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| Titel |
Hygroscopicity of organic compounds from biomass burning and their influence on the water uptake of mixed organic ammonium sulfate aerosols |
| VerfasserIn |
T. Lei, A. Zuend, W. G. Wang, Y. H. Zhang, M. F. Ge |
| 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 ; 14, no. 20 ; Nr. 14, no. 20 (2014-10-23), S.11165-11183 |
| Datensatznummer |
250119116
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| Publikation (Nr.) |
 copernicus.org/acp-14-11165-2014.pdf |
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| Zusammenfassung |
| Hygroscopic behavior of organic compounds, including
levoglucosan, 4-hydroxybenzoic acid, and humic acid, as well as their effects on the
hygroscopic properties of ammonium sulfate (AS) in internally mixed
particles are studied by a hygroscopicity tandem differential mobility
analyzer (HTDMA). The organic compounds used represent pyrolysis products of
wood that are emitted from biomass burning sources. It is found that humic
acid aerosol particles only slightly take up water, starting at RH (relative humidity) above
~70%. This is contrasted by the continuous water absorption of
levoglucosan aerosol particles in the range 5–90% RH. However, no
hygroscopic growth is observed for 4-hydroxybenzoic acid aerosol particles.
Predicted water uptake using the ideal solution theory, the AIOMFAC model
and the E-AIM (with UNIFAC) model are consistent with measured hygroscopic
growth factors of levoglucosan. However, the use of these models without
consideration of crystalline organic phases is not appropriate to describe
the hygroscopicity of organics that do not exhibit continuous water uptake,
such as 4-hydroxybenzoic acid and humic acid. Mixed aerosol particles
consisting of ammonium sulfate and levoglucosan, 4-hydroxybenzoic acid, or
humic acid with different organic mass fractions, take up a reduced amount
of water above 80% RH (above AS deliquescence) relative to pure ammonium
sulfate aerosol particles of the same mass. Hygroscopic growth of mixtures
of ammonium sulfate and levoglucosan with different organic mass fractions
agree well with the predictions of the thermodynamic models. Use of the
Zdanovskii–Stokes–Robinson (ZSR) relation and AIOMFAC model lead to good
agreement with measured growth factors of mixtures of ammonium sulfate with
4-hydroxybenzoic acid assuming an insoluble organic phase. Deviations of
model predictions from the HTDMA measurement are mainly due to the
occurrence of a microscopical solid phase restructuring at increased
humidity (morphology effects), which are not considered in the models.
Hygroscopic growth factors of mixed particles containing humic acid are well
reproduced by the ZSR relation. Lastly, the organic surrogate compounds
represent a selection of some of the most abundant pyrolysis products of
biomass burning. The hygroscopic growths of mixtures of the organic
surrogate compounds with ammonium sulfate with increasing organics mass
fraction representing ambient conditions from the wet to the dry seasonal
period in the Amazon basin, exhibit significant water uptake prior to the
deliquescence of ammonium sulfate. The measured water absorptions of
mixtures of several organic surrogate compounds (including levoglucosan)
with ammonium sulfate are close to those of binary mixtures of levoglucosan
with ammonium sulfate, indicating that levoglucosan constitutes a major
contribution to the aerosol water uptake prior to (and beyond) the
deliquescence of ammonium sulfate. Hence, certain hygroscopic organic
surrogate compounds can substantially affect the deliquescence point of
ammonium sulfate and overall particle water uptake. |
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