBL? Did the author assume a fixed altitude to consider MBL?
• Line 196-200: In terms of this kind of analysis, how about calculating the ratio of the fraction of V-containing particles within MBL and above MBL (Fig. 4(a) divided by Fig. 4 (b))? This might draw an important suggestion for the spread of V-containing particles in the entire atmosphere.
• Line 205: I do not follow how to estimate this 60% contribution.
• Line 233-234: If this point is critical to mention the regional (Atlantic/Pacific and Northern/Southern Hemisphere) characteristics, how about including the information of available data numbers to calculate the V/mass fraction in this figure? If the analyzed data numbers are similar over all regions, the comparison will be meaningful, but such comparison could be meaningless under the different data numbers.
• Line 236: It is also noticed that the mass fraction of vanadium was almost the same level over the northern and southern hemispheres. In general, the northern hemisphere could be polluted rather than the southern hemisphere. Did this result suggest the ship exhaust will have an impact on entire the globe? This point is not discussed, but it will be helpful for a detailed discussion.
• Line 241-243: I agree that high sulfur content is consistent with the previous study of Myrphy et al., but the data in Figure 6 pointed out almost all (except three data) of data in this study included 85% sulfate. This value seems to be higher than previous study. Is there some discussion (such as regional difference and/or sampling period) regarding this difference?
• Figure 1(b): The legend for the yellow color will be a typo in their name and measurement period. Please confirm. In addition, the altitude is converted into AGL? or ASL? I guess that this will be unified in all analyses and figures, but please clarify the unit when introducing Figure 1.
• Figure 4: For a clear reading, it may be better to unify four colors (each season) to be consistent with Fig. 3.
• Figure 6: Why this analysis is not divided into four ATom campaigns? Were there no distinguishment by campaigns?

Technical comments;

• Line 178 and Line 180: The author's name of Zhou is redundant information in this sentence.
• Line 223: “Fig. S3” seems to be “Fig. 3”. Please confirm.

The authors present data on the distribution of vanadium-containing ship exhaust particles in the atmosphere, measured during regular flights over large areas of the world's oceans at different altitudes. This is a unique dataset and the authors report on the prevalence of these particles also in remote regions and high altitudes. Ageing mechanisms and the chemistry of vanadium-containing particles are discussed in the context of the altitude-dependent particle number fractions and their chemical composition.

The study provides valuable insights into the distribution of ship emission particles, a prerequisite for a better understanding of their climate impact. The manuscript is technically sound and interesting. There are a few points that could help to further improve the manuscript:

 

- When emphasizing the importance of ship emissions, the authors could consider to also provide some newer literature, that also addresses the current changes due to the fuel regulations, e.g. Kuittinen et al. Environ. Sci. Technol. 2021, 55, 1, 129–138, Jonson et al., Atmos. Chem. Phys., 2020, 20, 11399 —11422, Anders et al., Environ. Sci.: Atmos., 2023, 3, 1134-1144 etc.

- line 30: In the abstract, the amount of annual PM emissions was given as 1.2 Tg/y, here as 1.67 Tg/y PM.10. Also, please provide a reference.

- line 110: Traditionally, the particle’s sulphur content is evaluated by the negative charged sulphate ions and sulphuric acid. I understand that the compact aircraft-deployable design of PALMS only allows for unipolar measurements, but could the authors provide a brief statement on the evaluation of sulphur content via S+ and SO+, particularly regarding potential interference with carbon cluster from soot at m/z=48? 

- line 113-115: The strong NO+ signal compared to e.g. Ault (2010) and Passig (2021) can be attributed to the wavelength of the used ArF-Excimer laser. In a direct comparison of a 248 nm KrF-laser with a 193 nm ArF laser, it could be shown that the 248 nm laser is much more sensitive to iron and transition metals due to a resonance effect, but the 193 nm laser is more effective in ionizing NO+ and nitrogen-containing organics, see Passig et al., ACP, 20, 7139–7152, 2020. Ault et al. used Nd:YAG lasers at 266 nm, a wavelength more comparable to the KrF excimer laser than to the ArF laser.

- lines 159-162: Anthropogenic particles in the respective size mode are subject to long-range transport. So, why exclude particles detected over land and in polar regions? While shipping activity is much lower in the polar regions, the particles there are important for climate impacts, e.g. through deposition on ice and albedo changes. Were there not enough V-containing particles detected? The exclusion of these areas should be better justified.

- lines 163-170: The conservative determination of V particles from shipping is appropriate. An important consideration is the ageing of these particles. Both an increase and a decrease in the organic carbon content of the particles is possible during ageing and would have a direct effect on particle identification using the criteria of V+/VO+ peak intensity relative to neighbouring peaks. This is discussed later in the manuscript, but may be briefly mentioned already here.

- General comment: I am missing the total number of V-particles in the respective measurements/flights. I may have overlooked it, but this information would give an estimate of the statistical quality.

- lines 201-214: Could the authors provide an example of these diluted plumes? For example as a plot in the supplement?

- Figure 5: Again, I am missing absolute particle numbers. If the feature in the tropical Pacific is attributed to a single ship plume, as stated in the main text, I assume the particle numbers to be relatively low. Since sampling time is limited and particle concentration in the free remote atmosphere is low, low particle numbers are an inherent problem of such measurements and not a drawback of the study.

- line 255: Did you really observe a sufficient signal of oxalate in positive mode? I cannot see this signal in the mass spectra (Fig. 2).