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| Titel |
The influences of mass loading and rapid dilution of secondary organic aerosol on particle volatility |
| VerfasserIn |
K. R. Kolesar, C. Chen, D. Johnson, C. D. Cappa |
| 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 ; 15, no. 16 ; Nr. 15, no. 16 (2015-08-21), S.9327-9343 |
| Datensatznummer |
250119983
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| Publikation (Nr.) |
 copernicus.org/acp-15-9327-2015.pdf |
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| Zusammenfassung |
| The thermally induced evaporation of secondary organic aerosol (SOA) has
been characterized for SOA formed from the dark ozonolysis of α-pinene at initial mass concentrations ranging from 1 to 800 μg m−3. Temperature-dependent particle size distributions were
measured using a thermodenuder and the resulting mass thermograms were
compared between the SOA formed at the various SOA mass concentrations.
Negligible differences were observed between the mass thermograms for SOA
concentrations < 300 μg m−3. At higher SOA
concentrations, the observed mass thermograms indicated the SOA was actually
slightly less volatile than the SOA at lower concentrations; this is likely
an artifact due to either saturation of the gas phase or to
recondensation during cooling. The thermograms observed when the SOA was
formed at high concentrations (> 380 μg m−3) and
then rapidly isothermally diluted to low concentrations (1–20 μg m−3) were identical to those for the SOA that was initially formed
at low concentrations. The experimental results were compared to a kinetic
model that simulates particle evaporation upon heating in a thermodenuder
for a given input volatility distribution and particle composition. Three
cases were considered: (1) the SOA was composed of semi-volatile monomer
species with a volatility distribution based on that derived previously from
consideration of SOA growth experiments; (2) the initial SOA was composed
almost entirely of non-volatile dimers that decompose upon heating into
their semi-volatile monomer units, which can then evaporate; and (3) where a
volatility distribution was derived by fitting the model to the observed
mass thermograms. It was found that good agreement is obtained between model
predictions and the observations when the particle composition is
dominated by either compounds of low volatility or by dimers. These same models
were used to simulate isothermal evaporation of the SOA and were found to be
broadly consistent with literature observations that indicate that SOA
evaporation occurs with multiple timescales. The use of the semi-volatile
monomer volatility distribution fails to reproduce the observed evaporation.
The presence of dimers and larger oligomers in secondary organic aerosol
formed from products of the reaction of α-pinene and O3 has
been well established in laboratory studies. However, the timescale and
relative importance of the formation of oligomers or low-volatility
compounds in the growth and evaporation of SOA has been debated. This study
provides further support that low-volatility compounds and oligomers are
formed in α-pinene + O3 in high abundances and suggests that
their formation occurs rapidly upon particle formation. |
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