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| Titel |
Diffusivity Measurements of Volatile Organics in Levitated Viscous Aerosol Particles |
| VerfasserIn |
Sandra Bastelberger, Ulrich Krieger, Beiping Luo, Thomas Peter |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150243
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| Publikation (Nr.) |
 EGU/EGU2017-14681.pdf |
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| Zusammenfassung |
| Field measurements indicating that atmospheric secondary aerosol (SOA) particles can be
present in a highly viscous, glassy state have spurred numerous studies addressing low water
diffusivities in glassy aerosols, focusing on kinetic limitations to hygroscopic growth and the
plasticizing effect of water. Less is known about diffusion limitations of organic molecules
and oxidants in viscous matrices and how these might affect atmospheric chemistry and
gas-particle phase partitioning of complex mixtures with constituents of different volatility.
Often viscosity data has been used to infer diffusivity via the Stokes- Einstein relationship
even though strong deviations from this relationship have been observed for matrices of high
viscosity. In this study, we provide a quantitative estimate for the diffusivity of
a volatile organic in a viscous matrix. Evaporation of single particles generated
from an aqueous solution of sucrose and a small quantity of volatile tetraethylene
glycol (PEG-4) is investigated in an electrodynamic balance at controlled relative
humidity (RH) and temperature conditions, thereby varying the viscosity of the sucrose
matrix. The evaporative loss of tetraethylene glycol as determined by Mie resonance
spectroscopy is used in conjunction with a diffusion model to retrieve translational
diffusion coefficients of tetraethylene glycol. The evaporation of PEG-4 shows a
pronounced RH and temperature dependence and is severely depressed for RH 30%
corresponding to diffusivities < 10−14 cm2/s at temperatures as high as 15 ∘C, implying that
atmospheric volatile organic compounds (VOC) can be subject to severe diffusion
limitations in glassy SOA. Comparison of the experimentally derived diffusivities with
viscosity estimates for the ternary system reveals a breakdown of the Stokes-Einstein
relationship. |
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