Comments on Marine-Derived Water-Soluble Organic Nitrogen in Coastal Air: Influence of Ocean Productivity on Atmospheric Nitrogen Cycling, by Tang J. et al.

This is an interesting article on providing data and results on the origins of WSON (and WSIN) in a coastal area in Thailand (Bangkok). Different approaches are used, chemical speciation, back-trajectories, source apportionment and remote sensing derived data.

The tasks are well implemented and interesting results are obtained. However, there is a need for a very relevant review before accepting this article to ACP. Some refers to the methodology, others to the need of additional data analyses and some about interpretation of results. See below general and specific comments.

GENERAL

1. To obtain the relevance of specific contributions of a source to an atmospheric pollutant/component, one to several years of sampling are needed, but samples should be obtained constantly along the year to obtain representative annual data. If excluded periods and more intensively sampling is done in specific ones, the relevance of specific contributions can be not representative. Here you sampled more intensively in some, and avoided others.
2. Should one use special sampling protocols, denuders, filter packs,…… to avoid the lost of NH4+, NO3- and ON, or the artifact formation? How this may influence your results?
3. To show the relevance of biogenic marine WSON contribution (in abstract and main text) you should use the % contribution to total WSN, not only the contribution for each air mass.
4. The fact that WSON or WSIN are high in marine air masses does not necessary mean that these have a marine biogenic origin. IN many studies at coastal sites using receptor modelling with PMF, there are ‘aged marine’ sources enriched in SIA and sometimes in SOA, and high loads of SIA are attributed to i) the interaction of anthropogenic H2SO4, HNO3 and NH4NO3 and NH4HSO4/(NH4)2SO4 with NaCl, interaction of anthropogenic SOA and N species may also occur; ii) Shipping emissions are anthropogenic and these may account for large emissions of SOA’s and SIA’s precursors that may be enriched in marine air masses; and iii) transport of anthropogenically polluted air masses may increase the background of SOA and SIA in marine air masses.
5. Co-linearity of PM contributing sources (shipping and biogenic precursors for example) or insolation causing high T, and high SOA and SIA production together with high emissions from photosynthesis of plankton,………. Should be considered in the discussions.
6. The N isotope analyses would have provided a more solid support for the biogenic and anthropogenic origin.
7. 1-5 above should be deeply discussed and results and conclusions modulated according these.

SPECIFIC

Abstract

R35-37. This argument on supporting a ‘persistent marine source’  is not convincing me on the relevance of marine biogenic WSON (see general comments 3 and 4. If the relative proportion is the same that one in continental air mases, why the source should be different?

R39-40: See comment 1 and add information to contribution of WSON of SSA-PMF to total WSN and WSON (average of the year, but taking into account comment 1).

R40:  % contribution to what? Total N, total WSN, total WSON?

Abstract general: modulate results and conclusions based on general comments 1 to 5)

INTRODUCTION

R82-R87. Yes, this is the main challenge. State how do you intend to overcome limitations.

R91 better define euthrophication as : excessive richness of nutrients in a body of water, affecting ecosystems, or something similar, not only the increase of N concentrations.

MATHERIALS AND METHODS

R107: Sampling 24 h. See comment 2 above discuss how the loss or gains

R110-R115 Please discuss the issue of comment 1, and give the n. of samples per season. R140 define SOA, you will used it.

R151 use OC that you defined and N instead of nitrogen

R213 nss SO42- (non sea salt SO42-) points to major marine origin? Was it ss SO42- instead?

R213 what about NO3-?

R14-216, although the long range atmospheric transport may contribute to nssSO42-???????? nssSO42- is anthropogenic!!!, why biogenic sources prevailed? Re-write

RESULTS

R270-R373, is an increase from 2.7% to 3.8% in the Mediterranean compared this study is enough to underscore the relevance in this region co0mpared to the first?

R280-R297. Very speculative conclusions or interpretations. Please consider general comments 4 and 5 here.

R298-301: Why higher under mixed air masses and very similar with marine and continental

R300-303: You say that when coming from continental air masses the influence of anthropogenic emissions is high, but in the marine ones biogenic and shipping are the main. Shipping is anthropogenic. Furthermore, you attribute shipping emissions only to the harbour activities, and the marine transport is contributing a lot to NOx shipping emissions, not only during the periods staying in the harbours. That’s why NECA areas are related to abate NOx as O3 and PM precursors.

R305: NH4 and NO3-2 instead of ammonium and nitrate

R315-316: Continental region like Hawaii islands???????????

R318: marine background by anthropogenically polluted background

R320 and R326 use ON acronym

R321 use WSTN acronym

R323-R324, what about the shipping emissions of in addition of the biogenic ones. Numerous ships emit a lot of NOx during their movements into the sea

R340 shipping instead of ship, SO42- instead of sulfate

R342 fossil fuel combustion instead of fossil combustion

R343, Mg2+ instead of Mg

The whole page 9: There are also highly anthropogenically polluted regions by emissions from the continent and also by the shipping emissions, especially in this region with high shipping density. This can be enriched in marine air masses.

Page 9: You need to describe for the 7 factors, their chemical profile and show major and minor components for each factor. Specially for SSA, what other components it brings if you attribute all these to biogenic origin?

Page 383 to 398: IN which factors are nssSO42-, NH4+ and NO3, WSIBN will be mostly anthropogenic

R359 and R410 use ON acronym.

R410 SSA is a complex mixture of organic but mainly inorganic, isnt’it?

R421 aerosol carbon by aerosol’s carbon

CONCLUSIONS

Consider general comments above to draw the conclusions. Define again acronyms in this section, and when defined use only acronym.

FORMAT IN ALL TEXT

In results: Present always mean± std (min-max). Ion R69 you doit like this in R275-6 you give min-max (mean± std)

Define all acronyms, N, S, ON, WSTN, WSON, IN, WSIN,…. And once defined, use always the acronym, now these are defined in most cases (not N, nor S, ……..) and thse acronyms and complete spelling is used alternatively along the paper. Ex nitrogen (N) is not used as N but later you use ON as acronym defined in R51 but fully spelled in R55, R73, re-defined in R89,……

Atmospheric organic nitrogen plays an increasingly recognized role in nitrogen cycling, yet its contribution from marine biological processes remains poorly constrained in coastal environments. This study investigates WSON in total suspended particulate matter collected over one year at a coastal urban site in Bangkok, Thailand. By combining chemical measurements, PMF source apportionment, air-mass trajectory analysis, and a trajectory-based chlorophyll-a exposure metric, the manuscript demonstrates that sea spray aerosols associated with marine biological activity represent a substantial source of WSON under marine-influenced conditions. Overall, the manuscript is well written, and conclusions are generally supported by the presented results. The following suggestions are provided to the authors for further revision before the final publication.

1. Page 9, lines 265-267: The observed negative correlation between TSP and precipitation is statistically significant and consistent with wet scavenging effects. However, given the relatively low R²value, precipitation alone appears to exert a secondary control on TSP variability. The authors may consider slightly revising the wording to better reflect the limited explanatory power of precipitation in this relationship.
2. Page 10, lines272-273, 278-279: The statements “underscoring the relevance of water-soluble nitrogen in this region” and “suggesting possible common sources or formation pathways” are rather general and add limited interpretive value.
3. Page 10, lines 294-297; Page 11, lines 303-308: The discussion of wet scavenging effects on WSON and the WSON/WSTN ratio is somewhat difficult to follow and appears internally inconsistent. On the one hand, wet scavenging is invoked to partly explain the lower WSON levels during marine-influenced periods, which largely coincide with the rainy season. On the other hand, the lack of a significant correlation between WSON and precipitation is used to argue that WSON exhibits distinct scavenging behavior compared to WSIN.
4. Page 13, lines 374-377: Nitroaromatics represent only a subset of nitrogen-containing organic species contributing to WSON. If their role is considered important, I suggest either providing supporting quantitative evidence or moderating the wording to reflect the limited compositional constraints.
5. Page 13, line 378: The reported range “33%–37.7%” shows inconsistent significant figures. Please consider revising the values to a consistent precision
6. Page 15, lines 410-425: The discussion sections about extensive background statements on marine productivity and SSA-related processes could be condensed to improve clarity and to emphasize the novel results of the present study.
7. Page 16, lines 438-440: The conclusion that marine biogenic organic matter is a primary source of WSON during marine air-mass influence is mainly based on correlation analyses. While the observed relationships are suggestive, correlation alone does not provide sufficient evidence to establish source dominance.