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| Titel |
Tropospheric nitrogen dioxide column retrieval from ground-based zenith–sky DOAS observations |
| VerfasserIn |
F. Tack, F. Hendrick, F. Goutail, C. Fayt, A. Merlaud, G. Pinardi, C. Hermans, J.-P. Pommereau, M. Van Roozendael |
| 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. 6 ; Nr. 8, no. 6 (2015-06-10), S.2417-2435 |
| Datensatznummer |
250116430
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| Publikation (Nr.) |
 copernicus.org/amt-8-2417-2015.pdf |
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| Zusammenfassung |
| We present an algorithm for retrieving tropospheric nitrogen dioxide
(NO2) vertical column densities (VCDs) from ground-based zenith–sky
(ZS) measurements of scattered sunlight. The method is based on a four-step
approach consisting of (1) the differential optical absorption spectroscopy
(DOAS) analysis of ZS radiance spectra using a fixed reference spectrum
corresponding to low NO2 absorption, (2) the determination of the
residual amount in the reference spectrum using a Langley-plot-type method,
(3) the removal of the stratospheric content from the daytime total measured
slant column based on stratospheric VCDs measured at sunrise and sunset, and
simulation of the rapid NO2 diurnal variation, (4) the retrieval of
tropospheric VCDs by dividing the resulting tropospheric slant columns by
appropriate air mass factors (AMFs). These steps are fully characterized and
recommendations are given for each of them. The retrieval algorithm is
applied on a ZS data set acquired with a multi-axis (MAX-) DOAS instrument
during the Cabauw (51.97° N, 4.93° E, sea level)
Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI)
held from 10 June to 21 July 2009 in the
Netherlands. A median value of 7.9 × 1015 molec cm−2 is found for
the retrieved tropospheric NO2 VCDs, with maxima up to 6.0 × 1016 molec cm−2. The error budget assessment indicates that the
overall error σTVCD on the column values is less than 28%. In
the case of low tropospheric contribution, σTVCD is estimated to be
around 39% and is dominated by uncertainties in the determination of the
residual amount in the reference spectrum. For strong tropospheric pollution
events, σTVCD drops to approximately 22% with the largest
uncertainties on the determination of the stratospheric NO2 abundance
and tropospheric AMFs. The tropospheric VCD amounts derived from ZS
observations are compared to VCDs retrieved from off-axis and direct-sun
measurements of the same MAX-DOAS instrument as well as to data from a
co-located Système d'Analyse par Observations Zénithales (SAOZ)
spectrometer. The retrieved tropospheric VCDs are in good agreement with the
different data sets with correlation coefficients and slopes close to or
larger than 0.9. The potential of the presented ZS retrieval algorithm is
further demonstrated by its successful application on a 2-year data set,
acquired at the NDACC (Network for the Detection of Atmospheric Composition
Change) station Observatoire de Haute Provence (OHP; Southern France). |
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