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| Titel |
Tropospheric NO2 vertical column densities over Beijing: results of the first three years of ground-based MAX-DOAS measurements (2008-2011) and satellite validation |
| VerfasserIn |
J. Z. Ma, S. Beirle, J. L. Jin, R. Shaiganfar, P. Yan, 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 ; 13, no. 3 ; Nr. 13, no. 3 (2013-02-07), S.1547-1567 |
| Datensatznummer |
250017646
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| Publikation (Nr.) |
 copernicus.org/acp-13-1547-2013.pdf |
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| Zusammenfassung |
| Ground-based measurements of scattered sunlight by the Multi Axis
Differential Optical Absorption Spectroscopy (MAX-DOAS) have been carried out
at an urban site (39.95° N, 116.32° E) in Beijing megacity
since 6 August 2008. In this study, we retrieved the tropospheric NO2
vertical column densities (VCDs) over Beijing from these MAX-DOAS
observations from August 2008 to September 2011. Over this period, the
daytime (08:00–17:00 Beijing Time (BJT, which equals UTC + 8)) mean tropospheric NO2 VCDs varied
from 0.5 to 13.3 with an average of 3.6 during summertime, and from 0.2 to
16.8 with an average of 5.8 during wintertime, all in units of 1016 molecules cm−2.
The average diurnal variation patterns of tropospheric
NO2 over Beijing appeared to be rather different from one season to
another, indicating differences in the emission strength and atmospheric
lifetime. In contrast to previous studies, we find a small weekly cycle of
the tropospheric NO2 VCD over Beijing. The NO2 VCD in the late
afternoon was the largest on Saturday and the lowest on Sunday, and in the
morning it reached a clear maximum on Wednesday. We also find a post-Olympic
Games effect, with 39–54% decrease in the tropospheric NO2 VCD over
Beijing estimated for August of 2008, compared to the following years. The
tropospheric NO2 VCDs derived by our ground MAX-DOAS measurements show a
good correlation with SCIAMACHY and OMI satellite data. However, compared
with the MAX-DOAS measurements, the satellite observations underestimate the
tropospheric NO2 VCDs over Beijing systematically, by 43% for
SCIAMACHY and 26–38% for OMI (DOMINO v2.0 and DOMINO v1.02). Based on
radiative transfer simulations, we show that the aerosol shielding effect can
explain this underestimation, while the gradient smoothing effect caused by
the coarse spatial resolution of the satellite observations could play an
additional role. |
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