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| Titel |
Improving satellite retrievals of large tropospheric NO2 columns |
| VerfasserIn |
Andreas Richter, Andreas Hilboll, John P. Burrows |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250096175
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| Publikation (Nr.) |
 EGU/EGU2014-11669.pdf |
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| Zusammenfassung |
| Satellite observations of tropospheric NO2 amounts are based on application of the
Differential Optical Absorption Spectroscopy (DOAS) method to space-borne nadir
measurements of the backscattered solar radiation. In the DOAS method, the effects of
absorption and radiative transfer are usually treated separately to facilitate rapid data
analysis. In most cases, this approximation is valid and only small uncertainties are
introduced.
During the dramatic pollution episode in China in January 2013, tropospheric NO2
retrievals on GOME-2 data suffered from significantly increased residuals leading to rejection
of the retrievals as having poor quality. Closer inspection of the fits revealed systematic
residuals which could be explained by the wavelength dependence of the air mass
factor (AMF) for absorbers located close to the surface. At the large NO2 columns
present during the event, this effect becomes significant. In addition, the spectral
signature of the temperature dependence of the NO2 absorption cross-section could be
detected.
In this study, GOME-2 data for high NO2 situations are evaluated systematically for
usually neglected effects such as the AMF and temperature dependence. Using
semi-empirical approaches, solutions are proposed to improve the quality of retrievals under
these conditions. In addition, the potential for retrieving useful information from
the magnitude of these effects is evaluated and it is shown, that some qualitative
deductions on the vertical position of the NO2 absorption can be made under favourable
conditions. |
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