Modeling the Binding Free Energy of Large Atmospheric Sulfuric Acid-Ammonia Clusters

Morten Engsvang; Jonas Elm

doi:10.1021/acsomega.1c07303

Modeling the Binding Free Energy of Large Atmospheric Sulfuric Acid-Ammonia Clusters

^*Corresponding author for this work

Department of Chemistry
iCLIMATE Aarhus University Interdisciplinary Centre for Climate Change - iCLIMATE Aarhus University Interdisciplinary Centre for Climate Change, Langelandsgade

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaper › Journal article › Research › peer-review

9 Citations (Scopus)

Abstract

Sulfuric acid and ammonia are believed to account for a large fraction of new-particle formation in the atmosphere. However, it remains unclear how small clusters grow to larger sizes, eventually ending up as stable aerosol particles. Here we present the largest sulfuric acid-ammonia clusters studied to date using quantum chemical methods by calculating the binding free energies of (SA)_n(A)_nclusters, with n up to 20. Based on benchmark calculations, we apply the B97-3c//GFN1-xTB level of theory to calculate the cluster structures and thermochemical parameters. We find that the cluster structures drastically evolve at larger sizes. We identify that an ammonium ion is fully coordinated in the core of the cluster at n = 7, and at n = 13 we see the emergence of the first fully coordinated bisulfate ion. We identify multiple ammonium and bisulfate ions that are embedded in the core of the cluster structure at n = 19. The binding free energy per acid-base pair levels out around n = 8-10, indicating that at a certain point the thermochemistry of the clusters converges toward a constant value.

Original language	English
Journal	ACS Omega
Volume	7
Issue	9
Pages (from-to)	8077-8083
Number of pages	7
ISSN	2470-1343
DOIs	https://doi.org/10.1021/acsomega.1c07303
Publication status	Published - 8 Mar 2022

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title = "Modeling the Binding Free Energy of Large Atmospheric Sulfuric Acid-Ammonia Clusters",

abstract = "Sulfuric acid and ammonia are believed to account for a large fraction of new-particle formation in the atmosphere. However, it remains unclear how small clusters grow to larger sizes, eventually ending up as stable aerosol particles. Here we present the largest sulfuric acid-ammonia clusters studied to date using quantum chemical methods by calculating the binding free energies of (SA)n(A)nclusters, with n up to 20. Based on benchmark calculations, we apply the B97-3c//GFN1-xTB level of theory to calculate the cluster structures and thermochemical parameters. We find that the cluster structures drastically evolve at larger sizes. We identify that an ammonium ion is fully coordinated in the core of the cluster at n = 7, and at n = 13 we see the emergence of the first fully coordinated bisulfate ion. We identify multiple ammonium and bisulfate ions that are embedded in the core of the cluster structure at n = 19. The binding free energy per acid-base pair levels out around n = 8-10, indicating that at a certain point the thermochemistry of the clusters converges toward a constant value.",

author = "Morten Engsvang and Jonas Elm",

note = "Funding Information: J.E. thanks the Independent Research Fund Denmark Grant 9064-00001B and the Swedish Research Council Formas project no. 2018-01745-COBACCA for financial support. The numerical results presented in this work were obtained at the Centre for Scientific Computing, Aarhus ( http://phys.au.dk/forskning/cscaa/ ). Publisher Copyright: {\textcopyright} 2022 American Chemical Society. All rights reserved.",

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PY - 2022/3/8

Y1 - 2022/3/8

N2 - Sulfuric acid and ammonia are believed to account for a large fraction of new-particle formation in the atmosphere. However, it remains unclear how small clusters grow to larger sizes, eventually ending up as stable aerosol particles. Here we present the largest sulfuric acid-ammonia clusters studied to date using quantum chemical methods by calculating the binding free energies of (SA)n(A)nclusters, with n up to 20. Based on benchmark calculations, we apply the B97-3c//GFN1-xTB level of theory to calculate the cluster structures and thermochemical parameters. We find that the cluster structures drastically evolve at larger sizes. We identify that an ammonium ion is fully coordinated in the core of the cluster at n = 7, and at n = 13 we see the emergence of the first fully coordinated bisulfate ion. We identify multiple ammonium and bisulfate ions that are embedded in the core of the cluster structure at n = 19. The binding free energy per acid-base pair levels out around n = 8-10, indicating that at a certain point the thermochemistry of the clusters converges toward a constant value.

AB - Sulfuric acid and ammonia are believed to account for a large fraction of new-particle formation in the atmosphere. However, it remains unclear how small clusters grow to larger sizes, eventually ending up as stable aerosol particles. Here we present the largest sulfuric acid-ammonia clusters studied to date using quantum chemical methods by calculating the binding free energies of (SA)n(A)nclusters, with n up to 20. Based on benchmark calculations, we apply the B97-3c//GFN1-xTB level of theory to calculate the cluster structures and thermochemical parameters. We find that the cluster structures drastically evolve at larger sizes. We identify that an ammonium ion is fully coordinated in the core of the cluster at n = 7, and at n = 13 we see the emergence of the first fully coordinated bisulfate ion. We identify multiple ammonium and bisulfate ions that are embedded in the core of the cluster structure at n = 19. The binding free energy per acid-base pair levels out around n = 8-10, indicating that at a certain point the thermochemistry of the clusters converges toward a constant value.

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Modeling the Binding Free Energy of Large Atmospheric Sulfuric Acid-Ammonia Clusters

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