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| Titel |
Improved AIOMFAC model parameterisation of the temperature dependence of activity coefficients for aqueous organic mixtures |
| VerfasserIn |
G. Ganbavale, A. Zuend, C. Marcolli, 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 ; 15, no. 1 ; Nr. 15, no. 1 (2015-01-14), S.447-493 |
| Datensatznummer |
250119307
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| Publikation (Nr.) |
 copernicus.org/acp-15-447-2015.pdf |
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| Zusammenfassung |
| This study presents a new, improved
parameterisation of the temperature dependence of activity
coefficients in the AIOMFAC (Aerosol Inorganic–Organic Mixtures
Functional groups Activity Coefficients) model applicable for
aqueous as well as water-free organic solutions. For
electrolyte-free organic and organic–water mixtures the AIOMFAC
model uses a group-contribution approach based on UNIFAC (UNIversal
quasi-chemical Functional-group Activity Coefficients). This
group-contribution approach explicitly accounts for interactions
among organic functional groups and between organic functional
groups and water. The previous AIOMFAC version uses a simple
parameterisation of the temperature dependence of activity
coefficients, aimed to be applicable in the temperature range from
~ 275 to ~ 400 K. With the goal to improve the
description of a wide variety of organic compounds found in
atmospheric aerosols, we extend the AIOMFAC parameterisation for the
functional groups carboxyl, hydroxyl, ketone, aldehyde, ether,
ester, alkyl, aromatic carbon-alcohol, and aromatic hydrocarbon to
atmospherically relevant low temperatures. To this end we introduce a new parameterisation for the temperature dependence. The improved
temperature dependence parameterisation is derived from classical
thermodynamic theory by describing effects from changes in molar
enthalpy and heat capacity of a multi-component system. Thermodynamic
equilibrium data of aqueous organic and water-free organic mixtures
from the literature are carefully assessed and complemented with new
measurements to establish a comprehensive database, covering a wide
temperature range (~ 190 to ~ 440 K) for many of the
functional group combinations considered. Different experimental
data types and their processing for the estimation of AIOMFAC model
parameters are discussed. The new AIOMFAC parameterisation for the
temperature dependence of activity coefficients from low to high
temperatures shows an overall improvement of 28% in comparison
to the previous model version, when both versions are compared to our
database of experimentally determined activity coefficients and related
thermodynamic data. When comparing the previous and new AIOMFAC model
parameterisations to the subsets of experimental data with all temperatures
below 274 K or all temperatures above 322 K (i.e. outside a 25 K margin
of the reference temperature of 298 K), applying the new parameterisation
leads to 37% improvement in each of the two temperature ranges considered.
The new parameterisation of AIOMFAC agrees well with a large number of experimental
data sets. Larger model–measurement discrepancies were found particularly for some of
the systems containing multi-functional organic compounds. The affected systems
were typically also poorly represented at room temperature and further improvements
will be necessary to achieve better performance of AIOMFAC in these cases (assuming
the experimental data are reliable). The performance of the AIOMFAC parameterisation
is typically better for systems containing relatively small organic compounds and
larger deviations may occur in mixtures where molecules of high structural
complexity such as highly oxygenated compounds or molecules of high molecular mass (e.g. oligomers) prevail.
Nevertheless, the new parameterisation enables the calculation of activity
coefficients for a wide variety of different aqueous/water-free organic
solutions down to the low temperatures present in the upper troposphere. |
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