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| Titel |
Cloud effects in satellite observed tropospheric NO2 |
| VerfasserIn |
Andreas Richter, Andreas Hilboll, Achim Zien, John P. Burrows |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052905
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| Zusammenfassung |
| Satellite observations of atmospheric composition have become an important tool in the
investigation of tropospheric chemistry. In particular, retrievals of tropospheric NO2 columns
from nadir scattered light observations of the GOME, SCIAMACHY, OMI, and GOME-2
instruments have been applied in many studies as they can be linked to NOx emissions from a
variety of sources.
As the retrievals of NO2 are performed in the visible part of the spectrum, clouds have a
large impact on the results. Optically thick clouds shield the NO2 below the cloud from the
satellite view, thereby limiting the sensitivity of the observations. However, as the result of
multiple scattering within the cloud and enhanced backscatter from the cloud top, the
sensitivity to NO2 within the upper part of the cloud and above cloud top is enhanced.
Depending on the vertical structure of the cloud and the relative vertical position of absorber
and cloud, NO2 signals can be much reduced or even enhanced in the presence of
clouds.
Here, we present a statistical analysis of GOME-2 and SCIAMACHY NO2
observations taken at different cloud fractions. The results show surprisingly small cloud
effects in many regions, and systematic cloud induced enhancements of NO2 in
regions dominated by pollution transport and biomass burning. Analysis of the
impact of cloud top on the signal shows the expected larger enhancement over
lower clouds in some regions, but not in all. The results have implications for the
interpretation of cloudy satellite observations and the assumptions on the vertical NO2
distribution. |
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