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| Titel |
Effects of molecular weight and temperature on liquid–liquid phase separation in particles containing organic species and inorganic salts |
| VerfasserIn |
Y. You, A. K. Bertram |
| 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. 3 ; Nr. 15, no. 3 (2015-02-09), S.1351-1365 |
| Datensatznummer |
250119395
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| Publikation (Nr.) |
 copernicus.org/acp-15-1351-2015.pdf |
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| Zusammenfassung |
| Atmospheric particles containing organic species and inorganic salts may
undergo liquid–liquid phase separation when the relative humidity varies
between high and low values. To better understand the parameters that affect
liquid–liquid phase separation in atmospheric particles, we studied the
effects of molecular weight and temperature on liquid–liquid phase
separation in particles containing one organic species mixed with either
ammonium sulfate or ammonium bisulfate. In the molecular-weight-dependent
studies, we measured liquid–liquid phase separation relative humidity (SRH)
in particles containing ammonium sulfate and organic species with large
molecular weights (up to 1153 Da). These results were combined with recent
studies of liquid–liquid phase separation in the literature to assess if
molecular weight is a useful parameter for predicting SRH. The combined
results, which include results from 33 different particle types, illustrate
that SRH does not depend strongly on molecular weight (i.e., a clear
relationship between molecular weight and SRH was not observed). In the
temperature-dependent studies, we measured liquid–liquid phase separation in
particles containing ammonium sulfate mixed with 20 different organic
species at 244 ± 1 K, 263 ± 1 K, and 278 ± 1 K; a few particles were also studied at
290 ± 1 K. These new results were
combined with previous measurements of the same particle types at 290 ± 1 K. The combined SRH data illustrate that for the organic–ammonium
sulfate particles studied, the SRH does not depend strongly on temperature.
At most the SRH varied by 9.7% as the temperature varied from 290 to
244 K. The high SRH values (> 65%) in these experiments may
explain the lack of temperature dependence. Since water is a plasticizer,
high relative humidities can lead to high water contents, low viscosities,
and high diffusion rates in the particles. For these cases, unless the
temperature is very low, liquid–liquid phase separation is not expected to
be kinetically inhibited. The occurrence of liquid–liquid phase separation
and SRH did depend strongly on temperature over the range of 290–244 K for
particles containing α,4-dihydroxy-3-methoxybenzeneacetic acid mixed
with ammonium bisulfate. For this particle type, a combination of low
temperatures and low water content likely favored kinetic inhabitation of
the liquid–liquid phase separation by slow diffusion rates in highly viscous
particles. The combined results suggest that liquid–liquid phase separation
is likely a common occurrence in atmospheric particles at temperatures from
244–290 K, although particles that do not undergo liquid–liquid phase
separation are also likely common. |
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