Preprints
https://doi.org/10.5194/ar-2025-30
https://doi.org/10.5194/ar-2025-30
30 Sep 2025
 | 30 Sep 2025
Status: this preprint is currently under review for the journal AR.

Effect of humidity on the first steps of atmospheric new particles formation: Computational study of hydrated molecular clusters

Ivo Neefjes, Yosef Knattrup, Haide Wu, Georg Baadsgaard Trolle, Jonas Elm, and Jakub Kubečka

Abstract. To improve computational modeling of hydrated atmospheric molecular clusters, we systematically evaluated quantum-chemical methods for predicting accurate structural and energetic properties of clusters containing a variety of atmospherically relevant acids and bases, with up to five water molecules. We find that the commonly applied ωB97X-D/6-31++G(d,p) method with DLPNONormalPNO–CCSD(T0)/aug-cc-pVTZ electronic energy correction is suitable for hydrated clusters. Composite density functional methods such as B97-3c, r2SCAN-3c and ωB97X-3c are effective for pre-screening or modeling large clusters, while the local natural orbital approach LNO–CCSD(T)/aug′-cc-pVTZ is well-suited for accurate refinement due to its low memory requirements, high accuracy, and favorable computational scaling. Nevertheless, the ωB97X-3c method has a reasonable accuracy even without the electronic energy correction.

We also assessed thermochemical corrections beyond the conventional harmonic oscillator approximation applied only to the lowest free-energy structure. For the limiting cases of no corrections and the ideal maximum corrections, we calculated hydration distributions and particle formation rates, with a specific emphasis on sulfuric acid–ammonia (SA–AM), sulfuric acid–dimethylamine (SA–DMA), and methanesulfonic acid–methylamine (MSA–MA) clusters. Hydration of small clusters is generally limited, with only selected SA- and MSA-containing clusters showing substantial hydration. Due to the high water concentration in the atmosphere, hydration equilibrates fast, increasing the number of accessible states, and thus stabilizing clusters. However, its effect on cluster formation and new particle formation is highly system dependent.

MSA–MA particle formation rates are more sensitive to hydration than those of SA–AM or SA–DMA, though the enhancement remains modest. Despite being more hydrated than SA–DMA clusters, MSA–MA clusters form new particles at relatively low rates, comparable to SA–AM. Under typical atmospheric conditions, SA–DMA is expected to dominate new particle formation, even at high humidity.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Aerosol Research. The authors have no other competing interests to declare.

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.
Share
Ivo Neefjes, Yosef Knattrup, Haide Wu, Georg Baadsgaard Trolle, Jonas Elm, and Jakub Kubečka

Status: open (until 11 Nov 2025)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
Ivo Neefjes, Yosef Knattrup, Haide Wu, Georg Baadsgaard Trolle, Jonas Elm, and Jakub Kubečka

Data sets

neefjes25_hydration Ivo Neefjes et al. https://github.com/elmjonas/ACDB/tree/master/Articles/neefjes25_hydration

Model code and software

JKCS 2.1 Jakub Kubečka https://github.com/kubeckaj/JKCS2.1

Ivo Neefjes, Yosef Knattrup, Haide Wu, Georg Baadsgaard Trolle, Jonas Elm, and Jakub Kubečka

Viewed

Total article views: 53 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
43 8 2 53 9 0 0
  • HTML: 43
  • PDF: 8
  • XML: 2
  • Total: 53
  • Supplement: 9
  • BibTeX: 0
  • EndNote: 0
Views and downloads (calculated since 30 Sep 2025)
Cumulative views and downloads (calculated since 30 Sep 2025)

Viewed (geographical distribution)

Total article views: 54 (including HTML, PDF, and XML) Thereof 54 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 05 Oct 2025
Download
Short summary
We investigated how water vapor affects the earliest steps of atmospheric aerosol formation, a key process influencing clouds and climate. By benchmarking quantum-chemical methods, we identified reliable approaches for modeling hydrated molecular clusters of common atmospheric acids and bases. We show that humidity moderately stabilizes certain clusters but only modestly alters particle formation rates. These findings sharpen our understanding of clusters and their role in aerosol formation.
Share
Altmetrics