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| Titel |
Liquid-liquid phase separation and morphology of internally mixed dicarboxylic acids/ammonium sulfate/water particles |
| VerfasserIn |
M. Song, C. Marcolli, U. K. Krieger, A. Zuend, T. Peter |
| 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 ; 12, no. 5 ; Nr. 12, no. 5 (2012-03-13), S.2691-2712 |
| Datensatznummer |
250010871
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| Publikation (Nr.) |
 copernicus.org/acp-12-2691-2012.pdf |
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| Zusammenfassung |
| Knowledge of the physical state and morphology of internally mixed
organic/inorganic aerosol particles is still largely uncertain. To obtain
more detailed information on liquid-liquid phase separation (LLPS) and
morphology of the particles, we investigated complex mixtures of
atmospherically relevant dicarboxylic acids containing 5, 6, and 7 carbon
atoms (C5, C6 and C7) having oxygen-to-carbon atomic ratios (O:C) of 0.80,
0.67, and 0.57, respectively, mixed with ammonium sulfate (AS). With
micrometer-sized particles of C5/AS/H2O, C6/AS/H2O and
C7/AS/H2O as model systems deposited on a hydrophobically coated
substrate, laboratory experiments were conducted for various
organic-to-inorganic dry mass ratios (OIR) using optical microscopy and
Raman spectroscopy. When exposed to cycles of relative humidity (RH), each
system showed significantly different phase transitions. While the
C5/AS/H2O particles showed no LLPS with OIR = 2:1, 1:1 and 1:4 down to
20% RH, the C6/AS/H2O and C7/AS/H2O particles exhibit LLPS
upon drying at RH 50 to 85% and ~90%, respectively, via
spinodal decomposition, growth of a second phase from the particle surface
or nucleation-and-growth mechanisms depending on the OIR. This suggests that
LLPS commonly occurs within the range of O:C < 0.7 in tropospheric
organic/inorganic aerosols. To support the comparison and interpretation of
the experimentally observed phase transitions, thermodynamic equilibrium
calculations were performed with the AIOMFAC model. For the C7/AS/H2O
and C6/AS/H2O systems, the calculated phase diagrams agree well with
the observations while for the C5/AS/H2O system LLPS is predicted by
the model at RH below 60% and higher AS concentration, but was not
observed in the experiments. Both core-shell structures and partially
engulfed structures were observed for the investigated particles, suggesting
that such morphologies might also exist in tropospheric aerosols. |
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