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| Titel |
EQSAM4 - Aerosol water parameterization for atmospheric modeling |
| VerfasserIn |
Swen Metzger, Benedikt Steil, Li Xu, Joyce Penner, Jos Lelieveld  |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050810
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| Zusammenfassung |
| We introduce version 4 of the EQuilibrium Simplified Aerosol Model (EQSAM4). The model
is designed for atmospheric modeling and based on CPU efficient parameterizations that
allow a sufficiently fast and accurate estimation of the overall aerosol liquid water content
(AWC) and the required Relative Humidity of Deliquescence (RHD) - central in
atmospheric chemistry and climate modeling. The main advantage of the revised model is its
simplicity and predictive capability. The concept is based on a set of analytical functions (all
of the form axx) that approximate the computationally comprehensive minimization of the
Gibbs free energy and therefore allows to non-iteratively calculate the RHD based AWC of a
droplet distribution that is in equilibrium with the ambient air, containing either single or
mixed solutes. Our equations are a function of relative humidity (RH) and only require a
single parameter νi(aq) for the entire range (0-1) of water activity (aw(aq)). νi(aq) acts as an
effective solute-solute and solute-solvent ion-ion and surface interaction parameter.
νi(aq) is pre-scribed in EQSAM4 by look-up tables and determined by fitting our
analytical equations to measurements assuming approximately flat surfaces. To
account for surface tensions, or other size effects, νi(aq) can be altenratively derived
from other empirical coefficients, or reference models, through the various relations
presented. AWC distributions calculated with a global chemistry-climate model (EMAC)
indicate that the EQSAM4 parameterizations are in general agreement with the
more explicit thermodynamic model ISORROPIA2. AWC box model results of
major single salt solutions (i.e. containing NaCl, NH4NO3, (NH4)2SO4, NH4HSO4,
NaHSO4), and the corresponding mixed solutions, further nicely compare with
those of the thermodynamic reference model E-AIM. The AWC of mixed solutions
can be optionally obtained with EQSAM4 by calculating mean values of νi(aq)
from all single solutes in the mixed solution. This new mixing rule of EQSAM4
complements the widely used additive approach of partial water masses of single solutes
(ZSR-relation). |
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