Influence of oceanic ventilation and terrestrial transport on the atmospheric volatile chlorinated hydrocarbons over the Western Pacific

Liu, Shan-Shan; Ni, Jie; Song, Jin-Ming; Gao, Xu-Xu; He, Zhen; Yang, Gui-Peng

doi:https://doi.org/10.5194/egusphere-2025-251

Preprints

https://doi.org/10.5194/egusphere-2025-251

Preprints

24 Feb 2025

| 24 Feb 2025

Influence of oceanic ventilation and terrestrial transport on the atmospheric volatile chlorinated hydrocarbons over the Western Pacific

Shan-Shan Liu, Jie Ni, Jin-Ming Song, Xu-Xu Gao, Zhen He, and Gui-Peng Yang

Abstract. Volatile chlorinated hydrocarbons (VCHCs), key ozone-depleting substances and greenhouse gases, depend on oceanic emission and uptake for their atmospheric budget. However, data on VCHCs in the Western Pacific remain limited. This study investigated the distribution and sources of VCHCs (CHCl₃, C₂HCl₃, CCl₄, and CH₃CCl₃) in the Western Pacific during 2019–2020. Elevated seawater concentrations of CHCl₃ and C₂HCl₃ in the Kuroshio-Oyashio Extension (KOE) were driven by mesoscale eddies enhancing primary productivity, while CCl₄ and CH₃CCl₃ concentrations were mainly influenced by atmospheric inputs. Atmospheric concentrations of VCHCs decreased from coastal to open ocean areas, with terrestrial air masses from Eastern Asia contributing significantly. Additionally, atmospheric CHCl₃ and C₂HCl₃ concentrations were positively correlated with Chl-a in the KOE region. These findings suggested that both atmospheric transport from the continent and ocean emissions could influence CHCl₃ and C₂HCl₃ levels. However, analysis of sea-to-air fluxes and saturation anomalies showed that atmospheric transport primarily influenced atmospheric CHCl₃ and C₂HCl₃ concentrations. The estimated sea-to-air flux indicated that the Western Pacific acted as a source for CHCl₃ and C₂HCl₃ but a sink for CCl₄ and CH₃CCl₃, with the potential to absorb 17 ± 2 % of CCl₄ emissions from Eastern China, 7 ± 5 % from Eastern Asia, and 3 ± 1 % of global emissions. Additionally, this region accounted for 8 ± 4 % of the global oceanic absorption of CCl₄. These findings underscored the Western Pacific’s key role in regulating atmospheric CCl₄ concentrations and mitigating its accumulation in Eastern Asia, providing essential data for global VCHCs emission and uptake estimates.

Received: 23 Jan 2025 – Discussion started: 24 Feb 2025

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

Download & links

Preprint (PDF, 4649 KB)

Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
Preprint (4649 KB)

Supplement (2551 KB)

Download & links

The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Journal article(s) based on this preprint

06 Nov 2025

Influence of oceanic ventilation and terrestrial transport on the atmospheric volatile chlorinated hydrocarbons over the Western Pacific

Shan-Shan Liu, Jie Ni, Jin-Ming Song, Xu-Xu Gao, Zhen He, and Gui-Peng Yang

Atmos. Chem. Phys., 25, 14967–14986, https://doi.org/10.5194/acp-25-14967-2025,https://doi.org/10.5194/acp-25-14967-2025, 2025

Short summary

Shan-Shan Liu, Jie Ni, Jin-Ming Song, Xu-Xu Gao, Zhen He, and Gui-Peng Yang

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-251', Anonymous Referee #1, 05 Jul 2025

Ocean plays an important role on the biogeochemical cycle of volatile chlorinated hydrocarbons. However, due to scarce data, our understanding is limited about Western Pacific. Quantitative analysis of marine CCl4 emission or sink help us to narrow or even close the gap of CCl4, thus the topic of this paper is very important.
This manuscript presents an interesting data set of measurements of CHCl3, C2HCl3, CCl4 and CH3CCl3 from both atmosphere and sea water, and present sea-to-air fluxes in globally important region where in addition very little data has been published previously. The manuscript is well structured and generally appropriately written. However, there are a number of problems mainly connected to the data analysis and interpretation that should be addressed first.
First of all, the variation of atmospheric CCl4 is with 10% and the atmospheric concentration of CH3CCl3 and C2HCl3 in only several ppts, so that the quality of sample analysis is essential for this study. The authors presented precision for CCl4 as 4% and precision of C2HCl3 is 3% in the supplement material. Generally, the precision will be much worse if the concentration is smaller. In this study, the concentration of C2HCl3 is almost two orders of magnitude lower compared to CCl4 concentration. I doubt why the precision of C2HCl3 are even better than CCl4. Can the author provide more detailed information how these precisions were achieved?
For the second, the calibration method described in lines 199-204. How much the uncertainties introduced by the dilution? For VCHCs at ppt level, normally calibration scales are applied in calibration to minimize the inconsistent between standards. I also doubt the comparison between this study and AGAGE background is misleading due to the calibration method.
For the third, the variation of atmospheric CCl4 in this study is similar to its analysis precision. So the authors need to prove the changes of atmospheric CCl4 is not caused by the measurement uncertainties and be aware not to over-interpretation the concentration differences.
For the fourth, in section 3.1, the authors ascribe the elevated concentrations of VCHCs to the influence of polluted air mass from mainland or east China may not correct. From Fig 3 and Fig 4, the trajectories of air mass with high observed concentration are generally from Siberia and Northeast China, and then pass Japan. However, from the recent publications, these regions are not the major source of VCHCs and there is no report of fluorine/chlorine chemistry located in these regions. It should be noted most of the trajectories in figure 4 did not cover North China or East China mentioned in the references.
Last but not least, both two surveys conducted in autumn and winter. Concerning the seasonal variation of marine microalgae and seawater temperature, wind speed, the sea-to-air flux obtained by this study might be bias from yearly average.

Citation: https://doi.org/10.5194/egusphere-2025-251-RC1
- AC2: 'Reply on RC1', Gui-Peng Yang, 09 Sep 2025
  
  We sincerely appreciate the reviewer’s valuable comments and suggestions, which have greatly helped us improve the manuscript. Following the reviewer’s comments, we have revised the manuscript accordingly, with all changes highlighted in blue. For the reviewer’s convenience, a detailed point-by-point response is provided in the supplementary file “Reply to Referee 1. pdf”.
  
  Citation: https://doi.org/10.5194/egusphere-2025-251-AC2
RC2:
'Comment on egusphere-2025-251', Anonymous Referee #2, 06 Jul 2025
General comments
This paper reports results of two measuring campaigns of selected volatile chlorinated hydrocarbons in the Western Pacific. Air and surface water samples were simultaneously taken to estimate the equilibrium deviation and to calculate fluxes. This is a challenging project that generated a substantial amount of data. It is interesting research, but the manuscript needs some further improvement.
Two sampling campaigns were organised. One from October 31, 2019, to December 1, 2019, and the second from October 3, 2019, to January 5, 2020. Both campaigns roughly cover a 2 - 3 months period in the same season. Therefore, seasonal effects are not included and so, the validity of the results as yearly averages is not guaranteed. In this sense ln. 716-717 in the conclusions should be interpreted with reticence.
The area covered is about 4500 km S-N and 4000 km EW at the equator. It would be valuable adding information on the number of sampling locations (they are indicated in Fig. 1 but not always very clear) and the number of samples per location. The distribution of the concentrations is graphically presented in fig. 3. It would be good adding statistical data on the concentration distributions e.g. as box plots.
Data for Henry’s law constants are taken from Schwardt (2021). Temperature dependence equations are used to correct for the seawater temperature. Schwardt used the EPICS method to determine air/water partitioning using deionised water. It is known that H also depends on salinity. Date from the literature show a 30 % of H for tetrachloromethane when salinity increases from 0 to 35 ppt at 25°C. Reported salinity of the samples in the study is roughly 35 ppt (Fig. 12). So, is salinity considered, if not what would be the effect on the calculated fluxes by increasing H values with 30 %?
The analytical methods are described. However, some detailed but relevant information is not reported: argumentation on why using GC-Ms for air samples and GC_ECD for water samples; type of GC column used for air samples; number of data points on which calibration curves and RSBs are calculated. In Table S3 information about MDL is given. The definition of MDL as used here is not reported. Is it the instrumental MDL or the overall method (including, sampling, transportation, storage sample preparation) MDL. RSDs on MDL are all below 10 % even 3 %. So, this looks more like instrumental MDL. The difference is important because this affects results of equation 9 and so the calculated fluxes.
Detailed comments
p.3 ln 51. My suggestion is avoiding subjective phrasing “very short-lived” (less than six months). Compared with CCl4 this lifetime is short but not in absolute terms. As an example, isoprene about 1 h; aromatic hydrocarbons in the order of days.
55 “disproportionately” compared with what?

Ln. 100-102. Li et al. (2024) Is this statement general or specific for Eastern China? The concentration distribution in fig. 4 in that reference paper (comparing sectors) is highly skewed, with mean values highly influenced by a few large concentrations. I suggest drawing the readers attention to this point to avoid pointing too fast to some specific sectors.
Ln. 202 Please add the number of concentration levels for the calibration curves.
Ln. 207 S3. Please add the number of data to calculate RSD. Which definition of MDL was used and check layout of the table.
Ln. 209. Were seawater samples taken always at the same depth? If so, which? A bit confusing that in this line there is (0-5m).
Ln. 216 For water sample analysis a GC-ECD method is used while for air it is GC-MS. Any specific reasons? For the water sample analysis, the type of GC column is specified but not for air samples. Was the same Gc column used. If not, please add information on the Gc column used for air sample analysis.
Ln. 205-252. I assume that Henry’s constant is dimensionless. Please specify. Why using concentrations in pmol/L which is equal to nmol/m³? I prefer the latter because then it fits better with the equation where F is given as nmol.m^-2.d^-1.
Fig. 3. A large amount of information is presented in this figure. Maybe it would be good mentioning the different concentration scales and units. CCl₄ from 74-84 pptv: CH₃CCl₃ from 1.6-2.6 pptv. Because the same-coloured dot stands for quite different concentrations. Or even better to report boxplots for the concentration distributions e.g. as supplementary material.
Citation: https://doi.org/10.5194/egusphere-2025-251-RC2
- AC1: 'Reply on RC2', Gui-Peng Yang, 09 Sep 2025
  
  We sincerely appreciate the reviewer’s valuable comments and suggestions, which have greatly helped us improve the manuscript. Following the reviewer’s comments, we have revised the manuscript accordingly, with all changes highlighted in blue. For the reviewer’s convenience, a detailed point-by-point response is provided in the supplementary file “Reply to Referee 2. pdf”.
  
  Citation: https://doi.org/10.5194/egusphere-2025-251-AC1
AC3: 'Comment on egusphere-2025-251', Gui-Peng Yang, 09 Sep 2025

We sincerely thank the editor for giving us the opportunity to revise our manuscript and express our heartfelt gratitude to the editor and reviewers for their valuable and constructive comments. We have carefully revised the manuscript in response to these comments and made every effort to improve its quality. A detailed point-by-point response to the reviewers’ comments is attached for your kind consideration.

Citation: https://doi.org/10.5194/egusphere-2025-251-AC3

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-251', Anonymous Referee #1, 05 Jul 2025

Ocean plays an important role on the biogeochemical cycle of volatile chlorinated hydrocarbons. However, due to scarce data, our understanding is limited about Western Pacific. Quantitative analysis of marine CCl4 emission or sink help us to narrow or even close the gap of CCl4, thus the topic of this paper is very important.
This manuscript presents an interesting data set of measurements of CHCl3, C2HCl3, CCl4 and CH3CCl3 from both atmosphere and sea water, and present sea-to-air fluxes in globally important region where in addition very little data has been published previously. The manuscript is well structured and generally appropriately written. However, there are a number of problems mainly connected to the data analysis and interpretation that should be addressed first.
First of all, the variation of atmospheric CCl4 is with 10% and the atmospheric concentration of CH3CCl3 and C2HCl3 in only several ppts, so that the quality of sample analysis is essential for this study. The authors presented precision for CCl4 as 4% and precision of C2HCl3 is 3% in the supplement material. Generally, the precision will be much worse if the concentration is smaller. In this study, the concentration of C2HCl3 is almost two orders of magnitude lower compared to CCl4 concentration. I doubt why the precision of C2HCl3 are even better than CCl4. Can the author provide more detailed information how these precisions were achieved?
For the second, the calibration method described in lines 199-204. How much the uncertainties introduced by the dilution? For VCHCs at ppt level, normally calibration scales are applied in calibration to minimize the inconsistent between standards. I also doubt the comparison between this study and AGAGE background is misleading due to the calibration method.
For the third, the variation of atmospheric CCl4 in this study is similar to its analysis precision. So the authors need to prove the changes of atmospheric CCl4 is not caused by the measurement uncertainties and be aware not to over-interpretation the concentration differences.
For the fourth, in section 3.1, the authors ascribe the elevated concentrations of VCHCs to the influence of polluted air mass from mainland or east China may not correct. From Fig 3 and Fig 4, the trajectories of air mass with high observed concentration are generally from Siberia and Northeast China, and then pass Japan. However, from the recent publications, these regions are not the major source of VCHCs and there is no report of fluorine/chlorine chemistry located in these regions. It should be noted most of the trajectories in figure 4 did not cover North China or East China mentioned in the references.
Last but not least, both two surveys conducted in autumn and winter. Concerning the seasonal variation of marine microalgae and seawater temperature, wind speed, the sea-to-air flux obtained by this study might be bias from yearly average.

Citation: https://doi.org/10.5194/egusphere-2025-251-RC1
- AC2: 'Reply on RC1', Gui-Peng Yang, 09 Sep 2025
  
  We sincerely appreciate the reviewer’s valuable comments and suggestions, which have greatly helped us improve the manuscript. Following the reviewer’s comments, we have revised the manuscript accordingly, with all changes highlighted in blue. For the reviewer’s convenience, a detailed point-by-point response is provided in the supplementary file “Reply to Referee 1. pdf”.
  
  Citation: https://doi.org/10.5194/egusphere-2025-251-AC2
RC2:
'Comment on egusphere-2025-251', Anonymous Referee #2, 06 Jul 2025
General comments
This paper reports results of two measuring campaigns of selected volatile chlorinated hydrocarbons in the Western Pacific. Air and surface water samples were simultaneously taken to estimate the equilibrium deviation and to calculate fluxes. This is a challenging project that generated a substantial amount of data. It is interesting research, but the manuscript needs some further improvement.
Two sampling campaigns were organised. One from October 31, 2019, to December 1, 2019, and the second from October 3, 2019, to January 5, 2020. Both campaigns roughly cover a 2 - 3 months period in the same season. Therefore, seasonal effects are not included and so, the validity of the results as yearly averages is not guaranteed. In this sense ln. 716-717 in the conclusions should be interpreted with reticence.
The area covered is about 4500 km S-N and 4000 km EW at the equator. It would be valuable adding information on the number of sampling locations (they are indicated in Fig. 1 but not always very clear) and the number of samples per location. The distribution of the concentrations is graphically presented in fig. 3. It would be good adding statistical data on the concentration distributions e.g. as box plots.
Data for Henry’s law constants are taken from Schwardt (2021). Temperature dependence equations are used to correct for the seawater temperature. Schwardt used the EPICS method to determine air/water partitioning using deionised water. It is known that H also depends on salinity. Date from the literature show a 30 % of H for tetrachloromethane when salinity increases from 0 to 35 ppt at 25°C. Reported salinity of the samples in the study is roughly 35 ppt (Fig. 12). So, is salinity considered, if not what would be the effect on the calculated fluxes by increasing H values with 30 %?
The analytical methods are described. However, some detailed but relevant information is not reported: argumentation on why using GC-Ms for air samples and GC_ECD for water samples; type of GC column used for air samples; number of data points on which calibration curves and RSBs are calculated. In Table S3 information about MDL is given. The definition of MDL as used here is not reported. Is it the instrumental MDL or the overall method (including, sampling, transportation, storage sample preparation) MDL. RSDs on MDL are all below 10 % even 3 %. So, this looks more like instrumental MDL. The difference is important because this affects results of equation 9 and so the calculated fluxes.
Detailed comments
p.3 ln 51. My suggestion is avoiding subjective phrasing “very short-lived” (less than six months). Compared with CCl4 this lifetime is short but not in absolute terms. As an example, isoprene about 1 h; aromatic hydrocarbons in the order of days.
55 “disproportionately” compared with what?

Ln. 100-102. Li et al. (2024) Is this statement general or specific for Eastern China? The concentration distribution in fig. 4 in that reference paper (comparing sectors) is highly skewed, with mean values highly influenced by a few large concentrations. I suggest drawing the readers attention to this point to avoid pointing too fast to some specific sectors.
Ln. 202 Please add the number of concentration levels for the calibration curves.
Ln. 207 S3. Please add the number of data to calculate RSD. Which definition of MDL was used and check layout of the table.
Ln. 209. Were seawater samples taken always at the same depth? If so, which? A bit confusing that in this line there is (0-5m).
Ln. 216 For water sample analysis a GC-ECD method is used while for air it is GC-MS. Any specific reasons? For the water sample analysis, the type of GC column is specified but not for air samples. Was the same Gc column used. If not, please add information on the Gc column used for air sample analysis.
Ln. 205-252. I assume that Henry’s constant is dimensionless. Please specify. Why using concentrations in pmol/L which is equal to nmol/m³? I prefer the latter because then it fits better with the equation where F is given as nmol.m^-2.d^-1.
Fig. 3. A large amount of information is presented in this figure. Maybe it would be good mentioning the different concentration scales and units. CCl₄ from 74-84 pptv: CH₃CCl₃ from 1.6-2.6 pptv. Because the same-coloured dot stands for quite different concentrations. Or even better to report boxplots for the concentration distributions e.g. as supplementary material.
Citation: https://doi.org/10.5194/egusphere-2025-251-RC2
- AC1: 'Reply on RC2', Gui-Peng Yang, 09 Sep 2025
  
  We sincerely appreciate the reviewer’s valuable comments and suggestions, which have greatly helped us improve the manuscript. Following the reviewer’s comments, we have revised the manuscript accordingly, with all changes highlighted in blue. For the reviewer’s convenience, a detailed point-by-point response is provided in the supplementary file “Reply to Referee 2. pdf”.
  
  Citation: https://doi.org/10.5194/egusphere-2025-251-AC1
AC3: 'Comment on egusphere-2025-251', Gui-Peng Yang, 09 Sep 2025

We sincerely thank the editor for giving us the opportunity to revise our manuscript and express our heartfelt gratitude to the editor and reviewers for their valuable and constructive comments. We have carefully revised the manuscript in response to these comments and made every effort to improve its quality. A detailed point-by-point response to the reviewers’ comments is attached for your kind consideration.

Citation: https://doi.org/10.5194/egusphere-2025-251-AC3

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Gui-Peng Yang on behalf of the Authors (23 Sep 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (28 Sep 2025) by Tao Wang

AR by Gui-Peng Yang on behalf of the Authors (30 Sep 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (30 Sep 2025) by Tao Wang

AR by Gui-Peng Yang on behalf of the Authors (08 Oct 2025) Manuscript

Journal article(s) based on this preprint

06 Nov 2025

Influence of oceanic ventilation and terrestrial transport on the atmospheric volatile chlorinated hydrocarbons over the Western Pacific

Shan-Shan Liu, Jie Ni, Jin-Ming Song, Xu-Xu Gao, Zhen He, and Gui-Peng Yang

Atmos. Chem. Phys., 25, 14967–14986, https://doi.org/10.5194/acp-25-14967-2025,https://doi.org/10.5194/acp-25-14967-2025, 2025

Short summary

Shan-Shan Liu, Jie Ni, Jin-Ming Song, Xu-Xu Gao, Zhen He, and Gui-Peng Yang

Supplement

https://doi.org/10.5194/egusphere-2025-251-supplement

Shan-Shan Liu, Jie Ni, Jin-Ming Song, Xu-Xu Gao, Zhen He, and Gui-Peng Yang

Viewed

Total article views: 766 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	Supplement	BibTeX	EndNote
680	51	35	766	32	33	40

HTML: 680
PDF: 51
XML: 35
Total: 766
Supplement: 32
BibTeX: 33
EndNote: 40

Views and downloads (calculated since 24 Feb 2025)

Month	HTML	PDF	XML	Total
Feb 2025	51	5	3	59
Mar 2025	33	5	3	41
Apr 2025	31	3	2	36
May 2025	23	9	2	34
Jun 2025	26	3	1	30
Jul 2025	46	11	5	62
Aug 2025	77	2	0	79
Sep 2025	365	3	15	383
Oct 2025	27	9	4	40
Nov 2025	1	1	0	2

Cumulative views and downloads (calculated since 24 Feb 2025)

Month	HTML	PDF	XML	Total
Feb 2025	51	5	3	59
Mar 2025	33	5	3	41
Apr 2025	31	3	2	36
May 2025	23	9	2	34
Jun 2025	26	3	1	30
Jul 2025	46	11	5	62
Aug 2025	77	2	0	79
Sep 2025	365	3	15	383
Oct 2025	27	9	4	40
Nov 2025	1	1	0	2

Viewed (geographical distribution)

Total article views: 780 (including HTML, PDF, and XML) Thereof 780 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 06 Nov 2025

Download

The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Preprint (4649 KB)
Metadata XML

Short summary

Volatile chlorinated hydrocarbons (VCHCs) harm the ozone layer and climate, but the role of the Western Pacific in their atmospheric budget is unclear. This study showed ocean ventilation and terrestrial transport shape VCHCs levels. The Western Pacific emits some VCHCs while absorbing CCl₄, helping reduce its levels in Eastern Asia. These findings highlight the ocean’s key role in regulating atmospheric VCHCs and provide essential data to refine global estimates of VCHCs atmospheric budgets.


Total:	0
HTML:	0
PDF:	0
XML:	0