The manuscript is mainly describing the specific effects of ocean emission and terrestrial input on the atmospheric NMHCs in a representative marginal sea. While the impact of terrestrial input on the coastal environment is widely recognized, a more detailed discussion has been lacking. The authors address the influence mechanism of terrestrial land-based inputs on nearshore atmospheric NMHCs, taking into the distance from the shore and relevant parameters of air masses, and assess the relative contributions from land and ocean sources. This is meaningful to deepen the understanding of how terrestrial input affecting the marine environment near the coast. I think the manuscript is suitable for publication in the ACP after a revision.

Major comments or suggestions:

1.    The positive matrix factorization model is the methodology employed by the authors to deconvolute the source factors of atmospheric NMHCs and assess their respective contributions. The authors should provide a more detailed exposition on the principles of this approach in Method section to enhance clarity and understanding. 

2.    While the authors have made a clear statement regarding the significant difference in NMHCs between urban and marine atmosphere, there is still a need for a more explicit expression on the distribution characteristics of NMHCs, especially in the marine atmosphere. It is advisable to make advancements in the description within the main text, ideally supplemented with relevant Figure for a comprehensive view.

3.    Obviously, the distance from the land to the oceanic station is a crucial parameter in the authors’ discussion. However, I didn’t find any information about the source of distance data or an introduction to the relevant calculation method. The authors should explicitly provide details on these aspects for clarity and transparency in the manuscript.

4.    The authors have employed an innovative approach in assessing the impact of sea-air flux on the marine NMHCs, by calculating the atmospheric lifetime-weighted concentrations of different gases. In this way, the variabilities of atmospheric reactivities of different gases were considered simultaneously when examining the relationship between flux and concentration. It is found intriguing and seemed effective. Furthermore, the authors could extend this novel idea to the discussion about the air mass. Both of land retention and transport time of air masses serve as indicators of air mass characteristics, reflecting the impact of land-based inputs. Combining these two parameters to collectively explore the impact of air masses on NMHCs might offer a new perspective, potentially leading to fresh discoveries

Minor comments:

1 Show the standard deviation when you mentioned average, like line 266 “the mean (range) concentration of ethane, propane, i-butane, and n-butane was 2.26 (0.277-5.72), 2.95 (0.149-20.1), 2.57 (BD-27.6), and……”

2 line 358 “ethane possesses an atmospheric lifetime of approximately 78 d at 24 h [•OH] concentration of 6×105 molecules cm-3……”.  References are needed to illustrated the source and credibility of the data used here.

3 line 468 “ozone formation potential (OFP) of NMHCs was calculated using OFP = MIR × C…” The calculation description should be in the method section and clearly present the specific constants used in the equation and their literature sources.

4 Is it necessary to include both the full term and abbreviation ‘NMHCs’ in the caption of each Figure? Generally, after the initial mention in the text, subsequent references can use the abbreviation alone for conciseness.

5 Increase the font size of the text in the Figures to make them more readable.

This paper presents an analysis of canister measurements of NMHCs at several coastal Chinese cities and over the Chinese marginal seas (along with seawater measurements) to assess the relative impact of oceanic versus terrestrial sources over the seas. Their analysis, which used back trajectories and air-sea fluxes calculated from their measurements, determined that alkanes were primarily impacted by terrestrial sources, whereas alkenes had a larger contribution from oceanic ventilation, with higher NMHC ocean fluxes closer to the coast. PMF analysis confirmed these findings, and provided a more detailed source apportionment of the contributions from industrial, vehicle, terrestrial, and oceanic sources.

I found this paper to be relatively well-written and provides new data in a region that has not been frequently studied. However, as is the conclusions are underwhelming; the fact that this study “highlights the significant influence of terrestrial outflow on the distribution and composition of NMHCs in the nearshore atmosphere of China…”doesn’t seem to me a surprising or new finding. I think the paper needs to do more to demonstrate the implications of this—it begins to do so in lines 467-478 with the discussion of ozone formation potential, but I think it needs more. I suggest editing down some of the correlation and distance analysis earlier in the paper (which all reiterates the same conclusions) and expanding the final section. Perhaps the authors could include a modeling analysis on the impact of air quality (ozone and SOA) over the marginal seas? Or, they could at least expand the source apportionment section and do more to highlight what are the underlying air quality implications? I would support publication after this main concern has been addressed.

Specific comments

Line 57-60: There are several more recent studies that provide higher/different global VOC ocean emission estimates than Guenther et al. (1995). Suggest providing a range here to expand the literature review and also highlight how uncertain these fluxes here.

Section 2.7: More detail is needed here to explain the PMF model set-up and what is meant by the scaled residuals shown in Fig. S1.

Lines 338-334: This analysis is interesting—were there also any temperature and/or windspeed differences within and beyond 100 km from shore? Also, could the authors find a way to reference Fig 5a and b here, rather than just listing the total (alkanes+alkenes) emissions in text? It’s a nice figure and I find it easier to digest than the numbers in Table 1, but right now I don’t think those panels are actually referenced in the document.

Technical comments:

Line 45: suggest deleting the word “second” before “organic”

Line 108: Tables are being referenced out of order here. Suggest reordering to avoid this.

Line 177: “analyzed” should be “analyze”

Line 181: “yield” should be “yielding”

Line 359-361: this sentence is awkward, consider revising.

Line 364: “life-weighted” should be “lifetime-weighted”

Line 366: “acknowledging” should be “acknowledges”

Line 399: “NHMCs” should be “NMHCs”

Figure 5e and f: “Slpoe” should be “Slope” in these two panels

Figure S2: Suggest changing the panel titles to eliminate the “@Dummy=first”