Articles | Volume 4, issue 1
https://doi.org/10.5194/ar-4-1-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/ar-4-1-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
07 Jan 2026
Research article |
| 07 Jan 2026
| 07 Jan 2026
Thermodynamic benchmarking of hydrated atmospheric clusters in early particle formation
Ivo Neefjes
Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
Yosef Knattrup
Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
Georg Baadsgaard Trolle
Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
Jonas Elm
Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark
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Aerosol Research, 3, 237–251, https://doi.org/10.5194/ar-3-237-2025, https://doi.org/10.5194/ar-3-237-2025, 2025
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Aerosols, a large uncertainty in climate modeling, can be formed when gas vapors and particles begin sticking together. Traditionally, these particles are assumed to behave like hard spheres that only stick together upon head-on collisions. In reality, particles can attract each other over distances, leading to more frequent sticking events. We found that traditional models significantly undercount these events, with real sticking rates being up to 2.4 times higher.
Huan Yang, Ivo Neefjes, Valtteri Tikkanen, Jakub Kubečka, Theo Kurtén, Hanna Vehkamäki, and Bernhard Reischl
Atmos. Chem. Phys., 23, 5993–6009, https://doi.org/10.5194/acp-23-5993-2023, https://doi.org/10.5194/acp-23-5993-2023, 2023
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We present a new analytical model for collision rates between molecules and clusters of arbitrary sizes, accounting for long-range interactions. The model is verified against atomistic simulations of typical acid–base clusters participating in atmospheric new particle formation (NPF). Compared to non-interacting models, accounting for long-range interactions leads to 2–3 times higher collision rates for small clusters, indicating the necessity of including such interactions in NPF modeling.
Ivo Neefjes, Roope Halonen, Hanna Vehkamäki, and Bernhard Reischl
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Collisions between ionic and dipolar molecules and clusters facilitate the formation of atmospheric aerosol particles, which affect global climate and air quality. We compared often-used classical approaches for calculating ion–dipole collision rates with robust atomistic computer simulations. While classical approaches work for simple ions and dipoles only, our modeling approach can also efficiently calculate reasonable collision properties for more complex systems.
Yosef Knattrup, Ivo Neefjes, Jakub Kubečka, and Jonas Elm
Aerosol Research, 3, 237–251, https://doi.org/10.5194/ar-3-237-2025, https://doi.org/10.5194/ar-3-237-2025, 2025
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Aerosols, a large uncertainty in climate modeling, can be formed when gas vapors and particles begin sticking together. Traditionally, these particles are assumed to behave like hard spheres that only stick together upon head-on collisions. In reality, particles can attract each other over distances, leading to more frequent sticking events. We found that traditional models significantly undercount these events, with real sticking rates being up to 2.4 times higher.
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Galib Hasan, Haide Wu, Yosef Knattrup, and Jonas Elm
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Aerosol formation is an important process for our global climate. However, there are high uncertainties associated with the formation of new aerosol particles. We present quantum chemical calculations of large atmospheric molecular clusters composed of sulfuric acid (SA), ammonia (AM), and dimethylamine (DMA). We find that mixed SA–AM–DMA systems cluster more efficiently for freshly nucleated particles compared to pure SA–AM and SA–DMA systems.
Haide Wu, Yosef Knattrup, Andreas Buchgraitz Jensen, and Jonas Elm
Aerosol Research, 2, 303–314, https://doi.org/10.5194/ar-2-303-2024, https://doi.org/10.5194/ar-2-303-2024, 2024
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The exact point at which a given assembly of molecules represents an atmospheric molecular cluster or a particle remains ambiguous. Using quantum chemical methods, here we explore a cluster-to-particle transition point. Based on our results, we deduce a property-based criterion for defining freshly nucleated particles (FNPs) that act as a boundary between discrete cluster configurations and bulk particles.
Astrid Nørskov Pedersen, Yosef Knattrup, and Jonas Elm
Aerosol Research, 2, 123–134, https://doi.org/10.5194/ar-2-123-2024, https://doi.org/10.5194/ar-2-123-2024, 2024
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Aerosol formation is an important process for our global climate. While inorganic species have been shown to be important for aerosol formation, there remains a large gap in our knowledge about the exact involvement of organics. We present a new quantum chemical procedure for screening relevant organics that for the first time allows us to obtain direct molecular-level insight into the organics involved in aerosol formation.
Jonas Elm, Aladár Czitrovszky, Andreas Held, Annele Virtanen, Astrid Kiendler-Scharr, Benjamin J. Murray, Daniel McCluskey, Daniele Contini, David Broday, Eirini Goudeli, Hilkka Timonen, Joan Rosell-Llompart, Jose L. Castillo, Evangelia Diapouli, Mar Viana, Maria E. Messing, Markku Kulmala, Naděžda Zíková, and Sebastian H. Schmitt
Aerosol Research, 1, 13–16, https://doi.org/10.5194/ar-1-13-2023, https://doi.org/10.5194/ar-1-13-2023, 2023
Huan Yang, Ivo Neefjes, Valtteri Tikkanen, Jakub Kubečka, Theo Kurtén, Hanna Vehkamäki, and Bernhard Reischl
Atmos. Chem. Phys., 23, 5993–6009, https://doi.org/10.5194/acp-23-5993-2023, https://doi.org/10.5194/acp-23-5993-2023, 2023
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Atmos. Chem. Phys., 22, 13449–13466, https://doi.org/10.5194/acp-22-13449-2022, https://doi.org/10.5194/acp-22-13449-2022, 2022
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Sulfate aerosols have a strong influence on climate. Due to the reduction in sulfur-based fossil fuels, natural sulfur emissions play an increasingly important role. Studies investigating the climate relevance of natural sulfur aerosols are scarce. We study the water uptake of such particles in the laboratory, demonstrating a high potential to take up water and form cloud droplets. During atmospheric transit, chemical processing affects the particles’ composition and thus their water uptake.
Jingwen Xue, Fangfang Ma, Jonas Elm, Jingwen Chen, and Hong-Bin Xie
Atmos. Chem. Phys., 22, 11543–11555, https://doi.org/10.5194/acp-22-11543-2022, https://doi.org/10.5194/acp-22-11543-2022, 2022
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·OH/·Cl initiated indole reactions mainly form organonitrates, alkoxy radicals and hydroperoxide products, showing a varying mechanism from previously reported amines reactions. This study reveals carcinogenic nitrosamines cannot be formed in indole oxidation reactions despite radicals formed from -NH- H abstraction. The results are important to understand the atmospheric impact of indole oxidation and extend current understanding on the atmospheric chemistry of organic nitrogen compounds.
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Atmos. Chem. Phys., 22, 11155–11172, https://doi.org/10.5194/acp-22-11155-2022, https://doi.org/10.5194/acp-22-11155-2022, 2022
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Robin Wollesen de Jonge, Jonas Elm, Bernadette Rosati, Sigurd Christiansen, Noora Hyttinen, Dana Lüdemann, Merete Bilde, and Pontus Roldin
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This study presents a detailed analysis of the OH-initiated oxidation of dimethyl sulfide (DMS) based on experiments performed in the Aarhus University Research on Aerosol (AURA) smog chamber and the gas- and particle-phase chemistry kinetic multilayer model (ADCHAM). We capture the formation, growth and chemical composition of aerosols in the chamber setup by an improved multiphase oxidation mechanism and utilize our results to reproduce the important role of DMS in the marine boundary layer.
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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.
We investigated how water vapor affects the earliest steps of atmospheric aerosol formation, a...
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