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the Creative Commons Attribution 4.0 License.
| 05 Jun 2024
Exploring the Crucial Role of Atmospheric Carbonyl Compounds in Regional Ozone heavy Pollution: Insights from Intensive Field Observations and Observation-based modelling in the Chengdu Plain Urban Agglomeration, China
Abstract. Gaseous carbonyl compounds serve as crucial precursors and intermediates in atmospheric photochemical reactions, significantly contributing to ambient ozone formation. To investigate the impact of gaseous carbonyls on regional ozone pollution, simultaneous field observations and observation-based modelling of ambient carbonyls were conducted at nine sites within the Chengdu Plain Urban Agglomeration (CPUA), China during August 4–18, 2019, when three episodes of regional heavy ozone pollution occurred across eight cities within CPUA. Throughout the study, the total mixing ratios of 15 carbonyls ranged from 10.70 to 35.18 ppbv, in which formaldehyde (48.1 %), acetone (19.9 %), and acetaldehyde (17.5 %) were most abundant within the CPUA. Ambient levels of carbonyls and ozone showed some positive correlations in space (especially pronounced around Chengdu in both northern and southern directions) and in diurnal variations with higher concentrations of carbonyls during ozone pollution episodes. Photochemical reactivity analysis emphasized the significant contributions of carbonyls, especially formaldehyde and acetaldehyde, to ozone formation. The ozone formation sensitivity for sites experiencing severe ozone pollution were classified as VOCs-limited regime, while others were categorized as transitional regime. Local primary emissions, mutual air transportation among cities within the CPUA and photochemical secondary processes were recognized to contribute significantly to the production or the contamination of carbonyls in ambient air, with alkenes and alkanes being important secondary precursors of carbonyls. This study highlights the pivotal role of carbonyls in heavy ozone pollution within the CPUA, China, providing valuable scientific insights to guide the development of effective countermeasures for regional ozone pollution control in the future.
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RC1: 'Comment on egusphere-2024-1204', Rob MacKenzie, 22 Aug 2024
Review of “Exploring the Crucial Role of Atmospheric Carbonyl Compounds in Regional Ozone heavy Pollution: Insights from Intensive Field Observations and Observation-based modelling in the Chengdu Plain Urban Agglomeration, China”
Authors: Jiemeng Bao, Xin Zhang, Zhenhai Wu, Li Zhou, Jun Qian, Qinwen Tan, Fumo Yang, Junhui Chen, Yunfeng Li, Hefan Liu, Liqun Deng, and Hong Li
https://doi.org/10.5194/egusphere-2024-1204
Review by editor Rob MacKenzie.
Note: after many unsuccessful attempts to find a second reviewer, I am providing this review as editor. This study utilises observations and modelling of a short period in August 2019 to study severe ozone pollution in the Chengdu Plain region of China. The major finding reported is the importance of carbonyl compounds, but the significance of carbonyls to ozone formation is generally well-known and many papers have been published even on the current situation across China. It would be better to frame the paper in terms of whether the known importance of carbonyls can account for the ozone production; that is, whether it is the abundance, or some additional chemistry, that makes the carbonyls so important in this context. The manuscript may be suitable for publication after major revision.
Major comments
- Poor use of the literature: There is very poor coverage of the early work on carbonyls, which results in the appearance that carbonyls have only just been discovered in the literature. Guenther et al. 2012 is not an appropriate reference for the photolysis of carbonyls (even a textbook such as Seinfeld and Pandis would be better). The introduction should use more modern references to point out how understanding has progressed since the early studies, not to stand-in for the earlier work.
- Poor framing of research question (lines 86-88). The research gap identified here is too broad to be very meaningful: the literature is full of evaluations of the specific roles of carbonyls in ozone production. Again, in lines 89-105, especially lines 103-105, the precise research gap is not identified with sufficient precision.
- When the research has been properly framed (addressing points 1 and 2, above), the Results & Discussion and Conclusions sections should be modified accordingly.
Minor comments
L39, Abstract: I think “alkenes and alkanes being important secondary precursors of carbonyls” should be “alkenes and alkanes being important precursors of secondary carbonyls” – because it is the carbonyls that are secondary, not the alkanes and alkenes.
Ll48-49. It is not sufficient to support the introductory statement with a citation from 2004. The importance of carbonyls to ozone and SOA has been known for decades and described by earlier authors.
Ll63-65. Please give some indication of the concentrations and the size of the diurnal variation reported in these papers so that the reader can immediately compare with what is in the current paper.
Ll80-81: This statement is a bit too strong; it is perfectly possible to measure formaldehyde (which the abstract says is ~50% of the carbonyls of concern in this study) from space.
Ll94-97: a statement as strong as this requires support from the literature. Similarly, the sentence following on lines 98-99.
L135: OBM should be defined on first use.
Figure 1 caption is insufficiently detailed and should at least say what is shown on left and right-hand panels. It is not clear what “9 mg.m3/grid” means, especially since the colour on the map appear to be interpolated to a smooth surface rather than gridded.
L201: is “TO-15” a method or a chemical or family of chemicals? Please clarify the two uses in this paragraph and define PAMS on line 211.
L203: “mass chromatography” should be “mass spectrometry”
L227 “Inferring ozone formation sensitivity” is better English
Ll243-250. Better to use lower case k for rate constants so as not to confuse with equilibrium constants. The rate is not given by eq (1) but by the right-hand side of eq (1) times the concentration of OH.
Ll251-255: What are the units of OFP and MIR_i?
L326: Is there a citation, url, or business address for the MeteoInfo software and Trajstat plug-in?
Ll345-346. Ozone is insoluble, so a little more explanation of why precipitation alleviated ozone pollution is needed here.
Fig 3. I will not insist, but if you have the opportunity to re-draw this figure using colour scales that are easier for those with colour-blindness, that would be good.
L385. I think this should be “the average total concentration of the 15 carbonyls…”
Table 1. The caption should state where the reader can find an explanation of the column headings. The caption should read “Daily mean +/- standard error…” (or standard deviation, whichever it is).
L397ff: please do not switch from names of cities to acronyms inconsistently. It is best to remind the reader by using both name and acronym at first, before using just one.
L423: specie is not the singular of species – replace with ‘carbonyl’
L428: replace ‘concentrations’ with ‘measured’, since not all carbonyls have been measured.
L431: funny that MACR appears but not methyl vinyl ketone, since both are produced in roughly equal measure from isoprene. Acetone is the only ketone that appears in Table 1. Is that to be expected?
L466: deposition would also play a part in a diurnal cycle of this kind.
Figure 5. It is difficult to interpret this figure without a better caption. Unit for L_OH should be s-1 (i.e., lowercase s). Negative indices and solidus (‘/’) notation should not be used together. Negative indices should be used consistently throughout the document.
L524: every compound listed in Table 1 is an aldehyde except acetone, so this sentence presumably means simply that acetone is at higher concentration?
Figure 9: the caption does not explain the figure sufficiently well. The maps could be ‘zoomed’ closer into the area of interest.
Citation: https://doi.org/10.5194/egusphere-2024-1204-RC1 -
AC1: 'Reply on RC1', jiemeng Bao, 18 Sep 2024
### Response to Editor Rob MacKenzie's Comments
Dear Editor,
Thank you for your detailed review and for providing valuable feedback on our manuscript. We appreciate your efforts to improve the clarity and scientific rigor of the study. Below, we address the major and minor comments point by point.
Major Comments:
- Poor use of literature:
We have expanded the introduction to include a more comprehensive review of early work on carbonyl compounds. The reference to Guenther et al. (2012) for photolysis has been replaced with more appropriate sources, such as Seinfeld and Pandis (2016), to better represent the progression in the understanding of carbonyl chemistry. The revised introduction now reflects both early foundational studies and more recent advances, improving the context of carbonyl compounds' roles in ozone formation.
- Poor framing of the research question (lines 86-88):
We have refined the framing of the research question to focus on whether it is the abundance of carbonyls or specific additional chemistry that explains their importance in ozone formation in this context. This adjustment provides a clearer and more focused research gap that addresses whether current knowledge can fully account for the observed ozone production in the Chengdu Plain.
- Results & Discussion and Conclusions:
Based on the revised research question, we have made corresponding changes to the Results & Discussion and Conclusions sections. These sections now emphasize whether the importance of carbonyls is due to their abundance or other specific chemical mechanisms, as observed in the study region.
Minor Comments:
- L39 (Abstract):
We have revised the sentence to “alkenes and alkanes being important precursors of secondary carbonyls” to clarify that the carbonyls are secondary.
- L48-49:
The introductory statement has been updated with a more recent reference that reflects the ongoing importance of carbonyl compounds in ozone and secondary organic aerosol (SOA) formation.
3.L63-65:
We have added quantitative data on the concentrations and diurnal variations reported in the cited papers, allowing readers to directly compare the values with those from our study.
- L80-81:
We have revised the statement to "Urban areas generally exhibit higher carbonyl levels than suburban and rural areas due to human activities."
5.L94-97 and L98-99:
We have provided additional references to support the strong statements made in these sections.
- L135:
The term "OBM" (Observation-Based Model) is now defined at its first appearance in the manuscript.
- Figure 1 caption:
The caption for Figure 1 has been expanded to clarify the content of the left and right images. We have also explained the legend in the right panel and ensured the description matches the presentation in the figure. "9 μg·m⁻³/grid" refers to each color representing 9 μg·m⁻³.
- L201 (TO-15 and PAMS):
We have clarified that TO-15 refers to a method for measuring volatile organic compounds (VOCs), and we have defined PAMS (Photochemical Assessment Monitoring Stations).
- L203:
“Mass chromatography” has been corrected to “mass spectrometry.”
- L227:
We have rephrased the sentence to “Inferring ozone formation sensitivity” to improve clarity.
- Ll243-250:
We have changed the rate constant notation to lowercase 'k' and clarified that the rate is given by the right-hand side of eq (1) multiplied by the concentration of OH.
- Ll251-255:
The units for OFP (Ozone Formation Potential) and MIR (Maximum Incremental Reactivity) have been added for clarity.
- L326 (MeteoInfo and Trajstat):
We have included a URL for the MeteoInfo software and Trajstat plug-in in the text.
- Ll345-346 (Ozone solubility):
We have provided a more detailed explanation of how precipitation alleviates ozone pollution, despite ozone’s insolubility, by discussing the removal of ozone precursors from the atmosphere through wet deposition.Although ozone itself is not easily removed by rain, precipitation reduces ozone pollution by washing away its precursors, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs), decreasing sunlight exposure, and enhancing atmospheric dispersion.
- Figure 3 (Color-blindness):
We have adjusted the color scale in Figure 3 to make it more accessible for color-blind readers.
- L385:
We have corrected the sentence to read “the average total concentration of the 15 carbonyls...”.
- Table 1 (Daily mean and standard error):
The caption for Table 1 has been revised to state: “Daily mean ± standard error (or standard deviation, as appropriate)...” and now includes an explanation of the column headings.
- L397 (City names and acronyms):
We ensured consistency in city names and abbreviations throughout the manuscript and clarified the relationship between site names and cities when first mentioned in Figure 1.
- L423 (Specie vs species):
We have replaced “specie” with “species” to correct this grammatical error.
- L428 (Concentrations vs measured):
We have revised the sentence to "measured" to clarify that not all carbonyls have been measured.
- L431 (MACR and methyl vinyl ketone):
MVK and other ketones were not detected, possibly due to the limitations of the TO-15 method. The TO-15 method is primarily used to detect volatile organic compounds (VOCs) in the air, with a focus on lower molecular weight VOCs such as hydrocarbons, halogenated hydrocarbons, and aromatics. Although the TO-15 method can detect certain aldehydes and ketones, its detection sensitivity and efficiency may not be sufficient for specific compounds like MVK and other ketones.
- L466 (Deposition and diurnal cycle):
We have mentioned deposition as a contributing factor to the diurnal cycle of carbonyls, in addition to their chemical production and loss processes.
- Figure 5 (Units and notation):
We have revised the figure caption and unit labels to ensure consistency in the use of notation and correct units (s⁻¹).
- L524 (Acetone concentration):
We have clarified that 这个句子中的aldehyde 是指的乙醛。
- Figure 9 caption (Zooming in):
We have improved the caption for Figure 9, providing a clearer explanation of what the figure shows. Additionally, we have zoomed in on the area of interest to make the maps easier to interpret.
We hope that these revisions have addressed all of your concerns. Thank you again for your valuable feedback, and we look forward to your further comments.
Citation: https://doi.org/10.5194/egusphere-2024-1204-AC1
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RC2: 'Comment on egusphere-2024-1204', Anonymous Referee #2, 27 Sep 2024
This study provides a comprehensive examination of carbonyl concentrations, their atmospheric chemical reactivity, sources, as well as their impact on ozone pollution. While the work is valuable, several major and minor issues were unclear and needed to be further addressed before it can be considered for publication.
Abstract
1. Since many of the values reported in the paper are averages across multiple sites, it is recommended to include the standard deviations. For example, Lines 27-28, Lines 340-341, Lines 425-426, and other relevant sections.
2. “The ozone formation sensitivity for sites experiencing severe ozone pollution were classified as VOCs-limited regime, while others were categorized as transitional regime”. This statement is ambiguous. Does this refer to sites with varying degrees of ozone pollution, or does it pertain to the same site experiencing different stages of an ozone episode?
Method:
3, Lines 177-178: Why were 6 samples collected over three days? Was it because these were ozone pollution days? Does the inconsistency in the VOCs and carbonyls collection times cause uncertainties in subsequent analysis?
4, Some subtitles are not appropriate. For example, “Ambient levels comparison” is suggested to revise to “Ozone pollution assessment criteria”, and it is recommended to delete Lines 221-226. “Ozone formation sensitivity inferring” should be changed to “Ozone formation sensitivity”, “Secondary formation mechanism investigation” is not suitable as a subtitle.
5, Please clarify the mechanism used by the OBM model.
6, References are needed in the RIR calculation.
7, The measurement instruments for NO2 and CO (as shown in Figure 2 and Figure 3), as well as the time resolutions, were not introduced in the method section.
Results and Discussion
8, Line 357: Does “O3-8” refer to the “maximum daily average 8h ozone concentration”?
9, Lines 449-451: Drawing a conclusion based solely on a comparison with 2010 seems insufficient.
10, The diurnal variation of the carbonyl compounds on weekdays and weekends appears to be irrelevant. I suggest removing this paragraph.
11, Line 519: How is the positive correlation observed?
12, Line 540: Which figure does “Fig.3.9”refer to?
Figures:
13, Fig. 1: Please include the data sources for both figures.
14, For Figure 3a, how is the average O3 concentration calculated? Is it the average over the entire day, or is it the maximum daily average 8h ozone (MDA8) average? Additionally, O3 and NO2 seem relatively consistent in this figure. How about the temporal and spatial variations of VOCs and carbonyl compounds?
15, Figure 6: Please use different markers to distinguish EP1, EP2 and EP3.
Citation: https://doi.org/10.5194/egusphere-2024-1204-RC2
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