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Biosurfactants as CCN: comparison between on-line and off-line measurements
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We are presenting the CCN properties for the bacterial compounds rhamnolipid and surfactin, which are extremely strong surfactants. Three organic:sodium chloride mixtures with mass percentages of 80:20, 50:50 and 20:80 were measured for each biosurfactant. Both on-line Cloud Condensation Nuclei Counter (CCNC) and off-line osmolality combined with surface tension measurements were performed to obtain two sets of critical supersaturations for various dry particle diameters. The critical supersaturations measured by the CCNC were systematically higher than the corresponding supersaturations derived from osmolality/surface tension measurements. A simple surface partitioning-adaption was applied to the off-line data and resulted in a correlation with the results from CCNC measurements for both mixtures with 20 wt% biosurfactant and the 50 wt% rhamnolipid mixture but not for the mixtures with 80 wt% biosurfactant and the 50 wt% surfactin mixture. An explanation can be unreliable CCNC results from the surfactin mixtures as we suspect poor dissolvement of the organic crystals. The choice of the assumed biosurfactant density also has an effect which should not be ignored. However, this indicate that the experimental method using osmolality and surface tension measurements together with a simple surface partitioning model can be used for strongly surfactant compounds as long as they do not dominate the particle mass. We also conclude that biosurfactants in mixed potential CCN particles can activate at relatively low supersaturation compared to other organic mixtures. Still, the critical supersaturation increases with increasing surfactant fraction.

National Category
Natural Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-45695OAI: oai:DiVA.org:su-45695DiVA: diva2:369353
Available from: 2010-11-10 Created: 2010-11-10 Last updated: 2010-11-11Bibliographically approved
In thesis
1. The influence of biogenic organic compounds on cloud formation
Open this publication in new window or tab >>The influence of biogenic organic compounds on cloud formation
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aerosols and clouds provide the largest uncertainty in the atmospheric radiation budget. The main focus of this thesis was to investigate the ability of organic compounds in aerosol particles to form clouds, and more specifically those emitted by living organisms.

The cloud forming properties of the highly water-soluble methyltetrols and polyols, which are compounds produced by plants and fungi that are common in aerosol, were studied. All compounds and their salt mixtures have a moderate potential to serve as cloud condensation nuclei (CCN). They are thus not likely to have a significant global impact on cloudiness.

The potential presence of surfactants released by microorganisms was investigated for aerosols sampled at different locations. Very low surface tension values were measured for these aerosol extracts (30 mN/m), which implies that these aerosols have good CCN properties and indicate the presence of biosurfactants. Their occurrence in aerosols still needs to be confirmed directly by chemical identification.

Reactions of organic compounds in sulfate salt solutions exposed to UV-light were studied and found to produce surface active compounds. Thus, mixed sulfate/organic aerosol could have more favourable CCN properties after exposure to light than when kept in the dark. The surface active compounds were proposed to be long-chained organosulfates with hydrophilic and hydrophobic parts, similar to other amphiphilic surfactants.

Mixtures of salt and strong surfactants formed by bacteria were studied using two different techniques for determining their CCN properties. There were inconsistencies between the two methods which could be accounted for by surface partitioning. The studied mixtures were determined to be good potential CCN material in both techniques.

All these aspects require further investigation, but if the impact of strong biogenic surfactants on cloud formation is confirmed, a new link between living organisms and climate would be identified.

Place, publisher, year, edition, pages
Stockholm: Department of Applied Environmental Science (ITM), Stockholm University, 2010. 43 p.
Keyword
biogenic, aerosol, CCN, water-soluble, microorganisms, surfactant, organosulfate
National Category
Natural Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-45714 (URN)978-91-7447-175-5 (ISBN)
Public defence
2010-12-17, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, 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 4: Manuscript. Available from: 2010-11-25 Created: 2010-11-10 Last updated: 2010-11-30Bibliographically approved

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