the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Mar 2024
Technical note: Influence of different averaging metrics and temporal resolutions on aerosol pH calculated by thermodynamic modeling
Abstract. Aerosol pH is commonly used to characterize the acidity of aqueous aerosols and is of significant scientific interest due to its close relationship with atmospheric processes. Estimation of ambient aerosol pH usually relies on the thermodynamic modeling approach. In the existing chemical transport model and field observation studies, the temporal resolution of the input chemical and meteorological data into thermodynamic models varied substantially ranging from less than an hour to a year because of the inconsistency in the resolution of the original data and the aggregation of time-series data in some studies. Furthermore, the average value of aerosol pH has been represented by diverse metrics of central tendency in existing studies. This study attempts to evaluate the potential discrepancies in the calculated average aerosol pH arising from differences in both averaging metrics and temporal resolutions based on the ISORROPIA-II thermodynamic model and the example datasets prepared by the GEOS-Chem chemical transport model simulation. Overall, we find that the variation in the temporal resolutions of input data may lead to a change of up to more than two units in the average pH, and that the averaging metrics calculated based on the pH value of individual samples may be about two units higher than the averaging metrics calculated based on the activity of hydrogen ions. Accordingly, we recommend that the chosen averaging metrics and temporal resolutions should be stated clearly in future studies to ensure comparability of the average aerosol pH between models and/or observations.
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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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Supplement
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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
(992 KB) - Metadata XML
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Supplement
(1147 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-479', Anonymous Referee #2, 18 Mar 2024
The pH of aerosols is a crucial parameter that significantly impacts the entire atmospheric chemical process, and it is of utmost importance to accurately assess its value. This article primarily focuses on the issues of averaging methods and temporal resolution that are often overlooked in the process of calculating pH. It is found that these two factors can lead to differences in pH values ranging from 0.5 to 2 units, with the potential to affect the sulfate formation rate by up to two times. This is a meaningful study that provides important insights for our further understanding of the influencing factors of pH. I agree with the publication of this article in ACP. There are a few minor issues that need to be addressed before that.
(1) I did not see how the value of activity of H+ used in calculating pH was obtained. It would be helpful to make this clearer in the article.
(2) The authors have discussed how averaging methods and temporal resolution can lead to significant differences in pH. It would be more helpful if they could provide more specific recommendations on how to use these.
(3) It seems that the x-axis in Figure 2(d) differs from the other sub-figures.
Citation: https://doi.org/10.5194/egusphere-2024-479-RC1 - AC1: 'Reply on RC1', Shaojie Song, 25 Apr 2024
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RC2: 'Comment on egusphere-2024-479', Anonymous Referee #1, 27 Mar 2024
In this manuscript, Wang et al. quantity the inconsistencies in reported aerosol pH values that can arise from different averaging metrics and temporal resolutions of the pH calculation that are commonly used in field and modeling studies. They apply different averaging metrics and time resolutions to an ensemble of data generated from atmospheric chemistry model simulations for the North China Plain over the winter season. They show differences in the “average” pH of up to 2 units and emphasize the importance of specifying the averaging metrics and temporal resolution in the future.
The paper highlights an important but oft-neglected point about comparing aerosol pH values reported by different studies. The paper is well-written and the conclusions are based on sound analysis.
The following are my concerns about the paper and suggestions for improvement:
1. It would be better if the authors could recommend some best practices that future studies could follow when reporting average pH values, given that pH and H+ molality are non-conserved quantities and their arithmetic mean has little physical meaning, but also considering the practicalities of field studies. Should field studies report other relevant data that would make it easier to compare their findings to other studies or models? The main recommendation of the manuscript is that studies should "clearly state their chosen averaging metrics,” but it seems from Table S1 that most studies already do that. The submission would be more significant if the authors could be more insightful in their recommendations.
2. The submission would also be stronger if it included a discussion of the measures of dispersion, as they are important when statistically comparing different pH datasets.
3. The study used model data for the winter season. How different would the variations in “average” pH values be in the summer?
4. Fig. 1 shows several pH values above 6. Does ISORROPIA consider carbonate equilibrium in this case? If not, it is better not to include these values in the analysis.
Citation: https://doi.org/10.5194/egusphere-2024-479-RC2 - AC2: 'Reply on RC2', Shaojie Song, 25 Apr 2024
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-479', Anonymous Referee #2, 18 Mar 2024
The pH of aerosols is a crucial parameter that significantly impacts the entire atmospheric chemical process, and it is of utmost importance to accurately assess its value. This article primarily focuses on the issues of averaging methods and temporal resolution that are often overlooked in the process of calculating pH. It is found that these two factors can lead to differences in pH values ranging from 0.5 to 2 units, with the potential to affect the sulfate formation rate by up to two times. This is a meaningful study that provides important insights for our further understanding of the influencing factors of pH. I agree with the publication of this article in ACP. There are a few minor issues that need to be addressed before that.
(1) I did not see how the value of activity of H+ used in calculating pH was obtained. It would be helpful to make this clearer in the article.
(2) The authors have discussed how averaging methods and temporal resolution can lead to significant differences in pH. It would be more helpful if they could provide more specific recommendations on how to use these.
(3) It seems that the x-axis in Figure 2(d) differs from the other sub-figures.
Citation: https://doi.org/10.5194/egusphere-2024-479-RC1 - AC1: 'Reply on RC1', Shaojie Song, 25 Apr 2024
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RC2: 'Comment on egusphere-2024-479', Anonymous Referee #1, 27 Mar 2024
In this manuscript, Wang et al. quantity the inconsistencies in reported aerosol pH values that can arise from different averaging metrics and temporal resolutions of the pH calculation that are commonly used in field and modeling studies. They apply different averaging metrics and time resolutions to an ensemble of data generated from atmospheric chemistry model simulations for the North China Plain over the winter season. They show differences in the “average” pH of up to 2 units and emphasize the importance of specifying the averaging metrics and temporal resolution in the future.
The paper highlights an important but oft-neglected point about comparing aerosol pH values reported by different studies. The paper is well-written and the conclusions are based on sound analysis.
The following are my concerns about the paper and suggestions for improvement:
1. It would be better if the authors could recommend some best practices that future studies could follow when reporting average pH values, given that pH and H+ molality are non-conserved quantities and their arithmetic mean has little physical meaning, but also considering the practicalities of field studies. Should field studies report other relevant data that would make it easier to compare their findings to other studies or models? The main recommendation of the manuscript is that studies should "clearly state their chosen averaging metrics,” but it seems from Table S1 that most studies already do that. The submission would be more significant if the authors could be more insightful in their recommendations.
2. The submission would also be stronger if it included a discussion of the measures of dispersion, as they are important when statistically comparing different pH datasets.
3. The study used model data for the winter season. How different would the variations in “average” pH values be in the summer?
4. Fig. 1 shows several pH values above 6. Does ISORROPIA consider carbonate equilibrium in this case? If not, it is better not to include these values in the analysis.
Citation: https://doi.org/10.5194/egusphere-2024-479-RC2 - AC2: 'Reply on RC2', Shaojie Song, 25 Apr 2024
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Haoqi Wang
Xiao Tian
Wanting Zhao
Jiacheng Li
Haoyu Yu
Yinchang Feng
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(992 KB) - Metadata XML
-
Supplement
(1147 KB) - BibTeX
- EndNote
- Final revised paper