the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Oct 2024
Gas-phase Observations of Accretion Products from Stabilized Criegee Intermediates in Terpene Ozonolysis with Two Dicarboxylic Acids
Abstract. Criegee intermediates (CIs), forming from the ozonolysis of alkenes, are highly reactive species with diverse reaction pathways, with important roles in atmospheric chemistry. This study focuses on the formation of accretion products through reactions of thermally stabilized CIs (sCIs) from the ozonolysis of three different terpenes (α-pinene, β-pinene, and β-caryophyllene) with malonic and oxalic acids. Our experimental results demonstrate that these reactions efficiently produce the expected accretion products, though with apparent variations in yields depending on the specific terpene and acid involved. To our knowledge, these are the first direct gas-phase observations of expected adducts from terpene-derived sCIs and carboxylic acids, paving the way for a better understanding of the importance and atmospheric implications of these reactions, especially in terms of aerosol-forming capabilities of these large product molecules.
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RC1: 'Comment on egusphere-2024-3323', Anonymous Referee #1, 13 Nov 2024
The authors describe ozonolysis experiments to characterize accretion products from stabilized Criegee intermediate reactions with malonic acid and oxalic acid, and they further couple these results with field measurements that suggest evidence of the reactions occurring in the troposphere. This is a valuable contribution to understanding the range and the atmospheric impact of carbonyl oxide reactions. I have some questions and suggestions for the authors:
First, there are two kinds of yields being discussed in lines 177 on, and the relationship between the two is somewhat confusing. There is the yield of the accretion product in the ozonolysis, and there is the (inferred) yield of the stabilized Criegee intermediate in the ozonolysis. These two are related in these experiments by a third yield -- the branching to the accretion product in the elementary reaction of the Criegee intermediate with the acid -- and by competing kinetic processes in the system (as described in the manuscript). I think I figured it all out, but maybe some clarifying nomenclature and a few explanatory equations would make it easier.
Second, I don’t understand the explanation that is given for the anomalous behavior of the CH2OO reactions from the β-caryophyllene ozonolysis. The manuscript states that “these species” are semi-volatile and so the concentration doesn’t respond rapidly to changes in the ozonolysis rate. But what are “these species”? If they are the accretion products of CH2OO with the acids, why don’t these same compounds show that behavior when β-pinene ozonolysis is their source? Maybe I don’t understand the experiment completely -- can it be explained more clearly?
Finally, from a fundamental physical chemistry point of view, it is not unexpected that these reactions would be rapid and that there would be significant branching to the stabilized product, as is supported by the computation in the supplement. The authors report CIMS measurements at Hyytiälä, which are suggestive of a detectable contribution of these reactions in the boreal forest. For other field measurements where potential signatures of similar Criegee intermediate – acid chemistry were detected (Caravan et al., Nat. Geosci. 17, 219–226 (2024)), the best estimates of the relevant emission inventories and gas phase kinetics were insufficient to explain the concentrations observed in the field. If the C11-C13 species in Figure S9 were attributable to Criegee accretion reactions, do the authors have an idea how close the kinetics of the present reactions would come to describing their field observations?
In addition I noticed some small typographical issues -- the Ahrens et al. reference seems to have become garbled; the rate coefficients in Table S2 are referred to as "rates" and have incorrect units.
Citation: https://doi.org/10.5194/egusphere-2024-3323-RC1 -
RC2: 'Comment on egusphere-2024-3323', Anonymous Referee #2, 15 Nov 2024
The authors present a study of the products formed in a flow reactor during the ozonolysis of a-pinene, b-pinene, and b-caryopyllene in the presence of the dicarboxylic acids malonic acid and oxalic acid using nitrate ion chemical ionisation mass spectrometry. Re-analysis of previously reported work on the ozonolysis of kaurene is also presented in light of recent work.
The paper is well presented and will be of interest to the community. I have only minor comments that should be addressed prior to publication.
Line 50: Are there any direct gas-phase observations of larger SCIs that can be discussed here?
Line 52 (and more generally): It would be helpful to include a figure, perhaps in the supplementary material, that shows the structures for the key species (such as kaurene) being discussed.
Line 60: How do the ambient concentrations of malonic acid and oxalic acid compare to other organic acids? Which organic acids are most likely to be encountered by Criegee intermediates derived from terpenes in the atmosphere?
Line 93: It would be helpful to include a brief description of the calculations in the main text as well as providing detailed information in the supplementary information.
Line 96: ‘L. Vereecken’ to ‘Vereecken’.
Line 101: ‘found in the Supplementary’ to ‘found in the Supplementary Information’.
Line 102: ‘Gibbs free energy’ to ‘Gibbs free energies’.
Line 120 (and elsewhere): ‘syn’ and ‘anti’ should be italicised.
Line 205: It would be helpful to highlight the information provided in the supplementary information here.
Line 240 onwards: Are there any links that can be made with measurements reported in other work in other locations? For example, the results reported by Caravan et al. (and highlighted in the other review).
There are some formatting issues with the references.
Citation: https://doi.org/10.5194/egusphere-2024-3323-RC2
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