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| Titel |
Real refractive indices and volatility of secondary organic aerosol generated from photooxidation and ozonolysis of limonene, α-pinene and toluene |
| VerfasserIn |
H. Kim, S. E. Paulson |
| 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. 15 ; Nr. 13, no. 15 (2013-08-09), S.7711-7723 |
| Datensatznummer |
250085619
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| Publikation (Nr.) |
 copernicus.org/acp-13-7711-2013.pdf |
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| Zusammenfassung |
| Thermodenuding particles can provide insights into aerosol composition and
may be a way to create particles in laboratory chambers that better mimic the
atmosphere. The relative volatility of secondary organic aerosol (SOA) was
investigated by evaporating organics from the particles using a thermodenuder
(TD) at temperatures between ∼60 and 100 °C. Volatility was
influenced by the parent hydrocarbon, oxidation chemistry and relative
humidity (RH). For SOA generated from ozonolysis, limonene had lower
volatility than α-pinene, and OH scavengers had no influence on
volatility. For photooxidation, α-pinene SOA was slightly more
volatile than limonene SOA. Increasing RH also modestly increased
volatility, while toluene SOA was unaffected by heating to 98 °C.
For both α-pinene and limonene, the concentration of NOx
and the HC / NOx ratio had no discernible effect on SOA
volatility. Refractive indices for the original and denuded particles were
retrieved from polar nephelometer measurements using parallel and
perpendicular polarized 532 nm light. Retrievals were performed with a
genetic algorithm method using Mie–Lorenz scattering theory and measured
particle size distributions. Retrieved refractive indices for the SOA before
thermodenuding varied between 1.35 and 1.61 depending on several factors,
including parent hydrocarbon, oxidation chemistry, and SOA generation
temperature. For high NOx SOA, as particles shrink, their
refractive index returns to the value of the corresponding size particles
before heating (limonene) or slightly higher (α-pinene). For low
NOx however, the resulting refractive index is 0.05 ± 0.02
lower than the corresponding size undenuded particles. Additionally, for
α-pinene SOA from ozonolysis with OH radical scavenger, resulting
refractive indices were higher by about 0.03 after heating. Consistent with
no change in size, refractive indices of toluene SOA were unaffected by
heating. Finally, refractive index data available to date are reviewed,
leading to the suggestion that the most representative values for
mr at λ =532 nm for biogenic and anthropogenic SOA are
1.44 and 1.55, respectively. |
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