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Updated: Dec 17, 2025
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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
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Impact of Quantum Chemistry Parameter Choices and Cluster Distribution Model Settings on Modeled Atmospheric Particle
Vitus Besel1, Jakub Kubečka1, Theo Kurtén2
1University of Helsinki, Physicum, Gustaf Hällströmin Katu 2, 00560 Helsinki, Finland.
The Journal of Physical Chemistry. A
|June 23, 2020
Summary
Accounting for monomer symmetry significantly increases new particle formation rates in the sulfuric acid-ammonia system. Including quasi-harmonic corrections decreases rates and alters concentration dependence, improving model accuracy.
Area of Science:
- Atmospheric Chemistry
- Aerosol Science
- Computational Chemistry
Background:
- New particle formation (NPF) is a key process in atmospheric aerosol science, influencing climate and air quality.
- Accurate prediction of NPF rates requires sophisticated modeling that incorporates chemical and physical parameters.
- Previous models often simplified or omitted certain physical considerations, potentially leading to inaccuracies.
Purpose of the Study:
- To investigate the influence of various physical parameters on new particle formation rates in the sulfuric acid-ammonia system.
- To refine the Atmospheric Cluster Dynamics Code (ACDC) by incorporating advanced quantum chemistry and simulation techniques.
- To improve the agreement between model predictions and experimental data from atmospheric chambers.
Main Methods:
- Utilized quantum chemistry calculations and cluster distribution dynamics simulations (ACDC).
- Systematically evaluated the impact of monomer rotational symmetry numbers, cluster symmetry, and quasi-harmonic corrections.
- Assessed the influence of maximum cluster size and boundary conditions on simulated NPF rates.
Main Results:
- Consistent consideration of monomer rotational symmetry numbers significantly increased predicted NPF rates.
- Quasi-harmonic corrections for low-frequency vibrational modes generally decreased NPF rates and altered their dependence on sulfuric acid concentration.
- Improved agreement was observed with Cosmics Leaving OUtdoor Droplets (CLOUD) chamber data when using new input data and corrections.
Conclusions:
- Accurate representation of monomer symmetry is crucial for predicting sulfuric acid-ammonia NPF rates.
- Quasi-harmonic corrections are essential for capturing the correct concentration dependence of NPF.
- The refined ACDC model with updated inputs and corrections provides a more accurate representation of atmospheric NPF.
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