Sulfuric acid and amines in atmospheric clustering : first-principles investigations

The physical phenomena involving minuscule atmospheric aerosol particles pose many important and currently unresolved questions. The research presented in this doctoral dissertation concentrates on one of the most fundamental of these questions: where do the smallest particles come from? This thesis investigates the very first steps of new-particle formation, that is, atmospherically relevant molecular clustering. The main tools used in the research were electronic structure calculations and first-principles molecular dynamics simulations basically, applied quantum mechanics. The lead role in the presented cluster studies is played by sulfuric acid. Sulfuric acid is known to correlate well with the aerosol particle formation observations in most locations. However, it is further known that sulfuric acid alone cannot be responsible for the ambient observations. In the past, various formation mechanisms to explain the observations have been suggested, most popular being those involving some combination of water, ammonia, oxidized organics or ions together with sulfuric acid. Although all of these agents have a stabilizing effect on the clustering of sulfuric acid, in general the magnitude of the stabilization is too weak to account for most of the atmospheric measurements. In this thesis, the role of various amine compounds (especially that of dimethylamine) in sulfuric acid driven clustering is investigated. Amines are some of the few basic compounds that are known to exist in the atmosphere. According to the electronic structure calculations, amines stabilize the smallest sulfuric acid clusters much more strongly than the earlier standard candidate ammonia. Further calculations suggest that dimethylamine also enhances the growth of the small clusters with respect to sulfuric acid much more effectively than am- monia. Based on the electronic structure calculations, the stabilizing effect of the amines is strong enough, so that even relatively small concentrations can be expected to significantly enhance the sulfuric acid driven new-particle formation. This theoretical prediction has later been confirmed experimentally. The dynamics and stability of the small sulfuric acid and dimethylamine clusters were further studied by first-principles molecular dynamics simulations. In equilibrium, the clusters exhibited pronounced thermal molecular motion, which was observed to be anharmonic. Direct collision simulations revealed rich dynamical behavior, leading to cluster structures differing from both the equilibrium simulations and the static electronic structure calculations. The performed first-principles molecular dynamics simulations demonstrate that the method is well fitted to investigate the atmospheric molecular clustering, and suggest that in future formation free energy calculations, the entropic contributions merit a more detailed treatment.

Grantor dc:publisher

Helsingin yliopisto

Year dc:date.issued

2014

Author dc:creator

• Loukonen, Ville

• teoreettinen fysiikka

Statement dc:rights

• Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
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Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/10138/44951

OAI record oai:identifier

https://helda.helsinki.fi/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Ahelda.helsinki.fi%3A10138%2F44951