This work analyzed the ON abundance, sources, and its influence on aerosol light absorption in the marine atmosphere over East Asian marginal seas. The results highlight that continental outflows of air masses played important roles in regulating the formation of ON and the light absorption of marine aerosols. The quantitative ON data in marine aerosols are valuable for evaluating the effects of aerosol deposition on the marine ecosystem. It can be published in ACP after addressing the following comments:

Section 2.2: In this work, total ON is quantified by a newly developed IN&ON analyzer. Water-soluble nitrogen and inorganic nitrogen are analyzed by a TN analyzer and ion chromatography. I understand the difference between water-soluble TN and IN is widely used to calculate WSON. However, have the authors compared the quantitative difference of nitrogen between IN&ON analyzer and ion chromatography? Would the inter-instrument quantitative differences influence the quantification accuracy of WSON?

Lines 135-144: How about the seasonal variation of organic carbon in marine aerosols? Is there any difference in temporal variations and sources between ON and OC in marine aerosols over marginal seas?

Lines 174-189: I may suggest adding some specific examples of ON formation from aged biomass burning or secondary nitrate formation processes.

Lines 201-213: Could the authors provide more explanation of the dust-related ON formation? Is organic nitrogen transported from the dust source region by dust storms, or is it secondarily formed during long-range transport?

Specific comments:

Lines 127-128: Please list the concentration ranges of ON over open ocean and in polluted continental environments for clear comparison.

The legend in Fig. 1 (a) is small and difficult to read.

Lines 247-250: Please show specific nitrogen-containing organic compounds to explain the higher light absorption capability of organic nitrogen in atmospheric aerosols.

Line 57: Change “emitted” to “emit”.

Line 199: Change “orgnaic” to “organic”.

Lines 291-293: Revise this sentence for clarity.

This manuscript presents valuable and timely data on aerosol ON over East Asian marginal seas. The analytical methods are state-of-the-art, and the source apportionment provides important insights into the sources and transformations of ON. The finding that continental ON drives light absorption has important implications for understanding the optical properties of marine aerosols.

However, the manuscript has several areas that require clarification and strengthening before it can be accepted for publication. The methodological details need to be expanded, particularly regarding the measurement techniques and PMF analysis. The interpretation of the dust source of ON needs to be refined. The figures, especially Figure 6, need to be improved for clarity. Statistical testing should be performed to verify the significance of key results.

The authors should address the comments (find details below), particularly the methodological clarifications, statistical analysis, and refinement of the dust source interpretation. With these revisions, the manuscript would make a significant contribution to our understanding of organic nitrogen in marine aerosols and its role in aerosol optical properties.

Major Comments:

Methodology and Data Quality

Q1 The authors state that total suspended particles (TSP) and PM₂.₅ were simultaneously collected, but the manuscript primarily focuses on PM₂.₅ data. However, Figure 1d and the discussion of the dust episode reference Ca²⁺ concentrations in TSP (line 142). This inconsistency needs clarification. Were all analyses performed on PM₂.₅ samples, or were some species measured in TSP? If both size fractions were analyzed, why is the focus exclusively on PM₂.₅? This is particularly important because dust particles can be coarse-mode, and the ON associated with dust might be under-represented in PM₂.₅ measurements.

Q2 The sample numbers vary substantially across seasons (autumn: 9, spring: 22, summer: 20). While the authors acknowledge this limitation, the small autumn sample size (n=9) raises concerns about the statistical robustness of the seasonal comparisons, especially given the relatively large standard deviations. The authors should consider whether any autumn samples were potentially impacted by specific events that could skew the seasonal average, and discuss this limitation more explicitly.

Q3 The calculation of WION = ON - WSON (line 97) assumes that WSON is a subset of ON. However, the ON measurement (by the aerosol IN&ON analyzer) and WSTN measurement (by TOC/TN analyzer) are based on different analytical principles. Could there be systematic differences between these methods that affect the WION calculation? The authors should provide more information on the comparability of these two methods.

Q4 The blank correction procedures are only briefly mentioned (line 105). Given the low ON concentrations in marine environments, the blank contributions could be significant. The authors should provide more details on: (a) the blank levels and their variability, (b) whether field blanks were subtracted from each sample, and (c) the detection limits for ON, WSON, and WION.

Source Apportionment

Q5 The PMF analysis uses 11 input parameters (line 116), but the manuscript does not specify whether the data were normalized or scaled. Given that concentrations span several orders of magnitude (e.g., ON ~0.35 μg/m³ vs. NO₃⁻-N ~0.63 μg/m³), proper scaling is critical. The authors should describe their pre-processing steps and justify their choice of uncertainty calculations.

Q6  The PMF resolves five factors, but the "aged biomass burning" factor (factor 1) and "secondary nitrate formation" factor (factor 3) both appear to be associated with anthropogenic secondary pollutants. Figure 4 shows that these two factors together account for the majority of ON in autumn. However, the distinction between these factors is not entirely clear. Factor 1 is characterized by K⁺, EC, WSOC, and secondary inorganic ions, while factor 3 is dominated by nitrate. Given that biomass burning also produces nitrate, how well-separated are these factors? The authors should provide more detail on the factor profiles (e.g., as a supplementary figure) and explain the rationale for keeping these as separate factors rather than combining them into a single "anthropogenic secondary" factor.

Q7  The correlation between ON from secondary nitrate formation and RH (Figure S5) is interesting, but the analysis appears to be based on limited data points. For autumn (n=9) and spring (n=22), the authors should consider whether the observed correlations are statistically significant given the small sample sizes. Additionally, what is the mechanism for RH dependence specifically for nitrate-derived ON, and why would this dependence differ between seasons?

Q8 The contribution of dust to ON in spring reaches 55%, with >80% during the dust episode. However, the authors also note that dust ON correlates with nitrate aerosol concentration (Figure S6). This suggests that the dust-associated ON may actually be formed through heterogeneous reactions with anthropogenic pollutants during transport, rather than being primary dust ON. The authors should consider whether this should be discussed as "dust-mediated formation of ON" rather than simply "dust source" of ON.

Optical Properties

Q9 The use of Abs₃₀₀ to represent light absorption is a significant methodological choice. While 300 nm is commonly used in BrC studies, why was this wavelength chosen rather than the more widely used 365 nm? The authors use MAE₃₀₀, but MAE₃₆₅ would be more comparable to existing literature (see e.g., Dasari et al., 2019 Science Advances). If the data are available, the authors should consider presenting results at 365 nm and discussing any differences.

Q10 The statement that "water-soluble organic nitrogen drove the light absorption" (line 238) is supported by Figure 5a, which shows a strong correlation between Abs₃₀₀ of WSOM and WSOM for all seasons. However, Figure 5a shows only the correlation with WSOM concentration, not specifically with WSON. The authors should clarify whether the observed absorption is truly driven by nitrogen-containing organic compounds, or whether it simply correlates with the bulk WSOM concentration (which would include non-nitrogenous chromophores as well).

Q11  Figure 5d shows no clear trend for WIOM MAE₃₀₀ vs. WION/WIOC in autumn and summer. The authors attribute this to the dominance of water-soluble organics in these seasons, but this explanation is somewhat circular. Could there be other factors, such as different chromophore compositions or photobleaching, that affect the absorption capability? The authors should discuss alternative explanations.

Q12  The conclusion that "continental aerosol ON modulated the light absorption by organic aerosols over marginal seas" (lines 293-295) is supported by Figure 6, but the correlation between continental WSON and Abs₃₀₀ (r=0.80) is based on combined data from all seasons. Would this correlation hold within individual seasons? And why is there no correlation with marine-generated ON? The authors should provide more nuanced discussion of these relationships.

Interpretation and Context

Q13 The manuscript emphasizes the role of anthropogenic secondary pollutants in ON formation, but the relative importance of gas-phase vs. aqueous-phase formation pathways is not clearly distinguished. The authors discuss both VOC oxidation with NOx (gas-phase) and aqueous reactions (lines 194-197), but the PMF factor "secondary nitrate formation" likely includes both pathways. The authors should clarify whether they can distinguish between these mechanisms based on their data, and what the implications are for the solubility and optical properties of the resulting ON.

Q14 The discussion of marine sources (lines 214-221) is relatively brief. Given the summer cruise was dominated by marine air masses, and marine sources contributed 53% of ON in summer, this section deserves more attention. What specific types of marine-derived ON compounds are expected? How do their chemical properties and optical characteristics compare to continental ON? The authors only mention amino acids and protein-like matter, but there is a growing literature on marine-derived brown carbon that could be referenced.

Q15 The authors highlight that "organic matter in dust aerosols among the source regions usually has weak light absorption capability" (line 272), and that absorption increases during transport. This is an important point, but it is not supported by direct measurements. Do the authors have data on the absorption properties of dust before and after mixing with anthropogenic pollutants? If not, this statement should be framed as a hypothesis rather than a conclusion.

Q16 The implications for marine ecosystems and biogeochemical cycling are only briefly discussed in the introduction and conclusion. Given the significance of nitrogen deposition for marine productivity, the authors should elaborate on how the observed ON concentrations and sources might affect nutrient supply to the YBS and potentially the broader East Asian marginal seas. How do the ON deposition fluxes compare to IN deposition? What fraction of the total nitrogen deposition is ON in this region?

Minor Comments:

Lines 19-20: The statement "ON abundance, sources, or its influence on organic aerosol absorption remain unclear in marine atmosphere" could be more precise. While knowledge gaps exist, there have been previous studies on ON in marine aerosols (as cited). The authors should clarify what specific aspects remain unclear.

Lines 23-24: The range of ON contribution to total nitrogen (4%-60%) is quite broad. The authors should mention whether this range represents seasonal variability, spatial variability, or measurement uncertainty.

Line 26: "aged biomass burning and secondary nitrate formation were the most important sources" - this is a conclusion from the study, and would be better placed in the discussion rather than the abstract.

Line 100: The calculation of OM = OC × 1.6 uses a standard factor that may not be appropriate for all aerosol types (especially dust-containing samples where mineral matter contributes to mass but not OM). The authors should justify this choice or discuss its limitations.

Line 112: The input parameters for PMF include "Abs₃₀₀ by WIOM and WSOM." How were these absorption values incorporated into the PMF model? Were they used as tracers or as variables to be apportioned? This should be clarified.

Lines 117-118: The statement that "85% of the runs were acceptable" is vague. What criteria were used to determine acceptability? The authors should provide more detail on the diagnostic metrics used (e.g., Q/Qexp values, residual analysis).

Figure 1d: The time series shows Ca²⁺ concentrations, but the y-axis label indicates these are TSP concentrations, while the other species are PM₂.₅. The authors should either make the figure more clearly labeled or explain why Ca²⁺ is shown as TSP while ON and IN are PM₂.₅.   

Lines 135-136: The statement "following the abundance order of autumn > spring > summer" could be misleading since the differences between autumn and spring (0.50 vs. 0.37 μgN/m³) may not be statistically significant given the standard deviations and sample sizes. The authors should perform statistical tests (e.g., t-test, ANOVA) to determine if the seasonal differences are significant.

Lines 152-154: The discussion of WSON > WION and the relative fractions is interesting, but the authors should provide more context on what WSON/WION ratios have been observed in other marine environments and what they imply about aerosol aging.

Figure 3: The correlations between ON, WSON, WION and K⁺, nitrate, and Ca²⁺ are shown separately by season. However, the r-values are presented without p-values. The authors should include significance levels to indicate which correlations are statistically robust.

Lines 288-292: The conclusion that "water-soluble ON drove light absorption" and "both WSON and WION played important roles" during dust storms is somewhat contradictory to the earlier statement that "water-soluble organic nitrogen drove the light absorption" (line 238). The authors should clarify that the relative importance of WSON vs. WION depends on the season and source influences.

Line 293-295: The conclusion that "marine-generated ON played a minor role in the light absorption" is based on the data, but the authors should consider whether this might be due to the specific optical properties of marine-derived ON (e.g., less chromophoric) or simply lower concentrations.

Others:

Throughout the manuscript, the formatting of units is inconsistent (e.g., "μgN/m³" vs. "μg N/m³"). The authors should standardize units throughout.

Fig. 1: 

1. The color scales in panels (a-c) are not clearly defined. What do the different colors represent? Is it ON concentration or another variable?

2. Panel (d) shows a dust episode marked in orange, but the criteria for defining this episode are not specified (e.g., Ca²⁺ concentration threshold). The authors should provide this information.

3. The figure caption should specify that panels (a-c) show PM₂.₅ ON concentrations.

Fig. 5:

1. Panels (a) and (b) show Abs₃₀₀ vs. WSOM and WIOM, but the y-axis label is incomplete. It should read "Abs₃₀₀ (Mm⁻¹)" or similar.

2. Panels (c) and (d) show MAE₃₀₀ vs. ON/OC ratios, but the units for MAE are not provided in the figure. The equation for MAE (line 110) shows units of m² g⁻¹, but this should be confirmed.

3. The data points in panels (c) and (d) appear to be from different seasons but are colored inconsistently. The caption should clarify which color corresponds to which season.

Supp. Figs:

1. Figure S1 shows 72-hr backward trajectories. The authors should specify whether these trajectories are for PM₂.₅ samples or TSP samples, and whether the altitude of 500 m is representative of the boundary layer.

2. Figure S2 shows Q/Qexp variation with solution numbers. The authors should explain what Qexp represents and why the minimum in Q/Qexp occurs at 5 factors.

3. Figure S3 is not referenced in the main text. The authors should either reference it or remove it.

4. Figure S4 shows PMF results vs. measurements. The authors should provide statistical metrics (e.g., R², slope, intercept) to assess the goodness of fit. 

Other aspects for consideration :

1. The discussion of brown nitrogen (Li et al., 2025b) is brief (lines 224-225). Given that this is a key recent finding, the authors should discuss how their results compare to or extend these global estimates.

2. The role of dust in ON formation (lines 210-213) could be better contextualized with previous studies on heterogeneous reactions on dust surfaces.

3. The comparison with other marine regions (lines 126-128) could be expanded. What are the typical ON concentrations in other marginal seas (e.g., Mediterranean, South China Sea)?