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| Titel |
Dual-wavelength light-scattering technique for selective detection of volcanic ash particles in the presence of water droplets |
| VerfasserIn |
Z. Jurányi, H. Burtscher, M. Loepfe, M. Nenkov, E. Weingärtner |
| 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 ; 8, no. 12 ; Nr. 8, no. 12 (2015-12-10), S.5213-5222 |
| Datensatznummer |
250116722
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| Publikation (Nr.) |
 copernicus.org/amt-8-5213-2015.pdf |
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| Zusammenfassung |
A new method is presented in this paper which analyses the scattered
light of individual aerosol particles simultaneously at two
different wavelengths in order to retrieve information on the
particle type. We show that dust-like particles, such as volcanic
ash, can be unambiguously discriminated from water droplets on
a single-particle level. As a future application of this method, the
detection of volcanic ash particles should be possible in a humid
atmosphere in the presence of cloud droplets. The characteristic behaviour of pure water's refractive index
can be used to separate water droplets and dust-like particles which
are commonly found in the micrometre size range in the ambient
air. The low real part of the water's refractive index around
2700–2800 nm results in low scattered light intensities
compared to e.g. the visible wavelength range, and this feature can
be used for the desired particle identification.
The two-wavelength measurement set-up was theoretically and
experimentally tested and studied. Theoretical calculations were
done using Mie theory. Comparing the ratio of the scattered light at
the two wavelengths (visible-to-IR (infrared), R value) for water droplets and different dust
types (basalt, andesite, African mineral dust, sand, volcanic ash,
pumice) showed at least 9-times-higher values (on average 70 times)
for water droplets than for the dust types at any diameter within
the particle size range of 2–20 μm. The envisaged
measurement set-up was built up into a laboratory prototype and was
tested with different types of aerosols. We generated aerosols from
the following powders, simulating dust-like particles: cement dust,
ISO 12103-1 A1 Ultrafine Test Dust and ash from the 2012 eruption of
the Etna volcano. Our measurements verified the theoretical
considerations; the median experimental R value is 8–21 times higher
for water than for the "dust" particles. |
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