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| Titel |
Do atmospheric aerosols form glasses? |
| VerfasserIn |
B. Zobrist, C. Marcolli, D. A. Pedernera, T. Koop |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 17 ; Nr. 8, no. 17 (2008-09-03), S.5221-5244 |
| Datensatznummer |
250006361
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| Publikation (Nr.) |
 copernicus.org/acp-8-5221-2008.pdf |
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| Zusammenfassung |
| A new process is presented by which water soluble organics might influence ice nucleation, ice
growth, chemical reactions and water uptake of aerosols in the upper troposphere: the formation of
glassy aerosol particles. Glasses are disordered amorphous (non-crystalline) solids that form when
a liquid is cooled without crystallization until the viscosity increases exponentially and
molecular diffusion practically ceases. The glass transition temperatures, Tg,
homogeneous ice nucleation temperatures, Thom, and ice melting temperatures,
Tm, of various aqueous inorganic, organic and multi-component solutions are investigated
with a differential scanning calorimeter. The investigated solutes are: various polyols, glucose,
raffinose, levoglucosan, an aromatic compound, sulfuric acid, ammonium bisulfate and mixtures of
dicarboxylic acids (M5), of dicarboxylic acids and ammonium sulfate (M5AS), of two polyols, of
glucose and ammonium nitrate, and of raffinose and M5AS. The results indicate that aqueous
solutions of the investigated inorganic solutes show Tg values that are too low to be of
atmospheric importance. In contrast, aqueous organic and multi-component solutions readily form
glasses at low but atmospherically relevant temperatures (≤230 K). To apply the
laboratory data to the atmospheric situation, the measured phase transition temperatures were
transformed from a concentration to a water activity scale by extrapolating water activities
determined between 252 K and 313 K to lower temperatures. The obtained state diagrams
reveal that the higher the molar mass of the aqueous organic or multi-component solutes, the higher
Tg of their respective solutions at a given water activity. To a lesser extent,
Tg also depends on the hydrophilicity of the organic solutes. Therefore, aerosol
particles containing larger (≳150 g mol−1) and more hydrophobic organic
molecules are more likely to form glasses at intermediate to high relative humidities in the upper
troposphere. Our results suggest that the water uptake of aerosols, heterogeneous chemical
reactions in aerosol particles, as well as ice nucleation and ice crystal growth can be
significantly impeded or even completely inhibited in organic-enriched aerosols at upper
tropospheric temperatures with implications for cirrus cloud formation and upper tropospheric
relative humidity. |
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