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| Titel |
SCIAMACHY tropospheric NO2 over Switzerland: estimates of NOx lifetimes and impact of the complex Alpine topography on the retrieval |
| VerfasserIn |
D. Schaub, D. Brunner, K. F. Boersma, J. Keller, D. Folini, B. Buchmann, H. Berresheim, J. Staehelin |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 7, no. 23 ; Nr. 7, no. 23 (2007-12-07), S.5971-5987 |
| Datensatznummer |
250005270
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| Publikation (Nr.) |
 copernicus.org/acp-7-5971-2007.pdf |
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| Zusammenfassung |
| This study evaluates NO2 vertical tropospheric column
densities (VTCs) retrieved from measurements of the Scanning
Imaging Absorption Spectrometer for Atmospheric Chartography
(SCIAMACHY) above Switzerland and the Alpine region. The close
correlation between pixel averaged NOx emission rates
from a spatially and temporally highly resolved inventory and the
NO2 VTCs under anticyclonic meteorological conditions
demonstrates the general ability of SCIAMACHY to detect sources of
NOx pollution in Switzerland. This correlation is further
used to infer seasonal mean NOx lifetimes carefully
taking into account the influence of the strong diurnal cycle in
NOx emissions on these estimates. Lifetimes are estimated
to 3.6 (±0.8) hours in summer and 13.1 (±3.8) hours in
winter, the winter value being somewhat lower than previous
estimates. A comparison between the 2003-2005 mean NO2 VTC
distribution over Switzerland and the corresponding 1996–2003 mean
from the Global Ozone Monitoring Experiment (GOME) illustrates the
much better capability of SCIAMACHY to resolve regional scale
pollution features. However, the comparison of seasonal averages
over the Swiss Plateau with GOME and ground based in situ
observations indicates that SCIAMACHY exhibits a too weak seasonal
cycle with comparatively high values in summer and low values in
winter. A problem likely contributing to the reduced values in
winter (not reported in earlier literature) is the use of
inaccurate satellite pixel surface pressures derived from a coarse
resolution global model in the retrieval. The marked topography in
the Alpine region can lead to deviations of several hundred meters
between the model assumed and the real pixel-averaged surface
height. A sensitivity study based on selected clear sky SCIAMACHY
NO2 VTCs over the Swiss Plateau and two fixed a priori
NO2 profile shapes indicates that inaccurate pixel surface
pressures affect retrieved NO2 columns over complex terrain by
up to 40%. For retrievals in the UV-visible spectral range with a
decreasing sensitivity towards the earth's surface, this effect is
of major importance when the NO2 resides close to the ground,
a situation most frequently observed during winter. |
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