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| Titel |
Analysis of the hygroscopic and volatile properties of ammonium sulphate seeded and unseeded SOA particles |
| VerfasserIn |
N. K. Meyer, J. Duplissy, M. Gysel, A. Metzger, J. Dommen, E. Weingärtner, M. R. Alfarra, A. S. H. Prévôt, C. Fletcher, N. Good, G. McFiggans, A. M. Jönsson, M. Hallquist, U. Baltensperger, Z. D. Ristovski |
| 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 ; 9, no. 2 ; Nr. 9, no. 2 (2009-01-28), S.721-732 |
| Datensatznummer |
250006752
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| Publikation (Nr.) |
 copernicus.org/acp-9-721-2009.pdf |
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| Zusammenfassung |
| The volatile and hygroscopic properties of ammonium sulphate seeded and
unseeded secondary organic aerosol (SOA) derived from the photo-oxidation
of atmospherically relevant concentrations of α-pinene were studied.
The seed particles were electrospray generated ammonium sulphate
((NH4)2SO4) having diameters of approximately 33 nm with a
quasi-mono-disperse size distribution (geometric standard deviation σg=1.3).
The volatile and hygroscopic properties of both seeded and
unseeded SOA were simultaneously measured with a VH-TDMA (volatility –
hygroscopicity tandem differential mobility analyzer). VH-TDMA
measurements of unseeded SOA show a decrease in the hygroscopic growth (HGF)
factor for increased volatilisation temperatures such that the more volatile
compounds appear to be more hygroscopic. This is opposite to the expected
preferential evaporation of more volatile but less hygroscopic material, but
could also be due to enhanced oligomerisation occurring at the higher
temperature in the thermodenuder. In addition, HGF measurements of seeded
SOA were measured as a function of time at two relative humidities, below
(RH 75%) and above (RH 85%) the deliquescence relative humidity (DRH)
of the pure ammonium sulphate seeds. As these measurements were conducted
during the onset phase of photo-oxidation, during particle growth, they
enabled us to find the dependence of the HGF as a function of the volume
fraction of the SOA coating. HGF's measured at RH of 85% showed a
continuous decrease as the SOA coating thickness increased. The measured
growth factors show good agreements with ZSR predictions indicating that, at
these RH values, there are only minor solute-solute interactions. At 75%
RH, as the SOA fraction increased, a rapid increase in the HGF was observed
indicating that an increasing fraction of the (NH4)2SO4 is
subject to a phase transition, going into solution, with an increasing
volume fraction of SOA. To our knowledge this is the first time that SOA
derived from photo-oxidised α-pinene has been shown to affect the
equilibrium water content of inorganic aerosols below their DRH. For SOA
volume fractions above ~0.3 the measured growth factor followed
roughly parallel to the ZSR prediction based on fully dissolved
(NH4)2SO4 although with a small difference that was just
larger than the error estimate. Both incomplete dissolution and negative
solute-solute interactions could be responsible for the lower HGF observed
compared to the ZSR predictions. |
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