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| Titel |
Mass-based hygroscopicity parameter interaction model and measurement of atmospheric aerosol water uptake |
| VerfasserIn |
E. Mikhailov, S. Vlasenko, D. Rose, U. Pöschl |
| 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 ; 13, no. 2 ; Nr. 13, no. 2 (2013-01-21), S.717-740 |
| Datensatznummer |
250017597
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| Publikation (Nr.) |
 copernicus.org/acp-13-717-2013.pdf |
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| Zusammenfassung |
In this study we derive and apply a mass-based hygroscopicity parameter
interaction model for efficient description of concentration-dependent water
uptake by atmospheric aerosol particles with complex chemical composition.
The model approach builds on the single hygroscopicity parameter model of
Petters and Kreidenweis (2007). We introduce an observable mass-based
hygroscopicity parameter κm which can be deconvoluted into a
dilute hygroscopicity parameter (κm0) and additional
self- and cross-interaction parameters describing non-ideal solution
behavior and concentration dependencies of single- and multi-component
systems.
For reference aerosol samples of sodium chloride and ammonium sulfate, the
κm-interaction model (KIM) captures the experimentally observed
concentration and humidity dependence of the hygroscopicity parameter and is
in good agreement with an accurate reference model based on the Pitzer
ion-interaction approach (Aerosol Inorganic Model, AIM). Experimental
results for pure organic particles (malonic acid, levoglucosan) and for
mixed organic-inorganic particles (malonic acid – ammonium sulfate) are
also well reproduced by KIM, taking into account apparent or equilibrium
solubilities for stepwise or gradual deliquescence and efflorescence
transitions.
The mixed organic-inorganic particles as well as atmospheric aerosol samples
exhibit three distinctly different regimes of hygroscopicity: (I) a
quasi-eutonic deliquescence & efflorescence regime at low-humidity where
substances are just partly dissolved and exist also in a non-dissolved
phase, (II) a gradual deliquescence & efflorescence regime at
intermediate humidity where different solutes undergo gradual dissolution or
solidification in the aqueous phase; and (III) a dilute regime at high
humidity where the solutes are fully dissolved approaching their dilute
hygroscopicity.
For atmospheric aerosol samples collected from boreal rural air and from
pristine tropical rainforest air (secondary organic aerosol) we present
first mass-based measurements of water uptake over a wide range of relative
humidity (1–99.4%) obtained with a new filter-based differential
hygroscopicity analyzer (FDHA) technique. For these samples the
concentration dependence of κm can be described by a simple KIM
model equation based on observable mass growth factors and a total of only
six fit parameters summarizing the combined effects of the dilute
hygroscopicity parameters, self- and cross-interaction parameters, and
solubilities of all involved chemical components. One of the fit parameters
represents κm0 and can be used to predict critical dry
diameters for the activation of cloud condensation nuclei (CCN) as a
function of water vapor supersaturation according to Köhler theory. For
sodium chloride and ammonium sulfate reference particles as well as for
pristine rainforest aerosols consisting mostly of secondary organic matter,
we obtained good agreement between the KIM predictions and measurement data
of CCN activation.
The application of KIM and mass-based measurement techniques shall help to
bridge gaps in the current understanding of water uptake by atmospheric
aerosols: (1) the gap between hygroscopicity parameters determined by
hygroscopic growth measurements under sub-saturated conditions and by CCN
activation measurements at water vapor supersaturation, and (2) the gap
between the results of simplified single parameter models widely used in
atmospheric or climate science and the results of complex multi-parameter
ion- and molecule-interaction models frequently used in physical chemistry
and solution thermodynamics (e.g., AIM, E-AIM, ADDEM, UNIFAC, AIOMFAC). |
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