the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Mar 2025
Reaction between perfluoroaldehydes and hydroperoxy radical in the atmosphere: Reaction mechanisms, reaction kinetics modelling, and atmospheric implications
Abstract. Linear perfluoroaldehydes are important products formed in the atmospheric oxidation of industrial fluorinated compounds. However, their atmospheric lifetimes are incompletely known. Here, we employ high level quantum chemistry methods and a dual-level strategy for kinetics to probe the reactions of C2F5CHO and C3F7CHO with HO2. Our calculated results unveil almost equal activation enthalpies at 0 K for perfluoroaldehyde reaction with HO2, indicating that the carbon chain length minimally influences reaction thermodynamics. Interestingly, the present findings reveal that anharmonicity remarkably enhances the reaction rate constant, whereas multi-structural anharmonicity, recrossing, and tunnelling effects exhibit lesser impacts in the C2F5CHO/C3F7CHO + HO2 reaction. In particular, the atmospheric lifetimes for C2F5CHO and C3F7CHO, approximately 14.4–31.3 hours and 21.6–51.8 hours by HO2 are much shorter than those via OH radical, underscoring the dominant removal role of HO2 toward C2F5CHO and C3F7CHO in the atmosphere. Since GEOS-Chem simulation shows that the concentration of HO2 is at least 102 times higher than that of OH radical in Russia, Malaysia, and parts of Africa, the reactions of C2F5CHO and C3F7CHO with HO2 radicals dominate over those with OH radicals and play more vital role in the atmospheric chemical processes of these regions. This study enhances our understanding of the chemical transformations of linear perfluoroaldehydes and provides a scientific foundation for strategies aimed at mitigating their emissions.
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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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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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Journal article(s) based on this preprint
Interactive discussion
Status: closed
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CC1: 'Comment on egusphere-2024-4179', Rabu Changmai, 18 Mar 2025
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AC3: 'Reply on CC1', Bo Long, 30 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4179/egusphere-2024-4179-AC3-supplement.pdf
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AC3: 'Reply on CC1', Bo Long, 30 May 2025
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RC1: 'Comment on egusphere-2024-4179', Anonymous Referee #1, 22 Mar 2025
This study provides valuable insights into the atmospheric degradation pathways of linear perfluoroaldehydes (PFAs) via reactions with HO₂ radicals. The combination of high-level quantum chemical calculations, kinetic modeling, and atmospheric simulations offers a comprehensive understanding of the roles of HO₂ in modulating PFAs’ lifetimes. The work is timely and addresses a critical gap in the atmospheric chemistry of PFASs. The conclusions are well-supported by the data, and the manuscript is well-organized. However, several clarifications and minor revisions are required to enhance clarity, strengthen methodological justification, and improve readability. I recommend acceptance after minor revisions.
Specific Comments
1. Abstract
(a) The statement “the atmospheric lifetimes for C2F5CHO and C3F7CHO, approximately 14.4-31.3 hours and 21.6-51.8 hours by HO2 are much shorter than those via OH radical,” it is not validated. (lines 15-16)
2. Introduction
(a) Alternating use of "perfluoroaldehydes" (in tittle) and "linear perfluoroaldehydes" may confuse readers.
(b) The transition from PFAS’s GWP to perfluoroaldehyde sources (lines 25-30) is unclear.
(c) The literature review focuses solely on OH and Cl radicals, omitting potential roles of other oxidants (e.g., O₃, NO₃). (lines 35-49)
(d) The long sentence "Moreover, the rate constant of Cl atoms with CnF2n+1CHO (1,2, 3, 4) is around 2 × 10-12 cm3 molecule-1s-1, which is slightly faster than that of the OH radical reactions." (lines 46-47) has poor readability and unclear notes.
3.Computational Methods
(a) In section 2.1, the “CCSD(T)-F12a/cc-pVTZ-F12” method is mentioned, but the text fails to demonstrating its applicability to perfluorinated compound systems. (lines 75-78)
4. Results and Discussion
(a) Figure 1 contains no relevant information. “The result shows that the specific reaction scale factors are 0.955 for TS1 (See Figure 1) and 0.956 for TS2 (See Figure 1)”. (lines 95-96)
(b) Grammatical error in “The torsion of the C-C bond gives produces multiple conformers”. (lines 152-153)
(c) Figure 3’s X-axis label (“Number of alkyl functional groups”) is misleading, as the compounds are perfluorinated. (lines 180-185)
(c) The calculated high-pressure limit rate constants (e.g., k1=5.42×10−14-3.35×10 −12 cm³ molecule⁻¹ s⁻¹) lack comparison with experimental data or analogous systems (e.g., non-fluorinated aldehydes + HO₂), reducing confidence in the results. (lines 204-207)
(e) There is inconsistency in the units used for atmospheric lifetimes. Table 2 reports lifetimes in seconds, while the discussion section uses hours. The authors should standardize the units throughout the manuscript to avoid confusion. (lines 250-255)
5. Atmospheric Implications
(a) The GEOS-Chem simulation results (Lines 273–287) focus on HO₂/OH ratios but do not discuss diurnal variation, which could affect the dominance of HO₂ pathways.
(b) The prospect for future research is somewhat brief and doesn’t adequately take into account the current study’s limitations and possible areas for expansion. (lines 321-325)
6. References
(a) Some of the cited references are incomplete or incorrect.
Lee, B. H., Munger, J. W., Wofsy, S. C., Rizzo, L. V., Yoon, J. Y. S., Turner, A. J., Thornton, J. A., and Swann, A. L. S.: Sensitive Response of Atmospheric Oxidative Capacity to the Uncertainty in the Emissions of Nitric Oxide (NO) From Soils 450 in Amazonia, Geophysical Research Letters, 51, 1-10, https://doi.org/10.1029/2023GL107214, 2024. (lines 448-450)
Long, B., Bao, J. L., and Truhlar, D. G.: Rapid unimolecular reaction of stabilized Criegee intermediates and implications for atmospheric chemistry, Nature Communications, 10, 1–8, https://doi.org/10.1038/s41467-019-09948-7, 2019. (lines 473-474)
Xia, D., Zhang, H., Ju, Y., Xie, H., Su, L., Ma, F., Jiang, J., Chen, J., and Francisco, J. S.: Spontaneous Degradation of the “Forever Chemicals” Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs) on Water Droplet Surfaces, https://doi.org/10.1021/jacs.4c00435, 2024. (lines 548-550)
Citation: https://doi.org/10.5194/egusphere-2024-4179-RC1 -
AC2: 'Reply on RC1', Bo Long, 30 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4179/egusphere-2024-4179-AC2-supplement.pdf
-
AC2: 'Reply on RC1', Bo Long, 30 May 2025
-
RC2: 'Comment on egusphere-2024-4179', Anonymous Referee #2, 28 Mar 2025
Zegang Dong and coworkers have carried out an extensive theoretical investigation on the gas phase reaction between two perfluoroaldehydes and hydroperoxyl radical and estimated their atmospheric implications. The work is extensive, the theoretical model is well chosen and already shown to be appropriate for similar class of reactions, the results are properly presented and explained.
However, the work falls severely short in originality and fails to provide any new insight, and is simply an extension of their earlier work (J. Am. Chem. Soc. 2022, 144, 19910−19920). Both the reactions studied here are close replica, mechanistically, energetically and kinetically, of the reaction between CF3CHO and HO2 studied in their previous work. As the reactions are always centered at the carbonyl group of reacting aldehydes, with no involvement of the side chains, this is very much expected that a mere elongation of the side chain would not have any dramatic effect on the reactions.
The only new analysis that is available in this work is a GEOS-Chem based atmospheric modelling of the studied reactions to estimate their atmospheric implications. However, that analysis also does not provide any new information that was not known from the work cited above. Similar to CF3CHO, the two larger perfluoroaldehydes studied here also show that reaction with HO2 is more dominant atmospheric removal process compared to reaction with OH.
Therefore, the conclusion that this work “provide new insight into atmospheric degradation of linear perfluorinated aldehydes by HO2 radical” is not supported by the results at all. At most, the study provides new data that shows the atmospheric degradations of larger perfluoroaldehydes by HO2 are very similar to that of CF3CHO which has already been reported earlier.
The most baffling aspect of this work is the sudden introduction of NO into the reaction scheme and an attempt to show the title reaction as a source of formic acid and COF2. However, there is no attempt to calculate the rate constant of the reactions involving NO, which would be required to have any realistic estimate of the importance of NO in determining the atmospheric fate of the studied perfluoroaldehydes. Therefore, the conclusion that “under NO conditions this pathway may be a source of HCOOH and COF2 in the troposphere” is completely unfounded without proper kinetic analysis, including lifetime calculations, of these reaction channels.
Based on the above observations, I cannot recommend this work for publication in Atmospheric Chemistry and Physics.
Citation: https://doi.org/10.5194/egusphere-2024-4179-RC2 -
AC1: 'Reply on RC2', Bo Long, 30 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4179/egusphere-2024-4179-AC1-supplement.pdf
-
AC1: 'Reply on RC2', Bo Long, 30 May 2025
Interactive discussion
Status: closed
-
CC1: 'Comment on egusphere-2024-4179', Rabu Changmai, 18 Mar 2025
Line 95: In addition, multi-structural torsional anharmonicity involving reactant and transition state were all calculated using MS-T method (multi-structural method for torsional anharmonicity.
How was this done? Can you please elaborateCitation: https://doi.org/10.5194/egusphere-2024-4179-CC1 -
AC3: 'Reply on CC1', Bo Long, 30 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4179/egusphere-2024-4179-AC3-supplement.pdf
-
AC3: 'Reply on CC1', Bo Long, 30 May 2025
-
RC1: 'Comment on egusphere-2024-4179', Anonymous Referee #1, 22 Mar 2025
This study provides valuable insights into the atmospheric degradation pathways of linear perfluoroaldehydes (PFAs) via reactions with HO₂ radicals. The combination of high-level quantum chemical calculations, kinetic modeling, and atmospheric simulations offers a comprehensive understanding of the roles of HO₂ in modulating PFAs’ lifetimes. The work is timely and addresses a critical gap in the atmospheric chemistry of PFASs. The conclusions are well-supported by the data, and the manuscript is well-organized. However, several clarifications and minor revisions are required to enhance clarity, strengthen methodological justification, and improve readability. I recommend acceptance after minor revisions.
Specific Comments
1. Abstract
(a) The statement “the atmospheric lifetimes for C2F5CHO and C3F7CHO, approximately 14.4-31.3 hours and 21.6-51.8 hours by HO2 are much shorter than those via OH radical,” it is not validated. (lines 15-16)
2. Introduction
(a) Alternating use of "perfluoroaldehydes" (in tittle) and "linear perfluoroaldehydes" may confuse readers.
(b) The transition from PFAS’s GWP to perfluoroaldehyde sources (lines 25-30) is unclear.
(c) The literature review focuses solely on OH and Cl radicals, omitting potential roles of other oxidants (e.g., O₃, NO₃). (lines 35-49)
(d) The long sentence "Moreover, the rate constant of Cl atoms with CnF2n+1CHO (1,2, 3, 4) is around 2 × 10-12 cm3 molecule-1s-1, which is slightly faster than that of the OH radical reactions." (lines 46-47) has poor readability and unclear notes.
3.Computational Methods
(a) In section 2.1, the “CCSD(T)-F12a/cc-pVTZ-F12” method is mentioned, but the text fails to demonstrating its applicability to perfluorinated compound systems. (lines 75-78)
4. Results and Discussion
(a) Figure 1 contains no relevant information. “The result shows that the specific reaction scale factors are 0.955 for TS1 (See Figure 1) and 0.956 for TS2 (See Figure 1)”. (lines 95-96)
(b) Grammatical error in “The torsion of the C-C bond gives produces multiple conformers”. (lines 152-153)
(c) Figure 3’s X-axis label (“Number of alkyl functional groups”) is misleading, as the compounds are perfluorinated. (lines 180-185)
(c) The calculated high-pressure limit rate constants (e.g., k1=5.42×10−14-3.35×10 −12 cm³ molecule⁻¹ s⁻¹) lack comparison with experimental data or analogous systems (e.g., non-fluorinated aldehydes + HO₂), reducing confidence in the results. (lines 204-207)
(e) There is inconsistency in the units used for atmospheric lifetimes. Table 2 reports lifetimes in seconds, while the discussion section uses hours. The authors should standardize the units throughout the manuscript to avoid confusion. (lines 250-255)
5. Atmospheric Implications
(a) The GEOS-Chem simulation results (Lines 273–287) focus on HO₂/OH ratios but do not discuss diurnal variation, which could affect the dominance of HO₂ pathways.
(b) The prospect for future research is somewhat brief and doesn’t adequately take into account the current study’s limitations and possible areas for expansion. (lines 321-325)
6. References
(a) Some of the cited references are incomplete or incorrect.
Lee, B. H., Munger, J. W., Wofsy, S. C., Rizzo, L. V., Yoon, J. Y. S., Turner, A. J., Thornton, J. A., and Swann, A. L. S.: Sensitive Response of Atmospheric Oxidative Capacity to the Uncertainty in the Emissions of Nitric Oxide (NO) From Soils 450 in Amazonia, Geophysical Research Letters, 51, 1-10, https://doi.org/10.1029/2023GL107214, 2024. (lines 448-450)
Long, B., Bao, J. L., and Truhlar, D. G.: Rapid unimolecular reaction of stabilized Criegee intermediates and implications for atmospheric chemistry, Nature Communications, 10, 1–8, https://doi.org/10.1038/s41467-019-09948-7, 2019. (lines 473-474)
Xia, D., Zhang, H., Ju, Y., Xie, H., Su, L., Ma, F., Jiang, J., Chen, J., and Francisco, J. S.: Spontaneous Degradation of the “Forever Chemicals” Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs) on Water Droplet Surfaces, https://doi.org/10.1021/jacs.4c00435, 2024. (lines 548-550)
Citation: https://doi.org/10.5194/egusphere-2024-4179-RC1 -
AC2: 'Reply on RC1', Bo Long, 30 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4179/egusphere-2024-4179-AC2-supplement.pdf
-
AC2: 'Reply on RC1', Bo Long, 30 May 2025
-
RC2: 'Comment on egusphere-2024-4179', Anonymous Referee #2, 28 Mar 2025
Zegang Dong and coworkers have carried out an extensive theoretical investigation on the gas phase reaction between two perfluoroaldehydes and hydroperoxyl radical and estimated their atmospheric implications. The work is extensive, the theoretical model is well chosen and already shown to be appropriate for similar class of reactions, the results are properly presented and explained.
However, the work falls severely short in originality and fails to provide any new insight, and is simply an extension of their earlier work (J. Am. Chem. Soc. 2022, 144, 19910−19920). Both the reactions studied here are close replica, mechanistically, energetically and kinetically, of the reaction between CF3CHO and HO2 studied in their previous work. As the reactions are always centered at the carbonyl group of reacting aldehydes, with no involvement of the side chains, this is very much expected that a mere elongation of the side chain would not have any dramatic effect on the reactions.
The only new analysis that is available in this work is a GEOS-Chem based atmospheric modelling of the studied reactions to estimate their atmospheric implications. However, that analysis also does not provide any new information that was not known from the work cited above. Similar to CF3CHO, the two larger perfluoroaldehydes studied here also show that reaction with HO2 is more dominant atmospheric removal process compared to reaction with OH.
Therefore, the conclusion that this work “provide new insight into atmospheric degradation of linear perfluorinated aldehydes by HO2 radical” is not supported by the results at all. At most, the study provides new data that shows the atmospheric degradations of larger perfluoroaldehydes by HO2 are very similar to that of CF3CHO which has already been reported earlier.
The most baffling aspect of this work is the sudden introduction of NO into the reaction scheme and an attempt to show the title reaction as a source of formic acid and COF2. However, there is no attempt to calculate the rate constant of the reactions involving NO, which would be required to have any realistic estimate of the importance of NO in determining the atmospheric fate of the studied perfluoroaldehydes. Therefore, the conclusion that “under NO conditions this pathway may be a source of HCOOH and COF2 in the troposphere” is completely unfounded without proper kinetic analysis, including lifetime calculations, of these reaction channels.
Based on the above observations, I cannot recommend this work for publication in Atmospheric Chemistry and Physics.
Citation: https://doi.org/10.5194/egusphere-2024-4179-RC2 -
AC1: 'Reply on RC2', Bo Long, 30 May 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-4179/egusphere-2024-4179-AC1-supplement.pdf
-
AC1: 'Reply on RC2', Bo Long, 30 May 2025
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Zegang Dong
Chaolu Xie
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1016 KB) - Metadata XML
-
Supplement
(1453 KB) - BibTeX
- EndNote
- Final revised paper
Line 95: In addition, multi-structural torsional anharmonicity involving reactant and transition state were all calculated using MS-T method (multi-structural method for torsional anharmonicity.
How was this done? Can you please elaborate