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Titel |
Development and application of a low-cost, portable DOAS system for stratospheric composition monitoring over the Argentinean Patagonia and Antarctic stations. |
VerfasserIn |
Marcelo Raponi, Rodrigo Jiménez, Pablo Ristori, Elian Wolfram, Jorge Tocho, Eduardo Quel |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250044443
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Zusammenfassung |
A significant fraction of the Argentinean population is seasonally exposed to elevated UV
radiation, particularly during severe stratospheric ozone destruction episodes in Antarctica. In
order to provide early alert, global monitoring and to improve our understanding of these
phenomena, various Argentinean and international organizations maintain stratospheric
composition remote sensing sites from the southern tip of Argentina (Patagonia) to
Antarctica. The understating of the ozone destruction dynamics will be significantly
improved if more sites were available. For instance, the Laser and Applications Research
Center, CEILAP (CITEFA-CONICET, Argentina) carries out systematic measurements of
stratospheric ozone and tropospheric water vapor profiles at Rio Gallego (51º 36’ S, 69º 19’
W, 15 m asl) by means of LIDAR systems. Besides the active systems, the site possesses
different passive instruments (GUV-541, UV-B and UV-A radiometers, SAOZ spectrometer,
CIMEL sunphotometer) all of them working in synergy. The goal of this work
is to present the design and development of a new compact atmospheric remote
sensing system, able to determine the vertical column concentration in column (VCD)
of multiple trace gases. We have developed a low-cost, portable passive DOAS
system, ERO-DOAS, wich circumvents the cost limitations associated with new fixed
monitoring sites. It is composed of commercial spectrophotometer (HR4000, Ocean
Optics), a 400-μm core, 6-m long optic fiber, and a home-made automatic external
shutter. We have developed a LabVIEW® based software for spectrometer/shutter
control and data acquisition, and a MATLAB® based software for spectral data
reduction. In the work we highlight the main characteristics of the system’s components
and we describe the visual interface implemented to controls the operation of the
whole system, and the calculation algorithms to process the measured zenithal
spectra, postulating the strategies implemented to solve the challenge. Also, we
present measurements carry out at the Marambio Antarctic Base (64Ë 14’ S; 56Ë
37’ W, 197 m asl) during the months of January - February of 2008, using the
ERO-DOAS. The NO2 and O3 VCD are derived from solar spectra acquired during
the twilights (zenithal angles between 87Ë - 92Ë ), using the DOAS (Differential
Optical Absorption Spectroscopy) technique. The biggest contribution to these
spectra comes from the stratosphere, atmosphere layer that we want to study. The
analysis is carried out by solving the Beer-Lambert-Bouger (BLB) law for all the
atmospheric absorbers and a quasi-continuous wavelength range. The algorithm
minimizes the fitting residuals to the BLB law, having as unknown the slant column
density of the species to determine. The effects of Rayleigh and Mie scattering,
fluorescence and most of the Raman scattering are accounted for and subtracted out
using a high-pass polynomial filter. We compare the data acquired by our DOAS
system with co-located measurements performed with EVA, a visible absorption
spectrometer operated by the Instituto Nacional de Técnica Aeroespacial (INTA), Spain.
Additionally, a comparative study is presented among the ground-based signals and those
obtained by the instrument OMI (AURA satellite). The bigger mistake sources
associated with the comparison between AURA satellite observations and those
carried out from earth are: a) NOx daily cycle, b) NO2 natural variability, and c) NO2
tropospheric sensibility. In the case of Marambio, it hasn’t relevance since it is
non polluted places and the tropospheric NO2 level is very low. We observe that
the NO2 has a strong photochemical variability during the day. This variability is
associated with the solar cycle, the NOx vertical distribution, the temperature in the high
layers of the atmosphere and sometimes (in high latitudes) of other active species. |
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