the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Jan 2023
The variation of particle number size distribution during the rainfall: wet scavenging and air masses changing
Guangdong Niu
Ximeng Qi
Liangduo Chen
Shiyi Lai
Xin Huang
Jiaping Wang
Xuguang Chi
Wei Nie
Veli-Matti Kerminen
Tuukka Petäjä
Markku Kulmala
Aijun Ding
Abstract. Below-cloud wet scavenging is an important pathway to remove atmospheric aerosols. The below-cloud wet scavenging coefficient (BWSC) is the value to describe the ability of rainfall to remove aerosols. The reported BWSCs obtained from the field measurements are much higher than the theory, but the reason for this remains unclear. In this study, based on the long-term field measurements in the Yangtze River Delta of eastern China, we find 28 % of the rainfall events are high BWSC events. The high BWSC events show the sudden decrease of particle number concentration in all size bins near the end of rainfall. By investigating the circulation patterns, backward trajectories and the variations of simultaneously observed atmospheric components, we find the cause of the high BWSC events is the air masses changing but not the wet scavenging. The change of air masses is always followed by the rainfall processes and cannot be screened out by the traditional meteorological criteria, which would cause the overestimation of BWSC. After excluding the high BWSC events, the observed BWSC is close to the theory and is correlated with the rainfall intensity and particle number concentrations prior to rainfall. This study highlights the discrepancy between the observed BWSC and the theoretical value may not be as large as it is currently believed. To obtain reasonable BWSCs and parameterization from field measurements, the effect of air masses changing during rainfall needs to be carefully considered.
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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
(1984 KB) - Metadata XML
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Supplement
(1588 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Guangdong Niu et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-33', Anonymous Referee #1, 06 Feb 2023
Overall, this manuscript makes a nice contribution to understanding observations of below-cloud wet scavenging and the need to remove air-mass changes. It deserves to be published. However, I have some comments that I’d like to be addressed. I’m particularly concerned about Figure 8 and its interpretation, and this is the focus of my last 4 comments.
The manuscript needs a general review of English (including title and throughout). Generally, the issues don’t prevent the points from being understood, but things can be cleaned up to make the manuscript a bit easier to read. As an example with the title, it would be more common to say, “The variation of the particle number size distribution during the rainfall: wet scavenging and air masses changing”
Section 2.2: The criteria listed here have somewhat arbitrarily chosen cutpoints. How sensitive are the results to changes in these cutpoints?
Figure 2: I found it hard to see the “theory” curve on the plot (the pink was very light), please make it darker or make it a line.
Figure 2: What assumptions were made for the “theory” curve? The rainfall rate and the rain size distribution will affect this curve. Related, the rain conditions for each of the obs studies on the plot may different, so it’s worth discussing these potential differences.
L241-242: I don’t understand this statement. It might be because I’m not sure what a “backwards air mass” is (do you mean “back trajectory”?).
Figure 6: Is there a reason why type iv is not plotted here? Should mention why.
Figure 7: The CO change here seems like the most straightforward evidence of the airmass change, given that it’s a non-scavenged species. Not necessary, but this could be made more prominent in the paper (e.g., abstract, moving it forward in the results, etc.).
Figure 8: What size are these BWSC coefficients for? Is it for the total number of particles, regardless of their size? If true, this complicates the interpretation of the figure since there is likely a correlation between the particle number concentration and the size of the particles. I recommend instead making this plot for the BWSC for a specific size, which makes for a fairer comparison (or at least having this as a second panel).
L327-329: It does not make physical sense that the BWSC depends on number concentration. Below-cloud wet scavenging is a 1st-order loss process, particles should not be influencing other particles’ ability to be scavenged. It seems much more likely that particle number and the average size of the particles are at least somewhat correlated, and that is driving the relationship here. This is why making Figure 8 show the BWSC for a specific size would be easier to interpret. (Also, is there a relationship between rain rate or the rain drop size distribution and the number of particles? A correlation here seems less likely than the relationship between particle number and particle size, but worth checking since it could also influence the interpretation of Figure 8.)
L341-342: How? Below-cloud wet scavenging is a first-order process. It should not depend on the number. However, it does depend on particle size. See the two comments above. The interpretation here seems incorrect.
L342-344: Unless the particle concentrations are extremely high, below-cloud scavenging should be removing particle number much faster than coagulation.
Citation: https://doi.org/10.5194/egusphere-2023-33-RC1 - AC1: 'Reply on RC1', Ximeng Qi, 29 May 2023
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RC2: 'Comment on egusphere-2023-33', Anonymous Referee #2, 04 Apr 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-33/egusphere-2023-33-RC2-supplement.pdf
- AC2: 'Reply on RC2', Ximeng Qi, 29 May 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-33', Anonymous Referee #1, 06 Feb 2023
Overall, this manuscript makes a nice contribution to understanding observations of below-cloud wet scavenging and the need to remove air-mass changes. It deserves to be published. However, I have some comments that I’d like to be addressed. I’m particularly concerned about Figure 8 and its interpretation, and this is the focus of my last 4 comments.
The manuscript needs a general review of English (including title and throughout). Generally, the issues don’t prevent the points from being understood, but things can be cleaned up to make the manuscript a bit easier to read. As an example with the title, it would be more common to say, “The variation of the particle number size distribution during the rainfall: wet scavenging and air masses changing”
Section 2.2: The criteria listed here have somewhat arbitrarily chosen cutpoints. How sensitive are the results to changes in these cutpoints?
Figure 2: I found it hard to see the “theory” curve on the plot (the pink was very light), please make it darker or make it a line.
Figure 2: What assumptions were made for the “theory” curve? The rainfall rate and the rain size distribution will affect this curve. Related, the rain conditions for each of the obs studies on the plot may different, so it’s worth discussing these potential differences.
L241-242: I don’t understand this statement. It might be because I’m not sure what a “backwards air mass” is (do you mean “back trajectory”?).
Figure 6: Is there a reason why type iv is not plotted here? Should mention why.
Figure 7: The CO change here seems like the most straightforward evidence of the airmass change, given that it’s a non-scavenged species. Not necessary, but this could be made more prominent in the paper (e.g., abstract, moving it forward in the results, etc.).
Figure 8: What size are these BWSC coefficients for? Is it for the total number of particles, regardless of their size? If true, this complicates the interpretation of the figure since there is likely a correlation between the particle number concentration and the size of the particles. I recommend instead making this plot for the BWSC for a specific size, which makes for a fairer comparison (or at least having this as a second panel).
L327-329: It does not make physical sense that the BWSC depends on number concentration. Below-cloud wet scavenging is a 1st-order loss process, particles should not be influencing other particles’ ability to be scavenged. It seems much more likely that particle number and the average size of the particles are at least somewhat correlated, and that is driving the relationship here. This is why making Figure 8 show the BWSC for a specific size would be easier to interpret. (Also, is there a relationship between rain rate or the rain drop size distribution and the number of particles? A correlation here seems less likely than the relationship between particle number and particle size, but worth checking since it could also influence the interpretation of Figure 8.)
L341-342: How? Below-cloud wet scavenging is a first-order process. It should not depend on the number. However, it does depend on particle size. See the two comments above. The interpretation here seems incorrect.
L342-344: Unless the particle concentrations are extremely high, below-cloud scavenging should be removing particle number much faster than coagulation.
Citation: https://doi.org/10.5194/egusphere-2023-33-RC1 - AC1: 'Reply on RC1', Ximeng Qi, 29 May 2023
-
RC2: 'Comment on egusphere-2023-33', Anonymous Referee #2, 04 Apr 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-33/egusphere-2023-33-RC2-supplement.pdf
- AC2: 'Reply on RC2', Ximeng Qi, 29 May 2023
Peer review completion
Journal article(s) based on this preprint
Guangdong Niu et al.
Guangdong Niu et al.
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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
(1984 KB) - Metadata XML
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(1588 KB) - BibTeX
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