Ethylamine-Driven Amination of Organic Particles: Mechanistic Insights via Key Intermediates Identification

Liu, Peiqi; Gao, Jigang; Hu, Yulong; Yuan, Wenhao; Zhou, Zhongyue; Qi, Fei; Zeng, Meirong

doi:https://doi.org/10.5194/egusphere-2025-4260

Preprints

https://doi.org/10.5194/egusphere-2025-4260

Preprints

16 Sep 2025

| 16 Sep 2025

Ethylamine-Driven Amination of Organic Particles: Mechanistic Insights via Key Intermediates Identification

Peiqi Liu, Jigang Gao, Yulong Hu, Wenhao Yuan, Zhongyue Zhou, Fei Qi, and Meirong Zeng

Abstract. Atmospheric amines critically contribute to secondary aerosols formation via heterogeneous reactions, yet the molecular mechanisms governing heterogeneous amination chemistry of aerosols remain unclear. Here, we utilize an integrated tandem flow-tube system coupled with online ultrahigh-resolution mass spectrometry to elucidate the amination chemistry of ethylamine (EA) with representative organic aerosol components, including C₂₀-C₅₄ secondary ozonides (SOZs), C₁₇-C₂₇ carboxylic acids, and aldehydes. Our experiments provide evidence for the formation of four key intermediates: hydroxyl peroxyamines, amino hydroperoxides, peroxyamines, and amino ethers, which mediate SOZs conversion to hydroxyimines, amides, and imines. Furthermore, dihydroxylamines and hydroxylamines are identified as characteristic intermediates in carboxylic acids and aldehydes amination. Quantitative heterogeneous reactivity measurements (Δγ_eff) reveal that SOZs exhibit a pronounced inverse dependence on carbon chain length, e.g., C₂₁ SOZ (Δγ_eff = 1.0 × 10^-4) > C₄₉ SOZ (Δγ_eff = 5.7 × 10^-6), with consistently lower reactivity than acids and aldehydes, e.g., C₁₇ acid (Δγ_eff = 2.3 × 10^-4). The amination mechanism of SOZs is initiated by EA addition, followed by either hydroxyl peroxyamines-mediated dehydration yielding hydroxyimines and amides, or amino hydroperoxides-driven H₂O₂ elimination forming imines. For carboxylic acids and aldehydes, EA addition leads to dihydroxylamines and hydroxylamines formation, which subsequently dehydrate to produce amides and imines. These findings provide a mechanistic framework for understanding amine-driven aerosol aging processes that affects atmospheric chemistry, air quality, and climate systems.

Received: 31 Aug 2025 – Discussion started: 16 Sep 2025

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

Download & links

Preprint (PDF, 1800 KB)

Supplement (11954 KB)

Download & links

Preprint (1800 KB)
Metadata XML
Supplement (11954 KB)
BibTeX
EndNote

Peiqi Liu, Jigang Gao, Yulong Hu, Wenhao Yuan, Zhongyue Zhou, Fei Qi, and Meirong Zeng

Status: final response (author comments only)

RC1:
'Comment on egusphere-2025-4260', Anonymous Referee #1, 10 Oct 2025
This paper investigated the heterogeneous amination of ethylamine with three representative organic aerosols (SOZs, carboxylic acids, and aldehydes). A tandem flowtube reactor coupled with online APPI-HRMS was employed to elucidate the ethylamine-driven amination chemistry. The identification of key intermediates and the proposal of novel reaction pathways provide valuable mechanistic insights. Quantification of differential effective uptake coefficients across a wide range of carbon chain lengths for SOZs and carbonyls is particularly valuable for advancing atmospheric chemistry models. The manuscript is well-written, and conclusions are well-supported by the experimental data. I recommend this work for publication, and some minor comments can be considered.
In the introduction, the authors justify the use of squalene as a model system. However, a brief statement for selecting ethylamine as the model amine, compared to more commonly studied amines (e.g., ammonia or dimethylamine), can be helpful. Is it due to its atmospheric relevance, reactivity, or as a simpler model for primary amines?

The use of APPI-HRMS is critical to the identification of intermediates and products. To facilitate a better assessment of the methodology, it is suggested to provide key instrumental parameters in the supplementary information. These should include, but not be limited to: the ionization mode used (positive/negative), mass resolution, mass range scanned, and vaporizer temperature.

The mass spectrum in Figure 3b would be more clearly distinguishable if the different product classes (adducts, -H₂O, -H₂O₂) were labeled with different colors or symbols directly on the spectrum.

The identification of the four key intermediates is a core finding of this work. For clarity, it is suggested to add a simplified schematic flowchart, either in Figure 4 or as a supplementary figure, to summarize the competing pathways and subsequent consumption pathways. This would facilitate visualization of the complex reaction network.

For the newly proposed intermediates (peroxyamines and amino ethers), it is suggested to provide their exact mass and compare them with the experimentally observed m/z values in a supplementary table. Listing representative intermediates and products observed for each SOZ in this table can provide additional evidence for their identification.

Technical corrections:
There are inconsistencies in the terminology used for differential effective uptake coefficients, which are sometimes wrriten as “∆γ_eff” and sometimes abbreviated as “∆γ”.

Line 203, “see Sect. 3.2 for mechanistic details,” but the mechanistic details are in Sect. 3.3. Please correct it.

Line 254, “has be demonstrated”, this should be correct to “has been demonstrated”

Line 268, “C₃₂O₅₅O₂N (peroxyamine)” should be corrected to C₃₂H₅₅O₂

Line 269, “C₃₂O₅₇O₃N” should be corrected to C₃₂H₅₇O₃
Citation: https://doi.org/10.5194/egusphere-2025-4260-RC1
RC2: 'Comment on egusphere-2025-4260', Anonymous Referee #2, 13 Oct 2025

This manuscript presents a mechanistic study of the heterogeneous reactions between ethylamine and SOZs (carboxylic acids and aldehydes) by using the flowtube reactor coupled with online APPI-HRMS. The direct identification of featured intermediates enables the proposal of a comprehensive amination mechanism. The quantitative measurement of effective uptake coefficients of the organic aerosols upon ethylamine exposure provides valuable data for understanding the evolution of atmospheric aerosols. I recommend publication of this work with minor revisions.

1. It is suggested to provide the material of the tandem flow-tube (e.g., Pyrex, stainless steel).

2. The range of O3 concentration is not mentioned in the paper. It is suggested that this parameter be clarified, as it is critical for the SOZ formation.

3. A supplementary table, listing values of γeff,2FT and γeff,1FT for representative SOZs, carboxylic acids, and aldehydes, can be useful to add.

4. The curves for different intermediates (e.g., dihydroxylamine vs. hydroxylamine) in Figure 6 are distinguished only by color. Adding distinct symbol types would improve the clarity of the figure.

5. It seems that the caption for Figure 6 mentions “Relative abundance”, which does not align with the y-axis label “Signal (arb. unit)”. Please update the caption to ensure the consistency between the figure and its description.

6. Line 30, the phrase “initiates through the nucleophilic attack” should be grammatically expressed as “is initiated by a nucleophilic attack”.

7. Line 38, “ethylamine and on a C15 SOZ” contains a superfluous conjunction. For clarity, this should be corrected to “ethylamine on a C15 SOZ”.

8. Line 116-117, the sentence “the net contribution of heterogeneous reactions… were quantitatively determined” has a subject-verb agreement error. Please correct it to “the net contribution... was quantitatively determined.”

9. Check the capitalization style of the article titles in the references. It seems that there is an inconsistency in the use of capitalization, specifically regarding sentence case vs. title case. It is recommended to standardize the format according to the journal's guidelines.

10. Both relative humidity and pH are critical factors influencing the heterogeneous reactions involving amines. Thus, if the reaction system has recorded humidity and pH data, it is advisable to explicitly state them in the manuscript.

Citation: https://doi.org/10.5194/egusphere-2025-4260-RC2

Peiqi Liu, Jigang Gao, Yulong Hu, Wenhao Yuan, Zhongyue Zhou, Fei Qi, and Meirong Zeng

Supplement

https://doi.org/10.5194/egusphere-2025-4260-supplement

Peiqi Liu, Jigang Gao, Yulong Hu, Wenhao Yuan, Zhongyue Zhou, Fei Qi, and Meirong Zeng

Viewed

Total article views: 1,852 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	Supplement	BibTeX	EndNote
1,789	52	11	1,852	19	9	8

HTML: 1,789
PDF: 52
XML: 11
Total: 1,852
Supplement: 19
BibTeX: 9
EndNote: 8

Views and downloads (calculated since 16 Sep 2025)

Month	HTML	PDF	XML	Total
Sep 2025	1,681	7	6	1,694
Oct 2025	108	45	5	158

Cumulative views and downloads (calculated since 16 Sep 2025)

Month	HTML	PDF	XML	Total
Sep 2025	1,681	7	6	1,694
Oct 2025	108	45	5	158

Viewed (geographical distribution)

Total article views: 1,704 (including HTML, PDF, and XML) Thereof 1,704 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 30 Oct 2025

Short summary

This study examines ethylamine reactions with organic aerosols, showing secondary ozonides react more slowly than carboxylic acids or aldehydes, with decreasing reactivity as carbon chains lengthen. Advanced techniques revealed key intermediates (hydroxyl peroxyamines, amino hydroperoxides) and novel pathways, establishing a quantitative framework linking molecular processes to aerosol aging for atmospheric chemistry models.


Total:	0
HTML:	0
PDF:	0
XML:	0