the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jun 2025
Chloric Acid-Driven Nucleation Enhanced by Dimethylamine and Sulfuric acid in the Arctic: Mechanistic Study
Abstract. Chlorine radicals are strong oxidizing agents in the atmosphere, and the process of chlorine oxidation results in the formation of chloric acid (HClO3, CA). Recent studies have shown that CA is prevalent in the Arctic boundary layer. However, the contribution of chlorine-containing species to oceanic new particle formation (NPF) has not been fully revealed. It is expected that CA is involved in the oceanic nucleation process. In this study, the enhancement of CA-based NPF by dimethylamine (DMA) and sulfuric acid (SA) was comparatively investigated at the molecular level using density-functional theory (DFT) and atmospheric cluster dynamics simulation (ACDC). The results show that DMA can form clusters with CA through hydrogen bonding, halogen bonding and proton transfer, which reduces the energy barrier for CA-based cluster formation and significantly improves the thermodynamic stability of CA clusters. The cluster formation rate of CA-DMA cluster system is higher than that of the CA-SA cluster system. The CA-DMA cluster system in the Arctic atmosphere contributes to NPF. These findings may help to reveal some of the missing sources of the Arctic NPF. The present study contributes to a deeper understanding of the influence of oceanic chlorine-containing constituents on the oceanic NPF.
- Preprint
(1190 KB) - Metadata XML
-
Supplement
(2705 KB) - BibTeX
- EndNote
Status: open (until 07 Aug 2025)
-
CC1: 'Comment on egusphere-2025-861', James Brean, 27 Jun 2025
reply
This manuscript presents simulations of the clustering of chloric acid (CA) with dimethylamine (DMA), and of CA with sulfuric acid (SA), using quantum chemical methods. While the modelling appears technically sound, I see two substantial issues with the framing and interpretation of the results.
First, the manuscript lacks a clear connection to Arctic atmospheric chemistry, despite suggesting relevance to this region in the title. There are no Arctic measurements presented, and beyond a brief reference to Tham et al., the discussion does not engage meaningfully with existing observations or constraints in polar environments. I am not sure the word “Arctic” belongs in the title nor abstract. However, as there are observations of chloric acid in the Arctic, it does indeed belong in the discussion.
Second, some of the conclusions appear overstated given the results. For example, the abstract states: “It is expected that CA is involved in the oceanic nucleation process,” but to my knowledge, no direct evidence currently supports this. The comparison between CA–DMA and CA–SA cluster formation rates in the abstract is also slightly misleading in my view, as CA–SA is not thought to form clusters efficiently, and a comparison with more atmospherically relevant systems (SA-DMA, HIO3-DMA) would provide more meaningful context, especially as the former of these has good experimental evidence. Similarly, the statement that “the CA–DMA cluster system in the Arctic atmosphere contributes to NPF” seems premature. In Figure 3, the evaporation rate of (CA)3(DMA)3 clusters is many orders of magnitude higher than that reported by other authors for (SA)3(DMA)3, and in Figure 4 it is only at temperatures of 238 K (roughly the north pole in the dead of winter) and DMA of 100 ppt (more than is typically observed in the middle of a city) that the authors simulate nucleation rates of ~1 /cm3 s. These conditions are unlikely to co-occur in the Arctic boundary layer (although there are likely some measurements of DMA in these regions, it's more likely ~1 pptv than 100).
The manuscript would benefit from focusing on the finding that chloric acid is unlikely to contribute to new particle formation under tropospheric conditions. This negative result is still valuable, as it helps narrow the range of plausible NPF mechanisms and guides future work.
Citation: https://doi.org/10.5194/egusphere-2025-861-CC1 -
RC1: 'Comment on egusphere-2025-861', Anonymous Referee #1, 14 Jul 2025
reply
Wang et al. comparatively studied chloric acid (CA)-based nucleation enhanced by dimethylamine (DMA) and sulfuric acid (SA) in the Arctic oceanic atmosphere. The manuscript uses quantum chemistry calculations combined with ACDC simulations to obtain the cluster thermodynamic data, nucleation rate and cluster growth pathway. A main finding is that the nucleation rate of CA-DMA system is higher than that of the CA-SA system and CA-DMA nucleation contributes to new particle formation (NPF) in the Arctic. This is currently a hot research topic relevant to the contribution of chlorine-containing species to marine NPF. The provided descriptions and figures support the results. After the authors address the following comments and questions, I will recommend the manuscript for publication.
(1) Introduction: There is no description about the relevance of chlorine cycle and chloric acid. The sources of chloric acid should be discussed.
(2) How did the authors obtain the global minima of (CA)1-4 clusters? Please provide the configurations of (CA)1-4 in the Figure 1.
(3) What is the boundary clusters of CA-SA system?
(4) Line 220, What is PA? PA is not above-mentioned. If the authors also investigated the CA-PA nucleation mechanism in this study, please provide the relevant descriptions in the preceding sections.
(5) As shown in Figures 4 and 5a, J seems to be lower at 258.15 K than that at 278.15 K, which is in contrast with the description “the decrease in temperature further increases the J value of the CA-DMA cluster system to a higher level”. Please check and explain this.
(6) Line 231 and Figure 5b, in my opinion, the Arctic atmosphere is relatively pristine, therefore, I question whether [DMA] can reach 10 ppt. If the actual [DMA] is very low in the Arctic, CA-DMA nucleation may not effectively contribute to Arctic NPF based on the J values of Figure 5b.
(7) Figure 6 shows the growth paths of CA-DMA system at 278.15 K, [CA] = 106 cm-3 and [DMA] = 1 ppt. However, the absolute J of CA-DMA is very low (10-13 cm-3 s-1) at this condition. I think the authors should mainly study the growth path at the condition that J is efficient, e.g. at 238.15 K and high precursor concentration.
(8) All the figures in the SI should be explained in the manuscript, otherwise readers may find it difficult to understand the necessity of including such materials in the SI.
(9) Many minor mistakes are shown in the manuscript, e.g., line 47, formatting error in the reference citation, “O’ dowdg”; lines 110-111, grammatical error, “based on the ωB97X-D/6-31++G(d,p) theory level is performed on the geometry”; line 159, “CA atom” should be “Cl atom”; line 157, “O-O...O-Cl” should be “O-Cl...O-Cl” et al. The authors should totally and carefully recheck the whole manuscript and correct all the mistakes.
(10) Some sentences are redundant and some expression is unclear and unnecessarily verbose in the manuscript, e.g., lines 117-119, “The free energy of formation (ΔG) of individual clusters is calculated at different temperatures 238, 258, and 278 K.” or “The ΔG of individual clusters is calculated at different temperatures.” should be deleted; lines 185-188, “The smaller value of ∑γ means that the stability of CA-DMA clusters is higher and the clusters shrink further.” or “The smaller value of ∑γ implies the higher stability of CA-DMA clusters and further contraction of the clusters.” should be deleted; lines123-125 and lines 127-129, Two sentences can be summarized to one sentence; lines 126, “……the experimental results obtained using the birth and death equations” is incorrect since birth-death equations is used to obtain ACDC simulation results rather than experimental results. Please carefully recheck the whole manuscript, delete the redundant sentences and rewrite the inappropriate expression.
Citation: https://doi.org/10.5194/egusphere-2025-861-RC1
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 109 | 18 | 10 | 137 | 8 | 7 | 7 |
- HTML: 109
- PDF: 18
- XML: 10
- Total: 137
- Supplement: 8
- BibTeX: 7
- EndNote: 7
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1