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| Titel |
Connecting the solubility and CCN activation of complex organic aerosols: a theoretical study using solubility distributions |
| VerfasserIn |
I. Riipinen, N. Rastak, S. N. Pandis |
| 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 ; 15, no. 11 ; Nr. 15, no. 11 (2015-06-10), S.6305-6322 |
| Datensatznummer |
250119799
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| Publikation (Nr.) |
 copernicus.org/acp-15-6305-2015.pdf |
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| Zusammenfassung |
| We present a theoretical study investigating the cloud activation of
multicomponent organic particles. We modeled these complex mixtures using
solubility distributions (analogous to volatility distributions in the VBS,
i.e., volatility basis set, approach), describing the mixture as a set of
surrogate compounds with varying water solubilities in a given range. We
conducted Köhler theory calculations for 144 different mixtures with
varying solubility range, number of components, assumption about the organic
mixture thermodynamics and the shape of the solubility distribution, yielding
approximately 6000 unique cloud condensation nucleus (CCN)-activation points.
The results from these comprehensive calculations were compared to three
simplifying assumptions about organic aerosol solubility: (1) complete
dissolution at the point of activation; (2) combining the aerosol solubility
with the molar mass and density into a single effective hygroscopicity
parameter κ; and (3) assuming a fixed water-soluble fraction
ϵeff. The complete dissolution was able to reproduce
the activation points with a reasonable accuracy only when the majority
(70–80%) of the material was dissolved at the point of activation. The
single-parameter representations of complex mixture solubility were confirmed
to be powerful semi-empirical tools for representing the CCN activation of
organic aerosol, predicting the activation diameter within 10% in most
of the studied supersaturations. Depending mostly on the condensed-phase
interactions between the organic molecules, material with solubilities larger
than about 0.1–100 g L−1 could be treated as soluble in the CCN
activation process over atmospherically relevant particle dry diameters and
supersaturations. Our results indicate that understanding the details of the
solubility distribution in the range of 0.1–100 g L−1 is thus
critical for capturing the CCN activation, while resolution outside this
solubility range will probably not add much information except in some
special cases. The connections of these results to the previous observations
of the CCN activation and the molecular properties of complex organic mixture
aerosols are discussed. The presented results help unravel the mechanistic
reasons behind observations of hygroscopic growth and CCN activation of
atmospheric secondary organic aerosol (SOA) particles. The proposed
solubility distribution framework is a promising tool for modeling the
interlinkages between atmospheric aging, volatility and water uptake of
atmospheric organic aerosol. |
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