the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Investigating the contribution of grown new particles to cloud condensation nuclei with largely varying pre-existing particles – Part 2: Modeling chemical drivers and 3-D NPF occurrence
Ming Chu
Xing Wei
Shangfei Hai
Huiwang Gao
Yujiao Zhu
Nan Ma
Juan Hong
Xiaohong Yao
Abstract. In this study, we utilized a 20-bin WRF-Chem (Weather Research and Forecast coupled with Chemistry regional model) to investigate the contributions of chemical drivers to the growth of newly formed particles, as well as to simulate the three-dimensional dynamics of new particle formation (NPF) events over the North China Plain during a summer campaign in 2019, which was reported in the accompanying paper. The model demonstrated good performance in replicating the occurrence of NPF, the growth pattern of newly formed particles, and the number concentration of particles in the size range of 10–40 nm in five events between June 29 and July 6. This period was characterized by a high frequency of NPF occurrence (>60 %). During this time, the model was also able to accurately reproduce the levels of organics in PM1.0 relative to observations, and to reasonably replicate the levels of SO42- and NH4+ in PM1.0, as well as PM2.5 mass concentrations. Therefore, we further analyzed three NPF events with distinct particle growth characteristics: Case 1, featuring observable growth of newly formed particles to cloud condensation nuclei (CCN) size on July 1–2; Case 2, characterized by continuous growth of new particles for several hours without any net contribution to CCN on July 3; and Case 3, where no detectable continuous growth of newly formed particles was observed on July 6. In these instances, the model tended to overpredict the condensation of H2SO4 vapor during daytime and the formation of NH4NO3 during nighttime, resulting in an overestimation of the hygroscopicity parameter of nanometer particles. Nevertheless, the model was able to reasonably reproduce the CCN (cloud condensation nuclei) at a super saturation (SS) of 0.4 % on days with NPF, compared to the observations. This was because the overestimation effect caused by inorganics was offset by the model's underestimation of CCN originating from submicron-sized particles. Additionally, three-dimensional simulations of NPF events have demonstrated some key findings. Firstly, NPF consistently initiates at the upper fraction of the planetary boundary layer (PBL) before expanding. Secondly, during daytime growth of newly formed particles in the PBL, organics play a dominant role, whereas the primary chemical drivers shift to inorganic species in the free troposphere. However, to confirm these findings, vertical observations are required.
- Preprint
(3285 KB) - Metadata XML
-
Supplement
(879 KB) - BibTeX
- EndNote
Ming Chu et al.
Status: open (until 04 Oct 2023)
-
RC1: 'Comment on egusphere-2023-540', James Hudson, 14 Sep 2023
reply
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-540/egusphere-2023-540-RC1-supplement.pdf
-
RC2: 'Comment on egusphere-2023-540', Anonymous Referee #2, 24 Sep 2023
reply
The manuscript entitled “Investigating the contribution of grown new particles to cloud condensation nuclei with largely varying preexisting particles - Part 2: Modeling chemical drivers and 3-D NPF occurrence” is a modeling study of new particle formation events in the North China Plane. Modeling studies such as these can be helpful for understanding new particle formation, as they provide possible insights into difficult-to-measure aspects of new particle formation such as the horizontal and vertical extent of events. The often-repeated quote “All models are wrong, but some are useful.” (attributed to George Box) is a useful mantra to consider when assessing the scientific value of a study such as this. Certainly, models such as WRF-Chem are quite sophisticated in their ability to handle some chemical and meteorological conditions, but I feel this paper also displays some of the pitfalls of modeling studies, such as their reliance on accurate emissions data for compounds that are actually quite difficult to measure. In my opinion, the most significant weakness of this manuscript is the lack of objective standards applied to the assessment of model performance: specifically the use of statements such as “the model does a good job …” without objective standards to base such statements on.
In my view, this manuscript may be publishable in Atmos. Chem. Phys., but only after addressing numerous concerns outlined below. My comments are preceded by a numbering system that states the page and line number of the passage in question.
Comments:
5-16: The use of the term "good" is not really useful. What means "good" to the authors does not mean the same to the reader. Indeed, I would object that the agreement is good here, even in the time period selected by the authors (and I agree that the fit is horrible outside the period). I strongly suggest removing "good" here and letting the statistical tests tell the story so that the reader can make a judgement on whether this is acceptable.
5-21: If there is a benchmark provided by the USEPA then I would say that going back to my prior comment "meets the benchmarks" should be replaced with "good". But I cannot find this in the references. If this is an oversight. the authors need to provide a reference to this benchmark.
5-28: Again, I strongly suggest that the authors refrain from making this sweeping statement because, as they state in subsequent sentences, the fit appears to be good for sulfate but quite bad for nitrate and ammonium.
5-34: It's easy to blame measurements here, but I think it's even more likely that the model is not getting source emissions correct. For their analysis to be respected I suggest that the authors reflect on how their model could be getting things wrong as well.
5:35: I am not sure why we are talking about Beijing measurements here. It doesn’t really seem to add a lot to this study, since it’s a different locale.
6-14: there are a lot of plots in the main manuscript and some, like Figs 4 and 5, I think can easily go into the supplement. That is because they are referring not to the site that is the focus of this study, but to an urban Beijing site.
6-20: I would maintain that the correlations between measured and modeled ammonium are just about as bad as those for nitrate, even during the "NPF" period. Please comment on this.
8-30: I would say that there are poor correlations for all plots, especially given that the data are presented on a log-scale. If the authors think that a correlation is "reasonable," then please let the reader know by what basis you judge this.
11:2: Again, if there is a metric for assessing whether the model did a good job it's important to state that rather than just say it did a good job.
Minor comments:
1-30: In the abstract especially, it is important to avoid ambiguous statements. Thus I would avoid the term "CCN size," since the ability of a particle to become CCN depends on size and composition as well as SS.
2-12: These reviews are quite old. Please supplement with more recent reviews on the topic.
2-30: replace with "becoming CCN" since size AND composition is important.
2-31: There have been many recent studies of NPF in the NCP, so what do the authors mean about "updated study"? What about those studies have not addressed this question?
3-1: This line of reasoning suggests that 3D modeling is on par with measuring approaches, but each has unique aspects that they contribute and each has issues. The discussion needs to be more nuanced.
3-9: remove "In the literature"
3-25: "in terms of" is not the correct phrase. replace with something like "focusing on"
3-32: I am not sure what this means for a modeling study to discuss observations and what a "particle signal" refers to. Certainly "disappearing" should be replaced with "disappear" in order to be grammatically correct ... but what is a "signal"?
4-3: Usually when a sentence starts with "on one hand" it is because later there will be a different perspective provided (the "other hand"). Why is this phrase necessary for this sentence?
4-13: what does this mean "a combination was used"? For what? I also note that an SMPS system always includes a CPC. Is this an additional one used for some other purpose? I think the authors mean to say that an SMPS was used for the size distribution during this time.
4-17: it would be helpful for the reader to know about the inlet dimensions (length and diameter) in order to assess the degree to which losses might be important.
5-10: units need to be added on each statement of the rate constant, even though you state the units above.
5-32: Shouldn't Fig. 4 be referenced here? If not, how is this statement justified?
6-33: This is likely not due to the shrinkage of grown new particles, but rather an air mass change that brings in particles of differing age. Please rephrase this. Perhaps adding wind direction to the plot would also provide insights into the cause of this change in the size distribution.
7-9: Please comment on how and to what extent the model accounts for vertical mixing. In many studies, NPF is found to be initiated aloft and vertical transport is seen to be an essential part of the complete picture of the mechanisms of NPF. What does this model suggest? If this is discussed later in the paper, a reference to that here might be appropriate.
7-11: Apologies if this was already stated earlier but what are the "goal values" and how were they assigned?
7-27: How does the fact that the model dramatically overpredicts both ammonum and nitrate during these two days affect the interpretation of the modeling results? I would suggest a discussion of this at least. After reading the next paragraph, it seems that this topic comes up so perhaps including some reference to this here would be appropriate. Perhaps something like "an analysis of kappa confirms that this could be an overestimated effect"
8-19: I suggest putting Fig 9 into the supplement since there are so many plots shown in the main text.
8-36: I thought that the inclusion is that the model overestimated the organic composition during the NPF period? Again, the use of the word "reasonably" allows for a broad interpretation.
9-4: use of "steer" in this context seems odd. It is not a synonym for control. This is probably a result of using ChatGPT for grammar (which I would NOT recommend!).
9-18: Similar to my previous statements, I think it's OK to just show one of these plots (Fig 11 for instance) and put 12 in the SI.
9-22: "3D occurrence" is an odd phrase. I would suggest "3-D spatial distribution" or "3-D evolution"
9-35: Could this observed spatial inhomogeneity contribute to the "shrinking" effect observed in the size distribution? It seems possible.
10-11: correct grammar "disappear". Also what does "signals" refer to? THis is a fundamental question for understanding this entire section.
10-14: See my question about about "signals no longer observable". In this entire section the word "signal" needs to be defined or replaced.
10-35: Lagrangian
11:4: I would disagree with Ncc(0.4%). I also don't think it did very well with some of the species mentioned later in this sentence.
11:13: Why, if growth is dominated by organics, is understanding inorganic species the key for modeling NPF?
Fig 8 e-h - I personally feel that the 3D representation of these pie charts is distracting and unnecessary. In general I support the thought that the simpler way to represent data (without what Tufte called "Chartjunk") is bes
Citation: https://doi.org/10.5194/egusphere-2023-540-RC2
Ming Chu et al.
Ming Chu et al.
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 216 | 44 | 14 | 274 | 19 | 5 | 8 |
- HTML: 216
- PDF: 44
- XML: 14
- Total: 274
- Supplement: 19
- BibTeX: 5
- EndNote: 8
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1