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| Titel |
Broadband measurements of aerosol extinction in the ultraviolet spectral region |
| VerfasserIn |
R. A. Washenfelder, J. M. Flores, C. A. Brock, S. S. Brown, Y. Rudich |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 4 ; Nr. 6, no. 4 (2013-04-03), S.861-877 |
| Datensatznummer |
250017865
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| Publikation (Nr.) |
 copernicus.org/amt-6-861-2013.pdf |
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| Zusammenfassung |
| Aerosols influence the Earth's radiative budget by scattering and absorbing
incoming solar radiation. The optical properties of aerosols vary as a
function of wavelength, but few measurements have reported the wavelength
dependence of aerosol extinction cross sections and complex refractive
indices. We describe a new laboratory instrument to measure aerosol optical
extinction as a function of wavelength, using cavity enhanced spectroscopy
with a broadband light source. The instrument consists of two broadband
channels which span the 360–390 and 385–420 nm spectral regions using two
light emitting diodes (LED) and a grating spectrometer with charge-coupled
device (CCD) detector. We determined aerosol extinction cross sections and
directly observed Mie scattering resonances for aerosols that are purely
scattering (polystyrene latex spheres and ammonium sulfate), slightly
absorbing (Suwannee River fulvic acid), and strongly absorbing (nigrosin
dye). We describe an approach for retrieving refractive indices as a function
of wavelength from the measured extinction cross sections over the
360–420 nm wavelength region. The retrieved refractive indices for PSL and
ammonium sulfate agree within uncertainty with the literature values for this
spectral region. The refractive index determined for nigrosin is 1.78 (± 0.03)
+ 0.19 (± 0.08)i at 360 nm and 1.63 (± 0.03) + 0.21
(± 0.05)i at 420 nm. The refractive index determined for Suwannee
River fulvic acid is 1.71 (± 0.02) + 0.07 (± 0.06)i at 360 nm
and 1.66 (± 0.02) + 0.06 (± 0.04)i at 420 nm. These laboratory
results support the potential for a field instrument capable of determining
ambient aerosol optical extinction, average aerosol extinction cross section,
and complex refractive index as a function of wavelength. |
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