the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Aug 2023
Chamber studies of OH + dimethyl sulfoxide and dimethyl disulfide: insights into the dimethyl sulfide oxidation mechanism
Abstract. The oxidation of dimethyl sulfide (DMS) in the marine atmosphere represents an important natural source of non-sea-salt sulfate aerosol, but the chemical mechanisms underlying this process remain uncertain. While recent studies have focused on the role of the peroxy-radical isomerization channel in DMS oxidation, this work revisits the impact of the other channels (OH addition, OH abstraction followed by bimolecular RO2 reaction) on aerosol formation from DMS. Due to the presence of common intermediate species, the oxidation of dimethyl sulfoxide (DMSO) and dimethyl disulfide (DMDS) can shed light on these two DMS reaction channels; they are also both atmospherically relevant species in their own right. This work examines the OH-oxidation of DMSO and DMDS, using chamber experiments monitored by chemical ionization mass spectrometry and aerosol mass spectrometry to study the full-range of sulfur-containing products under low- and high-NO conditions. The oxidation of both compounds is found to lead to rapid aerosol formation (which does not involve the intermediate formation of SO2), with a substantial fraction (14–47 % S yield for DMSO, and 5–21 % for DMDS) of reacted sulfur ending up in the particle phase, and the highest yields observed under elevated NO conditions. Aerosol is observed to consist mainly of sulfate, methanesulfonic acid, and methanesulfinic acid. In the gas phase, the NOX dependence of several products, including SO2 and S2-containing organosulfur species, suggest reaction pathways not included in current mechanisms. Based on the commonalities with the DMS oxidation mechanism, DMSO and DMDS results are used to reconstruct DMS aerosol yields; these reconstructions roughly match DMS aerosol yield measurements from the literature but differ in composition, underscoring remaining uncertainties in sulfur chemistry. This work indicates that both the abstraction and addition channels contribute substantially to rapid aerosol formation from DMS, and highlights the need for more study into the fate of small sulfur radical intermediates (e.g., CH3S, CH3SO2, CH3SO3) that play central roles in the DMS oxidation mechanism.
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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.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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Supplement
(4413 KB) - BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-1912', Anonymous Referee #1, 27 Sep 2023
This is a nice manuscript detailing a series of experiments meant to probe the molecular pathways contributing to aerosol formation from DMDS and DMSO. The authors present a detailed discussion of the results, their relation to previous published results and the implications of the agreements or lack thereof. I support the publication of this manuscript but think that the author could do a little bit to add some context to ambient conditions in the discussion section to place their results in perspective. Very well written and clear. Timely results in this resurgence of marine sulfur interest.
One thing that is apparent throughout this manuscript and in previous studies of sulfur oxidation is the role of water in the product yields and distributions, particularly aerosol. This study, performed in dry conditions (< 5% relative humidity), while expertly done, seems to have limited application to the true atmospheric environment where these oxidation schemes are likely to occur in regions where aqueous aerosols are present, e.g., MBL, higher wind speeds that drive DMS emissions & sea spray. It would be good if the authors would try to put their results in context with respect to how we can think about the result in the marine environment. Where may these results apply relative to other chamber experiments that utilized conditions > 5% relative humidity.
Does temperature play a role in the product distributions as it does with DMS oxidation, OH addition versus abstraction? Similar to the ambient water question how may this impact the application of these result to an explicit chemical mechanism in ambient conditions? Perhaps additional discussion on the impact of experimental conditions, e.g. temperature.
Page 10, line ~235: Does experiment order matter here? Is there residual NOx in the chamber that could be impacting product distributions such as those seen on replicate runs. Also how does the NOX in the replicate HONO runs compare? Could NOx dependencies explain the changes between the replicate (red) HONO runs?
Page 10, line 252: Maybe give the range of NOx concentrations used and how it compares to this study. Lower (high) NOX here versus previous studies?
Page 14, line 344: It seems a bit selective to label MSIA differently between the DMSO and DMDS experiments. If you cannot tell the difference between MSIA and other two sulfur containing peaks you must make that blanket statement for all MSIA determined from the AMS spectra. AMS MSIA in all experiments should therefore be labeled as MSIA*.
S.1.3 What are the NOx and SO2 monitors used in this experiment? Considering the low NOx condition what are the detection limits of the two instruments?
Citation: https://doi.org/10.5194/egusphere-2023-1912-RC1 -
RC2: 'Comment on egusphere-2023-1912', Anonymous Referee #2, 13 Oct 2023
Publisher’s note: this comment was edited on 16 October 2023. The following text is not identical to the original comment, but the adjustments were minor without effect on the scientific meaning.
This study focuses on the oxidation of DMSO and DMDS, two sulfur compounds directly emitted in the atmosphere but also formed during the oxidation of DMS. The experimental work was performed in an atmospheric simulation chamber for different levels of NOx in dry conditions. The oxidation was performed by OH radicals. One of the goals of the experiments was the investigation of the aerosol formation for different conditions. The identification of different products via NH4-CIMS was also used to validate the expected chemical mechanisms.
The manuscript is well written, and with a good structure and the figures are clear and useful. Though, I find the message for the gas-phase a little bit weak. For the DMSO oxidation the finding from this study is not in agreement with the currently used mechanisms. In the paper 3 alternative mechanisms are suggested though for neither rate coefficients are given so that it is not possible to test them. I would recommend to provide rate coefficients (even just best estimates from SAR could help) and even the most likely paths so that those could be tested on other experiments maybe helping in finding the correct mechanism.
During the oxidation of DMSO ozone was also introduced and it was mentioned that it did not change the product distribution. Why was ozone injected? Was there any expectation that the product distribution would change?
Once these two comments are considered I think the manuscript is ready for publication.
Citation: https://doi.org/10.5194/egusphere-2023-1912-RC2 - AC1: 'Comment on egusphere-2023-1912', Matthew B. Goss, 17 Nov 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-1912', Anonymous Referee #1, 27 Sep 2023
This is a nice manuscript detailing a series of experiments meant to probe the molecular pathways contributing to aerosol formation from DMDS and DMSO. The authors present a detailed discussion of the results, their relation to previous published results and the implications of the agreements or lack thereof. I support the publication of this manuscript but think that the author could do a little bit to add some context to ambient conditions in the discussion section to place their results in perspective. Very well written and clear. Timely results in this resurgence of marine sulfur interest.
One thing that is apparent throughout this manuscript and in previous studies of sulfur oxidation is the role of water in the product yields and distributions, particularly aerosol. This study, performed in dry conditions (< 5% relative humidity), while expertly done, seems to have limited application to the true atmospheric environment where these oxidation schemes are likely to occur in regions where aqueous aerosols are present, e.g., MBL, higher wind speeds that drive DMS emissions & sea spray. It would be good if the authors would try to put their results in context with respect to how we can think about the result in the marine environment. Where may these results apply relative to other chamber experiments that utilized conditions > 5% relative humidity.
Does temperature play a role in the product distributions as it does with DMS oxidation, OH addition versus abstraction? Similar to the ambient water question how may this impact the application of these result to an explicit chemical mechanism in ambient conditions? Perhaps additional discussion on the impact of experimental conditions, e.g. temperature.
Page 10, line ~235: Does experiment order matter here? Is there residual NOx in the chamber that could be impacting product distributions such as those seen on replicate runs. Also how does the NOX in the replicate HONO runs compare? Could NOx dependencies explain the changes between the replicate (red) HONO runs?
Page 10, line 252: Maybe give the range of NOx concentrations used and how it compares to this study. Lower (high) NOX here versus previous studies?
Page 14, line 344: It seems a bit selective to label MSIA differently between the DMSO and DMDS experiments. If you cannot tell the difference between MSIA and other two sulfur containing peaks you must make that blanket statement for all MSIA determined from the AMS spectra. AMS MSIA in all experiments should therefore be labeled as MSIA*.
S.1.3 What are the NOx and SO2 monitors used in this experiment? Considering the low NOx condition what are the detection limits of the two instruments?
Citation: https://doi.org/10.5194/egusphere-2023-1912-RC1 -
RC2: 'Comment on egusphere-2023-1912', Anonymous Referee #2, 13 Oct 2023
Publisher’s note: this comment was edited on 16 October 2023. The following text is not identical to the original comment, but the adjustments were minor without effect on the scientific meaning.
This study focuses on the oxidation of DMSO and DMDS, two sulfur compounds directly emitted in the atmosphere but also formed during the oxidation of DMS. The experimental work was performed in an atmospheric simulation chamber for different levels of NOx in dry conditions. The oxidation was performed by OH radicals. One of the goals of the experiments was the investigation of the aerosol formation for different conditions. The identification of different products via NH4-CIMS was also used to validate the expected chemical mechanisms.
The manuscript is well written, and with a good structure and the figures are clear and useful. Though, I find the message for the gas-phase a little bit weak. For the DMSO oxidation the finding from this study is not in agreement with the currently used mechanisms. In the paper 3 alternative mechanisms are suggested though for neither rate coefficients are given so that it is not possible to test them. I would recommend to provide rate coefficients (even just best estimates from SAR could help) and even the most likely paths so that those could be tested on other experiments maybe helping in finding the correct mechanism.
During the oxidation of DMSO ozone was also introduced and it was mentioned that it did not change the product distribution. Why was ozone injected? Was there any expectation that the product distribution would change?
Once these two comments are considered I think the manuscript is ready for publication.
Citation: https://doi.org/10.5194/egusphere-2023-1912-RC2 - AC1: 'Comment on egusphere-2023-1912', Matthew B. Goss, 17 Nov 2023
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Supplement
(4413 KB) - BibTeX
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- Final revised paper