This study presents a detailed assessment of marine organic aerosols over the western Pacific ocean including their radiative effects.

This is an interesting and thorough study which highlights the importance of MPOA. I have few comments (especially regarding the radiative calculations) that should be addressed before I can recommend publication.

Major comment

1. Uncertainty

Throughout the manuscripts, the authors often provide estimates (model or observations) with 2 to 3 significant digits.  This is unwarranted given the uncertainties/errors in both model and observations. The authors need to carefully revise their estimates so that they properly reflects the expected accuracy/precision. 

2. Indirect effect (Section 4.5)

It’s essential that the authors assess whether the estimated DRE and IRE are significant relative to natural variability. In particular, it's likely that the small increases found over land are just natural variability.

Line 22

“Apparently” -> be more specific

Fig. 2. It would be interesting to show the contribution of the different components of PM in the model (e.g., sulfate, dust, sea salt, moa , …). This will help support the discussion of this figure. (See for instance line 371)

Fig. 3. I suggest to more clearly distinguish the different sites. At the moment, the figure layout makes it look like a single time series. What is the uncertainty in the observations?

Fig. 4

The authors  highlight improvements in the model performance on 4/12 and 4/10 (Fig. 4b) but it seems MOA degrades the model performance for all other dates between 4/05 and 4/16 (but 4/7). There should be acknowledged 

Line 253. What is temporal resolution of biomass burning emissions

Line 272. Aren’t there missing data in the daily Chlorophyll L3 product? How was this handled?

Line 465. Could SOA from isoprene also be important?

Line 482. Please provide the same statistics for open sea vs coastal. It looks like the model is biased low in coastal regions and a little high over the open ocean.

Line 608-610 please provide uncertainty for these estimates

Fig. 6 Is it possible to show the contribution of different aerosol types to the overall AOD (at least the MOA)?

Line 731-732 The number of significant figures seem unwarranted. It’s not clear to me how the comparison between model and measurements is performed. 

Line 747. I don’t understand this comparison. What are the Arnold emissions for isoprene in the region analyzed here?

Line 900 “W” missing in front of m-2

Line 1033: add “-“ in front of 0.14 

In "Seasonal characteristics of emission, distribution, and radiative effect of marine organic aerosols over the western Pacific Ocean: an investigation with coupled regional climate-aerosol model," Li et al. examines marine organic aerosol (MOA) over the western Pacific Ocean for the year 2014 using the RIEMS-Chem model. Model is validated against observations, and properties such as MOA emission, concentration, and direct and indirect radiative effects are examined. The study is comprehensive and thorough, and publication can be advised after addressing the following comments. 

Main comments:

- Please revise the descriptions for determining the radiative effects (comments 16, 17, and 23 below) and the interpretation of atmospheric adjustments (comments 25 and 26 below).

- Have cloud properties been validated for this model before? How pristine are the remote marine clouds, particularly where strong IRE_MOA are found? (comment 18 below)

- Please provide more discussion on why IRE_MOA is greater than IRE_sea salt, and why IRE_sea salt is weaker than DRE_sea salt (comment 21 below).

All comments:

1. In the abstract, lines 26-29, please clarify if the max and min seasons refer to MOA emission or concentration. 

2. Lines 94-98: Should this information be in the methods section instead of the introduction? 

3. Please define the boundaries (e.g. latitude/longitude bounds) of the model domain as well as for FYB and NWP in the main text. 

4. What is the model resolution and time step? 

5. Line 711: negative correlation between ____(?) and sea salt emission 

6. Line 735: Where are equations (2) and (3) defined? 

7. Line 767: How far inland does "inland areas" refer to? 

8. Is 2014 a typical and representative year in terms of meteorology in the western Pacific region? Please discuss this particularly in the context of modelled MOA emission and concentration results in pages 27-28. 

9. Line 814: Perhaps rewrite the sentence starting with "Furthermore" as "Furthermore, SON has the second highest average precipitation in the NWP (Table 9), which caused... and contributed to..." 

10. Line 820: Please specify "within the model domain" after "latitudes" 

11. Line 853: southern parts of "the model domain" in the western Pacific 

12. Please clarify whether land grids are included when regional (e.g. for NWP and FYB) averages are quoted 

13. Line 894: Please clarify how the 10% difference in relative humidity may affect the DRE 

14. Line 903-907: Any insights on why the seasonal trend in EYB is different from that in NWP? 

15. Line 912: Have sea salt and anthropogenic aerosol been validated in this model before? If not, please add "in this simulation" after "Pacific" in line 913 

16. Instead of two radiation calls to calculate IRE as stated on line 936, is it not the case that the whole calculation for cloud properties as outlined in lines 946 to 950 is called twice? If yes, please amend as necessary. 

17. Line 941: Does this equation not also apply for DRE? It doesn't seem particularly helpful in differentiating DRE and IRE calculations. 

18. How pristine are the marine clouds in the model (e.g. median Nc and drop radius)? Both before and after addition of MOA. How does it compare to observations -- does it provide a realistic background condition on which MOA's impact can be determined?

19. Line 963 and figure 10 in general: How is the relationship between the spatial distribution of IRE and that of clouds? 

20. Line 964: Which regions? 

21. Line 1011: Any speculations on why IRE_MOA is generally stronger than IRE_sea salt in this study? Sea salt mass and number should both be greater than MOA (is it?). Is it a matter of size? Hygroscopicity? Also, why is IRE_sea salt weaker than DRE_sea salt, in contrast to both MOA and anthropogenic aerosol?

22. Line 1041 and other instances: Please don't state "all aerosols" if only MOA, sea salt, and anthropogenic aerosol are included, to the exclusion of dust, biogenic OCs, etc. 

23. Please describe early on and more clearly in section 4.5 what simulations are used to determine DRE_ari and IRE_aci. Firstly, to make clear that these are not the same simulations as those used to calculate DRE_MOA and IRE_MOA, and secondly, to clarify that the ones used to determine DRE_ari are not the same as the ones for IRE_aci (which is currently implied in line 1066: "between the two simulations"). 

24. Lines 1073 and 1075: W m-2 instead of W m-3 

25. Line 1074: Comments relating to the atmospheric response and adjustment: Should this not be examined from comparison between (DRE_ari-DRE_MOA) and (IRE_aci-IRE_MOA)? 

26. Relating to the above, for line 1074 and line 1079, it's not just the positive values. Fast response and adjustments may alter the magnitude of the radiative effects without resulting in positive values.  

27. Line 1128: "all" --> "sea spray and anthropogenic" 

28. Table 1 and in general for model validation: Are the simulation values that of the model grid containing the observation site? Please specify in the methods description or beginning of results.