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| Titel |
Wavelength and NOx dependent complex refractive index of SOAs generated from the photooxidation of toluene |
| VerfasserIn |
T. Nakayama, K. Sato, Y. Matsumi, T. Imamura, A. Yamazaki, A. Uchiyama |
| 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. 2 ; Nr. 13, no. 2 (2013-01-16), S.531-545 |
| Datensatznummer |
250017586
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| Publikation (Nr.) |
 copernicus.org/acp-13-531-2013.pdf |
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| Zusammenfassung |
| Recently, secondary organic aerosols (SOAs) generated from anthropogenic
volatile organic compounds have been proposed as a possible source of
light-absorbing organic compounds, "brown carbon," in the urban atmosphere.
However, the atmospheric importance of these SOAs remains unclear due to
limited information about their optical properties. In this study, the
complex refractive index (RI, m = n-ki values at 405, 532, and
781 nm of the SOAs generated during the photooxidation of toluene
(toluene-SOAs) under a variety of initial nitrogen oxide (NOx = NO + NO2) conditions were examined by photoacoustic
spectroscopy (PAS) and cavity ring-down spectroscopy (CRDS). The complex
RI-values obtained in the present study and reported in the literature
indicate that the k-value, which represents the light absorption of the
toluene-SOAs, increased to shorter wavelengths at <532 nm, and the
n-value also increased to shorter wavelengths from 781 to 355 nm. The
k-values at 405 nm were found to increase from 0.0018 to 0.0072 with
increasing initial NOx concentration from 109 to 571 ppbv. The
nitrate to organics ratio of the SOAs determined using a high-resolution
time-of-flight aerosol mass spectrometer (H-ToF-AMS) also increased with
increasing initial NOx concentration. The RI-values of the SOAs
generated during the photooxidation of 1,3,5-trimethylbenzene in the presence
of NOx (1,3,5-TMB-SOAs) were also determined to investigate the
influence of the chemical structure of the precursor on the optical
properties of the SOAs, and it was found that the light absorption of the
1,3,5-TMB-SOAs is negligible at all of the wavelengths investigated (405,
532, and 781 nm). These results can be reasonably explained by the
hypothesis that nitroaromatic compounds, such as nitrocresols, are the major
contributors to the light absorption of the toluene-SOAs. Using the obtained
RI-values, mass absorption cross sections of the toluene-SOAs at 405 nm were
estimated to be 0.08–0.52 m2g−1 under typical conditions in an
urban atmosphere during the daytime. These results indicate that light
absorption by the SOAs potentially contributes to the radiation balance at
ultraviolet wavelengths below ~400 nm, specifically when the mass
concentrations of the anthropogenic SOAs are significant compared with other
light-absorbing particles. |
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