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| Titel |
Comparison of tropospheric NO2 vertical columns in an urban environment using satellite, multi-axis differential optical absorption spectroscopy, and in situ measurements |
| VerfasserIn |
D. Mendolia, R. J. C. D'Souza, G. J. Evans, J. Brook |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 10 ; Nr. 6, no. 10 (2013-10-31), S.2907-2924 |
| Datensatznummer |
250085097
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| Publikation (Nr.) |
 copernicus.org/amt-6-2907-2013.pdf |
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| Zusammenfassung |
| Tropospheric NO2 vertical column densities have been retrieved and compared
for the first time in Toronto, Canada, using three methods of differing
spatial scales. Remotely sensed NO2 vertical column densities,
retrieved from multi-axis differential optical absorption spectroscopy and
satellite remote sensing, were evaluated by comparison with in situ vertical
column densities estimated using a pair of chemiluminescence monitors
situated 0.01 and 0.5 km a.g.l. (above ground level). The chemiluminescence
measurements were corrected for the influence of NOz, which reduced the
NO2 concentrations at 0.01 and 0.5 km by an average of 8 ± 1%
and 12 ± 1%, respectively. The average absolute decrease in the
chemiluminescence NO2 measurement as a result of this correction was
less than 1 ppb. The monthly averaged ratio of the NO2 concentration at
0.5 to 0.01 km varied seasonally, and exhibited a negative linear
dependence on the monthly average temperature, with Pearson's R = 0.83.
During the coldest month, February, this ratio was 0.52 ± 0.04, while
during the warmest month, July, this ratio was 0.34 ± 0.04,
illustrating that NO2 is not well mixed within 0.5 km above ground
level. Good correlation was observed between the remotely sensed and in situ
NO2 vertical column densities (Pearson's R value ranging from 0.72 to 0.81),
but the in situ vertical column densities were 52 to 58% greater than
the remotely sensed columns. These results indicate that NO2 horizontal
heterogeneity strongly impacted the magnitude of the remotely sensed
columns. The in situ columns reflected an urban environment with major
traffic sources, while the remotely sensed NO2 vertical column
densities were representative of the region, which included spatial
heterogeneity introduced by residential neighbourhoods and Lake Ontario.
Despite the difference in absolute values, the reasonable correlation
between the vertical column densities determined by three distinct methods
increased confidence in the validity of the values provided by each
measurement technique. |
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