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| Titel |
Humidity-dependent phase state of SOA particles from biogenic and anthropogenic precursors |
| VerfasserIn |
E. Saukko, A. T. Lambe, P. Massoli, T. Koop, J. P. Wright, D. R. Croasdale, D. A. Pedernera, T. B. Onasch, A. Laaksonen, P. Davidovits, D. R. Worsnop, A. Virtanen |
| 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. 16 ; Nr. 12, no. 16 (2012-08-17), S.7517-7529 |
| Datensatznummer |
250011400
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| Publikation (Nr.) |
 copernicus.org/acp-12-7517-2012.pdf |
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| Zusammenfassung |
The physical phase state (solid, semi-solid, or liquid) of secondary organic
aerosol (SOA) particles has important implications for a number of
atmospheric processes. We report the phase state of SOA particles spanning a
wide range of oxygen to carbon ratios (O / C), used here as a surrogate for SOA
oxidation level, produced in a flow tube reactor by photo-oxidation of
various atmospherically relevant surrogate anthropogenic and biogenic
volatile organic compounds (VOCs). The phase state of laboratory-generated
SOA was determined by the particle bounce behavior after inertial impaction
on a polished steel substrate. The measured bounce fraction was evaluated as
a function of relative humidity and SOA oxidation level (O / C) measured by an
Aerodyne high resolution time of flight aerosol mass spectrometer (HR-ToF
AMS).
The main findings of the study are: (1) biogenic and anthropogenic SOA
particles are found to be amorphous solid or semi-solid based on the measured
bounced fraction (BF), which was typically higher than 0.6 on a 0 to 1 scale.
A decrease in the BF is observed for most systems after the SOA is exposed to
relative humidity of at least 80% RH, corresponding to a RH at impaction of
55%. (2) Long-chain alkanes have a low BF (indicating a "liquid-like", less
viscous phase) particles at low oxidation levels (BF < 0.2 ± 0.05 for O / C =
0.1). However, BF increases substantially upon increasing oxidation.
(3) Increasing the concentration of sulphuric acid (H2SO4) in solid
SOA particles (here tested for longifolene SOA) causes a decrease in BF
levels. (4) In the majority of cases the bounce behavior of the various SOA
systems did not show correlation with the particle O / C. Rather, the molar
mass of the gas-phase VOC precursor showed a positive correlation with the
resistance to the RH-induced phase change of the formed SOA particles. |
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