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| Titel |
Competition between water uptake and ice nucleation by glassy organic aerosol particles |
| VerfasserIn |
T. Berkemeier, M. Shiraiwa, U. Pöschl, 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 ; 14, no. 22 ; Nr. 14, no. 22 (2014-11-27), S.12513-12531 |
| Datensatznummer |
250119194
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| Publikation (Nr.) |
 copernicus.org/acp-14-12513-2014.pdf |
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| Zusammenfassung |
| Organic aerosol particles play a key role in climate by serving as nuclei
for clouds and precipitation. Their sources and composition are highly
variable, and their phase state ranges from liquid to solid under
atmospheric conditions, affecting the pathway of activation to cloud
droplets and ice crystals. Due to slow diffusion of water in the particle
phase, organic particles may deviate in phase and morphology from their
thermodynamic equilibrium state, hampering the prediction of their influence
on cloud formation. We overcome this problem by combining a novel
semi-empirical method for estimation of water diffusivity with a kinetic
flux model that explicitly treats water diffusion. We estimate timescales
for particle deliquescence as well as various ice nucleation pathways for a
wide variety of organic substances, including secondary organic aerosol
(SOA) from the oxidation of isoprene, α-pinene, naphthalene, and
dodecane. The simulations show that, in typical atmospheric updrafts, glassy
states and solid/liquid core-shell morphologies can persist for long enough
that heterogeneous ice nucleation in the deposition and immersion mode can
dominate over homogeneous ice nucleation. Such competition depends strongly
on ambient temperature and relative humidity as well as humidification rate
and particle size. Due to differences in glass transition temperature,
hygroscopicity and atomic O / C ratio of the different SOA, naphthalene SOA particles
have the highest potential to act as heterogeneous ice nuclei. Our findings
demonstrate that kinetic limitations of water diffusion into organic aerosol
particles are likely to be encountered under atmospheric conditions and can
strongly affect ice nucleation pathways. For the incorporation of ice
nucleation by organic aerosol particles into atmospheric models, our results
demonstrate a demand for model formalisms that account for the effects of
molecular diffusion and not only describe ice nucleation onsets as a
function of temperature and relative humidity but also include updraft
velocity, particle size and composition. |
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