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| Titel |
Tropospheric NO2 column densities deduced from zenith-sky DOAS measurements in Shanghai, China, and their application to satellite validation |
| VerfasserIn |
D. Chen, B. Zhou, S. Beirle, L. M. Chen, T. Wagner |
| 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 ; 9, no. 11 ; Nr. 9, no. 11 (2009-06-05), S.3641-3662 |
| Datensatznummer |
250007357
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| Publikation (Nr.) |
 copernicus.org/acp-9-3641-2009.pdf |
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| Zusammenfassung |
| Zenith-sky scattered sunlight observations using differential optical
absorption spectroscopy (DOAS) technique were carried out in Shanghai, China
(31.3° N, 121.5° E) since December 2006. At this polluted urban site,
the measurements provided NO2 total columns in the daytime. Here, we
present a new method to extract time series of tropospheric vertical column
densities (VCDs) of NO2 from these observations. The derived
tropospheric NO2 VCDs are important quantities for the estimation of
emissions and for the validation of satellite observations. Our method makes
use of assumptions on the relative NO2 height profiles and the diurnal
variation of stratospheric NO2 VCDs. The main error sources arise from
the uncertainties in the estimated stratospheric slant column densities
(SCDs) and the determination of tropospheric NO2 air mass factor (AMF).
For a polluted site like Shanghai, the accuracy of our method is
conservatively estimated to be <25% for solar zenith angle (SZA) lower
than 70°. From simultaneously performed long-path DOAS measurements, the
NO2 surface concentrations at the same site were observed and the
corresponding tropospheric NO2 VCDs were estimated using the assumed
seasonal NO2 profiles in the planetary boundary layer (PBL). By making
a comparison between the tropospheric NO2 VCDs from zenith-sky and
long-path DOAS measurements, it is found that the former provides more
realistic information about total tropospheric pollution than the latter, so
it's more suitable for satellite data validation. A comparison between the
tropospheric NO2 VCDs from ground-based zenith-sky measurements and
SCIAMACHY was also made. Satellite validation for a strongly polluted area
is highly needed, but exhibits also a great challenge. Our comparison shows
good agreement, considering in particular the different spatial resolutions
between the two measurements. Remaining systematic deviations are most
probably related to the uncertainties of satellite data caused by the
assumptions on aerosol properties as well as the layer heights of aerosols
and NO2. |
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