Measurement Report: Molecular Dynamics of Organic Aerosol in the Wintertime East China Sea Driven by East Asian Outflows

Li, Hao; Qin, Xiaofei; Xu, Jian; Gao, Qianqian; Bi, Kai; Deng, Zhaoze; Liu, Jianguo; Zheng, Haitao; Ren, Xiaoyu; Wang, Xiaofei; Deng, Congrui; Huang, Kan

doi:10.5194/egusphere-2026-4499

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https://doi.org/10.5194/egusphere-2026-4499

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01 Sep 2026

| 01 Sep 2026

Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Measurement Report: Molecular Dynamics of Organic Aerosol in the Wintertime East China Sea Driven by East Asian Outflows

Hao Li, Xiaofei Qin, Jian Xu, Qianqian Gao, Kai Bi, Zhaoze Deng, Jianguo Liu, Haitao Zheng, Xiaoyu Ren, Xiaofei Wang, Congrui Deng, and Kan Huang

Abstract. Organic aerosol (OA) represents a significant component in the marine atmosphere, yet its chemical composition and sources remain poorly constrained owing to its relatively sparse observations in coastal regions. This study investigates molecular characteristics and evolution of OA by high-resolution mass spectrometry during winter over the East China Sea. The detected thousands of organic compounds exhibited low O/C ratios (0–0.6) but broad H/C distributions. Over 95 % (ESI+) and 60 % (ESI-) of detected molecules were highly sensitive to air mass origins, revealing the dynamic interplay between marine and anthropogenic emissions. The CHON subgroup dominated the ESI+ mode (55 – 58 %), while the dominant subgroups in the ESI- mode varied with atmospheric processes. The CHON- subgroup fraction surged substantially during pollution episodes, particularly for nitro-aromatics. The CHOS- subgroup was more sensitive to aqueous-phase reactions and facilitated by elevated SO₂/SO₄²⁻ levels, leading to the formation of organosulfate (O/S ≥ 4). Marine biomarkers persisted across all periods, indicating pronounced resilience of marine emissions even in winter. The bulk volatility increased during polluted periods, particularly for CHON- and CHN+ subgroups, driven by primary emissions and suppressed oxidation. This study demonstrates that continental outflows, atmospheric secondary processes, and persistent marine emissions collectively complicated OA molecular characteristics over the East China Sea.

Received: 25 Jul 2026 – Discussion started: 01 Sep 2026

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Hao Li, Xiaofei Qin, Jian Xu, Qianqian Gao, Kai Bi, Zhaoze Deng, Jianguo Liu, Haitao Zheng, Xiaoyu Ren, Xiaofei Wang, Congrui Deng, and Kan Huang

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RC1:
'Comment on egusphere-2026-4499', Anonymous Referee #2, 11 Sep 2026 reply
This manuscript presents a systematic analysis of the molecular composition of atmospheric organic aerosols at a coastal site in the East China Sea under the influence of different air masses, based on nearly one‑month field sampling. By comparing the evolution of organic molecular characteristics under different air mass influence, the study highlights the regulating effects of terrestrial and marine emissions on coastal organic aerosols. The manuscript may be considered for acceptance after revision. However, several questions need to be further addressed:
In Figure 1, the air masses passing over the Yellow Sea are defined as marine background atmosphere (MBGA), which appears reasonable. However, have the authors considered that the Yellow Sea is geographically close to land, and its air composition may not represent the pure marine signature typical of open‑ocean environments. For the air masses from northern China in Figure 1b, the altitude over land is high (> 2000 m), exceeding the terrestrial boundary‑layer height. Can such air masses accumulate terrestrial pollutants? Moreover, these air masses spend most of their trajectory over the Bohai and Yellow Seas, and descend to below 500 m near the sampling site. Is it plausible that the so‑called northern China terrestrial air mass is actually influenced by terrestrial emissions from the Yangtze River Delta region together with ship emissions over the sea?

Section 2.1: What does “18:00 to 07:00⁺¹” mean? What is the purpose of sampling using two different filter?

Section 2.2: “Aerosol chemical components analysis including water‑soluble ions and carbonaceous species were conducted by an Ion Chromatograph.” What carbonaceous species were measured using ion chromatography? Organic acids? This information is not documented in the text.

For mass‑spectrometry measurements, the full‑scan mode was set over m/z 50 to 1700. Why were only molecules within m/z 50‑800 further analyzed? Were the m/z > 800 species excluded due to low signal intensity or low abundance?

In Supporting Information Table S2, SO₂ and NO₂ data are absent for MBGA samples. How can SOR and NOR be calculated without these datasets? In addition, the calculation formulas for SOR and NOR should be provided.

The data source for downward short‑wave radiation flux should be specified.

Section 3.2: The m/z distributions observed during PE_North and PE_East were consistent with those reported for biomass burning, coal combustion, and vehicle exhaust emissions. This statement is questionable. Source apportionment of organic compounds cannot be reliably inferred solely from m/z distributions; specific tracers or typical source‑specific compounds are required.

The x‑axis of Figure 4a needs explicit annotation. Does it represent pollution level? How is this calculated? In Figure 4b, why are CHN‑containing compounds not shown in the ESI⁻ ionization mode?

Line 406: Why do CHOS+ and CHOS- compounds exhibit higher DBE values relative to other compound classes? Can this feature be linked to ship emissions at sea?

The terms BBOA and HOA are mentioned in the manuscript, yet their definitions are missing. How did the authors classify BBOA and HOA? Was the classification based on the typical marker compounds of BBOA identified in this study?

11.According to the authors’ interpretation, if palmitic acid is derived from Ocean, MBGA samples should theoretically show higher relative intensities of palmitic acid. However, comparable relative intensities of palmitic acid are observed across the three sample groups. Does this observation imply substantial terrestrial contributions, or potential background contamination during laboratory handling?
Formatting issues: Several descriptions in the text require consistency. For instance, CHON and CHON⁻ in the Abstract. Line 368: “Figure 4b and Table S3reveal decreased”, a space is missing.

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Citation: https://doi.org/10.5194/egusphere-2026-4499-RC1
RC2: 'Comment on egusphere-2026-4499', Anonymous Referee #1, 21 Sep 2026 reply

Measurement Report: Molecular Dynamics of Organic Aerosol in the Wintertime East China Sea Driven by East Asian Outflows
Li et al., 2026
This paper presented a very in depth analysis of the molecular characteristic of organic aerosol measured over the East China Sea by high-performance liquid chromatograph coupled with quadrupole time-of-flight mass spectrometer with electrospray ionization source. The analysis separates OA according to total mass concentration and back trajectories into 3 groups: marine background air and two pollution groups (east and west) to demonstrate how continental outflow and atmospheric secondary processes can impact the OA molecular characteristics. The reporting on individual compounds, compound groups and their related properties (abundance, double bond equivalent, oxidation state, volatility etc.) is extremely thorough, but this also impedes the readability of the manuscript as it is very dense. This level of characterization is a value contribution to the field, however, several major and minor comments should be addressed.
Major comments:
More discussion is needed earlier in the paper of how to interpret the measurement technique and the trends across sub groups (CHO etc), across ESI+ and ESI-, and across studies. More details on what species are detected by the ESI technique, what factors influence the relative intensity, and why the ESI+ and ESI- modes detect different species. How do methodological difference impact comparison with other studies? How does having the separate ESI+ and ESI- affect comparisons to generic CHO/CHON/CHOS etc groups for other papers?
Section 3.4.1 should come earlier in the discussion. It would help for understanding how to interpret differences/similarities in the ESI+ and ESI- trends in Section 3.3 and how to interpret comparison to other studies. Some of these discussions in Section 3.4.1 are repetition of Section 3.3. Some of the possible explanations should be rolled together with Section 3.3 (i.e., Lines 519 – Elevated O/C ratios suggest enriched oxygenated functional groups…, Line 525 – Unique components during PE_North may derived from ….)
Something similar to Section 3.4.1 but to cover the overlap between the ESI+ and ESI- would be very valuable and support the discussion about the technique. This could go together with Section 3.4.2 and go before sections 3.2 and 3.3. The molecular level detail can then support the observed trends from 3.2 and 3.3. This better understanding of the overlap between ESI+ and ESI- and the measurement technique would also be helpful when trends differ for ESI+ and ESI- (Eg. CHOS+ shows lower O/C for PE_North and PE_East relative to MGBA but CHOS- shows higher O/C for PE_North and PE_East relative to MGBA; or the different relative abundance of the CHO/CHON/CHOS etc and how they change the three profiles).
Section 3.2, 3.3, and 3.5 are incredibly dense, with a lot of text descriptions of the figures/tables. It is difficult to follow the main takeaways and build the overall picture, especially with the split of the ESI+ and ESI- not always sharing the same story. It may make more sense/be clearer to just present the figures and tables, and then describe each profile/period and how the various parameters support the interpretation for that profile/period.
How were the carbon oxidation state groups assigned (section beginning Line 430): HOA, BBOA, SV-OOA, LV-OOA etc.? Was there some kind of PMF? This assignment needs more explanation, including the following discussion. Line 441: “This pattern aligned with the enhanced contributions of biomass burning emissions and aging processes during atmospheric transport” – doesn’t this pattern suggest that there ARE enhanced contributions of biomass burning and aging? Or do you already know there are enhanced contribution of biomass burning of aging (separately) and this is consistent?
Line 496: Elaborate on why the CHOS+/- and CHONS+/- subgroups are so different than the other literature in Figure 5. Does the detailed analysis from Section 3.3 help explain, connect the dots between these sections and those findings. Is this related to the deviation from literature in Figure 9? Line 662: “Despite methodological differences in solvent extraction affecting absolute volatility magnitudes…” – more explanation is needed here on why the results from this study shown in Figure 9 deviate, and how the methodological differences impact the other observations from the study? Why is the relationship from this study so much lower?
Figure 7: Include the total number of compounds and compounds within each category (CHO- etc) for each case. Are these all of the 125 compounds the were common to all three periods/profiles in the ESI-? Why do you focus only on the 5 categories presented here? More details on Figure 7d. Error bars (horizontal and vertical) for 7d? Where does the data come from? Were the signals lumped into OC bins? For all the periods together? Text in Section 3.4.2 – what is the significance of a correlation with OC? What does this reveal? How is this a “temporal trend” (Line 600)?
Section 3.5: very dense description of Figure 8 – difficult to follow the main take-aways. Also would be valuable to connect the volatility distribution and discussion that follows (Line 660 and on) to the other evolution/differences in properties described above in Section 3.2 and 3.3, but this depth of analysis may not be necessary for measurement report.
How will the data from this study be useful for climate models?
Manuscript could benefit from editing by native English speaker. In particular, there are several instances where the tense switches. In addition, there are instances when the language needs to be more precise to differentiate when the data “suggests” or “is consistent with [previous studies/observations, other data within the study, or some phenomena that is offered as explanation]” as opposed to when the data is truly proving/showing something. Finally there are instances when the comparison/period under discussion is not clear. Several of these instances have been noted in the minor comments along with grammatical suggestions for improved readability.
Minor comments:
Please accept grammar suggestions as suggestions only.
Check sig figs, reducing sig figs in tables could improve readability.
Figure 1: How were the back trajectories categorized? Looking at some of the more ambiguous cases, it’s not clear how the category was decided. Or first, it was decided whether it was polluted or background based on the concentrations, and then only the polluted were separated into north or east?
Line 53: grammar suggestion: replace “which have legitimately been responsible for a pronounced biological cycle and climate effect” with “which are in turn responsible for pronounced biological cycle and climate effects”
Line 58: originate instead of originated
Line 64: account instead of accounted
Line 72: “and are comparable in magnitude…” this doesn’t make sense grammatically, what are comparable?
Line 83: are instead of were; also what is emitted – the saccharides or the particulate matter, it is not clear
Line 84: from what area/region/ time of year is this composition information from (Frossard, Lawler, Hasenecz studies); also are instead of were
Line 98: propose “differences in marine organic aerosol chemical composition” instead of “contrasts in marine organic aerosols”
Line 122: Allen H Goldstein should just appear as Goldstein
Line 130: variables instead of constants? Or parameters?
Line 137: exhibit instead of exhibited
Line 138: subgroup fractions instead of subgroups fraction
Line 166 and elsewhere: ensure scientific notation for units
Line 166 and 167: designated instead of donated
Line 169: at instead of in
Line 170 until instead of till
Line 192: Can you comment on whether you expect halogens in the organic composition?
Line 193: use subscripts for CcHhOoNnSs to indicate the number of each atom
Line 200: X_c (subscript c) and elsewhere in manuscript; identify instead of identified
Line 205: functional instead of function
Line 207: Aliphatic??
Line 214-215: propose to change to “which represents the distribution of organic compounds between gas and particle phase at thermodynamic equilibrium”
Line 230: describe what the dataset is. Where were the measurements taken? Who runs the monitoring station? What is the time resolution?
Line 251: Is there a basis for the cutoff point of 10 ug m^-3 for defining pollution episodes? Do you have a reference? The value of 8.1 times higher WSII for PE (Line 255) and the averages for polluted vs background depends on how you define the cutoff point (also for the components that follow). What is the value of providing this factor? Possibly it makes sense for you to discuss the concentration differences after defining the back trajectories because they show that based on the cutoff, the MGBA does originate over the open and the PE originate over land.
Line 269 characterized by higher SO2 (not characterized of higher SO2…)
Line 272: omit “discussed above”; consider provide instead of provided
Table S2: What does the _Path mean here? More explanation on these measurements and where they come from? Define NOR and SOR. Define ALWC. In the table caption mention that the ALWC is calculated.
Figure 3: Label CHNS* with asterix in the figure legends
Line 314: Not entirely sure what you are comparing here. Is this for MGBA, PE_East, and PE_North all compared to the cited study? Did the previous study use the same measurement technique with separate ESI+ and ESI-?
Line 320: suggest, “but were also abundantly present…” instead of “but also abundantly presented”. Should include a reference to these compounds being abundantly present in aerosol from various sources.
Line 322 - 332: “During MGBA…” – this section reads as if you determined this, but is based on literature (which you have cited), so I think you mean the observations are consistent with these phenomena and studies?
Line 337: “PE-East demonstrated substantial regional influences (Fig 1c), where…” this language and presentation is awkward – pointing towards Fig 1c doesn’t demonstrate the regional influences, maybe the placement of the reference to the figure doesn’t make sense, maybe you mean to say that regional influences contributed to the PE_East organic aerosol chemical profile…
Line 343: unclear what you mean by “contrasting patterns”
Line 368: space needed between “Table S3” and “reveal”
Line 368-370: decreased and increased with respect to what? You mean the PE_north and PE_east relative to MGBA?
Figure S1: For ESI- the CHONS fractions appear to have a different colour scale than the rest (no light blue, and dark brown)
Table S3: Why is CHN split out for ESI+ but not ESI-? The O(N)/C in the table heading is confusing, could have a footnote.
Line 377: promote instead of promoted
Line 378: drive instead of drove
Line 386: “were mainly detected in the ESI+ mode with minor quantities, and only vanishing part of them can be found in the ESI- mode” suggest “negligible amounts”
Line 394: “Furthermore, this significant decrease in H/C was accompanied by a slight increase in OSc (except for CHON-), which was different from the synchronous rise in O/C, H/C, and OSc reported in secondary-process-dominated regions (Zhang et al., 2025).” – this is confusing and appear contradictory to me when you say “except for CHON”. Do you mean that the OSc is not “slight increase” but is “significantly increased” as you metnioend in the next sentence? Is the part that is different from the cited paper just that you see a decrease in H/C whereas they see an increase in H/C? You also see the increase in O/C and OSc. Also in this section in general when you talk about ‘increasing trend’ and increases you mean for polluted compared to MBGA?
Line 408: “CHOS+ molecules demonstrated notably high average DBE…” – not clear which profile (MGBA/PE_East/PE_North) you are talking about here.
Line 420: “Over 90% of CHOS- compounds….rising from …. and 2.74 ± 2.17”. You need to add ‘respectively here’ or make it clear the order of the profiles/periods. Does the over 90% of CHOS- stat apply for both PE profiles? In the next sentence, the increase in O/S >=4 increasing from 25% to 40%, does this stat apply for both PE profiles?
Line 425: could explain better how these sources/processes are linked to the properties of higher O/C, OSc, H/C, CHOS-
Line 445: explain CRAMs-like structure (what it is) and why this supports this paragraph.
Figure 5: label should not have clean and group 1 and group 2 but MGBA and PE_East and PE_North?
Line 477: include the roman numerals for each category in the text
Line 513: How does the underscore the strong temporal heterogeneity if this is an overall picture of each period?
Figure 8: Where is the CHONS for MBGA in the ESI+ (a) panel? For “% total compounds intensity” is this the same as total relative intensity? This would be more consistent with terminology you have been using.
Section 3.5, text beginning Line 615: Make it clear in the text if the percentages refer to the percentage of relative intensity to the total intensity, or by number of species. (I think it is the former).
Line 643: They are not really pollution “episodes”, that word gives the impression of more distinct events (also use of “episode” in Lines 646 and 647).
Line 749: “Our findings provide critical constraints for climate models, with profound implications for regional climate predictability and emission control strategies” – this may be overstated. How will this data be used to constrain climate models?
Figure 9: error bars? Also note that you use HNI here in the labels, but you also refer to these measurements as ECS (East China Sea, example Line 475). Could reduce the number of acronyms.
Table S7: reference to the range of each area is given in Table S3 – should be S6?
Table S8: “The fractions of volatility organic compounds”. Could have better table title. Also they are percentages not fractions.
Table S9: Missing information. References? Are these averages? Measured when and what area and what time of year?
Figure S2: Describe what the regions are in the figure caption. Ie. “The grey dotted boxes delineate the Van Krevelen classes as defined in Table S6”. Also in Table S6 and Figure S2 the caption has a typo Kervelen instead of Krevelen.
Figure S4: What is the additional value of S4
Figure S7: very tiny – can this be bigger?

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Citation: https://doi.org/10.5194/egusphere-2026-4499-RC2

Hao Li, Xiaofei Qin, Jian Xu, Qianqian Gao, Kai Bi, Zhaoze Deng, Jianguo Liu, Haitao Zheng, Xiaoyu Ren, Xiaofei Wang, Congrui Deng, and Kan Huang

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Measurement Report: Molecular Dynamics of Organic Aerosol in the Wintertime East China Sea Driven by East Asian Outflows H. Li et al. https://doi.org/10.6084/m9.figshare.33103328

Hao Li, Xiaofei Qin, Jian Xu, Qianqian Gao, Kai Bi, Zhaoze Deng, Jianguo Liu, Haitao Zheng, Xiaoyu Ren, Xiaofei Wang, Congrui Deng, and Kan Huang

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Short summary

Our results show that continental pollution and ocean emissions continuously mix, with chemical reactions producing new compounds. During polluted periods, nitrogen- and sulfur-containing molecules increased sharply. Notably, marine-derived signatures remained present even in winter, highlighting the ocean's persistent influence. This complexity affects how particles impact regional air quality, underscoring the need to consider both land and sea sources in environmental models.


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