Role of base strength, cluster structure and charge in sulfuric-acid-driven particle formation

In atmospheric sulfuric-acid-driven particle formation, bases are able to stabilize the initial molecular clusters and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medi...

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Bibliographic Details
Published in:Atmospheric chemistry and physics 2019-08, Vol.19 (15), p.9753-9768
Main Authors: Myllys, Nanna, Kubečka, Jakub, Besel, Vitus, Alfaouri, Dina, Olenius, Tinja, Smith, James Norman, Passananti, Monica
Format: Article
Language:English
Subjects:
Abundance
Ammonia
Analysis
Atmospheric models
Atmospheric physics
Atmospheric research
Basicity
Guanidine
Kinetics
Low concentrations
Molecular clusters
Neutral particles
Organic chemistry
Particle formation
Protons
Quantum chemistry
Stabilizing
Sulfuric acid
Sulphuric acid
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Summary:In atmospheric sulfuric-acid-driven particle formation, bases are able to stabilize the initial molecular clusters and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medium strong (dimethylamine) and very strong (guanidine) bases as representative atmospheric base compounds, and we systematically investigate their ability to stabilize sulfuric acid clusters. Using quantum chemistry, we study proton transfer as well as intermolecular interactions and symmetry in clusters, of which the former is directly related to the base strength and the latter to the structural effects. Based on the theoretical cluster stabilities and cluster population kinetics modeling, we provide molecular-level mechanisms of cluster growth and show that in electrically neutral particle formation, guanidine can dominate formation events even at relatively low concentrations. However, when ions are involved, charge effects can also stabilize small clusters for weaker bases. In this case the atmospheric abundance of the bases becomes more important, and thus ammonia is likely to play a key role. The theoretical findings are validated by cluster distribution experiments, as well as comparisons to previously reported particle formation rates, showing a good agreement.
ISSN:1680-7324
1680-7316
1680-7324
DOI:10.5194/acp-19-9753-2019