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| Titel |
On the Response Time of Single Levitated Particles of Atmospherically Relevant Composition to Changes in Relative Humidity at Low Temperatures |
| VerfasserIn |
Daniel Lienhard, Ulrich Krieger |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074597
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| Zusammenfassung |
| Recent studies have shown that atmospheric aerosol particles can adopt an amorphous solid
state, particularly under cold and dry conditions. The diffusion of water molecules in these
particles is believed to be slow enough such that the particles are not able to equilibrate
immediately to changes in the relative humidity. This retarded response has consequences for
both the heterogeneous chemistry on these particles and their ability to act as cloud
condensation nuclei. In this work, we present the experimentally observed signatures of
particles which showed kinetically impeded water uptake and release. Single levitated
particles, 2 to 20 microns in radius, are levitated without wall contact in an electrodynamic
balance and analyzed with optical techniques. Further, we demonstrate that these
signatures can be used to compute the liquid-phase water diffusion coefficient in the
concentration range where the liquid-phase diffusion limits the equilibration to
the gas phase, i.e. in the highly concentrated range for most aqueous systems. As
heterogeneous crystallization is suppressed, the procedure described here is sensible
to a concentration and temperature range where traditional methods to measure
diffusion coefficients might produce unsatisfying results. The model substances
investigated in this study can be regarded as surrogates for atmospheric aerosol.
The derived diffusion coefficients together with literature data on pure water are
parameterized as a function of concentration and temperature and can be used to directly
calculate the response time of aerosol particles to changes in the ambient conditions. |
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