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| Titel |
Influence of particle-phase state on the hygroscopic behavior of mixed organic–inorganic aerosols |
| VerfasserIn |
N. Hodas, A. Zuend, W. Mui, R. C. Flagan, J. H. Seinfeld |
| 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. 9 ; Nr. 15, no. 9 (2015-05-05), S.5027-5045 |
| Datensatznummer |
250119693
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| Publikation (Nr.) |
 copernicus.org/acp-15-5027-2015.pdf |
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| Zusammenfassung |
| Recent work has demonstrated that organic and mixed organic–inorganic
particles can exhibit multiple phase states depending on their chemical
composition and on ambient conditions such as relative humidity (RH). To
explore the extent to which water uptake varies with particle-phase
behavior, hygroscopic growth factors (HGFs) of nine laboratory-generated,
organic and organic–inorganic aerosol systems with physical states ranging
from well-mixed liquids to phase-separated particles to viscous liquids or
semi-solids were measured with the Differential Aerosol Sizing and
Hygroscopicity Spectrometer Probe at RH values ranging from 40 to 90%.
Water-uptake measurements were accompanied by HGF and RH-dependent
thermodynamic equilibrium calculations using the Aerosol Inorganic-Organic
Mixtures Functional groups Activity Coefficients (AIOMFAC) model. In
addition, AIOMFAC-predicted growth curves are compared to several simplified
HGF modeling approaches: (1) representing particles as ideal, well-mixed
liquids; (2) forcing a single phase but accounting for non-ideal
interactions through activity coefficient calculations; and (3) a
Zdanovskii–Stokes–Robinson-like calculation in which complete separation
of the inorganic and organic components is assumed at all RH values,
with water uptake treated separately in each of the individual phases. We
observed variability in the characteristics of measured hygroscopic growth
curves across aerosol systems with differing phase behaviors, with growth
curves approaching smoother, more continuous water uptake with decreasing
prevalence of liquid–liquid phase separation and increasing oxygen : carbon
ratios of the organic aerosol components. We also observed indirect evidence
for the dehydration-induced formation of highly viscous semi-solid phases
and for kinetic limitations to the crystallization of ammonium sulfate at
low RH for sucrose-containing particles. AIOMFAC-predicted growth curves are
generally in good agreement with the HGF measurements. The performances of
the simplified modeling approaches, however, differ for particles with
differing phase states. This suggests that no single simplified modeling
approach can be used to capture the water-uptake behavior for the diversity
of particle-phase behavior expected in the atmosphere. Errors in HGFs
calculated with the simplified models are of sufficient magnitude to produce
substantial errors in estimates of particle optical and radiative properties,
particularly for the assumption that water uptake is driven by absorptive
equilibrium partitioning with ideal particle-phase mixing. |
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