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| Titel |
Inherent calibration of a blue LED-CE-DOAS instrument to measure iodine oxide, glyoxal, methyl glyoxal, nitrogen dioxide, water vapour and aerosol extinction in open cavity mode |
| VerfasserIn |
R. Thalman, R. Volkamer |
| 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 ; 3, no. 6 ; Nr. 3, no. 6 (2010-12-22), S.1797-1814 |
| Datensatznummer |
250001376
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| Publikation (Nr.) |
 copernicus.org/amt-3-1797-2010.pdf |
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| Zusammenfassung |
| The combination of Cavity Enhanced Absorption Spectroscopy (CEAS) with
broad-band light sources (e.g. Light-Emitting Diodes, LEDs) lends itself to
the application of cavity enhanced Differential Optical Absorption
Spectroscopy (CE-DOAS) to perform sensitive and selective point measurements
of multiple trace gases and aerosol extinction with a single instrument. In
contrast to other broad-band CEAS techniques, CE-DOAS relies only on the
measurement of relative intensity changes, i.e. does not require knowledge
of the light intensity in the absence of trace gases and aerosols (I0).
We have built a prototype LED-CE-DOAS instrument in the blue spectral range
(420–490 nm) to measure nitrogen dioxide (NO2), glyoxal (CHOCHO),
methyl glyoxal (CH3COCHO), iodine oxide (IO), water vapour (H2O)
and oxygen dimers (O4). We demonstrate the first direct detection of
methyl glyoxal, and the first CE-DOAS detection of CHOCHO and IO. The
instrument is further inherently calibrated for light extinction from the
cavity by observing O4 or H2O (at 477 nm and 443 nm) and measuring
the pressure, relative humidity and temperature independently. This approach
is demonstrated by experiments where laboratory aerosols of known size and
refractive index were generated and their extinction measured. The measured
extinctions were then compared to the theoretical extinctions calculated
using Mie theory (3–7 × 10−7cm−1). Excellent agreement is found
from both the O4 and H2O retrievals. This enables the first
inherently calibrated CEAS measurement at blue wavelengths in open cavity
mode, and eliminates the need for
sampling lines to supply air to the cavity, i.e., keep the cavity enclosed
and/or aerosol free. Measurements in open cavity mode are demonstrated for
CHOCHO, CH3COCHO, NO2, H2O and aerosol extinction. Our
prototype LED-CE-DOAS provides a low cost, yet research grade innovative
instrument for applications in simulation chambers and in the open
atmosphere. |
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