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Surface-Active cis-Pinonic Acid in Atmospheric Droplets: A Molecular Dynamics Study
Stockholm University, Faculty of Science, Department of Meteorology .
Stockholm University, Faculty of Science, Department of Meteorology .
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2010 (English)In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 1, no 4, 769-773 p.Article in journal (Refereed) Published
Abstract [en]

Water vapor in the atmosphere can condensate and form cloud droplets when there is a certain amount of humidity and a presence of cloud condensation nuclei, and organic solutes called surfactants can significantly lower the surface tension of water-one of the parameters determining cloud droplet population. We here present a molecular dynamics study of the behavior of cis-pinonic acid, a commonly found organic compound in cloud condensation nuclei, and its effect on the surface tension of water clusters. Specifically, the decrease in surface tension is found to depend on not only the concentration of the organic compound but also the droplet size due to the spontaneous assembly of the surfactant molecules on the droplet surface. This leads to the conclusion that the partitioning of the surfactant between the bulk and surface plays an important role in the behavior of atmospheric aerosol particles and thus in their availability for cloud formation.

Place, publisher, year, edition, pages
2010. Vol. 1, no 4, 769-773 p.
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology; Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-50130DOI: 10.1021/jz9004784ISI: 000277040600018OAI: oai:DiVA.org:su-50130DiVA: diva2:380590
Note

authorCount :5

Available from: 2010-12-21 Created: 2010-12-21 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Beyond Köhler theory: Molecular dynamics simulations as a tool for atmospheric science
Open this publication in new window or tab >>Beyond Köhler theory: Molecular dynamics simulations as a tool for atmospheric science
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the results from molecular dynamics (MD) simulations of nanoaerosol clusters are discussed. The connecting link of these studies is the Köhler theory, which is the theory of condensational growth and activation of cloud droplets to form clouds. By investigating parameters such as the surface tension, state of mixture and morphology of nanoaerosol particles, conclusions can be drawn to improve the Köhler theory to include the effects of organic compounds previously unaccounted for.

For the terrestrial environment, the simulations show that the natural surfactant cis-pinonic acid, an oxidation product evaporated from boreal trees, spontaneously accumulates at the surface of nanoaerosol clusters and thereby reduces the surface tension. The surface tension depression is related to the concentration of the surfactant and the size of the clusters. Surface tension is an important parameter of the Köhler theory. A decrease of the surface tension can lower the critical water vapour supersaturation needed for cloud droplet activation, giving rise to more, but smaller cloud droplets (Twomey effect) which in turn could change the optical properties of the cloud. It was also shown that the three organic surfactants, being model compounds for so called Humic-like substances (HULIS) have the ability to form aggregates inside the nanoaerosol clusters. These HULIS aggregates can also promote the solubilization of hydrophobic organic carbon in the form of fluoranthene, enabling soot taking part in cloud drop formation.

Dissolved intermediately surface-active free amino acids were shown to be of some relevance for cloud formation over remote marine areas. The MD simulations showed differences between the interacting forces for spherical and planar interfaces of amino acids solutions.

This thesis has emphasized the surface-active properties of organic compounds, including model HULIS and amino acids and their effect on surface tension and molecular orientation including aggregate formation in nanoaerosol clusters and their activation to form droplets. This thesis shows that the Köhler equation does not fully satisfactory describe the condensational growth of nano-sized droplets containing organic surfactants. Different approaches are suggested as revisions of the Köhler theory.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2013. 64 p.
Keyword
Köhler theory, molecular dynamics, surface tension, aggregate, climate
National Category
Meteorology and Atmospheric Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-83208 (URN)978-91-7447-619-4 (ISBN)
Public defence
2013-02-08, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 5: Manuscript.

Available from: 2013-01-17 Created: 2012-12-05 Last updated: 2013-01-23Bibliographically approved

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