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| Titel |
New representation of water activity based on a single solute specific constant to parameterize the hygroscopic growth of aerosols in atmospheric models |
| VerfasserIn |
S. Metzger, B. Steil, L. Xu, J. E. Penner, J. Lelieveld  |
| 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 ; 12, no. 12 ; Nr. 12, no. 12 (2012-06-22), S.5429-5446 |
| Datensatznummer |
250011278
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| Publikation (Nr.) |
 copernicus.org/acp-12-5429-2012.pdf |
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| Zusammenfassung |
| Water activity is a key factor in aerosol thermodynamics and hygroscopic
growth. We introduce a new representation of water activity (aw),
which is empirically related to the solute molality (μs) through a
single solute specific constant, νi. Our approach is widely
applicable, considers the Kelvin effect and covers ideal solutions at high
relative humidity (RH), including cloud condensation nuclei (CCN) activation.
It also encompasses concentrated solutions with high ionic strength at low RH
such as the relative humidity of deliquescence (RHD). The constant νi
can thus be used to parameterize the aerosol hygroscopic growth over a wide
range of particle sizes, from nanometer nucleation mode to micrometer coarse
mode particles. In contrast to other aw-representations, our
νi factor corrects the solute molality both linearly and in exponent
form x · ax. We present four representations of our basic aw-parameterization at different levels of complexity for different
aw-ranges, e.g. up to 0.95, 0.98 or 1. νi is constant over
the selected aw-range, and in its most comprehensive form, the
parameterization describes the entire aw range (0–1). In this
work we focus on single solute solutions. νi can be pre-determined
with a root-finding method from our water activity representation using an
aw−μs data pair, e.g. at solute saturation using RHD
and solubility measurements. Our aw and supersaturation
(Köhler-theory) results compare well with the thermodynamic reference
model E-AIM for the key compounds NaCl and (NH4)2SO4
relevant for CCN modeling and calibration studies. Envisaged applications
include regional and global atmospheric chemistry and climate modeling. |
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