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| Titel |
Computation of liquid-liquid equilibria and phase stabilities: implications for RH-dependent gas/particle partitioning of organic-inorganic aerosols |
| VerfasserIn |
A. Zuend, C. Marcolli, T. Peter, 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 ; 10, no. 16 ; Nr. 10, no. 16 (2010-08-24), S.7795-7820 |
| Datensatznummer |
250008721
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| Publikation (Nr.) |
 copernicus.org/acp-10-7795-2010.pdf |
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| Zusammenfassung |
| Semivolatile organic and inorganic aerosol species
partition between the gas and aerosol particle phases to maintain
thermodynamic equilibrium. Liquid-liquid phase separation into an
organic-rich and an aqueous electrolyte phase can occur in the aerosol as a
result of the salting-out effect. Such liquid-liquid equilibria (LLE) affect
the gas/particle partitioning of the different semivolatile compounds and
might significantly alter both particle mass and composition as compared to a
one-phase particle. We present a new liquid-liquid equilibrium and
gas/particle partitioning model, using as a basis the group-contribution
model AIOMFAC (Zuend et al., 2008). This model allows the reliable
computation of the liquid-liquid coexistence curve (binodal), corresponding
tie-lines, the limit of stability/metastability (spinodal), and further
thermodynamic properties of multicomponent systems. Calculations for ternary and
multicomponent alcohol/polyol-water-salt mixtures suggest that LLE are a
prevalent feature of organic-inorganic aerosol systems. A six-component
polyol-water-ammonium sulphate system is used to simulate effects of
relative humidity (RH) and the presence of liquid-liquid phase separation on
the gas/particle partitioning. RH, salt concentration, and hydrophilicity
(water-solubility) are identified as key features in defining the region of a
miscibility gap and govern the extent to which compound partitioning is
affected by changes in RH. The model predicts that liquid-liquid phase
separation can lead to either an increase or decrease in total particulate
mass, depending on the overall composition of a system and the particle water
content, which is related to the hydrophilicity of the different organic and
inorganic compounds. Neglecting non-ideality and liquid-liquid phase
separations by assuming an ideal mixture leads to an overestimation of the
total particulate mass by up to 30% for the composition and RH range
considered in the six-component system simulation. For simplified
partitioning parametrizations, we suggest a modified definition of the
effective saturation concentration, Cj*, by including water and
other inorganics in the absorbing phase. Such a Cj* definition
reduces the RH-dependency of the gas/particle partitioning of semivolatile
organics in organic-inorganic aerosols by an order of magnitude as compared
to the currently accepted definition, which considers the organic species
only. |
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