High-resolution observation of stable carbon isotope ratios of water-soluble organic carbon in particle/gas phases at an urban site in China: Using an improved isotope ratio mass spectrometry method

Yu, Hao-Ran; Zhang, Yan-Lin; Cao, Fang; Yang, Xiao-Ying; Xie, Tian; Zhang, Yu-Xian; Xue, Yongwen

doi:https://doi.org/10.5194/amt-2022-239

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https://doi.org/10.5194/amt-2022-239

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30 Sep 2022

| 30 Sep 2022

Status: this preprint has been withdrawn by the authors.

High-resolution observation of stable carbon isotope ratios of water-soluble organic carbon in particle/gas phases at an urban site in China: Using an improved isotope ratio mass spectrometry method

Hao-Ran Yu, Yan-Lin Zhang, Fang Cao, Xiao-Ying Yang, Tian Xie, Yu-Xian Zhang, and Yongwen Xue

Abstract. A high time resolution synchronous sampling method along with determination of stable carbon isotopes of gaseous water-soluble organic carbon (WSOCg) and particulate water-soluble organic carbon (WSOCp) was realized in this research through equipment modification and method improvement. It was found that WSOCg has significant higher concentration than WSOCp and a more depleted δ¹³C. Both concentrations of WSOCp and WSOCg have the seasonal variation characteristics of high in winter (WSOCp = 15.7 ± 3.9 μg/m³; WSOCg = 42.4 ± 6.0 μg/m³) and low in summer (WSOCp = 5.9 ± 1.8 μg/m³; WSOCg = 25.2 ± 5.2 μg/m³), with greater increase in WSOCp (167 %) than that in WSOCg (68 %). During wintertime, WSOCp and WSOCg had similar daily variation characteristics of concentration, and opposite daily variation characteristics of δ¹³C. WSOCp had a bimodal distribution with obvious low value at sunrise and sunset, while δ¹³C-WSOCp had a unimodal distribution with low in daytime (-24.6 ± 1.1 ‰) and high in nighttime (-22.3 ± 1.7 ‰). WSOCg and δ¹³C-WSOCg had same distribution with high in daytime and (49.3 ± 8.8 μg/m³; -27.9 ± 1.1 ‰) low in nighttime (38.3 ± 4.6 μg/m³; -29.9 ± 0.4 ‰). Combining the δ¹³C variation characteristics with the synchronous observation results of meteorological conditions, gaseous precursor pollutants, gaseous oxidants, gaseous acids and fine particle components, the restriction factors of WSOC gas-particle distribution mechanism were discussed. The presence of radiation rather than its intensity decided whether generations process of WSOCp and WSOCg are divided, for δ¹³C-WSOC of two phases showed significant correlation only during daytime. Meteorological conditions, gaseous precursor pollutants, gaseous oxidants and gaseous acids restrict the gas particle distribution of WSOC by affecting the aging process of WSOCp and WSOCg, gas-particle conversion ratio of semi-volatile organic compounds (SVOC) and the gas phase and liquid phase generation ratio of WSOCp. At the same time, the gas-particle distribution process of WSOC is strongly related to the formation of secondary inorganic ions (nitrate, sulfate, ammonium), and the gas-particle distribution between gaseous nitrous acid and nitrite.

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Hao-Ran Yu, Yan-Lin Zhang, Fang Cao, Xiao-Ying Yang, Tian Xie, Yu-Xian Zhang, and Yongwen Xue

Interactive discussion

Status: closed

RC1:
'Comment on amt-2022-239', Anonymous Referee #1, 31 Oct 2022

This study developed a new method and system to determine stable carbon isotope in both the water-soluble organic carbon in the gaseous and particle phases. The novelty of this study lies in the method and its potential application. They also found the difference in WSOC mass concentration and the isotope composition between the day and night samples. Although the explanation of the influencing factors for the differences remains unresolved, I strongly recommend it for a quick publication after they can address the following specific comments.

Specific comments:

Line 26-27: the sentence was not clear.

The authors should use the isotope expression more carefully. For examples: lower, higher, depleted or enriched. For example, to say that "one sample is enriched in 15N relative to another because of …" is proper usage. Phrases such as "a sample has an enriched d15N value" are misuses of terminology.

Line 38-40: rewording is necessary

Line 149: details are needed here,

Was the method for 13C in WSOC improved or optimized compared to the previous method. If so, the details should be given or highlighted.

The influences of the metrological condition and chemical composition should be reordered. the mechanism for the WSOCg-WSOCp distribution was not well explained and further discussion is needed.

Citation: https://doi.org/10.5194/amt-2022-239-RC1
- AC1:
  'Reply on RC1', Haoran Yu, 28 Nov 2022
  
  Thank you very much for your comments and advises on our paper! They have been encouraging and constructive. We have learnt quite a lot from it. After carefully studying the comments and advises, we have made corresponding changes to our paper. Details of the revisions are attached in pdf named "Reply on RC1". Please don't hesitate to contact us if you have other questions or advises!
  
  Citation: https://doi.org/10.5194/amt-2022-239-AC1
  - RC2: 'Reply on AC1', Anonymous Referee #1, 01 Dec 2022
    
    I'm satisfied with the modifications made by the authors. some problems and mistakes have been corretect. I would recommand the publication of this MS
    
    Citation: https://doi.org/10.5194/amt-2022-239-RC2
    
    AC2: 'Reply on RC2', Haoran Yu, 02 Dec 2022
    
    Once again, thank you very much for your kind work and consideration on our paper! On behalf of my co-authors, we would like to express our great appreciation to editor and reviewers. Thank you and best regards!
    
    Citation: https://doi.org/10.5194/amt-2022-239-AC2
RC3:
'Comment on amt-2022-239', Anonymous Referee #2, 08 Dec 2022

This paper presents ambient, simultaneous WSOC concentration measurements in gas- and particle phase, sampled in summer and winter in Nanjing, China. For winter, isotopic ratios for bulk WSOC in both phases are given. It aims to interpret concentration and d13C differences for the two phases. The use of carbon isotope ratios for the study of atmospheric pollution and the chemistry of organic compounds in the atmosphere is a newly emerging tool. Yet, there is hitherto relatively little information on isotopic signatures of sources and less understanding for the processes altering the pollutants from emission to sampling. Therefore, such data, as showed here, are valuable. Nevertheless, they have to be presented and interpreted in a proper way prior publishing.

General comments

1) One main criticism to this manuscript is related to the methodological part.

Section 3.1 promises to describe the ‘Improvement of determination method’. What was concretely improved compared to the existing methods?

Further, Fig 5b is redundant. It is showing that the slope of the line describing d13C measured by the method vs standard d13C is increasing when the blank becomes more important, which should be already clear from the mathematical point of view. Then, do the fitted lines to the measurements (described by logarithmic relations?) make any physical sense? Remove, give instead the relation for the sample d13C dependence on the blank (Eq. 1 in Fisseha et al 2006, or Eq1-7 in Zhang et al. 2019). Anyhow, one should take any of these two studies as an example for describing a method development (including tests of the standard samples recovery, quality control and quality assurance procedures...)

2) given that the paper announces method improvement to measure very low amounts of WSOC, I miss a discussion on systematic errors. Please elaborate and based on that, what is the statistical significance of the day/night isotopic variations (are they still ‘unimodal’, ‘bimodal’)?

3) Another concern is the way how the interpretation of these valuable ambient data is introduced. See for instance lines352-359:

‘Increase of O3 leaded to enrichment of d13C-WSOCp and dilution of d13C-WSOCg on an extremely significant level (p<0.01). Similar with NO2, neither WSOCp nor WSOCg had correlation with concentration of O3, which means none variation of emission intensity of WSOC source when d13C changed. It was believed that SVOC conversed more to WSOCp under high concentration of O3, leading to of dilution of d13C-WSOCg. The aging of WSOCp was promoted at the same time, leading to enrichment of d13C-WSOCp. Dilution of d13C-WSOCg caused by conversion from SVOC to WSOCp exceeded enrichment of d13C-WSOCg caused by aging of WSOCg, leading to a more dilute d13C-WSOCg, indicating that O3 tends to react with SVOC rather than WSOCg’

Disregarding the extremely non-scientific used language, which makes very difficult for the reader to follow the text, the authors postulate in the beginning of this paragraph (and similarly throughout the whole discussion section) a causality which might be true or not. They combine, in this case, O3 with WSOC data. They observe a trend, here, increasing of O3 and WSOCp d13C and decreasing of WSOCg d13C. Their interpretation is: the increase in ozone leads to an increase in d13C in particles and decrease in gas-phase. Not always, when other processes causing opposite trends would act stronger. In the next lines, different hypotheses are eventually given, potential chemical and physical WSOC processes are described together with their impact on the isotopic ratios, which is mostly well done.

My recommendation: reorganize completely the discussion part 3.3 (lines259-430) and partially the conclusions part 4 (lines444-455) as following: (i) first describe the data trends, avoid at this point any conclusions. (ii)Further discuss the prevailing processes, mention potential changes in d13C due to these processes. (iii) Finally conclude using ‘this might explain the observed trend’.

4) To ease the overall understanding:

- a discussion in the introduction is mandatory, emphasizing the potential but also the limitations when using isotopic information. based on literature, mention all atmospheric processes impacting the WSOC isotopic ratios and indicate the linked variations in d13C depending on the ambient conditions. The studies of Kawamura’s group are very useful for that goal.

Generally, reorganize the whole introduction. It is understandable that it contains a lot of information, but make it more systematic (separate the sources, mixing from physical and chemical processing)

- throughout the paper: descriptions such as 'conversion', 'transformation'.... should be replaced by specific terms used in the atmospheric research: volatilization, condensation, partitioning between gas- and particle phase...

5) the graphical abstract gives the impression that the 5.9 per mil difference between the isotopic ratios of gas and particle phase is due solely to 'circulation' (is here ‘atmospheric transport’ meant?). The authors should change the picture to make clear that ALL processes mentioned in lines298-310 contribute (even at different degrees) to the observed fractionation.

6) throughout the manuscript and in the graphical abstract:

d13C is a number which can only be big or small. Depletion (not ‘dilution’) and enrichment are used together with an isotope (12C or 13C) to describe a change, e.g. in the course of a chemical reaction, the reactant becomes more and more enriched in 13C.

Revise that everywhere!

Specific comments:

1) The literature research for this manuscript is not satisfactory, should be thoroughly redone.

- lines107-111

‘The main scavenging pathway of VOCs is its reaction with OH radical and ozone, and these atmospheric oxidants tend to react with VOCs depleted d13C (reverse dynamic isotope effect), resulting in the d13C enrichment of residual VOCs in the atmosphere and d13C dilution of particles as oxidation products (Anderson, et al., 2004; Rudolph, et al., 2003; Rudolph, et al., 2000).’

The mentioned citations deal exclusively with gas-phase reactions! For compound specific isotope ratios in particles, check for instance the publications by Irei et al.

What is the ‘reverse dynamic isotope effect’? Remove that idiom throughout the manuscript.

- cite preferably the original publications

- line 301: replace Gensch et al. 2014 by Fisseha et al. 2009

- you might still use Gensch et al. in the introduction, since it gives valuable information on principles, potential and limitation of the isotopic research.

- remove Cao et al. throughout the manuscript and look for the original information (in Fig 4 by Cao, isotopic ratio ranges for C4 and C3 plants are presented the other way round. In the lines above, while the study by Martinelli et al. is suitable to cite, Moura et al. investigates the plant material isotopic ratios in sediments. There are a lot more appropriate studies on the isotopic ratio of plant material and emission related to that.)

2) Linear regression analyses can be done when a linear relationship between two variables is expected (based on physics laws)

- lines275-286 and figure 5. Due to the complexity of the prevailing processes. in none of these cases a linear regression analysis makes sense, neither the ‘derived r2’.

3) remove equation F1 (line 322)

This makes sense only in a compound specific study, where single SVOCs are measured.

Other comments:

- please elaborate the source for the numbers in Table 1

- line205: ‘However, determination values have obvious peak area independence in this range of carbon content (Fig. 3a).’

On the contrary, Fig 3a shows that there is a d13C dependence, which was already shown 2006 by Fisseha et al. Revise!

Editorial revisions:

At this point, there are no specific revisions. First, the whole paper should be thoroughly revised by an English native speaker.

Citation: https://doi.org/10.5194/amt-2022-239-RC3
- AC3: 'Reply on RC3', Haoran Yu, 10 Jan 2023
  
  Thank you very much for your comments and advises! They have effectively helped us improve our manuscript. After carefully studying the comments and advises, we have made corresponding changes to our paper. Details of the revisions are attached in pdf named "Reply on RC3". Please don't hesitate to contact us if you have other questions or advises!
  
  Citation: https://doi.org/10.5194/amt-2022-239-AC3

Interactive discussion

Status: closed

RC1:
'Comment on amt-2022-239', Anonymous Referee #1, 31 Oct 2022

This study developed a new method and system to determine stable carbon isotope in both the water-soluble organic carbon in the gaseous and particle phases. The novelty of this study lies in the method and its potential application. They also found the difference in WSOC mass concentration and the isotope composition between the day and night samples. Although the explanation of the influencing factors for the differences remains unresolved, I strongly recommend it for a quick publication after they can address the following specific comments.

Specific comments:

Line 26-27: the sentence was not clear.

The authors should use the isotope expression more carefully. For examples: lower, higher, depleted or enriched. For example, to say that "one sample is enriched in 15N relative to another because of …" is proper usage. Phrases such as "a sample has an enriched d15N value" are misuses of terminology.

Line 38-40: rewording is necessary

Line 149: details are needed here,

Was the method for 13C in WSOC improved or optimized compared to the previous method. If so, the details should be given or highlighted.

The influences of the metrological condition and chemical composition should be reordered. the mechanism for the WSOCg-WSOCp distribution was not well explained and further discussion is needed.

Citation: https://doi.org/10.5194/amt-2022-239-RC1
- AC1:
  'Reply on RC1', Haoran Yu, 28 Nov 2022
  
  Thank you very much for your comments and advises on our paper! They have been encouraging and constructive. We have learnt quite a lot from it. After carefully studying the comments and advises, we have made corresponding changes to our paper. Details of the revisions are attached in pdf named "Reply on RC1". Please don't hesitate to contact us if you have other questions or advises!
  
  Citation: https://doi.org/10.5194/amt-2022-239-AC1
  - RC2: 'Reply on AC1', Anonymous Referee #1, 01 Dec 2022
    
    I'm satisfied with the modifications made by the authors. some problems and mistakes have been corretect. I would recommand the publication of this MS
    
    Citation: https://doi.org/10.5194/amt-2022-239-RC2
    
    AC2: 'Reply on RC2', Haoran Yu, 02 Dec 2022
    
    Once again, thank you very much for your kind work and consideration on our paper! On behalf of my co-authors, we would like to express our great appreciation to editor and reviewers. Thank you and best regards!
    
    Citation: https://doi.org/10.5194/amt-2022-239-AC2
RC3:
'Comment on amt-2022-239', Anonymous Referee #2, 08 Dec 2022

This paper presents ambient, simultaneous WSOC concentration measurements in gas- and particle phase, sampled in summer and winter in Nanjing, China. For winter, isotopic ratios for bulk WSOC in both phases are given. It aims to interpret concentration and d13C differences for the two phases. The use of carbon isotope ratios for the study of atmospheric pollution and the chemistry of organic compounds in the atmosphere is a newly emerging tool. Yet, there is hitherto relatively little information on isotopic signatures of sources and less understanding for the processes altering the pollutants from emission to sampling. Therefore, such data, as showed here, are valuable. Nevertheless, they have to be presented and interpreted in a proper way prior publishing.

General comments

1) One main criticism to this manuscript is related to the methodological part.

Section 3.1 promises to describe the ‘Improvement of determination method’. What was concretely improved compared to the existing methods?

Further, Fig 5b is redundant. It is showing that the slope of the line describing d13C measured by the method vs standard d13C is increasing when the blank becomes more important, which should be already clear from the mathematical point of view. Then, do the fitted lines to the measurements (described by logarithmic relations?) make any physical sense? Remove, give instead the relation for the sample d13C dependence on the blank (Eq. 1 in Fisseha et al 2006, or Eq1-7 in Zhang et al. 2019). Anyhow, one should take any of these two studies as an example for describing a method development (including tests of the standard samples recovery, quality control and quality assurance procedures...)

2) given that the paper announces method improvement to measure very low amounts of WSOC, I miss a discussion on systematic errors. Please elaborate and based on that, what is the statistical significance of the day/night isotopic variations (are they still ‘unimodal’, ‘bimodal’)?

3) Another concern is the way how the interpretation of these valuable ambient data is introduced. See for instance lines352-359:

‘Increase of O3 leaded to enrichment of d13C-WSOCp and dilution of d13C-WSOCg on an extremely significant level (p<0.01). Similar with NO2, neither WSOCp nor WSOCg had correlation with concentration of O3, which means none variation of emission intensity of WSOC source when d13C changed. It was believed that SVOC conversed more to WSOCp under high concentration of O3, leading to of dilution of d13C-WSOCg. The aging of WSOCp was promoted at the same time, leading to enrichment of d13C-WSOCp. Dilution of d13C-WSOCg caused by conversion from SVOC to WSOCp exceeded enrichment of d13C-WSOCg caused by aging of WSOCg, leading to a more dilute d13C-WSOCg, indicating that O3 tends to react with SVOC rather than WSOCg’

Disregarding the extremely non-scientific used language, which makes very difficult for the reader to follow the text, the authors postulate in the beginning of this paragraph (and similarly throughout the whole discussion section) a causality which might be true or not. They combine, in this case, O3 with WSOC data. They observe a trend, here, increasing of O3 and WSOCp d13C and decreasing of WSOCg d13C. Their interpretation is: the increase in ozone leads to an increase in d13C in particles and decrease in gas-phase. Not always, when other processes causing opposite trends would act stronger. In the next lines, different hypotheses are eventually given, potential chemical and physical WSOC processes are described together with their impact on the isotopic ratios, which is mostly well done.

My recommendation: reorganize completely the discussion part 3.3 (lines259-430) and partially the conclusions part 4 (lines444-455) as following: (i) first describe the data trends, avoid at this point any conclusions. (ii)Further discuss the prevailing processes, mention potential changes in d13C due to these processes. (iii) Finally conclude using ‘this might explain the observed trend’.

4) To ease the overall understanding:

- a discussion in the introduction is mandatory, emphasizing the potential but also the limitations when using isotopic information. based on literature, mention all atmospheric processes impacting the WSOC isotopic ratios and indicate the linked variations in d13C depending on the ambient conditions. The studies of Kawamura’s group are very useful for that goal.

Generally, reorganize the whole introduction. It is understandable that it contains a lot of information, but make it more systematic (separate the sources, mixing from physical and chemical processing)

- throughout the paper: descriptions such as 'conversion', 'transformation'.... should be replaced by specific terms used in the atmospheric research: volatilization, condensation, partitioning between gas- and particle phase...

5) the graphical abstract gives the impression that the 5.9 per mil difference between the isotopic ratios of gas and particle phase is due solely to 'circulation' (is here ‘atmospheric transport’ meant?). The authors should change the picture to make clear that ALL processes mentioned in lines298-310 contribute (even at different degrees) to the observed fractionation.

6) throughout the manuscript and in the graphical abstract:

d13C is a number which can only be big or small. Depletion (not ‘dilution’) and enrichment are used together with an isotope (12C or 13C) to describe a change, e.g. in the course of a chemical reaction, the reactant becomes more and more enriched in 13C.

Revise that everywhere!

Specific comments:

1) The literature research for this manuscript is not satisfactory, should be thoroughly redone.

- lines107-111

‘The main scavenging pathway of VOCs is its reaction with OH radical and ozone, and these atmospheric oxidants tend to react with VOCs depleted d13C (reverse dynamic isotope effect), resulting in the d13C enrichment of residual VOCs in the atmosphere and d13C dilution of particles as oxidation products (Anderson, et al., 2004; Rudolph, et al., 2003; Rudolph, et al., 2000).’

The mentioned citations deal exclusively with gas-phase reactions! For compound specific isotope ratios in particles, check for instance the publications by Irei et al.

What is the ‘reverse dynamic isotope effect’? Remove that idiom throughout the manuscript.

- cite preferably the original publications

- line 301: replace Gensch et al. 2014 by Fisseha et al. 2009

- you might still use Gensch et al. in the introduction, since it gives valuable information on principles, potential and limitation of the isotopic research.

- remove Cao et al. throughout the manuscript and look for the original information (in Fig 4 by Cao, isotopic ratio ranges for C4 and C3 plants are presented the other way round. In the lines above, while the study by Martinelli et al. is suitable to cite, Moura et al. investigates the plant material isotopic ratios in sediments. There are a lot more appropriate studies on the isotopic ratio of plant material and emission related to that.)

2) Linear regression analyses can be done when a linear relationship between two variables is expected (based on physics laws)

- lines275-286 and figure 5. Due to the complexity of the prevailing processes. in none of these cases a linear regression analysis makes sense, neither the ‘derived r2’.

3) remove equation F1 (line 322)

This makes sense only in a compound specific study, where single SVOCs are measured.

Other comments:

- please elaborate the source for the numbers in Table 1

- line205: ‘However, determination values have obvious peak area independence in this range of carbon content (Fig. 3a).’

On the contrary, Fig 3a shows that there is a d13C dependence, which was already shown 2006 by Fisseha et al. Revise!

Editorial revisions:

At this point, there are no specific revisions. First, the whole paper should be thoroughly revised by an English native speaker.

Citation: https://doi.org/10.5194/amt-2022-239-RC3
- AC3: 'Reply on RC3', Haoran Yu, 10 Jan 2023
  
  Thank you very much for your comments and advises! They have effectively helped us improve our manuscript. After carefully studying the comments and advises, we have made corresponding changes to our paper. Details of the revisions are attached in pdf named "Reply on RC3". Please don't hesitate to contact us if you have other questions or advises!
  
  Citation: https://doi.org/10.5194/amt-2022-239-AC3

Hao-Ran Yu, Yan-Lin Zhang, Fang Cao, Xiao-Ying Yang, Tian Xie, Yu-Xian Zhang, and Yongwen Xue

Supplement

https://doi.org/10.5194/amt-2022-239-supplement

Hao-Ran Yu, Yan-Lin Zhang, Fang Cao, Xiao-Ying Yang, Tian Xie, Yu-Xian Zhang, and Yongwen Xue

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Short summary

We developed a high time resolution method for determining the δ¹³C values of WSOCp and WSOCg by combination of wet oxidation pretreatment and IRMS. With improvement of oxidation method and determination method, δ¹³C value of liquid sample with a carbon content between 0.5 to 5 μg can be determined with an accuracy of 0.6 ‰. Using this method, the δ¹³C value of WSOCp and WSOCg in winter of 2021 at an urban site of Nanjing were determined, which were -25.9 ± 0.7 ‰ and -29.9 ± 0.9 ‰ respectively.


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