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| Titel |
Measuring and modeling the hygroscopic growth of two humic substances in mixed aerosol particles of atmospheric relevance |
| VerfasserIn |
I. R. Zamora, M. Z. Jacobson |
| 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. 17 ; Nr. 13, no. 17 (2013-09-09), S.8973-8989 |
| Datensatznummer |
250085682
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| Publikation (Nr.) |
 copernicus.org/acp-13-8973-2013.pdf |
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| Zusammenfassung |
| The hygroscopic growth of atmospheric particles affects atmospheric chemistry
and Earth's climate. Water-soluble organic carbon (WSOC) constitutes a
significant fraction of the dry submicron mass of atmospheric aerosols, thus
affecting their water uptake properties. Although the WSOC fraction is
comprised of many compounds, a set of model substances can be used to
describe its behavior. For this study, mixtures of Nordic aquatic fulvic
acid reference (NAFA) and Fluka humic acid (HA), with various combinations of inorganic
salts (sodium chloride and ammonium sulfate) and other representative organic
compounds (levoglucosan and succinic acid), were studied. We measured the
equilibrium water vapor pressure over bulk solutions of these mixtures as a
function of temperature and solute concentration. New water activity
(aw) parameterizations and hygroscopic growth curves at
25 °C were calculated from these data for particles of equivalent
composition. We examined the effect of temperature on the water activity and
found a maximum variation of 9% in the 0–30 °C range, and
2% in the 20–30 °C range. Five two-component mixtures were
studied to understand the effect of adding a humic substance (HS), such as
NAFA and HA, to an inorganic salt or a saccharide. The deliquescence point at
25 °C for HS-inorganic mixtures did not change significantly from
that of the pure inorganic species. However, the hygroscopic growth of
HA / inorganic mixtures was lower than that exhibited by the pure salt, in
proportion to the added mass of HA. The addition of NAFA to a highly soluble
solute (ammonium sulfate, sodium chloride or levoglucosan) in water had the
same effect as the addition of HA to the inorganic species for most of the
water activity range studied. Yet, the water uptake of these NAFA mixtures
transitioned to match the growth of the pure salt or saccharide at high
aw values. The remaining four mixtures were based on chemical
composition data for different aerosol types. As expected, the two solutions
representing organic aerosols (40% HS/40% succinic acid/20%
levoglucosan) showed lower water uptake than the two solutions representing
biomass burning aerosols (25% HS/27% succinic acid/18%
levoglucosan/30% ammonium sulfate). However, interactions in
multicomponent solutions may be responsible for the large variation of the
relative water uptake of identical mixtures containing different HSs above a
water activity of 0.95. The ZSR (Zdanovskii, Stokes, and Robinson) model was able to predict reasonably well the
hygroscopic growth of all the mixtures below aw = 0.95, but
produced large deviations for some multicomponent mixtures at higher values. |
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