the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jun 2025
NH3 Converts Criegee Intermediates to Nitrogenous Organics
Abstract. Ammonia (NH3), the dominant alkaline gas in the atmosphere, plays a critical role in urban air quality, but its molecular-level interactions with organics remain poorly understood. Here, we uncover a hidden chemical pathway: NH3 efficiently scavenges stable Criegee intermediates (SCI) – critical radical in organic aerosol formation. Using high-resolution Orbitrap mass spectrometry, we capture the first real-time evidence of NH3 reacting with styrene-derived C7-SCI to form a hazardous peroxide amine (C7H9O2N) while suppressing traditional SCI-driven aerosol components like benzoic acid and oligomers. Due to unstable bond of peroxide in the molecule, C7H9O2N can further decompose into more stable compounds (imine C7H7N and amide C7H7ON). This study discovered a critical reaction pathway for the formation of organic amines through the reaction of NH3 and SCI, which not only bridges a critical gap in understanding NH3’s role in aerosol chemistry but also exposes a previously overlooked health risk from nitrogen-enriched particulate matter.
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RC1: 'Comment on egusphere-2025-2240', Anonymous Referee #1, 18 Jul 2025
The authors present a study of styrene ozonolysis in the presence of ammonia, and report the suppression of SOA formation in the presence of ammonia and observations of species that indicate reactions of stabilised Criegee intermediates with ammonia.
The authors present some interesting results, but the manuscript is generally lacking in detail. At present the manuscript does little more than present observations. Real-time measurements are referred to, which indicate the potential to determine reaction kinetics, but none are reported. It would be beneficial to at least report timescales/kinetics for production of the species observed and, ideally, estimated yields that could be used in atmospheric models. The manuscript should be significantly improved prior to publication to include further details of the experiments and more comprehensive description of the analysis and modelling of results.
Other comments are listed below:
Line 14: Criegee intermediates should be more correctly referred to as zwitterions than radicals.
Line 17: What is the expected atmospheric lifetime of the species C7H9O2N?
Line 35: What are typical emission rates or atmospheric concentrations of styrene in urban/industrial regions? How significant is the atmospheric loss of styrene to reaction with ozone compared to the reaction with OH?
Line 37: It would help to give the structures of the Criegee intermediates (and for other species discussed in the manuscript).
Line 52: Define FEP.
Line 54: What were the typical concentrations/concentration ranges used in the experiments?
Line 75: It would help to provide more details of the experimental procedures and conditions in the main text. Which species were measured? What was the timescale for the measurements?
Line 92: How certain is the mechanism for benzoic acid formation? It would help to show a schematic of the mechanism. Is there any evidence for combined effects of ammonia and water? Studies of Criegee intermediate kinetics using photolytic precursors have demonstrated cooperative effects of water and ammonia on Criegee intermediate chemistry (e.g. Chao et al., J. Phys. Chem. A, 123, 1337-1342, 2019).
Line 140: What is ‘the general decomposition principle of peroxides’? References and details are needed here. What is known about the stability of the species being discussed?
Citation: https://doi.org/10.5194/egusphere-2025-2240-RC1 -
RC2: 'Comment on egusphere-2025-2240', Anonymous Referee #2, 09 Sep 2025
Li et al. have utilized Orbitrap mass spectrometry to examine the products from the ozonolysis of styrene in the presence vs. absence of ammonia. In the presence of ammonia, the authors report the formation of a peroxide amine, which they attribute to the reaction of ammonia with the styrene-derived 7-carbon Criegee intermediate. They observe a reduction in other products that they attribute to Criegee intermediate-driven SOA formation, such as benzoic acid. This study provides new mechanistic insights on the potential contribution for ozonolysis driven intermediates to contribute to the formation of tropospheric SOA, but requires significant edits for clarity and accuracy. Comments and recommended edits follow:
Line 33: There have been several studies published on the reactions of Criegee intermediates with ammonia and amines that were conducted prior to the previous study by these authors which should be cited:
S. Jørgensen, A. Gross, Theoretical Investigation of the Reaction between Carbonyl Oxides and Ammonia, JPCA (2009).
Liu, C. Yin, M. C. Smith, S. Liu, M. Chen, X. Zhou, C. Xiao, D. Dai, J. J.-M. Lin, K. Takahashi, W. Dong, X. Yang, Kinetics of the reaction of the simplest Criegee intermediate with ammonia: a combination of experiment and theory, PCCP (2018).
J. P. Misiewicz, S. N. Elliott, K. B. Moore, H. F. Schaefer, Re-examining ammonia addition to the Criegee intermediate: converging to chemical accuracy, PCCP (2018).
W. Chao, C. Yin, K. Takahashi, J. J. M. Lin, Effects of water vapor on the reaction of CH2OO with NH3, PCCP (2019).
R. Chhantyal-Pun, R. J. Shannon, D. P. Tew, R. L. Caravan, M. Duchi, C. Wong, A. Ingham, C. Feldman, M. R. McGillen, M. A. H. Khan, I. O. Antonov, B. Rotavera, K. Ramasesha, D. L. Osborn, C. A. Taatjes, C. J. Percival, D. E. Shallcross, A. J. Orr-Ewing, Experimental and computational studies of Criegee intermediate reactions with NH3 and CH3NH2. PCCP (2019).
Line 53 (and line 14 of the SM): define FEP.
Line 55: Please provide concentration ranges of styrene, O3, and NH3 used.
Line 72 (and SM Line 46): Which unimolecular and bimolecular reactions of the styrene-derived Criegee intermediates were included in the mechanism aside from the reaction with NH3?
Line 78: Do you use SOA yield to refer to SOA total mass, or number of particles?
Line 78: What are the uncertainties on your reported 4.9% yield of SOA?
Line 80: Provide the ranges of reported SOA yields for the studies cited to demonstrate that these are in line with the current work.
Line 83: Suggest rephrasing “breaks up” with “competes with” or similar for clarity.
Line 89: Do you see any evidence in the mass spectra for the sequential insertion of the 1 and/or 7 carbon Criegee intermediates into the initial peroxide amine reaction product (e.g., oligomerization).
Line 92: Please provide a reference for a study that demonstrates the formation of benzoic acid from the C7 Criegee intermediate with water.
Line 95: Do you see any evidence for the water-mediated enhancement of the Criegee intermediate reaction with ammonia in your experiments, as reported by the Lin group? (I imagine that the MCM mechanism you are using in your analysis doesn’t include this process):
W. Chao, C. Yin, Y.-L. Li, K. Takahashi, J. J.-M. Lin, Synergy of Water and Ammonia Hydrogen Bonding in a Gas-Phase Reaction, JPCA (2019)
W. Chao, C. Yin, K. Takahashi, J. J.-M. Lin, Effects of water vapor on the reaction of CH2OO with NH3, PCCP (2019)
Figure1 (upper): please add error bars.
Figure 1 (middle): Are there any mass peaks which do not have changes in intensity in the presence vs absence of ammonia?
Figure 1(lower): Please can you explain the rationale for changing the concentration of both ammonia and water in the red vs. blue datasets, rather than keeping one of the co-reactant concentrations the same.
Line 112: Please cite the (aforementioned) papers prior to the 2024 Li et al. work where the reaction mechanism for the reaction of Criegee intermediates with ammonia has been deduced.
Line 127: Please provide details of the iodometry kinetics measurements in Section 2.
Figure 2 (a-g): Changing between labelling the (detected) protonated m/z and the (actual) product m/z in these figures is confusing. Perhaps the labelling can be made clearer, for example in (g) by providing both the actual molecular mass, and the mass at which the molecule was detected.
Figure 2(g): Oligomers in the context of Criegee intermediates typically mean products that result from the insertion of several Criegee intermediate molecules into a single co-reactant molecule, via sequential reactions. I believe that you are here referring to products resulting from the self-reaction(s) of Criegee intermediates, and so this distinction should be clearly made.
Line 139: Peroxides have been detected in both laboratory studies and in the field in the gas phase. Why do you think that this peroxide amine (which you detect here) would not survive under atmospherically relevant conditions? Please provide references for your proposed decomposition mechanism for this peroxide under atmospherically relevant conditions.
Lines 149-150: Please provide supporting references that the C7 Criegee intermediates definitively lead to the formation of SOA via benzoic acid and oligomers, or adjust your statement accordingly.
Line 151: You state that the peroxide amine will ‘rapidly’ decompose to an imine and amide, but you detect the peroxide amine in the present work. Given your experimental conditions, can you determine a lower limit of the lifetime of the peroxide amine?
Line 163: Does your analysis account for the nucleation of peroxide amines onto existing particles, or just for new particle formation?
General comment: it is unclear in the manuscript which species were detected in the gas or particle phase.
SM Line 22: Please provide concentration of n-hexane used for OH scavenging.
Citation: https://doi.org/10.5194/egusphere-2025-2240-RC2
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