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| Titel |
A curved multi-component aerosol hygroscopicity model framework: Part 2 – Including organic compounds |
| VerfasserIn |
D. O. Topping, G. B. McFiggans, H. Coe |
| 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 ; 5, no. 5 ; Nr. 5, no. 5 (2005-05-26), S.1223-1242 |
| Datensatznummer |
250002806
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| Publikation (Nr.) |
 copernicus.org/acp-5-1223-2005.pdf |
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| Zusammenfassung |
| This paper describes the inclusion of organic particulate material within
the Aerosol Diameter Dependent Equilibrium Model (ADDEM) framework described
in the companion paper applied to inorganic aerosol components. The
performance of ADDEM is analysed in terms of its capability to reproduce the
behaviour of various organic and mixed inorganic/organic systems using
recently published bulk data. Within the modelling architecture already
described two separate thermodynamic models are coupled in an additive
approach and combined with a method for solving the Kohler equation in order
to develop a tool for predicting the water content associated with an
aerosol of known inorganic/organic composition and dry size. For development
of the organic module, the widely used group contribution method UNIFAC is
employed to explicitly deal with the non-ideality in solution. The UNIFAC
predictions for components of atmospheric importance were improved
considerably by using revised interaction parameters derived from
electro-dynamic balance studies. Using such parameters, the model was found
to adequately describe mixed systems including 5–6 dicarboxylic acids, down
to low relative humidity conditions. By comparison with electrodynamic
balance data, it was also found that the model was capable of capturing the
behaviour of aqueous aerosols containing Suwannee River Fulvic acid, a
structure previously used to represent the functionality of complex oxidised
macromolecules often found in atmospheric aerosols. The additive approach
for modelling mixed inorganic/organic systems worked well for a variety of
mixtures. As expected, deviations between model predictions and measurements
increase with increasing concentration. Available surface tension models,
used in evaluating the Kelvin term, were found to reproduce measured data
with varying success. Deviations from experimental data increased with
increased organic compound complexity. For components only slightly soluble
in water, significant deviations from measured surface tension depression
behaviour were predicted with both model formalisms tested. A Sensitivity
analysis showed that such variation is likely to lead to predicted growth
factors within the measurement uncertainty for growth factor taken in the
sub-saturated regime. Greater sensitivity was found for the value of dry
density used in the assumed form of the dried out aerosol. Comparison with a
coupled thermodynamic approach showed that assumed values for interactions
parameters may lead to erroneous results where a simple additive approach
may provide more accurate results. However, where available, the use of
coupled thermodynamics can better reproduce measured behaviour. Further work
(and laboratory data) is required to assess whether this difference lies
within the experimental uncertainty of observed hygroscopic behaviour for a
variety of systems. |
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