the Creative Commons Attribution 4.0 License.
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
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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
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